NOTE [Gann, 68, 337～341; June, 1977] INHIBITORY EFFECT OF MEPITIOSTANE ON THE GROWTH OF MAMMARY TUMOR OF A RAT Osamu TAKATANI and Soichi KUMAOKA National Cancer Center Hospital* Mepitiostane (2α, 3α-epithio-5α-androstan-17β-yl 1-methoxycyclopentyl ether) is an orally active anti-estrogenic and anabolic-androgenic steroid com- pound. Mepitiostane administered orally suppressed the growth of transplanted estrogen-dependent mammary tumor in rats. This result was compared with the oral administration of fluoxymesterone, which is widely used orally for treatment of advanced breast cancer. Experimental result showed that Me- pitiostane has a more dominant antitumor activity than fluoxymesterone. There- fore, this new compound may be useful for clinical treatment of breast cancer. In 1965, Takeda and his colleagues10) syn- thesized 2α, 3α-epithio-5α-androstan-17β-ol (epitiostanol) and its biological activities were reported by Miyake et al.5,6) Takatani9) had studied its antitumor activity by using mam- mary tumors of rats and mice. Miyake7,8) reported that a derivative of epitiostanol, 2α, 3α-epithio-5α-androstan-17β-yl 1-metho- xycyclopentyl ether (Mepitiostane) was a new and orally active anti-estrogenic and anabolic-androgenic steroid compound. It does not possess the characteristic alkyl struc- ture at 17α-position (Fig. 1). In this paper, the effect of Mepitiostane on the growth of transplanted estrogen-de- pendent mammary tumor in rats is reported as a second study of sequential studies on epitiostanol.9) Materials and Methods Mammary fibroadenoma from a female rat of the Sprague-Dawley strain was supplied by Dr . R. Fukunishi, Department of Pathology , Ehime University Medical School. This hormone-de- pendent tumor was transplanted into 7- to 8-week- old female rats of the same strain weighing about Fig. 1. Structural formulae 200g, according to the methods worked out by Huggins et al.2,3) and by Glen et al .1) Two frag- *Tsukiji 5 -1-1 , Chuo-ku, Tokyo 104(高 谷 治,熊 岡 爽 一). 68(3) 1977 337 O. TAKATANI AND S. KUMAOKA 338 Gann MEPITIOSTANE AND MAMMARY TUMOR 1ments (3 × 3 × 3mm) were subcutaneously trans- not differ between the experiment in 1973 planted into bilateral inguinal region. About 5 and the present experiment. In groups 3 weeks later, when the tumor growth became and 4, tumor growth was markedly suppress- evident, the tumor-bearing rats were divided into three or more groups, each consisting of 20rats. ed. Mean scores of the tumor and various Epitiostanol,provided by Shionogi & Co., organ weights at the end of the experiment Osaka, was dissolved in sesame oil and injected are shown in Table I. subcutaneously in a dose of 1mg/0.1ml, 6 times A discernible difference was observed in a week for 9 weeks. Mepitiostane, also supplied by Shionogi, was dissolved in sesame oil and made tumor weight between the control and the to flow into the stomach with doses of 30, 10, or steroid-treated group. However, there was 3mg/0.2ml, 6 times a week for 9 weeks. Fluoxy- no significant difference between epitiostanol mesterone (Halotestine),supplied by Upjohn & and fluoxymesterone or Mepitiostane. In con- Co., U. S. A., was also dissolved in sesame oil and administered by the same method in a dose of trast to those of control group, the weight of 10mg/0.2ml, 6 times a week for 9 weeks. ovaries and adrenals was reduced greatly in The rats were sacrificed after 9 weeks. The tu- groups 2 and 4. The kidney weight increased mor and 6 organs (ovary, uterus, kidney, adrenal, more significantly in the three steroid-treated liver, and spleen) were excised and weighed. Two experimental schedules were used. In Experiment groups compared to the control group. I, the tumor-bearing female rats were divided into Experiment II: This experiment was con- four groups of about 20rats in each group. They ducted in order to estimate the minimum were treated under the following schedule: responsive dosage of Mepitiostane. In the Group 1 (Tumor-bearing control): 0.2ml ses- case of group 6 the tumor growth was signifi- ame oil given orally per day. Group 2: 1mg/day of epitiostanol injected sub- cantly suppressed (P = 0.05) when compared cutaneously. with the control group. The reproducibility of Group 3: 10mg/0.2ml/day of fluoxymesterone tumor suppressing action of fluoxymesterone administered orally. was recognized in experiments I (group 3) Group 4: 10mg/0.2ml/day of Mepitiostane ad- and II (group 6). Various doses of Mepitio- ministered orally. In Experiment II, the tumor-bearing experi- stane such as 30, 10, and 3mg/day were mental animals were divided into 5 groups, each administered orally and the tumor growth composed of 20rats, and treated as follows: was suppressed greatly (P = 0.01) in all the Group 5 (Tumor-bearing control): Treated as in Experiment I. groups in contrast to that of the control Group 6: 10mg/0.2ml/day of fluoxymesterone group. The inhibitive effect on tumor growth administered orally. was greater in