A CEBPB/IL-1β/TNF-α Feedback Loop Drives Drug Resistance to Venetoclax and MDM2 Inhibitors in Monocytic Leukemia

• IL-1 and TNF-α specifically increase CEBPB levels and protect M4/M5 cells from venetoclax and MDM2 inhibitors, but not M0/M1 leukemia cells.

• CEBPB-IL-1/TNF-α-monocyte differentiation positive feedback loop promotes intrinsic and extrinsic drug resistance in M4/M5 leukemia.

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 (FAB 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 promotes monocytic differentiation, suppresses CASP3 and CASP6, and upregulates MCL1, BCL2A1, and the IL-1/TNF-α/NF-κB pathway members, conferring drug resistance to a broad range of MDM2 inhibitors, BH3 mimetics, and venetoclax combinations. Additionally, aberrant monocytes in M4/M5 leukemia produce elevated levels of IL-1 and TNF-α, which promotes 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 FAB subtype, indicating a drug induced compensatory protection mechanisms. A combination of venetoclax/ idasanutlin with inhibitors that block IL-1/TNF-α pathway, demonstrate synergistic cytotoxicity in M4/M5 AML. As such, we uncovered a targetable positive feedback loop involving CEBPB, IL-1/TNF-α, and monocyte differentiation in M4/M5 leukemia, which promotes both intrinsic and extrinsic drug resistance, along with drug-induced protection against venetoclax and MDM2 inhibitors.