Apoptotic Effects of Bilirubin on Skin Cancer Cell Lines SK-MEL-3 (Melanoma) and A431 (Non-Melanoma)

Background: Bilirubin has long been exclusively considered as a potentially dangerous sign of liver diseases, but it is currently regarded as a reliable signaling molecule as well. Objective: This study investigated the effects of unconjugated bilirubin on survival, proliferation, apoptotic and cell arrest capacities of melanoma SKMEL-3 and non-melanoma A431 skin cancer cells in comparison with normal Human Dermal Fibroblast (HDF) cells. Methods: The MTT assay test was used to identify survival and the IC50 at various concentrations of bilirubin on SKMEL-3, A431, and HDF cells for 24h and 48h. The comet assay technique was used to investigate genotoxicity effects, and flow cytometry was run to investigate apoptotic and cell arresting effects of bilirubin on the cells. The gene expression of cyclin D1, cyclin E1, survivin, Bcl-2, and p53 was investigated by qRT-PCR. The molecular docking of bilirubin on CDKs (Cyclin-Dependent Kinases 2, 4, and 6) and pro-apoptotic factors Bad, Bak, Bax, Bid, Bik, and Bim was performed by Autodock software version 2. Results: The IC50 of bilirubin on HDF, A431, and SKMEL-3 cells was 125, 115, and 95 μM at 24h and 115, 100, and 75 μM at 48h, respectively. Although cell arrest in the G1 phase occurred in all cells, bilirubin induced genotoxicity and apoptosis in SKMEL-3 and A431 cancer cells more pronouncedly than those in normal HDF cells. Conclusion: Bilirubin led to cell arrest in the G1 phase in SKMEL-3, A431, and HDF cells. Additionally, bilirubin induced apoptotic pathways in SKMEL-3 and A431 cancer cells.