Rosuvastatin–Quercetin Co-Loaded Chitosan Nanoparticles for Triple-Negative Breast Cancer: In Vitro Evaluation and Mechanistic Insights

Triple-negative breast cancer (TNBC) presents significant therapeutic challenges due to its aggressive nature, limited molecular targets, and frequent development of resistance to treatment. This study aimed to develop chitosan nanoparticles co-loaded with rosuvastatin and quercetin (Ro–Qu@CSNPs) and evaluate their in vitro anticancer activity, selectivity, and potential modulation of the HMGCR–RhoA signaling pathway. Ro–Qu@CSNPs were prepared and characterized. Their cytotoxicity was assessed against MDA-MB-231 TNBC cells and non-tumorigenic MCF-10A mammary epithelial cells. Additionally, we examined cell cycle distribution, types of cell death, HMGCR mRNA expression, and RhoA activation. Ro–Qu@CSNPs showed the lowest IC50 in MDA-MB-231 cells (7.791 ± 0.26 µg/mL) and the highest selectivity index (4.74) among the treatments tested. Treatment with Ro–Qu@CSNPs resulted in G0/G1 cell cycle arrest, with the percentage of apoptotic cells increasing from 0.77% in untreated cells to 22.46%. Furthermore, HMGCR mRNA expression and RhoA-GTP activity decreased to 0.155-fold and 0.353-fold of their respective control values. In conclusion, Ro–Qu@CSNPs exhibited preferential cytotoxicity toward MDA-MB-231 cells, leading to cell cycle arrest and apoptotic cell death, and were associated with reduced HMGCR–RhoA expression and RhoA-GTP activity. These in vitro investigations support further study of this nanoformulation as a hopeful approach for TNBC.