Cytochrome P450 2D6 Enzyme Research Articles

Metabolomics reveals biomarkers in human urine and plasma to predict cytochrome P450 2D6 (CYP2D6) activity.

Background and PurposeIndividualized assessment of cytochrome P450 2D6 (CYP2D6) activity is usually performed through phenotyping following administration of a probe drug to measure the enzyme's activity. To avoid any iatrogenic harm (allergic drug reaction, dosing error) related to the probe drug, the development of non‐burdensome tools for real‐time phenotyping of CYP2D6 could significantly contribute to precision medicine. This study focuses on the identification of markers of the CYP2D6 enzyme in human biofluids using an LC‐high‐resolution mass spectrometry‐based metabolomic approach.Experimental ApproachPlasma and urine samples from healthy volunteers were analysed before and after intake of a daily dose of paroxetine 20 mg over 7 days. CYP2D6 genotyping and phenotyping, using single oral dose of dextromethorphan 5 mg, were also performed in all participants.Key ResultsWe report four metabolites of solanidine and two unknown compounds as possible novel CYP2D6 markers. Mean relative intensities of these features were significantly reduced during the inhibition session compared with the control session (n = 37). Semi‐quantitative analysis showed that the largest decrease (−85%) was observed for the ion m/z 432.3108 normalized to solanidine (m/z 398.3417). Mean relative intensities of these ions were significantly higher in the CYP2D6 normal–ultrarapid metabolizer group (n = 37) compared with the poor metabolizer group (n = 6). Solanidine intensity was more than 15 times higher in CYP2D6‐deficient individuals compared with other volunteers.Conclusion and ImplicationsThe applied untargeted metabolomic strategy identified potential novel markers capable of semi‐quantitatively predicting CYP2D6 activity, a promising discovery for personalized medicine.

Acute pharmacogenetic dystonic reactions in a family with the CYP2D6 *41 allele: a case report

BackgroundDystonia is a known neurological complication of certain medications; however, the mechanism behind such effects is often undetermined. Similarly, the clinical pharmacogenomic effects associated with various alleles of the cytochrome P450 family of proteins, and their role in acute dystonic reactions, are also presently unknown.Case presentationWe describe a woman presenting with acute dystonic reactions to ondansetron, prochlorperazine, and metoclopramide followed by persistent focal dystonia. A similar family history was reported in her siblings and her father to prochlorperazine, drugs all metabolized by the cytochrome P450 2D6 (CYP2D6) enzyme. Pharmacogenomic testing indicated the patient was heterozygous for the intermediate metabolizer *41 allele (CYP2D6 2988G>A, NM_000106.6:c.985+39G>A, rs28371725). Her father was homozygous for this CYP2D6 *41 allele, and consequently, her siblings were obligate carriers.ConclusionsThe metabolism of ondansetron, metoclopramide, or prochlorperazine in patients with the *41 CYP2D6 allele has not been studied. In this family, clinical evidence implicates the *41 CYP2D6 allele as causing extrapyramidal adverse pharmacologic reactions. Patients with a family history of medication-induced dystonia involving these medications should be considered for pharmacogenomic testing, and patients carrying the *41 CYP2D6 allele should consider reduction or avoidance of CYP2D6-mediated medications to minimize the potential risk of adverse extrapyramidal effects.

Cytochrome P450 2D6 genotype-phenotype characterization through population pharmacokinetic modeling of tedatioxetine.

The cytochrome P450 (CYP) 2D6 enzyme exhibits large interindividual differences in metabolic activity. Patients are commonly assigned a CYP2D6 phenotype based on their CYP2D6 genotype, but there is a lack of consensus on how to translate genotypes into phenotypes, causing inconsistency in genotype‐based dose recommendations. The aim of this study was to quantify and compare the impact of different CYP2D6 genotypes and alleles on CYP2D6 metabolism using a large clinical data set. A population pharmacokinetic (popPK) model of tedatioxetine and its CYP2D6‐dependent metabolite was developed based on pharmacokinetic data from 578 subjects. The CYP2D6‐mediated metabolism was quantified for each subject based on estimates from the final popPK model, and CYP2D6 activity scores were calculated for each allele using multiple linear regression. The activity scores estimated for the decreased function alleles were 0.46 (CYP2D6*9), 0.34 (CYP2D6*10), 0.01 (CYP2D6*17), 0.65 (CYP2D6*29), and 0.21 (CYP2D6*41). The CYP2D6*17 and CYP2D6*41 alleles were thus associated with the lowest CYP2D6 activity, although only the difference to the CYP2D6*9 allele was shown to be statistically significant (p = 0.02 and p = 0.05, respectively). The study provides new in vivo evidence of the enzyme function of different CYP2D6 genotypes and alleles. Our findings suggest that the activity score assigned to CYP2D6*41 should be revisited, whereas CYP2D6*17 appears to exhibit substrate‐specific behavior. Further studies are needed to confirm the findings and to improve the understanding of CYP2D6 genotype–phenotype relationships across substrates.

Validation of a Population Pharmacokinetic Model of Vortioxetine Using Therapeutic Drug Monitoring Data.

