75504-34-6Relevant articles and documents
Potential beneficial metabolic interactions between tamoxifen and isoflavones via cytochrome P450-mediated pathways in female rat liver microsomes
Chen, Jun,Halls, Steven C.,Alfaro, Joshua F.,Zhou, Zhaohui,Hu, Ming
, p. 2095 - 2104 (2004)
Purpose. This study aims to evaluate a cytochrome P450-based tamoxifen-isoflavone interaction and to determine the mechanisms responsible for inhibitory effects of isoflavones (e.g., genistein) on the formation of α-hydroxytamoxifen. Methods. Metabolism studies were performed in vitro using female rat liver microsomes. The effects of genistein and an isoflavone mixture on tamoxifen metabolism and the inhibition mechanism were determined using standard kinetic analysis, preincubation, and selective chemical inhibitors of P450. Results. Metabolism of tamoxifen was saturable with K m values of 4.9 ± 0.6, 14.6 ± 2.2, 25 ± 5.9 μM and Vmax values of 34.7 ± 1.4, 297.5 ± 19.2, 1867 ± 231 pmol min-1 mg-1 for α-hydroxylation, N-desmethylation, and N-oxidation, respectively. Genistein (25 μM) inhibited α-hydroxylation at 2.5 μM tamoxifen by 64% (p A combination of three (genistein, daidzein, and glycitein) to five isoflavones (plus biochanin A and formononetin) inhibited tamoxifen α-hydroxylation to a greater extent but did not decrease the formation of identified metabolites. The inhibition on α-hydroxylation by genistein was mixed-typed with a Ki , value of 10.6 μM. Studies using selective chemical inhibitors showed that tamoxifen α-hydroxylation was mainly mediated by rat CYP1A2 and CYP3A1/2 and that genistein 3'-hydroxylation was mainly mediated by rat CYP1A2, CYP2C6 and CYP2D1. Conclusions. Genistein and its isoflavone analogs have the potential to decrease side effects of tamoxifen through metabolic interactions that inhibit the formation of α-hydroxytamoxifen via inhibition of CYP1A2.
Endoxifen and other metabolites of tamoxifen inhibit human hydroxysteroid sulfotransferase 2A1 (hSULT2A1)
Squirewell, Edwin J.,Qin, Xiaoyan,Duffel, Michael W.
, p. 1843 - 1850 (2014)
Although tamoxifen is a successful agent for treatment and prevention of estrogen-dependent breast cancer, its use has been limited by the low incidence of endometrial cancer. Human hydroxysteroid sulfotransferase 2A1 (hSULT2A1) catalyzes the formation of an a-sulfooxy metabolite of tamoxifen that is reactive toward DNA, and this has been implicated in its carcinogenicity. Also, hSULT2A1 functions in the metabolism of steroid hormones such as dehydroepiandrosterone (DHEA) and pregnenolone (PREG). These roles of hSULT2A1 in steroid hormone metabolism and in generating a reactive metabolite of tamoxifen led us to examine its interactions with tamoxifen and several of its major metabolites. We hypothesized that metabolites of tamoxifen may regulate the catalytic activity of hSULT2A1, either through direct inhibition or through serving as alternate substrates for the enzyme. We found that 4-hydroxy-N-desmethyltamoxifen (endoxifen) is a potent inhibitor of hSULT2A1-catalyzed sulfation of PREG and DHEA, with Kivalues of 3.5 and 2.8 μM, respectively. In the hSULT2A1-catalyzed sulfation of PREG, 4-hydroxytamoxifen (4-OHTAM) and N-desmethyltamoxifen (N-desTAM) exhibited Kivalues of 12.7 and 9.8 mM, respectively, whereas corresponding Kivalues of 19.4 and 17.2 μM were observed with DHEA as substrate. A Kivalue of 9.1 μM was observed for tamoxifen-N-oxide with DHEA as substrate, and this increased to 16.9 mM for the hSULT2A1-catalyzed sulfation of PREG. Three metabolites were substrates for hSULT2A1, with relative sulfation rates of 4-OHTAM > N-desTAM > > endoxifen. These results may be useful in interpreting ongoing clinical trials of endoxifen and in improving the design of related molecules. Copyright
Human flavin-containing monooxygenase 1 and its long-sought hydroperoxyflavin intermediate
Catucci, Gianluca,Cheropkina, Hanna,Fenoglio, Ivana,Gilardi, Gianfranco,Marucco, Arianna,Sadeghi, Sheila J.
