Silibinin Triggers Mitochondrial Apoptosis and Declines Clonogenic Potential in Detroit 562 Human Pharyngeal Carcinoma Cells

Background and Objectives: Oropharyngeal squamous cell carcinoma (OPSCC) is a common type of head and neck cancer with a progressive incidence in recent years. The limitations and the side effects associated with the current treatments require new therapeutic alternatives. Silibinin (SIL) is a phytocompound with multifaceted properties that has demonstrated antitumor effects in several types of cancer. The aim of this study was to assess the potential anticancer effects of SIL in Detroit 562 human pharyngeal cancer cells, an ideal model for HPV-negative OPSCC. Materials and Methods: Detroit 562 cells and HGF-1- human gingival fibroblasts were used as experimental models. For the mechanistic investigations, different methods, such as MTT assay, bright field microscopy, immunofluorescence staining, and specific assays and kits were applied to quantify intracellular ROS production, activation of caspases, and the colony formation assay. Results: Treatment with SIL (25–200 µM) for 48 h induced a selective cytotoxic effect in Detroit 562 cancer cells, being minimally toxic to healthy cells. The cytotoxic mechanism of action was characterized by a decreased cell viability, morphological alterations, elevation of intracellular ROS, decreased mitochondrial potential, mitochondrial and nuclear dysmorphologies, activation of caspases 9 and 3/7 and apoptosis occurrence, and decreased long-term colony formation. Conclusions: These findings show that SIL could represent a potential alternative therapy for HPV-negative OPSCC by triggering mitochondrial apoptosis and exerting a decline in the colonogenicity of Detroit 562 cancer cells.