STUDY ON THE ANTITUMOR ACTIVITIES AND THE TOXICITIES OF ZHENGGUANGMYCINS A₅ AND A₂

Zhengguangmycin, an antitumor antibiotic complex consisting of more than ten components, is produced by Streptornyces pingyangensis n. sp. isolated from a soil sample collected in Pingyang, Zhejiang province. Two components of zhengguangmycin, namely A₂ and A₅ were found to be identical with bleomycins A₂ and A₅ respectively. As bleomycin presently available for clinical use contains bleomycin A₂ as its major component, the biological activities of zhengguangmycin A₅ were studied in comparison with those of zhengguangmycin A₂. The main differences found are as follows; (1) On an equal LD₅₀ basis the inhibitory effect of A₅ on transplantable esophageal carcinoma SGA-73 in mice is much stronger than that of A₂; (2) The concenrration of A₅ attained in the mouse esophageal carcinoma tissue as determined by microbiological assay is much higher than that of A₂; (3) As shown by light and electron microscopy A₅ appears to be less injurious to the mouse lung than A₂ on an equal body weight dosage basis and (4) A₅ appears to be less toxic to the mouse in acute toxicity experiments. These results suggest that zhengguangmycin A₅ possesses more desirable properties than A₂ as an antitumor agent.