CYP3A4*22 is Related to Increased Plasma Levels of 4-Hydroxytamoxifen and Partially Compensates for Reduced CYP2D6 Activation of Tamoxifen

Abstract

Aim: To evaluate the impact of CYP3A4*22 in the formation of endoxifen (EDF) and hydroxytamoxifen (HTF), under different CYP2D6 genotypic backgrounds. Materials & methods: 178 patients were enrolled in the study. CYP2D6 and CYP3A4 genotyping and tamoxifen (TAM) and metabolites quantification were performed. Results: EDF concentrations were lower in poor (2.77 ng ml^-1) and CYP2D6 intermediate metabolizers (5.84 ng ml^-1), comparing to functional group (EM-F) (10.67 ng ml^-1, p < 0.001). HTF and TAM levels were respectively 47 and 53% higher in CYP3A4*22 carriers compared with *1/*1 patients in the whole group. Patients with impaired CYP2D6 metabolism and carriers of CYP3A4*22 had EDF levels comparable to CYP2D6 EM-F group (9.06 and 10.67 ng ml^-1, p = 0.247). Conclusion: The presence of CYP3A4*22 might compensate the reduction of EDF concentrations related to CYP2D6 inactivity, especially due to increased HTF concentrations.

Original submitted 19 November 2014; Revision submitted 21 January 2015

Keywords::

• 4-hydroxytamoxifen
• CYP3A4
• CYP2D6
• endoxifen
• genotype
• tamoxifen

Financial & competing interests disclosure

This work was supported by Fundo de Incentivo à Pesquisa e Eventos do Hospital de Clínicas de Porto Alegre (FIPE-HCPA), CNPq/FNRS (CNPq registry number 485013/2013-4) and FAPERGS (registry number 1255-2551/13-2) grants. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Ethical conduct of research

The authors state that they have obtained appropriate institutional review board approval or have followed the principles outlined in the Declaration of Helsinki for all human or animal experimental investigations. In addition, for investigations involving human subjects, informed consent has been obtained from the participants involved.

Additional information

Funding

This work was supported by Fundo de Incentivo à Pesquisa e Eventos do Hospital de Clínicas de Porto Alegre (FIPE-HCPA), National Council for Scientific and Technological Development (CNPq/FNRS) (CNPq registry number 485013/2013-4) and FAPERGS, Fundação De Amparo À Pesquisa Do Estado Do Rio Grande Do Su (registry number 1255-2551/13-2) grants. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. No writing assistance was utilized in the production of this manuscript.