PROPOSED MERGER

YOUR VOTE IS VERY IMPORTANT

To the stockholders of MEI Pharma, Inc. and Infinity Pharmaceuticals, Inc.:

The boards of directors of MEI Pharma, Inc., a Delaware corporation (“MEI”) and Infinity Pharmaceuticals Inc., a Delaware corporation (“Infinity”), have agreed upon a transaction in which Infinity will become a wholly-owned subsidiary of MEI. On February 22, 2023, MEI, Infinity, and Meadow Merger Sub, Inc. (“Merger Sub”), a Delaware corporation and a wholly-owned subsidiary of MEI, entered into an Agreement and Plan of Merger (the “Merger Agreement”), pursuant to which Merger Sub will merge with and into Infinity, with Infinity surviving as a wholly owned subsidiary of MEI, and the surviving company of the merger, which transaction is referred to herein as the “Merger.” MEI following the Merger is referred to herein as the combined company.

We are sending this joint proxy statement/prospectus to you to ask you to vote in favor of this transaction and other matters.

If the Merger is consummated, at the effective time of the Merger (the “Effective Time”) each share of Infinity’s common stock, par value $0.001 per share, (the “Infinity Common Stock”), issued and outstanding immediately prior to the Effective Time (other than shares of Infinity Common Stock held in treasury, if any) will be automatically converted into the right to receive 0.052245 shares (the “Exchange Ratio”) of the common stock, par value $0.00000002 per share, of MEI (the “MEI Common Stock”), subject to customary equitable adjustment in the event of any recapitalization, stock split, reverse stock split or similar change.

In addition, each outstanding option to purchase shares of Infinity Common Stock (each, an “Infinity Stock Option”) will become fully vested in accordance with the terms of the underlying stock option agreement. Each Infinity Stock Option will be assumed at the Effective Time by MEI and converted into a stock option to purchase shares of MEI Common Stock. The number of shares of MEI Common Stock underlying each such assumed Infinity Stock Option will be equal to the product of (i) the number of shares of Infinity Common Stock underlying the applicable Infinity Stock Option immediately prior to the Effective Time multiplied by (ii) the Exchange Ratio, with the resulting number of shares of MEI Common Stock rounded down to the nearest whole share, and the exercise price per share of each such assumed Infinity Stock Option will be equal to (a) the per share exercise price applicable to such Infinity Stock Option immediately prior to the Effective Time divided by (b) the Exchange Ratio, with the resulting exercise price per share rounded up to the nearest whole cent. Except as noted above, each assumed and converted Infinity Stock Option will continue to be governed by substantially the same terms and conditions (after giving effect to the full acceleration of vesting of such Infinity Stock Option in connection with the Merger) as were applicable to such Infinity Stock Option immediately prior to the Effective Time. Before the Effective Time, each outstanding Infinity restricted stock unit (each, an “Infinity RSU”) will become fully vested, and the shares of Infinity Common Stock subject to such Infinity RSU will be distributed in accordance with the terms of the applicable restricted stock unit agreement. The shares of Infinity Common Stock issued upon the vesting of Infinity RSUs will be treated as shares of Infinity Common Stock issued and outstanding immediately prior to the Effective Time in accordance with the terms and conditions of the Merger Agreement. No Infinity RSUs will be outstanding from and after the Effective Time.

Each share of MEI Common Stock and option to purchase MEI Common Stock that is issued and outstanding at the Effective Time will remain issued and outstanding, and such shares and options will be unaffected by the

Merger. Immediately after the Merger, MEI stockholders as of immediately prior to the Merger are expected to own approximately 58% of the outstanding shares of the combined company, and Infinity stockholders are expected to own approximately 42% of the outstanding shares of the combined company.

Your vote is very important. We cannot complete the Merger unless the Infinity stockholders vote to adopt the Merger Agreement and the MEI stockholders vote to approve the issuance of MEI Common Stock. Abstentions or failures to properly cast an affirmative vote for the adoption of the Merger Agreement by any Infinity stockholder will have the same effect as a vote against the adoption of the Merger Agreement. This document is a prospectus relating to the shares of MEI Common Stock to be issued in the Merger and a joint proxy statement for Infinity and MEI to solicit proxies for their respective special meetings of stockholders. It contains answers to frequently asked questions and a summary of the important terms of the Merger, Merger Agreement, and related transactions, followed by a more detailed discussion.

More information about MEI, Infinity, the Merger Agreement and the transactions contemplated thereby (collectively the “Contemplated Transactions”), and the proposals is contained in the accompanying joint proxy statement/prospectus. MEI and Infinity urge you to read the accompanying joint proxy statement/prospectus carefully and in its entirety. IN PARTICULAR, YOU SHOULD CAREFULLY CONSIDER THE MATTERS DISCUSSED UNDER “RISK FACTORS” BEGINNING ON PAGE 26 OF THE ACCOMPANYING JOINT PROXY STATEMENT/PROSPECTUS.

MEI and Infinity are excited about the opportunities the Merger brings to MEI and Infinity stockholders. Thank you for your consideration and continued support.

Sincerely,

Neither the U.S. Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of the accompanying joint proxy statement/prospectus. Any representation to the contrary is a criminal offense.

MEI PHARMA, INC.

San Diego, California

NOTICE OF SPECIAL MEETING OF MEI STOCKHOLDERS

To the Stockholders of MEI Pharma, Inc.:

The MEI Special Meeting will be held for the following purposes:

Your vote is important. The majority of the votes cast by MEI stockholders entitled to vote on the proposal at the MEI Special Meeting is required for approval of the MEI Nasdaq Proposal and the MEI Adjournment Proposal. Approval of the MEI Nasdaq Proposal is a condition to the completion of the Merger. Therefore, the Merger cannot be consummated without the approval of the MEI Nasdaq Proposal. The MEI Nasdaq Proposal is described in more detail in the section titled “Matters Being Submitted To A Vote Of MEI Stockholders” in the accompanying joint proxy statement/prospectus, which you should read carefully in its entirety before you vote. A copy of the Merger Agreement is attached as Annex A to the accompanying joint proxy statement/prospectus.

Even if you plan to virtually attend the MEI Special Meeting, MEI requests that you sign and return the enclosed proxy card or voting instruction form or vote by Internet or phone to ensure that your shares will be represented at the MEI Special Meeting if you are unable to virtually attend. You may change or revoke your proxy at any time before it is voted at the MEI Special Meeting.

After careful consideration, the MEI board of directors (with Sujay R. Kango recusing himself from the vote) has approved the Merger Agreement and has determined that it is advisable to consummate the Merger. The MEI board of directors (with Sujay R. Kango recusing himself from the vote) has approved the MEI Nasdaq Proposal and the MEI Adjournment Proposal described in the accompanying joint proxy statement/prospectus and recommends that its stockholders vote “FOR” the proposals described in the accompanying joint proxy statement/prospectus.

By Order of MEI’s Board of Directors,

NOTICE OF SPECIAL MEETING OF INFINITY STOCKHOLDERS

To the Stockholders of Infinity Pharmaceuticals, Inc.:

The Infinity Special Meeting will be held for the following purposes:

Your vote is important. The affirmative vote of the holders of a majority of the outstanding shares of Infinity Common Stock entitled to vote thereon is required for approval of the Infinity Merger Proposal. Any abstention or failure to properly cast an affirmative vote for the Infinity Merger Proposal will have the same effect as a vote against the Infinity Merger Proposal. Assuming a quorum is present, the affirmative vote of a majority in voting power of the shares of Infinity Common Stock which are present virtually or by proxy and entitled to vote thereon is required for approval of the Infinity Compensation Proposal and the Infinity Adjournment Proposal. Approval of the Infinity Merger Proposal is a condition to the completion of the Merger. Therefore, the Merger cannot be completed without the approval of the Infinity Merger Proposal. The Infinity Merger Proposal is described in more detail in the section

titled “Matters Being Submitted To A Vote Of Infinity Stockholders” in the accompanying joint proxy statement/prospectus, which you should read carefully in its entirety before you vote. A copy of the Merger Agreement is attached as Annex A to the accompanying joint proxy statement/prospectus.

Even if you plan to virtually attend the Infinity Special Meeting, Infinity requests that you sign and return the enclosed proxy card or vote by Internet or phone to ensure that your shares will be represented at the Infinity Special Meeting if you are unable to virtually attend. You may change or revoke your proxy at any time before it is voted at the Infinity Special Meeting.

By Order of Infinity’s Board of Directors,

Seth A. Tasker

Senior Vice President, Chief Business Officer, and Secretary

Cambridge, Massachusetts

ABOUT THIS JOINT PROXY STATEMENT/PROSPECTUS

This document, which forms part of a registration statement on Form S-4 filed with the SEC by MEI, constitutes a prospectus of MEI under the Securities Act of 1933, as amended (the “Securities Act”), with respect to the issuance of shares of MEI Common Stock to Infinity stockholders pursuant to the Merger Agreement. This document also constitutes a joint proxy statement of MEI and Infinity under Section 14(a) of the Securities Exchange Act of 1934 as amended (the “Exchange Act”). It also constitutes a notice of meeting with respect to the Infinity Special meeting, at which Infinity stockholders will be asked to consider and vote on the adoption of the Merger Agreement and certain related matters, and the MEI Special Meeting, at which MEI stockholders will be asked to consider and vote on the approval of the issuance of MEI Common Stock pursuant to the Merger Agreement.

Infinity has supplied all information contained in this joint proxy statement/prospectus relating to Infinity, and MEI has supplied all information contained in this joint proxy statement/prospectus relating to MEI.

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CAUTIONARY STATEMENT CONCERNING FORWARD-LOOKING STATEMENTS AND INDUSTRY AND MARKET DATA

This joint proxy statement/prospectus contains forward-looking statements that involve substantial risks and uncertainties. All statements other than statements of historical facts contained in this prospectus, including statements regarding future financial condition, business strategy and plans and objectives of management of either MEI and Infinity, or the combined company, as applicable for future operations, are forward-looking statements. In some cases, you can identify forward-looking statements by terminology such as “anticipate,” “believe,” “continue,” “could,” “design,” “estimate,” “expect,” “intend,” “may,” “plan,” “potentially,” “predict,” “seek,” “should,” “will” or the negative of these terms or other similar expressions.

All statements other than statements of historical fact are statements that could be deemed forward-looking statements. These forward-looking statements include, but are not limited to, statements concerning the following:

You should not rely upon forward-looking statements as predictions of future events. Neither Infinity nor MEI can assure you that the events and circumstances reflected in the forward-looking statements will be achieved or occur. In addition, statements that “we believe” and similar statements reflect the beliefs and opinions on the relevant subject of Infinity, MEI or the combined company, as applicable. These statements are based upon information available as of the date of this prospectus, and while Infinity, MEI or the combined company, as applicable, believes such information forms a reasonable basis for such statements, such information may be limited or incomplete.

Actual results could differ materially from those contained in any forward-looking statement as a result of various factors, including, without limitation:

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If any of these risks or uncertainties materializes or any of these assumptions proves incorrect, the results of Infinity, MEI or the combined company could differ materially from the forward-looking statements. All forward-looking statements in this joint proxy statement/prospectus are current only as of the date on which the statements were made. Infinity and MEI do not undertake any obligation to publicly update any forward-looking statement to reflect events or circumstances after the date on which any statement is made or to reflect the occurrence of unanticipated events, except as otherwise required by the federal securities laws.

In addition, this joint proxy statement/prospectus includes statistical and other industry and market data that was obtained from independent industry publications and research, surveys and studies conducted by independent third parties as well as MEI’s and Infinity’s estimates. The market data used in this prospectus involves a number of assumptions and limitations, and you are cautioned not to give undue weight to such data. Industry publications and third-party research, surveys and studies generally indicate that their information has been obtained from sources believed to be reliable, although they do not guarantee the accuracy or completeness of such information. MEI’s and Infinity’s estimates include assumptions based on their respective industry knowledge, industry publications, third-party research and other surveys. While MEI and Infinity believe that their respective internal assumptions and estimates are reasonable, no independent source has verified such assumptions or estimates.

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QUESTIONS AND ANSWERS ABOUT THE MERGER

The following are answers to some questions that you, as a stockholder of MEI Pharma, Inc. (“MEI”) or a stockholder of Infinity Pharmaceuticals, Inc. (“Infinity”), may have regarding the proposed combination between MEI and Infinity and the proposals to be considered at the MEI Special Meeting and the Infinity Special Meeting. This section does not provide all the information that might be important to you with respect to the proposed combination between MEI and Infinity. MEI and Infinity urge you to carefully read the remainder of this joint proxy statement/prospectus, including the annexes.

