The incorporation of labeled nucleic acid precursors into the DNA and RNA of mouse skin was determined following applications of the carcinogen 9,10-dimethyl-1,2-benzanthracene (DMBA), the noncarcinogen 1,2,3,4-dibenzanthracene (1,2,3,4-DBA), and the cocarcinogen A1 isolated from croton oil. It was shown that DMBA stimulates the biosynthesis of DNA and RNA after a period of temporary inhibition (24 hr). 1,2,3,4-DBA induces only a very marked stimulation of RNA, while DNA replication is not affected at all. Cocarcinogen A1 stimulates the synthesis of DNA and RNA without the initial inhibition of synthesis during the first 24 hr after application; this was observed following DMBA treatment. The significance of the above results is briefly discussed in the light of the two-stage hypothesis of carcinogenesis.

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This work was supported in part by Deutscher Akademischer Austauschdienst (Bad Godesberg, Germany) and by the Instituto Nacional de la Investigacion Cientifica, México, D. F. Parts of this work were presented at the annual meeting of the Gesellschaft für Physiologische Chemie, Marburg, Germany, 1966.

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©1969 American Association for Cancer Research.
1969
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