Ms. Susan Pietropaolo reports

APTOSE TO HOLD INTERIM CLINICAL UPDATE WEBCAST ON SATURDAY, JUNE 10, 2023

Aptose Biosciences Inc.'s management team will provide a clinical update on Saturday, June 10, 2023, at 12 p.m. EST/6 p.m. CEST, in conjunction with EHA 2023 International Congress of the European Hematology Association in Frankfurt, Germany. The webcast event will include an interim review of Aptose's lead compound tuspetinib, a myeloid kinase inhibitor, currently being tested as a monotherapy and in combination with venetoclax in the phase 1/2 Aptivate trial.

Tuspetinib, administered as a once-daily oral tablet, is a precision-targeted kinase inhibitor designed to suppress a select handful of kinases known to drive proliferation of acute myeloid leukemia (AML) while maintaining a favourable safety profile. Aptose management will highlight additional insights from the completed phase 1/2 dose escalation clinical trial of tuspetinib and review early trends from the continuing Aptivate trial.

Aptose clinical update webcast details

Date and time: Saturday, June 10, 2023, 12 p.m. ET

Participant dial-in

Toll-free investors dial: 1-877-407-9039

Toll/international investors dial: 1-201-689-8470

Conference ID: 13739137

The slides will be available on Aptose's website and the webcast of the presentation will be archived shortly after the conclusion of the event.

In addition, an abstract on tuspetinib was recently published in EHA's open-access library.

Abstract: PB1766

Title: In vitro acquired resistance to the oral myeloid kinase inhibitor tuspetinib creates synthetic lethal vulnerability to venetoclax

Session title: acute myeloid leukemia -- biology and translational research

Tuspetinib (TUS) is a once-daily oral agent that potently inhibits JAK1/2, SYK, RSK1/2, wildtype and mutant forms of FLT3, and mutant forms of KIT kinases, thereby simultaneously suppressing multiple oncogenic signalling pathways that mediate resistance to various drugs. TUS as a single agent has generated complete remissions in relapsed/refractory (R/R) acute myeloid leukemia (AML) patients with diverse mutations and demonstrated favourable safety in a phase 1 trial (NCT03850574). TUS is now in a phase 1/2 expansion trial (Aptivate) for R/R AML patients with high unmet need as a monotherapy and as a doublet in combination with venetoclax. The clinical activity against diverse mutational subpopulations led Aptose to investigate alterations in AML cells that may give rise to TUS resistance, and to understand the sensitivity of resistant isolates to venetoclax and other agents used to treat AML.

Resistance to TUS in MOLM-14 cells required prolonged high-level drug exposure, but ultimately yielded a stable phenotype. Strikingly, acquired TUS resistance generated a synthetic lethal vulnerability in which the cells were unusually hypersensitive to venetoclax. This suggests that concurrent administration of TUS and venetoclax may be advantageous clinically as TUS and venetoclax could act in concert to discourage the emergence of drug resistance during treatment.

About Aptose Biosciences Inc.

Aptose Biosciences is a clinical-stage biotechnology company developing precision medicines addressing unmet medical needs in oncology, with an initial focus on hematology. The company's small-molecule cancer therapeutics pipeline includes products designed to provide single-agent efficacy and to enhance the efficacy of other anti-cancer therapies and regimens without overlapping toxicities. The company has two clinical-stage oral kinase inhibitors under development for hematologic malignancies: tuspetinib (HM43239), an oral, myeloid kinase inhibitor being studied as monotherapy and in combination therapy in the Aptivate international phase 1/2 expansion trial in patients with relapsed or refractory acute myeloid leukemia (AML); and luxeptinib (CG-806), an oral, dual lymphoid and myeloid kinase inhibitor in phase 1 a/b stage development for the treatment of patients with relapsed or refractory hematologic malignancies.

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