EM-652 (SCH57068), a pure SERM having complete antiestrogenic activity in the mammary gland and endometrium

In order to minimize the risks of endometrial cancer and the development of resistance to antiestrogen therapy, we have synthesized the orally active antiestrogen EM-652 which is the most potent of the known antiestrogens and exerts pure antiestrogenic activity in the mammary gland and endometrium. EM-652 inhibits the AF-1 and AF-2 functions of both ERalpha and beta while the inhibitory action of OH-TAM is limited to AF-2. EM-652, thus, inhibits Ras-induced transcriptional activity and blocks SRC-1-stimulated activity of the two receptors. The absence of blockade of AF-1 by OH-TAM could explain why resistance develops to Tamoxifen treatment. Not only the development, but also the growth of established DMBA-induced mammary carcinoma is inhibited by treatment with EM-800, the prodrug of EM-652. EM-652 is the most potent antiestrogen to inhibit the growth of human breast cancer ZR-75-1, MCF-7 and T-47D cells in vitro. When incubated with human Ishikawa endometrial carcinoma cells, EM-800 has no stimulatory effect on the estrogen-sensitive parameter alkaline phosphatase activity. When administered to ovariectomized animals, EM-800 prevents bone loss, and lowers serum cholesterol and triglyceride levels. EM-800 has shown benefits in women with breast cancer who had failed Tamoxifen. The above-summarized preclinical and clinical data clearly suggest the interest of studying this compounds in the neoadjuvant and adjuvant settings and, most importantly, for the prevention of breast and uterine cancer.