Confocal microscopy showed that purified Bt 18 toxin bound to the periphery of CEM-SS cells, suggesting that the binding site could be a cell surface receptor. This finding

coincided with immunofluorescent findings of Kitada et al. in a study of the cytocidal action of parasporin-2 on cancer cells [23]. It was found that parasporin-2 was distributed at the cell periphery and the immunostaining pattern was the same as the native distribution of cadherin, a cell-cell adhesion protein in the plasma membrane [23]. In addition, increased binding of the biotinylated toxin on CEM-SS cells was SBI-0206965 observed when the incubation period was increased. The extent of binding

was seen to be most remarkable at 24 hours. On the other hand, no biotinylated purified Bt 18 toxin was detected at all test intervals in human T lymphocytes except at 24 hours. Even at 24 hours, the extent of binding on human T lymphocytes was minimal or much less remarkable when compared to CEM-SS cells. Such weak or minimal binding of the purified toxin on human T lymphocytes coincided with the fact that purified Bt 18 toxin did not exert cytotoxic activity on human T lymphocytes. Conclusions In conclusion, purified Bt 18 toxin binds to the periphery of CEM-SS, suggesting that the toxin most likely binds to a cell surface receptor, which is specific to the toxin.

It is most likely that purified Bt 18 toxin binds to binding sites that differ from crude Btj toxin or crude Bt 22 toxin. Although Selleckchem Ferrostatin-1 confounding factors and limitations were present at high concentrations, Rucaparib datasheet at low concentrations of anticancer drugs, there was little competition between purified Bt 18 toxin and the drugs used in this study, suggesting that purified Bt 18 toxin most likely binds to different binding sites on CEM-SS when compared to the anticancer drugs. Hence, the mechanism of action of purified Bt 18 toxin may differ from that of the anticancer drugs used in this study. Such data prompts us to carry out further investigations, such as drug synergism between purified Bt 18 toxin and commercially available anticancer drugs and in vivo studies. Acknowledgements This work was funded by the International Medical University, Malaysia (grant number: IMU123/2006). The IMU also provided the required facilities in this study. The Institute of Bioscience, University Putra Malaysia (Malaysia) provided the confocal and related facilities used in this study. References 1. Aronson AI, Shai Y: Why Bacillus thuringiensis insecticidal toxins are so effective: unique features of their mode of action. FEMS Microbio Let 2001, 195:1–8.CrossRef 2.