The estrogen receptor: a logical target for the prevention of breast cancer with antiestrogens

Cutaneous neoplasia in ferrets, rabbits, and guinea pigs

The frequency of common cutaneous tumors in ferrets, rabbits, and guinea pigs is summarized, with descriptions of their appearance and behavior, prognosis, and treatment options. This information assists clinicians when talking to clients, and helps owners make an informed decision whether or not to pursue aggressive treatment or to palliate.

Trilostane in advanced breast cancer

Antiestrogens, principally tamoxifen, and aromatase inhibitors have been used as the first- and second-line therapy in patients with advanced postmenopausal breast cancer for many years. However, some patients acquire resistance to these treatments and, at present, further endocrine treatment is achieved by merely substituting the current medication with a different antiestrogen or aromatase inhibitor. Trilostane offers an alternative endocrine treatment due to its unique mode of action. It is an allosteric modulator of the estrogen receptor and targets both the estrogen- and growth factor-dependent pathways through which estradiol stimulates cell proliferation. In clinical trials, trilostane has been shown to be an effective treatment for breast cancer in patients who have relapsed after receiving treatment with one or more forms of endocrine therapy. Ongoing and future clinical trials are examining the potential for the use of trilostane in premenopausal breast cancer, as well as in other malignancies such as prostate cancer.

In utero alcohol exposure increases mammary tumorigenesis in rats

Findings in humans and animal models suggest that in utero hormonal and dietary exposures increase later breast cancer risk. Since alcohol intake by adult women consistently increases their breast cancer risk, we wondered whether maternal alcohol consumption during pregnancy increases female offspring's mammary tumorigenesis. In our study, pregnant female rats were pair-fed isocaloric diets containing either 0 (control), 16 or 25 g alcohol kg(-1) feed between days 7 and 19 of gestation. These alcohol exposures generate blood alcohol levels that correspond to low and moderate alcohol consumption and are lower than those that induce foetal alcohol syndrome. Serum oestradiol levels were elevated in pregnant rats exposed to alcohol (P<0.003). When adult, female offspring of alcohol-exposed dams developed significantly more 7,12-dimethylbenz[a]anthracene -induced mammary tumours, compared to the controls (tumour multiplicity; mean+/-s.e.m., controls: 2.0+/-0.3, 16 g alcohol: 2.7+/-0.4 and 25 g alcohol: 3.7+/-0.4; P<0.006). In addition, the mammary epithelial tree of the alcohol-exposed offspring was denser (P<0.004) and contained more structures that are susceptible for the initiation of breast cancer (P<0.001). Immunohistochemical assessment indicated that the mammary glands of 22-week-old in utero alcohol-exposed rats contained elevated levels of oestrogen receptor-alpha (P<0.04) that is consistent with the changes in mammary gland morphology. In summary, maternal alcohol intake during pregnancy increases female offspring's mammary tumorigenesis, perhaps by programming the foetal mammary gland to exhibit persistent alterations in morphology and gene expression. It remains to be determined whether an increase in pregnancy oestradiol levels mediated alcohol's effects on offspring's mammary tumorigenesis.

Antiangiogenic and antitumor effects of a protein kinase Cbeta inhibitor in human breast cancer and ovarian cancer xenografts

In cell culture, the compound 317615 2HCl, a potent inhibitor of VEGF-stimulated HUVEC proliferation, was not very effective against MX-1 breast cancer cells (IC50= 8.1 microM) or SKOV-3 ovarian carcinoma cells (IC50 = 9.5 microM). Exposure to combinations of paclitaxel or carboplatin and 317615 x 2HCl with MX-1 cells in culture resulted in cell survival that reflected primarily additivity of the two agents. Exposure of SKOV-3 cells to paclitaxel or carboplatin along with 317615 2HCl resulted in cell survivals that reflected additivity of 317615 x 2HCl with paclitaxel and greater-than-additive cytotoxicity with carboplatin. Administration of 317615 x 2HCI orally twice daily to nude mice bearing subcutaneous MX-1 tumors or SKOV-3 tumors resulted in a decreased number of intratumoral vessels as determined by CD31 and CD105 staining with decreases of 35% and 43% in MX-1 tumors and 60% and 75% in SKOV-3 tumors, respectively. 317615 x 2HCl was an active antitumor agent against the MX-1 xenograft and increased the tumor growth delay produced by paclitaxel by 1.7-fold and the tumor growth delay produced by carboplatin by 3.8-fold. Administration of 317615 x 2HCl also increased the tumor growth delay produced by fractionated radiation therapy in the MX-1 tumor. Treatment with 317615 x 2HCl alone increased the lifespan of animals bearing intraperitoneal SKOV-3 xenografts by 1.9 fold compared with untreated control animals. The combination of paclitaxel and 317615 x 2HCl resulted in 100% 120-day survival of SKOV-3 bearing animals. Administration of 317615 x 2HCl along with carboplatin to animals bearing the SKOV-3 tumor produced a 1.8-fold increase in lifespan compared with carboplatin alone. 317615 x 2HCl is a promising new antiangiogenic agent that is in early phase clinical testing.

