Characterization of DNA repair elicited by carcinogens and drugs in the hepatocyte primary culture/DNA repair test.

The autoradiographic unscheduled DNA synthesis measured in the hepatocyte primary culture/DNA repair test after exposure to chemical carcinogens was characterized. In order to document that this synthesis was occurring in nonreplicated DNA, density labeled, replicated DNA was separated from nonreplicated DNA by cesium chloride gradient centrifugation. Incorporation of [3H] thymidine into nonreplicated DNA was detected after exposure of hepatocytes to methyl methanesulfonate, an activation independent carcinogen, or N-2-acetylaminofluorene, an activation-dependent carcinogen, but not with fluorene, a noncarcinogen. N-4-Acetylaminofluorene, a mutagenic compound of uncertain carcinogenicity, also caused DNA repair. Both the autoradiographic assay and density gradient centrifugation detected incorporation of [3H] thymidine into DNA from the same hepatocyte preparation. By using density gradient centrifugation, DNA repair was detected in hepatocytes following exposure to the antihistamines pyrilamine maleate and tripelennamine HCl. Methapyrilene failed to elicit repair. Thus this study (1) verifies that the unscheduled DNA synthesis seen in the hepatocyte primary culture/DNA repair test after carcinogen exposure in DNA repair And (2) confirms the induction of DNA repair by pyrilamine maleate and tripelennamine HCl but not by methapyrilene.