Summit Therapeutics 6K Completion of $25 million subscription | SMMT 10 Jan 19

Summit Therapeutics (SMMT) 6-KCompletion of $25 million subscription

Exhibit 2.1

EXECUTION VERSION

REGISTRATION RIGHTS AGREEMENT

This REGISTRATION RIGHTS AGREEMENT (this “Agreement”) is made and entered into as of January 9, 2019 by and among Summit Therapeutics plc, a public limited company incorporated in England and Wales with the Registrar of Companies of England and Wales (the “Company”), and the “Investor” named in that certain Securities Purchase Agreement by and among the Company and the Investor (the “Purchase Agreement”). Capitalized terms used herein have the respective meanings ascribed thereto in the Purchase Agreement unless otherwise defined herein.

The parties hereby agree as follows:

1. Certain Definitions.

As used in this Agreement, the following terms shall have the following meanings:

“Investors” means the Investor identified in the Purchase Agreement and any Permitted Transferee of the Investor who is a subsequent holder of Registrable Securities.

“Prospectus” means (i) the prospectus included in any Registration Statement, as amended or supplemented by any prospectus supplement, with respect to the terms of the offering of any portion of the Registrable Securities covered by such Registration Statement and by all other amendments and supplements to the prospectus, including post-effective amendments and all material incorporated by reference in such prospectus, and (ii) any “free writing prospectus” as defined in Rule 405 under the 1933 Act.

“Register,” “registered” and “registration” refer to a registration made by preparing and filing a Registration Statement or similar document in compliance with the 1933 Act (as defined below), and the declaration or ordering of effectiveness of such Registration Statement or document.

“Registrable Securities” means (i) the Purchased ADSs and (ii) any other securities issued or issuable with respect to or in exchange for such Purchased ADSs, whether by merger, charter amendment or otherwise ; provided, that, a security shall cease to be a Registrable Security upon (A) sale pursuant to a Registration Statement or a valid exemption under the 1933 Act, or (B) such security becoming eligible for sale without restriction by the Investors pursuant to Rule 144 and without the requirement to be in compliance with Rule 144(c)(1) (or any successor thereto) promulgated under the 1933 Act. Notwithstanding the foregoing, no Ordinary Shares of the Company (including the Underlying Securities) shall be Registrable Securities.

“Registration Statement” means any registration statement of the Company under the 1933 Act that covers the resale of any of the Registrable Securities pursuant to the provisions of this Agreement, amendments and supplements to such Registration Statement, including post-effective amendments, all exhibits and all material incorporated by reference in such Registration Statement.

“Required Investors” means the Investor (or Investors) holding a majority of the Registrable Securities outstanding from time to time.

“SEC” means the U.S. Securities and Exchange Commission.

2. Registration.

(a) Registration Statement. Promptly following the date that is one hundred eighty (180) days after the Closing Date, but no later than two hundred ten (210) days after the Closing Date (the “Filing Deadline”), the Company shall use commercially reasonable efforts to prepare and file with the SEC one Registration Statement covering the resale of all of the Registrable Securities. Subject to any SEC comments, such Registration Statement shall include the plan of distribution attached hereto asExhibit A; provided, however, that no Investor shall be named as an “underwriter” in such Registration Statement without the Investor’s prior written consent. Such Registration Statement also shall cover, to the extent allowable under the 1933 Act and the rules promulgated thereunder (including Rule 416), such indeterminate number of additional ADSs resulting from stock splits, stock dividends or similar transactions with respect to the Ordinary Shares underlying the Registrable Securities. Such Registration Statement (and each amendment or supplement thereto, and each request for acceleration of effectiveness thereof) shall be provided in accordance with Section 3(c) to the Investors prior to its filing or other submission.

(b) Expenses. The Company will pay all expenses associated with each Registration Statement, including filing and printing fees, the Company’s counsel and accounting fees and expenses, costs associated with clearing the Registrable Securities for sale under applicable state securities laws and listing fees, but excluding discounts, commissions, fees of underwriters, selling brokers, dealer managers or similar securities industry professionals with respect to the Registrable Securities being sold.

