Restoring p53 wild-type conformation in TP53-Y220C-mutant acute myeloid leukemia

TP53-Y220C is a recurrent hot spot mutation in cancers and leukemias. It is observed predominantly in acute myeloid leukemia (AML)/myelodysplastic syndromes among hematological malignancies and is associated with poor outcome. The mutation creates a structural pocket in the p53 protein. PC14586 (rezatapopt) is a small molecule designed to bind to this pocket and thus restore a p53 wild-type (p53-WT) conformation. We demonstrate that PC14586 converts p53-Y220C into a p53-WT conformation and activates p53 transcriptional targets but surprisingly induces limited/no apoptosis in TP53-Y220C AML. Mechanistically, MDM2 induced by PC14586-activated conformational p53-WT and the nuclear exporter exportin 1 (XPO1) reduce the transcriptional activities of p53, which are fully restored by inhibition of MDM2 and/or XPO1. Importantly, p53-WT protein can bind to B-cell lymphoma 2 (BCL-2), competing with BCL-2-associated X protein (BAX) in the BH3 binding pocket of BCL-2, and also binds to BCL-xL and myeloid cell leukemia 1 (MCL-1). However, such binding by PC14586-activated conformational p53-WT is not detected. Pharmacological inhibition of the BCL-2/BAX interaction with venetoclax fully compensates for this deficiency, induces massive cell death in AML cells and stem/progenitor cells in vitro, and prolongs survival of TP53-Y220C AML xenografts in vivo. Collectively, we identified transcription-dependent and -independent mechanisms that limit the apoptogenic activities of reactivated conformational p53-WT and suggest approaches to optimize apoptosis induction in TP53-mutant leukemia. A clinical trial of PC14586 in TP53-Y220C AML/myelodysplastic syndromes has recently been initiated. This trial was registered at www.ClinicalTrials.gov as #NCT06616636.