The BCL-2 inhibitor venetoclax combined with hypomethylating agents or low-dose cytarabine represents an important new therapy for older or unfit patients with acute myeloid leukemia (AML). We analyzed 81 patients receiving these venetoclax-based combinations to identify molecular correlates of durable remission, response followed by relapse (adaptive resistance), or refractory disease (primary resistance). High response rates and durable remissions were typically associated with NPM1 or IDH2 mutations, with prolonged molecular remissions prevalent for NPM1 mutations. Primary and adaptive resistance to venetoclax-based combinations was most commonly characterized by acquisition or enrichment of clones activating signaling pathways such as FLT3 or RAS or biallelically perturbing TP53. Single-cell studies highlighted the polyclonal nature of intratumoral resistance mechanisms in some cases. Among cases that were primary refractory, we identified heterogeneous and sometimes divergent interval changes in leukemic clones within a single cycle of therapy, highlighting the dynamic and rapid occurrence of therapeutic selection in AML. In functional studies, FLT3 internal tandem duplication gain or TP53 loss conferred cross-resistance to both venetoclax and cytotoxic-based therapies. Collectively, we highlight molecular determinants of outcome with clinical relevance to patients with AML receiving venetoclax-based combination therapies.

Resistance to chemotherapy is a major problem in cancer treatment, and it is frequently associated with failure of tumor cells to undergo apoptosis. Birinapant, a clinical SMAC mimetic, had been designed to mimic the interaction between inhibitor of apoptosis proteins (IAPs) and SMAC/Diablo, thereby relieving IAP-mediated caspase inhibition and promoting apoptosis of cancer cells. We show that acute myeloid leukemia (AML) cells are sensitive to birinapant-induced death and that the clinical caspase inhibitor emricasan/IDN-6556 augments, rather than prevents, killing by birinapant. Deletion of caspase-8 sensitized AML to birinapant, whereas combined loss of caspase-8 and the necroptosis effector MLKL (mixed lineage kinase domain-like) prevented birinapant/IDN-6556-induced death, showing that inhibition of caspase-8 sensitizes AML cells to birinapant-induced necroptosis. However, loss of MLKL alone did not prevent a caspase-dependent birinapant/IDN-6556-induced death, implying that AML will be less likely to acquire resistance to this drug combination. A therapeutic breakthrough in AML has eluded researchers for decades. Demonstrated antileukemic efficacy and safety of the birinapant/emricasan combination in vivo suggest that induction of necroptosis warrants clinical investigation as a therapeutic opportunity in AML.

PURPOSE The B-cell lymphoma 2 (BCL-2) inhibitor venetoclax has an emerging role in acute myeloid leukemia (AML), with promising response rates in combination with hypomethylating agents or low-dose cytarabine in older patients. The tolerability and efficacy of venetoclax in combination with intensive chemotherapy in AML is unknown. PATIENTS AND METHODS Patients with AML who were ≥ 65 years (≥ 60 years if monosomal karyotype) and fit for intensive chemotherapy were allocated to venetoclax dose-escalation cohorts (range, 50-600 mg). Venetoclax was administered orally for 14 days each cycle. During induction, a 7-day prephase/dose ramp-up (days −6 to 0) was followed by an additional 7 days of venetoclax combined with infusional cytarabine 100 mg/m2 on days 1-5 and idarubicin 12 mg/m2 intravenously on days 2-3 (ie, 5 + 2). Consolidation (4 cycles) included 14 days of venetoclax (days −6 to 7) combined with cytarabine (days 1-2) and idarubicin (day 1). Maintenance venetoclax was permitted (7 cycles). The primary objective was to assess the optimal dose schedule of venetoclax with 5 + 2. RESULTS Fifty-one patients with a median age of 72 years (range, 63-80 years) were included. The maximum tolerated dose was not reached with venetoclax 600 mg/day. The main grade ≥ 3 nonhematologic toxicities during induction were febrile neutropenia (55%) and sepsis (35%). In contrast to induction, platelet recovery was notably delayed during consolidation cycles. The overall response rate (complete remission [CR]/CR with incomplete count recovery) was 72%; it was 97% in de novo AML and was 43% in secondary AML. During the venetoclax prephase, marrow blast reductions (≥ 50%) were noted in NPM1-, IDH2-, and SRSF2-mutant AML. CONCLUSION Venetoclax combined with 5 + 2 induction chemotherapy was safe and tolerable in fit older patients with AML. Although the optimal postremission therapy remains to be determined, the high remission rate in de novo AML warrants additional investigation (ANZ Clinical Trial Registry No. ACTRN12616000445471).