IntroductionVortioxetine is an antidepressant primarily metabolized by the polymorphic enzyme cytochrome P450 (CYP) 2D6. A population pharmacokinetic (popPK) model of vortioxetine and its CYP2D6-dependent metabolite was recently published.ObjectiveThe aim of the current study was to assess the predictive performance of the popPK model using vortioxetine concentration measurements from a clinical setting. Furthermore, the study aimed to evaluate the ability of different CYP2D6 phenotype classification systems to provide accurate concentration predictions.MethodsOverall, 1388 patients receiving vortioxetine treatment were identified from a therapeutic drug monitoring (TDM) database in Oslo, Norway; 334 CYP2D6-genotyped patients with 502 serum concentrations of vortioxetine, analysed by a validated ultra-high-performance liquid chromatography–high-resolution mass spectrometry (UHPLC-HRMS) method, were retrospectively included. The performance of the vortioxetine popPK model was tested on the clinical data from the TDM database.ResultsOverall, the model had a good ability to predict vortioxetine concentrations measured in clinical practice, with a slight tendency to overpredict concentrations. Using simulation-based diagnostics, 76% of the prediction-corrected TDM concentrations were within the 90% prediction interval based on 1000 simulated data sets. Prediction-based diagnostics showed the best performance for CYP2D6 poor and ultrarapid metabolizers, with a median prediction error (MDPE) of 12% and 23%, respectively, while the poorest performance was observed for normal metabolizers, with an MDPE of 66%. In the comparison of different CYP2D6 phenotype classification systems, the use of differentiated activity scores for decreased function alleles did not improve the concentration predictions. Grouping the CYP2D6 genotypes into the four conventional phenotype groups provided predictions closest to the TDM measured concentrations.ConclusionTDM data provide a unique insight into real-world clinical practice with vortioxetine. The tendency of the popPK model to overpredict vortioxetine concentrations measured in TDM may be attributed to several factors, including poor treatment compliance for some patients and, to a lesser extent, lack of information on patient characteristics and misspecified CYP2D6 alleles. To optimize personalized therapy with vortioxetine, real-world clinical data sets originating from different ethnicities need to be studied in the future.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40262-021-01029-7.

Effects of Genetic Polymorphism in CYP2D6, CYP2C19, and the Organic Cation Transporter OCT1 on Amitriptyline Pharmacokinetics in Healthy Volunteers and Depressive Disorder Patients.

The tricyclic antidepressant amitriptyline is frequently prescribed but its use is limited by its narrow therapeutic range and large variation in pharmacokinetics. Apart from interindividual differences in the activity of the metabolising enzymes cytochrome P450 (CYP) 2D6 and 2C19, genetic polymorphism of the hepatic influx transporter organic cation transporter 1 (OCT1) could be contributing to interindividual variation in pharmacokinetics. Here, the impact of OCT1 genetic variation on the pharmacokinetics of amitriptyline and its active metabolite nortriptyline was studied in vitro as well as in healthy volunteers and in depressive disorder patients. Amitriptyline and nortriptyline were found to inhibit OCT1 in recombinant cells with IC50 values of 28.6 and 40.4 µM. Thirty other antidepressant and neuroleptic drugs were also found to be moderate to strong OCT1 inhibitors with IC50 values in the micromolar range. However, in 35 healthy volunteers, preselected for their OCT1 genotypes, who received a single dose of 25 mg amitriptyline, no significant effects on amitriptyline and nortriptyline pharmacokinetics could be attributed to OCT1 genetic polymorphism. In contrast, the strong impact of the CYP2D6 genotype on amitriptyline and nortriptyline pharmacokinetics and of the CYP2C19 genotype on nortriptyline was confirmed. In addition, acylcarnitine derivatives were measured as endogenous biomarkers for OCT1 activity. The mean plasma concentrations of isobutyrylcarnitine and 2-methylbutyrylcarnitine were higher in participants with two active OCT1 alleles compared to those with zero OCT1 activity, further supporting their role as endogenous in vivo biomarkers for OCT1 activity. A moderate reduction in plasma isobutyrylcarnitine concentrations occurred at the time points at which amitriptyline plasma concentrations were the highest. In a second, independent study sample of 50 patients who underwent amitriptyline therapy of 75 mg twice daily, a significant trend of increasing amitriptyline plasma concentrations with decreasing OCT1 activity was observed (p = 0.018), while nortriptyline plasma concentrations were unaffected by the OCT1 genotype. Altogether, this comprehensive study showed that OCT1 activity does not appear to be a major factor determining amitriptyline and nortriptyline pharmacokinetics and that hepatic uptake occurs mainly through other mechanisms.

Cytochrome P450 2C19 enzyme, Cytochrome P450 2C9 enzyme, and Cytochrome P450 2D6 enzyme allelic variants and its possible effect on drug metabolism: A retrospective study.

