(Z)-4-Hydroxytamoxifen

Estrogen receptors (ER) are members of the superfamily of ligand-modulated nuclear receptors that mediate the actions of steroid hormones, vitamin D, retinoids, and thyroid hormones. ER is activated in vivo when bound by naturally occurring estrogens such as 17α-estradiol. In addition to regulating these physiological processes, estrogen also plays a central role in stimulating breast cancer growth. (Z)-Tamoxifen is a first generation selective ER modulators that is currently approved by the FDA and is widely used to treat estrogen-dependent breast cancers. Its active metabolite, (Z)-4-Hydroxytamoxifen, is a potent estrogen receptor modulator.

In vitro: (Z)-4-hydroxytamoxifen binds to ER with 8-fold higher affinity than tamoxifen. It was found that only the Z isomer has the required antiestrogenic activity; the (E)-4-hydroxytamoxifen has only about 5% of its affinity for the ER [1].

In vivo: The antioestrogenic activities of (Z)-4-hydroxytamoxifen and tamoxifen were determined after oral administration. (Z)-4-hydroxytamoxifen was administered to groups of immature rats which also received s.c. injections of 0-2 μg oestradiol. Both compounds produced a dose-related decrease in uterine wet weight when compared with the oestradiol-treated controls. At a dose of 1 μg/day, the antiuterotrophic effects of (Z)-4-hydroxytamoxifen and tamoxifen were not significantly different but at 5μg/day, (Z)-4-hydroxytamoxifen was more active (P < 0.01). (Z)-4-hydroxytamoxifen therefore appears to retain its potent antioestrogenic activity after oral administration [2].

Clinical trial: Up to now, (Z)-4-Hydroxytamoxifen is still in the preclinical development stage.

Reference:
[1] Donna D.  Yu and Barry M. Forman. Simple and Efficient Production of (Z)-4-Hydroxytamoxifen, a Potent Estrogen Receptor Modulator. J. Org. Chem. 2003, 68, 9489-9491
[2] Jordan VC, Collins MM, Rowsby L, Prestwich G.  A monohydroxylated metabolite of tamoxifen with potent antioestrogenic activity. J Endocrinol. 1977 Nov;75(2):305-16.

Synthesis of (Z)-4-hydroxytamoxifen and (Z)-2-[4-[1-(p-hydroxyphenyl)-2-phenyl]-1butenyl]phenoxyacetic acid.[Pubmed:12076167]

J Org Chem. 2002 Jun 28;67(13):4608-11.

The synthesis of (Z)-4-Hydroxytamoxifen and (Z)-2-[4-[1-(p-hydroxyphenyl)-2-phenyl]-1-butenyl]phenoxyacetic acid was accomplished using a McMurry reaction as the key step. The perfluorotolyl derivatives of the McMurry products enabled the separation of the minor undesirable geometrical isomer. The methodology proceeds without E,Z isomerization, employs a very mild final debenzylation step compatible with a large array of functional groups, and can be applied to the generation of a variety of 4-hydroxytamoxifen analogues.

Simple and efficient production of (Z)-4-hydroxytamoxifen, a potent estrogen receptor modulator.[Pubmed:14629178]

J Org Chem. 2003 Nov 28;68(24):9489-91.

A McMurry coupling reaction and selective crystallization were used to develop a simple and efficient two-step synthesis of (Z)-4-Hydroxytamoxifen (2a). This compound is an active metabolite of tamoxifen, a selective estrogen receptor (ER) modulator widely used to treat breast cancer. The synthesis employed 1,1-bis(4-hydroxyphenyl)-2-phenylbut-1-ene (1) as a useful building block.

Synthesis and sulfatase inhibitory activities of (E)- and (Z)-4-hydroxytamoxifen sulfamates.[Pubmed:10021916]

Bioorg Med Chem Lett. 1999 Jan 18;9(2):141-4.

