A heat stable protein toxin (drCT-I) from the Indian Viper (Daboia russelli russelli) venom having antiproliferative, cytotoxic and apoptotic activities

A heat stable 7.2 kDa protein toxin (drCT-I) has been purified and crystallized from Indian Daboia russelli russelli venom (Roy Choudhury et al., 2006. Acta Cryst. F Struct Biol Cryst Commun, 62(Pt. 3), 292). The N-terminal (first 20) amino acid sequence of drCT-I was LKCNKLVPLFYKTCPAGKNL, which showed sequence homology to cytotoxins isolated from Naja venom. drCT-I has been evaluated for anticancer activity against EAC cells in vivo and human leukemic cells (U937, K562) in vitro. drCT-I (125 μg/kg, i.p/day for 10 days) significantly decreased EAC cell count, cell viability (p<0.001p<0.001) and significantly increased the survival time of tumour bearing mice (T/C% 178.64, p<0.01p<0.01) in comparison to untreated tumour bearing control. drCT-I, produced dose and time-dependent inhibition of U937 and K562 cell growth and had an IC50 of 8.9 and 6.7 μg/ml respectively after 24 h treatment. The reduced MTT values after drCT-I treatment indicated its cytotoxic nature, which supported its antiproliferative action. Scanning electron microscopy and confocal microscopy in U937 and K562 cells after drCT-I treatment indicated certain features of apoptosis such as membrane blebbing, perforations, nuclear fragmentation. The induction of apoptosis was further confirmed by phosphatidylserine externalization observed using annexinV-FITC/PI staining and flow cytometric analysis. drCT-I brought about apoptosis by G1 phase arrest of the cell cycle. The effect of drCT-I on normal human peripheral blood mononuclear cell (PBMNC) viability and cytotoxicity was studied in culture and was found to be lower than that on U937 and K562 cells. Thus both in vivo and in vitro experimental results suggested that drCT-I possessed anticancer potential.