PRESS RELEASE




AB SCIENCE PROVIDES INITIAL PHASE 1 DATA FOR THE COMBINATION OF AB8939 WITH VENETOCLAX FOR
THE TREATMENT OF REFRACTORY OR RELAPSED ACUTE MYELOID LEUKEMIA

Paris, 16 October 2025, 9pm CET

AB Science SA (Euronext - FR0010557264 - AB) today provides an update on its AB8939 program in acute
myeloid leukemia (AML).
The webcast presentation is available on the company’s website, in the section « Press
Releases »: https://www.ab-science.com/news-and-media/press-releases/
Highlights of the presentation are the following:
- In monotherapy, AB8939 has shown activity in MECOM, with long OS benefit
- In combination therapy :
o There is a strong rationale to combine AB8939 with Venetoclax, as the combination treatment is
well-tolerated and both molecules have different and complementary targets in cancer cells
o The disease control rate is 100% (3/3) and the partial response rate is 100% (3/3), including one
patient in complete remission
o These results were obtained after the first cycle of treatment (14 days of treatment) in patients
receiving third- or fourth-line treatment, two of whom had previously progressed on venetoclax
in combination with other chemotherapies
- Next step is to finish phase 1 in combination and to launch an expansion study in around 15 AML patients
eligible to AB8939 + Venetoclax at the right dose
Nicholas J. Short, MD, Associate Professor and Co-Lead of Section of Developmental Therapeutics,
Department of Leukemia, MD Anderson Cancer Center, said, "Early data suggest that AB8939 (monotherapy
and/or combination) could have significant activity in the highest risk subtypes of AML. If similar responses
rates and safety are observed during trial expansion, AB8939 is well-positioned for development in adverse-
risk AML in frontline and salvage settings."
Christian Auclair, PharmD, PhD, Professor Emeritus, Cofounder and former director of the PhD program in
oncology at Institut Gustave Roussy, Paris-Saclay University, said, "The dual property of AB8939 targeting
both cancer cells and cancer stem cells makes AB8939 a molecule of choice for the treatment of high risk
leukemia by reducing the frequency of relapses. It is furthermore a perfectly tolerated molecule characterized
by a lack of bone marrow toxicity."
Professor Olivier Hermine, MD, President of the Scientific Committee of AB Science and member of the
Académie des Sciences in France said, "The fact that the combination of AB8939 and venetoclax exhibits low
hematological toxicity is very important as it can allow patients to receive multiple cycles of treatment and
maintain a satisfactory quality of life."

Medical need in AML and AB8939 mechanism of action
In AML, there are several registered drugs but 70% of patients relapse and die creating a persistent unmet
medical need. AML remains the most lethal leukemia in humans.
AML is a heterogenous disease with outcome highly dependent on genetic factors. TP53 mutation has a very
poor prognosis, NRAS, with a median overall survival of 5.5 months. KRAS mutant has a poor prognosis, with
a median OS of 12.1 months. MECOM also has a very poor prognosis in AML, with a median OS of 5.5 months
in relapsed or refractory setting.
The challenge in AML is the recurrence of tumors due to a combination of two factors: The resistance of
cancer cells to chemotherapy and the relapse due to persistence of cancer stem cells. This challenge may be
overcome by AB8939 dual mechanism of action.
- First, AB8939 is able to block the proliferation of leukemia cells through microtubules disruption, not
being subject to multidrug resistance as it does not bind to PgP, responsible of efflux outside the
cells, and not being degraded by the myeloperoxidase enzyme.
- Second, AB8939 targets leukemia cancer stem cells though inhibition of ALDH and favors the bone
marrow repopulation of normal progenitors.

AB8939 non-clinical data
- AB8939 has shown in vitro activity in Ara-C (cytarabine is one of the standard of care) resistant patients
cell lines, including adverse genetic MECOM, TP53 mutated. Analysis of cell lines responsive to AB8939
shows that AB8939 is effective in cell lines with TP53 mutation, MECOM and complex karyotypes, when
ARAC and azacitidine is not effective.
- AB8939 increased survival and has an additive effect in combination with Venetoclax (another standard
of care) in vivo in a Mecom grafted PDX mice model.
- AB8939 increased survival and had an additive effect in combination with Vidaza (another standard of
care) in vivo in the same Mecom PDX#C1005 mice model.
- AB8939 was able to eradicate Leukemia Cancer Stem Cells in vivo in a human PDX AML mice model,
which is compatible with targeting of stem cells via the ALDH.

