Impacts of cytochrome P450 2D6 (CYP2D6) genetic polymorphism in tamoxifen therapy for breast cancer impactos do polimorfismo genético do citocromo P450 2D6 (CYP2D6) na terapia com tamoxifeno para câncer de mama

Abstract Tamoxifen (TMX) is the main drug used both in pre and postmenopausal women as adjuvant treatment for hormone receptor-positive breast cancer. An important barrier to the use of TMXis the development ofdrug resistance causedby molecular processes related to genetic and epigenetic mechanisms, such as the actions of cytochrome P450 2D6 (CYP2D6) polymorphisms and of its metabolites. The present study aimed to review recent findings related to the impact of CYP2D6 polymorphisms and how they can affect the results of TMX in breast cancer treatment. The keywords CYP2D6, tamoxifen, and breast cancer were searched in the PubMed, Scopus, The Cochrane Library, Scielo, and Bireme databases. Studies related to other types of neoplasms or based on other isoenzymes from cytochrome P450, but not on CYP2D6, were excluded. The impact of CYP2D6 polymorphisms in the TMX resistance mechanism remains unclear. The CYP2D6 gene seems to contribute to decreasing the efficacy of TMX, while the main mechanism responsible for therapy failure, morbidity, and mortality is the progression of the disease.

Resumo Otamoxifeno é a principal drogaque pode ser utilizada comotratamentohormonal adjuvante empacientesportadoras de câncer demamareceptor hormonal positivotanto na pré- quanto na pós-menopausa.Umadasmaiores barreirasemseu uso é o desenvolvimento de resistência medicamentosa causada por meio de processos moleculares relacionados a mecanismos genéticos e epigenéticos, como a ação dos polimorfismos do gene citocromo P450 2D6 (CYP2D6) e seus metabólitos.Opresente estudo busca revisar as descobertas recentes acerca dos impactos dos polimorfismos do gene CYP2D6 e de como eles podem afetar os resultados do tamoxifeno na terapêutica do câncer de mama. As palavras-chave CYP2D6, tamoxifeno e câncer de mama foram buscadas nas bases de dados Pubmed, Scopus, The Cochrane Library, Scielo e Bireme. Estudos relacionados com outros tipos de câncer ou relacionados a outras isoenzimas do citocromo P450 que não o CYP2D6 foram excluídos. O impacto do polimorfismo do CYP2D6 nos mecanismos de resistência ao tamoxifeno permanecem controversos. O gene CYP2D6 parece reduzir a eficácia do TMX; entretanto, os principais fatores associados a falha terapêutica são morbimortalidade e a progressão da doença

Clinical Pharmacogenetic Testing and Application: Laboratory Medicine Clinical Practice Guidelines

Pharmacogenetic testing for clinical applications is steadily increasing. Correct and adequate use of pharmacogenetic tests is important to reduce unnecessary medical costs and adverse patient outcomes. This document contains recommended pharmacogenetic testing guidelines for clinical application, interpretation, and result reporting through a literature review and evidence-based expert opinions for the clinical pharmacogenetic testing covered by public medical insurance in Korea. This document aims to improve the utility of pharmacogenetic testing in routine clinical settings.

Relevance of the ancestry for the variability of the Drug-Metabolizing Enzymes CYP2C9, CYP2C19 and CYP2D6 polymorphisms in a multiethnic Costa Rican population / Relevancia de la ancestría para la variabilidad de polimorfismos de las enzimas metabolizadoras de fármacos CYP2C9, CYP2C19 y CYP2D6 en una población multiétnica de Costa Rica

Abstract:CYP2C9, CYP2C19 and CYP2D6 metabolize around 40 % of drugs and their genes vary across populations. The Costa Rican population has a trihybrid ancestry and its key geographic location turns it into a suitable scenario to evaluate interethnic differences across populations. This study aims to describe the diversity of CYP2C9, CYP2C19 and CYP2D6 polymorphisms in Costa Rican populations in the context of their ancestry. A total of 448 healthy individuals were included in the study: Bribri (n= 47), Cabécar (n= 27), Maleku (n= 16), Guaymí (n= 30), Huetar (n= 48), Chorotega (n= 41), Admixed/Mestizos from the Central Valley/Guanacaste (n= 189), and Afro-Caribbeans (n= 50) from Limón. CYP2C9 (alleles *2, *3, *6) and CYP2C19 (*2, *3, *4, *5, *17) genotypes were determined by Real-Time PCR. African, European and Native American ancestry were inferred using 87 ancestry informative markers. The frequency of the decreased activity allele CYP2C9*2 is lower in the self-reported Amerindian groups compared to the admixed population, and the highest frequencies of CYP2C19*2 (null activity) and the CYP2C19*17 (increased activity) were found in the self-reported AfroCaribbean population. Moreover, a frequency of 0.7 % CYP2C9 gPMs in the Admixed population and a variable frequency of CYP2C19 gUMs (0.0-32.6 %, more prevalent in Afro-Caribbeans) in Costa Rican populations, was found. Finally, the following alleles were positively correlated with genomic African ancestry and negatively correlated with genomic Native American ancestry: CYP2D6*5 (null activity), CYP2D6*17 (decreased activity), CYP2D6*29 (decreased activity) and CYP2C19*17 (increased activity). No correlation for CYP2C9 polymorphisms and genomic ancestry was found. Further studies assessing the CYP2C9 and CYP2C19 sequence in these populations, preferentially by sequencing these genes, are warranted. Rev. Biol. Trop. 64 (3): 1067-1076. Epub 2016 September 01.