We report the development of (E)- and (Z)-4-Hydroxytamoxifen sulfamates as estrone sulfatase inhibitors, potential therapeutic agents for the treatment of breast cancer. Both compounds competitively inhibit estrone sulfatase isolated from rat liver with apparent Ki of 35.9 microM for (E)-4-hydroxytamoxifen sulfamate and an apparent Ki of > 500 microM for the (Z) isomer.

Small molecule-triggered Cas9 protein with improved genome-editing specificity.[Pubmed:25848930]

Nat Chem Biol. 2015 May;11(5):316-8.

Directly modulating the activity of genome-editing proteins has the potential to increase their specificity by reducing activity following target locus modification. We developed Cas9 nucleases that are activated by the presence of a cell-permeable small molecule by inserting an evolved 4-hydroxytamoxifen-responsive intein at specific positions in Cas9. In human cells, conditionally active Cas9s modify target genomic sites with up to 25-fold higher specificity than wild-type Cas9.

Comprehensive evaluation of tamoxifen sequential biotransformation by the human cytochrome P450 system in vitro: prominent roles for CYP3A and CYP2D6.[Pubmed:15159443]

J Pharmacol Exp Ther. 2004 Sep;310(3):1062-75.

We performed comprehensive kinetic, inhibition, and correlation analyses in human liver microsomes and experiments in expressed human cytochromes P450 (P450s) to identify primary and secondary metabolic routes of tamoxifen (TAM) and the P450s catalyzing these reactions at therapeutically relevant concentrations. N-Desmethyl-TAM formation catalyzed by CYP3A4/5 was quantitatively the major primary metabolite of TAM; 4-hydroxy-TAM formation catalyzed by CYP2D6 (and other P450s) represents a minor route. Other minor primary metabolites include alpha -, 3-, and 4'-hydroxyTAM and one unidentified metabolite (M-I) and were primarily catalyzed by CYP3A4, CYP3A5, CYP2B6/2C19, and CYP3A4, respectively. TAM secondary metabolism was examined using N-desmethyl- and 4-hydroxy-TAM as intermediate substrates. N-Desmethyl-TAM was predominantly biotransformed to alpha-hydroxy N-desmethyl-, N-didesmethyl-, and 4-hydroxy N-desmethyl-TAM (endoxifen), whereas 4-hydroxy-TAM was converted to 3,4-dihydroxyTAM and endoxifen. Except for the biotransformation of N-desmethyl-TAM to endoxifen, which was exclusively catalyzed by CYP2D6, all other routes of N-desmethyl- and 4-hydroxy-TAM biotransformation were catalyzed predominantly by the CYP3A subfamily. TAM and its primary metabolites undergo extensive oxidation, principally by CYP3A and CYP2D6 to metabolites that exhibit a range of pharmacological effects. Variable activity of these P450s, brought about by genetic polymorphisms and drug interactions, may alter the balance of TAM effects in vivo.

A monohydroxylated metabolite of tamoxifen with potent antioestrogenic activity.[Pubmed:591813]

J Endocrinol. 1977 Nov;75(2):305-16.

The oestrogenic and antioestrogenic properties of tamoxifen and its monohydroxylated (monohydroxytamoxifen) and dihydroxylated (dihydroxytamoxifen) metabolites have been investigated in the immature rat. Whether administered orally or subcutaneously, monohydroxytamoxifen was more active than tamoxifen as an antioestrogen. Dihydroxytamoxifen was less active than tamoxifen as an antioestrogen, but this derivative alone was unable to induce a uterotrophic response. Both metabolites of tamoxifen were potent inhibitors of the binding of [3H]oestradiol to oestrogen receptors in vitro. It is possible that the metabolites play a supportive role in the antioestrogenic activity of tamoxifen. The potent activity of monohydroxytamoxifen in vivo and in vitro suggests that this compound could be an important new tool for the subcellular investigation of oestrogenic and antioestrogenic events.