The objective of the present study was to assess the allelic variations of Cytochrome P450 (CYP) enzymes Cytochrome P450 2C19 (CYP2C19), Cytochrome P450 2C9 (CYP2C9), and Cytochrome P450 2D6 (CYP2D6) as they play a major role in drug metabolism. The interindividual genetic variabilities of these enzymes can account for different responsiveness as well as concentration fluctuations for a particular drug.During the period of 2017 to 2018 a total of 54 patients have received pharmacogenetic testing at the Department of Genetics and Molecular Medicine at Kaunas Clinics. According to the genotype-metabolic phenotypes of CYP2C19, CYP2D6, CYP2C9 enzymes patients were classified according to the guidelines by Clinical Pharmacogenetics Implementation Consortium (CPIC): normal metabolizers (NMs), intermediate metabolizers (IMs), rapid metabolizers (RMs), ultrarapid metabolizers (UMs), and poor metabolizers (PMs).CYP2C19 enzyme allelic distribution: 18 patients (33.33%) with ∗1/∗1 genotype were NMs; 14 patients (25.93%) with ∗1/∗2; ∗2/∗17 genotypes were classified as IMs; 15 patients (27.78%) possessed ∗1/∗17 genotype and were RMs; 4 patients (7.4%) had ∗17/∗17 genotype with increased enzyme activity compared with RMs, were classified as UMs; 3 patients (5.56%) had ∗2/∗2 genotype and were marked as PMs. CYP2D6 enzyme allelic distribution: 26 patients (48.148%) contained ∗1/∗1,∗2/∗2,∗1/∗2,∗1/∗41,∗2/∗41 genotypes with normal enzymatic function so were accounted as NMs; 21 patients (38.89%) with ∗1/∗5, ∗2/∗4, ∗10/∗41, ∗1/∗4, ∗1/∗3, ∗2/∗5, ∗2/∗4, ∗2/∗6 genotypes were accounted as IMs; 2 patients (3.7%) possessed ∗2XN genotype and were accounted as UMs and 5 patients (9.26%) possessed ∗4/∗5,∗4/∗10,∗4/∗9,∗4/∗41 genotypes and had non-functional enzymatic activity so were accounted as PMs; CYP2C9 enzyme allelic distribution: 44 patients (81.48%) with∗1/∗1 genotype were NMs; 10 patients (18.52%) with ∗1/∗2;∗1/∗3 genotypes were IMs.The results of our study indicate that deviations from the normal enzymatic activity is common amongst Lithuanian people and combinatory genotyping of CYP2D6, CYP2C9, and CYP2C19 has to be promoted as an advanced method because of most commonly prescribed medicines like analgesics, antihypertensive, antidepressants are metabolized by multiple pathways involving enzymes in the CYP450 family.

Interaction of silymarin components and their sulfate metabolites with human serum albumin and cytochrome P450 (2C9, 2C19, 2D6, and 3A4) enzymes

Silymarin is a mixture of flavonolignans isolated from the fruit of milk thistle (Silybum marianum (L.) Gaertner). Milk thistle extract is the active ingredient of several medications and dietary supplements to treat liver injury/diseases. After the oral administration, flavonolignans are extensively biotransformed, resulting in the formation of sulfate and/or glucuronide metabolites. Previous studies demonstrated that silymarin components form stable complexes with serum albumin and can inhibit certain cytochrome P450 (CYP) enzymes. Nevertheless, in most of these investigations, silybin was tested; while no or only limited information is available regarding other silymarin components and metabolites. In this study, the interactions of five silymarin components (silybin A, silybin B, isosilybin A, silychristin, and 2,3-dehydrosilychristin) and their sulfate metabolites were examined with human serum albumin and CYP (2C9, 2C19, 2D6, and 3A4) enzymes. Our results demonstrate that each compound tested forms stable complexes with albumin, and certain silymarin components/metabolites can inhibit CYP enzymes. Most of the sulfate conjugates were less potent inhibitors of CYP enzymes, but 2,3-dehydrosilychristin-19-O-sulfate showed the strongest inhibitory effect on CYP3A4. Based on these observations, the simultaneous administration of high dose silymarin with medications should be carefully considered, because milk thistle flavonolignans and/or their sulfate metabolites may interfere with drug therapy.

Clinical CYP2D6 Genotyping to Personalize Adjuvant Tamoxifen Treatment in ER-Positive Breast Cancer Patients: Current Status of a Controversy

Simple SummaryTamoxifen is an important adjuvant endocrine therapy in estrogen receptor (ER)-positive breast cancer patients. It is mainly catalyzed by the enzyme CYP2D6 into the most active metabolite endoxifen. Genetic variation in the CYP2D6 gene influences endoxifen formation and thereby potentially therapy outcome. However, the association between CYP2D6 genotype and clinical outcome on tamoxifen is still under debate, as contradictory outcomes have been published. This review describes the latest insights in both CYP2D6 genotype and endoxifen concentrations, as well CYP2D6 genotype and clinical outcome, from 2018 to 2020.Tamoxifen is a major option for adjuvant endocrine treatment in estrogen receptor (ER) positive breast cancer patients. The conversion of the prodrug tamoxifen into the most active metabolite endoxifen is mainly catalyzed by the enzyme cytochrome P450 2D6 (CYP2D6). Genetic variation in the CYP2D6 gene leads to altered enzyme activity, which influences endoxifen formation and thereby potentially therapy outcome. The association between genetically compromised CYP2D6 activity and low endoxifen plasma concentrations is generally accepted, and it was shown that tamoxifen dose increments in compromised patients resulted in higher endoxifen concentrations. However, the correlation between CYP2D6 genotype and clinical outcome is still under debate. This has led to genotype-based tamoxifen dosing recommendations by the Clinical Pharmacogenetic Implementation Consortium (CPIC) in 2018, whereas in 2019, the European Society of Medical Oncology (ESMO) discouraged the use of CYP2D6 genotyping in clinical practice for tamoxifen therapy. This paper describes the latest developments on CYP2D6 genotyping in relation to endoxifen plasma concentrations and tamoxifen-related clinical outcome. Therefore, we focused on Pharmacogenetic publications from 2018 (CPIC publication) to 2021 in order to shed a light on the current status of this debate.

