A chromopeptide antineoplastic antibiotic isolated from the bacterium Streptomyces parvulus. Dactinomycin intercalates between adjacent guanine-cytosine base pairs, blocking the transcription of DNA by RNA polymerase; it also causes single-strand DNA breaks, possibly via a free-radical intermediate or an interaction with topoisomerase II. Check for active clinical trials using this agent. (NCI Thesaurus)