Q: Why am I receiving this joint proxy statement/prospectus?

A: MEI, Infinity and Meadow Merger Sub, Inc. (“Merger Sub”), a Delaware corporation and a wholly-owned subsidiary of MEI, have entered into an Agreement and Plan of Merger (as may be amended from time to time, the “Merger Agreement”). The Merger Agreement provides, among other things, that, upon the terms and subject to the conditions set forth in the Merger Agreement, Merger Sub will merge with and into Infinity, with Infinity surviving the Merger as a wholly-owned subsidiary of MEI. A copy of the Merger Agreement is included in this joint proxy statement/prospectus as Annex A.

The Merger cannot be completed unless, among other things, Infinity stockholders adopt the Merger Agreement. The approval of the Merger Agreement by MEI stockholders is not required for the Merger to be completed; however, the Merger cannot be completed unless MEI stockholders have approved the issuance of shares to effect the Merger. MEI stockholders are asked to approve the issuance of shares of MEI’s common stock, $0.00000002 par value per share (“MEI Common Stock”), to Infinity stockholders in exchange for their shares of Infinity’s common stock, par value $0.001 per share (the “Infinity Common Stock”).

MEI and Infinity are using this document as a proxy statement to solicit proxies from MEI’s stockholders and Infinity’s stockholders in connection with proposals relating to the Merger at the MEI Special Meeting and Infinity Special Meeting, respectively. MEI is using this document as a prospectus by which MEI will offer and issue MEI Common Stock in connection with the Merger.

This joint proxy statement/prospectus contains important information about the Merger and the proposals being voted on at the MEI Special Meeting and the Infinity Special Meeting. You should read it carefully and in its entirety. The enclosed materials allow MEI stockholders to have their shares voted by proxy without attending the MEI Special Meeting, which will be held virtually, and the Infinity stockholders to have their shares voted by proxy without attending the Infinity Special Meeting, which will be held virtually. Your vote is important. We encourage you to submit your proxy as soon as possible.

Q: What am I being asked to vote on?

A: At the MEI Special Meeting, MEI stockholders will be asked to consider and vote on the following proposals:

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At the Infinity Special Meeting, Infinity stockholders will be asked to consider and vote on the following proposals:

Q: Why are MEI and Infinity proposing the Merger?

A: The boards of directors of MEI and Infinity (with the exception of Sujay R. Kango who recused himself from the vote) each believe that the Merger will provide substantial strategic and financial benefits to their respective companies and stockholders. To review the reasons for the Merger, see “The Merger—MEI’s Reasons for the Merger; Recommendation of the MEI Board” and “The Merger—Infinity’s Reasons for the Merger; Recommendation of the Infinity Board” for more information.

Q: What will Infinity stockholders receive in the Merger?

A: At the effective time of the Merger (the “Effective Time”), each share of Infinity Common Stock outstanding at that time (other than certain shares of Infinity Common Stock that may be cancelled pursuant to the terms and conditions of the Merger Agreement) will be converted into the right to receive a number of shares of MEI Common Stock equal to the Exchange Ratio (as defined below), subject to adjustment as described in this joint proxy statement/prospectus.

Q: What is the Exchange Ratio?

A: Each share of Infinity Common Stock issued and outstanding immediately prior to the Merger (other than shares of Infinity Common Stock held in treasury, if any) shall be automatically converted into the right to receive 0.052245 shares of MEI Common Stock (the “Exchange Ratio”). The Exchange Ratio is subject to customary equitable adjustment in the event of any recapitalization, stock split, reverse stock split or similar change.

Q: Are Infinity stockholders guaranteed to receive exactly 0.052245 shares of MEI Common Stock for each share of Infinity Common Stock exchanged in the Merger?

A: Yes, subject to equitable adjustments to the exchange ratio in the event of a stock split, recapitalization, or similar event involving one of the party’s stock. See “Risk Factors” and “The Merger Agreement—Merger Consideration.”

Q: What equity stake will Infinity stockholders hold in MEI immediately following the Merger?

A: Upon the Closing of the Merger, based upon the number of shares of MEI Common Stock expected to be issued in the Merger and an unadjusted Exchange Ratio, pre-Merger MEI stockholders will own approximately 58% of the outstanding equity of the combined company and pre-Merger Infinity stockholders will own approximately 42% of the outstanding equity of the combined company.

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Q: When and where is the MEI Special Meeting?

Q: When and where is the Infinity Special Meeting?

Q: What do I need to do now?

A: After you have carefully read this joint proxy statement/prospectus and have decided how you wish to vote your shares, please vote your shares promptly so that your shares are represented and voted at the MEI Special Meeting or the Infinity Special Meeting, respectively, even if you plan on attending. If you hold your shares in your name as a stockholder of record, you must complete, sign and mail your proxy card in the enclosed postage-paid return envelope as soon as possible or vote by Internet or phone, following the instructions on your proxy card. If you hold your shares in “street name” through a bank, broker or other nominee, you must direct that organization how to vote in accordance with the instructions you have received from it.

Q: What constitutes a quorum for the MEI Special Meeting?

Q: What constitutes a quorum for the Infinity Special Meeting?

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Q: What is the vote required to approve each proposal?

A: Approval of the MEI Nasdaq Proposal or the MEI Adjournment Proposal requires the majority of the votes cast by MEI stockholders entitled to vote on the proposal. Assuming a quorum is present, if you mark “ABSTAIN” on your proxy card or when voting by Internet or phone, fail to submit a proxy, or fail to vote at the MEI Special Meeting with respect to the MEI Nasdaq Proposal or MEI Adjournment Proposal, it will have “NO EFFECT” on the proposal.

Approval of the Infinity Merger Proposal requires the affirmative vote of the holders of a majority of the outstanding shares of Infinity Common Stock entitled to vote thereon. Assuming a quorum is present, if you mark “ABSTAIN” on your proxy card or when voting by Internet or phone, or you attend the Infinity Special Meeting and either fail to submit a proxy or fail to vote at the Infinity Special Meeting with respect to the Infinity Merger Proposal, it will have the same effect as a vote “AGAINST” the proposal. Approval of each of the Infinity Compensation Proposal and the Infinity Adjournment Proposal requires the affirmative vote of the holders of a majority in voting power of the shares of Infinity Common Stock which are present virtually or by proxy and entitled to vote on the proposal. Assuming a quorum is present, if you mark “ABSTAIN” on your proxy card or when voting by Internet or phone, fail to submit a proxy, or fail to vote at the Infinity Special Meeting with respect to the Infinity Compensation Proposal or Infinity Adjournment Proposal, it will have the same effect as a vote “AGAINST” the proposal.

Q: How does the MEI board of directors recommend that I vote at the MEI Special Meeting?

A: The MEI board of directors (with Sujay R. Kango recusing) recommends that MEI’s stockholders vote “FOR” the MEI Nasdaq Proposal and, “FOR” the MEI Adjournment Proposal.

Q: How does the Infinity board of directors recommend that I vote at the Infinity Special Meeting?

A: The Infinity board of directors (with Sujay R. Kango recusing) recommends that Infinity’s stockholders vote “FOR” each of the Infinity Merger Proposal, the Infinity Compensation Proposal and the Infinity Adjournment Proposal.

Q: As an Infinity stockholder, why is my vote important?

A: The Merger will not be completed unless Infinity stockholders vote to approve the Infinity Merger Proposal. Your vote is important no matter how many shares you own. Please take the time to vote. Take a moment to read the instructions below. Choose the way to vote that is easiest and most convenient for you and cast your vote as soon as possible. Any abstention or failure to properly cast an affirmative vote if your shares of Infinity Common Stock for the Infinity Merger Proposal will have the same effect as a vote against the Infinity Merger Proposal.

Q: Who can vote at the MEI Special Meeting?

A: Holders of outstanding shares of MEI Common Stock as of the close of business on the MEI Record Date are eligible to vote at the MEI Special Meeting.

Q: Who can vote at the Infinity Special Meeting?

A: Holders of outstanding shares of Infinity Common Stock on the Infinity Record Date are eligible to vote at the Infinity Special Meeting.

Q: Am I a MEI stockholder of record or a beneficial owner? Why does this matter?

A: If on the MEI Record Date your shares were registered directly in your name with MEI’s transfer agent, Computershare Trust Company, N.A., then you are a stockholder of record with respect to those shares.

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If on the MEI Record Date your shares were held in an account at a broker, bank or other similar organization as your nominee, then you are the beneficial owner of shares held in “street name” and these proxy materials are being forwarded to you by that organization. The organization holding your account is considered the stockholder of record for purposes of voting at the MEI Special Meeting.

The form in which you own your shares affects how you vote your shares and how you can change your vote.

Q: Am I an Infinity stockholder of record or a beneficial owner? Why does this matter?

A: If, on the Infinity Record Date, your shares were registered directly in your name with Infinity’s transfer agent, American Stock Transfer & Trust Company, LLC, then you are a stockholder of record with respect to those shares.

If, on the Infinity Record Date, your shares were held in an account at a broker, bank or other similar organization as your nominee, referred to as being held in “street name,” then you are the beneficial owner of such shares and these proxy materials are being forwarded to you by that organization. The organization holding your account is considered the stockholder of record for purposes of voting at the Infinity Special Meeting. The form in which you own your shares affects how you vote your shares and how you can change your vote.

Q: How do I attend the MEI Special Meeting or Infinity Special Meeting and how can I vote my shares?

A: MEI and Infinity are conducting virtual special meetings so their stockholders can participate from any geographic location with internet connectivity. MEI and Infinity have designed the format of the virtual online special meetings to provide stockholders the same ability to participate that they would have at an in-person meeting.

To attend the MEI Special Meeting, you must go to the meeting website at www.meetnow.global/M44PQGZ and enter the 16-digit control number found on your proxy card or voting instruction form sent to you by your bank, broker or other nominee. Once admitted, during the MEI Special Meeting, you may vote, submit questions and view the list of stockholders entitled to vote at the MEI Special Meeting by following the instructions available on the meeting website.

To attend the Infinity Special Meeting, you must go to the meeting website at www.virtualshareholdermeeting.com/INFI2023SM and enter the 16-digit control number found on your proxy card or voting instruction form sent to you by your bank, broker or other nominee. Once admitted, during the Infinity Special Meeting, you may vote, submit questions and view the list of stockholders entitled to vote at the Infinity Special Meeting by following the instructions available on the meeting website.

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Regardless of whether you plan to participate in the MEI Special Meeting or Infinity Special Meeting, it is important that your shares be represented and voted at the MEI Special Meeting or Infinity Special Meeting, respectively. Accordingly, MEI and Infinity encourage you to vote in advance of the MEI Special Meeting and Infinity Special Meeting.

Q: How can I vote my shares of MEI Common Stock?

A: For each proposal, you may vote “FOR” or “AGAINST” each proposal, or “ABSTAIN” from voting on such proposal.

If you are a stockholder of record, you may vote by proxy via telephone, over the Internet or by returning a proxy card, or you may vote online at the MEI Special Meeting. Regardless of whether you plan to participate in the MEI Special Meeting, we urge you to vote by proxy to ensure your vote is counted. You may still participate in the MEI Special Meeting and vote online during the MEI Special Meeting if you have already voted by proxy.

If you are a beneficial owner, you may vote your shares by directing the broker, bank or other similar organization that holds your shares as your nominee on how to vote the shares in your account. Please refer to the voting instructions provided by your broker, bank or other nominee. Many organizations allow beneficial owners to give voting instructions via telephone or the Internet, as well as in writing. If you are a beneficial owner and would like to vote your shares at the MEI Special Meeting, please contact your broker, bank or other nominee for instructions and documents that may be required in order to do so.

Q: How can I vote my shares of Infinity Common Stock?

A: If you are the “record holder” of your shares, meaning that you own your shares in your own name and not through a bank or brokerage firm, you may vote in one of four ways:

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If you are a beneficial owner, you may vote your shares by directing the broker, bank or other similar organization that holds your shares as your nominee on how to vote the shares in your account. Please refer to the voting instructions provided by your broker, bank or other nominee. Many organizations allow beneficial owners to give voting instructions via telephone or the Internet, as well as in writing. If you are a beneficial owner and would like to vote your shares at the Infinity Special Meeting, please contact your broker, bank or other nominee for instructions and documents that may be required in order to do so.