(i) The Company shall use commercially reasonable efforts to have each Registration Statement declared effective as soon as practicable. The Company shall notify the Investors by facsimile ore-mail as promptly as practicable, and in any event, within twenty-four (24) hours, after any Registration Statement is declared effective and shall simultaneously provide the Investors with copies of any related Prospectus to be used in connection with the sale or other disposition of the securities covered thereby.

(ii) For not more than sixty (60) consecutive days or for a total of not more than one hundred five (105) days in any twelve (12) month period, the Company may suspend the use of any Prospectus included in any Registration Statement contemplated by this Section in the event that the Company determines in good faith that such suspension is necessary to (A) delay the disclosure of materialnon-public information concerning the Company, the disclosure of which at the time is not, in the good faith opinion of the Company, in the best interests of the Company, (B) amend or supplement the affected Registration Statement or the related Prospectus so that such Registration Statement or Prospectus shall not include an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein, in the case of the Prospectus in light of the circumstances under which they were made, not misleading, (C) permit the Company to conduct a sale of securities or other financing that is not a sale of Registrable Securities or (D) file a

replacement Registration Statement covering the resale of Registrable Securities in connection with the expiration or anticipated expiration of an effective Registration Statement (an “Allowed Delay”); provided, that the Company shall promptly (a) notify each Investor in writing of the commencement of an Allowed Delay, but shall not (without the prior written consent of an Investor) disclose to such Investor any materialnon-public information giving rise to an Allowed Delay, (b) advise the Investors in writing to cease all sales under such Registration Statement until the end of the Allowed Delay and (c) use commercially reasonable efforts to terminate an Allowed Delay as promptly as practicable.

(d) Rule 415; Cutback. If at any time the SEC takes the position that the offering of some or all of the Registrable Securities in a Registration Statement is not eligible to be made on a delayed or continuous basis under the provisions of Rule 415 under the 1933 Act or requires any Investor to be named as an “underwriter,” the Company shall use commercially reasonable efforts to persuade the SEC that the offering contemplated by such Registration Statement is a valid secondary offering and not an offering “by or on behalf of the issuer” as defined in Rule 415 and that none of the Investors is an “underwriter.” The Investors shall have the right to select one legal counsel to review and oversee any registration or matters pursuant to this Section 2(d), including participation in any meetings or discussions with the SEC regarding the SEC’s position and to comment on any written submission made to the SEC with respect thereto, which counsel shall be designated by the holders of a majority of the Registrable Securities. No such written submission with respect to this matter shall be made to the SEC to which the Investors’ counsel reasonably objects. In the event that, despite the Company’s commercially reasonable efforts and compliance with the terms of this Section 2(d), the SEC refuses to alter its position, the Company shall (i) remove from such Registration Statement such portion of the Registrable Securities (the “Cut Back Shares”) and/or (ii) agree to such restrictions and limitations on the registration and resale of the Registrable Securities as the SEC may require to assure the Company’s compliance with the requirements of Rule 415 (collectively, the “SEC Restrictions”); provided, however, that the Company shall not agree to name any Investor as an “underwriter” in such Registration Statement without the prior written consent of such Investor. Anycut-back imposed on the Investors pursuant to this Section 2(d) shall be allocated among the Investors on a pro rata basis and shall be applied first to any of the Registrable Securities of such Investor as such Investor shall designate, unless the SEC Restrictions otherwise require or provide or the Investors otherwise agree. From and after such date as the Company is able to effect the registration of such Cut Back Shares, the Company shall use commercially reasonable efforts to file a Registration Statement relating to such Cut Back Shares and to have such Registration Statement declared effective by the SEC.