groups 7, 8, and 9 than in Group 7: 3mg/0.2ml/day of Mepitiostane ad- group 6. No toxic effect or side effect was ministered orally. observed in experimental animals. Group 8: 10mg/0.2ml/day of Mepitiostane ad- Results of this experiment are presented ministered orally. Group 9: 30mg/0.2ml/day of Mepitiostane ad- in Table II. The growth of fibroadenoma in ministered orally. rats was suppressed by the administration of 3mg/day of Mepitiostane. Very similar sup- Results pression was possible by the daily administra- Experiment I: The tumors of the control tion of 10 or 30mg of this compound . There- group increased almost linearly in size. In fore, it is assumed that the minimum respon- group 2, the growth rate of the tumor was sive dosage of Mepitiostane is less than 3mg/ markedly low. Group 2 was the active control day. in this experiment, and epitiostanol showed as much inhibition as testosterone propionate Discussion which had been reported in 1973.9) The Epitiostanol is a new anti-estrogenic com- tumor responsiveness to these compounds did pound applicable as an antitumor agent for 68(3) 1977 339 O. TAKATANI AND S. KUMAOKA advanced breast cancer. It has been given by ing tumor growth is estimated to be 3mg/ intramuscular injection in clinical treatment . day or less. Miyake8) reported that the oral Its evident effect on tumor growth was re- administration of Mepitiostane produced ported by the Japanese Cooperative Group marked myotrophic and androgenic activities on Hormonal Treatment for Breast Cancer4) which resembled those of fluoxymesterone. in 1973. In the effective cases, epitiostanol At the same time, its oral administration was administered for more than 6 or 12 scarcely increased bromsulphalein retention months. We found that the oral use of Me- rate (BSP), plasma GOT and GPT activities, pitiostane, a derivative of epitiostanol, sup- or plasma cholesterol levels. Treatment with pressed the tumor growth considerably in methyltestosterone and oxymetholone caused the experimental animals and that this sup- abnormal bromsulphalein retention rate and pression was similar to that brought about plasma GOT activity while the effect of by the injection of epitiostanol. Hormone fluoxymesterone was moderate. Therefore, dependence of rat fibroadenoma of the breast Miyake emphasized that this compound had was established by Huggins, and the growth- the least liver toxicity among the orally inhibiting response might be regarded as an administered anabolic-androgenic steroids. effective indicator for the treatment of mam- Conclusively, the present experimental re- mary cancer. These investigations are sequen- sults show that Mepitiostane has an excellent tial screening studies of the derivatives of antitumor activity by its oral use and, there- epithiostanol on antitumor activity in hor- fore, this compound may be useful for clinical mone-dependent animal mammary tissues; treatment of advanced breast cancer. the first was on epitiostanol and the second As a preliminary experiment, the serum on Mepitiostane. In this study, hormone- prolactin level was measured in a limited independent tumor of autonomous growth number of animals, which were given Mepi- and androgen-dependent tumor were not tiostane, epitiostanol, or fluoxymesterone, used because the growth of estrogen-inde- and the control. Serum prolactin levels at pendent autonomous tumor was not always the end of the experiment were 55.4 ± 24.9 supressed by androgens. Mepitiostane admin- (8) for the control, 35.6 ± 4.2 (10) for Me- istered orally produces the same effect on pitiostane, 32.0 ± 7.5 (10) for fluoxymes- transplantable fibroadenoma in female Spra- terone, and 29.4 ± 4.3 for epitiostanol (10) gue-Dawley rats as that by the injection of (figures in parentheses indicate the number epitiostanol, because they have similar basic of animals). Accordingly, it is assumed that chemical structures. the antitumor activity of orally administered The effect by Mepitiostane was compared Mepitiostane is not the results of a secondary with that produced by fluoxymesterone which action through the inhibition of prolactin is widely used orally for treatment of advanc- secretion from the pituitary glands. The ed breast cancer. Table II indicates a con- mechanism of its antitumor effect is probably siderable difference in these two compounds the same as that of androgen or epitiostanol. in terms of growth inhibiting action, which agrees with the results presented by Miyake.8) We are grateful to Drs. Takede and Miyake of However, in Experiment I, no significant Shionogi Research Laboratory for giving us the compounds and for valuable suggestions.We also difference was observed between these two thank Dr. Nagasawa and Ms. Yanai of the Nation- compounds (Table I). In both of our experi- al Cancer Center Research Institute, Pharmaco- ments orally administered Mepitiostane sup- logical Division, and Mr. Kagami for their tech- pressed the growth of fibroadenoma.