BET inhibition disrupts the FOXM1-MYC axis to induce BRCAness and enhance PARP inhibitor response.

Homologous recombination (HR) proficiency underlies intrinsic and acquired resistance to PARP inhibitors (PARPi). We identify a BRD4-dependent FOXM1-MYC transcriptional axis that sustains HR gene expression and limits PARPi response. ENCODE analyses revealed extensive co-occupancy of FOXM1 and MYC at regulatory regions of DNA repair genes, including BRCA1/2 and RAD51 paralogs, suggesting a shared HR program. Functionally, transient knockdown of FOXM1 or MYC reduced BRCA1/RAD51 transcripts, whereas sustained FOXM1 silencing triggered adaptive MYC upregulation that preserved HR output, indicating compensatory control. BET inhibition with (+)-JQ1 diminished FOXM1/MYC promoter occupancy at BRCA1 and RAD51, downregulated HR genes, and synergized with PARPi in viability and clonogenic assays. A BRD4 degrader (ZBC260) achieved potent BRD4 depletion at low nanomolar doses, suppressed FOXM1/MYC and HR gene expression, enhanced PARP1 trapping, and produced strong synergy with olaparib, including in patient-derived cancer cells. Clinically, BRD4 is highly expressed in ovarian cancer and independently predicts poor survival, outperforming FOXM1 and MYC. These data establish BRD4-directed disruption of the FOXM1-MYC axis as a strategy to induce "BRCAness" and broaden PARPi efficacy.