Cytotoxicity of benzo[a]pyrene diol epoxide is associated with premature arrest of nascent strand elongation in serum-stimulated monkey kidney cells.

The relationship between the density of adducts on the DNA of monkey kidney cells caused by benzo[a] pyrene diol epoxide (BaP-DE) and the amount of cytotoxicity and DNA synthesis inhibition was examined. Above 1.7 microM, BaP-DE was maximally cytotoxic; whereas, at concentrations below 0.8 microM, colony-forming efficiency was the same as controls even though DNA adducts and DNA synthesis inhibition could be seen at these lower concentrations. Adduct analysis showed a linear relationship between DNA binding and applied BaP-DE concentration with no evidence of parental strand nicking over the concentrations at which adducts were measured. Analysis of nascent DNA synthesis following BaP-DE treatment showed that premature arrest of strand elongation and inhibition of DNA segment maturation were both factors contributing to the decreased level of DNA synthesis caused by BaP-DE. Above 1.7 mM, BaP-DE arrested strand elongation at subreplicon sizes which correlated with the average interadduct distances estimated from DNA binding studies. Lower, nontoxic concentrations permitted the completion of replicons, but inhibited the maturation of these nascent segments. Flow cytometric analysis of the cell cycle distributions of cells after BaP-DE treatment at concentrations which inhibited proper maturation of newly synthesized DNA showed that cells did progress through the G2 phase of the cell cycle and did divide with fragmented newly synthesized DNA. The results of these studies suggest that growth-dependent toxicity is not simply proportional to template adduct level but rather that major toxicity results when adduct levels exceed one/strand/replicon due to the inability of the replication apparatus to complete genome segments containing multiple adducts with replicons.