Selective estrogen-receptor modulator

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Selective estrogen receptor modulators (SERMs) are a class of compounds that act on the estrogen receptor.1 A characteristic that distinguishes these substances from pure receptor agonists and 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. Phytoserms are SERMs from a botanical source.

Members and uses

Nolvadex (tamoxifen) 20-milligram tablets (UK)

SERMs are used dependent on their pattern of action in various tissues:

Name Uses Effects/location
clomifene used in anovulation antagonist at hypothalamus
femarelle managing menopause symptoms, osteoporosis agonist at brain and bone
ormeloxifene contraception agonist at bone; antagonist at breast and uterus
raloxifene osteoporosis, breast cancer agonist at bone; antagonist at breast and uterus
tamoxifen breast cancer agonist at bone and uterus, antagonist at breast
toremifene breast cancer
lasofoxifene osteoporosis, breast cancer, vaginal atrophy agonist at the bone, antagonist at breast and uterus
ospemifene vaginal atrophy, dysparunia agonist at the bone, antagonist at breast and uterus

Other members include afimoxifene, arzoxifene, and bazedoxifene.

Some SERMs may be good replacements for hormone replacement therapy (HRT), which had been commonly used to treat menopause symptoms until the publication of wide scale studies showing that HRT slightly increases the risk of breast cancer 2 and thrombosis.3 Some of the above agents still have significant side-effects that contraindicate widespread use.

Mechanism of action

Estrogenic compounds span a spectrum of activity ranging from:

  • full agonists (agonistic in all tissues) such as the natural endogenous hormone estrogen
  • mixed agonists/antagonistics (agonistic in some tissues while antagonist in others) such as tamoxifen (a SERM)
  • pure antagonists (antagonistic in all tissues) such as fulvestrant (ICI-182780).

The mechanism of mixed agonism/antagonism may differ depending on the chemical structure of the SERM, but, for at least for some SERMs, it appears to be related to (1) the ratio of co-activator to co-repressor proteins in different cell types and (2) the conformation of the estrogen receptor induced by drug binding, which in turn determines how strongly the drug/receptor complex recruits co-activators (resulting in an agonist response) relative to co-repressors (resulting in antagonism). For example, the prototypical SERM tamoxifen acts as an antagonist in breast and conversely an agonist in uterus. The concentration of steroid receptor co-activator 1 (SRC-1; NCOA1) is higher in uterus than in breast, therefore SERMs such as tamoxifen are more agonistic in uterus than in breast. In contrast, raloxifene behaves as an antagonist in both tissues. It appears that raloxifene more strongly recruits co-repressor proteins and consequently is still an antagonist in the uterus despite the higher concentration of co-activators relative to co-repressors.45

Actions

The actions of SERMs on various tissues:

See also

References

  1. ^ Riggs BL, Hartmann LC (2003). "Selective estrogen-receptor modulators -- mechanisms of action and application to clinical practice". N Engl J Med 348 (7): 618–29. doi:10.1056/NEJMc030651. PMID 12584371. 
  2. ^ Reeves GK, Beral V, Green J, Gathani T, Bull D (November 2006). "Hormonal therapy for menopause and breast-cancer risk by histological type: a cohort study and meta-analysis". Lancet Oncol. 7 (11): 910–8. doi:10.1016/S1470-2045(06)70911-1. PMID 17081916. 
  3. ^ Rossouw JE, Anderson GL, Prentice RL, LaCroix AZ, Kooperberg C, Stefanick ML, Jackson RD, Beresford SA, Howard BV, Johnson KC, Kotchen JM, Ockene J; Writing Group for the Women's Health Initiative Investigators (July 2002). "Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results From the Women's Health Initiative randomized controlled trial". JAMA 288 (3): 321–33. doi:10.1001/jama.288.3.321. PMID 12117397. 
  4. ^ Shang Y, Brown M (2002). "Molecular determinants for the tissue specificity of SERMs". Science 295 (5564): 2465–8. doi:10.1126/science.1068537. PMID 11923541. 
  5. ^ Smith CL, O'Malley BW (2004). "Coregulator function: a key to understanding tissue specificity of selective receptor modulators". Endocr Rev 25 (1): 45–71. doi:10.1210/er.2003-0023. PMID 14769827. 

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