Silibinin enhances the antitumor effect of radiotherapy in melanoma cells and potentiates immunogenic cell death-associated markers

Melanoma is an aggressive skin malignancy with limited response to radiotherapy (RT). This study investigated whether silibinin enhances RT-induced cytotoxicity and immunogenic cell death (ICD) in melanoma cells. Human A375 and murine B16-F10 melanoma cells were treated with silibinin, RT, or their combination. Cell viability and combination index (CI) values were evaluated. Apoptosis was quantified by flow cytometry, and caspase-dependent apoptosis was further investigated by measuring cleaved caspase-3 levels using ELISA with or without Z-VAD-FMK. ICD induction was evaluated by calreticulin (CRT) surface exposure and extracellular release of high-mobility group box 1 (HMGB1) and heat shock protein 70 (HSP70). Combination of silibinin with RT exhibited moderate synergistic anticancer effects in A375 and B16-F10 cell lines, as indicated by CI values < 1. Combination treatment significantly decreased cell viability and increased apoptosis compared with monotherapies. Increased cleaved caspase-3 levels were attenuated by Z-VAD-FMK, confirming caspase-dependent apoptosis. ICD markers, including CRT exposure HMGB1/ HSP70 release, were elevated in both cell lines and further enhanced by combination therapy. Silibinin promotes RT-induced apoptosis and ICD-associated markers. These finding support further investigation of silibinin as a potential adjunct to RT in melanoma cell lines.