, (2021/09/22)
Out of the five isoforms of human flavin-containing monooxygenase (hFMO), FMO1 and FMO3 are the most relevant to Phase I drug metabolism. They are involved in the oxygenation of xenobiotics including drugs and pesticides using NADPH and FAD as cofactors. Majority of the characterization of these enzymes has involved hFMO3, where intermediates of its catalytic cycle have been described. On the other hand, research efforts have so far failed in capturing the same key intermediate that is responsible for the monooxygenation activity of hFMO1. In this work we demonstrate spectrophotometrically the formation of a highly stable C4a-hydroperoxyflavin intermediate of hFMO1 upon reduction by NADPH and in the presence of O2. The measured half-life of this flavin intermediate revealed it to be stable and not fully re-oxidized even after 30 min at 15 °C in the absence of substrate, the highest stability ever observed for a human FMO. In addition, the uncoupling reactions of hFMO1 show that this enzyme is 2O2 with no observable superoxide as confirmed by EPR spin trapping experiments. This behaviour is different from hFMO3, that is shown to form both H2O2 and superoxide anion radical as a result of ～50% uncoupling. These data are consistent with the higher stability of the hFMO1 intermediate in comparison to hFMO3. Taken together, these data demonstrate the different behaviours of these two closely related enzymes with consequences for drug metabolism as well as possible toxicity due to reactive oxygen species.
Human flavin-containing monooxygenase 3 on graphene oxide for drug metabolism screening
Castrignanò, Silvia,Gilardi, Gianfranco,Sadeghi, Sheila J.
, p. 2974 - 2980 (2015/03/18)
Human flavin-containing monooxygenase 3 (hFMO3), a membrane-bound hepatic protein, belonging to the second most important class of phase-1 drug-metabolizing enzymes, was immobilized in its active form on graphene oxide (GO) for enhanced electrochemical response. To improve protein stabilization and to ensure the electrocatalytic activity of the immobilized enzyme, didodecyldimethylammonium bromide (DDAB) was used to mimic lipid layers of biological membranes and acted as an interface between GO nanomaterial and the hFMO3 biocomponent. Grazing angle attenuated total reflectance Fourier transform infrared (GATR-FT-IR) experiments confirmed the preservation of the protein secondary structure and fold. Electrochemical characterization of the immobilized enzyme with GO and DDAB on glassy carbon electrodes was carried out by cyclic voltammetry, where several parameters including redox potential, electron transfer rate, and surface coverage were determined. This systems biotechnological application in drug screening was successfully demonstrated by the N-oxidation of two therapeutic drugs, benzydamine (nonsteroidal anti-inflammatory) and tamoxifen (antiestrogenic widely used in breast cancer therapy and chemoprevention), by the immobilized enzyme.
Tamoxifen stimulates calcium entry into human platelets
Dobrydneva, Yuliya,Weatherman, Ross V.,Trebley, Joseph P.,Morrell, Melinda M.,Fitzgerald, Megan C.,Fichandler, Craig E.,Chatterjie, Nithiananda,Blackmore, Peter F.
, p. 380 - 390 (2008/03/12)
The anti-estrogenic drug tamoxifen, which is used therapeutically for treatment and prevention of breast cancer, can lead to the development of thrombosis. We found that tamoxifen rapidly increased intracellular free calcium [Ca]i in human platelets from
TREATMENT OF HYPERPROLIFERATIVE DISEASES WITH N-OXIDES OF ESTROGEN RECEPTOR MODULATORS
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Page/Page column 67-68, (2008/06/13)
The invention relates to N-oxides of tamoxifen analogs having activity for treating hyperproliferative disorders. Pharmaceutical compositions comprising therapeutically effective amount of an N-oxide of an estrogen receptor modulator, or a pharmaceuticall
