Relationship between Sensitivity of Cells from Patients with Hereditary Cutaneous Malignant Melanoma to Killing and Mutations by 4-Nitroquinoline 1-Oxide and Adduct Formation

Abstract Hereditary cutaneous malignant melanoma (HCMM) is an autosomal domiant disease and develops mostly in patients with the hereditary dysplastic nevus syndrome (DNS). A previous study from this laboratory showed that fibroblasts derived from skin biopsies of four HCMM/DNS patients and one DNS patient were significantly more sensitive to the cytotoxic and mutagenic effects of 4-nitroquinoline 1-oxide (4-NQO) than three fibroblast cell lines from normal newborn males and one from a 45-yr-old normal donor. The survival curves of the HCMM/DNS or DNS cell lines fell into two groups, one with a slope approximately twice as steep as the controls and one with a slope approximately 3 times as steep. This marked difference in survival curves disappeared if the same cell lines were exposed to 4-hydroxyaminoquinoline 1-oxide, a partially reduced metabolite of the parent compound, suggesting that the difference in sensitivity reflected a difference in the cells9 ability to metabolize the parent compound into a more reactive form. To see if such increased sensitivity to the cytotoxic effect of 4-NQO was an identifying characteristic of cells from HCMM/DNS and DNS patients and whether cells derived from unaffected members of such families were also more sensitive to 4-NQO than the controls, the survival curves of a series of 40 coded cell lines, derived from patients, family members, or normal donors of various ages, were compared in a blind study. The slopes of the survival curves of all the HCMM/DNS and DNS cell lines proved to be 2- to 3-fold steeper than those of the four previously studied control cell lines, bringing the total to nine of nine and eight of eight, respectively. Ten of the 28 coded cell lines from nonaffected family members or normal, age-matched donors proved to be as resistant as the four previously studied control cell lines and another foreskin-derived control cell line, bringing the total of relatively resistant cell lines to 15 of 33. However, the rest were just as sensitive as the cells from the patients. Mutagenesis studies showed that increased sensitivity to killing by 4-NQO was accompanied by increased sensitivity to mutation induction. Relatively sensitive and relatively resistant cell lines were treated with tritiated 4-NQO and assayed for survival and for the number of 4-NQO residues bound to DNA. The relationship between the number of adducts formed and cell survival was linear, with the relatively sensitive cell lines exhibiting the higher level of residues. These results indicate that the increased sensitivity to the killing effect of 4-NQO is not specific to HCMM/DNS or DNS patients, but that the observed increased sensitivity reflects an increased ability to metabolize 4-NQO into a form that binds to DNA.