Int J Med Sci. 2013 May 27;10(7):932-7.

Influence of CYP2D6 Polymorphisms on Serum Levels of Tamoxifen Metabolites in Spanish Women with Breast Cancer.

Mercedes Zafra-Ceres1, Tomas de Haro1, Esther Farez-Vidal2, Isabel Blancas3, Fernando Bandres4, Eduardo Martinez de Dueñas5, Enrique Ochoa-Aranda6 Jose A. Gomez-Capilla1, 2, Carolina Gomez-Llorente7. 

  1. Clinical Biochemistry Services, San Cecilio University Hospital. Avd/ Doctor Olóriz s/n 18012, Granada, Spain
  2. Department of Biochemistry and Molecular Biology III and Immunology, Faculty of Medicine Avd/Madrid s/n 18071, Granada, Spain
  3. Department of Oncology, San Cecilio University Hospital. Avd/Doctor Olóriz s/n 18012, Granada, Spain
  4. Aula de Estudios Avanzados. Fundación Tejerina. Madrid. Spain
  5. Department of Oncology, Hospital Provincial de Castellón. Avd/ Dr. Clará, nº 19, 12002 Castellón. Spain.
  6. Molecular Biopathology Laboratory. Hospital Provincial de Castellón. Avd/ Dr. Clará, nº 19 12002. Castellón, Spain.
  7. Department of Biochemistry and Molecular Biology II, Institute of Nutrition and Food Technology, Center for Biomedical Research, University of Granada, Granada. Avd/Conocimiento s/n 18100 Armilla, Granada, Spain

Abbreviations: ER+: estrogen-receptor positive; EM: extensive metabolizer; IM: intermediate metabolizer; UM: ultra-rapid metabolizer; PM: poor metabolizer; 4-OH tamoxifen: 4-hidroxy tamoxifen

Corresponding author:

Dr. Carolina Gomez-Llorente

Department of Biochemistry and Molecular Biology II, Institute of Nutrition and Food Technology, Center of Biomedical Research, University of Granada, Avd/Conocimiento s/n, 18100 Armilla, Granada, Spain.

Tel +34 958241000 ext.20322 Mobile: +34 686458391 Fax number: +34 958243391 E-mail: gomezll@ugr.es

 

ABSTRACT

Background Estrogen receptor–positive breast cancer tumors depend on estrogen signaling for their growth and replication and can be treated by anti-estrogen therapy with tamoxifen. Polymorphisms of the CYP2D6 and CYP2C19 genes are associated with an impaired response to tamoxifen. The study objective was to investigate the impact of genetic polymorphisms in CYP2D6 and CYP2C19 on the pharmacokinetics of tamoxifen and its metabolites in Spanish women with estrogen receptor-positive breast cancer who were candidates for tamoxifen therapy.

Methods: We studied 90 women with estrogen receptor-positive breast cancer, using the AmpliChip CYP450 test to determine CYP2D6 and CYP2C19 gene variants. Plasma levels of tamoxifen and its metabolites were quantified by high-performance liquid chromatography.

Results The CYP2D6 phenotype was extensive metabolizer in 80%, intermediate metabolizer in 12.2%, ultra-rapid metabolizer in 2.2%, and poor metabolizer in 5.6% of patients, and the allele frequency was 35.0% for allele *1, 21.0% for *2, and 18.9% for *4. All poor metabolizers in this series were *4/*4, and their endoxifen and 4-hydroxy tamoxifen levels were 25% lower than those of extensive metabolizers. CYP2C19*2 allele, which has been related to breast cancer outcomes, was detected in 15.6% of the studied alleles.

Conclusion CYP2D6*4/*4 genotype was inversely associated with 4-hydroxy tamoxifen and endoxifen levels. According to these results, CYP2D6 and CYP2C19 genotyping appears advisable before the prescription of tamoxifen therapy.

Keywords: CYP2D6, CYP2C19, genetic diagnosis, estrogen-positive breast cancer, endoxifen, tamoxifen

PMID: 23781139

 

SUPPLEMENT

Breast cancer is the most common cancer worldwide and the second leading cause of death by cancer. Estrogen and progesterone (steroid hormones) have been implicated in the pathogenesis of breast cancer . Estrogen receptor–positive (ER+) tumors depend on estrogen signaling for their growth and replication and can be treated by anti-estrogen therapy with tamoxifen or an aromatase inhibitor.

