NSC 630176, herein referred to as depsipeptide, shows a lack of cross resistance with several commonly used cytotoxic agents such as vincristine, 5-fluorouracil, mitomycin C and cyclophosphamide (2). However, it has been defined as a P-glycoprotein (Pgp) substrate by COMPARE analysis of the National Cancer Institute (NCI) drug screen cytotoxicity profile (4).