Na⁺/H⁺ Exchanger 1 Inhibition Overcomes Venetoclax Resistance in Acute Myeloid Leukemia

Despite advances with novel targeted agents (e.g., BCL-2 or IDH inhibitors) combined with chemotherapy for acute myeloid leukemia (AML), drug resistance persists. We investigated whether blocking Na⁺/H⁺ exchanger 1 (NHE1) could enhance AML cell sensitivity to the BCL-2 inhibitor venetoclax and sought to determine the molecular mechanisms. Our results demonstrated that co-treatment with venetoclax and the NHE1 inhibitor 5-(N,N-hexamethylene) amiloride (HMA) synergistically induced apoptosis in both venetoclax-sensitive and -resistant leukemic cell lines. Specifically, the combination significantly increased apoptosis in venetoclax-resistant THP-1 cells to 72.28% (17.79% with 100 nM venetoclax and 10.15% with 10 μM HMA alone; p < 0.001). Conversely, another venetoclax-resistant line, U-937, showed no significant apoptotic response to the combination. In THP-1 cells, this synergy was mediated via a caspase-dependent programmed cell death pathway, evidenced by an increased BAX/BCL-2 ratio, mitochondrial cytochrome c release, and subsequent caspase-9 and caspase-3 activation. Furthermore, co-treatment downregulated the anti-apoptotic protein MCL-1 and reduced PI3K and Akt phosphorylation, suggesting that inhibition of these survival pathways also contributed to the synergistic effect. Inhibition of NHE1 may substantially enhance venetoclax sensitivity in certain AML models, particularly in venetoclax-resistant THP-1 cells but not in U-937, highlighting biological diversity and the probable involvement of alternative survival pathways.