Didemnins are cyclic depsipeptide compounds isolated from a tunicate (ascidian, or sea-squirt) of the genus Trididemnum (family of Didemnidæ) that were collected in the Caribbean Sea. They were first isolated in 1978 at the University of Illinois.[1]
Although more than nine didemnins (didemnins A-E, G, X and Y) have been isolated from the extract of Trididemnum solidum, didemnin B is the one that possesses the most potent biological activities.[2] It is a strong antiviral agent against both DNA and RNA viruses such as herpes simplex virus type 1, a strong immunosuppressant that shows some potential in skin graft[3] and is also very cytotoxic. It shows strong activity against murine leukemia cells.[4] Large amounts of didemnin B were chemically synthesized and it was advanced to clinical trials by the National Cancer Institute. It has completed phase II human clinical trials against adenocarcinoma of the kidney,[5] advanced epithelial ovarian cancer,[6] and metastatic breast cancer.[7] Unfortunately, the compound exhibited high toxicity through a high incidence of anaphylactic reactions in patients and trials were terminated.[8]
The didemnin analog plitidepsin was in phase II clinical trials as of 2003.[9]