16α-Hydroxyestrone

16α-Hydroxyestrone (16α-OH-E1), or hydroxyestrone, also known as estra-1,3,5(10)-triene-3,16α-diol-17-one, is an endogenous steroidal estrogen and a major metabolite of estrone, as well as an intermediate in the biosynthesis of estriol.^[1][2] It is a potent estrogen similarly to estrone, and it has been suggested that the ratio of 16α-hydroxyestrone to 2-hydroxyestrone, the latter being much less estrogenic in comparison and even antiestrogenic in the presence of more potent estrogens like estradiol, may be involved in the pathophysiology of breast cancer.^[1] Conversely, 16α-hydroxyestrone may help to protect against osteoporosis.^[1]

16α-Hydroxyestrone

Names
IUPAC name 3,16α-Dihydroxyestra-1,3,5(10)-trien-17-one
Systematic IUPAC name (2R,3aS,3bR,9bS,11aS)-2,7-Dihydroxy-11a-methyl-2,3,3a,3b,4,5,9b,10,11,11a-decahydro-1H-cyclopenta[a]phenanthren-1-one
Other names Hydroxyestrone; 16-Hydroxyestrone
Identifiers
CAS Number	566-76-7 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:776
ChemSpider	103012
ECHA InfoCard	100.164.941
PubChem CID	115116
UNII	JY611949JU Y
CompTox Dashboard (EPA)	DTXSID901047947
InChI InChI=1S/C18H22O3/c1-18-7-6-13-12-5-3-11(19)8-10(12)2-4-14(13)15(18)9-16(20)17(18)21/h3,5,8,13-16,19-20H,2,4,6-7,9H2,1H3/t13-,14-,15+,16-,18+/m1/s1
SMILES C[C@]12CC[C@H]3[C@H]([C@@H]1C[C@H](C2=O)O)CCC4=C3C=CC(=C4)O
Properties
Chemical formula	C18H22O3
Molar mass	286.371 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

In terms of relative binding affinity (RBA) for the rat uterine estrogen receptor, 16α-hydroxyestrone showed 2.8% of the affinity of estradiol.^[3] For comparison, estrone had 11% of the affinity and estriol had 10% of the affinity of estradiol.^[3] In contrast to other estrogens, the binding of 16α-hydroxyestrone to the estrogen receptor is reported to be covalent and irreversible.^[4][5][6][7] 16α-Hydroxyestrone has been reported to have 25% of the vaginal estrogenic potency of estradiol.^[3] The maximal uterotrophic and antigonadotropic effect of 16α-hydroxyestrone was equivalent to those of estradiol and estriol, indicating that 16α-hydroxyestrone is a fully effective estrogen.^[3][8] However, 16α-hydroxyestrone was much less potent than estradiol or estrone.^[8]

The C3 and C16α diacetate ester of 16α-hydroxyestrone, hydroxyestrone diacetate (brand names Colpoginon, Colpormon, Hormobion, and Hormocervix), has been marketed and used medically as an estrogen in Europe.^[9][10]

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Selected biological properties of endogenous estrogens in rats

