|Synonyms||Oestetrol; E4; 15α-Hydroxyestriol; Estra-1,3,5(10)-triene-3,15α,16α,17β-tetrol; Donesta; Estelle|
|Biological half-life||28 hours|
|Chemical and physical data|
|Molar mass||304.38 g/mol|
|3D model (JSmol)|
Estetrol (E4), or oestetrol, is a weak estrogen steroid hormone which is found in detectable levels only during pregnancy. It is closely related to estriol, which is also a weak estrogen that is found in high quantities only during pregnancy. Along with estradiol (E2), estrone (E1), and estriol (E3), estetrol is a major estrogen in the body.
The data indicate that E4 may be suitable for use in several indications including hormonal contraception, menopausal hormone therapy (both hot flashes and vaginal atrophy), breast cancer, prostate cancer and osteoporosis. Estetrol is being developed as estrogenic component in the oral contraceptive pill (as estetrol/drospirenone) and for hormone replacement therapy by Mithra Pharmaceuticals (Belgium). Pantarhei Oncology B.V. (The Netherlands) is developing estetrol for the treatment of breast cancer and prostate cancer.
Estetrol is synthesized during pregnancy only in the fetal liver from estradiol (E2) and estriol (E3) by the two enzymes 15α- and 16α-hydroxylase. Alternatively, estetrol is synthesized with 15α-hydroxylation of 16α-hydroxy-DHEA sulfate as an intermediate step. It appears in maternal serum at around week 9 of pregnancy. After birth the neonatal liver rapidly loses its capacity to synthesize E4 because these two enzymes are no longer expressed.
Estetrol reaches the maternal circulation through the placenta and was already detected at nine weeks of pregnancy in maternal urine. During the second trimester of pregnancy high levels were found in maternal plasma, with steadily rising concentrations of unconjugated E4 to about 1 ng/mL (> 3 nmol/L) towards the end of pregnancy. So far the physiological function of E4 is unknown. The possible use of E4 as a marker for fetal well-being has been studied quite extensively. However, due to the large intra- and inter-individual variation of maternal E4 plasma levels during pregnancy this appeared not to be feasible.
E4 is an estrogen. Since 2001, it has been studied extensively as a medication. High oral absorption and bioavailability with a 2–3 hours elimination half-life in the rat has been established. In the human E4 showed a high and dose-proportional oral bioavailability and a long terminal elimination half-life of about 28 hours.
Results from in vitro studies showed that E4 binds highly selective to the estrogen receptors with preference for the ERα form of the receptor unlike ethinylestradiol and estradiol. Also in contrast with E2, E4 does not bind to sex hormone-binding globulin (SHBG), and unlike ethinylestradiol, does not stimulate the hepatic production of SHBG in vitro.
The properties of E4 have also been investigated in a series of highly predictive, well validated pharmacological in vivo rat models. In these models, E4 exhibited estrogenic effects on the vagina, the uterus (both myometrium and endometrium), body weight, bone mass, bone strength, hot flushes and on ovulation (inhibition). All these effects of E4 were dose-dependent with maximal effects at comparable dose levels. Surprisingly, E4 prevented tumour development in a DMBA mammary tumour model to an extent and at a dose level similar to the anti-estrogen tamoxifen and to ovariectomy. This anti-estrogenic effect of E4 in the presence of E2 has also been observed in in vitro studies using human breast cancer cells.
Estetrol, also known as 15α-hydroxyestriol or as estra-1,3,5(10)-triene-3,15α,16α,17β-tetrol, is a naturally occurring estrane steroid and derivative of estrin (estratriene). It has four hydroxyl groups, which explains the abbreviation E4.
- List of investigational hormonal agents § Estrogenics
- List of investigational sexual dysfunction drugs
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