Effect of dehydrodidemnin B on human colon carcinoma cell lines

Didemnins are cytotoxic agents belonging to a depsipeptide family isolated from marine tunicates. In the present study, a new member, dehydrodidemnin B (DDB), isolated from the mediterranean tunicate Aplidium albicans, was used. The effect of the drug on human colon cultured cell lines was tested using multiple approaches: proliferation studies, long term survival after three hours of exposure to DDB by means of a clonogenic assay and the decrease of the protooncogen, ornithine decarboxylase, activity. A dehydrodidemnin B concentration of 10(-8) M completely inhibited cell growth. The IC50 obtained using the MTT proliferation test, indicated that the most proliferative cell line (CT-2) was the most sensitive to the drug. Using a clonogenic assay a clear dose-response was obtained for the three cell lines used; HT-29 cell line showed the minimum survival after 3 hours of dehydrodidemnin B treatment. A dose-dependent decrease in ornithine decarboxylase activity was also observed in three cell lines assayed. The data presented indicate that the dehydrodidemnin B is a potent cytotoxic agent on rapidly dividing human colon cancer cells.