Exhibit 4.15

Execution Version

September 27, 2021

STRICTLY CONFIDENTIAL

Addex Therapeutics Ltd

Chemin des Mines 9,

CH-1202 Geneva

Switzerland

Attn: Tim Dyer, Chief Executive Officer

Dear Mr. Dyer:

This letter agreement (this “Agreement”) constitutes the agreement between Addex Therapeutics Ltd (the “Company”) and H.C. Wainwright & Co., LLC (“Wainwright”), that Wainwright shall serve as the exclusive agent, advisor or underwriter in any offering in the United States (each, an “Offering”) of equity securities of the Company (the “Securities”) during the Term (as hereinafter defined) of this Agreement. The terms of each Offering and the Securities issued in connection therewith shall be mutually agreed upon by the Company and Wainwright and nothing herein implies that Wainwright would have the power or authority to bind the Company and nothing herein implies that the Company shall have an obligation to issue any Securities. It is understood that Wainwright’s assistance in an Offering will be subject to the satisfactory completion of such investigation and inquiry into the affairs of the Company as Wainwright deems appropriate under the circumstances and to the receipt of all internal approvals of Wainwright in connection with an Offering. The Company expressly acknowledges and agrees that Wainwright’s involvement in an Offering is strictly on a reasonable best efforts basis and that the consummation of an Offering will be subject to, among other things, market conditions. The execution of this Agreement does not constitute a commitment by Wainwright to purchase the Securities and does not ensure a successful Offering of the Securities or the success of Wainwright with respect to securing any other financing on behalf of the Company. Wainwright may retain other brokers, dealers, agents or underwriters on its behalf in connection with an Offering.

A.Compensation; Reimbursement. At the closing of each Offering (each, a “Closing”), the Company shall compensate Wainwright as follows:

Cash Fee. The Company shall pay to Wainwright a cash fee, or as to an underwritten Offering an underwriter discount, equal to 6.75% of the aggregate gross proceeds raised in each Offering; provided, that such cash fee shall be reduced to 3.375% of the aggregate gross proceeds raised in any Offering from the current investors in the Company listed on Annex A(1) hereto or from insiders in the Company listed on Annex A(2) hereto (together, the “Identified Investors”).

Expense Allowance. Out of the proceeds of each Closing, the Company also agrees to pay Wainwright (a) a management fee equal to 1.0% of the gross proceeds raised in each Offering, provided that the management fee shall not be due on any securities sold to the Identified Investors; (b) $15,000 for non-accountable expenses (to be increased to $25,000 in case of a public Offering); (c) up to $100,000 for fees and expenses of legal counsel and other out-of-pocket expenses actually incurred and documented; plus any additional amount payable by the Company pursuant to Paragraph D.3 hereunder; provided, however, that such amount in no way limits or impairs the indemnification and contribution provisions of this Agreement.

Tail. Wainwright shall be entitled to compensation under clause (A)(1) hereunder, calculated in the manner set forth therein, with respect to any public or private offering or other capital-raising transaction of the Company’s securities (“Tail Financing”) to the extent that the investors in such Tail Financing were investors whom Wainwright had contacted during the Term or introduced to the Company during the Term, if such Tail Financing is consummated at any time within the 12-month period following the date of this Agreement. For the avoidance of doubt, no fee pursuant to this Paragraph A.3 shall be payable to Wainwright with respect to the investors who are listed on Annex A (3) hereto.

B.Term and Termination of Engagement; Exclusivity. The term of Wainwright’s exclusive engagement will begin on the date hereof and end ninety (90) days thereafter (the “Term”). Notwithstanding anything to the contrary contained herein, the Company agrees that the provisions relating to the payment of fees, reimbursement of expenses, tail, indemnification and contribution, confidentiality, conflicts, independent contractor and waiver of the right to trial by jury will survive the Term to the extent provided herein. Notwithstanding anything to the contrary contained herein, the Company has the right to terminate the Agreement for cause in compliance with FINRA Rule 5110(g)(5)(B)(i). The exercise of such right of termination for cause eliminates the Company’s obligations with respect to the provisions relating to the tail fees. During the Term, the Company will not, and will not instruct its representatives to, other than in coordination with Wainwright, contact or solicit institutions, corporations or other entities or individuals in the United States as potential purchasers of the Securities. Furthermore, the Company agrees to consult with Wainwright during the Term as to all inquiries from prospective investors in connection with an Offering. .Additionally, except as set forth hereunder, the Company represents, warrants and covenants that no brokerage or finder’s fees or commissions are or will be payable by the Company or any subsidiary of the Company to any broker, financial advisor or consultant, finder, placement agent, investment banker, bank or other third-party with respect to any Offering.