3. Company Obligations. The Company will use commercially reasonable efforts to effect the registration of the Registrable Securities in accordance with the terms hereof, and pursuant thereto the Company will, as expeditiously as possible:

(a) use commercially reasonable efforts to cause such Registration Statement to remain continuously effective for a period that will terminate upon the earliest of (i) the date on which all Registrable Securities covered by such Registration Statement as amended from time to time, have been sold, (ii) the date on which all Registrable Securities covered by such Registration Statement may be sold without restriction pursuant to Rule 144 and without the requirement to be in compliance with Rule 144(c)(1) (or any successor thereto) promulgated

under the 1933 Act, and (iii) the fifth anniversary of the Closing Date (the “Effectiveness Period”), and advise the Investors promptly in writing when the Effectiveness Period has expired;

(b) use commercially reasonable efforts to prepare and file with the SEC such amendments and post-effective amendments to such Registration Statement and the related Prospectus promptly after the receipt of any SEC comments to the Registration Statement and as may be necessary to keep such Registration Statement effective for the Effectiveness Period and to comply with the provisions of the 1933 Act and the 1934 Act with respect to the distribution of all of the Registrable Securities covered thereby;

(c) provide copies to and permit any counsel designated by the Investors to review each Registration Statement and all amendments and supplements thereto (but excluding any documents incorporated by reference in such Registration Statement, amendments or supplements that are available on the SEC’s Electronic Data Gathering, Analysis, and Retrieval system (or any successor system)) no fewer than three (3) days prior to their filing with the SEC and not file any document to which such counsel reasonably objects;

(d) furnish to each Investor whose Registrable Securities are included in any Registration Statement (i) promptly after the same is prepared and filed with the SEC, if requested by the Investor, one (1) copy of any Registration Statement and any amendment thereto, each preliminary prospectus and Prospectus and each amendment or supplement thereto, and each letter written by or on behalf of the Company to the SEC or the staff of the SEC, and each item of correspondence from the SEC or the staff of the SEC, in each case relating to such Registration Statement (other than any portion of any thereof which contains information for which the Company has sought confidential treatment), and (ii) such number of copies of a Prospectus, including a preliminary prospectus, and all amendments and supplements thereto and such other documents as each Investor may reasonably request in order to facilitate the disposition of the Registrable Securities owned by such Investor that are covered by such Registration Statement;

(e) use commercially reasonable efforts to (i) prevent the issuance of any stop order or other suspension of effectiveness and, (ii) if such order is issued, obtain the withdrawal of any such order at the earliest practical moment;

(f) prior to any public offering of Registrable Securities, use commercially reasonable efforts to register or qualify or cooperate with the Investors and their counsel in connection with the registration or qualification of such Registrable Securities for the offer and sale under the securities or blue sky laws of such jurisdictions requested by the Investors and do any and all other commercially reasonable acts or things necessary or advisable to enable the distribution in such jurisdictions of the Registrable Securities covered by the Registration Statement; provided, however, that the Company shall not be required in connection therewith or as a condition thereto to (i) qualify to do business in any jurisdiction where it would not otherwise be required to qualify but for this Section 3(f), (ii) subject itself to general taxation in any jurisdiction where it would not otherwise be so subject but for this Section 3(f), or (iii) file a general consent to service of process in any such jurisdiction;

(g) use commercially reasonable efforts to cause all Registrable Securities covered by a Registration Statement to be listed on each securities exchange, interdealer quotation system or other market on which similar securities issued by the Company are then listed;

(h) promptly notify the Investors, at any time prior to the end of the Effectiveness Period, upon discovery that, or upon the happening of any event as a result of which, the Prospectus includes an untrue statement of a material fact or omits to state any material fact required to be stated therein or necessary to make the statements therein not misleading in light of the circumstances then existing, and promptly prepare, file with the SEC and furnish to such holder a supplement to or an amendment of such Prospectus as may be necessary so that such Prospectus shall not include an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading in light of the circumstances then existing;

(i) otherwise use commercially reasonable efforts to comply with all applicable rules and regulations of the SEC under the 1933 Act and the 1934 Act, including, without limitation, Rule 172 under the 1933 Act, file any final Prospectus, including any supplement or amendment thereof, with the SEC pursuant to Rule 424 under the 1933 Act, promptly inform the Investors in writing if, at any time during the Effectiveness Period, the Company does not satisfy the conditions specified in Rule 172 and, as a result thereof, the Investors are required to deliver a Prospectus in connection with any disposition of Registrable Securities and take such other actions as may be reasonably necessary to facilitate the registration of the Registrable Securities hereunder; and make available to its security holders, as soon as reasonably practicable, an earnings statement covering a period of at least twelve (12) months, beginning after the effective date of each Registration Statement, which earnings statement shall satisfy the provisions of Section 11(a) of the 1933 Act, including Rule 158 promulgated thereunder; and

