Midostaurin drug interaction profile: a comprehensive assessment of CYP3A, CYP2B6, and CYP2C8 drug substrates, and oral contraceptives in healthy participants

PURPOSE

Midostaurin, approved for treating FLT-3-mutated acute myeloid leukemia and advanced systemic mastocytosis, is metabolized by cytochrome P450 (CYP) 3A4 to two major metabolites, and may inhibit and/or induce CYP3A, CYP2B6, and CYP2C8. Two studies investigated the impact of midostaurin on CYP substrate drugs and oral contraceptives in healthy participants.

METHODS

Using sentinel dosing for participants' safety, the effects of midostaurin at steady state following 25-day (Study 1) or 24-day (Study 2) dosing with 50 mg twice daily were evaluated on CYP substrates, midazolam (CYP3A4), bupropion (CYP2B6), and pioglitazone (CYP2C8) in Study 1; and monophasic oral contraceptives (containing ethinylestradiol [EES] and levonorgestrel [LVG]) in Study 2.

RESULTS

In Study 1, midostaurin resulted in a 10% increase in midazolam peak plasma concentrations (Cmax), and 3-4% decrease in total exposures (AUC). Bupropion showed a 55% decrease in Cmax and 48-49% decrease in AUCs. Pioglitazone showed a 10% decrease in Cmax and 6% decrease in AUC. In Study 2, midostaurin resulted in a 26% increase in Cmax and 7-10% increase in AUC of EES; and a 19% increase in Cmax and 29-42% increase in AUC of LVG. Midostaurin 50 mg twice daily for 28 days ensured that steady-state concentrations of midostaurin and the active metabolites were achieved by the time of CYP substrate drugs or oral contraceptive dosing. No safety concerns were reported.

CONCLUSION

Midostaurin neither inhibits nor induces CYP3A4 and CYP2C8, and weakly induces CYP2B6. Midostaurin at steady state has no clinically relevant PK interaction on hormonal contraceptives. All treatments were well tolerated.

Uncoupling of Cytochrome P450 2B6 and stimulation of reactive oxygen species production in pharmacogenomic alleles affected by interethnic variability

Cytochrome P450 mediated substrate metabolism is generally characterized by the formation of reactive intermediates. In vitro and in vivo reaction uncoupling, results in the accumulation and dissociation of reactive intermediates, leading to increased ROS formation. The susceptibility towards uncoupling and altered metabolic activity is partly modulated by pharmacogenomic alleles resulting in amino acid substitutions. A large variability in the prevalence of these alleles has been demonstrated in CYP2B6, with some being predominantly unique to African populations. The aim of this study is to characterize the uncoupling potential of recombinant CYP2B6*1, CYP2B6*6 and CYP2B6*34 metabolism of specific substrates. Therefore, functional effects of these alterations on enzyme activity were determined by quantification of bupropion, efavirenz and ketamine biotransformation using HPLC-MS/MS. Determination of H2O2 levels was performed by the AmplexRed/horseradish peroxidase assay. Our studies of the amino acid substitutions Q172H, K262R and R487S revealed an exclusive use of the peroxide shunt for the metabolism of bupropion and ketamine by CYP2B6*K262R. Ketamine was also identified as a trigger for the peroxide shunt in CYP2B6*1 and all variants. Concurrently, ketamine acted as an uncoupler for all enzymes. We further showed that the expressed CYP2B6*34 allele results in the highest H2O2 formation. We therefore conclude that the reaction uncoupling and peroxide shunt are directly linked and can be substrate specifically induced with K262R carriers being most likely to use the peroxide shunt and R487S carrier being most prone to reaction uncoupling. This elucidates the functional diversity of pharmacogenomics in drug metabolism and safety.