Therapeutic Drug Monitoring of Psychotropics as a Diagnostic Tool for CYP2D6 Poor Metabolizer Phenotype.

Interpatient variability in cytochrome P450 2D6 (CYP2D6) enzyme activity alters the serum concentrations of most psychotropics, which often have narrow therapeutic indices. Therefore, preemptive knowledge of CYP2D6 activity is desired. However, accessible indicators for deficient CYP2D6 activity are necessary because genotyping all patients prescribed CYP2D6 metabolized drugs is often not feasible or cost-effective. In this study, the predictive value of the ratio between a CYP2D6 substrate and its metabolite, known as the metabolic ratio (MR), the dose-corrected serum concentration of substrate (CDR), and the dose-corrected sum concentration of substrate and metabolite (Sum CDR) of venlafaxine, risperidone, aripiprazole, and nortriptyline were determined to predict the CYP2D6 poor metabolizer (PM) phenotype. The area-under-the-receiver operator characteristic curve, as well as the sensitivity, specificity, and positive and negative predictive values of the optimal thresholds, were calculated. Although the MR, CDR, and Sum CDR all predicted the CYP2D6 PM phenotype, the predictive value of the MR was most robust for venlafaxine and aripiprazole, and the Sum CDR was inferior for all 3 psychotropics. MRs of venlafaxine, risperidone, and aripiprazole, and CDR of nortriptyline showed an area-under-the-receiver operator characteristics (95% confidence interval) of 97.2% (94.7%-99.6%), 93.0% (88.8%-97.2%), 97.8% (95.4%-100.0%), and 85.6% (78.0%-93.1%), respectively. Thresholds of the log(MR) of ≥0.1 for venlafaxine, ≥0.0 for risperidone, and ≥1.5 for aripiprazole, and log(CDR) ≥0.5 for nortriptyline produced >92% sensitivity and >64% specificity. If therapeutic drug monitoring is available, the thresholds presented here could serve as a diagnostic tool for the CYP2D6 PM phenotype of psychiatric patients prescribed the aforementioned psychotropic medications.

Impact of Pharmacogenomic Information on Values of Care and Quality of Life Associated with Codeine and Tramadol-Related Adverse Drug Events

ObjectiveTo assess the potential impact of Pharmacogenomic (PGx) variation in cytochrome P450 2D6 (CYP2D6) enzyme function, using loss in quality-adjusted life years (QALYs) associated with treatment problems, and the willingness to pay to avoid treatment problems from patients’ and payers’ perspectives. Patients and MethodsThe study included patients prescribed tramadol or codeine, or both, between January 1, 2005, and December 31, 2017. Demographic information and adverse drug events, including adverse drug events and poor pain control, were collected from the electronic health records using natural language processing techniques and review by trained abstractors. Patients’ willingness to pay and QALY estimates were based on comprehensive literature review. The CYP2D6 phenotypes were divided into 4 groups: ultra-rapid metabolizers, normal metabolizers, intermediate metabolizers, and poor metabolizers. ResultsAmong the 2860 identified patients, 63 (2%) were ultrarapid metabolizers, 1449 (50%) were normal metabolizers, 1155 (40%) were intermediate metabolizers, and 193 (7%) were poor metabolizers. The patients’ average estimated willingness-to-pay value to avoid treatment problems was $23 per month; poor metabolizers developed problems with the highest estimated willingness-to-pay value ($32 per month). The mean QALY loss among all patients was 0.024 QALYs (8.8 healthy days); poor metabolizers had the highest loss (0.027 QALYs, 9.9 healthy days). ConclusionPatients with various phenotypes developed different treatment problem profiles. Poor CYP2D6 metabolizers developed problems with highest willingness to pay, and they might potentially benefit most from PGx-guided treatment and problem prevention.

CYP2D6 genotype may moderate measures of brain structure in methamphetamine users.

