Onxeo

Pre-Annual General Meeting Information • May 16, 2023

Combined General Meeting of June 6, 2023: availability of preparatory documents and participation & voting procedures

Paris (France), May 16, 2023 - 06:00 pm CEST - Onxeo S.A. (Euronext Growth Paris: ALONX), a clinicalstage biotechnology company specializing in the development of innovative drugs targeting tumor DNA Damage Response (DDR) and driver oncogenes, today announced the availability of preparatory documents for its Combined General Meeting to be held on Tuesday, June 6, 2023 at 2:00 pm at the Renaissance Paris Nobel Tour Eiffel Hotel, 55 avenue Raymond Poincaré, 75116 Paris.

The notice of meeting, including the agenda and the proposed resolutions, was published in the BALO on April 28, 2023, and the convening notice will be published in the BALO and in a legal gazette on May 17, 2023.

In order to submit their votes, shareholders may, in accordance with the procedures described in the notice of meeting published in the BALO on April 28, 2023:

• attend the meeting in person;
• vote by mail, using a voting form;
• or by giving a proxy to the Chairman of the General Meeting or to a third party.

All documents relating to this general meeting are available on the Company's website in the General Meetings section.

If you have any questions, please contact the Investor Relations team by e-mail at the dedicated address ag2023@onxeo.com.

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About Onxeo

Onxeo (Euronext Growth Paris: ALONX) is a clinical-stage biotechnology company developing innovative oncology drugs targeting tumor DNA-binding functions through unique mechanisms of action in the sought-after field of DNA Damage Response (DDR). The Company is focused on bringing early-stage first-in-class or disruptive compounds from translational research to clinical proof-of-concept, a value-creating inflection point appealing to potential partners.

platON™ is Onxeo's proprietary chemistry platform of DNA decoy therapeutics, which generates new innovative compounds and broaden the Company's product pipeline.

AsiDNA, the first compound from platON, is a highly differentiated, clinical-stage first-in-class candidate in the field of DNA damage response (DDR) applied to oncology. Its DNA decoy therapeutic mechanism acting upstream of multiple DDR pathways results in distinctive antitumor properties, including the ability to prevent or abrogate tumor resistance to targeted therapies such as PARP inhibitors and strong synergy with tumor DNA-damaging agents such as radiochemotherapy. AsiDNA is currently being studied in Europe and the US in combination with other treatment modalities in difficult-to-treat solid tumors.

OX425, the second compound from platON, is a novel pan-DDR Decoy with high antitumor activity. It also mediates multiple immunostimulatory effects by activating the STING pathway. OX425 is currently undergoing IND-enabling preclinical development.

For more information, visit www.onxeo.com.

Forward looking statements

This communication expressly or implicitly contains certain forward-looking statements concerning Onxeo and its business. Such statements involve certain known and unknown risks, uncertainties and other factors, which could cause the actual results, financial condition, performance or achievements of Onxeo to be materially different from any future results, performance or achievements expressed or implied by such forward-looking statements. Onxeo is providing this communication as of this date and does not undertake to update any forward-looking statements contained herein as a result of new information, future events or otherwise. For a discussion of risks and uncertainties which could cause actual results, financial condition, performance or achievements of Onxeo to differ from those contained in the forward-looking statements, please refer to the risk factors described in the most recent Company's registration document or in any other periodic financial report and in any other press release, which are available free of charge on the websites of the Company Group (www.onxeo.com) and/or the AMF (www.amffrance.org)..

Contacts

Onxeo

Investor Relations investors@onxeo.com +33 1 45 58 76 00

Media Relations Arthur Rouillé NewCap onxeo@newcap.eu +33 1 44 71 00 15

Investor Relations / Strategic Communication Dušan Orešanský / Nicolas Fossiez NewCap onxeo@newcap.eu +33 1 44 71 94 92