ResumenCYP2C9, CYP2C19 y CYP2D6 metabolizan aproximadamente el 40 % de los fármacos y los genes que las codifican varían en las distintas poblaciones humanas. La población costarricense posee ancestría trihíbrida y su posición geográfica estratégica la convierten en un escenario idóneo para evaluar la variabilidad interétnica en sus poblaciones multiétnicas. El presente estudio tiene como objetivo describir la diversidad de los polimorfismos CYP2C9, CYP2C19 y CYP2D6 en las poblaciones costarricenses en el contexto de su ancestría. Un total de 448 individuos sanos fueron incluidos: Bribri (n= 47), Cabécar (n= 27), Maleku (n= 16), Guaymí (n= 30), Huetar (n= 48), Chorotega (n= 41), mestizos del Valle Central y Guanacaste (n= 189) y afrocaribeños de Limón (n= 50). Los genotipos CYP2C9 (alelos *2, *3, *6) y CYP2C19 (*2, *3, *4, *5 y *17) fueron determinados mediante PCR tiempo real. Las ancestrías africana, europea y nativa americana fueron inferidas usando 87 marcadores informativos de ancestría. La frecuencia del alelo de actividad disminuida CYP2C9*2 fue menor en los grupos autodefinidos de amerindios que en la población mestiza y las frecuencias más altas de CYP2C19*2 (actividad nula) y CYP2C19*17 (actividad incrementada) se encontraron en la población autodefinida afrocaribeña. Asimismo, se encontró una frecuencia de gPMs CYP2C9 de 0.7 % en la población mestiza y una frecuencia variable de gUMs CYP2C19 (0.0 a 32.6 %, más prevalente en afrocaribeños) en las poblaciones costarricenses. Por último, los siguientes alelos fueron positivamente correlacionados con la ancestría africana y negativamente con la ancestría nativa americana: CYP2D6*5 (actividad nula), CYP2D6*17, CYP2D6*29 (ambos de actividad disminuida) y CYP2C19*17 (actividad incrementada). No se encontró correlación entre los polimorfismos CYP2C9 y la ancestría. Se requieren estudios posteriores que evalúen la secuencia de CYP2C9 y CYP2C19 en estas poblaciones, preferiblemente mediante la secuenciación de estos genes.

Genetic Polymorphism of CYP2D6 and Clomiphene Concentrations in Infertile Patients with Ovulatory Dysfunction Treated with Clomiphene Citrate

CYP2D6 is primarily responsible for the metabolism of clomiphene citrate (CC). The purpose of the present study was to investigate the relationship between CYP2D6 genotypes, concentrations of CC and its major metabolites and drug response in infertility patients. We studied 42 patients with ovulatory dysfunction treated with only CC. Patients received a dose of 100 mg/day CC on days 3-7 of the menstrual cycle. CYP2D6 genotyping and measurement of CC and the major metabolite concentrations were performed. Patients were categorized into CC responders or non-responders according to one cycle response for the ovulation. Thirty-two patients were CC responders and 10 patients were non-responders with 1 cycle treatment. The CC concentrations were highly variable within the same group, but non-responders revealed significantly lower (E)-clomiphene concentration and a trend of decreased concentrations of active metabolites compared to the responders. Nine patients with intermediate metabolizer phenotype were all responders. We confirmed that the CC and the metabolite concentrations were different according to the ovulation status. However, our results do not provide evidence for the contribution of CYP2D6 polymorphism to either drug response or CC concentrations.

