ABSTRACT
Studies examined the binding of radiolabeled 7,12-dimethylbenz[a]anthracene (DMBA) to epithelial DNA of hamster cheek pouch (HCP) maintained in organ explant culture. Adduct formation was studied as functions of [3H]DMBA dose, of the time after single [3H]DMBA applications, and of the route by which the DMBA was administered--either topically or in the culture media. Total DMBA-DNA adduct formation [total binding index (TBI)] was determined by DNA-bound 3H activity, and qualitative binding characteristics were further studied by high-pressure liquid chromatography. [3H]DMBA was applied either in the culture media at concentrations of 0.005-0.5 micrograms/ml or topically in mineral oil or ethanol in doses of 0.005-0.5 micrograms to each tissue fragment. Histopathologic changes in DMBA-treated HCP fragments included substantial aberrations in maturation of cornified and keratin layers and focal squamatization and dysplasia of the basal epithelium--considerable tissue necrosis was encountered in the high-DMBA-dose groups. Dose-response data were qualitatively similar among treatment types, with the greatest TBIs in topical ethanol groups and the lowest TBIs in culture medium groups. Kinetics of adduct formation and removal showed a rapid increase in TBIs to peak values at 24-72 hours followed by a biphasic decrease in TBIs, which leveled off at 7%-20% of peak values at 120-240 hours. Chromatographic analyses of selected samples at various times from all treatment groups showed three major peaks that are likely to be the same 1,2,3,4-tetrahydro-3,4-dihydroxy-1, 2-oxide-deoxyribonucleoside adducts observed in other rodent in vivo and cell culture systems. These results are consistent with those of other laboratories studying DMBA-DNA interactions and suggest that in vitro studies of DMBA-treated HCP explants are useful in studying the molecular nature of DMBA-DNA interactions in oral mucosal carcinogenesis.
Subject(s)
9,10-Dimethyl-1,2-benzanthracene/metabolism , DNA/metabolism , Mouth Mucosa/metabolism , Animals , Cheek , Cricetinae , Dose-Response Relationship, Drug , Kinetics , Male , Mesocricetus , Organ Culture TechniquesABSTRACT
Studies examined the in vivo binding of radiolabeled 7,12-dimethylbenz(a)anthracene (DMBA) to hamster cheek pouch epithelial DNA. Adduct formation was studied as functions of [3H]DMBA dose and of the time after single [3H]DMBA applications in mineral oil. Total DMBA-DNA adduct formation was determined by DNA-bound 3H activity, and qualitative binding characteristics were further studied by high-pressure liquid chromatography. Adduct formation 24 h after single [3H]DMBA applications rapidly increased from DMBA concentrations of 0.05-5.0 micrograms. While binding also increased from DMBA concentrations of 5.0-50.0 micrograms, the variability in adduct formation at 50.0 micrograms was considerable. Adduct formation following single 5.0-micrograms [3H]DMBA applications rose slowly to a peak value of 76 pmol DMBA/mg DNA at 36 h. This level decreased very slowly in a biphasic manner through 240 h, at which time the adduct levels were 23% of maximum. Adduct levels of 1.5 pmol/mg DNA were measured as late as 5 wk after a single 5.0-micrograms [3H]DMBA application. Chromatographic analyses of the 24-, 36-, and 96-, and 240-h samples showed three major peaks which are likely to be 1,2,3,4-tetrahydro-3,4-dihydroxy-1,2-oxide-deoxyribonucleoside adducts. While these analyses were limited by the small amounts of radioactivity which could be retrieved from [3H]DMBA-treated pouches, the study suggests that the DMBA-induced hamster cheek pouch carcinoma may be useful in some molecular in vivo studies of chemical-DNA interactions in carcinogenesis.