Pharmacogenetic Influence on Stereoselective Steady-State Disposition of Bupropion

Bupropion is used for treating depression, obesity, and seasonal affective disorder, and for smoking cessation. Bupropion is commonly prescribed, but has complex pharmacokinetics and interindividual variability in metabolism and bioactivation may influence therapeutic response, tolerability, and safety. Bupropion is extensively and stereoselectively metabolized, the metabolites are pharmacologically active, and allelic variation in cytochrome P450 (CYP) 2B6 affects clinical hydroxylation of single-dose bupropion. Genetic effects on stereoselective disposition of steady-state bupropion are not known. In this preplanned secondary analysis of a prospective, randomized, double-blinded, crossover study which compared brand and generic bupropion XL 300 mg drug products, we measured steady-state enantiomeric plasma and urine parent bupropion and primary and secondary metabolite concentrations. This investigation evaluated the influence of genetic polymorphisms in CYP2B6, CYP2C19, and P450 oxidoreductase on the disposition of Valeant Pharmaceuticals Wellbutrin brand bupropion in 67 participants with major depressive disorder. We found that hydroxylation of both bupropion enantiomers was lower in carriers of the CYP2B6*6 allele and in carriers of the CYP2B6 516G>T variant, with correspondingly greater bupropion and lesser hydroxybupropion plasma concentrations. Hydroxylation was 25-50% lower in CYP2B6*6 carriers and one-third to one-half less in 516T carriers. Hydroxylation of the bupropion enantiomers was comparably affected by CYP2B6 variants. CYP2C19 polymorphisms did not influence bupropion plasma concentrations or hydroxybupropion formation but did influence the minor pathway of 4'-hydroxylation of bupropion and primary metabolites. P450 oxidoreductase variants did not influence bupropion disposition. Results show that CYP2B6 genetic variants affect steady-state metabolism and bioactivation of Valeant brand bupropion, which may influence therapeutic outcomes. SIGNIFICANCE STATEMENT: Bupropion, used for depression, obesity, and smoking cessation, undergoes metabolic bioactivation, with incompletely elucidated interindividual variability. We evaluated cytochrome P450 (CYP) 2B6, CYP2C19 and P450 oxidoreductase genetic variants and steady-state bupropion and metabolite enantiomers disposition. Both enantiomers hydroxylation was lower in CYP2B6*6 and CYP2B6 516G>T carriers, with greater bupropion and lesser hydroxybupropion plasma concentrations. CYP2C19 polymorphisms did not affect bupropion or hydroxybupropion but did influence minor 4'-hydroxylation of bupropion and primary metabolites. CYP2B6 variants affect steady-state bupropion bioactivation, which may influence therapeutic outcomes.

Brain-derived neurotrophic factor Val66Met and CYP2B6 polymorphisms as predictors for ketamine effectiveness in patients with treatment-resistant depression

BACKGROUND

Converging lines of evidence indicate that ketamine is a rapid antidepressant for individuals with treatment-resistant depression. Hitherto, no reliable a priori predictors of ketamine response have been reported. Pharmacogenetic biomarkers have yielded mixed results regarding potential candidate genes associated with ketamine's biochemistry as reliable predictors of response.

AIMS

No studies have examined the effects of Val66Met and CYP2B6 genotypes on patients receiving repeated infusions of intravenous ketamine.

METHODS

In all, 85 participants with major depressive disorder who had previously received four infusions of intravenous ketamine were recruited to the foregoing study. Buccal swabs were collected and genotype variants across the Val66Met and CYP2B6 genes were analyzed. A repeated measures mixed linear model was used to assess change in depressive symptoms, suicidality, and anxiety, correcting for sex and age. Multiple regression was run to determine whether these genetic markers were associated with treatment efficacy for depressive severity, suicidal ideation, anxiolytic response, and degree of dissociation to intravenous ketamine.

RESULTS

Participants experienced significant overall reductions in depression, suicide, and anxiety. Overall, 25% met the response criteria and 15% met the remission criteria. However, Val66Met and CYP2B6 did not significantly predict changes in symptoms of depression, suicide, anxiety, or average dissociation.

