The Natural Quassinoid Brusatol Enhances Venetoclax Efficacy and Overcomes Resistance in Myeloid Leukemias.

While venetoclax-based combinations have shown promising results in acute myeloid leukemia (AML), the remission duration is generally short, warranting strategies to further improve efficacy and overcome resistance. Here, we show that the natural quassinoid brusatol induces cell-cycle arrest and apoptosis in multiple AML cell lines while enhancing venetoclax efficacy irrespective of inherent or acquired resistance. Mechanistically, brusatol increased p53 protein expression, leading to upregulation of its target genes/proteins, including CDKN1A (p21) and BBC3 (PUMA). Genetic deletion of TP53 attenuated brusatol-induced apoptosis and its synergy with venetoclax, supporting p53 activation as a central mechanism underlying the anti-leukemia response. Furthermore, the combination synergistically decreased mitochondrial membrane potential and respiratory activity, causing accumulation of reactive oxygen species in AML cells. Although brusatol and venetoclax exhibited limited effects individually, their combination markedly reduced leukemia burden and significantly prolonged survival in three independent cell line-derived xenograft models, including venetoclax-resistant and -refractory models. Notably, brusatol increased normal leukocyte and platelet counts while reducing leukemic infiltration in both bone marrow and extramedullary sites. These findings provide mechanistic insight into the synergistic effects of the brusatol-venetoclax combination, supporting further evaluation of this therapeutic strategy in myeloid leukemias.