Characterization of the Human Cytochrome P450 Forms Involved in Metabolism of Tamoxifen to Its α-Hydroxy and α,4-Dihydroxy Derivatives

Notley, L.; Crewe, K; Taylor, Paul J.; Lennard, M. S.; Gillam, Elizabeth M. J.

doi:10.1021/tx050140s

Cited by 35 publications

(23 citation statements)

References 37 publications

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“…In conclusion, assessment of the kinetics of tamoxifen metabolism by expressed P450 enzymes suggest that tamoxifen ␣-hydroxylation is mediated primarily by CYP3A4, whereas tamoxifen N-demethylation is efficiently mediated by both CYP3A4 and CYP3A5. These findings corroborate previously published findings (Crewe et al, 1997;Desta et al, 2004;Notley et al, 2005). More importantly, our assessment using genotyped HLM strongly suggests that polymorphic expression of CYP3A5 significantly affects the in vitro clearance values for N-DMT formation but not ␣-OHT formation.…”

Section: Discussionsupporting

confidence: 92%

“…N-DMT is further hydroxylated by CYP2D6 to form endoxifen, which is a considerably more potent antiestrogen than TAM (Desta et al, 2004;Lim et al, 2006). Several earlier studies identified the role of CYP3A4 in the formation of N-DMT and ␣-OHT (Crewe et al, 1997;Desta et al, 2004;Notley et al, 2005). ␣-OHT is further activated by sulfotransferases to form an electrophilic carbocation that is capable of reacting with DNA.…”

Section: Introductionmentioning

confidence: 99%

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Assessment of the Impact of CYP3A Polymorphisms on the Formation of α-Hydroxytamoxifen and N-Desmethyltamoxifen in Human Liver Microsomes

Mugundu

Sallans²,

Guo³

et al. 2011

Drug Metab Dispos

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ABSTRACT:Tamoxifen, an antiestrogen used in the prevention and treatment of breast cancer, is extensively metabolized by cytochrome P450 enzymes. Its biotransformation to ␣-hydroxytamoxifen (␣-OHT), which may be genotoxic, and to N-desmethyltamoxifen (N-DMT), which is partially hydroxylated to 4-hydroxy-N-DMT (endoxifen), a potent antiestrogen, is mediated by CYP3A enzymes. However, the potential contribution of CYP3A5 and the impact of its low-expression variants on the formation of these metabolites are not clear. Therefore, we assessed the contributions of CYP3A4 and CYP3A5 and examined the impact of CYP3A5 genotypes on the formation of ␣-OHT and N-DMT, by using recombinant CYP3A4 and CYP3A5 and human liver microsomes (HLM) genotyped for CYP3A5 variants. We observed that the catalytic efficiency [intrinsic clearance (CL int )] for ␣-OHT formation with recombinant CYP3A4 was 5-fold higher than that with recombinant CYP3A5 (0.81 versus 0.16 nl ⅐ min ؊1 ⅐ pmol cytochrome P450 ؊1). There was no significant difference in CL int values between the three CYP3A5-genotyped HLM (*1/*1, *1/*3, and *3/*3). For N-DMT formation, the CL int with recombinant CYP3A4 was only 1.7-fold higher, relative to that with recombinant CYP3A5. In addition, the CL int for N-DMT formation by HLM with CYP3A5*3/*3 alleles was approximately 3-fold lower than that for HLM expressing CYP3A5*1/*1. Regression analyses of tamoxifen metabolism with respect to testosterone 6␤-hydroxylation facilitated assessment of CYP3A5 contributions to the formation of the two metabolites. The CYP3A5 contributions to ␣-OHT formation were negligible, whereas the contributions to N-DMT formation ranged from 51 to 61%. Our findings suggest that polymorphic CYP3A5 expression may affect the formation of N-DMT but not that of ␣-OHT.

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Section: Discussionsupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Assessment of the Impact of CYP3A Polymorphisms on the Formation of α-Hydroxytamoxifen and N-Desmethyltamoxifen in Human Liver Microsomes

Mugundu

Sallans²,

Guo³

et al. 2011

Drug Metab Dispos

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“…The latter strongly inhibited CYP3A4 while also being metabolized by it. However, there are few reports about the inhibition of specific P450 isoenzymes by antitumor agents, eg, by thiotepa [42,43] , tamoxifen [44,45] and the less well-known sorafenib [46] . Our results showed that cytochrome P450 CYP3A4 did not metabolize C-1311 in cells, confirming our hypothesis that overexpression of this enzyme might modulate the cellular response of CHO cells following C-1311 treatment, even though CYP3A4 does not participate in metabolic transformations.…”

Section: Discussionmentioning

confidence: 99%

CYP3A4 overexpression enhances apoptosis induced by anticancer agent imidazoacridinone C-1311, but does not change the metabolism of C-1311 in CHO cells

