Protection by WR-3689 against gamma-ray-induced intestinal damage: comparative effect on clonogenic cell survival,...

The aminophosphorothioate WR-3689 was characterized for its ability to protect mouse jejunal cells in vivo from single doses of X or gamma radiation. First, the effect of the drug on the survival of jejunal stem cells was examined using a clonogenic end point, the crypt microcolony assay. When WR-3689 was administered 30 min prior to whole-body irradiation, the number of surviving crypt cells was markedly increased at all doses of the drug, although protection began to level out at doses larger than 600 mg/kg. Protection was maximal when the drug was given 30 min before whole-body irradiation and declined rapidly with both shorter and longer intervals. Protection factors (PFs) were obtained by measuring survival curves for clonogenic crypt cells as a function of radiation dose; WR-3689 given 30 min before whole-body irradiation protected jejunum in the microcolony assay with a PF of 1.26 +/- 0.02, 1.50 +/- 0.10, and 1.65 +/- 0.10 at doses of 200, 400, and 800 mg/kg, respectively. Next, the effect of WR-3689 on the survival of jejunal stem cells was determined by assaying the survival of mice given X-ray doses to the whole abdomen in the range leading to death from the gastrointestinal syndrome. The PFs based on the LD50 values for 11-day survival were 1.31 +/- 0.05 (200 mg/kg) and 1.48 +/- 0.05 (400 mg/kg). Crypt-cell survival and animal survival were thus modified to a similar extent by this agent. Finally, the effect of WR-3689 on the induction of DNA single-strand breaks (SSBs) in jejunal cells was measured using an adaptation of the alkaline elution methodology. In mice treated with WR-3689 (400 or 800 mg/kg) 30 min prior to whole-body irradiation with 10 Gy there was no significant reduction in the number of DNA SSBs induced either in samples of the jejunum or in the cycling crypt cells, providing further evidence that there is no simple relationship between the modification of DNA SSBs and the survival of jejunal stem cells.