Combined use of gemcitabine and radiation in mice.

The aim of this study was to explore, in a murine tumor, if the effectiveness of radiation, in doses and schedules commonly used in clinical practice is potentiated by the combined use of the recently developed drug gemcitabine. Gemcitabine (30-360 mg/kg b.w.) was administered i.p. in female C3D2F1 mice bearing a mammary adenocarcinoma alone or combined with X-rays. Firstly, gemcitabine (single administration) was administered alone or at 20 min, 4 h, and 24 h before X-ray treatments. The significant effect observed only at 24 h time interval, depended on the X-ray dose and not on the gemcitabine dose. Secondly, 4 gemcitabine administrations every 3 days were used in fractionated combined schedules (overall treatment time of 10 days). We studied the relationship among different doses of gemcitabine, alone or combined with 10 daily X-ray treatments (2 Gy/fraction). We observed an interactive effect of gemcitabine up to its threshold dose of 60 mg/kg/fraction. Furthermore, 10 X-ray daily treatments and 4 X-ray treatments every 3 days (total doses 20-40 Gy) were performed with gemcitabine 60 mg/kg/fraction to study the effect of different doses and schedules of X-rays. Tumor growth delays increase with higher X-ray doses, and this occurs more with 4 X-ray treatments than with 10 X-ray treatments. Our results re-affirm the uselessness of high gemcitabine doses, and indicate the effectiveness of combined gemcitabine-radiation fractionated protocols.