Susceptibility of Fanconi's Anemia Lymphoblasts to DNA-cross-linking and Alkylating Agents¹

In order to develop the usefulness of Fanconi's anaemia (FA) lymphoblast lines for biochemical and genetic studies, we have determined their sensitivity to a variety of DNA-damaging chemicals. We have adapted a growth inhibition protocol in which the sensitivity of a cell line is characterized by the drug concentration yielding a 50% inhibition of growth (EC₅₀). The DNA-cross-linking agents, mitomycin C, nitrogen mustard, melphalan, 1,3-butadiene diepoxide, cis-diaminedichloroplatinum(II), and cyclophosphamide, were all more toxic to four FA cell lines than to five normal lines. Three lines, HSC 72 (FA), 99 (FA), and 230 (FA), had EC₅₀s that were 10 to 20 times lower than that of controls while the fourth line, HSC 62 (FA), had an intermediate EC₅₀. Three nitrosourea compounds were also more toxic to FA cells than to controls. However, 2 normal cell lines (HSC 92 and 93) had nitrosourea EC₅₀s 4 to 7 times lower than the other nine controls and overlapped the sensitivity of the intermediate [HSC 62 (FA)] cell line. The same 2 normal cell lines were also more sensitive than 12 other controls, including FA heterozygotes, xeroderma pigmentosum, and ataxia telangiectasia, to the monofunctional alkylating agents, ethyl methane sulfonate, methyl methane sulfonate, and N-methyl-N′-nitro-N-nitrosoguanidine. Heterogeneity was also found with FA lines. Two FA cell lines (HSC 72 and 230) had EC₅₀s lower than all control lines while one FA line (HSC 99) had an EC₅₀ similar to that of the resistant normal lines. FA and normal cells had nearly the same sensitivity to 4-nitroquinoline-1-oxide and bleomycin. These results demonstrate that FA lymphoblast lines are more sensitive than normal cell lines to all DNA-cross-linking agents examined. These cell lines should therefore be useful for the analysis of DNA cross-link repair and the biochemical defect in FA. We have also found an unexpected sensitivity of some FA and normal lines to monofunctional alkylating agents.