Clinical data - monotherapy
Phase 1 in monotherapy has been completed and phase 1 in combination has started.
The first two steps of the phase 1, evaluating the maximum tolerated dose (MTD) AB8389 monotherapy after
3 and 14 consecutive days, respectively, have been completed with 28 patients and 13 patients respectively.
For both regimen, the MTD was. 21.3 mg/m2.
AB8939 in monotherapy has shown activity in MECOM, based on non-clinical data and early clinical data,
with long OS benefit.

Clinical Data – combination therapy
There is a strong rationale to combine AB8939 with Venetoclax
- Both molecules have low hematologic toxicity. This combination is expected to be less toxic than
azacitidine + venetoclax as first-line treatment for AML
- Both molecules have different and complementary targets in cancer cells. There is an additive, even
synergistic, efficacy potential for the combination, with three mechanisms of action in one treatment.
o Venetoclax mechanism of action is to inhibit BCL2 pathway, a protein that prevents apoptosis
(programmed cell death) in cancer cells. BCL2 is a key factor in AML resistance, as it allows cancer
cells to survive despite treatment
o AB8939 is pro-apoptotic, destabilizing microtubule, and would benefit from BCL2 inhibition to
optimize apoptosis
o In addition, AB8939 specifically targets cancer stem cells by inhibiting ALDH, reducing resistance
to treatment and limiting the risk of relapse
In combination, AB8939 + venetoclax remarkably generated responses after the first cycle of treatment in
patients in Line 3 or 4 with high risk adverse profile, complex karyotypes, TP53, Mecom and NRAS mutation,
respectively. The disease control rate was 100% (3/3), and the partial response rate is 100% (3/3), including
one patient in complete remission. Two of the three patients had previously progressed on venetoclax in
combination with other chemotherapies.
AB8939 + venetoclax could become a new standard of care in particular for AML patients with adverse
genetics
- Venetoclax + Vidaza is the standard of care for aged patient not eligible to high dose chemotherapy in
Line 1
- Venetoclax + Vidaza is known to be poorly effective in TP53 and NRAS mutant
- AB8939 preliminary data give credit to the hypothesis that the combination AB8939+venetoclax could
become a new standard of care
- AB8939 + venetoclax is less toxic than other combinations, in particular on hema-toxicity

Next steps
The next step is to finish phase 1 in combination and to launch an expansion study in around 15 AML patients
eligible to AB8939 + Venetoclax at the right dose. The expansion phase is expected to generate robust
preliminary evidence of efficacy in the AML label to support the clinical development plan and beneficial
trigger partnership agreement.
There are currently 3 possibilities of registrational studies, not mutually exclusive, that we have started to
discuss with FDA and EMA:
- AB8939 + venetoclax in first line of treatment, with aged patients and or adverse genetics (tp53mut +
nras + kras + complex k + monosomy 5/7 + mecom)
- AB8939 + venetoclax in second or third line of treatment, all patients or adverse genetics
- AB8939 in MECOM in second or third line of treatment.

Addressable market with AB8939 in relapsed/refractory AML
Treatments in relapsed or refractory AML represent an estimated market size potential above EUR 2 billion
per annum.

