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Antiestrogens--tamoxifen, SERMs and beyond
1Hoffman-La Roche Inc., Nutley, NJ 07110, USA.
Abstract:
Estrogens play a central role in reproductive physiology. The cellular effects of estrogens are mediated by binding to nuclear receptors (ER) which activate transcription of genes involved in cellular growth control. At least two such receptors, designated ERalpha and ERbeta, mediate these effects in conjunction with a number of coactivators. These receptors can directly interact with other members of the steroid receptor superfamily. A complex cross-talk exists between the estrogen-signaling pathways and the downstream signaling events initiated by growth factors, such as epidermal growth factor and insulin-like growth factors. Estrogens are also a causative factor in the pathogenesis of a variety of neoplastic and non-neoplastic diseases, including breast cancer, endometrial cancer, endometriosis, and uterine fibroids, among others. Antiestrogens, such as tamoxifen, are widely used for the treatment of breast cancer. Tamoxifen produces objective tumor shrinkage in advanced breast cancer, reduces the risk of relapse in women treated for invasive breast cancer, and prevents breast cancer in high-risk women. Although, initially developed as an antiestrogen, tamoxifen can also prevent postmenopausal osteoporosis as well as reduce cholesterol, due to its estrogen-agonist effects. Its estrogen-agonist activity, however, can lead to significant side-effects such as endometrial cancer and thromboembolic phenomena. This has led to the concept of "ideal" selective estrogen receptor modulators (SERMs), drugs that would have the desired, tissue selective, estrogen-agonist or -antagonist effects. Raloxifene is a SERM which has the desirable mixed agonist/antagonist effects of tamoxifen but does not cause uterine stimulation. "Pure" antiestrogens may provide very potent estrogen-antagonist drugs, but are likely to be devoid of beneficial effects on bone and lipids. Future drug development efforts should focus on developing superior SERMs that have a greater efficacy against ER-positive tumors and do not cause hot flashes or thromboembolism, and explore combination strategies to simultaneously target hormone-dependent as well as hormone-independent breast cancer.
Insights
Estrogen receptors (ER) regulate cell growth and are implicated in diseases like breast cancer. Selective estrogen receptor modulators (SERMs) offer targeted therapies with potential for improved efficacy and reduced side effects.
Area of Science:
- Endocrinology
- Molecular Biology
- Oncology
Background:
- Estrogens are key regulators of reproductive physiology, mediating cellular effects via nuclear receptors (ERalpha and ERbeta).
- Estrogen signaling pathways interact with growth factor pathways, influencing cellular growth and disease pathogenesis.
- Estrogens are implicated in various neoplastic and non-neoplastic diseases, including breast and endometrial cancers.
Purpose of the Study:
- To review the role of estrogen receptors in cellular growth and disease.
- To discuss the therapeutic applications and limitations of antiestrogens and selective estrogen receptor modulators (SERMs).
- To highlight future directions in developing novel SERMs for breast cancer treatment.
Main Methods:
- Literature review of estrogen receptor function, signaling pathways, and therapeutic agents.
- Analysis of the mechanisms of action for antiestrogens like tamoxifen.
- Evaluation of the properties and clinical potential of SERMs such as raloxifene.
Main Results:
- Tamoxifen, an antiestrogen, shows efficacy in breast cancer treatment but possesses both agonist and antagonist effects, leading to side effects.
- Selective Estrogen Receptor Modulators (SERMs) aim to provide tissue-specific estrogenic effects, balancing therapeutic benefits with reduced adverse events.
- Raloxifene is a SERM with mixed agonist/antagonist effects, offering benefits without uterine stimulation.
Conclusions:
- SERMs represent a significant advancement in targeting estrogen-dependent conditions, particularly breast cancer.
- Future research should focus on developing superior SERMs with enhanced efficacy and fewer side effects, such as hot flashes and thromboembolism.
- Combination therapies targeting both hormone-dependent and independent pathways are crucial for comprehensive breast cancer management.