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Inhibitory Effect of Actinomycin D on the Induction of Rat Mammary Tumors by in Vitro Exposure to 7,12-Dimethylbenz(a)anthracene

Department of Oncologic Surgery [T. T., N. T., T. T.], and Department of Bacteriology and Serology [Y. T.], Research Institute for Microbial Diseases, Osaka University, Yamada-kami, Suita, Osaka, Japan

The inhibitory effect of actinomycin D on the induction of tumors by in vitro exposure of mammary glands to 7,12-dimethylbenz(a)anthracene was studied. When actinomycin D was given i.p. 24 hr before excision of the mammary glands, the induction of tumors by in vitro exposure of the glands to 7,12-dimethylbenz(a)anthracene was significantly decreased. On the other hand, when actinomycin D was administered 24 hr after excision, it had no effect on the induction of tumors.

In vitro exposure of excised glands to 7,12-dimethylbenz-(a)anthracene and actinomycin D significantly decreased tumor induction. However, the order of exposure to 7,12-dimethylbenz(a)anthracene and actinomycin D influenced the inhibitory effect of actinomycin D on tumor induction. Results indicated that this might be due to a difference in the amounts of 7,12-dimethylbenz(a)anthracene and actinomycin D bound to the mammary glands.

Received 9/26/74. Accepted 3/26/75.