ut the reed frog is not just a sentinel for danger, it may also signal hope in the fight against cancer. Hayes has found that his frog model can be used to screen for compounds that keep cancer from growing; in particular, agents that block the effects of estrogen. One such compound is the breast cancer drug, tamoxifen , one of the only effective treatments for this deadly disease.

	A	B	C	D
	Results of Dr. Hayes' tamoxifen research on African reed frogs: Frog A is the "control" animal. Frog B was treated with E2; Frog C was given the cancer drug tamoxifen; Frog D was given both E2 and tamoxifen. [ Click for a larger image.] Photos courtesy of Dr. Tyrone Hayes.

Since his reed frogs are so sensitive to human estrogens, Hayes wanted to know whether they were also sensitive to estrogen blockers, such as tamoxifen. To test whether tamoxifen is active in frogs, Hayes experimented with three groups of male reed frogs and compared them with normal frogs (the "control" group). One group was treated with an estrogen-like substance, E2. Another group was given just tamoxifen, and a third group was given both tamoxifen and E2. The control group and the tamoxifen-only group remained solid green, just like normal male reed frogs. The male frogs that were given just E2 developed prominent spots, while the frogs that were given both E2 and tamoxifen had only faint spots in their backs. This indicates that the human cancer drug blocked the action of estrogen in male frogs, preventing them from developing female coloration.

"This is an interesting effect," says Professor Hayes, "because tamoxifen will also block estrogen from causing mammary cancer cells to divide in women. So with this frog, we have a potential tool for screening anti-cancer compounds. This might be useful for the pharmaceutical industry in finding new treatments for cancer."

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