RNA polymerase I inhibitor BMH-21 promotes mutant p53 reactivation through nuclear zinc mobilization

RNA polymerase I (Pol I) inhibitors activate stress signaling pathways with therapeutic potential in cancer, yet the consequences of Pol I inhibition in p53-mutant tumors remain incompletely understood. Here, we compared the interactions of the Pol I inhibitors CX-5461 and BMH-21 with the p53 reactivators APR-246 and ZMC-1 in p53^R175H breast cancer cells. Whereas CX-5461 synergized with p53 reactivators, BMH-21 antagonized these combinations. Unexpectedly, BMH-21 alone restored mutant p53 transcriptional activity and promoted a shift toward a wild-type-like p53 conformation. Mechanistically, BMH-21 increased nuclear labile zinc levels, correlated with degradation of the Pol I catalytic subunit RPA194, and induced stabilization of the zinc-responsive stress factor NRF2. Limiting RPA194 degradation through FBXL14 depletion reduced both nuclear zinc flux and p53-dependent transcriptional activity, supporting a functional link between Pol I destabilization, zinc mobilization, and mutant p53 reactivation. Inhibition of p53 signaling enhanced BMH-21 cytotoxicity, indicating that mutant p53 reactivation promotes a protective stress response rather than cell death. Together, these findings demonstrate that Pol I inhibitors are functionally distinct and identify a previously unrecognized link between Pol I inhibition, zinc homeostasis, and mutant p53 regulation.