Nonresponders to Daily Paroxetine and Another SSRI in Men With Lifelong Premature Ejaculation: A Pharmacokinetic Dose-Escalation Study for a Rare Phenomenon

PURPOSE: Nonresponse to any selective serotonin reuptake inhibitor (SSRI) treatment is rare. In this study, we aimed to investigate ejaculation delay nonresponse to paroxetine treatment in men with lifelong premature ejaculation (PE) who were also known to be nonresponders to other SSRIs. MATERIALS AND METHODS: Five males with lifelong PE who were known nonresponders to paroxetine and other serotonergic antidepressants and eight males with lifelong PE who were specifically recruited were included. Blood sampling occurred 1 month and 1 day before the start of treatment and at the end of three consecutive series of 4 weeks of daily treatment with 10-, 20-, and 30-mg paroxetine, respectively. Blood samples for measurement of leptin and paroxetine were taken at 8:30 AM, 9:30 AM, 10:30 AM, and 11:30 AM, respectively. At 9:00 AM, one tablet of 10-, 20-, or 30-mg paroxetine was taken during the first, second, and third month, respectively. Intravaginal ejaculatory latency time (IELT) was measured with a stopwatch. The main outcome measures were the fold increase in the geometric mean IELT, serum leptin and paroxetine concentrations, body mass index (BMI), 5-HT1A receptor C-1019G polymorphism, and CYP2D6 mutations. RESULTS: Between the 7 paroxetine responders and 6 nonresponders, the fold increase in the geometric mean IELT was significantly different after daily 10-mg (p=0.003), 20-mg (p=0.002), and 30-mg paroxetine (p=0.026) and ranged from 2.0 to 8.8 and from 1.1 to 1.7, respectively. BMI at baseline and at the end of the study was not significantly different between responders and nonresponders. Serum leptin levels at baseline were similar in responders and nonresponders and did not change during treatment. The serum paroxetine concentration increased with increasing dosage and was not significantly different between responders and nonresponders. There was no association between the fold increase in the geometric mean IELT and serum paroxetine levels during the three treatment periods nor between leptin levels during the treatment periods and serum paroxetine levels. For the 5-HT1A receptor C-1019G variation, all responders had the CC genotype and all nonresponders had the GC genotype, respectively. CONCLUSIONS: Complete absence of paroxetine-induced ejaculation delay is presumably related to pharmacodynamic factors and perhaps to 5-HT1A receptor gene polymorphism.

Nonresponders to Daily Paroxetine and Another SSRI in Men With Lifelong Premature Ejaculation: A Pharmacokinetic Dose-Escalation Study for a Rare Phenomenon

PURPOSE: Nonresponse to any selective serotonin reuptake inhibitor (SSRI) treatment is rare. In this study, we aimed to investigate ejaculation delay nonresponse to paroxetine treatment in men with lifelong premature ejaculation (PE) who were also known to be nonresponders to other SSRIs. MATERIALS AND METHODS: Five males with lifelong PE who were known nonresponders to paroxetine and other serotonergic antidepressants and eight males with lifelong PE who were specifically recruited were included. Blood sampling occurred 1 month and 1 day before the start of treatment and at the end of three consecutive series of 4 weeks of daily treatment with 10-, 20-, and 30-mg paroxetine, respectively. Blood samples for measurement of leptin and paroxetine were taken at 8:30 AM, 9:30 AM, 10:30 AM, and 11:30 AM, respectively. At 9:00 AM, one tablet of 10-, 20-, or 30-mg paroxetine was taken during the first, second, and third month, respectively. Intravaginal ejaculatory latency time (IELT) was measured with a stopwatch. The main outcome measures were the fold increase in the geometric mean IELT, serum leptin and paroxetine concentrations, body mass index (BMI), 5-HT1A receptor C-1019G polymorphism, and CYP2D6 mutations. RESULTS: Between the 7 paroxetine responders and 6 nonresponders, the fold increase in the geometric mean IELT was significantly different after daily 10-mg (p=0.003), 20-mg (p=0.002), and 30-mg paroxetine (p=0.026) and ranged from 2.0 to 8.8 and from 1.1 to 1.7, respectively. BMI at baseline and at the end of the study was not significantly different between responders and nonresponders. Serum leptin levels at baseline were similar in responders and nonresponders and did not change during treatment. The serum paroxetine concentration increased with increasing dosage and was not significantly different between responders and nonresponders. There was no association between the fold increase in the geometric mean IELT and serum paroxetine levels during the three treatment periods nor between leptin levels during the treatment periods and serum paroxetine levels. For the 5-HT1A receptor C-1019G variation, all responders had the CC genotype and all nonresponders had the GC genotype, respectively. CONCLUSIONS: Complete absence of paroxetine-induced ejaculation delay is presumably related to pharmacodynamic factors and perhaps to 5-HT1A receptor gene polymorphism.

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.