Chronic methamphetamine use is linked to abnormalities in brain structure, which may reflect neurotoxicity related to metabolism of the drug. As the cytochrome P450 2D6 (CYP2D6) enzyme is central to the metabolism of methamphetamine, genotypic variation in its activity may moderate effects of methamphetamine on brain structure and function. This study explored the relationship between CYP2D6 genotype and measures of brain structure and cognition in methamphetamine users. Based on the function of genetic variants, a CYP2D6 activity score was determined in 82 methamphetamine-dependent (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition [DSM-IV] criteria) and 79 healthy-control participants who completed tests of cognitive function (i.e., attention, memory, and executive function); most were also evaluated with structural magnetic resonance imaging (MRI) (66 methamphetamine-dependent and 52 controls). The relationship between CYP2D6 activity score and whole brain cortical thickness differed by group (interaction p = 0.024), as increasing CYP2D6 activity was associated with thinner cortical thickness in the methamphetamine users (β = -0.254; p = 0.035), but not in control subjects (β = 0.095; p = 0.52). Interactions between CYP2D6 activity and group were nonsignificant for hippocampal volume (ps > 0.05), but both hippocampi showed trends similar to those observed for cortical thickness (negative relationships in methamphetamine users [ps < 0.05], and no relationships in controls [ps > 0.50]). Methamphetamine users had lower cognitive scores than control subjects (p = 0.007), but there was no interaction between CYP2D6 activity score and group on cognition (p > 0.05). Results suggest that CYP2D6 genotypes linked to higher enzymatic activity may confer risk for methamphetamine-induced deficits in brain structure. The behavioral consequences of these effects are unclear and warrant additional investigation.

Inhibitory Effects of Quercetin and Its Main Methyl, Sulfate, and Glucuronic Acid Conjugates on Cytochrome P450 Enzymes, and on OATP, BCRP and MRP2 Transporters.

Quercetin is a flavonoid, its glycosides and aglycone are found in significant amounts in several plants and dietary supplements. Because of the high presystemic biotransformation of quercetin, mainly its conjugates appear in circulation. As has been reported in previous studies, quercetin can interact with several proteins of pharmacokinetic importance. However, the interactions of its metabolites with biotransformation enzymes and drug transporters have barely been examined. In this study, the inhibitory effects of quercetin and its most relevant methyl, sulfate, and glucuronide metabolites were tested on cytochrome P450 (CYP) (2C19, 3A4, and 2D6) enzymes as well as on organic anion-transporting polypeptides (OATPs) (OATP1A2, OATP1B1, OATP1B3, and OATP2B1) and ATP (adenosine triphosphate) Binding Cassette (ABC) (BCRP and MRP2) transporters. Quercetin and its metabolites (quercetin-3′-sulfate, quercetin-3-glucuronide, isorhamnetin, and isorhamnetin-3-glucuronide) showed weak inhibitory effects on CYP2C19 and 3A4, while they did not affect CYP2D6 activity. Some of the flavonoids caused weak inhibition of OATP1A2 and MRP2. However, most of the compounds tested proved to be strong inhibitors of OATP1B1, OATP1B3, OATP2B1, and BCRP. Our data demonstrate that not only quercetin but some of its conjugates, can also interact with CYP enzymes and drug transporters. Therefore, high intake of quercetin may interfere with the pharmacokinetics of drugs.

Green Method Synthesised Graphene-Silver Electrochemical Nanobiosensors for Ethambutol and Pyrazinamide

A novel nanobiosensor was constructed with graphene oxide (GO) sheets coupled to pear extract-based green-synthesised silver nanoparticles (Ag-NPs) to which cytochrome P450-2D6 (CYP2D6) enzyme was attached. The biosensor was applied in the electrochemical detection of the tuberculosis (TB) treatment drugs, ethambutol (EMB) and pyrazinamide (PZA). The surface morphology of the green-synthesised nanocomposites was studied by performing High-Resolution Transmission Electron Microscopy (HR-TEM) and High-Resolution Scanning Electron Microscopy (HR-SEM). Fourier Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy were used for structural analysis, while Ultraviolet Visible (UV-Vis) Spectroscopy was used in the optical characterisation of the nanocomposite material. Electrochemical studies on glassy carbon electrode (GCE), which were done by Cyclic Voltammetry (CV), showed that the GO|Ag-NPs||GCE electrode was highly conductive, and thereby indicating its suitability as a platform for nanobiosensor development. The non-toxic and low-cost green GO|Ag-NPs|CYP2D6||GCE nanobiosensor was used to determine EMB and PZA. The very low limit of detection (LOD) values of the biosensor for EMB (0.2962 × 10−2 nM, S/N = 3) and PZA (0.897 × 10−2 nM, S/N = 3) demonstrate that the green nanobiosensor is more sensitive than other biosensors reported for EMB and PZA.

Association analysis of premature coronary artery disease and cytochrome P450 2D6 (CYP2D6) C100T and G1846A genetic variants and haplotypes in Iranian population

