Selective estrogen receptor modulator

Selective estrogen receptor modulators (SERMs) are a class of drugs that act on the estrogen receptor (ER). A characteristic that distinguishes these substances from pure ER agonists and antagonists (that is, full agonists and silent antagonists) is that their action is different in various tissues, thereby granting the possibility to selectively inhibit or stimulate estrogen-like action in various tissues. Selective estrogen receptor modulators (SERMs) are a class of drugs that act on the estrogen receptor (ER). A characteristic that distinguishes these substances from pure ER agonists and antagonists (that is, full agonists and silent antagonists) is that their action is different in various tissues, thereby granting the possibility to selectively inhibit or stimulate estrogen-like action in various tissues. SERMs are used for various estrogen-related diseases, including treatment of ovulatory dysfunction in the management of infertility, treatment and prevention of postmenopausal osteoporosis, treatment and reduction in risk of breast cancer and treatment of dyspareunia due to menopause. SERM is also used in combination with conjugated estrogens indicated for the treatment of estrogen deficiency symptoms, and vasomotor symptoms associated with menopause. SERMs are used dependent on their pattern of action in various tissues: Tamoxifen is a first-line hormonal treatment of ER-positive metastatic breast cancer. It is used for breast cancer risk reduction in women at high risk, and as adjuvant treatment of axillary node-negative and node-positive, ductal carcinoma in situ. Tamoxifen treatment is also useful in the treatment of bone density and blood lipids in postmenopausal women. Adverse effects include hot flushes and more serious is two to three times higher relative risk of developing endometrial cancer compared to women of an age-matched population. Toremifene, a chlorinated tamoxifen derivative, causes fewer DNA adducts in liver than seen with tamoxifen in preclinical studies and was developed to avoid hepatic carcinomas. It is used as endocrine therapy in women with ER/PR-positive stage 4 or recurrent metastatic breast cancer and has demonstrated similar efficacy compared to tamoxifen as adjuvant treatment of breast cancer and in the treatment of metastatic breast cancer. Raloxifene is used for prevention and treatment of postmenopausal osteoporosis and breast cancer prevention in high-risk postmenopausal women with osteoporosis. Preclinical and clinical reports suggest that it is considerably less potent than estrogen for the treatment of osteoporosis. It is associated with an acceptable endometrial profile and has not demonstrated tamoxifen-like effects in the uterus but has been associated with adverse effects such as venous thromboembolism and vasomotor symptoms, including hot flushes. Ospemifene is an analogous metabolite of toremifene. Unlike tamoxifen, toremifene is not a rat hepatocarcinogen and therefore ospemifene would also be a safer SERM than tamoxifen. It is used for the treatment of moderate to severe dyspareunia, a symptom of vulvar and vaginal atrophy associated with menopause. Clinical data on breast cancer are not available, but both in vitro and in vivo data suggest that ospemifene may have chemopreventive activity in breast tissue. Bazedoxifene is used as treatment for osteoporosis in postmenopausal women at increased risk of fracture. It has been shown to be relatively safe and well tolerated. It shows no breast or endometrial stimulation and in the first two years, the small increase is better in venous thromboembolism, and similar in the long term to other SERMs. The advantage of bazedoxifene over raloxifene is that it increases endothelial nitric oxide synthase activity and does not antagonize the effect of 17β-estradiol on vasomotor symptoms. The first tissue selective estrogen complex (TSEC) combines conjugated estrogens and the SERM bazedoxifene to blend their activities. The combination therapy is used in the treatment of moderate to severe vasomotor symptoms associated with menopause, prevention of postmenopausal osteoporosis as well as treatment of estrogen deficiency symptoms in non-hysterectomized postmenopausal women. The combination allows for the benefits of estrogen with regard to relief of vasomotor symptoms without estrogenic stimulation of the endometrium. SERMs are competitive partial agonists of the ER. Different tissues have different degrees of sensitivity to the activity of endogenous estrogens, so SERMs produce estrogenic or antiestrogenic effects depending on the specific tissue in question as well as the percentage of intrinsic activity (IA) of the SERM. An example of a SERM with high IA and thus mostly estrogenic effects is chlorotrianisene, while an example of a SERM with low IA and thus mostly antiestrogenic effects is ethamoxytriphetol. SERMs like clomifene and tamoxifen are comparatively more in the middle in their IA and their balance of estrogenic and antiestrogenic activity. Raloxifene is a SERM that is more antiestrogenic than tamoxifen; both are estrogenic in bone, but raloxifene is antiestrogenic in the uterus while tamoxifen is estrogenic in this part of the body.