(j) with a view to making available to the Investors the benefits of Rule 144 (or its successor rule) and any other rule or regulation of the SEC that may at any time permit the Investors to sell the ADSs to the public without registration, the Company covenants and agrees to: (i) make and keep public information available, as those terms are understood and defined in Rule 144, until the earlier of (A) six months after such date as all of the Registrable Securities may be sold without restriction by the holders thereof pursuant to Rule 144 or any other rule of similar effect or (B) such date as all of the Registrable Securities shall have been resold; (ii) file with the SEC in a timely manner all reports and other documents required of the Company under the 1934 Act; and (iii) furnish to each Investor upon request, as long as such Investor owns any Registrable Securities, (A) a written statement by the Company that it has complied with the reporting requirements of the 1934 Act, (B) a copy of the Company’s most recent Annual Report on Form20-F, and (C) such other information as may be reasonably requested in order to avail such Investor of any rule or regulation of the SEC that permits the selling of any such Registrable Securities without registration.

Notwithstanding the foregoing, it is understood and agreed that a Registration Statement may expire pursuant to the rules and regulations of the SEC on the date that is three years following the date it is declared effective by the SEC and that in such case either prior to or

promptly following such expiration time, the Company agrees to use commercially reasonable efforts to prepare, file and caused to be declared effective a replacement Registration Statement. It is agreed that the expiration of a Registration Statement pursuant to the rules and regulations of the SEC shall not represent a violation or breach of any of the Company’s obligations under this Agreement; provided that in such case the Company uses commercially reasonable efforts to file and caused to be declared effective a replacement Registration Statement.

4. Obligations of the Investors.

(a) It shall be a condition precedent to the obligations of the Company to take any action pursuant to Section 2 with respect to the Registrable Securities of any Investor that such Investor furnish in writing to the Company information regarding itself, the Registrable Securities held by it and the intended method of disposition of the Registrable Securities held by it, as shall be reasonably required to effect the registration of such Registrable Securities, and such Investor shall execute such documents in connection with such registration as the Company may reasonably request. At least five (5) Business Days prior to the first anticipated filing date of any Registration Statement, the Company shall notify each Investor of the information the Company requires from such Investor if such Investor elects to have any of the Registrable Securities included in such Registration Statement. An Investor shall provide such information to the Company at least two (2) Business Days prior to the first anticipated filing date of such Registration Statement if such Investor elects to have any of the Registrable Securities included in such Registration Statement.

(b) Each Investor, by its acceptance of the Registrable Securities, agrees to cooperate with the Company as reasonably requested by the Company in connection with the preparation and filing of a Registration Statement hereunder, unless such Investor has notified the Company in writing of its election to exclude all of its Registrable Securities from such Registration Statement.

(c) Each Investor agrees that, upon receipt of any notice from the Company of either (i) the commencement of an Allowed Delay pursuant to Section 2(c)(ii) or (ii) the happening of an event pursuant to Section 3(h) hereof, such Investor will immediately discontinue disposition of Registrable Securities pursuant to any Registration Statement covering such Registrable Securities, until the Investor is advised by the Company that such dispositions may again be made.

(d) Each Investor covenants and agrees that it will comply with the prospectus delivery requirements of the 1933 Act as applicable to it or an exemption therefrom in connection with sales of Registrable Securities pursuant to any Registration Statement.

