Evaluation of the in vivo radiosensitizing activity of etanidazole using tumor-bearing chick embryo

Abstract

Chick embryos have been used as alternative experimental animals in various research fields including virology immunology toxicology oncology and embryology. Until now there have been no in vivomodels using chick embryo to evaluate radiosensitizing activity. Here the in vivo radiosensitizing activity of etanidazole a well-known hypoxic cell radiosensitizer was evaluated using tumor-bearing chick embryo. On the basis of tumor growth drug administration and X-ray irradiation were performed on day 15 chick embryo with the endpoint being day 18 chick embryo. In day 15 chick embryo an X-ray irradiation dose of equal or less than 10 Gy did not cause significant tumor growth suppression. Intravenous administration of equal or less than 1.0 mg of etanidazole did not cause tumor growth suppression. Neither doses of equal or less than 8 Gy of irradiation nor 1.0 mg of etanidazole caused fatality of the chick embryo. On the basis of these results we evaluated the radiosensitizing effect of a combination treatment with 8 Gy of irradiation and 1.0 mg of etanidazole. As noted above 1.0 mg of etanidazole alone and 8 Gy of irradiation alone did not show tumor growth suppression. In contrast a combination treatment with 8 Gy of irradiation and 1.0 mg of etanidazole showed 35% of significant tumor growth suppression. Thus we succeeded in evaluating the in vivo radiosensitizing activity of etanidazole using tumor-bearing chick embryo. These results suggest that the use of tumor-bearing chick embryo may be part of a promising system for evaluating radiosensitizing activity.