Opposing action of estrogen receptors alpha and beta on cyclin D1 gene expression

Induction of cyclin D1 gene transcription by estrogen receptor alpha (ERalpha) plays an important role in estrogen-mediated proliferation. There is no classical estrogen response element in the cyclin D1 promoter, and induction by ERalpha has been mapped to an alternative response element, a cyclic AMP-response element at -57, with possible participation of an activating protein-1 site at -954. The action of ERbeta at the cyclin D1 promoter is unknown, although evidence suggests that ERbeta may inhibit the proliferative action of ERalpha. We examined the response of cyclin D1 promoter constructs by luciferase assay and the response of the endogenous protein by Western blot in HeLa cells transiently expressing ERalpha, ERalphaK206A (a derivative that is superactive at alternative response elements), or ERbeta. In each case, ER activation at the cyclin D1 promoter is mediated by both the cyclic AMP-response element and the activating protein-1 site, which play partly redundant roles. The activation by ERbeta occurs only with antiestrogens. Estrogens, which activate cyclin D1 gene expression with ERalpha, inhibit expression with ERbeta. Strikingly, the presence of ERbeta completely inhibits cyclin D1 gene activation by estrogen and ERalpha or even by estrogen and the superactive ERalphaK206A. The observation of the opposing action and dominance of ERbeta over ERalpha in activation of cyclin D1 gene expression has implications for the postulated role of ERbeta as a modulator of the proliferative effects of estrogen.

Comparison of the effects of EM-652 (SCH57068), tamoxifen, toremifene, droloxifene, idoxifene, GW-5638 and raloxifene on the growth of human ZR-75-1 breast tumors in nude mice

EM-652 exerts pure antiestrogenic activity in the mammary gland and endometrium, while tamoxifen, the antiestrogen most widely used for the treatment of breast cancer, exerts mixed antiestrogenic-estrogenic activity in these tissues. Our objective was to compare the agonistic and antagonistic effects of EM-652 with tamoxifen and 5 other antiestrogens on the growth of ZR-75-1 human breast xenografts in ovariectomized nude mice. During the 23 weeks of treatment at a daily oral dose of 50 microg, EM-652 was the only compound that decreased tumor size relative to pretreatment values, whereas the 6 other antiestrogens only decreased to various extents the progression rate stimulated by estrone. Under estrone stimulation, all groups of animals had more than 60% of their tumors in the progression category except for the EM-652-treated group, where only 7% of the tumors progressed. In the absence of estrone stimulation, progression was seen in 60%, 33%, 21% and 12% of tumors in the tamoxifen-, idoxifene-, toremifene- and raloxifene-treated groups, respectively, while only 4% of tumors progressed in the EM-652-treated group. The agonistic and antagonistic actions of each antiestrogen were also measured on endometrial epithelial cell thickness. Our present findings indicate that EM-652, in addition to being the most potent antiestrogen on human breast tumor growth, has no agonistic effect in breast and endometrial tissues. Since previous data have shown benefits of EM-652 on bone density and lipid profile, this compound could be an ideal candidate for chemoprevention of breast and uterine cancers, while protecting against osteoporosis and cardiovascular disease.

Nuclear receptors in cell life and death

The balance between cell proliferation and programmed cell death (apoptosis) determines body patterns during animal development and controls compartment sizes, tissue architecture and remodeling. The removal of primordial structures by apoptosis allows the organism to develop sex specifically and to adapt for novel functions at later stages; apoptosis also limits the size of evolving structures. It is a ubiquitous function that is essential for all cells. Although inappropriate regulation or execution of apoptosis leads to disease, such as cancer, there is now evidence for its great therapeutic potential. This would be particularly true if apoptosis could be targeted at defined cell compartments, rather than acting ubiquitously like chemotherapy. Here, we discuss the potential of nuclear receptor ligands, many of which act through their cognate receptors in defined body compartments as modulators of cell life and death, with special emphasis on the molecular pathways by which these receptors affect cell-cycle progression, survival and apoptosis.