5. Indemnification.

(a) Indemnification by the Company. The Company will indemnify and hold harmless each Investor and its officers, directors, members, employees and agents, successors and assigns, and each other person, if any, who controls such Investor within the meaning of the 1933 Act, against any losses, claims, damages or liabilities, joint or several, to which they may become subject under the 1933 Act or otherwise, insofar as such losses, claims, damages or

liabilities (or actions in respect thereof) arise out of or are based upon: (i) any untrue statement or alleged untrue statement or omission or alleged omission of any material fact contained in any Registration Statement, any preliminary Prospectus or final Prospectus, or any amendment or supplement thereof; (ii) any blue sky application or other document executed by the Company specifically for that purpose or based upon written information furnished by the Company filed in any state or other jurisdiction in order to qualify any or all of the Registrable Securities under the securities laws thereof (any such application, document or information herein called a “Blue Sky Application”); (iii) the omission or alleged omission to state in a Blue Sky Application a material fact required to be stated therein or necessary to make the statements therein not misleading; (iv) any violation by the Company or its agents of any rule or regulation promulgated under the 1933 Act applicable to the Company or its agents and relating to action or inaction required of the Company in connection with such registration; or (v) any failure to register or qualify the Registrable Securities included in any such Registration Statement in any state where the Company or its agents has affirmatively undertaken or agreed in writing that the Company will undertake such registration or qualification on an Investor’s behalf and will reimburse such Investor, and each such officer, director or member and each such controlling person for any legal or other expenses reasonably incurred by them in connection with investigating or defending any such loss, claim, damage, liability or action; provided, however, that the Company will not be liable in any such case if and to the extent that any such loss, claim, damage or liability arises out of or is based upon (i) an untrue statement or alleged untrue statement or omission or alleged omission so made in conformity with information furnished by such Investor or any such controlling person in writing specifically for use in such Registration Statement or Prospectus, (ii) the use by an Investor of an outdated or defective Prospectus after the Company has notified such Investor in writing that such Prospectus is outdated or defective, (iii) an Investor’s failure to send or give a copy of the Prospectus or supplement (as then amended or supplemented), if required (and not exempted) to the Persons asserting an untrue statement or omission or alleged untrue statement or omission at or prior to the written confirmation of the sale of Registrable Securities or (iv) the disposition of any Registrable Securities pursuant to any Registration Statement or Prospectus covering such Registrable Securities during an Allowed Delay.

(b) Indemnification by the Investors. Each Investor agrees, severally but not jointly, to indemnify and hold harmless, to the fullest extent permitted by law, the Company, its directors, officers, employees, stockholders and each person who controls the Company (within the meaning of the 1933 Act) against any losses, claims, damages, liabilities and expense (including reasonable attorney fees) resulting from any untrue statement of a material fact or any omission of a material fact required to be stated in any Registration Statement or Prospectus or preliminary Prospectus or amendment or supplement thereto or necessary to make the statements therein not misleading, to the extent, but only to the extent that such untrue statement or omission is contained in any information furnished in writing by such Investor to the Company specifically for inclusion in such Registration Statement or Prospectus or amendment or supplement thereto. In no event shall the liability of an Investor be greater in amount than the dollar amount of the proceeds (net of all expense paid by such Investor in connection with any claim relating to this Section 5 and the amount of any damages such Investor has otherwise been required to pay by reason of such untrue statement or omission) received by such Investor upon the sale of the Registrable Securities included in such Registration Statement giving rise to such indemnification obligation.

(c) Conduct of Indemnification Proceedings. Any person entitled to indemnification hereunder shall (i) give prompt notice to the indemnifying party of any claim with respect to which it seeks indemnification and (ii) permit such indemnifying party to assume the defense of such claim with counsel reasonably satisfactory to the indemnified party; provided that any person entitled to indemnification hereunder shall have the right to employ separate counsel and to participate in the defense of such claim, but the fees and expenses of such counsel shall be at the expense of such person unless (a) the indemnifying party has agreed to pay such fees or expenses, (b) the indemnifying party shall have failed to assume the defense of such claim and employ counsel reasonably satisfactory to such person or (c) in the reasonable judgment of any such person, based upon written advice of its counsel, a conflict of interest exists between such person and the indemnifying party with respect to such claims (in which case, if the person notifies the indemnifying party in writing that such person elects to employ separate counsel at the expense of the indemnifying party, the indemnifying party shall not have the right to assume the defense of such claim on behalf of such person); and provided, further, that the failure of any indemnified party to give notice as provided herein shall not relieve the indemnifying party of its obligations hereunder, except to the extent that such failure to give notice shall materially adversely affect the indemnifying party in the defense of any such claim or litigation. It is understood that the indemnifying party shall not, in connection with any proceeding in the same jurisdiction, be liable for fees or expenses of more than one separate firm of attorneys at any time for all such indemnified parties. No indemnifying party will, except with the consent of the indemnified party, which shall not be unreasonably withheld or conditioned, consent to entry of any judgment or enter into any settlement that does not include as an unconditional term thereof the giving by the claimant or plaintiff to such indemnified party of a release from all liability in respect of such claim or litigation.