Incidence % Relapse or
% Insured Drug Price Market Size
Region Case Refractory
Patients (4) (€) (per in Mio EUR)
(1) (2,3)
USA / CANADA 23,700 90% 100,000(5) 1 000 000
EUROPE 27,600 90% 60,000 770 000
APAC 27,800 30% 60,000 250 000
50%
INDIA 11,000 30% 60,000 100,000
LATAM 7,200 30% 60,000 65 000
MENA 3,900 30% 60,000 35 000
TOTAL 90,200 2 200 000
EUROPE = EU27 + Norway + United Kingdom + Switzerland ; APAC = Australia, People’s Republic of China , Japan, New Zealand,
Singapore, Taiwan ; LATAM = Argentina, Brazil, Chile, Colombia, Costa Rica, Mexico ; MENA = Algeria, Bahrain, Egypt, Israel,
Kuwait, Morocco, Oman, Qatar, Saudi Arabia, Tunisia, United Arab Emirates
(1) Zhou, Y et al. Global, regional, and national burden of acute myeloid leukemia, 1990–2021: a systematic analysis for the global
burden of disease study 2021. Biomark Res 12, 101 (2024).
(2) Ravandi F. Relapsed acute myeloid leukemia: Why is there no standard of care Best Pract Res Clin Haematol. 2013;26(3):253-
9
(3) Walter RB et al. Resistance prediction in AML: analysis of 4601 patients from MRC/NCRI, HOVON/SAKK, SWOG and MD
Anderson Cancer Center. Leukemia (2015) 29:312–20. .
(4) Estimated
(5) Choi M. et al. Costs per patient achieving remission with venetoclax-based combinations in newly diagnosed patients with
acute myeloid leukemia ineligible for intensive induction chemotherapy. Journal of Managed Care & Specialty Pharmacy
Volume 28, Number 9. https://doi.org/10.18553/jmcp.2022.22021

Intellectual property
AB8939 intellectual property rights in AML are secured until 2036 through a ‘composition of matter’ patent
and potentially 2041 with the 5 years extension and until 2044 in AML with chromosome abnormality,
including MECOM, through a ‘second medical use’ patent.
AB Science is the sole proprietary holder of AB8939 and its family of compounds.

Virtual conference attendees
The following individuals participated in the virtual conference:
▪ Nicholas J. Short, MD, Associate Professor and Co-Lead of Section of Developmental Therapeutics,
Department of Leukemia, MD Anderson Cancer Center
Professor Short is a clinical and translational investigator in adult acute leukemias, with a particular
emphasis on the development of phase I and II investigator-initiated clinical trials of novel agents and
combinations for patients with acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL).
His major contributions to leukemia research include: developing new immunotherapy-based frontline
regimens in Philadelphia chromosome-negative B-cell ALL, developing chemotherapy-free regimens in
Philadelphia chromosome-positive ALL, establishing the clinical utility of high-sensitivity next-generation
sequencing-based MRD assays in ALL, developing novel MRD-directed therapies in AML and ALL, and
developing novel regimens for older adults with FLT3-mutated AML. He serves as principal investigator
or co-principal investigator on over a dozen phase I and II clinical trials and has authored over 250 peer-
reviewed manuscripts in the field of leukemia. For his clinical and translational accomplishments in the
field of leukemia, he has been awarded the ASCO Young Investigator Award and the ASH Junior Faculty
Scholar in Clinical Research.
▪ Olivier Hermine, MD, PhD, Head of the Hematology Department at Necker-Enfants Malades Hospital,
Paris, France
Olivier Hermine is Professor of Hematology at Paris Descartes University, Head of the Hematology
Department at Necker-Enfants Malades Hospital, member of LYSA, and Director of the CALYM team
"Cellular and Molecular Mechanisms of Hematological Disorders and Therapeutic Implications" at the
IMAGINE Inserm U 116 CNRS ERL 8654 institute. He is also coordinator of the Reference Center for
Mastocytosis (CeReMast), co-founder and director of the scientific committee of AB Science.
His research topics include lymphoproliferative disorders linked to the hepatitis C virus, mantle cell
lymphomas, and the regulation of erythropoiesis. He is the author or co-author of more than 900
scientific publications.
▪ Christian Auclair, PharmD, PhD, Emeritus Professor
Professor Auclair holds a doctorate in pharmaceutical sciences. He is co-founder and former director of
the doctoral school of oncology at the Faculty of Medicine of Paris-Saclay University. He is former
director of the biology department at the École Normale Supérieure de Cachan (now ENS Paris-Saclay)
and director of UMR 8113 at the CNRS. He was also deputy scientific director of the CNRS's life sciences
department. He is the author of more than 120 publications in the field of antitumor pharmacology and
virology. He is co-founder and scientific advisor to AB Science.

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 developed in human medicine in oncology, neurological diseases,
inflammatory diseases and viral 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
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development and their potential or future performance.

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the Company which may not be successful or to the marketing authorizations granted by competent authorities or,
more generally, any factors that may affect 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 the forward-looking information and statements, subject to the applicable regulations, in
particular articles 223-1 et seq. of the AMF General Regulations.


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