CONCLUSIONS

This study contributes to the growing literature that ketamine efficacy is unlikely to be predicted by single genes, and a pleiotropic approach may likely be necessary for developing reliable predictors of clinical benefits.

The role of polymorphic cytochrome P450 gene (CYP2B6) in B-chronic lymphocytic leukemia (B-CLL) incidence and outcome among Egyptian patients

Cytochromes P450 (CYPs) play a prominent role in catalyzing phase I xenobiotic biotransformation and account for about 75% of the total metabolism of commercially available drugs, including chemotherapeutics. The gene expression and enzyme activity of CYPs are variable between individuals, which subsequently leads to different patterns of susceptibility to carcinogenesis by genotoxic xenobiotics, as well as differences in the efficacy and toxicity of clinically used drugs. This research aimed to examine the presence of the CYP2B6*9 polymorphism and its possible association with the incidence of B-CLL in Egyptian patients, as well as the clinical outcome after receiving cyclophosphamide chemotherapy. DNA was isolated from whole blood samples of 100 de novo B-CLL cases and also from 100 sex- and age-matched healthy individuals. The presence of the CYP2B6*9 (G516T) polymorphism was examined by PCR-based allele specific amplification (ASA). Patients were further indicated for receiving chemotherapy, and then they were followed up. The CYP2B6*9 variant indicated a statistically significant higher risk of B-CLL under different genetic models, comprising allelic (T-allele vs. G-allele, OR = 4.8, p < 0.001) and dominant (GT + TT vs. GG, OR = 5.4, p < 0.001) models. Following cyclophosphamide chemotherapy, we found that the patients with variant genotypes (GT + TT) were less likely to achieve remission compared to those with the wild-type genotype (GG), with a response percentage of (37.5% vs. 83%, respectively). In conclusion, our findings showed that the CYP2B6*9 (G516T) polymorphism is associated with B-CLL susceptibility among Egyptian patients. This variant greatly affected the clinical outcome and can serve as a good therapeutic marker in predicting response to cyclophosphamide treatment.

Characterization of CYP2B6 and CYP2A6 Pharmacogenetic Variation in Sub-Saharan African Populations

Genetic variation in CYP2B6 and CYP2A6 is known to impact interindividual response to antiretrovirals, nicotine, and bupropion, among other drugs. However, the full catalogue of clinically relevant pharmacogenetic variants in these genes is yet to be established, especially across African populations. This study therefore aimed to characterize the star allele (haplotype) distribution in CYP2B6 and CYP2A6 across diverse and understudied sub-Saharan African (SSA) populations. We called star alleles from 961 high-depth full genomes using StellarPGx, Aldy, and PyPGx. In addition, we performed CYP2B6 and CYP2A6 star allele frequency comparisons between SSA and other global biogeographical groups represented in the new 1000 Genomes Project high-coverage dataset (n = 2,000). This study presents frequency information for star alleles in CYP2B6 (e.g., *6 and *18; frequency of 21-47% and 2-19%, respectively) and CYP2A6 (e.g., *4, *9, and *17; frequency of 0-6%, 3-10%, and 6-20%, respectively), and predicted phenotypes (for CYP2B6), across various African populations. In addition, 50 potentially novel African-ancestry star alleles were computationally predicted by StellarPGx in CYP2B6 and CYP2A6 combined. For each of these genes, over 4% of the study participants had predicted novel star alleles. Three novel star alleles in CYP2A6 (*54, *55, and *56) and CYP2B6 apiece, and several suballeles were further validated via targeted Single-Molecule Real-Time resequencing. Our findings are important for informing the design of comprehensive pharmacogenetic testing platforms, and are highly relevant for personalized medicine strategies, especially relating to antiretroviral medication and smoking cessation treatment in Africa and the African diaspora. More broadly, this study highlights the importance of sampling diverse African ethnolinguistic groups for accurate characterization of the pharmacogene variation landscape across the continent.