(d) Contribution. If for any reason the indemnification provided for in the preceding paragraphs (a) and (b) is unavailable to an indemnified party or insufficient to hold it harmless, other than as expressly specified therein, then the indemnifying party shall contribute to the amount paid or payable by the indemnified party as a result of such loss, claim, damage or liability in such proportion as is appropriate to reflect the relative fault of the indemnified party and the indemnifying party, as well as any other relevant equitable considerations. No person guilty of fraudulent misrepresentation within the meaning of Section 11(f) of the 1933 Act shall be entitled to contribution from any person not guilty of such fraudulent misrepresentation. In no event shall the contribution obligation of a holder of Registrable Securities be greater in amount than the dollar amount of the proceeds (net of all expenses paid by such holder in connection with any claim relating to this Section 5 and the amount of any damages such holder has otherwise been required to pay by reason of such untrue or alleged untrue statement or omission or alleged omission) received by it upon the sale of the Registrable Securities giving rise to such contribution obligation.

6. Miscellaneous.

(a) Amendments and Waivers. This Agreement may be amended only by a writing signed by the Company and the Required Investors. The Company may take any action herein prohibited, or omit to perform any act herein required to be performed by it, only if the Company shall have obtained the written consent to such amendment, action or omission to act, of the Required Investors.

(b) Notices. All notices and other communications provided for or permitted hereunder shall be made as set forth in Section 10.4 of the Purchase Agreement.

(c) Assignments and Transfers by Investors. The provisions of this Agreement shall be binding upon and inure to the benefit of the Investors and their respective successors and assigns. An Investor may transfer or assign, in whole or from time to time in part, to one or more Affiliates its rights hereunder in connection with the transfer of Registrable Securities by such Investor to such Affiliate, provided that such Investor complies with all laws applicable thereto, and the provisions of the Purchase Agreement, and provides written notice of assignment to the Company promptly after such assignment is effected, and such Affiliate agrees in writing to be bound by all of the provisions contained herein.

(d) Assignments and Transfers by the Company. This Agreement may not be assigned by the Company (whether by operation of law or otherwise) without the prior written consent of the Required Investors, provided, however, that in the event that the Company is a party to a merger, consolidation, share exchange or similar business combination transaction in which the Purchased ADSs (or the Underlying Securities) are converted into the equity securities of another Person, from and after the effective time of such transaction, such Person shall, by virtue of such transaction, be deemed to have assumed the obligations of the Company hereunder, the term “Company” shall be deemed to refer to such Person and the term “Registrable Securities” shall be deemed to include the securities received by the Investors in connection with such transaction unless such securities are otherwise freely tradable by the Investors after giving effect to such transaction.

(e) Benefits of the Agreement. The terms and conditions of this Agreement shall inure to the benefit of and be binding upon the respective permitted successors and assigns of the parties. Nothing in this Agreement, express or implied, is intended to confer upon any party other than the parties hereto or their respective successors and assigns any rights, remedies, obligations, or liabilities under or by reason of this Agreement, except as expressly provided in this Agreement.

(f) Counterparts; Faxes. This Agreement may be executed in two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument. This Agreement may also be executed via facsimile, which shall be deemed an original.

(g) Titles and Subtitles. The titles and subtitles used in this Agreement are used for convenience only and are not to be considered in construing or interpreting this Agreement.

