In vitro antitumoral activity of soluble protein extracts of Bacillus thuringiensis

There are many studies about the antitumour effects of Bacillus toxins from different strains or subspecies in different parts of the world. Proteins that selectively kill tumor cells in vitro have potential as anticancer agents. The aim of this study was to evaluate the cytotoxic activity of soluble proteins extracts (SPE) from Mexican strains of B. thuringiensis on murine lymphoma L5178YR cell line. In vitro, L5178YR cells were treated with different concentrations of specific primers (SPE) from B. thuringiensis (0 to 39.85 �g/mL) and cellular viability was evaluated by MTT method and orange acridine/ethidium bromide staining. The mechanism of cell death was evaluated through caspase-3 activation by flow cytometry and TUNEL assays. The study results shows that SPE from B. thuringiensis (GM1-3 h, GM1-24 h, GM1-48 h, GM18-3 h, GM18-24 h, GM18-48 h, HD512-3 h, HD512-24 h, and HD512-48 h) affected the cell viability of L5178YR in a dose-dependent manner which presented higher cytotoxic effect of SPE collected at 3 h independent of the strain used; and the 7% SDS-PAGE presented an electrophoretic profile of proteins in a range of 10 to 100 kDa of the SPE B. thuringiensis. The cytotoxicity is through a mechanism of apoptosis because the caspase-3 activation and TUNEL assays corroborated this result. In conclusion, SPE derived from early culture (3 h) of B. thuringiensis (Bt) GM1, GM18 and HD-512 have in vitro cytotoxic potential on murine lymphoma L5178YR cell line through a mechanism of cell death by apoptosis.