Flow cytometric characterization of the response of Fanconi's anemia cells to mitomycin C treatment

DNA flow histogram analysis, using 33342 Hoechst as a stain, has been used to detect the effect of the potentially bifunctional alkylating agent, mitomycin C (MMC) on dermal fibroblasts from patients with Fanconi's anemia (FA), a hereditary human disease characterized by pancytopenia, hypersensitivity to DNA-crosslinking agents, congenital abnormalities, and a predisposition for neoplasia. At 24 or 48 hr after a 2-hr exposure to 0.05 or 0.10 μg/ml MMC, 3HdT incorporation was reduced to a greater extent in FA cells than in normal cells. Cells sorted from the last half of S phase showed a slightly greater inhibition of 3HdT incorporation than did those sorted from the first half of S. Fanconi's anemia cells exhibited a marked accumulation in the G2 + M peak of flow histograms following exposure to MMC. Twenty-four hr after treatment with 0.05 μg/ml MMC, the G2 + M fraction of FA cells (eight lines) increased to more than 0.5 from a control value of approximately 0.2. Both normals (six lines) and heterozygotes (eight lines) showed, on the average, much less of a G2 + M increment than did FA cells, even after exposure to 0.1 μg/ml MMC. Examination of cells sorted from the G2 + M peak revealed that MMC-treated FA cells were blocked prior to mitosis. To determine whether the response of FA cells was specific for a bifunctional alkylating agent, cells were also treated with ethylmethanesulfonate, a monofunctional agent. Twenty-four hours after exposure to 0.25 or 0.5 mg/ml ethylmethanesulfonate, FA and normal cells showed similar, small increases in the G2 + M peak. The results suggest the utility of flow cytometry in the diagnostic evaluation of fibroblasts from patients suspected of having Fanconi's anemia.