The authors have screened about thousand soil actinomycetes for their production of antitumor substances inhibiting ascites type of Ehrlich carcinoma of mice. The broth filtrate of about 5% of the strains, when 0.3 ml was daily intraperitoneally injected to mice bearing ascites type of Ehrlich carcinoma since the first day of the inoculation of one million tumor cells, inhibited the ascites increase and prolonged the survival period of mice. However, about 80% of these positive strains did not constantly produce antitumor substances thereafter, and the results in the further repeated tests fluctuated or were negative. Therefore, the percentage of the strains which produced constantly the antitumor substances in the repeated tests were 20% of the positive strains, that is, about 1% of the soil actinomycetes.

As it has been reported⁽¹⁾, the authors discovered an antitumor substance, sarkomycin,inhibiting Ehrlich carcinoma of mice⁽²⁾. Sarkomycin is an acidic substance. Therefore, the authors searched antitumor substances having basic characters. An antitumor subtance produced by one of the constantly positive strains was found to be basic, and the crude powder of this antitumor substance inhibited the ascites increase and prolonged the survival period, when 1.25 mcg was daily intraperitoneally injected to mice bearing ascites type of Ehrlich carcinoma. On the other hand, the mice tolerated the daily intraperitoneal injection of 250 mcg of this crude powder. The anti tumor substance was named pluramycin by the authors. It was further purified and it was confirmed that there were two kinds of pluramycins. One of them was dominating and was much stronger in the antitumor activity than the other. The authors named this main antitumor substance pluramycin A and another pluramycin B. Pluramycin A was purified and has been obtained in the crystalline state.

In the present paper the antitumor effect and toxicity of the crude power of pluramycins are presented. The antitumor effect and toxicity of pluramycin A crystal and the antitumor effect of the purified pluramycin B are also briefly described. The physical and chemical natures of pluramycins will be reported in another paper, but the antimicrobial effects of pluramycins are briefly recorded.