C.Information; Reliance. The Company shall furnish, or cause to be furnished, to Wainwright all information reasonably requested by Wainwright for the purpose of rendering services hereunder and conducting due diligence (all such information being the “Information”). In addition, the Company agrees to make available to Wainwright upon request from time to time the officers, directors, accountants, counsel (who shall not be required to disclose privileged information) and other advisors of the Company. The Company recognizes and confirms that Wainwright (a) will use and rely on the Information, including any documents provided to investors in each Offering (the “Offering Documents”) which shall

include any Purchase Agreement (as defined hereunder), and on information available from generally recognized public sources in performing the services contemplated by this Agreement without having independently verified the same; (b) does not assume responsibility for the accuracy or completeness of the Offering Documents or the Information and such other information; and (c) will not make an appraisal of any of the assets or liabilities of the Company. Upon reasonable request, the Company will meet with Wainwright or its representatives to discuss all information relevant for disclosure in the Offering Documents and will reasonably cooperate in any investigation undertaken by Wainwright thereof, including any document included or incorporated by reference therein. At each Offering, at the request of Wainwright, the Company shall deliver such legal letters (including, without limitation, negative assurance letters), opinions, comfort letters, officers’ and secretary certificates and good standing certificates, all in form and substance satisfactory to Wainwright and its counsel as is customary for such Offering. Wainwright shall be a third party beneficiary of any representations, warranties, covenants, closing conditions and closing deliverables made by the Company in any Offering Documents, including representations, warranties, covenants, closing conditions and closing deliverables made to any investor in an Offering.

D.Related Agreements. At each Offering, the Company shall enter into the following additional agreements:

Underwritten Offering. If an Offering is an underwritten Offering, the Company and Wainwright shall enter into a customary underwriting agreement in form and substance satisfactory to Wainwright and its counsel.

Best Efforts Offering. If an Offering is on a best efforts basis, the sale of Securities to the investors in the Offering will be evidenced by a purchase agreement (“Purchase Agreement”) between the Company and such investors in a form reasonably satisfactory to the Company and Wainwright. Wainwright shall be a third party beneficiary with respect to the representations, warranties, covenants, closing conditions and closing deliverables included in the Purchase Agreement. Prior to the signing of any Purchase Agreement, officers of the Company with responsibility for financial affairs will be reasonably available to answer inquiries from prospective investors.

Escrow, Settlement and Closing. If each Offering is not settled via delivery versus payment (“DVP”), the Company and Wainwright shall enter into an escrow agreement with a third party escrow agent pursuant to which Wainwright’s compensation and expenses shall be paid from the gross proceeds of the Securities sold. If the Offering is settled in whole or in part via DVP, Wainwright shall arrange for its clearing agent to provide the funds to facilitate such settlement; provided, however, if the clearing firm provides the funds in a best efforts offering and subsequent to such delivery an investor fails to provide the necessary funds to the clearing agent for such purchase of Securities, Wainwright shall instruct the clearing agent to promptly return any such Securities to the Company and the Company shall promptly return such investor’s purchase price to the clearing agent. The Company shall pay Wainwright closing costs, which shall also include the

reimbursement of the out-of-pocket cost of the escrow agent or clearing agent, as applicable, which closing costs shall not exceed $15,950.

