Cytotoxic and mutagenic effects of 1-nitropyrene and 1-nitrosopyrene in diploid human fibroblasts

The cytotoxic and mutagenic effects of 1-nitropyrene (1-NP) and its reduced metabolite 1-nitrosopyrene (1-NOP) were determined in diploid human fibroblasts. Conditions for the metabolic activation of the parent compound (1-NP) by human cells in culture were developed. The cytotoxic effect of 1-NP in normal cells was compared with that for repair-deficient xeroderma pigmentosum (XP) cells, and cells from a patient with hereditary cutaneous malignant melanoma (HCMM), which we have shown earlier are abnormally sensitive to 4-nitroquinoline-1-oxide. The slope of the survival curve for XP cells was 2.5 times steeper than that of normal cells; that of HCMM cells was intermediate. When these cells were exposed to 1-NOP, the slope of the survival curve for the XP cells was also 2.5 times steeper than normal but the HCMM cells showed a normal response, suggesting that their defect is not in repair of DNA adducts, but in activation. 1-NP and 1-NOP also proved to be mutagenic in the human cell assay. When compared on the basis of concentration, 1-NOP was much more mutagenic than 1-NP. But when the compounds were compared on the basis of equal cell killing or equal number of DNA adducts initially bound to DNA, they were very similar. An equal number of residues covalently bound to DNA caused approximately the same amount of cell killing for either compound. XP cells were killed by a 7-fold lower number of bound adducts, suggesting that the increased survival and decreased mutation induction in the normal cells reflects their ability to remove potentially cytotoxic and mutagenic lesions.