Abstract
The binding of three tritium‐labelled carcinogenic polycyclic hydrocarbons, 7,12‐dimethylbenz (a) anthracene (DMBA), benzo (a) pyrene (BP) and 3‐methylcholanthrene (MCA) to DNA in mouse skin has been studied in C57BL, DBA/2 and Swiss mice following topical application of the hydrocarbons. DNA isolated from the treated areas was hydrolysed to deoxyribonucleosides and chromatographed on Sephadex LH20 columns. The levels of binding of hydrocarbon to DNA were determined from the amount of radioactivity eluted from Sephadex LH20 columns in those fractions containing hydrocarbon‐DNA adducts and the radioactivity shown, by rechromatography on AG5OWX4 columns, to be due to tritium incorporation into normal deoxyribonucleosides was not included. C57BL mice were treated with doses of DMBA ranging from 0.025 μmol to 1 μmol/mouse and the levels of hydrocarbon bound to DNA 19 h after treatment were determined; there was no evidence for a threshold dose below which no binding to DNA occurs, and the same hydrocarbon‐DNA product peaks were obtained at all doses. The levels of binding of DMBA (1 μmol/mouse) to DNA in skin were compared in C57BL, DBA/2 and Swiss mice at times varying from 6 h to 8 days after treatment. DMBA became bound to similar extents in Swiss and C57BL mice and to a slightly greater extent in DBA/2 mice; the rate of disappearance of bound DMBA from DNA was similar in all three strains. DMBA (0.1 μmol/mouse) was bound to DNA in C57BL and DBA/2 mice to similar extents 19 h after treatment and to a slightly lesser extent in Swiss mice. The ratios of the sizes of the hydrocarbon‐DNA product peaks varied with the time after treatment, but were similar at any given time for the three strains. Both BP (1 μmol/mouse) and MCA (1 μmol/mouse) were bound to DNA to similar extents 19 h and 48 h after treatment in all three strains. BP (0.1 μmol/mouse) was bound to DNA in the order DBA/2>C57BL> Swiss 19 h after treatment. The levels of binding for all three hydrocarbons in the different strains do not show a correlation with the reported susceptibilities of the three strains to polycylic hydrocarbon carcinogenesis.