In
radiotherapy, tumor hypoxia is the main factor responsible for treatment resistance, and the development of radiosensitizers that can overcome this is imperative. However, many drugs that are effective in vitro and in vivo fail in clinical trials, and thus it is necessary to develop an animal model that can be used for the correct evaluation of pharmacokinetics and activity. Developing chicken eggs are commonly used in various research fields such as anticancer
drug sensitivity tests and
cardiotoxicity tests. We examined whether the radiosensitizing activity of
etanidazole, as a hypoxic cell radiosensitizer, could be evaluated using
tumor-bearing chick embryo. Following the
transplantation of mouse mammary
carcinoma EMT6 cells on day 11, a solid
tumor was formed on day 15 and an evaluation of the time-course of the
tumor revealed that the
tumor weight was the highest on day 18. The maximum dose of
etanidazole that did not affect
tumor growth and fetal survival was 1.0mg and the maximum X-ray dose was 8Gy.
Etanidazole was intravenously administered 10min prior to single dose X-ray irradiation. A significant
tumor growth inhibitory effect was confirmed with 1.0mg of
etanidazole in combination with 8Gy X-ray. In the case of mouse
colon cancer colon26 cells, the combination of 3.0mg of
etanidazole and 2Gy X-ray showed 2.79 times higher radiosensitizing activity than that observed for the control group. These results demonstrate that it is possible to evaluate the activity of radiosensitizers using
tumor-bearing chick embryo.