Anticancer activity of a low immunogenic protein toxin (BMP1) from Indian toad (Bufo melanostictus, Schneider) skin extract

Earlier, a protein (BMP1, MW-79kDa) had been isolated from Indian toad (Bufo melanostictus) skin aqueous extract possessed anticancer activity against EAC bearing mice (Bhattacharjee et al., 2011). In the present study, the anti-proliferative and apoptogenic activities of BMP1 have been evaluated in leukemic (U937 and K562) and hepatoma (HepG2) cells. BMP1 dose dependently inhibited U937 and K562 cell growth having IC₅₀ values of 49 μg/ml and 30 μg/ml respectively. The anti-proliferative activity of BMP1 was observed in MTT assay, proliferating cell nuclear antigen (PCNA) expression and cell cycle arrest study. Flow-cytometric data revealed that BMP1 arrested cell cycle in U937 and K562 cells at Sub-G1 and G1 phases. The BMP1-induced dose dependent expressions of CDKIs (p21^cip1 and p27^kip1) and inhibition of CDK2 and PCNA expression in HepG2 cells support the inhibition of cell proliferation due to G1 arrest. BMP1-induced apoptosis analyzed by annexin-V binding study and the DNA fragmentation by comet assay were correlated with the sub-G1 arrest. The parallel induction of bax and p53 expression in HepG2 cells and the up-regulation of caspase 3 and caspase 9 due to BMP1 treatment indicated the involvement of p53-dependent intrinsic pathway of apoptosis. BMP1 was found to be low immunogenic in nature.