Binding of [G- 3H]-7,12-dimethylbenz(α)anthracene to DNA of normal and of rapidly dividing hepatic cells of rats

Abstract

The administration of tritium-labeled 7,12-dimethylbenz(α)anthracene (DMBA) to rats at 24 h after partial hepatectomy resulted in its binding to DNA in small intestine and regenerating liver. The binding in regenerating liver, which began 3 h after i.v. administration of DMBA, reached a maximum at 6 h and declined at 24 h; the uptake in intestinal DNA was similar but there was no decline for 48 h. The DMBA-induced inhibition of DNA synthesis paralleled uptake; both were dose dependent. More than twice as much DMBA was bound in vitro to DNA that had been isolated from livers of immature rats or from those undergoing regeneration than to DNA from livers of young adults. Such a difference was also observed in vivo. The possibility that the binding of DMBA is causally related to inhibition of DNA synthesis and carcinogenesis is discussed. Two forms of binding were apparent. In one the attractive forces were weak. In the other the binding resisted extensive dialysis, solvent extraction and denaturation. That the tightly bound form involved unchanged hydrocarbon was shown by direct gas-chromatographic analysis of the DNA-DMBA complex. The amount of DMBA tightly bound after i.v. injection of biologically active doses of 12.5–25 mg/kg corresponded to about 10·10 3–20·10 3 molecules per regenerating rat liver cell genome. This kind of interaction with DNA, which may be causally related to the mechanism of DMBA-induced oncogenesis, does not appear to require prior metabolic activation of the agent.