In 1957, carzinostatin was found in our laboratory in the culture filtrate of Streptomyces carzinostaticus and its isolation and characteristics were reported by Shoji in 1961¹⁾. The antibiotic consisted of two components, A of high molecular weight and B of low molecular weight, and the coexistence of the two components was essential for inhibition of the growth of Ehrlich ascites tumor in mice. Biological studies so far reported^1~5) were therefore done with the mixture designated as carzinostatin complex. Owing to technical difficulties, purification of both of the components was discontinued. However, the antibiotic was too effective to be abandoned, and we resumed the study. We concentrated our effort first on the selection of more potent descendants of the producing strain. During the course of such study, one of the potent producers, Streptomyces carzinostaticus var. F-41, was found to produce an antibiotic which exerts its biological effects as a single entity. The antibiotic was an acidic polypeptide and had more pronounced inhibitory effect on ascites form of sarcoma 180 and on ascitic leukemia SN-36 in mice than that of carzinostatin complex. The antibiotic was designated as neocarzinostatin.

The present paper describes details of isolation, physicochemical properties, and antitumor activities of neocarzinostatin.