BackgroundPremature coronary artery disease (pCAD) is a heterogeneous disease affected by both genetic and environmental determinants. Cytochrome P450 2D6 (CYP2D6) enzyme plays an important role in the oxidation of drugs and inactivation of reactive species. Therefore, polymorphisms in CYP2D6 may lead to an increased susceptibility to pCAD. Here, we analyzed the association between C100T and G1846A polymorphisms of CYP2D6 gene with pCAD in a south Iranian population. MethodsMen under 45 and women under 55 years old enrolled in this study as 168 pCAD patients and 167 controls. Clinical characteristics of participants were assessed thorough clinical examination. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was applied for C100T and G1846A polymorphisms. ResultsThe results indicated that the history of smoking and hypertension were significantly associated with the incidence of pCAD (p < .05). However, results showed that allelic frequencies for none of the study polymorphisms in CYP2D6 were different between case and control groups. Furthermore, they were not associated with the risk of pCAD development in the study population. To better diagnosis of the molecular genetic basis of pCAD as a complex disease, this study used two-locus haplotypes of CYP2D6 polymorphisms as novel biomarkers for pCAD for the first time which also did not show a significant result. ConclusionThis study demonstrated no significant association of C100T and G1846A polymorphisms of CYP2D6 with pCAD in the south Iranian population. The possible explanation may be attributed to the differences in dissimilar ethnic, genetic, and environmental backgrounds, and also different sample sizes.

Prescribed Doses of CYP2D6-Metabolized Drugs and Hemodynamic Responses in Relation to CYP2D6 Genotype Among Older Patients Exposed to Polypharmacy.

BackgroundMany drugs with dose-dependent effects on hemodynamic variables are metabolized by cytochrome P450 2D6 (CYP2D6). The aim of this study was to compare prescribed dosages and hemodynamic responses of such drugs in relation to pharmacogenetic variability in CYP2D6 metabolism among patients aged ≥ 70 years exposed to polypharmacy.Materials and MethodsWe included 173 patients with detailed information about drug use. The patients were retrospectively subjected to CYP2D6 genotyping, which comprised the most common variant alleles encoding reduced, absent, or increased CYP2D6 metabolism. In order to compare dosages across different CYP2D6-metabolized drugs, all prescribed daily doses were harmonized to the ‘percent of a daily defined dose’ (DDD). The mean harmonized DDD was compared between genotype-predicted normal metabolizers (NMs) and patients with reduced or absent CYP2D6 enzyme activity, defined as intermediate or poor metabolizers (IMs/PMs). Blood pressure, pulse, and patient proportions with orthostatism and bradycardia were also compared between genotype subgroups.ResultsThe genotype-predicted phenotype subgroups comprised 79 NMs (45.7%), 75 IMs (43.4%), and 16 PMs (9.2%). There were no differences in dosing of CYP2D6 substrates between NMs and IMs/PMs (p = 0.76). A higher proportion of CYP2D6 IMs/PMs experienced orthostatism (p = 0.03), while there were no significant subgroup differences for the other hemodynamic variables.ConclusionIn this real-life clinical setting of patients aged ≥ 70 years, dosing of CYP2D6 substrates were not adjusted according to genotype-predicted CYP2D6 metabolism. The increased occurrence of orthostatism in patients with reduced/absent CYP2D6 metabolism may indicate that individualized dosing based on genotype has the potential to prevent adverse effects in these vulnerable patients.Electronic supplementary materialThe online version of this article (10.1007/s40266-020-00763-0) contains supplementary material, which is available to authorized users.

Dosage Appropriacy Evaluation of Oral Venlafaxine Related to CYP2D6 Genotype Using Physiologically Based Pharmacokinetic (PBPK) Model

Venlafaxine is an antidepressant drug of serotonin‐norepinephrine reuptake inhibitor (SNRI) class, used major depressive disorder, anxiety, and panic disorder patients. Desvenlafaxine, a major metabolite of venlafaxine mediated by cytochrome P450 2D6 (CYP2D6), is also used to treat depressive, anxiety disorder because it has pharmacological effect which inhibits reuptake of serotonin and norepinephrine. Therefore, sum of venlafaxine and desvenlafaxine concentration is important for adequate prediction of the drug response of venlafaxine. Venlafaxine is administrated 75mg/day conventionally, 225mg/day maximum. Venlafaxine is minorly metabolized to N‐desmethyl venlafaxine, and desvenlafaxine is metabolized to N, O‐didesmethyl venlafaxine, both compounds are inactive forms pharmacologically. Because CYP2D6*10 decreases its enzyme activity, and CYP2D6*4, CYP2D6*5 abolish its enzyme activity, the pharmacokinetics of venlafaxine and desvenlafaxine are considerably affected by CYP2D6 polymorphism. For an accurate evaluation of drug response followed CYP2D6 genotypes in venlafaxine and its metabolite, physiologically based pharmacokinetic (PBPK) model was used for concentration simulation of both compounds. In our study, we did an extensive investigation of literature and gathered pharmacokinetic profile data of venlafaxine and its metabolite. Through Engauge Digitizer®, pharmacokinetic profiles were extracted and converted to numerical values. For model development and verification, PK‐Sim® 8 software was used to get simulated values of pharmacokinetic parameters. Physiological and chemical parameters were inputted, and Vmax, Km values were adjusted to reflect the CYP2D6 enzyme activity difference. Extracted data and simulated data were compared using two‐fold error criteria. The ratio of simulated data and observed data in CYP2D6*1/*1, CYP2D6*1/*10, CYP2D6*10/*10, CYP2D6*5/*5 groups for AUC were 0.88, 1.24, 1.15, 0.72, Cmax were 0.80, 1.24, 1.14, 1.33, Tmax were 0.93, 0.87, 0.87, 0.87. All simulated data for model development were within suitable criteria, and data conducted diverse ethnic and dose for verification also were within criteria. Thus, it was confirmed that the PBPK model of venlafaxine and its metabolite had been properly developed. Based on the above model, we simulated blood concentration at 75mg, 150mg, 225mg dose, evaluated therapeutic effects and toxicity. In CYP2D6*1/*1, CYP2D6*1/*10, CYP2D6*10/*10 groups, the concentrations of active moiety were similar, but CYP2D6 PM was significantly increased. Because toxicity level was reached after 150mg administration of venlafaxine in CYP2D6 PM, dose reduction is mandatory required. In the future, through PBPK modeling, the adequacy of conventional dose of other drugs should be assessed, and individual dose adjustment will be made for maximum therapeutic effects and minimal toxicities.Development of PBPK model in venlafaxine and its metabolite according to CYP2D6 genotype. (A) CYP2D6*1/*1 (B) CYP2D6 PM (C) CYP2D6*1/*10 (D) CYP2D6*10/*10Figure 1venlafaxine 75mg dosage evaluation based on CYP2D6 genotype. dotted lines represent concentrations of optimal therapeutic responseFigure 2

