AB Science Achieves 67% ORR in Phase 1 Step 3 of AB8939 Plus Venetoclax for Relapsed AML

A 67% overall response rate in a population where standard-of-care regimens typically yield 10–30% positions AB Science's AB8939-plus-venetoclax combination as a clinically meaningful signal, even at this early stage. The completion of Step 3 of the Phase 1 study, reported 29 June 2026, also establishes the recommended Phase 2 dose (RP2D), a prerequisite before any pivotal programme can advance.

Six patients with relapsed or refractory acute myeloid leukemia (AML) were treated across two AB8939 dose levels, 16 mg/m² and 21.3 mg/m², each combined with venetoclax over a 14-day cycle. No dose-limiting toxicities (DLTs) and no hematological toxicity were observed at either level. Four of the six patients achieved an objective response: one complete remission with incomplete hematologic recovery (CRi) and three partial responses (PR). The remaining two achieved stable disease, producing a 100% disease control rate (DCR).

The patient population carried adverse-risk cytogenetics across the cohort, including TP53 mutation, complex karyotype, MECOM-rearrangement, and monosomy 5 and 7, profiles associated with aggressive disease course and high treatment resistance. Notably, two responding patients had previously progressed on venetoclax-based regimens, suggesting AB8939's microtubule-destabilising mechanism may circumvent acquired resistance pathways relevant to BCL-2 inhibitor combinations.

For CMC and process development teams, the 14-day cycle structure and the two-agent small-molecule combination introduce scheduling and compatibility considerations that will require formalisation ahead of Phase 2. AB8939's proposed ability to evade multi-drug resistance efflux mechanisms, while sparing non-tumoral stem cells, adds a layer of pharmacological complexity that will need to be reflected in formulation strategy and stability protocols as the programme scales.

All responses were observed after a single 14-day cycle in patients receiving second- to fourth-line therapy, a timeframe that will inform endpoint design and cycle-length justification in the forthcoming Phase 2 protocol submission.

Source: AB Science SA via GlobeNewswire, 29 June 2026.