Methadone pharmacokinetics in opioid agonist treatment: Influencing factors and clinical implications

BACKGROUND

A considerable inter-individual variability has been reported in the relationship between methadone doses applied and serum concentrations achieved in methadone maintenance treatment. However, the underlying causes for this variability are not fully understood.

OBJECTIVES

We investigated the influence of genetic, pathophysiological and pharmacological factors on serum methadone concentration-to-dose ratio (CDR) and discussed the clinical implications of the findings.

METHODS

We used data from two retrospective laboratory databases and a prospective cohort study to investigate the impact on methadone CDR of hepatic cytochrome P450 enzyme system (CYP) genetic polymorphisms, age, sex, concomitant medication, liver fibrosis and body mass index through linear mixed model analyses.

FINDINGS

A positive association was found between CDR and the homozygous CYP2B6*6 genotype, concurrent treatment with CYP3A4 inhibitors and body mass index. CDR was lower among women and during concomitant use of CYP inducers. CDR was not associated with age or the degree of liver fibrosis in our investigations.

CONCLUSIONS

This research work supports the need for individually tailored dosage considering the various factors that influence methadone CDR. The gained knowledge can contribute to reducing the risks associated with the treatment and optimizing the desired outcomes.

Pharmacogenetics of weight gain following switch from efavirenz- to integrase inhibitor-containing regimens

BACKGROUND

Excessive weight gain affects some persons with HIV after switching to integrase strand transfer inhibitor (INSTI)-containing antiretroviral therapy (ART). We studied associations between CYP2B6 genotype and weight gain after ART switch among ACTG A5001 and A5322 participants.

METHODS

Eligible participants switched from efavirenz- to INSTI-containing ART, had genotype data, and had weight data at least once from 4 weeks to 2 years post-switch. Multivariable linear mixed effects models adjusted for race/ethnicity, CD4, age, BMI and INSTI type assessed relationships between CYP2B6 genotype and estimated differences in weight change.

RESULTS

A total of 159 eligible participants switched ART from 2007 to 2019, of whom 138 had plasma HIV-1 RNA < 200 copies/mL (65 CYP2B6 normal, 56 intermediate, 17 poor metabolizers). Among participants with switch HIV-1 RNA < 200 copies/mL, weight increased in all 3 CYP2B6 groups. The rate of weight gain was greater in CYP2B6 poor than in CYP2B6 normal metabolizers overall, and within 9 subgroups (male, female, White, Black, Hispanic, dolutegravir, elvitegravir, raltegravir, and TDF in the pre-switch regimen); only in Hispanic and elvitegravir subgroups were these associations statistically significant ( P  < 0.05). Compared to normal metabolizers, CYP2B6 intermediate status was not consistently associated with weight gain.

CONCLUSION

CYP2B6 poor metabolizer genotype was associated with greater weight gain after switch from efavirenz- to INSTI-containing ART, but results were inconsistent. Weight gain in this setting is likely complex and multifactorial.

Impact of CYP2D6 and CYP2B6 phenotypes on the response to tramadol in patients with acute post-surgical pain

