Effect of vincristine or bleomycin on radiation-induced cell killing of mice spermatogonial stem cells: The importance of sequence and time interval

The effect of single doses of vincristine (VCR) or bleomycin (BLM) on mice spermatogonia was investigated, and the influence of either of these drugs on the radiation response of murine spermatogonial stem cells was examined. When assessed by flow cytometry, VCR (1.0 mg/kg) or BLM (100 mg/kg) reduced the survival in the differentiated spermatogonia to 4% and 37% of controls, respectively ( p < 0.05). VCR reduced the stem cells to 79% of controls ( p < 0.05), whereas BLM had no apparent effect on the stem cells ( p > 0.05). Drugs were administered intraperitoneally up to 28 days before or after local irradiation with 9 Gy. VCR produced significant enhancement of radiation-induced damage to spermatogonial stem cells, which was most prominent when administered 6 or 12 hr after irradiation. BLM administered before irradiation or 1 hr after radiotherapy produced significant enhancement.