Q: What if I return an MEI proxy card but do not make specific choices?

A: You will only receive a proxy card if you are the record holder of your shares of MEI Common Stock. If you return a signed proxy card without marking any voting selections, your shares will be voted “FOR” the MEI Nasdaq Proposal and “FOR” the MEI Adjournment Proposal, in accordance with the recommendation of the MEI board of directors (with Sujay R. Kango recusing). If any other matter is properly presented at the meeting, your proxy (one of the individuals named on your proxy card) will vote your shares using his or her best judgment.

Q: What if I return an Infinity proxy card but do not make specific choices?

A: You will only receive a proxy card if you are the record holder of your shares of Infinity Common Stock. If you return a signed proxy card without marking any voting selections, your shares will be voted “FOR” each of the Infinity Merger Proposal, the Infinity Compensation Proposal and the Infinity Adjournment Proposal in accordance with the recommendation of the Infinity board of directors (with Sujay R. Kango recusing). If any other matter is properly presented at the meeting, your proxy (one of the individuals named on your proxy card) will vote your shares using his or her best judgment.

Q: If my shares of MEI Common Stock or Infinity Common Stock are held in “street name” by my bank, broker or other nominee, will my bank, broker or other nominee automatically vote my shares for me?

A: No. If the shares you own are held in the name of a bank, broker or other nominee, also known as “street name,” that organization, as the record holder of your shares, is required to vote your shares according to your instructions. In order to vote your shares held in “street name,” you will need to follow the directions your bank, broker or other nominee provides you. Many banks, brokers or nominees also offer the option of voting over the Internet or by telephone, instructions for which would be provided by your bank, broker or nominee on your voting instruction form.

Under applicable stock exchange rules, banks, brokers and other nominees may use their discretion to vote “uninstructed” shares (i.e., shares of record held by banks, brokers or other nominees, but with respect to which the beneficial owner of such shares has not provided instructions on how to vote on a particular proposal) with

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respect to matters that are considered to be “discretionary.” Your bank, broker or other nominee will not be allowed to vote your shares with respect to certain “non-discretionary” items. A “broker non-vote” occurs when shares held by a bank, broker or other nominee in “street name” for a beneficial owner are voted on at least one proposal but not voted with respect to a particular proposal because that organization (i) has not received voting instructions from the beneficial owner for that proposal and (ii) lacks discretionary voting power to vote those shares for that proposal.

The Infinity Merger Proposal, the Infinity Compensation Proposal and the Infinity Adjournment Proposal are each expected to be treated as non-discretionary items. Accordingly, Infinity does not expect there to be broker non-votes at the Infinity Special Meeting.

The MEI Nasdaq Proposal and the MEI Adjournment Proposal are each expected to be treated as non-discretionary items. Therefore your bank, broker or other nominee cannot vote your shares of MEI Common Stock without your specific voting instructions. Because the only proposals for consideration at the MEI Special Meeting are non-routine proposals, it is not expected that there will be any broker non-votes at the MEI Special Meeting. However, if there are any broker non-votes, assuming a quorum is present they will have “NO EFFECT” on the outcome of the MEI Nasdaq Proposal and the MEI Adjournment Proposal.

If you are a beneficial owner and would like to vote your shares at the MEI Special Meeting or Infinity Special Meeting, please contact your broker, bank or other nominee for instructions and documents that may be required in order to do so.

Q: Can I change my vote?

A: Yes. If you are a record holder of MEI Common Stock, you can revoke your proxy and change your vote at any time before the final vote at the meeting.

A revocation or later-dated proxy received by MEI after the vote will not affect the vote.

If you are a record holder of Infinity Common Stock, you can change your vote and revoke your proxy at any time before the polls close at the Infinity Special Meeting. To do so you must do one of the following:

Your attendance at the Infinity Special Meeting alone will not change your vote or revoke your proxy.

Finally, if you are a beneficial holder (and hold your shares in “street name” through a bank, broker or other nominee), you should contact that organization to revoke your proxy or change your vote in accordance with its instructions.

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Q: How do I vote my Infinity 401(k) Plan shares?

Q: What happens if I fail to submit a proxy or I abstain from voting?

A: If you fail to submit a proxy or fail to instruct your bank, broker or other nominee to vote, assuming a quorum is present at the MEI Special Meeting, it will have no effect on the outcome of the MEI Nasdaq Proposal or the MEI Adjournment Proposal. An abstention occurs when an MEI stockholder returns a proxy with an “ABSTAIN” instruction or virtually attends the MEI Special Meeting and abstains from voting. Assuming a quorum is present, abstentions also will have “NO EFFECT” on such proposals.

If you fail to submit a proxy or fail to instruct your bank, broker or other nominee to vote, assuming a quorum is present at the Infinity Special Meeting (i) it will have no effect on the outcome of the Infinity Adjournment Proposal and Infinity Compensation Proposal, and (ii) it will have the effect of a vote “AGAINST” the Infinity Merger Proposal.

Q: Will Infinity equity awards be affected by the Merger?

A: At the Effective Time, each outstanding option to purchase shares of Infinity Common Stock (each, an “Infinity Stock Option”) will become fully vested in accordance with the terms of the underlying stock option agreement. Each Infinity Stock Option will be assumed at the Effective Time by MEI and converted into a stock option to purchase shares of MEI Common Stock. The number of shares of MEI Common Stock underlying each such assumed Infinity Stock Option will be equal to the product of (i) the number of shares of Infinity Common Stock underlying the applicable Infinity Stock Option immediately prior to the Effective Time multiplied by (ii) the Exchange Ratio, with the resulting number of shares of MEI Common Stock rounded down to the nearest whole share, and the exercise price per share of each such assumed Infinity Stock Option will be equal to (a) the per share exercise price applicable to such Infinity Stock Option immediately prior to the Effective Time divided by (b) the Exchange Ratio, with the resulting exercise price per share rounded up to the nearest whole cent. Except as noted above, each assumed and converted Infinity Stock Option will continue to be governed by substantially the same terms and conditions (after giving effect to the full acceleration of vesting of such Infinity Stock Option in connection with the Merger) as were applicable to such Infinity Stock Option immediately prior to the Effective Time.

Before the Effective Time, each outstanding Infinity restricted stock unit (each, an “Infinity RSU”) will become fully vested and the shares of Infinity Common Stock subject to such Infinity RSU will be distributed in accordance with the terms of the applicable restricted stock unit agreement. The shares of Infinity Common Stock issued upon the vesting of Infinity RSUs will be treated as shares of Infinity Common Stock issued and outstanding immediately prior to the Effective Time in accordance with the terms and conditions of the Merger Agreement. No Infinity RSUs will be outstanding from and after the Effective Time.

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Q: What will happen to the Infinity 2013 Employee Stock Purchase Plan, as amended?

A: Prior to the Effective Time, the Infinity board of directors will take action to terminate the purchase periods and offering periods then in effect under the terms of the Infinity 2013 Employee Stock Purchase Plan, as amended (the “Infinity ESPP”), and to exercise all outstanding options under the Infinity ESPP to the extent of accumulated payroll deductions as of a date specified by the Infinity board of directors. No options under the Infinity ESPP will be outstanding from and after the Effective Time.

Q: Who will solicit and pay the cost of soliciting proxies?

A: MEI has engaged Alliance Advisors, LLC to assist in the solicitation of proxies for the MEI Special Meeting. MEI estimates that it will pay Alliance Advisors, LLC a fee of approximately $35,000, plus reimbursement of reasonable expenses. MEI has agreed to indemnify Alliance Advisors, LLC against various liabilities and expenses that relate to or arise out of its solicitation of proxies (subject to certain exceptions).

Infinity has engaged Morrow Sodali LLC to assist in the solicitation of proxies for the Infinity Special Meeting and to provide related advice and informational support, for a services fee of $35,000 plus the reimbursement of customary disbursements. Infinity has agreed to indemnify Morrow Sodali LLC against various liabilities and expenses that relate to or arise out of its solicitation of proxies (subject to certain exceptions).

MEI and Infinity also may be required to reimburse banks, brokers and other custodians, nominees and fiduciaries or their respective agents for their expenses in forwarding proxy materials to beneficial owners of MEI common stock and Infinity common stock, respectively. MEI’s directors, officers and employees and Infinity’s directors, officers and employees also may solicit proxies, by telephone, by mail, by electronic means or in person. They will not be paid any additional amounts for soliciting proxies.

Q: What are the material U.S. federal income tax consequences of the Merger to Infinity stockholders?

A: The Merger is intended to qualify as a “reorganization” within the meaning of Section 368(a) of the Internal Revenue Code of 1986 (as amended, the “Code”). The completion of the Merger is, however, not conditioned on the Merger qualifying as a “reorganization” within the meaning of Section 368(a) of the Code or upon the receipt of an opinion of counsel to that effect. No assurance can be given that the Merger will qualify as a “reorganization” within the meaning of Section 368(a) of the Code.

Neither Infinity nor MEI has sought or intends to seek a ruling from the Internal Revenue Service (the “IRS”) or an opinion of counsel as to the U.S. federal income tax consequences of the Merger. If the IRS were to successfully challenge the qualification of the Merger as a “reorganization,” the tax consequences would differ materially from those described in this joint proxy statement/prospectus as discussed below under “Material U.S. Federal Income Tax Consequences of the Merger—Tax Consequences if the Merger Fails to Qualify as a Reorganization.”

Assuming the Merger qualifies as a “reorganization” within the meaning of Section 368(a) of the Code, subject to the limitations and qualifications described below under “Material U.S. Federal Income Tax Consequences of the Merger,” a U.S. Holder (as defined in the section titled “Material U.S. Federal Income Tax Consequences of the Merger”) will generally (i) not recognize any gain or loss upon the exchange of Infinity Common Stock for MEI Common Stock in the Merger (other than with respect to cash received in lieu of a fractional share of Infinity Common Stock), (ii) have a tax basis in the MEI Common Stock received in the Merger (including any fractional share of Infinity Common Stock for which cash is received) equal to the tax basis of the Infinity Common Stock surrendered in exchange therefor, and (iii) have a holding period for the MEI Common Stock received in the Merger (including any fractional share of Infinity Common Stock for which cash is received) that includes its holding period for its Infinity Common Stock surrendered in exchange therefor.

For further information, see “The Merger—Material U.S. Federal Income Tax Consequences of the Merger.”

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Q: If I am not in favor of the Merger, what are my rights?

A: Neither MEI stockholders nor Infinity stockholders are entitled to appraisal rights under the Delaware General Corporation Law (the “DGCL”). If they are not in favor of the Merger, MEI stockholders may vote against the MEI Nasdaq Proposal and Infinity stockholders may vote against the Infinity Merger Proposal. For more information, see the section entitled “No Appraisal Rights” beginning on page 175 of this joint proxy statement/prospectus. Information about how MEI stockholders may vote on the proposals being considered in connection with the Merger can be found under the section entitled “The Special Meeting of the MEI Stockholders” beginning on page 108 of this joint proxy statement/prospectus. Information about how Infinity stockholders may vote on the proposals being considered in connection with the Merger can be found under the section entitled “The Special Meeting of the Infinity Stockholders” beginning on page 116 of this joint proxy statement/prospectus.

Q: Should I send in my Infinity stock certificates now?

A: No. Please do not send in your Infinity stock certificates with your proxy. After the completion of the Merger, an exchange agent mutually acceptable to MEI and Infinity will send you instructions for exchanging Infinity stock certificates for the merger consideration.

Q: Whom may I contact if I cannot locate my Infinity stock certificate(s)?

A: If you are unable to locate your original Infinity stock certificate(s), you should contact Infinity’s transfer agent, American Stock Transfer & Trust Company, LLC, at 800-937-5449.

Q: What should I do if I hold my shares of Infinity Common Stock in book-entry form directly with Infinity’s transfer agent, as opposed to a physical stock certificate?

A: You are not required to take any special additional actions if your shares of Infinity Common Stock are not represented by a certificate and are instead held in book-entry form with Infinity’s transfer agent. After the completion of the Merger, an exchange agent mutually acceptable to Infinity and MEI will contact you to provide you with details regarding the merger consideration, including shares of MEI Common Stock in book-entry form and any cash to be paid instead of fractional shares in the Merger.

Q: What should I do if I receive more than one set of voting materials?

