Caspase mediated cytotoxicity of a yellow pigment produced by Exiguobacterium alkaliphilum on human cancer cell lines

Context: Investigation of microbial diversity for the identification of novel bioactive compounds or therapeutics is a more potential and incessant ongoing process for drug development research. Many tumors are generally metastasized at the time of diagnosis and restorative surgery is rarely achieved. As response rates to chemotherapy are low, surgery remains the only effective treatment. Consequently, a substantial need for new therapeutic options is essential. The promotion of apoptosis in cancer cells could potentially lead to the regression and improved prognosis of cancer. Aims: To assess the in vitro anticancer activity of the pigment extracted from E. alkaliphilum on cancer cell lines. Methods: The effect of a pigmented compound produced by Exiguobacterium alkaliphilum, isolated from a soil sample was investigated on various human cancer cell lines. Proliferation and viability were analyzed using cell counting and MTT cell proliferation assay. Quantification of lactate dehydrogenase (LDH), a cytosolic enzyme, which is an indicator of cellular toxicity was carried out. Apoptosis was determined by DNA fragmentation, and by colorimetric assays for caspases 3, 7 and 10. The cell cycle analysis was also performed using a flow cytometer, by fixing the cells with propidium iodide. The structural elucidation of the active compound was analyzed by GC-MS. Results: Pigment extracted from E. alkaliphilum showed a time and dose-dependent reduction of proliferation in HepG2, HeLa, MCF7, Jurkat and K562 cell lines with lower IC50 concentrations and induction of apoptosis was significantly evident from the caspase assay and DNA fragmentation. Conclusions: The pigment showed a significant anticancer property on cancer cell lines and this study thereby provides a rationale for pre-clinical and clinical evaluation for the effective treatment of cancer.