Association between Genetic Polymorphisms of CYP2D6 and Outcomes in Breast Cancer Patients with Tamoxifen Treatment

The aim of the study was to evaluate the association between genetic polymorphisms of CYP2D6 and outcomes in breast cancer patients with tamoxifen treatment. We evaluated the CYP2D6 genetic polymorphisms in 766 breast cancer patients. Among them, 110 patients whose samples were prospectively collected before surgery and treated with tamoxifen were included to evaluate the association between CYP2D6 and outcomes. The genotypes of CYP2D6 were categorized as extensive metabolizer (EM), intermediate metabolizer (IM), and poor metabolizer (PM) according to the activity score. The clinicopathologic features of 110 patients were not significantly different among the three groups except for the T-stage and nodal status. The high T-stage and axillary metastasis were more frequent in the PM group. While recurrence-free and overall survival in the PM group was poorer than the other groups, there was no significant difference between the EM and the IM group. The difference between the PM and the other groups on univariate analysis disappeared on multivariate analysis. These conflicting results suggest that the clinical value of CYP2D6 polymorphisms is still unclear and more large-sized and comprehensively designed trials are necessary.

[Study of polymorphism of CYP2D6*4 gene in susceptibility to breast cancer]

Breast cancer is the most frequent malignancy among women worldwide. Polymorphisms in Xenobiotic Metabolizing Enxymes [XEMs] and drugs such as P450 [CYP2D6] may increase susceptibility to breast cancer. Little is known about the association of CYP2D6*4 [1894 G to A] polymorphism and susceptibility to breast cancer. This study aimed to investigate the possible relationship of the CYP2D6 *4 gene polymorphism and breast cancer. One hundred women with confirmed breast cancer and 100 healthy women were the subject of this study. Subjects were assessed for the gene polymorphism of CYP2D6*D by a PCR-RFLP assay at Mashhad University of Medical Sciences in 2009. The collected data were analyzed by the SPSS using chi-square test and Fisher exact test. No correlation was found between CYP2D6*4 gene polymorphism and breast cancer [P=0.299]. Our results demonstrated that CYP2D6 *4 mutant displays a non-significant increased risk for breast cancer

CYP2D6 genotype and phenotype relationship in South Indians.

BACKGROUND: Genotypes of the drug-metabolizing enzyme CYP2D6 influence plasma levels of 25% of commonly prescribed drugs. This is the first study in India to investigate the genotype-phenotype relationship of CYP2D6. AIM: To study the influence of some CYP2D6 genotypes on the metabolism of its substrate dextromethorphan in healthy South Indian volunteers and to assess the contribution of the CYP2D6*10 and CYP2D6*4 alleles. MATERIALS AND METHODS: Twenty-six subjects from a previous CYP2D6 genotyping study of healthy volunteers were included for phenotyping in this study. Selected volunteers belonged to any one of three genotype groups:Group I - two normal activity alleles, Group II - one reduced activity allele and one normal activity allele and Group III - one loss of function allele along with either a wild type or reduced activity allele. Volunteers were phenotyped for the CYP2D6 enzyme using dextromethorphan as probe drug. Concentrations of the parent drug and metabolite dextrorphan were estimated using high performance liquid chromatography. Metabolic ratios were calculated as the ratio of parent drug to metabolite in 0-8h urine samples. STATISTICAL ANALYSIS: Metabolic ratios from each genotype group were compared using the Mann-Whitney test at 5% significance, to observe their difference between genotype groups. RESULTS: The mean metabolic ratios+/-SD in Groups I, II and III were 0.0039+/-0.0031, 0.0032+/-0.0017 and 0.0391+/-0.0331 respectively. The mean metabolic ratio of Group III was significantly higher when compared with Groups I or II. In heterozygous individuals, the *1 or *2 alleles compensated for the reduced enzyme activity due to the *10 allele. However, if a heterozygous individual had a *4 allele, the reduced enzyme activity could not be compensated by the *1 or *2 alleles. CONCLUSIONS: The CYP2D6 enzyme activity was found to be decreased in individuals carrying *4 or *5 alleles.The *1 or *2 allele could compensate for the reduced function due to *10 allele, but not for the loss of function due to *4 allele.

A Case Report of a Poor Metabolizer of CYP2D6 Presented with Unusual Responses to Nortriptyline Medication

We present a case with decreased metabolic activity of CYP2D6, a cytochrome P450 enzyme catalyzing the metabolism of nortriptyline (NT). Conventional dosage regimen led to toxic plasma concentration of NT and adverse effects such as dry mouth, constipation, and dizziness in this case with genotype CYP2D6*5/*10B. This case suggests the clinical usefulness of pharmacogenetic testing in individualized dosage adjustments of NT.