FINRA Amendments. Notwithstanding anything herein to the contrary, in the event that Wainwright determines that any of the terms provided for hereunder shall not comply with a FINRA rule, including but not limited to FINRA Rule 5110, then the Company shall agree to amend this Agreement (or include such revisions in the final underwriting agreement) in writing upon the request of Wainwright to comply with any such rules; provided that any such amendments shall not provide for terms that are less favorable to the Company than are reflected in this Agreement.

E.Confidentiality. In the event of the consummation or public announcement of any Offering, Wainwright shall have the right to disclose its participation in such Offering, including, without limitation, the Offering at its cost of “tombstone” advertisements in financial and other newspapers and journals.

F.Indemnity.

In connection with the Company’s engagement of Wainwright hereunder, the Company hereby agrees to indemnify and hold harmless Wainwright and its affiliates, and the respective controlling persons, directors, officers, members, shareholders, agents and employees of any of the foregoing (collectively the “Indemnified Persons”), from and against any and all claims, actions, suits, proceedings (including those of shareholders), damages, liabilities and expenses incurred by any of them (including the reasonable fees and expenses of counsel), as incurred, whether or not the Company is a party thereto (collectively a “Claim”), that are (A) related to or arise out of (i) any actions taken or omitted to be taken (including any untrue statements made or any statements omitted to be made) by the Company, or (ii) any actions taken or omitted to be taken by any Indemnified Person in connection with the Company’s engagement of Wainwright, or (B) otherwise relate to or arise out of Wainwright’s activities on the Company’s behalf under Wainwright’s engagement, and the Company shall reimburse any Indemnified Person for all expenses (including the reasonable fees and expenses of counsel) as reasonably incurred by such Indemnified Person in connection with investigating, preparing or defending any such claim, action, suit or proceeding, whether or not in connection with pending or threatened litigation in which any Indemnified Person is a party. The Company will not, however, be responsible for any Claim that is finally judicially determined to have resulted from the fraud, gross negligence or willful misconduct of any such Indemnified Person for such Claim. The Company further agrees that no Indemnified Person shall have any liability to the Company for or in connection with the Company’s engagement of Wainwright except for any Claim incurred by the Company as a result of such Indemnified Person’s fraud, gross negligence or willful misconduct.

The Company further agrees that it will not, without the prior written consent of Wainwright, settle, compromise or consent to the entry of any judgment in any pending or threatened Claim in respect of which indemnification may be sought

hereunder (whether or not any Indemnified Person is an actual or potential party to such Claim), unless such settlement, compromise or consent includes an unconditional, irrevocable release of each Indemnified Person from any and all liability arising out of such Claim.

Promptly upon receipt by an Indemnified Person of notice of any complaint or the assertion or institution of any Claim with respect to which indemnification is being sought hereunder, such Indemnified Person shall notify the Company in writing of such complaint or of such assertion or institution but failure to so notify the Company shall not relieve the Company from any obligation it may have hereunder, except and only to the extent such failure results in the forfeiture by the Company of substantial rights and defenses. If the Company is requested by such Indemnified Person, the Company may assume the defense of such Claim, including the employment of one counsel for all such Indemnified Persons (including local counsel, if necessary) and the payment of the fees and expenses of such counsel, provided, however, that such counsel shall be satisfactory to the Indemnified Persons and provided further that if the legal counsel to such Indemnified Persons reasonably determine that having common counsel would present such counsel with a conflict of interest or if the defendant in, or target of, any such Claim, includes both an Indemnified Person and the Company, and legal counsel to such Indemnified Person reasonably concludes that there may be legal defenses available to it or other Indemnified Persons different from or in addition to those available to the Company, such Indemnified Person will employ its one separate counsel (including local counsel, if necessary) to represent or defend him, her or it in any such Claim and the Company shall pay the reasonable fees and expenses of such counsel. If such Indemnified Person does not request that the Company assume the defense of such Claim, such Indemnified Person will be permitted to employ its own separate counsel (including local counsel, if necessary) to represent or defend him, her or it in any such Claim and the Company shall pay the reasonable fees and expenses of such counsel. Notwithstanding anything herein to the contrary, if the Company fails timely or diligently to defend, contest, or otherwise protect against any Claim, the relevant Indemnified Person shall have the right, but not the obligation, to defend, contest, compromise, settle, assert crossclaims, or counterclaims or otherwise protect against the same, and shall be fully indemnified by the Company therefor, including without limitation, for the reasonable fees and expenses of its counsel and all amounts paid as a result of such Claim or the compromise or settlement thereof.

