Determination of CYP2D6 *3, *4, and *10 frequency in women with breast cancer in São Luís, Brazil, and its association with prognostic factors and disease-free survival

The CYP2D6 enzyme is crucial for the metabolism of tamoxifen. The CYP2D6 gene is highly polymorphic, and individuals can be extensive, intermediate, or poor tamoxifen metabolizers. The aim of this study was to determine the frequencies of the CYP2D6 *3, *4, and *10 alleles in women with breast cancer who were treated with tamoxifen and analyze the association of enzyme activity with prognostic factors and disease-free survival. We observed a high frequency of CYP2D6 *10, with an allelic frequency of 0.14 (14.4%). The *3 allele was not present in the studied population, and *4 had an allelic frequency of 0.13 (13.8%). We conclude that patients with reduced CYP2D6 activity did not present worse tumor characteristics or decreased disease-free survival than women with normal enzyme activity, as the difference was not statistically significant. We also observed a high frequency of CYP2D6 *10, which had not been previously described in this specific population. This study is the first in north-northeastern Brazil that aimed to contribute to the knowledge of the Brazilian regional profile for CYP2D6 polymorphisms and their phenotypes. These findings add to the knowledge of the distribution of different polymorphic CYP2D6 alleles and the potential role of CYP2D6 genotyping in clinical practice prior to choosing therapeutic protocols.

Genetic variants in the cytochrome P450 2D6 gene in the Sri Lankan population.

INTRODUCTION: Cytochrome P450 2D6 (CYP2D6) enzymes are involved in the metabolism of a large number of commonly prescribed drugs such as antidepressants and cardiovascular drugs. The CYP2D6 *3, *4 and *14 variants associated with the loss of enzyme function; CYP2D6 *10 and *17 variants with reduced enzyme function; and CYP2D6 *2 variant with no effect on enzyme function. Establishing the frequency of these variant alleles in Sri Lankan population would be useful for optimizing pharmacotherapy with CYP2D6‑substrate drugs. OBJECTIVE: The objective of this study was to determine the prevalence of CYP2D6 *2, *3, *4, *10, *14 and *17 variants in the main ethnic groups in the Sri Lankan population. MATERIALS AND METHODS: A total of 90 deoxyribonucleic acid (DNA) samples (30 each from Sinhalese, Tamils and Moors) were selected from a DNA resource at the Human Genetic Unit, Faculty of Medicine, University of Colombo. This collection had been made for population genetic studies from a random population based volunteers. Genotyping was performed using published polymerase chain reaction/ restriction fragment length polymorphism methods. RESULTS: The prevalence of the CYP2D6 variants in Sinhalese, Sri Lankan Tamils and Moors respectively were CYP2D6 *2: 37%, 41.6% and 37.9%; CYP2D6 *3: 60.3%, 45% and 30%; CYP2D6 *4: 21.6%, 6.6% and 8.3%; CYP2D6 *10: 40%, 35% and 44%. CYP2D6 *14 and *17 variants were not identified. CONCLUSION: CYP2D6 *3, *4 and *10 variants, which are associated with reduced or loss of CYP2D6 enzyme function were found in our population in significant frequencies. CYP2D6*4, which is reported to be a Caucasian variant was also found in all three ethnic groups.

Use of Antidepressants in Patients with Breast Cancer Taking Tamoxifen / 한국유방암학회지

Tamoxifen, a selective estrogen modulator has been used for more than three decades to treat all stages of estrogen receptor (ER)-positive breast cancer and to prevent the disease. Tamoxifen is a pro-drug that requires metabolic activation to 4-hydroxytamoxifen and 4-hydroxy-N-desmethyltamoxifen (endoxifen) to elicit its pharmacological activity. Endoxifen has identical properties and potency with 4-hydroxytamoxifen, but is present in concentrations up to 10-fold higher than 4-hydroxytamoxifen. The cytochrome P450 2D6 (CYP2D6) enzyme plays a key role in converting tamoxifen into its active metabolites with significantly greater affinity for the ER and greater ability to inhibit cell proliferation. Genetic variants in the CYP2D6 gene may result in CYP2D6 enzymes with reduced or null activity, thereby decreasing the anti-cancer effect. In addition to genetic inactivation of CYP2D6, inhibitors of CYP2D6, including some antidepressants to treat hot flashes or depression in patients with breast cancer, may also alter enzyme activity and negatively affect the outcomes of patients receiving adjuvant tamoxifen. This article reviews and discusses the following issues: tamoxifen metabolism, antiproliferative effects of tamoxifen and its metabolites, CYP2D6 genetic polymorphisms, treatment for hot flashes and depression in breast cancer, and the pharmacological interactions between tamoxifen and antidepressants via CYP2D6. Although routine CYP2D6 testing is not recommended yet, coadministration of potent or intermediate CYP2D6 inhibitors in women taking tamoxifen should be avoided.