Session: 616. Acute Myeloid Leukemia: Novel Therapy, excluding Transplantation: Poster I
Hematology Disease Topics & Pathways:
AML, Adult, Diseases, Non-Biological, Therapies, Study Population, Myeloid Malignancies, pharmacology
AIMS: Primary objectives are to determine the safety and tolerability of APTO-253, to determine the maximum tolerated dose and the dose limiting toxicities (DLT), and to establish the recommended Phase 2 dose for future clinical trials in patients with R/R AML or high-risk MDS. Key secondary objectives are to assess the pharmacokinetic (PK) profile, pharmacodynamic (PD) activity, and preliminary evidence of antitumor activity.
METHODS: Eligible patients are those with R/R AML or high-risk MDS for which either standard treatment has failed, is no longer effective, or can no longer be administered safely. Treatment- emergent adverse events (TEAEs) and tumor responses are evaluated using International Working Group criteria. APTO-253 is administered by IV infusion once weekly on days 1, 8, 15, and 22 of each 28-day cycle; ascending dose cohorts will enroll at a starting dose of 20 mg/m2 with planned escalating to 403 mg/m2.
RESULTS: As of July 28, 2020, a total of 10 patients (age 66.1 ± 13.58 years, male 50%, female 50%, 8 AML and 2 MDS) have been treated with APTO-253 in this clinical trial at doses of 20 mg/m2 (n=1), 40 mg/m2 (n=1), 66 mg/m2 (n=4), and 100 mg/m2 (n=4). All 8 AML patients and 1 MDS patient were RBC and platelet transfusion dependent; 1 MDS patient was RBC transfusion dependent. No DLTs or drug-related serious adverse events have been reported. Possible drug related grade 2 TEAEs included fatigue, increased alkaline phosphatase, decreased appetite, hematoma, hypokalemia, thrombophlebitis, upper respiratory tract in 1 (10%) patient each. Only 1 TEAE of grade 3 or greater (fatigue, considered possibly drug-related) has occurred to date. Preliminary PK analysis showed plasma levels of APTO-253 were dose proportional. Cmax and AUC0-24h on cycle 1 day 1 (C1D1) were 0.18, 0.07, 0.28 ± 0.15 and 0.77 ± 0.63 µM and 0.08, 0.13, 1.14 ± 0.57, 1.84 ± 0.41 µM*h for dose levels of 20 mg/m2, 40 mg/m2, 66 mg/m2, and 100 mg/m2, respectively. Not surprisingly, Fe(253)3 was detected in the patients’ plasma immediately after dosing and at a significantly higher concentration than the APTO-253 monomer. For example, Cmax and AUC0-24h of Fe(253)3 on C1D1 of patients in Cohort 66 mg/m2 were 3- and 8-fold higher than the monomer at 0.92 ± 0.29 µM and 20.61 ± 9.01 µM*h, respectively. The levels of MYC mRNA in the whole blood, a PD biomarker of APTO-253 and Fe(253)3 measured by RT-qPCR, were reduced 20-48% at 24 h post-dose as compared to pre-dose in the first 3 cohorts (other samples of Cohort 100 mg/m2 in process), suggesting target engagement by the drug.
CONCLUSIONS: APTO-253 has been well-tolerated in patients treated with 20, 40, 66, and 100 mg/m2 over multiple cycles. PK analysis revealed APTO-253 monomer rapidly transformed to and co-existed with the Fe(253)3 complex in peripheral blood and their exposures resulted in suppression of MYC expression in whole blood samples from R/R AML and high-risk MDS patients. Enrollment of patients at the 150 mg/m2 dose level is underway and updated clinical data will be presented at the meeting.
Disclosures: Bejar: Aptose Biosciences, Inc: Current Employment, Current equity holder in publicly-traded company. Zhang: Aptose Biosciences, Inc.: Current Employment, Current equity holder in publicly-traded company. Rastgoo: Aptose Biosciences, Inc.: Current Employment, Current equity holder in publicly-traded company. Benbatoul: Aptose Biosciences, Inc.: Current Employment, Current equity holder in publicly-traded company. Jin: Aptose Biosciences, Inc.: Current Employment, Current equity holder in publicly-traded company. Thayer: Aptose Biosciences, Inc.: Current Employment, Current equity holder in publicly-traded company. Sheng: Aptose Biosciences, Inc.: Current Employment, Current equity holder in publicly-traded company. Chow: Aptose Biosciences, Inc.: Current Employment, Current equity holder in publicly-traded company. Montalvo-Lugo: Aptose Biosciences, Inc.: Current Employment, Current equity holder in publicly-traded company. Marango: Aptose Biosciences, Inc.: Current Employment, Current equity holder in publicly-traded company. Howell: Aptose Biosciences, Inc.: Current equity holder in publicly-traded company. Rice: Aptose Biosciences, Inc.: Current Employment, Current equity holder in publicly-traded company.
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