(h) Severability. Any provision of this Agreement that is prohibited or unenforceable in any jurisdiction shall, as to such jurisdiction, be ineffective to the extent of such prohibition or unenforceability without invalidating the remaining provisions hereof but shall be interpreted as if it were written so as to be enforceable to the maximum extent permitted by applicable law, and any such prohibition or unenforceability in any jurisdiction shall not invalidate or render unenforceable such provision in any other jurisdiction. To the extent

permitted by applicable law, the parties hereby waive any provision of law which renders any provisions hereof prohibited or unenforceable in any respect.

(i) Further Assurances. The parties shall execute and deliver all such further instruments and documents and take all such other actions as may reasonably be required to carry out the transactions contemplated hereby and to evidence the fulfillment of the agreements herein contained.

(j) Entire Agreement. This Agreement is intended by the parties as a final expression of their agreement and intended to be a complete and exclusive statement of the agreement and understanding of the parties hereto in respect of the subject matter contained herein. This Agreement supersedes all prior agreements and understandings between the parties with respect to such subject matter.

(k) Governing Law; Consent to Jurisdiction; Waiver of Jury Trial. This Agreement shall be governed by, and construed in accordance with, the internal laws of the State of New York without regard to the choice of law principles thereof. Each of the parties hereto irrevocably submits to the exclusive jurisdiction of the courts of the State of New York located in New York County and the United States District Court for the Southern District of New York for the purpose of any suit, action, proceeding or judgment relating to or arising out of this Agreement and the transactions contemplated hereby. Service of process in connection with any such suit, action or proceeding may be served on each party hereto anywhere in the world by the same methods as are specified for the giving of notices under this Agreement. Each of the parties hereto irrevocably consents to the jurisdiction of any such court in any such suit, action or proceeding and to the laying of venue in such court. Each party hereto irrevocably waives any objection to the laying of venue of any such suit, action or proceeding brought in such courts and irrevocably waives any claim that any such suit, action or proceeding brought in any such court has been brought in an inconvenient forum. EACH OF THE PARTIES HERETO WAIVES ANY RIGHT TO REQUEST A TRIAL BY JURY IN ANY LITIGATION WITH RESPECT TO THIS AGREEMENT AND REPRESENTS THAT COUNSEL HAS BEEN CONSULTED SPECIFICALLY AS TO THIS WAIVER.

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IN WITNESS WHEREOF, the parties have executed this Agreement or caused their duly authorized officers to execute this Agreement as of the date first above written.

Exhibit A

Plan of Distribution

The selling ADS holders, which as used herein includes donees, pledgees, transferees or othersuccessors-in-interest selling ADSs or interests in ADSs received after the date of this prospectus from a selling ADS holder as a gift, pledge, partnership distribution or other transfer, may, from time to time, sell, transfer or otherwise dispose of any or all of their ADSs or interests in ADSs on any stock exchange, market or trading facility on which the ADSs are traded or in private transactions. These dispositions may be at fixed prices, at prevailing market prices at the time of sale, at prices related to the prevailing market price, at varying prices determined at the time of sale, or at negotiated prices.

The selling ADS holders may use any one or more of the following methods when disposing of ADSs or interests therein:

– ordinary brokerage transactions and transactions in which the broker-dealer solicits purchasers;

– block trades in which the broker-dealer will attempt to sell the ADSs as agent, but may position and resell a portion of the block as principal to facilitate the transaction;

– purchases by a broker-dealer as principal and resale by the broker-dealer for its account;

– an exchange distribution in accordance with the rules of the applicable exchange;

– privately negotiated transactions;

– short sales effected after the date the registration statement of which this prospectus is a part is declared effective by the SEC;

– through the writing or settlement of options or other hedging transactions, whether through an options exchange or otherwise;

– broker-dealers may agree with the selling ADS holders to sell a specified number of such ADSs at a stipulated price per ADS;

– a combination of any such methods of sale; and

– any other method permitted by applicable law.

