Conjugation of Β-Sitosterol to Cupper Sulfide-Folic Acid Nanoparticles for Enhancement of Radiotherapy in MCF-7 and MDA-MB-231 Breast Cancer Cells

Breast cancer is still a primary cause of cancer-related deaths in women, underscoring the vital need for new therapeutic approaches. β-Sitosterol (βST) is a phytosterol known for its anticancer effects, but its clinical application is limited by poor bioavailability. Nanoparticle platforms, like folic acid-functionalized β-sitosterol-loaded PEG-coated CuS nanoparticles (FβPCS-NPs), offer a method to potentially boost βST's therapeutic effectiveness. This study evaluated the cytotoxic effects of FβPCS-NPs alone and in combination with radiotherapy (RT) on MCF-7 and MDA-MB-231 breast cancer cell lines. FβPCS-NPs were synthesized and characterized using TEM, SEM, FTIR, and XRD. MCF-7 and MDA-MB-231 cells were treated with varying concentrations (31.25–1000 µg/mL) of FβPCS-NPs, RT (0.25 Gy), or both. Cell viability was assessed via MTT assay, apoptosis via flow cytometry (Annexin V/PI staining), and molecular mechanisms (p53, Bcl-2, Bax) via Western blot. FβPCS-NPs exhibited dose-dependent cytotoxicity, with IC50 values of 50.93 µg/mL (MCF-7) and 94.3 µg/mL (MDA-MB-231). Combined FβPCS-NPs + RT significantly enhanced apoptosis (p < 0.01), increasing Sub-G1 populations and p53 expression while reducing Bcl-2. The combination also elevated PD-1 and CD8+ T-cell markers, suggesting immunomodulatory effects. FβPCS-NPs synergize with RT to enhance breast cancer cell death via apoptosis induction, p53 activation, and immune modulation. This combination represents a promising therapeutic strategy warranting further preclinical investigation.