A: MEI stockholders or Infinity stockholders may receive more than one set of voting materials, including multiple copies of this joint proxy statement/prospectus and multiple proxy cards. For example, if you hold shares of MEI Common Stock or Infinity Common Stock in more than one brokerage account, you will receive a separate voting instruction card for each brokerage account in which you hold such shares. If you are a holder of record of MEI Common Stock or Infinity Common Stock and your shares are registered in more than one name, you will receive more than one proxy card. Please complete, sign, date and return each proxy card and voting instruction form that you receive or otherwise follow the voting instructions set forth in this joint proxy statement/prospectus to ensure that you vote every share of MEI Common Stock or Infinity Common Stock, as appropriate, that you own.

Q: When do you expect to complete the Merger?

A: MEI and Infinity expect to complete the Merger in mid-2023, subject to any potential regulatory review or approval. However, neither MEI nor Infinity can assure you of when or if the Merger will be completed. Infinity must obtain the approval of Infinity’s stockholders for the Infinity Merger Proposal and MEI must obtain the approval of MEI’s stockholders for the MEI Nasdaq Proposal, and both parties must satisfy certain closing conditions. If the Merger is not satisfied prior to the outside date of August 31, 2023, either party may elect to

terminate the Merger Agreement, subject to certain caveats. See “The Merger Agreement—Conditions to the Completion of the Merger” for more information regarding conditions to the completion of the Merger.

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Q: What happens if the Merger is not completed?

A: If the Merger is not completed, Infinity stockholders will not receive any consideration for their shares of Infinity Common Stock in connection with the Merger. Instead, MEI and Infinity will remain independent, public companies and, assuming that MEI and Infinity are able to comply with the required listing standards, MEI Common Stock will continue to be traded on The Nasdaq Capital Market and Infinity Common Stock will continue to be traded on The Nasdaq Global Select Market. In addition, if the Merger Agreement is terminated in certain circumstances, MEI and Infinity may be required to pay a termination fee. See “The Merger Agreement—Termination” for a complete discussion of the circumstances under which a termination fee will be required to be paid.

Q: Where can I find the voting results of the MEI Special Meeting and the Infinity Special Meeting?

A: The preliminary voting results will be announced at the MEI Special Meeting and Infinity Special Meeting, respectively. In addition, within four business days following the MEI Special Meeting and Infinity Special Meeting, MEI and Infinity will each disclose the preliminary or, if available, final voting results of the MEI Special Meeting and Infinity Special Meeting on a Current Report on Form 8-K filed with the SEC. If preliminary voting results are disclosed, MEI and Infinity will each file an amended Current Report on Form 8-K with the SEC to disclose final voting results within four business days following certification of the final voting results.

Q: Is the completion of the Merger subject to a financing condition?

A: No. The completion of the Merger is not subject to any financing condition.

Q: How will I know when the other conditions to completion of the Merger have been satisfied?

A: As of the date of this joint proxy statement/prospectus, the parties have not satisfied the closing conditions to the Merger. If the closing conditions are satisfied, MEI and Infinity will each announce the closing of the Merger via the filing of a Current Report on Form 8-K with the SEC. There is also a possibility that the closing conditions to the Merger will not be satisfied prior to the outside date of August 31, 2023, after which date either party may elect to terminate the Merger Agreement, subject to certain caveats. As a result, it is possible that factors outside the control of both companies could result in the Merger being completed at a different time or not at all.

Infinity stockholders will not know the actual Exchange Ratio or the value of the MEI Common Stock to be received as merger consideration until after the date of the MEI Special Meeting and the Infinity Special Meeting. See “Risk Factors.”

Q: Are there any risks that I should consider in deciding whether to vote for the adoption of the Merger Agreement?

A: Yes. You should read and carefully consider the risk factors set forth in the “Risk Factors” section.

Q: Who can answer any questions I may have about the Merger or the transactions contemplated by the Merger Agreement?

A: If you have any questions about the Merger or the transactions contemplated by the Merger Agreement, or if you need additional copies of this joint proxy statement/prospectus, you should contact:

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RISK FACTORS

Risks Related to MEI’s Business

Risks Related to MEI’s Development Stage

MEI is currently operating in a period of capital markets disruption and economic uncertainty.

The U.S. capital markets are currently experiencing extreme volatility and disruption following the global outbreak of COVID-19, high inflation and the government response thereto, potential economic downturn, publicized failures in the regional banking sector, the war in Ukraine, and other global events. Disruptions in the capital markets in the past have resulted in illiquidity in parts of the capital markets. Future market disruptions and/or illiquidity would be expected to have an adverse effect on MEI’s business, financial condition, results of operations and cash flows. Unfavorable economic conditions also would be expected to increase MEI’s funding costs, limit its access to the capital markets or result in a decision by lenders not to extend credit to MEI. These events have limited and could continue to limit MEI’s investment considerations, limit its ability to grow and have a material negative impact on MEI’s operating results.

MEI will need substantial additional funds to progress the clinical trial programs for its drug candidates, and to develop new compounds. The actual amount of funds MEI will need will be determined by a number of factors, some of which are beyond MEI’s control.

MEI will need substantial additional funds to progress the clinical trial programs for its drug candidates and to develop any additional compounds. The factors that will determine the actual amount of funds that MEI will need to progress the clinical trial programs may include, but are not limited to, the following:

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MEI has been opportunistic in its efforts to obtain funding, and MEI expects to continue to evaluate various funding alternatives from time to time. If MEI obtains additional funding, it may adversely affect the market price of their common stock and may be dilutive to existing stockholders. If MEI is unable to obtain additional funds on favorable terms or at all, MEI may be required to cease or reduce its operations. MEI may sell additional shares of common stock, and securities exercisable for or convertible into shares of its common stock, or MEI may seek to obtain debt financing, in each case, to satisfy its capital and operating needs; however, such transactions will be subject to market conditions and there can be no assurance any such transactions will be completed.

MEI may be required to seek additional capital through marketing and distribution arrangements or other collaborations, strategic alliances or licensing arrangements with third parties at terms which may be unfavorable to MEI.

If MEI raises additional capital through marketing and distribution arrangements or other collaborations, strategic alliances or licensing arrangements with third parties, MEI may have to relinquish certain valuable rights to its product candidates, technologies, intellectual property, future revenue streams or research programs or grant licenses on terms that may not be favorable to MEI. MEI could also be required to seek collaborators for one or more of its current or future product candidates at an earlier stage than otherwise would be desirable or relinquish MEI’s rights to product candidates or technologies that it otherwise would seek to develop or commercialize itself. If MEI is unable to raise additional capital in sufficient amounts or on terms acceptable to MEI, MEI may have to significantly delay, scale back or discontinue the development or commercialization of one or more of its research and development initiatives. Any of the above events could significantly harm MEI’s business, prospects, financial condition and results of operations and cause the price of MEI’s Common Stock to decline.

MEI is a clinical research and development stage company and is likely to incur operating losses for the foreseeable future.

Risks Related to MEI Clinical Trials

The results of pre-clinical studies and completed clinical trials are not necessarily predictive of future results, and MEI’s current drug candidates may not have favorable results in later studies or trials.

Pre-clinical studies and Phase 1 and Phase 2 clinical trials are an expensive and uncertain process that may take years to complete. Pre-clinical studies and Phase 1 and Phase 2 clinical trials are usually not primarily designed to test the efficacy of a drug candidate, but rather to test safety, to study pharmacokinetics and pharmacodynamics, and to understand the drug candidate’s side effects at various doses and schedules. Favorable

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results in early studies or trials, as well as small studies or trials, may not be repeated in later studies or trials, including ongoing pre-clinical studies, large-scale Phase 3 clinical trials, or other studies intended as registration trials, and MEI’s drug candidates in later-stage trials may fail to show desired safety and efficacy despite having progressed through earlier-stage trials. Interim and top-line results, as well as any results from post-hoc data analyses, may also not be predictive of the final results of a clinical study and/or may not support product approval. The FDA also generally does not accept post-hoc data analyses as support for regulatory approval.

Comparisons of results across different studies should be viewed with caution as such comparisons are limited by a number of factors, including differences in study designs and populations. Such comparisons also will not provide a sufficient basis for any comparative claims following product approval. Unfavorable results from ongoing pre-clinical studies or clinical trials could result in delays, modifications or abandonment of ongoing or future clinical trials, or abandonment of a clinical program. Pre-clinical and clinical results are frequently susceptible to varying interpretations that may delay, limit or prevent regulatory approvals or commercialization. Negative or inconclusive results or adverse medical events during a clinical trial could cause a clinical trial to be delayed, repeated or terminated, or a clinical program to be abandoned.

The outbreak of the novel coronavirus disease, COVID-19, or other pandemic, epidemic or outbreak of an infectious disease may materially and adversely impact MEI’s business, including its preclinical studies and clinical trials.

In December 2019, the novel coronavirus disease, COVID-19, was identified in Wuhan, China. This virus has been declared a pandemic and has spread to multiple global regions. The outbreak and government measures taken in response have also had a significant impact, both direct and indirect, on businesses and commerce, as worker shortages have occurred; supply chains have been disrupted; facilities and production have been suspended; and demand for certain goods and services, such as medical services and supplies, has spiked, while demand for other goods and services, such as travel, has fallen. In response to the COVID-19 pandemic, “shelter in place” orders and other public health guidance measures were implemented across much of the U.S., Europe and Asia, including in the locations of MEI’s offices, clinical trial sites, key vendors and partners. Although some of such orders have been lifted in certain geographic locations, such measures may be, and, in some cases, have been re-implemented due an increase in the number of positive cases of COVID-19 or severity thereof, including cases attributable to new variants. These restrictions, as well as government restrictions on travel and a lack of public confidence in the safety of air travel and the use of public transportation have reduced and may continue to reduce the willingness of patients to participate in MEI’s clinical trials and the ability of regulatory officials and clinical monitors to perform visits of MEI’s clinical trial locations. As a result, MEI’s clinical development program timelines have been and may continue to be negatively affected by COVID-19, which could materially and adversely affect MEI’s business, financial condition and results of operations. Despite the vaccination of a large portion of the U.S. adult population, a significant portion of the global adult population remains unvaccinated. The ineffectiveness of vaccines or public perception thereof, including in combating new variants of the virus, could lead to increased governmental restrictions and changes in public behavior adversely affecting the economy.

As a result of the ongoing COVID-19 pandemic, or similar pandemics, and related “shelter in place” orders and other public health guidance measures, MEI has experienced disruptions that have materially and adversely impacted its clinical trials, including delays in patient enrollment. MEI may in the future experience disruptions that could materially and adversely impact its clinical trials, business, financial condition and results of operations, including:

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The foregoing may require that MEI consult with relevant review and ethics committees, Institutional Review Boards (“IRBs”), and the FDA. The foregoing may also impact the integrity of MEI’s study data. The effects of the ongoing COVID-19 pandemic may also increase the need for clinical trial patient monitoring and regulatory reporting of adverse effects.

The ongoing COVID-19 pandemic and the governmental response continues to rapidly evolve. In light of the ongoing COVID-19 pandemic, the FDA has issued a number of guidance documents, including guidance related to the potential effect of the ongoing COVID-19 pandemic on many clinical trial programs. The FDA also issued guidance on additional steps that are required to maintain GMPs during the pandemic, in addition to a number of other COVID-19 related guidance.

The extent to which the outbreak impacts MEI’s business, preclinical studies and clinical trials will depend on future developments, which are highly uncertain and cannot be predicted with confidence. If MEI or any of the third parties with whom MEI engages were to experience shutdowns or other business disruptions, MEI’s ability to conduct its business in the manner and on the timelines presently planned could be materially and negatively impacted.

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Changes in drug candidate manufacturing or formulation may result in additional costs or delay.

As drug candidates are developed through preclinical studies to late-stage clinical trials toward approval and commercialization, it is common that various aspects of the development program, such as manufacturing methods, manufacturing sites, formulation, and methods of delivery are altered along the way in an effort to optimize processes and results. Any of these changes could cause MEI drug candidates to perform differently and affect the results of planned clinical trials or other future clinical trials conducted with the altered materials. Such changes may also require additional studies to demonstrate the comparability of the product candidate using prior processes, formulation, or manufacturers, FDA notification, or FDA approval. Any of the foregoing could limit MEI’s future revenues and growth.

Risks Related to MEI’s Licensing and Collaboration Agreements

If third parties with whom MEI collaborates on the development and commercialization of MEI’s drug candidates do not satisfy their obligations, do not otherwise pursue development or commercialization of MEI’s drug candidates or if they terminate their agreements with MEI, MEI may not be able to develop or commercialize its drug candidates.

