gw-7604 and Endometrial-Neoplasms

The recognition of selective estrogen receptor modulation in the laboratory has resulted in the development of two selective estrogen receptor modulators (SERMs), tamoxifen and raloxifene, for clinical application in healthy women. SERMs are antiestrogenic in the breast but estrogen-like in the bones and reduce circulating cholesterol levels. SERMs also have different degrees of estrogenicity in the uterus. Tamoxifen is used specifically to reduce the incidence of breast cancer in premenopausal and postmenopausal women at risk for the disease. In contrast, raloxifene is used specifically to reduce the risk of osteoporosis in postmenopausal women at high risk for osteoporosis. The study of tamoxifen and raloxifene (STAR) trial is currently comparing the ability of these SERMs to reduce breast cancer incidence in high-risk postmenopausal women. There is intense interest in understanding the molecular mechanism(s) of action of SERMs at target sites in a woman's body. An understanding of the targeted actions of this novel drug group will potentially result in the introduction of new multifunctional medicines with applications as preventive agents or treatments of breast cancer and endometrial cancer, coronary heart disease, and osteoporosis.

Topics: Adult; Aged; Bone and Bones; Breast; Breast Neoplasms; Cardiovascular System; Cinnamates; Clinical Trials as Topic; Coronary Disease; Endometrial Neoplasms; Estrogen Replacement Therapy; Female; Heart; Hot Flashes; Humans; Middle Aged; Models, Biological; Organ Specificity; Osteoporosis; Postmenopause; Premenopause; Prospective Studies; Protein Structure, Tertiary; Raloxifene Hydrochloride; Randomized Controlled Trials as Topic; Receptors, Estrogen; Risk; Risk Assessment; Selective Estrogen Receptor Modulators; Stilbenes; Tamoxifen; Thrombophilia; Transcription, Genetic

Tamoxifen is the endocrine treatment of choice for all stages of estrogen receptor (ER)-positive breast cancer, and it is the first drug approved to reduce the incidence of breast cancer in high-risk women. Unfortunately, tamoxifen also possesses some estrogen-like effects in the uterus that cause a modest increase in the risk of endometrial cancer. GW5638 is a tamoxifen derivative with a novel carboxylic acid side chain with no uterotropic activity in the rat (Willson et al., J Med Chem, 1994, 37:1550-1552). We have compared and contrasted the actions of 4-hydroxytamoxifen (4-OHT, the active metabolite of tamoxifen) with GW7604 [the presumed metabolite of GW5638 in breast (MCF-7) and endometrial (ECC-1) cell lines in vitro]. GW7604 did not cause the growth of ECC-1 cells at any concentration (10(-11)-10(-6) M), but 4-OHT was weakly estrogen-like at low concentrations (10(-11)-10(-10) M). Compounds (10(-7) M) blocked the growth promoting action of estradiol (10(-10) M) in both ECC-1 and MCF-7 cells. Western blotting was used to show that GW7604 and raloxifene did not affect ER levels significantly, compared with controls, in MCF-7 cells; whereas the pure antiestrogen ICI182,780 decreased ER levels (P < 0.05). An assay system was used that can classify compounds into tamoxifen-like, raloxifene-like, or pure antiestrogens. The assay depends on the activation of the transforming growth factor alpha (TGFalpha) gene in situ by wild-type or D351Y mutant ER stably transfected into MDA-MB-231 cells (MacGregor-Schafer et al., Cancer Res, 1999, 59:4308-4313). GW7604 inhibited both estradiol (10(-9) M) and 4-OHT (10(-8), 10(-7) M) induction of TGFalpha in a concentration related manner (10(-9)-10(-6) M). GW7604 and raloxifene stimulated TGFalpha with the D351Y ER. In contrast, ICI 182,780 (10(-6) M) did not initiate TGFalpha and blocked the induction of TGFalpha with GW7604, raloxifene, and 4-OHT in D351Y-transfected cells. Using computer-assisted molecular models of ER complexes, we found that the antiestrogenic side chain of 4-OHT weakly interacted with the surface amino acid 351 (aspartate), but the carboxylic acid of GW7604 caused a strong repulsion of aspartate 351. We propose that GW7604 is less estrogen-like than 4-OHT, because it disrupts the surface charge around aa351 required for coactivator docking in the 4-OHT:ER complex. This charge is restored in the D351Y ER, thus converting GW7604 from an antiestrogen to an estrogen-like molecule.

Topics: Carcinoma; Cell Division; Cinnamates; Endometrial Neoplasms; Estrogen Receptor alpha; Estrogen Receptor Modulators; Estrogens; Female; Gene Expression Regulation; Humans; Models, Molecular; Receptors, Estrogen; RNA, Messenger; Selective Estrogen Receptor Modulators; Stilbenes; Tamoxifen; Transforming Growth Factor alpha; Tumor Cells, Cultured