The cytolytic action of all-D mastoparan M on tumor cell lines.

All-D and all-L mastoparan M, a tetradecapeptide toxin (INLKAIAALAKKLL-NH2) from hornet venom, were chemically synthesized in this study. Under circular dichroism investigation, all-D and L-mastoparan M adopted a 30% alpha-helical structure in 30% trifluroethanol solution but only a 10% á-helical structure in phosphate solution. After being added to the cultures of tumor cell lines in vitro, D-mastoparan (12.5 micrograms/ml) directly inhibited the growth of the tumor cell lines Colo 225 (59%), KB (38%), Hep-2 (63%), H226Br (43%) and HeLa (54%) determined by the MTT assay. We also found that D-mastoparan M has a higher potency of antitumor cell activity in vitro than L-mastoparan M. When examined under the scanning-beam electron microscope, hollow, shrunk and collapsed structures of tumor cells could be seen, after being mixed with D-mastoparan M. The appearance of these morphological alterations indicated that mastoparan M inhibits the growth of tumor cells by direct lysis of target cells.