MEI has in the past and may in the future enter into agreements to collaborate with third parties on the development, manufacturing or commercialization of its drug candidates in the future. In connection with these agreements, MEI may grant certain rights regarding the use of its patents and technology. The counterparties may be responsible for development, manufacturing or commercialization of MEI’s drug candidates and the costs related thereto.

MEI’s counterparties might not fulfill all of their obligations to MEI. In addition, the agreements with MEI’s counterparties provide the counterparties with substantial control of the development and commercialization of MEI’s drug candidates and discretion whether to devote resources to the full pursuit thereof or otherwise fail to fully pursue the development and commercialization of MEI’s drug candidates. Even without breaching their obligations to MEI, MEI’s counterparties may not devote adequate resources or otherwise pursue the development and commercialization of MEI’s drug candidates, whether as a result of their assessment of the likelihood of success of such efforts, for financial reasons or otherwise. MEI’s ability to receive revenue from its drug candidates may be dependent upon their efforts. If they fail to devote adequate resources or otherwise do not successfully develop, commercialize or manufacture MEI’s drug candidates, MEI may not receive the future milestone payments or royalties provided for in the agreement. In addition, under certain circumstances, including MEI’s failure to satisfy its obligations under the agreement, the counterparty may have the right to terminate the agreement.

MEI could also become involved in disputes with its counterparties, which could lead to delays in or termination of the agreement and time-consuming and expensive litigation or arbitration.

If MEI’s counterparties are unwilling or unable to fulfill their obligations or otherwise fail to fully pursue the development and commercialization of MEI’s drug candidates or if the agreement is terminated, MEI may lack sufficient resources to develop and commercialize its drug candidates on its own and may be unable to reach agreement with a suitable alternative collaborator. The failure to develop and commercialize MEI drug candidates would have a material adverse effect on MEI’s business, operating results, prospects and financial condition.

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MEI is subject to significant obligations to Presage in connection with MEI’s license of voruciclib, and MEI may become subject to significant obligations in connection with future licenses it obtains, which could adversely affect the overall profitability of any products MEI may seek to commercialize, and such licenses of drug candidates, the development and commercialization for which MEI is solely responsible, may never become profitable.

In September 2017, MEI entered into a license agreement with Presage (“the Presage License Agreement”). Under the terms of the agreement, Presage granted MEI exclusive worldwide rights to develop, manufacture and commercialize voruciclib, a clinical-stage, oral and selective CDK inhibitor, and related compounds. In exchange, MEI paid Presage $2.9 million and are obligated for additional potential payments of up to $181 million upon the achievement of certain development, regulatory and commercial milestones. MEI will also pay mid-single-digit tiered royalties on the net sales of any product successfully developed pursuant to such agreement. MEI may enter into similar agreements in the future that require it to make significant payments upon obtainment of development, regulatory or commercial milestones. MEI may be obligated to make milestone or royalty payments when it does not have the cash on hand to make these payments or have available cash for MEI’s other development efforts. These milestone and royalty payments could adversely affect the overall profitability for MEI of any products that it may seek to commercialize. In addition, if MEI fails to comply with its obligations under the license agreement, the counterparty may have the right to terminate the agreement. In such a case, MEI would lose its rights to the intellectual property covered by the license agreement and MEI would not be able to develop, manufacture or commercialize its drug candidates.

The profitability of MEI’s license agreement with Presage depends on the successful development, regulatory approval and commercialization of voruciclib. MEI is solely responsible for the development and commercialization of voruciclib, including the related costs. Drug development is a long, expensive and uncertain process and delay or failure can occur at any stage of MEI’s clinical trials. MEI cannot be certain that it will ever receive regulatory approval for voruciclib or that it will be successfully commercialized, even if approved.

MEI’s business strategy may include entry into additional collaborative or license agreements. MEI may not be able to enter into collaborative or license agreements or may not be able to negotiate commercially acceptable terms for these agreements.

MEI’s current business strategy may include the entry into additional collaborative or license agreements for the development and commercialization of its drug and drug candidates. The negotiation and consummation of these types of agreements typically involve simultaneous discussions with multiple potential collaborators or licensees and require significant time and resources. In addition, in attracting the attention of pharmaceutical and biotechnology company collaborators or licensees, MEI competes with numerous other third parties with product opportunities as well as the collaborators’ or licensees’ own internal product opportunities. MEI may not be able to consummate collaborative or license agreements, or MEI may not be able to negotiate commercially acceptable terms for these agreements.

If MEI does enter into such arrangements, it could be dependent upon the subsequent success of these other parties in performing their respective responsibilities and the cooperation of MEI’s partners. MEI’s collaborators may not cooperate with MEI or perform their obligations under MEI’s agreements with them. MEI cannot control the amount and timing of its collaborators’ resources that will be devoted to researching MEI product candidates pursuant to MEI’s collaborative agreements with them or whether MEI’s collaborators will comply with the applicable regulatory requirements. MEI’s collaborators may choose to pursue existing or alternative technologies in preference to those being developed in collaboration with MEI.

Under agreements with any collaborators or licensees MEI may work with in the future, MEI may rely significantly on them to, among other activities:

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If MEI does not consummate collaborative or license agreements, MEI may use its financial resources more rapidly on its drug development efforts, continue to defer certain development activities or forego the exploitation of certain geographic territories, any of which could have a material adverse effect on MEI’s business prospects. Further, MEI may not be successful in overseeing any such collaborative arrangements. If MEI fails to establish and maintain necessary collaborative or license relationships, MEI’s business prospects could suffer.

Collaboration agreements may not lead to development or commercialization of drug candidates in the most efficient manner, or at all. If any collaborations MEI might enter into do not result in the successful development and commercialization of drug candidates or if one of MEI’s collaborators subsequently terminates its agreement with MEI, MEI may not receive any future research funding or milestone or royalty payments under the collaboration. If MEI does not receive the funding it expects under the agreements, MEI’s development of its drug candidates could be delayed, and MEI may need additional resources to develop its drug candidates and its product platform. All of the risks relating to product development, regulatory approval and commercialization described in MEI’s Annual Report also apply to the activities of MEI’s collaborators. Moreover, should MEI’s collaborators not comply with the applicable regulatory or legal requirements, MEI and/or they, may be subject to regulatory enforcement action.

Risks Related to FDA and Non-U.S. Regulation

Final approval by regulatory authorities of MEI’s drug candidates for commercial use may be delayed, limited or prevented, any of which would adversely affect MEI’s ability to generate operating revenues.

MEI will not generate any operating revenue until MEI, a licensee, or a potential collaborator successfully commercialize one of MEI’s drug candidates. Currently, MEI has drug candidates at different stages of development, and each will need to successfully complete certain clinical studies and obtain regulatory approval before potential commercialization. MEI may experience unforeseen events during product development that may substantially delay or prevent product approval. For example, the FDA may order the temporary, or permanent, discontinuation of a clinical trial at any time if it believes that the clinical trial either is not being conducted in accordance with FDA requirements or presents an unacceptable risk to the clinical trial patients. An IRB may also require the clinical trial at the site to be halted, either temporarily or permanently, for failure to comply with the IRB’s requirements or if the trial poses an unexpected serious harm to clinical trial patients. The FDA or an IRB may also impose conditions on the conduct of a clinical trial. Clinical trial sponsors may also choose to discontinue clinical trials as a result of risks to clinical trial patients, a lack of favorable results, or changing business priorities.

The pre-clinical and clinical development, manufacturing, labeling, packaging, storage, recordkeeping, export, marketing and distribution, and other possible activities relating to MEI’s drug candidates are subject to extensive regulation by the FDA and other regulatory agencies. Failure to comply with applicable regulatory requirements may, either before or after product approval, subject MEI to administrative or judicially imposed sanctions that may negatively impact the approval of one or more of MEI’s drug candidates or otherwise negatively impact MEI’s business.

Neither collaborators, licensees nor MEI are permitted to market a drug candidate in the U.S. until the particular drug candidate is approved for marketing by the FDA. Specific pre-clinical data, chemistry, manufacturing and controls data, a proposed clinical trial protocol and other information must be submitted to the FDA as part of an IND application, and clinical trials may commence only after the IND application becomes effective. To market a new drug in the U.S., MEI must submit to the FDA and obtain FDA approval of an NDA. An NDA must be supported by extensive clinical and pre-clinical data, as well as extensive information regarding chemistry, manufacturing and controls to demonstrate the safety and effectiveness of the drug candidate.

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Obtaining approval of an NDA can be a lengthy, expensive and uncertain process. Regulatory approval of an NDA is not guaranteed. The number and types of pre-clinical studies and clinical trials that will be required for FDA approval varies depending on the drug candidate, the disease or condition that the drug candidate is designed to target and the regulations applicable to any particular drug candidate. The FDA may also require additional studies or data after a trial has begun or more studies or data than MEI otherwise has anticipated. Despite the time and expense exerted in pre-clinical and clinical studies, failure can occur at any stage, and MEI could encounter problems that delay its product candidate development, trigger additional requirements from the FDA, or that cause MEI to abandon clinical trials or to repeat or perform additional pre-clinical studies and clinical trials. The FDA can delay, limit or deny approval of a drug candidate for many reasons, and product candidate development programs may be delayed or may not be successful for many reasons including but not limited to, the following:

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MEI’s pre-clinical and clinical data, other information and procedures relating to a drug candidate may not be sufficient to support approval by the FDA or any other U.S. or foreign regulatory authority, or regulatory interpretation of these data and procedures may be unfavorable. MEI may not be successful in any effort to take advantage of expedited regulatory pathways for serious or life-threatening illnesses or to secure marketing authorization from the FDA. MEI may not be able to demonstrate that its product candidates provide a benefit over existing therapies and, when used in combination with other therapies, MEI may not be able to demonstrate that its product candidates contributed to any observed effect. MEI cannot be certain that any NDA it submits will be approved by the FDA for full or accelerated approval on a timely basis, if at all. Securing accelerated approval requires demonstrating a meaningful therapeutic benefit over available existing treatments. Accelerated approvals are based upon a surrogate endpoint that is reasonably likely to predict clinical benefit, or on a clinical endpoint that can be measured earlier than irreversible morbidity or mortality, that is reasonably likely to predict an effect on irreversible morbidity or mortality or other clinical benefit, taking into account the severity, rarity, or prevalence of the condition and the availability or lack of alternative treatments. If approved, the FDA will require post-marketing studies to verify clinical benefit. Failure to conduct required post-approval studies, or confirm a clinical benefit, will allow the FDA to withdraw the drug from the market on an expedited basis. Indeed, companies have previously withdrawn approved indications following failure to confirm a clinical benefit for their products. Moreover, in recent years, the accelerated approval pathway has come under significant FDA and public scrutiny. Accordingly, the FDA may be more conservative in granting accelerated approval or, if granted, may be more apt to withdrawal approval if clinical benefit is not confirmed. There may also be legislative or regulatory changes to the accelerated approval pathway which may impact the ability to obtain or maintain any such approvals, if received.

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Should MEI decide to seek accelerated approval, the FDA may not agree that the accelerated approval pathway is appropriate, may disagree with MEI’s chosen surrogate endpoints, or may find that the accelerated approval criteria are not met. Should the FDA disagree with MEI’s approach, MEI would be required to conduct additional clinical studies prior to submitting an NDA and prior to the FDA granting marketing approval. Moreover, should MEI receive accelerated approval for a product candidate, the FDA-approved label will indicate that the clinical benefit of the product has not been established and that continued approval is contingent upon verification of a clinical benefit in confirmatory trials.

MEI’s business and reputation may be harmed by any failure or significant delay in receiving regulatory approval for the sale of any drugs resulting from its drug candidates. As a result, MEI cannot predict when or whether regulatory approval will be obtained for any drug MEI develops. Additionally, other factors may serve to delay, limit or prevent the final approval by regulatory authorities of MEI drug candidates for commercial use, including, but not limited to:

Significant delays relating to any preclinical or clinical trials also could shorten any periods during which MEI may have the exclusive right to commercialize its product candidates or allow its competitors to bring products to market before MEI does. This may prevent MEI from receiving marketing approvals and impair MEI’s ability to successfully commercialize its product candidates and may harm its business and results of operations. If MEI experiences delays in obtaining approval, if MEI fails to obtain approval of a product candidate or if the label for a product candidate does not include the labeling claims necessary or desirable for the successful commercialization of that product candidate, the commercial prospects for such product candidate may be harmed and MEI’s ability to generate revenues from that product candidate will be materially impaired. Accordingly, the successful development of any of MEI’s drug candidates is uncertain and, accordingly, MEI may never commercialize any of these drug candidates or generate significant revenue.

