Ethynerone

Abstract: Of 172 beagle dogs administered oral contraceptive steroids for 5-7 years, 114 developed 1,156 nodules in the mammary gland region. Most of these nodules arose 2.5-3.5 years after initiation of treatment. Approximately 16% of the nodules were transient and disappeared spontaneously from the mammary gland during the study. A total of 925 nodules were present in 99 dogs at the time of death or necropsy. These nodules were classified as benign mammary dysplasias (7.0%), lobular or intraductal hyperplasias (31.4%), simple adenomas (20.8%), complex adenomas (25.4%), benign mixed tumors (5.3%), malignant tumors (3.6%), or nonmammary lesions (6.5%). Histologically, the mammary nodules were representative primarily of the hyperplasias and tumors that occur spontaneously in the mammary glands of the dog. The only major exception was the presence of 82 simple adenomas that had basaloid features. Most of the contraceptive-related mammary nodules developed in dogs receiving the combination of progestion and mestranol at 10 or 25 times the proposed human dosage. Control dogs and dogs receiving mestrenol alone had few mammary nodules. Combinations of anagestone acetate and mestranol and chloroethynyl norgestrel (WY-4355) and mestranol produced large numbers of nodules at 10 and 25 times the proposed human dosage, whereas ethynerone plus mestranol produced large numbers of nodules only at 25 times the proposed human dosage. Ethynerone, when given alone at 25 times the proposed human dosage, was associated with fewer mammary nodules. Malignant neoplasms were seen in dogs given 10 and 25 times the proposed human dosage of anagestone acetate plus mestranol and 25 times the proposed human dosage of WY-4355 plus mestranol and ethynerone plus mestranol. This study strongly associates certain combinations of progestin and mestranol with mammary neoplasia in dogs.

Abstract: Of 172 beagle dogs administered investigational oral contraceptive steroids for 2.4-5.2 years, 9 developed malignant mammary tumors. At necropsy their ages varied from 41 to 70 months, with a mean age of 4.9 years. The malignant tumors were observed in 1 dog that received ethynerone plus mestranol at 1.05 mg/kg/day and in 4 dogs that received chlorethynyl norgestrel plus mestranol at 1.05 mg/kg/day. Also, 4 dogs that received anagestone acetate plus mestranol at either 0.44 or 1.10 mg/kg/day developed malignant mammary tumors. Malignant tumors were not seen in 33 dogs administered mestranol at 0.02 and 0.05 mg/kg/day for 7 years or in 18 dogs given ethynerone without mestranol at 1.00 mg/kg/day for 5 years. No malignant tumors were observed in 18 control dogs maintained for 7 years without treatment. Three dogs had single malignant mammary nodules, 3 dogs had 2 malignant nodules, 2 dogs had 4-6 malignant nodules, and 1 dog in the treatment group given high dosages of ethynerone plus mestranol had 14 mammary nodules composed of fibrosarcoma. The malignant tumors were histologically classified as 5 anaplastic carcinomas, 2 solid carcinomas, 1 tubular adenocarcinoma, 1 squamous cell carcinoma, and 1 fibrosarcoma. Most dogs had only 1 histologic type of cancer (8/9 dogs); however, 1 dog had carcinomas of both solid and anaplastic types involving different glands. Metastases were present in 5 dogs and most often involved regional lymph nodes and lung.

Abstract: Metabolism of the 17 alpha-ethynyl group of the synthetic estrogen, 17 alpha-ethynylestradiol, by hepatic microsomes from female rhesus monkeys was studied. Incubation of 17 alpha-ethynylestradiol, labeled with 14C in both ethynyl group carbons, resulted in the formation of D-14C-homoestrone (identified by high performance liquid chromatography and gas chromatography-mass spectrometry) and 14CO2. The D-homoestrone appears to be formed by a rearrangement in which one ethynyl group carbon is incorporated into the D ring of the steroid (D-homoannulation) and the second is subsequently removed as CO2. Cofactor, inhibition, and subcellular fractionation studies on the rate of 14CO2 formation showed that the ethynyl group is oxidized by cytochrome P-450. Hepatic microsomes isolated from rhesus monkeys treated with phenobarbital, but not 3-methylcholanthrene or pregnenelone-16 alpha-carbonitrile, resulted in increased rates of 14CO2 formation. Oxidation of the 17 alpha-ethynyl group is postulated to produce a high energy intermediate which is rearranged by D-homoannulation. However, as an alternative reaction, this unstable intermediate might covalently bind and inactivate the cytochrome P-450 enzymes catalyzing its formation. In support of this hypothesis, both cytochrome P-450 concentrations and the rate of catalysis of the D-homoannulation pathway by this enzyme were significantly decreased in hepatic microsomes from rhesus monkeys which had been administered mestranol and/or ethynerone (17 alpha-ethynylated steroids) at dosage levels mimicking human exposure to oral contraceptive agents.

Abstract: A total of 213 treated and 16 control monkeys comprising 12 experimental groups was evaluated for determination of the long-term (10 years) effects of various dosages of a variety of synthetic oral contraceptive steroids on the mammary glands of rhesus monkeys. The steroid hormones included mestranol, ethynerone, a combination of mestranol and ethynerone, chlorethynyl norgestrel plus mestranol, and anagestone acetate plus mestranol. Various degrees of physiologic lobular hyperplasia and lactational changes were observed in association with all of these steroid hormones; these changes appeared dose-dependent. Mestranol caused a proliferative atypia ranging from a minimal to a moderate degree in 8 of 34 (23%) animals, but it was not dose-related. Eleven of 15 monkeys (73%) administered ethynerone developed proliferative atypia, ranging in degree from minimal to severe, including one invasive carcinoma and 2 lesions resembling intraductal carcinoma in the human. The mestranol and ethynerone combination produced a proliferative atypia in 22 of 52 animals (42%), including five identical to intraductal carcinoma in the human and one identical to lobular neoplasia. Of the 40 monkeys administered anagestone acetate and mestranol, 20 (50%) developed proliferative atypias; the atypias ranged from mild to severe and included five resembling intraductal carcinoma in human breast. The chloroethynyl norgestrel and mestranol combination induced proliferative atypia in 25 of 52 monkeys (49%); six of these atypias were severe and indistinguishable from intraductal carcinoma of the human breast; and one, if in the human breast, would reflect a solid variant of an invasive carcinoma. Only 2 of the 16 control monkeys (12%) developed proliferative atypias, and these were of minimal to mild degree. The occurrence of severe degrees of atypia identical to intraductal carcinoma in the human breast and invasive carcinoma associated with hormone administration suggests a carcinogenic effect.