Azacitidine, Venetoclax and Magrolimab in Newly Diagnosed and Relapsed Refractory Acute Myeloid Leukemia: Phase 1b/2 Study and Correlative Analysis

Purpose: Magrolimab is a monoclonal antibody directed against macrophage checkpoint CD47 on myeloid leukemia cells that was pre-clinically synergistic with azacitidine-venetoclax, warranting further clinical evaluation. Patients and Methods: In this phase 1b/2 study the triplet combination of azacitidine, venetoclax and magrolimab was evaluated in adult patients with frontline (ineligible for intensive chemotherapy) and relapsed/refractory AML. Azacitidine was dosed at 75mg/m2 for 7 days, venetoclax at 400 mg/day for 28 days, and magrolimab (recommended phase 2 dose [RP2D]) as follows: 1 mg/kg dose on days 1 and 4, 15 mg/kg on day 8, 30 mg/kg on day 11, 15 and 22 (cycle 1), followed by 30 mg/kg weekly for cycle 2, then 30 mg/kg every 2 weeks cycle 3 and beyond. The primary endpoint was RP2D for phase 1b and rates of composite complete response (CRc) in phase 2. Results: The frontline cohort included 54 patients (median age 70.1 years); 35 (64.8%) were TP53 mutated (TP53mut). CRc was attained in 34 patients (63%); 49% in TP53mut and 90% in the TP53 wild-type patients. At a median follow-up of 27.9 months, the median event free survival (EFS) and overall survival (OS) was 6.6 months and 9.8 months respectively; for TP53mut patients the median EFS and OS was 5.9 and 7.6 months, while for TP53 wild type it was 9.6 months and 13 months respectively. CRc in the relapsed/refractory cohort (n=52) was 29% and median OS was 3.9 months. The regimen was well tolerated; infections were the most common ≥ grade 3 adverse event (75.4%) with no immune toxicities or deaths related to therapy. scRNAseq was performed on 27 longitudinal samples from 11 TP53mut patients (8 responders). Gene set enrichment analysis revealed enrichment of IFNγ and TNFα signaling in non-responders at baseline, while erythroid differentiation was associated with resistance. Patients at relapse also showed up-regulated CD47 expression and elevated leukemia regeneration score. Conclusions: The triplet regimen was safe but did not lead to promising survival outcomes.