Oncology and psychiatry intersect

Ms. Patmore is a 51-year-old premenopausal female who presents to her family physician’s office with an ongoing episode of severe depression. She is accompanied by her daughter, who reports her mother’s inability to sleep, a lack of appetite, low energy and speech latency.1 Past medical history is significant for major depressive disorder (MDD) diagnosed five years ago and managed effectively in the past three years with the selective serotonin reuptake inhibitor (SSRI) fluoxetine (20 mg/d). Ms. Patmore’s daughter reports their family’s recent concerns that Ms. Patmore is becoming increasingly depressed, with similar characteristics as her initial depressive episodes five years previously.&#x0D; Ms. Patmore has a recent (1 year) history of estrogen-receptor positive invasive ductal carcinoma (IDC; T1N1 disease) that was identified on routine mammogram. She underwent a unilateral mastectomy 10 months ago and surgical reconstruction is pending. Post-operatively, Ms. Patmore began adjuvant therapy with oral tamoxifen (20 mg/d) as her cancer was found to be estrogen receptor (ER) positive.2 Her daughter reports that at that time, fluoxetine was replaced with the SSRI escitalopram (20 mg/d), owing to the propensity for drug interactions between certain SSRIs (including fluoxetine) and the cytochrome P450 (CYP) 2D6 enzyme, which metabolizes tamoxifen to its active metabolite, endoxifen.3 Over the past three months, Ms. Patmore’s depressive symptoms have returned and worsened.

Abstract P2-11-12: The influences of adherence to tamoxifen and CYP2D6 pharmacogenetics on plasma concentrations of the active metabolite (Z)-endoxifen in breast cancer

Abstract One-third of early breast cancer patients with estrogen receptor (ER) positive tumors treated with the selective estrogen receptor modulator tamoxifen either relapse or die from the disease in the following decade. Improvement of tamoxifen efficacy requires a better knowledge of factors determining outcome of which the medication-taking behavior, i.e. adherence, is a strong suspect. Discontinuation and non-adherence to tamoxifen are frequent and result in increased mortality. Commonly used methods to assess drug adherence such as prescription-refill patterns infer that the medication is taken exactly as prescribed yet, partial adherence or actual use of the medication cannot be controlled. An objective surrogate of tamoxifen adherence is the monitoring of drug concentrations in the patients’ plasma including the parent drug and its active metabolite (Z)-endoxifen (endoxifen), however individual concentrations depend on pharmacogene polymorphisms particularly those of the liver enzyme cytochrome P450 2D6 (CYP2D6). Patients without CYP2D6 variants have normal enzyme function (extensive metabolizer, EM) and achieve high endoxifen concentrations compared to patients with variants conferring absent activity (poor metabolizer, PM) or reduced activity (intermediate metabolizer, IM) who have significantly lower plasma concentrations of the active metabolite. A putative threshold of 5.9 ng/mL endoxifen has been proposed suggesting that patients with endoxifen concentration above or below threshold have lower or higher risk for recurrence, assuming that low endoxifen exposure in the tumor likely results in incomplete inhibition of ER-dependent growth signaling. During tamoxifen treatment it is therefore important that patients achieve clinically relevant endoxifen levels while at the same time avoid confounders of which adherence is a prime candidate. To this end, we investigated patients’ ability to achieve relevant plasma concentrations during tamoxifen treatment in relation to their CYP2D6 metabolizer status and their tamoxifen adherence behavior. Our prospective study included 192 Brazilian breast cancer patients treated with 20 mg tamoxifen daily. Two-thirds of the patients were premenopausal. Plasma levels of tamoxifen and its metabolites were measured by LC-MS/MS at 3, 6 and 12 months of treatment. Adherence to tamoxifen was evaluated by the questionnaire-based Morisky medication adherence scale. CYP2D6 polymorphisms were determined by MALDI-TOF mass spectrometry and real-time PCR. Adherence to tamoxifen decreased from 74% at month 3 to 64% at month 12, and explained 47% of the variability of tamoxifen plasma concentrations (P&amp;lt;.001). Accordingly, plasma monitoring of tamoxifen is useful to inform on tamoxifen adherence. Endoxifen concentrations were associated with CYP2D6 status and adherence. While CYP2D6 explained 26.4% of endoxifen variability at 12 months, the combination with adherence explained 40% (P&amp;lt;.001). The influence of low adherence to not achieving therapeutic endoxifen levels was highest in patients with non-compromised CYP2D6 function (EM phenotype, RR 3.65; 95% CI: 1.48-8.99). we conclude that for patients with intact CYP2D6 function adherence to tamoxifen is critical to achieve therapeutic endoxifen plasma levels. CYP2D6 phenotyping and endoxifen plasma monitoring may help to guide EM (and IM) patients to adhere to tamoxifen which is particularly relevant for premenopausal women who are at higher risk to not adhere to tamoxifen. Citation Format: Jose Claudio Casali da Rocha, Jeanine M Nardin, Werner Schroth, Thais A Almeida, Thomas Mürdter, Solange Picolotto, Evelyn CL Vendramini, Reiner Hoppe, Jenifer P Kogin, Diandra Miqueleto, Silvia DR Moraes, Matthias Schwab, Roberto F Pecoits-Filho, Hiltrud Brauch. The influences of adherence to tamoxifen and CYP2D6 pharmacogenetics on plasma concentrations of the active metabolite (Z)-endoxifen in breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-11-12.

