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Circadian variation in tamoxifen pharmacokinetics in mice and breast cancer patients.

ABSTRACT: The anti-estrogen tamoxifen is characterized by a large variability in response, partly due to pharmacokinetic differences. We examined circadian variation in tamoxifen pharmacokinetics in mice and breast cancer patients. Pharmacokinetic analysis was performed in mice, dosed at six different times (24-h period). Tissue samples were used for mRNA expression analysis of drug-metabolizing enzymes. In patients, a cross-over study was performed. During three 24-h periods, after tamoxifen dosing at 8 a.m., 1 p.m., and 8 p.m., for at least 4 weeks, blood samples were collected for pharmacokinetic measurements. Differences in tamoxifen pharmacokinetics between administration times were assessed. The mRNA expression of drug-metabolizing enzymes showed circadian variation in mouse tissues. Tamoxifen exposure seemed to be highest after administration at midnight. In humans, marginal differences were observed in pharmacokinetic parameters between morning and evening administration. Tamoxifen C(max )and area under the curve (AUC)0-8 h were 20 % higher (P < 0.001), and tamoxifen t(max) was shorter (2.1 vs. 8.1 h; P = 0.001), indicating variation in absorption. Systemic exposure (AUC0-24 h) to endoxifen was 15 % higher (P < 0.001) following morning administration. The results suggest that dosing time is of marginal influence on tamoxifen pharmacokinetics. Our study was not designed to detect potential changes in clinical outcome or toxicity, based on a difference in the time of administration. Circadian rhythm may be one of the many determinants of the interpatient and intrapatient pharmacokinetic variability of tamoxifen.

SUBMITTER: Binkhorst L

PROVIDER: S-EPMC4469299 | biostudies-literature | 2015 Jul

REPOSITORIES: biostudies-literature

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Circadian variation in tamoxifen pharmacokinetics in mice and breast cancer patients.

Binkhorst Lisette L Kloth Jacqueline S L JSL de Wit Annelieke S AS de Bruijn Peter P Lam Mei H MH Chaves Ines I Burger Herman H van Alphen Robbert J RJ Hamberg Paul P van Schaik Ron H N RHN Jager Agnes A Koch Birgit C P BCP Wiemer Erik A C EAC van Gelder Teun T van der Horst Gijsbertus T J GTJ Mathijssen Ron H J RHJ

Breast cancer research and treatment 20150607 1

The anti-estrogen tamoxifen is characterized by a large variability in response, partly due to pharmacokinetic differences. We examined circadian variation in tamoxifen pharmacokinetics in mice and breast cancer patients. Pharmacokinetic analysis was performed in mice, dosed at six different times (24-h period). Tissue samples were used for mRNA expression analysis of drug-metabolizing enzymes. In patients, a cross-over study was performed. During three 24-h periods, after tamoxifen dosing at 8 ...[more]

PMID: 26050156

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Project description:BACKGROUND:Tamoxifen is considered a prodrug of its active metabolite endoxifen, which is dependent on the CYP2D6 and CYP3A enzymes. Tamoxifen pharmacokinetic variability influences endoxifen exposure and, consequently, its clinical outcome. This study investigated the impact of hormonal status on the pharmacokinetics of tamoxifen and its metabolites in TAM-treated breast cancer patients. METHODS:TAM-treated breast cancer patients (n?=?40) previously believed to have CYP3A activity within the normal range based on oral midazolam and phenotyped as CYP2D6 normal metabolizers using oral metoprolol were divided into two groups according to premenopausal (n?=?20; aged 35-50?years) or postmenopausal (n?=?20; aged 60-79?years) status. All patients were treated with 20?mg/day tamoxifen for at least three months. Serial plasma samples were collected within the 24?h dose interval for analysis of unchanged tamoxifen, endoxifen, 4-hydroxytamoxifen and N-desmethyltamoxifen quantified by LC-MS/MS. CYP activities were assessed using midazolam apparent clearance (CYP3A) and the metoprolol/alfa-hydroxymetoprolol plasma metabolic ratio (CYP2D6). CYP3A4, CYP3A5 and CYP2D6 SNPs and copy number variation were investigated using TaqMan assays. RESULTS:Postmenopausal status increased steady-state plasma concentrations (Css) of tamoxifen (116.95 vs 201.23?ng/mL), endoxifen (8.01 vs 18.87?ng/mL), N-desmethyltamoxifen (485.16 vs 843.88?ng/mL) and 4-hydroxytamoxifen (2.67 vs 4.11?ng/mL). The final regression models included hormonal status as the only predictor for Css of tamoxifen [?-coef ± SE, p-value (75.03?±?17.71, p?=?0.0001)] and 4-hydroxytamoxifen (1.7822?±?0.4385, p?=?0.0002), while endoxifen Css included hormonal status (8.578?±?3.402, p?=?0.02) and race (11.945?±?2.836, p?=?0.007). For N-desmethyltamoxifen Css, the final model was correlated with hormonal status (286.259?±?76.766, p?=?0.0007) and weight (-?8.585?±?3.060, p?=?0.008). CONCLUSION:The premenopausal status was associated with decreased endoxifen plasma concentrations by 135% compared to postmenopausal status. Thus, the endoxifen plasma concentrations should be monitored mainly in the premenopausal period to maintain plasma levels above the efficacy threshold value. TRIAL REGISTRATION:RBR-7tqc7k.

Dataset Information

Circadian variation in tamoxifen pharmacokinetics in mice and breast cancer patients.

Publications

Circadian variation in tamoxifen pharmacokinetics in mice and breast cancer patients.

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