Photosensitization of human skin fibroblasts by vemurafenib promotes pleiotropic effects on membrane-enclosed organelles and apoptosis

Vemurafenib (VB), a BRAF inhibitor and a first-line treatment for unresectable or metastatic melanoma, is strongly phototoxic towards normal skin cells. Herein, we show that in cultured HS 68 human diploid dermal fibroblasts, low concentrations of VB suffice to promote photosensitization to low doses of UVA (similar to 5 J/cm(2)), as evidenced by a significant decrease in cell viability. In contrast to data obtained in chemico our results support a role for ROS (reactive oxygen species). Indeed, peroxidation of cellular lipids was observed which could be alleviated by the lipophilic antioxidant BHT (2,6-di-tert-butyl-4-methylphenol). Using in vivo confocal laser scanning microscopy and vital fluorescent probes it was shown at the single cell level that the plasma membrane and lipid-rich organelles, namely mitochondria, endoplasmic reticulum, and lysosomes, as well as actin fila-ments, were severely damaged by the UVA-induced VB-photosensitization. Finally, we showed that mitochon-drial impairment was concurrent with caspase 3/7 activation and cell death by apoptosis.

Automated summary

Vemurafenib (VB), a BRAF inhibitor used for melanoma, has strong phototoxicity to normal skin cells. Low concentrations of VB can sensitize skin cells to low doses of UVA, leading to decreased cell viability. This phototoxicity is caused by reactive oxygen species (ROS), which result in peroxidation of cellular lipids. In vivo experiments show that UVA-induced VB-photosensitization damages the plasma membrane, mitochondria, endoplasmic reticulum, lysosomes, and actin filaments, leading to mitochondrial impairment, caspase 3/7 activation, and apoptosis.