Studies on a New Antitumor Antibiotic, Largomycin. Iii

Of the components of largomycin, largomycin F-II was biologically the most active. It is active against Sarcina lutea PCI 1001 at 12.5 mcg/ml, Mycoplasma species at 0.7 mcg/ml and HeLa S-3 cells at 0.1-0.5 mcg/ml. Largomycin F-II exhibited antitumor activity with a chemotherapeutic index of about 100 for ascites tumor and mouse leukemia after 7-day consecutive treatment with 0.4-0.8 mg/kg/day. Against solid tumors, however, largomycin F-II is less active. The high chemotherapeutic index could be explained by its selective toxicity to tumor cells compared with its toxicity to two diploid types of cell of primate origin.