As shown by the antibiotic studies, microorganirms are rich sources of chemical compounds, and from the viewpoint of the present situation of cancer chemotherapy it is reasonable to search new antitumor substances in microbial products. Such antibiotics as actinomycins C and D¹⁾, puromycin²⁾, sarkomycin³⁾, azaserine⁴⁾, carzinophilin⁵⁾, actinoleukin⁶⁾, mitomycin⁷⁾, carcinomycin⁸⁾, pluramycin⁹⁾, gancidin¹⁰⁾, 6-diazo-5-oxo-norleucine¹¹⁾, toyokamycin, hygroscopin, fumigillin and melanomycin⁷⁾ have been reported to retard growth of transplantable neoplasms in animals. A trial of finding more effective and less toxic antitumor substances is continued in this laboratory. Since 1955, approximately 1300 soil actinomycetes have been studied for their formation of metabolic products suppressing growth of transplantable animal tumors. Crude filtrates from cultures of actinomycetes each in 0.3ml daily were intraperitoneally injected into mice bearing Ehrlich carcinoma of ascitic form or Crocker sarcoma 180 of the same form for 8 days since the day of inoculation of tumor cells. In the repeated animal experiments it was confirmed that by the method employed approximately 2% of soil actinomycetes produced antitumor substances, which prolonged the survival period as well as retarded the ascites increase. Of these antitumor agents, raromycin produced by strain No. 314 C₁ was studied in detail because of its low toxicity and its high effectiveness against both animal tumors.

The present paper describes the studies on the effect of the crude powder of raromycin on Ehrlich carcinoma and Crocker sarcoma 180; both solid and ascitic forms in mice. Detailed chemical and biological studies of this agent will be reported in other papers.