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- Title
Model‐Based Quantification of Impact of Genetic Polymorphisms and Co‐Medications on Pharmacokinetics of Tamoxifen and Six Metabolites in Breast Cancer.
- Authors
Puszkiel, Alicja; Arellano, Cécile; Vachoux, Christelle; Evrard, Alexandre; Le Morvan, Valérie; Boyer, Jean‐Christophe; Robert, Jacques; Delmas, Caroline; Dalenc, Florence; Debled, Marc; Venat‐Bouvet, Laurence; Jacot, William; Dohollou, Nadine; Bernard‐Marty, Chantal; Laharie‐Mineur, Hortense; Filleron, Thomas; Roché, Henri; Chatelut, Etienne; Thomas, Fabienne; White‐Koning, Melanie
- Abstract
Variations in clinical response to tamoxifen (TAM) may be related to polymorphic cytochromes P450 (CYPs) involved in forming its active metabolite endoxifen (ENDO). We developed a population pharmacokinetic (PopPK) model for tamoxifen and six metabolites to determine clinically relevant factors of ENDO exposure. Concentration‐time data for TAM and 6 metabolites come from a prospective, multicenter, 3‐year follow‐up study of adjuvant TAM (20 mg/day) in patients with breast cancer, with plasma samples drawn every 6 months, and genotypes for 63 genetic polymorphisms (PHACS study, NCT01127295). Concentration data for TAM and 6 metabolites from 928 patients (n = 27,433 concentrations) were analyzed simultaneously with a 7‐compartment PopPK model. CYP2D6 phenotype (poor metabolizer (PM), intermediate metabolizer (IM), normal metabolizer (NM), and ultra‐rapid metabolizer (UM)), CYP3A4*22, CYP2C19*2, and CYP2B6*6 genotypes, concomitant CYP2D6 inhibitors, age, and body weight had a significant impact on TAM metabolism. Formation of ENDO from N‐desmethyltamoxifen was decreased by 84% (relative standard error (RSE) = 14%) in PM patients and by 47% (RSE = 9%) in IM patients and increased in UM patients by 27% (RSE = 12%) compared with NM patients. Dose‐adjustment simulations support an increase from 20 mg/day to 40 and 80 mg/day in IM patients and PM patients, respectively, to reach ENDO levels similar to those in NM patients. However, when considering Antiestrogenic Activity Score (AAS), a dose increase to 60 mg/day in PM patients seems sufficient. This PopPK model can be used as a tool to predict ENDO levels or AAS according to the patient's CYP2D6 phenotype for TAM dose adaptation.
- Subjects
GENETIC polymorphisms; BREAST cancer; TAMOXIFEN; PHARMACOKINETICS; METABOLITES; ESTROGEN antagonists
- Publication
Clinical Pharmacology & Therapeutics, 2021, Vol 109, Issue 5, p1244
- ISSN
0009-9236
- Publication type
Article
- DOI
10.1002/cpt.2077