Cytochrome P450 2D6 polymorphism in eastern Indian population.

OBJECTIVES:Cytochrome P450 2D6 (CYP2D6) enzyme metabolizes a quarter of prescription drugs. Polymorphisms of CYP2D6 gene and resultant phenotypic variations in metabolic activity have been described in various populations. We assessed the prevalence of CYP2D6 activity phenotypes, employing dextromethorphan (DXM) as probe drug in subjects with at least two parental generations residing in eastern India.MATERIALS AND METHODS:Unrelated healthy subjects took 60 mg DXM after fasting overnight. Blood samples were collected 3 h after dosing and plasma separated. DXM and its primary metabolite dextrorphan (DXT) were measured by liquid chromatography with tandem mass spectrometry. The DXM-to-DXT metabolic ratio (MR) was obtained for each subject. Histogram of MR values suggested bimodal distribution. A polynomial regression equation derived through probit analysis was solved to identify the antimode of the MR values. Subjects with log(MR) < antimode were extensive metabolizers (EMs). Log(MR) ≥ antimode indicated poor metabolizers (PMs).RESULTS:We evaluated the results from 97 participants. The median MR was 0.209 (interquartile range: 0.090–0.609), while the antimode for MR was 3.055. From these, it was inferred that three subjects were PMs, while the rest were EMs. CYP2D6 polymorphism prevalence is low (3.09%; 95% confidence interval: 0.35%–6.54%) in the population of eastern India and matches the prevalence in other zones of the country.CONCLUSIONS:Differences in CYP2D6 activity has treatment implications and may lead to adverse events or therapeutic failure. Phenotyping of subjects receiving CYP2D6 metabolized drugs may help clinicians personalize treatment and avert adverse drug-drug interactions. However, the frequency of the PM phenotype is low in India, and routinely phenotyping for CYP2D6 activity will not be cost-effective. We cannot recommend it at this stage.

Clinical Relevance of CYP2D6 Polymorphisms in Patients of an Austrian Medical Practice: AFamily Practice-Based Observational Study.

BackgroundAround 20–30% of all prescribed drugs are estimated to be metabolised by the cytochrome P450 (CYP) 2D6 enzyme. In a medical practice, it is usually not known whether a patient is a poor, intermediate, normal or ultra-rapid metaboliser for CYP2D6-metabolised drugs.ObjectiveThis study aims to explore the clinical relevance and the extent of hazardous prescriptions by analysing the metaboliser status of patients already taking such drugs.MethodsThis is a family practice-based observational study performed in a rural practice for general and family medicine in Lower Austria providing care for approximately 2100 patients annually. In 287 consecutive patients, who had taken or were taking a drug metabolised by CYP2D6 during the last 3 years, the metaboliser status was analysed.ResultsThe genetic analysis of 287 patients resulted in 51.22% normal metabolisers, 38.68% intermediate metabolisers, 6.27% poor metabolisers and 3.83% ultra-rapid metabolisers. In 50 cases (poor metaboliser, intermediate metaboliser and ultra-rapid metaboliser, i.e. 17.42% of all tested patients taking a CYP2D6-specific drug), an altered gene function was identified, for which clinical guideline annotations, drug label annotations, or clinical annotations are available. Allele and genotype frequencies were in accordance with data from other European studies.ConclusionsIn 17.42% of all patients already taking a drug metabolised by CYP2D6, knowledge of the genetically defined metaboliser status would have been of immediate clinical relevance before prescribing the drug.ClinicalTrials.gov identifierNCT03859622.Electronic supplementary materialThe online version of this article (10.1007/s40801-019-00177-4) contains supplementary material, which is available to authorized users.