DNA damage and repair in patients receiving high-dose cyclophosphamide and radiation.

DNA damage and repair were assessed by alkaline sucrose gradients in the nonstimulated circulating mononuclear cells of 7 patients receiving high-dose cyclophosphamide (HDCy) and fractionated whole-body irradiation. Measurable damage produced by HDCy appeared to be repaired in about 60 hours. Damage from a radiation dose of 2 Gy was not completely repaired within 24 hours because DNA molecular weight was found to be decreased by an average of 22%. We attempted to assess the impact of HDCy on radiation damage repair by comparing blood irradiated and incubated in vitro before therapy with in vivo incubation following HDCy administration. Two hours after a radiation dose, repair appeared increased following HDCy. These results suggest the possibility that significant interaction at the DNA level may occur when HDCy and irradiation are administered together.