Tramadol is an important minor opioid prescribed for pain management. In this study, we analyzed the well-known impact of CYP2D6 genetic variation and 60 additional variants in eight candidate genes (i.e., ABCG2, SLCO1B1, CYP2D6, CYP2B6, CYP2C19, CYP2C9, CYP3A5, and CYP3A4) on tramadol efficacy and safety. Some 108 patients with pain after surgery admitted to a post-anesthesia care unit (PACU) and prescribed tramadol were recruited. They were genotyped, and tramadol M1/M2 metabolite concentrations were determined by a newly validated HPLC-MS/MS method. CYP2D6 intermediate (IM) and poor (PM) metabolizers showed lower M1 concentrations adjusted for dose/weight at 30 and 120 min compared to ultrarapid (UM) and normal (NM) metabolizers (univariate p < 0.001 and 0.020, multivariate p < 0.001 and 0.001, unstandardized β coefficients = 0.386 and 0.346, R2  = 0.146 and 0.120, respectively). CYP2B6 PMs (n = 10) were significantly related to a higher reduction in pain 30 min after tramadol intake (univariate p = 0.038, multivariate p = 0.016, unstandardized β coefficient = 0.224, R2  = 0.178), to lower PACU admission time (p = 0.007), and to lower incidence of adverse drug reactions (p = 0.038) compared to the other phenotypes. CYP3A4 IMs and PMs showed a higher prevalence of drowsiness and dizziness (p = 0.028 and 0.005, respectively). Our results suggest that the interaction of CYP2B6 and CYP2D6 phenotypes may be clinically relevant, pending validation of these results in large, independent cohorts. Additional research is required to clarify the impact of CYP3A4 genetic variation on tramadol response.

Single-nucleotide polymorphism in CYP1A1, CYP1B1, CYP2B6, CYP2C8, and CYP2C9 genes and their association with gastrointestinal cancer: A hospital-based case-control study

BACKGROUND

Cytochrome P450 (CYP) comprises a group of phase-I metabolizing enzymes that are important in xenobiotics metabolism. Genetic polymorphism of CYPs has been comprehensively studied for their association with a range of diseases. In this study, we assessed single-nucleotide polymorphism (SNP) of CYP1A, CYP1B, CYP2B, and CYP2C and their role in gastrointestinal (GI) cancer susceptibility in the rural population of Maharashtra.

MATERIALS AND METHODS

In this hospital-based case-control study, the association of polymorphism of CYP genes was studied by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. The study subjects included 200 clinically confirmed GI cancer patients and equal number of healthy controls. Odds ratio (OR) with 95% confidence interval (CI) and P value were evaluated to find out the level of association, where P ≤ 0.005 was considered statistically significant.

RESULTS

After the analysis of CYP1A1*2A (rs4646903), CYP1B1*3 (rs1059836), CYP2B6*5 (rs3211371), CYP2C8*2 (rs11572103), CYP2C9*2 (rs1799853), and CYP2C9*3 (rs1057910), we noticed that variant (T) allele of CYP2B6*5 possessed significantly elevated risk (OR = 4.43; 95% CI: 2.20-8.90; P < 0.0001) of GI cancer in studied population. The genotypic distribution of G/C heterozygote allele of CYP1B1*3 (OR = 0.19, 95% CI = 0.12-0.32; P < 0.0001) and homozygous variant C/C allele (OR = 0.24, 95% CI = 0.13-0.45; P < 0.0001) showed a negative association with the development of GI cancer.

CONCLUSION

The findings from this study supported that polymorphism of CYP2B6*5gene may be involved in the development of GI cancer. However, other SNPs of CYP1A, CYP1B, and CYP2C genes did not signify the risk for GI cancer in the studied population of rural Maharashtra.

Genetic polymorphisms of CYP2B6 is a risk of metabolic associated fatty liver disease in Chinese population

BACKGROUND

The expression and activity of cytochrome P450 2B6 (CYP2B6) may be related to the metabolic associated fat liver disease (MAFLD). Since constitutive androstane receptor (CAR) is a classic transcriptional regulator of CYP2B6, and the single nucleotide polymorphisms (SNPs) of CYP2B6 and CAR are both associated with adverse reactions of efavirenz, we hypothesized that genetic polymorphisms of CAR might also result in additional interindividual variability in CYP2B6. This study was devoted to explore the association between CYP2B6 and CAR SNPs and susceptibility to MAFLD.

