Breast cancer is one of the most prevalent types of cancer, and epidemiological and clinical studies have shown that approximately one-third of breast tumors are estrogen-dependent. This means that estrogens are required for the growth of such breast tumors in both premenopausal and postmenopausal patients. In postmenopausal women, in whom breast cancer most commonly occurs, breast tumor concentrations of estrone and estradiol are considerably higher than blood estrogen levels. Although retention of estrogens in breast tumors by high-affinity binding proteins contributes to the level of estrogens in tumors, estrogen concentrations in the breast are higher than plasma levels in breast cancer patients regardless of whether their tumors are estrogen receptor-positive (ER+) or receptor-negative (ER-). In situ formation of estrogen from estrogen biosynthetic precursors within tumors is now known to make a major contribution to the estrogen content of breast tumors.
Estrogenic effects are mediated by specific receptors located in the nucleus of estrogen-responsive cells. The receptor contains a hormone binding domain for binding estrogen, transcription activating domains, and a DNA binding domain. The binding of the receptor-hormone complex to estrogen response elements (ERE's) in the DNA of target genes is necessary for regulating gene transcription.
Drugs that competitively block estrogen binding to its receptor, termed anti-estrogens, are capable of inhibiting the stimulatory effects of the hormone on cell proliferation and are therefore useful in the clinical treatment of breast cancer. Clinically, estrogen receptor-positive tumors respond with a higher frequency to anti-estrogens than do tumors lacking a significant level of receptors.
Anti-estrogenic drugs fall into two chemical classes: nonsteroidal and steroidal. The nonsteroidal anti-estrogen tamoxifen (Nolvadex.RTM.) has been used as an adjunctive treatment for breast cancer following chemotherapy or radiation therapy. However, tamoxifen itself has estrogenic activity, resulting in an increased risk of endometrial cancer and possible recurrence of breast cancer after long-term therapy.
To date, little work has been done in the development of selective competitive antagonists of estrogen. Several steroidal anti-estrogens have been synthesized which lack estrogenic activity. Included among these are ICI 164,384, ICI 182,780 and Ru58668. See, e.g.: Wakeling et al. J. Steroid Biochem. 31:645-653 (1988), which pertains to ICI 164,384; Wakeling et al., Cancer Res. 51:3867-3873 (1991), and Wakeling et al., J. Steroid Biochem. Molec. Biol. 37:771-774 (1990), which pertain to ICI 182,780; and Van de Velde et al., Ann. N. Y. Acad. Sci. 761:164-175 (1995), Van de Velde et al., Pathol. Biol. 42:30 (1994), and Nique et al., Drugs Future 20:362-366 (1995), which relate to R458668. Unfortunately, these drugs are not orally active and must be administered in high doses intramuscularly. Furthermore, the manufacture of these drugs is laborious, requiring a complicated, 14-16 step synthesis with very low overall yields. A potent orally active steroidal anti-estrogen is not yet available for clinical use.
Accordingly, the present invention is directed to novel compounds that are extremely effective anti-estrogenic agents. The invention thus represents a significant advance in the art, particularly in the treatment of breast cancer and other diseases and conditions that are potentiated by the presence of estrogens.
The following references pertain to one or more aspects of the invention and as such may be of background interest to those skilled in the art: U.S. Pat. No. 2,840,581 to Hogg et al., which describes estradiol derivatives substituted at the 17-position with .dbd.CH--CH.sub.2 OH and having estradiol-like activity; U.S. Pat. No. 3,536,703 to Colton et al., which describes antimicrobial estradiol derivatives substituted at C-3 with methoxy, and at C-17 with various groups, including .dbd.C--CH.sub.2 --NR.sub.3.sup.+ (wherein R is hydrogen or lower alkyl or wherein two R groups form a cyclic structure); U.S. Pat. No. 3,716,530 to Krubiner et al., which describes steroids containing various substituents at the C-17 position, including an estradiol derivative substituted at C-17 with .dbd.CH--CH.sub.2 X, wherein X is halogen (stated to be useful as an intermediate in the synthesis of progestational compounds and antifungal agents); Blickenstaff et al., Steroids 46 (4,5): 889-902 (1985), which relates to estradiol derivatives having substituents at the 16-position bound to the steroid nucleus through a double bond, synthesized as part of a search for novel anti-cancer agents; French Patent No. 1,453,210, which shows estradiol analogs substituted at the 17.beta.-position with --C(CH.sub.2)--O--(CH.sub.2).sub.2 NR'R", wherein R' and R" may be alkyl or aralkyl; French Special Patent for Medications No. M3031, which relates to the synthesis of 3-hydroxy-20.alpha.-dimethylaminoethoxy-19-norpregna-1,3,5(10)-triene; and Qian et al., J. Steroid Biochem. 29(6):657-664 (1988), which evaluates the correlation between substitution at the 17-position of estradiol and possible anti-estrogenic activity, and describes estradiol analogs substituted at the 17.beta.-position with --O--(CH.sub.2).sub.2 --NR.sub.1 R.sub.2, wherein R.sub.1 and R.sub.2 are methyl, ethyl, cyclopentyl, cyclohexyl, or tetrahydropyranyl (none of the compounds were found to have anti-estrogenic activity).
No art of which applicants are aware, however, describes compounds as provided herein. To the best of applicants' knowledge, the compounds and methods of the invention are previously unknown and completely unsuggested by the art.