Aptose Presents Highlights from Clinical Update

Finalized Dose Escalation/Dose Exploration Trial in 77 R/R AML Patients
Favorable safety with monotherapy responses across four dose levels with no DLT in mutationally diverse and difficult to treat R/R AML Populations
TP53^MUT CR/CRh = 20% │ RAS^MUT CR/CRh = 22%

Completed Successful Type B EOP1 Meeting with US FDA
Monotherapy RP2D selected as 80mg daily and single arm accelerated path remains open

Initiated APTIVATE Expansion Trial with R/R AML
Tuspetinib monotherapy and Tuspetinib + Venetoclax (TUS/VEN) doublet show brisk enrollment
TUS/VEN doublet well tolerated, all patients remain on study, preliminary CR activity reported among
first patients treated

SAN DIEGO and TORONTO, June 10, 2023 (GLOBE NEWSWIRE) -- Aptose Biosciences Inc. (“Aptose” or the “Company”) (NASDAQ: APTO, TSX: APS), a clinical-stage precision oncology company developing highly differentiated oral kinase inhibitors to treat hematologic malignancies, today released highlights from a clinical update event held today, 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 here.

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 favorable 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 = 20% and RAS-mutated patients with a CR/CRh = 22%.
• Completed successful End of Phase 1 (EOP1) Meeting with US FDA for tuspetinib, and a monotherapy RP2D was selected as 80mg 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 + venetoclax (TUS/VEN), and enrollment has been brisk.
  • TUS/VEN doublet has been well tolerated, all patients remain on study, and preliminary CR activity has already been reported in patients previously treated with VEN.