Stabilization of a reactive, electrophilic carcinogen, benzo[a]pyrene diol epoxide, by mammalian cells

We have studied several features of the interactions of 7r,8t-dihydroxy-9t,10t-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE-I) with a DNA repair-proficient derivative of Chinese hamster ovary cells (CHO), AT3-2, and with a UV-light sensitive mutant, UVL-10, derived from AT3-2. Methods were developed for quantitating the amount of unhydrolysed BPDE-I associated with cells and for purifying DNA from cells under conditions where artificial labeling during preparation is minimized. In both cell types, about 30% of the BPDE-I added to a cell culture is rapidly taken up by the cells and is maintained in a cellular compartment in which the half-life of BPDE-I is about 10-fold longer than in aqueous medium. The kinetics of covalent binding to DNA were measured in both cell types and found to be described well by a single exponential process with a half-life of about 60 min. This is virtually identical to the half-life for intracellular hydrolysis of BPDE-I (57 min), consistent with the suggestion that this intracellular, relatively stable BPDE-I is responsible for binding.