Inorganic Phosphate Is Associated with RB1–E2F-Related Transcriptional and DNA Repair-Associated Changes Under Cisplatin Exposure in MDA-MB-231 Cells

Triple-negative breast cancer (TNBC) lacks effective targeted therapeutic strategies, and cisplatin resistance remains a major challenge in clinical treatment. This study aimed to investigate whether inorganic phosphate (Pi) influences cellular responses to cisplatin and to explore the potential molecular mechanisms involving RB1–E2F signaling, DNA repair regulation, and oxidative stress. Clinical associations between serum biochemical parameters and tumor histologic grade were evaluated in 246 patients with invasive ductal carcinoma. Triple-negative breast cancer cell line (MDA-MB-231), estrogen receptor-positive breast cancer cell line (MCF-7), and non-tumorigenic breast epithelial cell line (MCF-10A) were treated with control, Pi, cisplatin, or Pi combined with cisplatin.. Cellular proliferation, cell-cycle distribution, DNA damage, intracellular reactive oxygen species (ROS), inflammatory responses, and transcriptomic alterations were assessed using functional assays and RNA sequencing-based analyses. Pi levels showed an inverse association with tumor grade. In MDA-MB-231 cells, Pi combined with cisplatin resulted in enhanced growth inhibition, increased DNA damage accumulation, elevated cellular ROS production, and activation of inflammatory responses compared with cisplatin alone. Transcriptomic analyses revealed alterations in RB1–E2F-related transcriptional programs and reduced expression of DNA repair-associated gene sets. TCGA-BRCA analysis further indicated that elevated DNA repair pathway activity was associated with unfavorable survival outcomes. These findings suggest that Pi may modulate cisplatin responses through coordinated regulation of RB1–E2F signaling, DNA repair capacity, and oxidative stress responses, providing a potential mechanistic basis for further investigation of phosphate-associated therapeutic strategies in TNBC.