AB Science provides an update on its development plan and financial calendar following a sponsor Good Clinical Practice inspection

PRESS RELEASE

AB SCIENCE PROVIDES AN UPDATE ON ITS DEVELOPMENT PLAN AND FINANCIAL CALENDAR FOLLOWING A SPONSOR GOOD CLINICAL PRACTICE INSPECTION

• Confirmation of the relevance of having, among the first decisions of the new management, given priority to the development of a new quality management system

• Expected resumption of the AB8939 phase 1 (acute myeloid leukemia) in the first quarter of 2027, followed by the masitinib phase 3 (amyotrophic lateral sclerosis) in the last quarter of 2027, subject to assessment by the health authorities
• Masitinib program in sickle cell disease not affected
• Half-year financial report to be published by October 9, 2026 at the latest, outlining the Company’s new ambitions, followed by a webcast

Paris, September 29, 2026, 8am CET

AB Science S.A. (the “Company” or “AB Science”, Euronext – FR0010557264 – AB) today announces a revision of its operating plan and financial calendar following a “for cause” sponsor Good Clinical Practice (GCP) inspection, conducted from September 21 to 25 and involving five inspectors from three health authorities: France, Denmark and Greece.

The inspection report will be sent to the Company before the end of the year, and the Company will inform the market of any consequences for its development plan.

The preliminary findings brought to its attention at the close of the inspection support the new management in its decision to have given priority:

• to overhauling the quality management system, , initiated as early as 13 July 2026, in order to guarantee patient safety and ensure the robustness of the data generated by the studies conducted by the Company, and, as a result, their value;
• to reassessing the clinical trial protocols, giving priority to scientific merit over financial constraints.

• Development plan
  
  

In addition, on the basis of these preliminary findings, AB Science considers that its development plan will need to be adapted as follows:

• Step 1: Continue and complete the implementation of the new quality management system and carry out an external audit of this system before considering the resumption of new clinical studies. The Company expects to complete this work by the end of 2026 and will communicate on the subject at the beginning of fiscal year 2027.
• Step 2: Resumption of the phase 1 study in acute myeloid leukemia (compound AB8939) within the framework of this new quality assurance system, in order to demonstrate that AB Science is now able to produce clinical data that are sufficiently reliable to meet the requirements of the applicable standards, and to support its partnering efforts. AB8939 has generated encouraging activity results and remains a priority development focus for the Company. AB Science expects to be able to resume this study in early 2027, subject to a positive benefit-risk assessment by the health authorities, and will be able to confirm this timeline only on the basis of the final inspection report and the responses provided by the Company.
• Step 3: Resumption of the phase 3 study in amyotrophic lateral sclerosis (ALS) (compound masitinib) following a new inspection. AB Science plans to be able to resume this study in the fourth quarter of 2027, subject to a positive benefit-risk assessment by the health authorities, and will be able to confirm this timeline only on the basis of the final inspection report and the responses provided by the Company.
  
  

AB Science intends to use this delay relative to its initial timeline to consolidate its development plan.

• AB8939 program: a review is under way to optimize the design of step 4 of the phase 1 based on the available pharmacological and clinical data. The optimization concerns the choice of treatments combined with AB8939 as well as the patients to be included in this step.
• ALS program: a review is under way to enrich the design of the phase 3 ALS study, notably via the integration of biomarkers and their pre-specification in the study’s statistical analysis plan.

In addition, the collaborative masitinib program in sickle cell disease, of which Assistance Publique – Hôpitaux de Paris (AP-HP) is the sponsor, is not affected and should begin during the 1^st quarter of 2027, following the Company’s renewed guarantee to supply the masitinib needed to carry out this study.

Stéphane Ledermann, Chairman and Chief Executive Officer of AB Science, states: “I have no doubt about the signs of efficacy of our molecules, nor about the skills of the Company’s employees to carry out our clinical development program successfully. Strict and consistent compliance with good clinical practice is at the heart of our project for AB Science, so that our clinical data are robust, recognized and valuable.”

• Financial reporting calendar
  
  

As a result of this inspection, which mobilized all of its employees, the Company will make its half-year financial report as of June 30, 2026 available by October 9, 2026 at the latest.

The outlines of the Company’s new ambitions will be announced concurrently with the publication of the half-year financial report. A webcast, including a question-and-answer session, will be held in the days following this publication. Connection details will be communicated at a later date.

About masitinib

Masitinib is a novel oral tyrosine kinase inhibitor that is being developed to target mast cells and macrophages, key immune cells, through inhibition of a limited number of kinases. Through its activity on mast cells and microglial cells and therefore its inhibitory effect on the activation of the inflammatory process, masitinib may have an effect on the course of central nervous system diseases.

About AB8939

AB8939 is a new synthetic microtubule-destabilizing drug candidate. Preclinical data suggests that AB8939 has broad anticancer activity, with a notable advantage over standard chemotherapies that target microtubules of being able to overcome P-glycoprotein (Pgp) and myeloperoxidase (MPO) mediated drug resistance. Development of drug resistance often restricts the clinical efficacy of microtubule-targeting chemotherapy drugs (for example, taxanes and vinca alkaloids); thus, AB8939 has the potential to be developed in numerous oncology indications.

About AB Science

Founded in 2001, AB Science is a pharmaceutical company specializing in the research, development and commercialization of protein kinase inhibitors (PKIs), a class of targeted proteins whose action are key in signaling pathways within cells. Our programs target only diseases with high unmet medical needs, often lethal with short term survival or rare or refractory to previous line of treatment. AB Science has developed a proprietary portfolio of molecules and the Company’s lead compound, masitinib, has already been registered for veterinary medicine and is being developed in human medicine primarily in neurological diseases,. The company is headquartered in Paris, France, and listed on Euronext Paris (ticker: AB). Further information is available on AB Science’s website: www.ab-science.com.

Forward-looking Statements - AB Science

This press release contains forward-looking statements. These statements are not historical facts. These statements include projections and estimates as well as the assumptions on which they are based, statements based on projects, objectives, intentions, and expectations regarding financial results, events, operations, future services, product development, and their potential or future performance.

These forward-looking statements can often be identified by the words "expect", "anticipate", "believe", "intend", "estimate" or "plan" as well as other similar terms. While AB Science believes these forward-looking statements are reasonable, investors are cautioned that these forward-looking statements are subject to numerous risks and uncertainties that are difficult to predict and generally beyond the control of AB Science, which may imply that results and actual events significantly differ from those expressed, induced, or anticipated in the forward-looking information and statements. These risks and uncertainties include uncertainties related to the product development of the Company, which may not be successful, or to the marketing authorizations granted by competent authorities, or, more generally, any factors that may affect the marketing capacity of the products developed by AB Science, as well as those developed or identified in the public documents published by AB Science. AB Science disclaims any obligation or undertaking to update forward-looking information and statements, subject to the applicable regulations, in particular articles 223-1 et seq. of the AMF General Regulations.

For additional information, please contact:
AB Science Financial communication and public relations
investors@ab-science.com

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• 20260929 - AB Science - Communiqué VENG VF