Targeting PLK1-CBX8-GPX4 axis overcomes BRAF/EGFR inhibitor resistance in BRAFV600E colorectal cancer via ferroptosis

Metastatic BRAF^V600E colorectal cancer (CRC) confers poor prognosis and represents a therapeutic bottleneck. To identify resistance mechanisms of the mitogen-activated protein kinase (MAPK) pathway in BRAF^V600E CRC, we perform genome-wide CRISPR-Cas9 screening and discover that targeting glutathione peroxidase 4 (GPX4) overcomes resistance to BRAF inhibitor (BRAFi) combined with or without epidermal growth factor receptor inhibitor (EGFRi) in BRAF^V600E CRC. Specifically, BRAFi ± EGFRi upregulates GPX4 expression, which antagonizes therapy-induced ferroptosis. Moreover, polo-like kinase 1 (PLK1) substrate activation promotes PLK1 translocation to the nucleus, activating chromobox protein homolog 8 (CBX8) phosphorylation at Ser265 to drives GPX4 expression. Targeting PLK1 enhances BRAFi ± EGFRi inhibition and triggers ferroptosis in vitro, vivo, organoid, and patient-derived xenograft model. Collectively, we demonstrate a PLK1-CBX8-GPX4 signaling axis that relays the ferroptosis mechanism of therapeutic resistance and propose a clinically actionable strategy to overcome BRAFi ± EGFRi resistance in BRAF^V600E CRC.