Chromosome Aberrations in Xeroderma Pigmentosum Cells Exposed to the Carcinogens, 4-Nitroquinoline-1-oxide and N-Methyl-N'-nitro-nitrosoguanidine

The frequency of chromatid breaks and chromatid exchanges was estimated in cultured xeroderma pigmentosum (XP) cells and control cells exposed to the carcinogens 4-nitroquinoline-1-oxide (4NQO) and N-methyl-N′-nitro-nitrosoguanidine (MNNG). The level of DNA repair synthesis in the XP cells which were used in this study is about 21% of that found in cells of nonafflicted persons following exposure to 4NQO. The XP cells show an elevated sensitivity to the chromosome damaging effect of 4NQO. Doses of 4NQO, which have no effect on control cells, increased significantly the frequency of metaphase plates with chromosome aberrations in the XP cells over a 2 day period post-treatment. On the other hand the frequency of chromatid breaks and exchanges of XP cells resembled that found in control cells exposed to equimolar concentrations of MNNG. It appears likely, but unproven, that the different sensitivity of the XP cells towards 4NQO and MNNG is linked with their different capacity to repair 4NQO and MNNG induced DNA alterations.