The Company agrees that if any indemnity sought by an Indemnified Person hereunder is held by a court to be unavailable for any reason then (whether or not Wainwright is the Indemnified Person), the Company and Wainwright shall contribute to the Claim for which such indemnity is held unavailable in such proportion as is appropriate to reflect the relative benefits to the Company, on the one hand, and Wainwright on the other, in connection with Wainwright’s engagement referred to above, subject to the limitation that in no event shall the amount of Wainwright’s contribution to such Claim exceed the amount of fees actually received by Wainwright from the Company pursuant to Wainwright’s

engagement. The Company hereby agrees that the relative benefits to the Company, on the one hand, and Wainwright on the other, with respect to Wainwright’s engagement shall be deemed to be in the same proportion as (a) the total value paid or proposed to be paid or received by the Company pursuant to the applicable Offering (whether or not consummated) for which Wainwright is engaged to render services bears to (b) the fee paid or proposed to be paid to Wainwright in connection with such engagement.

The Company’s indemnity, reimbursement and contribution obligations under this Agreement (a) shall be in addition to, and shall in no way limit or otherwise adversely affect any rights that any Indemnified Person may have at law or at equity and (b) shall be effective whether or not the Company is at fault in any way.

G.Limitation of Engagement to the Company. The Company acknowledges that Wainwright has been retained only by the Company, that Wainwright is providing services hereunder as an independent contractor (and not in any fiduciary or agency capacity) and that the Company’s engagement of Wainwright is not deemed to be on behalf of, and is not intended to confer rights upon, any shareholder, owner or partner of the Company or any other person not a party hereto as against Wainwright or any of its affiliates, or any of its or their respective officers, directors, controlling persons (within the meaning of Section 15 of the Securities Act or Section 20 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”)), employees or agents. Unless otherwise expressly agreed in writing by Wainwright, no one other than the Company is authorized to rely upon this Agreement or any other statements or conduct of Wainwright, and no one other than the Company is intended to be a beneficiary of this Agreement. The Company acknowledges that any recommendation or advice, written or oral, given by Wainwright to the Company in connection with Wainwright’s engagement is intended solely for the benefit and use of the Company’s management and directors in considering a possible Offering, and any such recommendation or advice is not on behalf of, and shall not confer any rights or remedies upon, any other person or be used or relied upon for any other purpose. Wainwright shall not have the authority to make any commitment binding on the Company. The Company, in its sole discretion, shall have the right to reject any investor introduced to it by Wainwright.

H.Limitation of Wainwright’s Liability to the Company. Wainwright and the Company further agree that neither Wainwright nor any of its affiliates or any of its or their respective officers, directors, controlling persons (within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act), employees or agents shall have any liability to the Company, its security holders or creditors, or any person asserting claims on behalf of or in the right of the Company (whether direct or indirect, in contract, tort, for an act of negligence or otherwise) for any losses, fees, damages, liabilities, costs, expenses or equitable relief arising out of or relating to this Agreement or the services rendered hereunder, except for losses, fees, damages, liabilities, costs or expenses that arise out of or are based on any action of or failure to act by Wainwright and that are finally judicially determined to have resulted solely from the fraud, gross negligence or willful misconduct of Wainwright.

I.Governing Law. This Agreement shall be governed by and construed in accordance with the laws of the State of New York applicable to agreements made and to be

fully performed therein. Any disputes that arise under this Agreement, even after the termination of this Agreement, will be heard only in the state or federal courts located in the City of New York, State of New York. The parties hereto expressly agree to submit themselves to the jurisdiction of the foregoing courts in the City of New York, State of New York. The parties hereto expressly waive any rights they may have to contest the jurisdiction, venue or authority of any court sitting in the City and State of New York. Any rights to trial by jury with respect to any such action, proceeding or suit are hereby waived by Wainwright and the Company.

