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Selective estrogen receptor modulator

Drugs & Medication

Selective estrogen receptor modulator

Raloxifene | Tamoxifen

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Selective estrogen receptor modulators (SERMs) is a class of medication that acts on the estrogen receptor. A characteristic that distinguishes these substances from receptor agonists and antagonists is that their action is different for various tissues, thereby granting the possibility to selectively inhibit or stimulate estrogen-like action in various tissues.

Contents

Members

Members are:

Uses

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

  • clomifene is used in anovulation
  • raloxifene is used for osteoporosis and is being studied as a breast cancer preventative
  • tamoxifen and toremifene are used for breast cancer
  • ormeloxifene is used for contraception

Some SERMs may be good replacements for hormone replacement therapy (HRT), which recent studies have called into question, although the above agents still have an unacceptably high risk of thrombosis and other side-effects to allow for widespread use.

Method of action

Although the SERMs have no immediate structural relationship with 17β-estradiol, they are stereochemically similar to this estrogen.

There are three types of estrogen receptors, which are intracellular: α (α homodimer), β (β homodimer) and αβ (α- and β-receptor heterodimer). Different tissues have more or less of each class. In turn, each SERM has more affinity to one and less to the other estrogen receptor isoform. The α-receptor is generally stimulatory, but the β-receptor may inhibit the α-isoform as well as suppressing transcription independently.

Genes activated or suppressed by estrogen receptors generally have an estrogen response element sequence in their promotor.

Some SERMs, through this process, also augment the transcription of coactivator molecules, which may be indispensable for their pharmacological action.

Actions

The actions of SERMs on various tissues:

  • Pituitary gland - clomifene blocks estrogen action, leading to an increase of follicle-stimulating hormone.
    Uterus - tamoxifen may increase endometrial carcinoma risk, but raloxifene does not. Data on toremifene and clomifene is insufficient.
    Breast - all SERMs decrease breast cancer risk, and tamoxifen is mainly used for its ability to inhibit growth in estrogen receptor-positive breast cancer.
    Deep venous thrombosis - the risk may be elevated in all SERMs.
    Cholesterol and triglycerides - levels respond favorably to SERMs.
    Bone turnover and postmenopausal osteoporosis respond favorably to SERMs.
    Hot flashes are increased by all SERMs.

References

  • Riggs BL, Hartmann LC. Selective estrogen-receptor modulators - mechanisms of action and application to clinical practice. N Engl J Med 2003;348:618-29. PMID 12584371.

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