Yuanhuang Chen1, Lauren A Marcath2, Finn Magnus Eliassen3, Tone Hoel Lende3, Havard Soiland4,5, Gunnar Mellgren4,5, Thomas Helland1,4,5, Daniel Louis Hertz1. 1. Department of Clinical Pharmacy, University of Michigan College of Pharmacy, Ann Arbor, MI 48109-1065, USA. 2. Department of Pharmacotherapy, Washington State University College of Pharmacy & Pharmaceutical Sciences, Spokane, WA 99202, USA. 3. Department of Breast and Endocrine Surgery, Stavanger University Hospital, P.O. Box 8100, 4068 Stavanger, Norway. 4. Department of Clinical Science, University of Bergen, 5021 Bergen, Norway. 5. Hormone Laboratory, Department of Medical Biochemistry and Pharmacology, Haukeland University Hospital, 5021 Bergen, Norway.
Abstract
BACKGROUND: Tamoxifen, as a treatment of estrogen receptor positive (ER+) breast cancer, is a weak anti-estrogen that requires metabolic activation to form metabolites with higher anti-estrogenic activity. Endoxifen is the most-studied active tamoxifen metabolite, and endoxifen concentrations are highly associated with CYP2D6 activity. Associations of tamoxifen efficacy with measured or CYP2D6-predicted endoxifen concentrations have been inconclusive. Another active metabolite, 4-OHtam, and other, less active metabolites, Z-4'-endoxifen and Z-4'-OHtam, have also been reported to be associated with tamoxifen efficacy. METHOD: Genotype for 20 pharmacogenes was determined by VeriDose® Core Panel and VeriDose®CYP2D6 CNV Panel, followed by translation to metabolic activity phenotype following standard activity scoring. Concentrations of tamoxifen and seven metabolites were measured by UPLC-MS/MS in serum samples collected from patients receiving 20 mg tamoxifen per day. Metabolic activity was tested for association with tamoxifen and its metabolites using linear regression with adjustment for upstream metabolites to identify genes associated with each step in the tamoxifen metabolism pathway. RESULTS: A total of 187 patients with genetic and tamoxifen concentration data were included in the analysis. CYP2D6 was the primary gene associated with the tamoxifen metabolism pathway, especially the conversion of tamoxifen to endoxifen. CYP3A4 and CYP2C9 were also responsible for the metabolism of tamoxifen. CYP2C9 especially impacted the hydroxylation to 4-OHtam, and this involved the OATP1B1 (SLCO1B1) transporter. CONCLUSION: Multiple genes are involved in tamoxifen metabolism and multi-gene panels could be useful to predict active metabolite concentrations and guide tamoxifen dosing.
BACKGROUND:Tamoxifen, as a treatment of estrogen receptor positive (ER+) breast cancer, is a weak anti-estrogen that requires metabolic activation to form metabolites with higher anti-estrogenic activity. Endoxifen is the most-studied active tamoxifen metabolite, and endoxifen concentrations are highly associated with CYP2D6 activity. Associations of tamoxifen efficacy with measured or CYP2D6-predicted endoxifen concentrations have been inconclusive. Another active metabolite, 4-OHtam, and other, less active metabolites, Z-4'-endoxifen and Z-4'-OHtam, have also been reported to be associated with tamoxifen efficacy. METHOD: Genotype for 20 pharmacogenes was determined by VeriDose® Core Panel and VeriDose®CYP2D6 CNV Panel, followed by translation to metabolic activity phenotype following standard activity scoring. Concentrations of tamoxifen and seven metabolites were measured by UPLC-MS/MS in serum samples collected from patients receiving 20 mg tamoxifen per day. Metabolic activity was tested for association with tamoxifen and its metabolites using linear regression with adjustment for upstream metabolites to identify genes associated with each step in the tamoxifen metabolism pathway. RESULTS: A total of 187 patients with genetic and tamoxifen concentration data were included in the analysis. CYP2D6 was the primary gene associated with the tamoxifen metabolism pathway, especially the conversion of tamoxifen to endoxifen. CYP3A4 and CYP2C9 were also responsible for the metabolism of tamoxifen. CYP2C9 especially impacted the hydroxylation to 4-OHtam, and this involved the OATP1B1 (SLCO1B1) transporter. CONCLUSION: Multiple genes are involved in tamoxifen metabolism and multi-gene panels could be useful to predict active metabolite concentrations and guide tamoxifen dosing.
Entities:
Keywords:
CYP2C9; CYP2D6; CYP3A4; SLCO1B1; active metabolites; breast cancer; endoxifen; pharmacogenetics; tamoxifen
Authors: Keneuoe Cecilia Nthontho; Andrew Khulekani Ndlovu; Kirthana Sharma; Ishmael Kasvosve; Daniel Louis Hertz; Giacomo Maria Paganotti Journal: Pharmgenomics Pers Med Date: 2022-06-21