The selling ADS holders may, from time to time, pledge or grant a security interest in some or all of the ADSs owned by them and, if they default in the performance of their secured obligations, the pledgees or secured parties may offer and sell the ADSs, from time to time, under this prospectus, or under an amendment to this prospectus under Rule 424(b)(3) or other applicable provision of the Securities Act amending the list of selling ADS holders to include the

pledgee, transferee or other successors in interest as selling ADS holders under this prospectus. The selling ADS holders also may transfer the ADSs in other circumstances, in which case the transferees, pledgees or other successors in interest will be the selling beneficial owners for purposes of this prospectus.

In connection with the sale of ADSs or interests therein, the selling ADS holders may enter into hedging transactions with broker-dealers or other financial institutions, which may in turn engage in short sales of the ADSs in the course of hedging the positions they assume. The selling ADS holders may also sell ADSs short and deliver these securities to close out their short positions, or loan or pledge the ADSs to broker-dealers that in turn may sell these securities. The selling ADS holders may also enter into option or other transactions with broker-dealers or other financial institutions or the creation of one or more derivative securities which require the delivery to such broker-dealer or other financial institution of ADSs offered by this prospectus, which ADSs such broker-dealer or other financial institution may resell pursuant to this prospectus (as supplemented or amended to reflect such transaction).

The aggregate proceeds to the selling ADS holders from the sale of the ADSs offered by them will be the purchase price of the ADSs less discounts or commissions, if any. Each of the selling ADS holders reserves the right to accept and, together with their agents from time to time, to reject, in whole or in part, any proposed purchase of ADSs to be made directly or through agents. We will not receive any of the proceeds from this offering.

The selling ADS holders also may resell all or a portion of the ADSs in open market transactions in reliance upon Rule 144 under the Securities Act of 1933, provided that they meet the criteria and conform to the requirements of that rule.

The selling ADS holders and any underwriters, broker-dealers or agents that participate in the sale of the ADSs or interests therein may be “underwriters” within the meaning of Section 2(11) of the Securities Act. Any discounts, commissions, concessions or profit they earn on any resale of the ADSs may be underwriting discounts and commissions under the Securities Act. Selling ADS holders who are “underwriters” within the meaning of Section 2(11) of the Securities Act will be subject to the prospectus delivery requirements of the Securities Act.

To the extent required, the ADSs to be sold, the names of the selling ADS holders, the respective purchase prices and public offering prices, the names of any agents, dealer or underwriter, any applicable commissions or discounts with respect to a particular offer will be set forth in an accompanying prospectus supplement or, if appropriate, a post-effective amendment to the registration statement that includes this prospectus.

In order to comply with the securities laws of some states, if applicable, the ADSs may be sold in these jurisdictions only through registered or licensed brokers or dealers. In addition, in some states the ADSs may not be sold unless they have been registered or qualified for sale or an exemption from registration or qualification requirements is available and is complied with.

We have advised the selling ADS holders that the anti-manipulation rules of Regulation M under the Exchange Act may apply to sales of ADSs in the market and to the activities of the selling ADS holders and their affiliates. In addition, to the extent applicable we

will make copies of this prospectus (as it may be supplemented or amended from time to time) available to the selling ADS holders for the purpose of satisfying the prospectus delivery requirements of the Securities Act. The selling ADS holders may indemnify any broker-dealer that participates in transactions involving the sale of the ADSs against certain liabilities, including liabilities arising under the Securities Act.

We have agreed to indemnify the selling ADS holders against liabilities, including liabilities under the Securities Act and state securities laws, relating to the registration of the ADSs offered by this prospectus.

We have agreed with the selling ADS holders to keep the registration statement of which this prospectus constitutes a part effective until the earliest of (1) such time as all of the ADSs covered by this prospectus have been disposed of pursuant to and in accordance with such registration statement, (2) the date on which all of the ADSs may be sold without restriction pursuant to Rule 144 of the Securities Act or (3) the date that is five years after the date the ADSs were first sold to the selling ADS holders.

SUMMIT THERAPEUTICS PLC

/s/ Glyn Edwards

Name: Glyn Edwards

Title: Chief Executive Officer