The FDA may determine that MEI drug candidates have undesirable side effects that could delay or prevent regulatory approval or commercialization.

Undesirable side effects caused by MEI drug candidates could cause MEI, IRBs, and other reviewing entities or regulatory authorities to interrupt, delay, or halt clinical trials and could result in a more restrictive label or the delay or denial of regulatory approval by the FDA or other comparable foreign authorities. Undesirable side effects may also result in requirements for costly post-marketing testing and surveillance, or other requirements, including REMS, to monitor the safety or efficacy of the products. These could prevent MEI from commercializing and generating revenues from the sale of its drug candidates.

Many compounds that initially showed promise in clinical or earlier stage testing have later been found to cause side effects that prevented further development of the compound. In addition, adverse events which had initially been considered unrelated to the study treatment may later be found to be caused by the study treatment. Moreover, incorrect or improper use of MEI’s drug candidates could cause unexpected side effects or adverse events. If any of MEI’s drug candidates are associated with serious adverse events or undesirable side effects or

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have properties that are unexpected, MEI may need to abandon development or limit development of that drug candidate to certain uses or subpopulations in which the undesirable side effects or other characteristics are less prevalent, less severe or more acceptable from a risk-benefit perspective. The therapeutic-related side effects could affect patient recruitment or the ability of enrolled patients to complete the trial or result in potential product liability claims. Any of these occurrences may significantly harm MEI’s business, financial condition, results of operations, and prospects.

If MEI experiences delays or difficulties in the enrollment of patients in clinical trials, MEI’s completion of clinical trials and receipt of necessary regulatory approvals could be delayed or prevented.

MEI may not be able to initiate or continue conducting clinical trials for its drug candidates if MEI is unable to locate and enroll a sufficient number of eligible patients to participate in these trials as required by the FDA or similar regulatory authorities outside the U.S. Competitors of MEI may also have ongoing clinical trials for drug candidates that are intended to treat the same indications as MEI’s drug candidates, and patients who would otherwise be eligible for MEI clinical trials may instead enroll in clinical trials of MEI’s competitors’ drug candidates. Patient enrollment is affected by other factors including:

MEI’s inability to enroll a sufficient number of patients for its clinical trials would result in significant delays and could require MEI to abandon one or more clinical trials altogether. In particular, there may be low or slow enrollment, and the studies may enroll subjects that do not meet the inclusion criteria, requiring the erroneously enrolled subjects to be excluded and the trial population to be increased. Moreover, patients in MEI’s clinical trials may be at risk for dropping out of MEI studies if they are not experiencing relief of their disease. A significant number of withdrawn patients would compromise the quality of MEI’s data.

Enrollment delays in MEI’s clinical trials may result in increased development costs for MEI’s drug candidates, or the inability to complete development of MEI’s drug candidates, which would cause the value of MEI to decline, limit MEI’s ability to obtain additional financing, and materially impair MEI’s ability to generate revenues.

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Changes in funding for the FDA and other government agencies or future government shutdowns could cause delays in the submission and regulatory review of marketing applications, which could negatively impact MEI’s business or prospects.

The ability of the FDA to review and approve new products can be affected by a variety of factors, including government budget and funding levels, ability to hire and retain key personnel and accept submission, applications, and the payment of user fees, and statutory, regulatory, and policy changes, including the Congressional reauthorization of the FDA’s user fee bills. In addition, government funding of other government agencies that fund research and development activities is subject to the political process, which is inherently fluid and unpredictable.

Disruptions at the FDA and other agencies, including as a result of pandemics like COVID-19 and legislative actions, may also slow the time necessary for new drugs to be reviewed and/or approved by necessary government agencies, which would adversely affect MEI’s business. For example, Congress is currently negotiating reauthorization of the FDA user fee bills, which are critical to the FDA’s operations. Moreover, over the last several years, including for 35 days beginning on December 22, 2018, the U.S. government has shut down several times and certain regulatory agencies, such as the FDA, had to furlough critical FDA employees and stop critical activities. If a prolonged government shutdown occurs, if the FDA is required to furlough review staff or other necessary employees, or if agency operations are otherwise impacted, it could significantly affect the ability of the FDA to timely review and process MEI’s regulatory submissions, which could have a material adverse effect on MEI’s business or prospects.

Failure to obtain regulatory approval in foreign jurisdictions would prevent MEI from marketing its products internationally.

MEI may attempt to have its drug candidates marketed outside the U.S. In order to market MEI products in many non-U.S. jurisdictions, MEI must obtain separate international regulatory approvals and comply with numerous and varying regulatory requirements. To date, MEI has not filed for marketing approval for any of its drug candidates and may not receive the approvals necessary to commercialize its drug candidates in any market.

The approval procedure varies among countries and may include all of the risks associated with obtaining FDA approval. Further, the time required to obtain foreign regulatory approval may differ from that required to obtain FDA approval, and additional pre-clinical studies, clinical trials, other testing and data review may be required. MEI may not obtain foreign regulatory approvals on a timely basis, if at all. Additionally, approval by the FDA does not ensure approval by regulatory agencies in other countries, and approval by one foreign regulatory authority does not ensure approval by regulatory agencies in other foreign countries or by the FDA. However, a failure or delay in obtaining regulatory approval in one jurisdiction may have a negative effect on the regulatory approval process in other jurisdictions, including approval by the FDA. The failure to obtain regulatory approval in foreign jurisdictions could limit commercialization of MEI’s products, reduce MEI’s ability to generate profits and harm its business.

Any designation granted by the FDA for any of MEI’s product candidates may not lead to a faster development or regulatory review or approval process, and does not increase the likelihood that MEI’s product candidates will receive marketing approval. MEI may also not be able to obtain or maintain any such designation.

There are a number of FDA programs that are intended to speed the development of drugs that are intended to treat serious diseases and conditions when there is an unmet need, including Fast Track and Break Through Therapy Designation. Receipt of such designations is within the discretion of the FDA. Accordingly, even if MEI believes one of its drug candidates meets the criteria for a designation, the FDA may disagree. If MEI receives any designation, the potential reduced timelines associated with designation may introduce significant chemistry, manufacturing and controls challenges for product development as manufacturing development may need to take

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place at a faster pace than would otherwise be required because the FDA will expect that properly qualified and manufactured product be available at the time of product approval. In any event, the receipt of a designation for a product candidate may not result in a faster development process, review or approval compared to drugs considered for approval under conventional FDA procedures and does not assure ultimate approval by the FDA. In addition, even after granting a designation, the FDA may later decide that such product candidates no longer meet the conditions for qualification and rescind such designations.

Any orphan drug designations MEI receives may not confer marketing exclusivity or other benefits.

In the U.S., under the Orphan Drug Act, the FDA may grant orphan designation to a drug or biological product intended to treat a rare disease or condition. Such diseases and conditions are those that affect fewer than 200,000 individuals in the U.S., or if they affect more than 200,000 individuals in the U.S., there is no reasonable expectation that the cost of developing and making a drug available in the U.S. for these types of diseases or conditions will be recovered from sales of the drug. Orphan drug designation must be requested before submitting an NDA. If the FDA grants orphan drug designation, the identity of the therapeutic agent and its potential orphan use are disclosed publicly by that agency. Orphan drug designation does not convey any advantage in or shorten the duration of the regulatory review and approval process, but it can lead to financial incentives, such as opportunities for grant funding toward clinical trial costs, tax advantages and user-fee waivers. The EMA and the UK also have programs for orphan drugs.

There is no guarantee that a drug candidate will receive orphan drug designation. There is also no guarantee that MEI would be able to maintain any designations that it receives. For instance, orphan drug designation in the U.S., EU or UK may be revoked for a number of reasons. If a drug that has orphan designation subsequently receives the first FDA approval for the disease or condition for which it has such designation, the drug is entitled to orphan drug marketing exclusivity for a period of seven years. Orphan drug marketing exclusivity generally prevents the FDA from approving another application, including a full NDA, to market the same drug or biological product for the same orphan use for seven years, except in limited circumstances, including if the FDA concludes that the later drug is safer, more effective or makes a major contribution to patient care. For purposes of small molecule drugs, the FDA defines “same drug” as a drug that contains the same active moiety and is intended for the same use as the drug in question. MEI may not be able to obtain future orphan drug designations that it may apply for or maintain any orphan drug designations that MEI may receive. A designated orphan drug also may not receive orphan drug marketing exclusivity if it is approved for a use that is broader than the indication for which it received orphan designation or if it is deemed to be the same drug as a previously approved drug and cannot demonstrate clinical superiority. Similarly, in the EMA (and the MHRA), orphan drugs can receive an exclusivity period of ten years, but can be reduced to six years if the drug no longer meets the criteria for orphan drug designation or if the drug is sufficiently profitable so that market exclusivity is no longer justified. Orphan designation does not convey any advantage in, or shorten the duration of, the regulatory review and approval process.

Orphan drug exclusivity may be lost if the FDA, EMA or MHRA determines that the request for designation was materially defective or if the manufacturer is unable to assure sufficient quantity of the drug to meet the needs of patients with the rare disease or condition. Orphan drug exclusivity also may not protect a product from competition. For instance, the FDA may approve a drug that is the same drug with orphan exclusivity for a different indication or a different drug for the same indication as the orphan product. Even after an orphan product is approved, the FDA can also subsequently approve a product containing the same principal molecular features for the same condition if the FDA concludes that the latter product is clinically superior. The FDA may further grant orphan designation to multiple sponsors for the same compound or active molecule and for the same indication. If another sponsor receives FDA approval for such product before MEI does, MEI would be prevented from launching its product in the U.S. for the orphan indication for a period of at least seven years unless MEI can demonstrate clinical superiority.

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Risks Related to the Commercialization of MEI Drug Candidates

Even if MEI or MEI’s licensees receive regulatory approval to commercialize its drug candidates, MEI’s ability to generate revenues from any resulting products will be subject to a variety of risks, many of which are out of MEI’s control.

Even if MEI’s drug candidates obtain regulatory approval, resulting products may not gain market acceptance among physicians, patients, healthcare payers or the medical community. MEI believes that the degree of market acceptance and MEI’s ability to generate revenues from such products will depend on a number of factors, including, but not limited to, the following:

If any of MEI’s drugs are approved and fail to achieve market acceptance, MEI may not be able to generate significant revenue to achieve or sustain profitability.

If any products MEI develops become subject to unfavorable pricing regulations, third party reimbursement practices or healthcare reform initiatives, MEI’s ability to successfully commercialize its products will be impaired.

MEI’s future revenues, profitability and access to capital will be affected by the continuing efforts of governmental and private third party payers to manage, contain or reduce the costs of health care through various means, such as capping prices, limiting price increases, reducing reimbursement, and requiring rebates. MEI is also unsure of the impact of any future health care reform legislation or other changes in healthcare policy may have on MEI’s business or what actions federal, state, foreign and private payers may take or reforms that may be implemented in the future. Therefore, it is difficult to predict the effect of any potential reform on MEI’s business. MEI’s ability to commercialize its drug candidates successfully will depend, in part, on the extent to which reimbursement for the cost of such drug candidates and related treatments will be available from government health administration authorities, such as Medicare and Medicaid in the U.S., private health insurers and other organizations. Significant uncertainty exists as to the reimbursement status of newly approved health care products, particularly for indications for which there is no current effective treatment or for which medical care typically is not sought. Adequate third party coverage may not be available to enable MEI to maintain price levels sufficient to realize an appropriate return on its investment in research and development. If adequate coverage and reimbursement levels are not provided by government and third party payers for use of MEI products, MEI’s products may fail to achieve market acceptance without a substantial reduction in price or at all and MEI’s results of operations will be harmed. In addition, government regulation may restrict MEI’s business and financial relationships with health care providers and managed care intermediaries in ways that could impact MEI’s ability to successfully market its products.

Further, there has been heightened governmental scrutiny over the manner in which manufacturers set prices for their marketed products, which have resulted in several recent Congressional inquiries and proposed and enacted bills by Congress and the states designed to, among other things, bring more transparency to product pricing, review the relationship between pricing and manufacturer patient programs, and reform government program

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reimbursement methodologies for products. Most recently, in August 2022, President Biden signed into the law the Inflation Reduction Act of 2022 (the “IRA”) which among other things, contains multiple provisions that may impact the prices of drug products that are both sold into the Medicare program and throughout the United States.