2013

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Aim: To examine whether CYP3A4 overexpression influences the metabolism of anticancer agent imidazoacridinone C-1311 in CHO cells and the responses of the cells to C-1311. Methods: Wild type CHO cells (CHO-WT), CHO cells overexpressing cytochrome P450 reductase (CPR) [CHO-HR] and CHO cells coexpressing CPR and CYP3A4 (CHO-HR-3A4) were used. Metabolic transformation of C-1311 and CYP3A4 activity were measured using RP-HPLC. Flow cytometry analyses were used to examine cell cycle, caspase-3 activity and cell apoptosis. The expression of pH 6.0-dependent β-galactosidase (SA-β-gal) was studied to evaluate accelerated senescence. ROS generation was analyzed with CM-H 2 DCFDA staining. Results: CYP3A4 overexpression did not change the metabolism of C-1311 in CHO cells: the levels of all metabolites of C-1311 increased with the exposure time to a similar extent, and the differences in the peak level of the main metabolite M3 were statistically insignificant among the three CHO cell lines. In CHO-HR-3A4 cells, C-1311 effectively inhibited CYP3A4 activity without affecting CYP3A4 protein level. In the presence of C-1311, CHO-WT cells underwent rather stable G 2 /M arrest, while the two types of transfected cells only transiently accumulated at this phase. C-1311-induced apoptosis and necrosis in the two types of transfected cells occurred with a significantly faster speed and to a greater extent than in CHO-WT cells. Additionally, C-1311 induced ROS generation in the two types of transfected cells, but not in CHO-WT cells. Moreover, CHO-HR-3A4 cells that did not die underwent accelerated senescence. Conclusion: CYP3A4 overexpression in CHO cells enhances apoptosis induced by C-1311, whereas the metabolism of C-1311 is minimal and does not depend on CYP3A4 expression.

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“…These results might have a strong impact on the drug-drug interaction in multidrug therapy because C-1311 was applied in phase II clinical trials with anthracyclines (Capizzi et al, 2008) and will be used with other therapeutic agents. Until now the inhibition of selected P450 isoenzymes was reported just for a few antitumor agents, e.g., thiotepa (Jacobson et al, 2002;Richter et al, 2005) and tamoxifen (Sridar et al, 2002;Notley et al, 2005). Other drugs delivered more examples, for instance, carbamazepine (Pearce et al, 2005(Pearce et al, , 2008 or 17␣-ethynylestradiol (Lin et al, 2002).…”

Section: Discussionmentioning

confidence: 99%

The Imidazoacridinone Antitumor Drug, C-1311, Is Metabolized by Flavin Monooxygenases but Not by Cytochrome P450s

Potęga

Dabrowska²,

Niemira³

et al. 2011

Drug Metab Dispos

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ABSTRACT:5-Diethylaminoethylamino-8-hydroxyimidazoacridinone (C-1311) is an antitumor agent that is also active against autoimmune diseases. The intention of the present studies was to elucidate the role of selected liver enzymes in metabolism of C-1311 and the less active 8-methyl derivative, 5-diethylaminoethylamino-8-methoxyimidazoacridinone (C-1330). Compounds were incubated with rat liver microsomal fraction, with a set of 16 human liver protein samples, and with human recombinant isoenzymes of cytochrome P450, flavin monooxygenases (FMO), and UDPglucuronosyltransferase (UGT). Our results showed that C-1311 and C-1330 were metabolized with human liver microsomal enzymes but not with any tested human recombinant cytochromes P450 (P450s). Two of these, CYP1A2 and CYP3A4, were inhibited by both compounds. In addition, results of C-1311 elimination from hepatic reductase-null mice, in which liver NADPH-P450 oxidoreductase has been deleted indicated that liver P450s were slightly engaged in drug transformation. In contrast, both compounds were good substrates for human recombinant FMO1 and FMO3 but not for FMO5. The product of FMO metabolism, P FMO , which is identified as an N-oxide derivative, was identical to P3 R of liver microsomes. P3 R was observed even in the presence of the P450 inhibitor, 1-aminobenzotriazole, and it disappeared after heating. Therefore, FMO enzymes could be responsible for microsomal metabolism to P3 R ‫؍‬ P FMO . Glucuronidation on the 8-hydroxyl group of C-1311 was observed with liver microsomes supported by UDP-glucuronic acid and with recombinant UGT1A1, but it was not the case with UGT2B7. Summing up, we showed that, whereas liver P450 isoenzymes were involved in the metabolism of C-1311 to a limited extent, FMO plays a significant role in the microsomal transformations of this compound, which is also a specific substrate of UGT1A1.

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Characterization of the Human Cytochrome P450 Forms Involved in Metabolism of Tamoxifen to Its α-Hydroxy and α,4-Dihydroxy Derivatives

Cited by 35 publications

References 37 publications

Assessment of the Impact of CYP3A Polymorphisms on the Formation of α-Hydroxytamoxifen and N-Desmethyltamoxifen in Human Liver Microsomes

Assessment of the Impact of CYP3A Polymorphisms on the Formation of α-Hydroxytamoxifen and N-Desmethyltamoxifen in Human Liver Microsomes

CYP3A4 overexpression enhances apoptosis induced by anticancer agent imidazoacridinone C-1311, but does not change the metabolism of C-1311 in CHO cells

The Imidazoacridinone Antitumor Drug, C-1311, Is Metabolized by Flavin Monooxygenases but Not by Cytochrome P450s

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