On January 30, 2023 Aptose Biosciences Inc. ("Aptose") (NASDAQ: APTO, TSX: APS) reported the 120 mg monotherapy dosing of patients in the APTIVATE Phase 1/2 clinical trial of tuspetinib (formerly HM43239), an oral, mutation agnostic tyrosine kinase inhibitor (TKI) being developed for the treatment of patients with relapsed or refractory acute myeloid leukemia (R/R AML) (Press release, Aptose Biosciences, JAN 30, 2023, View Source [SID1234626632]). In parallel, another clinical response has been achieved by a R/R AML patient receiving 40 mg tuspetinib once daily orally in the original dose exploration trial, the second response at the recently launched low-dose 40 mg cohort.

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Tuspetinib, a once daily oral agent designed to simultaneously target SYK, JAK1/2, FLT3, and other kinases operative in AML, has thus far as a monotherapy safely delivered multiple complete remissions and clinical responses across four dose levels (40mg, 80mg, 120mg, and 160mg) in AML patients that previously had been failed by chemotherapy, BCL2 inhibitors, hypomethylating agents, FLT3 inhibitors, and hematopoietic stem cell transplants. Data were presented last month at the 2022 American Society of Hematology (ASH) (Free ASH Whitepaper) annual meeting by lead investigator Naval G. Daver, M.D., Associate Professor in the Department of Leukemia at MD Anderson Cancer Center, showing tuspetinib delivers single agent responses without prolonged myelosuppression or life-threatening toxicities in these very ill and heavily pretreated relapsed or refractory AML patients. Responses were observed in a broad range of mutationally-defined populations, including those with mutated forms of NPM1, MLL, TP53, NRAS, KRAS, DNMT3A, RUNX1, wild-type FLT3, ITD or TKD mutated FLT3, various splicing factors, and other genes.

Importantly, Aptose has elucidated a rationale for the superior safety profile of tuspetinib. While several kinase inhibitors require high exposures that exert near complete suppression of a single target to elicit responses, those agents often cause additional toxicity because they also cause extensive inhibition of that target in normal cells. In contrast, tuspetinib simultaneously suppresses a small suite of kinase-driven pathways critical for leukemogenesis. Consequently, tuspetinib achieves clinical responses at lower exposures with less overall suppression of each pathway, thereby avoiding many of the toxicities observed with competing agents.

The APTIVATE expansion trial is designed to confirm monotherapy activity through patient enrichment of specific mutationally defined AML populations, including TP53-mutant patients and FLT3-mutant patients who have been failed by a prior FLT3 inhibitor, as supported by FDA fast-track designation and a clinically significant response rate to date. In the APTIVATE expansion trial, tuspetinib also will be tested in combination with venetoclax. More information on the APTIVATE trial can be found on www.clinicaltrials.gov (here).

"We are pleased to have dosing underway in our APTIVATE clinical trial of tuspetinib in a very ill R/R AML population," said William G. Rice, Ph.D., Chairman, President, and Chief Executive Officer. "Tuspetinib has demonstrated noteworthy safety and mutation agnostic potency across a spectrum of AML patients with a diversity of adverse mutations, further distinguishing it from competing compounds and targeting a much larger AML population. This breadth of activity along with its significant safety profile has allowed us to define a precise clinical and commercial plan for tuspetinib in multiple lines of therapy, including its use in doublet and triplet combinations, as well as maintenance therapy."