Estrogen	ERTooltip Estrogen receptor RBATooltip relative binding affinity (%)	Uterine weight (%)	Uterotrophy	LHTooltip Luteinizing hormone levels (%)	SHBGTooltip Sex hormone-binding globulin RBATooltip relative binding affinity (%)
Control	–	100	–	100	–
Estradiol (E2)	100	506 ± 20	+++	12–19	100
Estrone (E1)	11 ± 8	490 ± 22	+++	?	20
Estriol (E3)	10 ± 4	468 ± 30	+++	8–18	3
Estetrol (E4)	0.5 ± 0.2	?	Inactive	?	1
17α-Estradiol	4.2 ± 0.8	?	?	?	?
2-Hydroxyestradiol	24 ± 7	285 ± 8	+b	31–61	28
2-Methoxyestradiol	0.05 ± 0.04	101	Inactive	?	130
4-Hydroxyestradiol	45 ± 12	?	?	?	?
4-Methoxyestradiol	1.3 ± 0.2	260	++	?	9
4-Fluoroestradiola	180 ± 43	?	+++	?	?
2-Hydroxyestrone	1.9 ± 0.8	130 ± 9	Inactive	110–142	8
2-Methoxyestrone	0.01 ± 0.00	103 ± 7	Inactive	95–100	120
4-Hydroxyestrone	11 ± 4	351	++	21–50	35
4-Methoxyestrone	0.13 ± 0.04	338	++	65–92	12
16α-Hydroxyestrone	2.8 ± 1.0	552 ± 42	+++	7–24	<0.5
2-Hydroxyestriol	0.9 ± 0.3	302	+b	?	?
2-Methoxyestriol	0.01 ± 0.00	?	Inactive	?	4
Notes: Values are mean ± SD or range. ER RBA = Relative binding affinity to estrogen receptors of rat uterine cytosol. Uterine weight = Percentage change in uterine wet weight of ovariectomized rats after 72 hours with continuous administration of 1 μg/hour via subcutaneously implanted osmotic pumps. LH levels = Luteinizing hormone levels relative to baseline of ovariectomized rats after 24 to 72 hours of continuous administration via subcutaneous implant. Footnotes: a = Synthetic (i.e., not endogenous). b = Atypical uterotrophic effect which plateaus within 48 hours (estradiol's uterotrophy continues linearly up to 72 hours). Sources: See template.

See also

• 2-Hydroxyestrone
• 2-Hydroxyestradiol
• 16β-Hydroxyestrone
• 16-Ketoestrone
• 16α-Hydroxydehydroepiandrosterone
• 16α-Hydroxyandrostenedione
• 15α-Hydroxydehydroepiandrosterone

References

1. Rakel D (2012). Integrative Medicine. Elsevier Health Sciences. pp. 338–339. ISBN 978-1-4377-1793-8.
2. Vitamins and Hormones. Academic Press. 7 September 2005. pp. 282–. ISBN 978-0-08-045978-3.
3. Fishman J, Martucci C (September 1980). "Biological properties of 16 alpha-hydroxyestrone: implications in estrogen physiology and pathophysiology". J. Clin. Endocrinol. Metab. 51 (3): 611–5. doi:10.1210/jcem-51-3-611. PMID 7190977.
4. Oettel M, Schillinger E (6 December 2012). Estrogens and Antiestrogens I: Physiology and Mechanisms of Action of Estrogens and Antiestrogens. Springer Science & Business Media. pp. 252–. ISBN 978-3-642-58616-3.
5. Swaneck GE, Fishman J (November 1988). "Covalent binding of the endogenous estrogen 16 alpha-hydroxyestrone to estradiol receptor in human breast cancer cells: characterization and intranuclear localization". Proc. Natl. Acad. Sci. U.S.A. 85 (21): 7831–5. Bibcode:1988PNAS...85.7831S. doi:10.1073/pnas.85.21.7831. PMC 282290. PMID 3186693.
6. Zhu BT, Conney AH (January 1998). "Functional role of estrogen metabolism in target cells: review and perspectives". Carcinogenesis. 19 (1): 1–27. doi:10.1093/carcin/19.1.1. PMID 9472688.
7. Kuhl H (2005). "Pharmacology of estrogens and progestogens: influence of different routes of administration" (PDF). Climacteric. 8 (Suppl 1): 3–63. doi:10.1080/13697130500148875. PMID 16112947. S2CID 24616324.
8. Velardo, Joseph Thomas (1964). "The Actions of Steroid Hormones on Estradiol-17β in Uterine Growth and Enzymorphology". Hormonal Steroids Biochemistry, Pharmacology, and Therapeutics. pp. 463–490. doi:10.1016/B978-0-12-395506-7.50065-0. ISBN 9780123955067.
9. Index Nominum 2000: International Drug Directory. Taylor & Francis. January 2000. pp. 1250–. ISBN 978-3-88763-075-1.
10. Muller NF, Dessing RP, European Society of Clinical Pharmacy (19 June 1998). European Drug Index: European Drug Registrations (Fourth ed.). CRC Press. pp. 289–. ISBN 978-3-7692-2114-5.