Influence of two contraceptives on induction of mammary cancer in rats

Effects of progestagens and Org OD14 in in vitro and in vivo tumor models

Sex steroids, in particular estradiol (E2) and progesterone (P4), play, together with other hormones and growth factors, a role in the development of normal breast tissue. The effect of four progestagens (norethisterone, 3-ketodesogestrel, gestodene and P4) and Org OD14, a steroid with weak estrogenic, progestagenic and androgenic properties were studied on growth of breast tumor cells in vitro using two subclones of MCF-7 (H and A) and T47D (S and A) cells. In addition, we investigated the effects of 3-ketodesogestrel, gestodene and Org OD14 on the growth of 7,12-dimethylbenz(a)anthracene(DMBA)-induced mammary tumors in rats. In the in vitro assays with MCF-7 cells norethisterone, 3-ketodesogestrel and gestodene stimulated growth only at high doses (> or = 10(-7) M), whereas P4 had no effect. Gestodene was more potent than 3-ketodesogestrel and norethisterone. Org OD14, stimulated cell growth at a dose of 10(-8) M, while E2 is active at 10(-10) M. In T47D-A cells similar effects were found, but the subclone S did not respond to the progestagens and Org OD14. The two T47D subclones also reacted differently to progestagens during growth stimulation with E2. In T47D-S the progestagens and Org OD14 inhibited, while in T47D-A these compounds did not modulate the effect of E2. In the DMBA model we found that gestodene and 3-ketodesogestrel were able to inhibit tumor growth to the same extent. Surprisingly, Org OD14 was even more effective in the DMBA model using the therapeutic approach. Using the prophylaxic approach tumor development was delayed and tumor growth was strongly suppressed. The inhibitory effects of Org OD14 on tumor growth in the DMBA model may be attributed to its mixed hormonal profile. From these studies we conclude that different cell lines and even subclones thereof respond quite differently to steroids. Both in vitro and in vivo studies are required to judge whether synthetic steroids might be involved in an increased risk for the development of breast tumors.

Hormone prevention of mammary carcinogenesis by norethynodrel-mestranol

The observation that the susceptibility of the mammary gland to chemical carcinogenesis is inversely related to its level of hormonally induced differentiation led us to test whether treatment of virgin rats with an estrogenic-progestagenic hormone combination protected the gland against this carcinogenesis. Virgin Sprague-Dawley rats aged 45, 55, 65, or 75 days had implanted subcutaneously for 21 days a pellet containing norethynodrel-mestranol (NM) (98.5%-1.5%) at two doses, a physiological or low dose (LD) of 0.5 mg, equivalent to the dose used in Enovid for contraception in humans, and a pharmacological or high dose (HD) of 5.0 mg. Twenty-one days after NM pellet removal, the mammary glands of 5 animals per group were examined for the number of terminal end buds (TEBs), terminal ducts (TDs), alveolar buds (ABs) and lobules, and the DNA labeling index (DNA-LI). The remaining animals received 8 mg 7,12-dimethylbenz(a) anthracene (DMBA)/100 g body weight, and tumorigenesis was evaluated at 24 weeks. The percentage of TEBs decreased with age, and further with NM treatment at both doses. Treatment did not significantly modify the percentage of TDs, but increased that of ABs in most groups. The DNA-LI of TEBs remained constant, even during aging and after treatment, whereas both aging and treatment reduced DNA-LI in TDs and ABs. Tumor incidence declined with increasing age from 75% to 44% in the 45 and 75 day-old control groups respectively. Adenocarcinoma incidence followed the same trend. NM treatment had a dose-related protective effect against development of tumors in general and of adenocarcinomas in particular. LD treatment resulted in a marginally significant reduction in adenocarcinoma incidence, whereas HD-treated animals were 0.24 times as likely as controls to develop carcinomas. There was a statistically significant correlation between the percentage of TEBs present in the gland at the time of carcinogen administration and the incidence of adenocarcinomas. It was concluded that treatment of virgin rats with the hormone combination norethynodrel-mestranol resulted in long lasting structural changes in the mammary gland which protected this organ from a subsequent carcinogenic insult.

Oral contraceptives: significance of their effects in man and relationship to findings in animal models

Combination oral contraceptives have been available since 1960. They contain both an estrogen and a progestogen and have been studied extensively in both lower animals and humans and have been the subject of special regulatory requirements for toxicological and clinical studies. The initial oral contraceptives, by today's standards, contained very high levels of both hormones. There has been a continuous decrease in the dose of both the estrogen and the progestogen during the past quarter century, with continued maintenance of high degree of effectiveness. This decrease of dosage has been stimulated by findings from prospective clinical trials and retrospective case control trials. As additional information has been gained with oral contraceptives, new benefits beyond their effectiveness as contraceptives have been realized. Today's oral contraceptives provide a high degree of effectiveness, low incidence of nuisance side effects, and low incidence of major adverse effects.