Abstract
MDM2 inhibitors are promising therapeutics for acute myeloid leukemia (AML) with wild-type TP53. Through an integrated analysis of functional genomic data from primary patient samples, we found that an MDM2 inhibitor, idasanutlin, like venetoclax, is ineffective against monocytic leukemia (French-American-British [FAB] subtype M4/M5). To dissect the underlying resistance mechanisms, we explored both intrinsic and extrinsic factors. We found that monocytic leukemia cells express elevated levels of CEBPB, which promote monocytic differentiation, suppress CASP3 and CASP6, and upregulate MCL1, BCL2A1, and the interleukin (IL-1)/tumor necrosis factor alpha (TNF-α)/NF-κB pathway members, thereby conferring drug resistance to a broad range of MDM2 inhibitors, BH3 mimetics, and venetoclax combinations. In addition, aberrant monocytes in M4/M5 leukemia produce elevated levels of IL-1 and TNF-α, which promote monocytic differentiation and upregulate inflammatory cytokines and receptors, thereby extrinsically protecting leukemia blasts from venetoclax and MDM2 inhibition. Interestingly, IL-1β and TNF-α only increase CEBPB levels and protect M4/M5 cells from these drugs but not M0/M1 leukemia cells. Treatment with venetoclax and idasanutlin induces compensatory upregulation of CEBPB and the IL-1/TNF-α/NF-κB pathway independent of the FAB subtype, indicating drug-induced compensatory protection mechanisms. The combination of venetoclax or idasanutlin with inhibitors that block the IL-1/TNF-α pathway demonstrates synergistic cytotoxicity in M4/M5 AML. As such, we uncovered a targetable positive feedback loop that involves CEBPB, IL-1/TNF-α, and monocyte differentiation in M4/M5 leukemia and promotes both intrinsic and extrinsic drug resistance and drug-induced protection against venetoclax and MDM2 inhibitors.