Sparing radiation-induced damage to the physis by radioprotectant drugs: laboratory analysis in a rat model.

The radioprotectant compound amifostine (S-2[3-aminopropylamino]-ethylphosphorothioic acid), administered prior to radiotherapy, has been demonstrated to provide differential protection of normal cells from the damaging effects of ionizing radiation. The aim of this pilot was to determine if amifostine could preserve the integrity of, or minimize the damage to, the physis during exposure to radiation in an animal model. Thirty weanling Sprague-Dawley rats were randomized into five groups of six animals each. Groups 1 and 2 received a single exposure to radiation consisting of 12.5 and 17.5 Gy, respectively. Groups 3 and 4 received similar exposures of 12.5 and 17.5 Gy, respectively, but with prior administration of amifostine at 100 mg/kg. Group 5 (control) received neither radiation nor amifostine. At 6 weeks, femoral and tibial lengths were measured in treated and untreated hindlimbs and compared with the baseline lengths to calculate growth. Concordant with previous reports in the literature, the radiation doses of 12.5 and 17.5 Gy reduced net femoral growth in length by a mean of 23% (range = 12-33%, SD = 7.41) and 59% (range = 54-64%, SD = 4.45), respectively, in the irradiated limb. Amifostine reduced anticipated growth loss normally resulting from a single 12.5-Gy radiation dose by 48.9% in the femur, 13.1% in the tibia, and 27.6% overall in the total limb (p < or = 0.05). Similarly, anticipated growth loss from a single 17.5-Gy radiation dose was reduced by 30.8% in the femur, 20.3% in the tibia, and 25.7% overall in the total limb (p < or = 0.05). Amifostine administered prior to clinically relevant radiation exposures significantly reduced the amount of anticipated growth arrest in our animal model.