Dr. William Rice reports

APTOSE PRESENTS HIGHLIGHTS FROM CLINICAL UPDATE

Aptose Biosciences Inc. has released highlights from a clinical update event held June 10, 2023, in conjunction with EHA 2023 International Congress of the European Hematology Association in Frankfurt, Germany. The event included an up-to-date review of clinical data for Aptose's two investigational products under development for hematologic malignancies: tuspetinib, an oral, myeloid kinase inhibitor in the phase 1/2 Aptivate trial in patients with relapsed or refractory acute myeloid leukemia (AML); and luxeptinib, 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. The webcast of the presentation is available on Aptose's website.

Aptose provided updated clinical findings with tuspetinib, a potent suppressor of FLT3, SYK, JAK 1/2, mutant forms of cKIT and the RSK1/2 kinases operative in AML:

• Completed tuspetinib dose escalation and dose exploration phase 1/2 trial in 77 R/R AML patients:
  • Tuspetinib demonstrated a favourable safety profile;
  • Tuspetinib delivered monotherapy responses across four dose levels with no DLT in mutationally diverse and difficult-to-treat R/R AML populations, including TP53-mutated patients with a CR/CRh equals 20 per cent and RAS-mutated patients with a CR/CRh equals 22 per cent;
• Completed successful end of phase 1 (EOP1) meeting with U.S. Food and Drug Administration for tuspetinib, and a monotherapy RP2D was selected as 80 milligrams daily, and all development paths remain open, including the single arm accelerated path;
• Initiated tuspetinib Aptivate expansion trial with R/R AML patients:
  • Tuspetinib is being administered as a monotherapy and as a combination doublet with tuspetinib plus venetoclax (TUS/VEN), and enrolment has been brisk;
  • TUS/VEN doublet has been well tolerated, all patients remain on study and a preliminary CR activity has already been reported in patients previously treated with VEN.

Aptose also reviewed clinical findings with the new G3 formulation of luxeptinib (Lux):

• 50-milligram G3 formulation with continuous dosing achieves roughly equivalent PK profile as 900-milligram original G1 formulation;
• Expect to dose escalate G3 formulation with continuous dosing in patients soon.

"We are delighted to have finalized our dose escalation and dose exploration phase 1/2 trial with tuspetinib (TUS), to have demonstrated single agent responses across four dose levels that had no DLTs and across a range of R/R AML populations with a diversity of adverse mutations," said Dr. William G. Rice, PhD, chairman, president and chief executive officer. "As part of our EOP1 meeting with the FDA, we designated 80 mg daily as our monotherapy recommended phase 2 dose (RP2D), and now we focus all attention on our Aptivate expansion trial to place monotherapy TUS in more patients with highly adverse mutations and to evaluate TUS in combination with venetoclax (VEN) as a doublet in R/R AML patients. Notably, to date, the doublet appears to be well tolerated, with all patients remaining on study, including a preliminary CR in a R/R AML patient who previously failed venetoclax. We look forward to accelerating testing of the doublet, adding MDS patients to our Aptivate trial and with the aim of moving into triplet therapy (TUS/VEN/HMA) in 1L AML patients."

About Aptose Biosciences Inc.

Aptose 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 therapeutic 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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