The inhibitory effect of 5-acetoxy-2-(4-acetoxyphenyl)-1-ethyl-3-methylindole (D 16726) on estrogen-dependent mammary tumors.

The antineoplastic activity of the antiestrogen 5-acetoxy-2-(4-acetoxyphenyl)-1-ethyl-3-methylindole (D 16726) was determined in several estrogen-dependent mammary tumor models. The growth of the DMBA-induced rat mammary carcinoma was inhibited by doses ranging from 1 to 12 mg/kg. The maximum decrease of tumor area was 67% (control + 635%). D 16726 was also active against MNU-induced rat mammary tumors and transplanted MXT tumors of the mouse. The growth of estrogen receptor-positive MCF-7 breast cancer cells was inhibited by the hydroxy derivative D 15414 (10(-8)-10(-5) M). Because of the high binding affinity of D 15414 for the estrogen receptor (RBA 6.7-10.0) and the lack of activity against hormone-independent MDA-MB 231 breast cancer cells, a specific mode of action involving the estrogen receptor is likely.