In addition, the U.S. government, state legislatures, and foreign governments have shown significant interest in implementing cost containment programs, including price-controls, restrictions on reimbursement, requirements for substitution of generic products for branded prescription drugs, and permitting importation of drugs from outside the U.S. to limit the growth of government paid health care costs. For example, the U.S. government has passed legislation requiring pharmaceutical manufacturers that participate in federal healthcare programs to provide rebates and discounts to certain entities and governmental payors. Further, Congress and the current administration have each indicated that it will continue to seek new legislative and/or administrative measures to control drug costs. Individual states in the U.S. have also been increasingly passing legislation and implementing regulations designed to control pharmaceutical product pricing, including price or patient reimbursement constraints, discounts, restrictions on certain product access and marketing cost disclosure and transparency measures, and, in some cases, designed to encourage importation from other countries and bulk purchasing.

MEI’s drug candidates are subject to ongoing government regulation both before and after regulatory approval.

Both before and after regulatory approval, MEI’s drug candidates are subject to strict and ongoing regulation. Compliance with such regulations may consume substantial financial and management resources and expose MEI and its collaborators to the potential for other adverse circumstances. For example, a regulatory authority can place restrictions on the sale or marketing of a drug in order to manage the risks identified during initial clinical trials or after the drug is on the market. A regulatory authority can condition the approval for a drug on costly post-marketing follow-up studies. Based on these studies, if a regulatory authority does not believe that the drug demonstrates a clinical benefit to patients or an acceptable safety profile, it could limit the indications for which a drug may be sold or revoke the drug’s marketing approval. In addition, identification of certain side effects either during clinical trials or after a drug is on the market may result in reformulation of a drug, additional pre-clinical and clinical trials, labeling changes, termination of ongoing clinical trials or withdrawal of approval. Any of these events could delay or prevent MEI from generating revenue from the commercialization of these drugs and cause MEI to incur significant additional costs.

Compliance with the applicable regulatory requirements may result in significant expenses and MEI and its third party contractors and collaborators may be subject to unannounced FDA and other regulatory authority inspections and assessments. Any failure to comply with the applicable regulatory requirements or problems with MEI’s drug candidates may result in regulatory enforcement or other actions, including:

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Non-compliance with any foreign jurisdictions’ requirements, including requirements regarding the protection of personal information, can also lead to significant penalties and sanctions.

Any of these events could prevent MEI from achieving or maintaining regulatory product approval and market acceptance of the particular drug candidate, if approved, or could substantially increase the costs and expenses of developing and commercializing such product, which in turn could delay or prevent MEI from generating significant revenues from its sale.

Other changes may also impact MEI’s ability to conduct studies and the approvability or marketability of MEI’s drug candidates, including changes in law, government regulation, or FDA policy, including review policies, which may be due to changes in the U.S. government and U.S. administration, or changes in medical practice or standard of care.

If MEI is slow or unable to adapt to changes in existing requirements, standards of care, or the adoption of new requirements or policies, or if MEI is not able to maintain regulatory compliance, MEI may lose any marketing approval that it may have obtained and be subject to regulatory enforcement action. Should any of the above actions take place, they could adversely affect MEI’s ability to achieve or sustain profitability.

MEI may not be able to establish the contractual arrangements necessary to develop, market and distribute its drug candidates.

A key part of MEI’s strategy is to establish contractual relationships with third parties to package, market and distribute its drug candidates. There is no assurance that MEI will be able to negotiate commercially acceptable licensing or other agreements for the future exploitation of its drug candidates, including continued clinical development, manufacture or marketing. If MEI is unable to successfully contract for these services, or if arrangements for these services are terminated, MEI may have to delay its commercialization program which will adversely affect its ability to generate operating revenues.

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MEI’s commercial opportunity will be reduced or eliminated if competitors develop and market products that are more effective, have fewer side effects or are less expensive than MEI’s drug candidates.

The development of drug candidates is highly competitive. A number of other companies have products or drug candidates that have either been approved or are in various stages of pre-clinical or clinical development that are intended for the same therapeutic indications for which MEI’s drug candidates are being developed. Some of these potential competing drug candidates are further advanced in development than MEI’s drug candidates and may be commercialized sooner. Even if MEI is successful in developing effective drugs, its compounds may not compete successfully with products produced by MEI’s competitors.

MEI’s competitors include pharmaceutical companies and biotechnology companies, as well as universities and public and private research institutions. In addition, companies active in different but related fields represent substantial competition for MEI. Many of MEI’s competitors developing oncology drugs have significantly greater capital resources, larger research and development staffs and facilities and greater experience in drug development, regulation, manufacturing and marketing than MEI does. These organizations also compete with MEI and its service providers, to recruit qualified personnel, and with MEI to attract partners for joint ventures and to license technologies that are competitive with MEI. As a result, MEI’s competitors may be able to more easily develop technologies and products that would render MEI’s technologies or its drug candidates obsolete or non-competitive.

MEI’s product candidates may face competition sooner than anticipated.

MEI’s product candidates, if approved, may face competition from other products that are the same as or similar to MEI’s product candidates. If the FDA or comparable foreign regulatory authorities approve generic or similar versions of any of MEI’s product candidates that receive marketing approval, or such authorities do not grant MEI’s products appropriate periods of regulatory exclusivity before approving generic or similar versions of MEI’s products, the sales of MEI’s products could be adversely affected.

Once an NDA is approved, the product will become a “reference listed drug” in the FDA’s Orange Book. Other applicants may then seek approval of generic versions of MEI’s products through submission of Abbreviated New Drug Applications (“ANDA”) in the U.S. Generic products may be significantly less costly to bring to market than the reference listed drug and companies that produce generic products are generally able to offer them at lower prices, and are generally preferred by third party payors. As a result, the FDA, the administration and Congress have recently taken steps to encourage increased generic drug competition in the market in an effort to bring down drug costs. Following the introduction of a generic drug, a significant percentage of the sales of any branded product or reference listed drug is typically lost to the generic product. Moreover, in addition to generic competition, MEI could face competition from other companies seeking approval of drug products that are similar to MEI’s using the 505(b)(2) regulatory pathway. Such applicants may be able to rely on MEI’s product candidates, if approved, or other approved drug products or published literature to develop drug products that are similar to MEI’s. The introduction of a drug product similar to MEI’s product candidates could expose MEI to increased competition.

Any ANDA or 505(b)(2) applicants seeking to rely upon any of MEI’s product candidates, if such product candidates are approved, would need to submit patent certification statements with their applications for any of MEI’s patents that are listed in the FDA’s Orange Book. There are detailed rules and requirements regarding the patents that may be submitted to the FDA for listing in the Orange Book. MEI may be unable to obtain patents covering its product candidates that contain one or more claims that satisfy the requirements for listing in the Orange Book. If one of MEI’s product candidates is approved and a patent covering that product candidate is not listed in the Orange Book, an ANDA or 505(b)(2) applicant would not have to submit a patent certification with regard to such patent to the FDA, in which case, MEI would not receive the protections provided by the Hatch Waxman Act.

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Moreover, if an ANDA or 505(b)(2) applicant files a paragraph IV challenge to any patents that MEI may list in the FDA’s Orange Book and if MEI does not file a timely patent infringement lawsuit, the ANDA or 505(b)(2) applicant would not be subject to a 30-month stay. If MEI did file such an action, the litigation or other proceedings to enforce or defend its intellectual property rights would likely be complex in nature, may be expensive and time consuming, may divert MEI’s management’s attention from its core business, and may result in unfavorable results that could adversely impact MEI’s ability to prevent third parties from competing with its products. Accordingly, upon approval of MEI’s product candidates MEI may be subject to generic competition or competition from similar products, or may need to commence patent infringement proceedings, which would divert its resources.

MEI currently anticipates that it may be eligible for five years of non-patent marketing exclusivity in the U.S. This exclusivity, however, would not prevent other companies from submitting full NDAs. To the extent MEI does not receive any anticipated periods of regulatory exclusivity or to the extent the FDA or foreign regulatory authorities approve any generic, similar, or other competing products, MEI’s business would be adversely impacted. Competition that MEI’s products may face from generic, similar, or other competing products could materially and adversely impact its future revenue, profitability, and cash flows and substantially limit MEI’s ability to obtain a return on the investments it has made in those product candidates.

Risks Related to MEI’s Reliance on Third Parties

MEI relies on third parties to conduct its clinical trials and pre-clinical studies. If those parties do not successfully carry out their contractual duties or meet expected deadlines, MEI’s drug candidates may not advance in a timely manner or at all.

In the course of MEI’s pre-clinical testing and clinical trials, MEI relies on third parties, including laboratories, investigators, CROs, manufacturers, and distributors to perform critical services. For example, MEI relies on third parties to conduct its clinical trials and many of its pre-clinical studies, which are required to be conducted consistent with regulations on GLPs and GCPs. CROs and study sites are responsible for many aspects of the trials, including finding and enrolling subjects for testing and administering the trials. Although MEI relies on these third parties to conduct its pre-clinical and clinical trials, MEI is responsible for ensuring that each of its trials are conducted in accordance with its investigational plan and protocol and that the integrity of the studies and resulting data is protected. While MEI has agreements governing the activities of such third parties, MEI has limited influence and control over their actual performance and activities. Moreover, the FDA and foreign regulatory authorities require MEI to comply with regulations and standards, commonly referred to as GCPs, for conducting, monitoring, recording, and reporting the results of clinical trials to ensure that the data and results are scientifically credible and accurate, and that the trial subjects are adequately informed of the potential risks of participating in clinical trials. MEI’s reliance on third parties does not relieve it of these responsibilities and requirements. These third parties may not be available when MEI needs them or, if they are available, may not devote sufficient time or resources to MEI’s studies, may not comply with all regulatory and contractual requirements, or may not otherwise perform their services in a timely or acceptable manner, and MEI may need to enter into new arrangements with alternative third parties and MEI’s clinical trials may be extended, delayed or terminated. These independent third parties may also have relationships with other commercial entities, some of which may compete with MEI. In addition, if such third parties fail to perform their obligations in compliance with MEI’s protocols or the applicable regulatory requirements, MEI’s trials may not meet regulatory requirements or may need to be repeated, MEI may not receive marketing approvals, or MEI or such third parties may face regulatory enforcement.

Agreements with third parties conducting or otherwise assisting with MEI’s clinical or preclinical studies might terminate for a variety of reasons, including a failure to perform by the third parties. If any of MEI’s relationships with these third parties terminate, MEI may not be able to enter into arrangements with alternative providers or to do so on commercially reasonable terms. Switching or adding additional third parties involves additional cost and requires management time and focus. In addition, there is a natural transition period when a new third party

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commences work. As a result, if MEI needs to enter into alternative arrangements, it could delay MEI’s product development activities and adversely affect its business. Though MEI carefully manages its relationships with third parties, there can be no assurance that MEI will not encounter challenges or delays in the future or that these delays or challenges will not have a material adverse impact on MEI’s business, financial condition and prospects, and results of operations.

Accordingly, as a result of MEI’s dependence on third parties, MEI may face delays, failures or cost increases outside of its direct control. These risks also apply to the development activities of collaborators, and MEI does not control their research and development, clinical trial or regulatory activities.

In addition, MEI will be required to report certain financial interests of its third party investigators if these relationships exceed certain financial thresholds or meet other criteria. The FDA or comparable foreign regulatory authorities may question the integrity of the data from those clinical trials conducted by investigators who may have conflicts of interest.

MEI also cannot assure you that upon inspection or review by a given regulatory authority, such regulatory authority will determine that any of MEI’s trials complies with the applicable regulatory requirements. In addition, MEI’s clinical trials must be conducted with drug candidates that were produced under cGMP conditions. Failure to comply with these regulations may require MEI to repeat clinical trials, which would delay the regulatory approval process. MEI is also required to register certain clinical trials and post the results of certain completed clinical trials on a government-sponsored database, ClinicalTrials.gov, within specified timeframes. Failure to do so can result in enforcement actions and adverse publicity.

MEI will depend on third party suppliers and contract manufacturers for the manufacturing of its drug candidates and have no direct control over the cost and timing of manufacturing these drug candidates. Increases in the cost of manufacturing MEI’s drug candidates or delays in manufacturing would increase its costs of conducting clinical trials and could adversely affect MEI’s future profitability.