The use of pharmacogenomic markers is important in oncology because of the frequently narrow therapeutic index of available drugs, the critical need for a favorable drug response, and the potentially life-threatening consequences of drug toxicity. In this respect, genetic polymorphisms of the CYP2D6 gene have been reported as the main cause of variation in the metabolism of tamoxifen, which has been the standard treatment for ER+ breast cancer for more than three decades [4-6]. N-desmethyl tamoxifen, the main metabolite found in the serum of treated patients, undergoes secondary metabolism to 4-hydroxy-N-desmethyl tamoxifen (endoxifen). CYP2D6 is the enzyme responsible for this conversion and also converts tamoxifen to 4-hydroxy tamoxifen (4-OH tamoxifen), which undergoes secondary metabolism to endoxifen [5]. The CYP2D6 gene is highly polymorphic and has more than 100 different allele forms, which can be classified as a function of the intensity of their enzyme activity as extensive metabolizer (EM), intermediate metabolizer (IM), poor metabolizer (PM), or ultra-rapid metabolizer (UM) phenotypes. CYP2C19 gene polymorphisms affect the metabolism of numerous drugs, including anti-depressants, and play an important role in the bioactivation of cyclophosphamide. The enzyme CYP2C19 also participates in the conversion of tamoxifen to active metabolites, and the CYP2C19 gene has more than 35 allele variants.

The clinical validity of CYP2D6 genotyping is not well established in breast cancer patients who are candidates for tamoxifen treatment. Hence, the ability to predict the prevalence of EM, IM, PM, and UM phenotypes in a given population would support the design of a practical genotyping protocol for routine clinical use. The main objective of this pilot study was to determine the allele frequencies of the most relevant variants of CPY2D6 and CPY2C19 genes and their association with tamoxifen metabolite levels as a function of CYP2D6 polymorphisms in patients with ER+ breast cancer from Granada (Spain).

The study included 90 women from San Cecilio University Hospital (Granada, Spain) with a histological diagnosis of ER+ non-invasive breast cancer and a Karnofsky index ≥ 80. All women received adjuvant tamoxifen (20 mg/day) during the study and for at least 4 months before the blood sampling for tamoxifen and metabolite determinations. None of the women in this study were receiving drugs that inhibit CYP2D6 function. All patients were non-metastatic at recruitment.

Significant differences were found in the comparison of 4-OH tamoxifen and endoxifen levels between EM and PM phenotypes (P<0.001).

Our findings on CYP2D6 and CYP2C19 polymorphisms in a group of Spanish women with ER+ breast cancer are broadly similar to reports in general Caucasian populations. Without previous genotyping, incorrect treatment would likely have been ordered for the appreciable number (5.6%) of our patients who had PM phenotype (CYP2D6*4 allele in homozygosis in all cases) and were found to have lower endoxifen and 4-OH tamoxifen levels.

Our findings suggest that genotyping studies may be desirable before tamoxifen is prescribed. However, our study has some limitations. We measured tamoxifen and its main metabolites, but it was recently shown that N-desmethyl tamoxifen is converted into Z-endoxifen by the CYP2D6 enzyme and into Z’-endoxifen by an unknown hepatic enzyme, and both have different levels of anti-estrogenic activity [36]. It would be of interest to explore the relationship between the CYP2D6 genotype and the levels of these isomers. In addition, although the sample size was adequate to yield significant differences, the results of this pilot study need to be confirmed in larger samples. Further studies are in progress by our group to develop guidelines on drug dosage as a function of CYP2D6 and CYP2C19 genotypes.

Acknowledgements

The authors are grateful to Dr. Josep Solé from Roche Diagnostics S.L (Spain) for his collaboration and comments on this paper and to Richard Davies for assistance with the English version. CGLL has a postdoctoral fellowship from the Plan Propio of the University of Granada.

Table 1 CYP2D6 phenotype and genotype frequencies in 90 women with estrogen receptor positive breast cancer.Table

Figure 1

Panel A

Figure_1-Panel_APanel B

Figure_1-Panel_BFigure 1. Plasma tamoxifen, endoxifen, 4-hydroxy (4-OH) tamoxifen, and N-desmethyl tamoxifen levels in women with estrogen receptor-positive breast cancer receiving adjuvant tamoxifen (20 mg/day) for 4 months. Data are expressed as means ± standard error. Panel A shows the significant difference (P <0.001) in 4-OH tamoxifen and endoxifen between extensive and poor CYP2D6 metabolizers (black bars = extensive metabolizers, white bars= intermediate metabolizers, grey bars = poor metabolizers). Panel B depicts tamoxifen and N-desmethyl tamoxifen levels in extensive, intermediate, and poor CYP2D6 metabolizers (non-significant difference) (black bars = extensive metabolizers, white bars= intermediate metabolizers, grey bars = poor metabolizers).

 

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