Targeting ATR and PI3Kα Pathways Promotes Ferroptosis in PIK3CA-Wildtype Platinum-Resistant Endometrial Cancer

Background/Objectives: Platinum resistance in endometrial cancer (EC) remains a significant therapeutic challenge, as tumors frequently bypass apoptotic cell death. Ferroptosis, an iron-dependent form of regulated cell death driven by lipid peroxidation, offers an alternative mechanism to target apoptosis-resistant cancers. This study evaluated whether combined inhibition of ATR and PI3Kα could induce cell death in platinum-resistant EC through apoptotic or ferroptotic pathways. Methods: A panel of EC cell lines, including patient-derived models with varying PIK3CA mutation status and platinum sensitivity, was treated with camonsertib (ATR inhibitor) and inavolisib (PI3Kα inhibitor). Cell death mechanisms were assessed through DNA damage indicators (γH2AX, comet assay, DNA fiber analysis), apoptosis markers (Annexin V, cleaved PARP, cleaved caspase 3), and ferroptosis markers (FerroOrange, xCT expression, redox homeostasis). Results: While monotherapies showed limited activity, dual ATR and PI3Kα inhibition produced additive/synergistic cytotoxicity across all EC cell lines, independent of platinum sensitivity or microsatellite stability status. Mechanistically, the treatment induced genotype-specific cell death: PIK3CA-mutant cells underwent apoptosis driven by catastrophic DNA damage accumulation, whereas PIK3CA-wildtype cells exhibited predominantly ferroptosis characterized by xCT downregulation and redox disruption. Conclusions: Our findings establish dual ATR and PI3Kα inhibition as a genotype-informed therapeutic strategy for platinum-resistant EC. PIK3CA mutation status may influence the mode of cell death, supporting its use as a predictive biomarker for patient stratification in future clinical applications.