A marine-derived, synthetic cyclic depsipeptide with potential antineoplastic activity. Elisidepsin is a derivative of a natural marine compound that belongs to a family of dehydro aminobutyric acid-containing peptides (kahalalides) isolated from the herbivorous marine mollusk Elysia rufescens. Although the primary mechanism of action has yet to be elucidated, this agent exhibits anti-proliferative activity in a wide variety of cancer cell types, including breast, colon, pancreas, lung, and prostate; it appears to induce oncolytic rather than apoptotic cell death.