MEI does not intend to manufacture its drug candidates themselves, and will rely on third parties for its drug supplies both for clinical trials and for commercial quantities in the future. MEI has taken the strategic decision not to manufacture active pharmaceutical ingredients (“API”), nor finished product, for its drug candidates, as these can be more economically supplied by third parties with particular expertise in this area. MEI has identified contract facilities that are registered with the FDA, have a track record of large- scale API and drug product manufacturing, and have already invested in capital and equipment. MEI has no direct control over the manufacturing of its drug candidates, or the cost thereof. If the contract manufacturers are unable to produce sufficient quantities of MEI’s drug candidates, as a result of a lack of available materials or otherwise, MEI’s ability to complete product candidate development and MEI’s future profitability would be adversely affected. If the cost of manufacturing increases, or if the cost of the materials used increases, these costs will be passed on to MEI, making the cost of conducting clinical trials more expensive. Increases in manufacturing costs could adversely affect MEI’s future profitability if MEI is unable to pass all of the increased costs along to its customers.

If these third party suppliers and contract manufacturers do not successfully carry out their contractual duties, meet expected deadlines or manufacture MEI’s drug candidates in accordance with regulatory requirements, if there are disagreements between MEI and such parties, or if such parties are unable to expand capacities to support commercialization of any of MEI’s drug candidates for which MEI obtains marketing approval, MEI may not be able to produce, or may be delayed in producing sufficient drug candidates to meet its supply requirements. Any delays in obtaining adequate supplies with respect to MEI’s drug candidates and components may delay the development or commercialization of its drug candidates.

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Further, MEI, along with its contract manufacturers, are required to comply with FDA requirements for cGMPs, related to product testing, quality assurance, manufacturing and documentation. MEI’s contract manufacturers may not be able to comply with the applicable FDA regulatory requirements, which could result in delays to MEI’s product development programs, could result in adverse regulatory actions against MEI or its contract manufacturers, and could prevent MEI from ultimately receiving product marketing approval. They also generally must pass an FDA preapproval inspection or assessment for conformity with cGMPs before MEI can obtain approval to manufacture its drug candidates and will be subject to ongoing, periodic, unannounced inspection or assessment by the FDA and corresponding state agencies to ensure strict compliance with cGMP, and other applicable government regulations and corresponding foreign standards. If MEI and its contract manufacturers fail to achieve and maintain high manufacturing standards in compliance with cGMP, MEI may experience manufacturing errors resulting in defective products that could be harmful to patients, product recalls or withdrawals, delays or interruptions of production or failures in product testing or delivery, clinical trial or other development program delays, delay or prevention of filing or approval of marketing applications for MEI’s products, cost overruns or other problems that could seriously harm MEI’s business. Not complying with FDA requirements could result in a product recall, costly and time-consuming corrective or preventative actions, or prevent commercialization of MEI’sdrug candidates and delay MEI’s business development activities. In addition, such failure could be the basis for the FDA to issue a warning or untitled letter or take other regulatory or legal enforcement action, including recall or seizure, total or partial suspension of production, suspension of ongoing clinical trials, refusal to approve pending applications or supplemental applications, and potentially civil and/or criminal penalties depending on the matter.

If MEI needs to replace any of its manufacturers or establish additional manufacturing arrangements, MEI may not succeed in its efforts. MEI’s drug candidates may compete with other products and drug candidates for access to manufacturing facilities. There are a limited number of manufacturers that operate under cGMP regulations and that are both capable of manufacturing for MEI and willing to do so. If MEI’s existing third party manufacturers, or the third parties that MEI engages in the future to manufacture a product or component for commercial sale or for MEI’s clinical trials should cease to continue to do so for any reason, MEI would likely experience delays in obtaining sufficient quantities of its drug candidates for MEI to meet commercial demand or to advance its clinical trials while MEI identifies and qualifies replacement suppliers. These third party facilities may also be affected by natural disasters, such as floods or fire, or such facilities could face manufacturing issues, such as contamination or regulatory findings following a regulatory inspection or assessment of such facility. In such instances, MEI may need to locate an appropriate replacement third party relationship, which may not be readily available or on acceptable terms, which would cause additional delay and increased expense. The addition of a new or alternative manufacturer may also require FDA approvals and may have a material adverse effect on MEI’s business.

MEI or its third party manufacturers may also encounter shortages in the raw materials, therapeutic substances, or active pharmaceutical ingredients necessary to produce MEI’s drug candidates in the quantities needed for its clinical trials or, if MEI’s drug candidates are approved, in sufficient quantities for commercialization or to meet an increase in demand. Such shortages may occur for a variety of reasons, including capacity constraints, delays or disruptions in the market, and shortages caused by the purchase of such materials by MEI’s competitors or others. MEI or its third party manufacturers’ failure to obtain the raw materials, therapeutic substances, or active pharmaceutical ingredients necessary to manufacture sufficient quantities of MEI’s drug candidates may have a material adverse effect on MEI’s business. If for any reason MEI is unable to obtain adequate supplies of its drug candidates or the components used to manufacture them, it will be more difficult for MEI to develop its drug candidates and compete effectively.

MEI relies on acquisitions or licenses from third parties to expand its pipeline of drug candidates.

MEI is not presently engaged in drug discovery activities. In order to expand MEI’s pipeline of drug candidates for future development, MEI may need to purchase or in-license any such drug candidates. The success of this strategy depends in large part on the combination of MEI’s regulatory and development capabilities and expertise

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and its ability to identify, select and acquire or in-license clinically-enabled product candidates on terms that are acceptable to MEI. Identifying, selecting and acquiring or in-licensing promising product candidates requires substantial technical expertise, and MEI has limited experience in identifying and integrating any acquired product candidates into its current infrastructure. Efforts to do so may not result in the actual acquisition or in-license of a particular drug candidate, potentially resulting in a diversion of MEI’s management’s time and the expenditure of its resources with no resulting benefit. If MEI is unable to identify, select and acquire or license suitable product candidates from third parties on terms acceptable to MEI, MEI’s business and prospects may be limited.

Risks Related to MEI’s Intellectual Property

MEI’s commercial success is dependent, in part, on obtaining and maintaining patent protection and preserving trade secrets, which cannot be guaranteed.

Patent protection and trade secret protection are important to MEI’s business and its future will depend, in part on MEI’s ability to maintain trade secret protection, obtain patents and operate without infringing the proprietary rights of others both in the U.S. and abroad. Litigation or other legal proceedings may be necessary to defend against claims of infringement, to enforce MEI’s patents or to protect its trade secrets. Such litigation could result in substantial costs and diversion of MEI’s management’s attention.

The patent positions of pharmaceutical and biotechnology companies can be highly uncertain and involve complex legal and factual questions. MEI acquired patents and patent applications related to voruciclib from Presage in 2017, and acquired both issued patents and pending patent applications related to ME-344 from Novogen in relation to its Isoflavone-based compounds, which MEI previously licensed from Novogen, in 2011. Additionally, Novogen had previously applied for patents in a number of countries with respect to the use of their isoflavone compounds, including ME-344. Finally, in September 2013, MEI acquired patents and patent applications related to zandelisib from Pathway Therapeutics, Inc.

The patent applications may not proceed to grant or may be amended to reduce the scope of protection of any patent granted. The applications and patents may also be opposed or challenged by third parties. MEI’s commercial success will depend, in part, on its ability to obtain and maintain effective patent protection for its compounds and their use in treating, preventing, or curing cancer, and to successfully defend patent rights in those technologies against third party challenges. As patent applications in the U.S. are maintained in secrecy until published or issued and as publication of discoveries in the scientific or patent literature often lag behind the actual discoveries, MEI cannot be certain that MEI or Presage were the first to make the inventions covered by the pending patent applications or issued patents referred to above or that MEI or Presage were the first to file patent applications for such inventions. Additionally, the breadth of claims allowed in biotechnology and pharmaceutical patents or their enforceability cannot be predicted. MEI cannot be sure that, should any patents issue, MEI will be provided with adequate protection against potentially competitive products. Furthermore, MEI cannot be sure that should patents issue, they will be of commercial value to MEI, or that private parties, including competitors, will not successfully challenge its patents or circumvent MEI’s patent position in the U.S. or abroad.

Claims by other companies that MEI infringes on their proprietary technology may result in liability for damages or stop MEI’s development and commercialization efforts.

The pharmaceutical industry is highly competitive, and patents have been applied for by, and issued to, other parties relating to products competitive with the compounds that MEI has acquired. Therefore, voruciclib, ME-344, and zandelisib, and any other drug candidates, may give rise to claims that they infringe the patents or proprietary rights of other parties existing now and in the future.

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Furthermore, to the extent that MEI or its consultants or research collaborators use intellectual property owned by others in work performed for MEI, disputes may also arise as to the rights in such intellectual property or in resulting know-how and inventions. An adverse claim could subject MEI to significant liabilities to such other parties and/or require disputed rights to be licensed from such other parties.

MEI has contracted formulation development and manufacturing process development work for its product candidates. This process has identified a number of excipients, or additives to improve drug delivery, which may be used in the formulations. Excipients, among other things, perform the function of a carrier of the active drug ingredient. Some of these identified excipients or carriers may be included in third party patents in some countries. MEI intends to seek a license if it decides to use a patented excipient in the marketed product or MEI may choose one of those excipients that does not have a license requirement.

MEI cannot be sure that any license required under any such patents or proprietary rights would be made available on terms acceptable to MEI, if at all. If MEI does not obtain such licenses, it may encounter delays in product market introductions, or may find that the development, manufacture or sale of products requiring such licenses may be precluded.

MEI may be subject to claims by third parties asserting that MEI or its employees have misappropriated their intellectual property, or claiming ownership of what MEI regards as its own intellectual property.

Many MEI employees and the employees of Kyowa Kirin and third parties upon which MEI relies to conduct its clinical trials were previously employed at universities or at other biotechnology or pharmaceutical companies, some of which may be competitors or potential competitors. Some of these employees executed proprietary rights, non-disclosure and non-competition agreements, or similar agreements, in connection with such previous employment. Although MEI tries to ensure that its employees do not use the proprietary information or know-how of others in their work for MEI, MEI may be subject to claims that MEI or these employees have used or disclosed intellectual property, including trade secrets or other proprietary information, of any such third party. Litigation may be necessary to defend against such claims. If MEI fails in defending any such claims, in addition to paying monetary damages, MEI may lose valuable intellectual property rights or personnel or sustain damages. Such intellectual property rights could be awarded to a third party, and MEI could be required to obtain a license from such third party to commercialize MEI’s technology or products. Such a license may not be available on commercially reasonable terms or at all. Even if MEI is successful in defending against such claims, litigation could result in substantial costs and be a distraction to management.

In addition, while MEI typically requires its employees, consultants, advisors and collaborators who may be involved in the development of intellectual property to execute agreements assigning such intellectual property to MEI, MEI may be unsuccessful in executing such an agreement with each party who in fact develops intellectual property that MEI regards as its own, which may result in claims by or against MEI related to the ownership of such intellectual property. If MEI fails in prosecuting or defending any such claims, in addition to paying monetary damages, MEI may lose valuable intellectual property rights. Even if MEI is successful in prosecuting or defending against such claims, litigation could result in substantial costs and be a distraction to MEI’s senior management and scientific personnel.

MEI may be subject to substantial costs stemming from its defense against third party intellectual property infringement claims.

Third parties may assert that MEI is using their proprietary information without authorization. Third parties may also have or obtain patents and may claim that technologies licensed to or used by MEI infringe their patents. If MEI is required to defend patent infringement actions brought by third parties, or if MEI sues to protect its own patent rights, MEI may be required to pay substantial litigation costs and managerial attention may be diverted from business operations even if the outcome is not adverse to MEI. In addition, any legal action that seeks damages or an injunction to stop MEI from carrying on its commercial activities relating to the affected

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technologies could subject MEI to monetary liability and require MEI or any third party licensors to obtain a license to continue to use the affected technologies. MEI cannot predict whether it would prevail in any of these types of actions or that any required license would be made available on commercially acceptable terms or at all.

General Business Risks

MEI faces a risk of product liability claims and claims may exceed MEI’s insurance limits.

MEI’s business exposes MEI to the risk of product liability claims. This risk is inherent in the manufacturing, testing and marketing of human therapeutic products. Moreover, regardless of merit or eventual outcome, liability claims can have other adverse consequences, including: