Damage-resistant DNA synthesis in Fanconi anemia cells treated with a DNA cross-linking agent.

Fanconi anemia (FA) is a recessive disorder associated with diverse congenital anomalies, progressive bone marrow failure, and a marked predisposition to develop cancer. At the cellular level, FA is characterized by a prolonged G(2) phase in proliferating cells and a marked hypersensitivity to both the cytotoxic and the clastogenic effects of agents which produce DNA interstrand cross-links. Treatment with these agents leads to even further prolongation of the G(2) phase in FA cells. We now show that FA cells, from four different complementation groups, fail to decrease their rates of replicative DNA synthesis, as do normal cells, following treatment with a DNA cross-linking agent. This may be responsible for the prolongation of the G2 phase seen in these cells, and suggests that the fundamental defect in response of FA cells to DNA cross-linking agents may be in the S phase, rather than the G(2) phase, of the cell cycle.