J.Notices. All notices hereunder will be in writing and sent by certified mail, hand delivery, overnight delivery or e-mail, if sent to Wainwright, at the address set forth on the first page hereof, e-mail: notices@hcwco.com, Attention: Head of Investment Banking, and if sent to the Company, to the address set forth on the first page hereof, e-mail: Tim Dyer Tim.Dyer@addextherapeutics.com, Attention: Chief Executive Officer. Notices sent by certified mail shall be deemed received five days thereafter, notices sent by hand delivery or overnight delivery shall be deemed received on the date of the relevant written record of receipt, notices sent by e-mail shall be deemed received as of the date and time they were sent.

K.Conflicts. The Company acknowledges that Wainwright and its affiliates may have and may continue to have investment banking and other relationships with parties other than the Company pursuant to which Wainwright may acquire information of interest to the Company. Wainwright shall have no obligation to disclose such information to the Company or to use such information in connection with any contemplated transaction. During the Term, Wainwright shall not provide advisory or capital markets services to any entity that has proposed, or, to Wainwright’s knowledge, intends to propose, to acquire, merge or otherwise combine with the Company.

L.Anti-Money Laundering. To help the United States government fight the funding of terrorism and money laundering, the federal laws of the United States require all financial institutions to obtain, verify and record information that identifies each person with whom they do business. This means Wainwright must ask the Company for certain identifying information, including a government-issued identification number (e.g., a U.S. taxpayer identification number) and such other information or documents that Wainwright considers appropriate to verify the Company’s identity, such as certified articles of incorporation, a government-issued business license, a partnership agreement or a trust instrument.

M.Miscellaneous. The Company represents and warrants that it has all requisite power and authority to enter into and carry out the terms and provisions of this Agreement and the execution, delivery and performance of this Agreement does not breach or conflict with any agreement, document or instrument to which it is a party or bound. This Agreement shall not be modified or amended except in writing signed by Wainwright and the Company. This Agreement shall be binding upon and inure to the benefit of both Wainwright and the Company and their respective assigns, successors, and legal representatives. If any provision of this Agreement is determined to be invalid or unenforceable in any respect, such determination will not affect such provision in any other respect, and the remainder of the Agreement shall remain in full force and effect. This Agreement may be executed in counterparts (including electronic counterparts), each of which shall be deemed an original but all of which together shall

constitute one and the same instrument. Signatures to this Agreement transmitted by electronic mail in “portable document format” (.pdf) form, or by any other electronic means intended to preserve the original graphic and pictorial appearance of a document, will have the same effect as physical delivery of the paper document bearing the original signature. The undersigned hereby consents to receipt of this Agreement in electronic form and understands and agrees that this Agreement may be signed electronically. In the event that any signature is delivered by electronic mail, or otherwise by electronic transmission evidencing an intent to sign this Agreement, such electronic mail or other electronic transmission shall create a valid and binding obligation of the undersigned with the same force and effect as if such signature were an original. Execution and delivery of this Agreement by electronic mail or other electronic transmission is legal, valid and binding for all purposes.

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In acknowledgment that the foregoing correctly sets forth the understanding reached by Wainwright and the Company, please sign in the space provided below, whereupon this letter shall constitute a binding Agreement as of the date indicated above.


		Very truly yours,

		H.C. WAINWRIGHT & CO., LLC


		By:
			Name:
			Title:
			Date:

Accepted and Agreed:


ADDEX THERAPEUTICS LTD

By: /s/ Tim Dyer
Name: Tim Dyer
Title: CEO

Annex A

Annex A(1): Current Investors in the Company

NEA, NLV, CAM Capital, Credit Suisse Asset Management, and all the investors syndicated by Herculis Partners and Semper during the 2015, 2017 and 2018 financing

Annex A(2): Insiders in the Company

All current officers and directors of the Company and Acorn Bioventures

Annex A(3): Current relationships

Investors and Insiders listed in Annex A(1) and A(2) plus Sofinnova Ventures, Sofinnova Partners, Abingworth, BVF, HBM, EcoR1 and Medicixi.