MATERIALS AND METHODS

A total of 590 objects of study (118 with MAFLD and 472 healthy control) between December 2014 and April 2018 were retrospectively enrolled. Twenty-two selected SNPs in CYP2B6 and CAR were genotyped with a custom-designed 48-plex SNP Scan TM® Kit. The frequencies of the alleles, genotypes and genetic models of the variants were compared between the two groups. The odds ratios (ORs) and the corresponding 95% confidence intervals (CIs) were calculated.

RESULTS

The T allele of rs3745274 in CYP2B6 was associated with a decreased risk for MAFLD (OR 0.610; 95% CI: 0.451-0.825, p = 0.001) which was still statistically significant after adjusting with Bonferroni method(p = 0.014) The allele, genotype and genetic model frequencies were similar in the two groups for the other twenty-one SNPs (all P > 0.05). There were no multiplicative or additive interactions between the SNPs.

CONCLUSION

Our study revealed that rs3745274 variants in CYP2B6 is associated with susceptibility to MAFLD in the Han Chinese population.

Genetic polymorphisms in CYP2B6 may be associated with lung cancer risk in the Chinese Han population

BACKGROUND

Our study aimed to elucidate the association between single nucleotide polymorphisms (SNPs) in CYP2B6 gene and susceptibility to lung cancer (LC).

METHODS

Five SNPs in CYP2B6 were genotyped in Chinese Han population (507 cases and 505 controls) utilizing Agena MassARRAY. The relationship between these SNPs and LC susceptibility was assessed using odds ratios, 95% confidence intervals, and χ2 tests. Additionally, multifactor dimensionality reduction was employed to analyze SNP-SNP interactions. Bioinformatics methods were applied to investigate the function of these SNPs.

RESULTS

We found that rs2099361 was associated with an increased susceptibility to LC in the codominant model (OR = 1.31, p = 0.045). Stratification analysis revealed the allele G at rs4803418 and the allele T at rs4803420 of CYP2B6 (BMI >24 kg/m2) were significantly linked to decreased susceptibility of LC. Conversely, the allele C at rs12979270 (BMI >24 kg/m2) showed increased susceptibility to LC. Moreover, a robust redundant relationship between rs12979270 and rs4803420 was identified in the study. According to the VannoPortal database, we found that rs4803420, rs12979270 and rs2099361 may modulate the binding affinity of LMNB1, SP1 and HDAC2, respectively.

CONCLUSIONS

Our results suggest that SNPs in the CYP2B6 gene play crucial roles in LC susceptibility.

Genetic polymorphisms effect on cyclophosphamide's tolerability and clinical efficacy in Egyptian patients with lupus nephritis

OBJECTIVES

Many studies were conducted to determine the association between genetic polymorphisms in CYP2B6 c.516G>T and cyclophosphamide (CYC) efficacy or toxicity, no studies were focused on both clinical efficacy and toxicity of CYC. This study aimed to investigate the relationship between the CYP2B6 c.516G>T polymorphism (rs 3745274) and 17 different parameters related to CYC efficacy and tolerability in Egyptian patients with lupus nephritis (LN).

METHODS

A prospective cohort study on 142 LN patients with a mean age of 36.26 was conducted at Kasr Al Ainy School of Medicine, Cairo University, Egypt after the exclusion of 14 patients due to receiving an interacting medication with CYC. All clinical parameters related to CYC efficacy or toxicity were recorded and compared between the different genotypes.

RESULTS

There was a statistically significant difference between different genotypes in 11 out of 13 of the studied efficacy-related parameters. Many of the studied clinical parameters revealed that CYC's efficacy was associated with the presence of the T allele. There was a statistically significant difference between different genotypes in hepatotoxicity, diarrhea, and blood-related toxicities.

CONCLUSION

To our knowledge, this study is the first study that focused on studying 17 different parameters related to CYC efficacy and tolerability. Our findings paint a picture of the function that CYP2B6 polymorphisms play in Egyptian LN patients. Pre-treatment evaluation of CYP2B6 rs 3745274 may account for some individual differences in treatment response.

Pharmacogenetic interactions of efavirenz or rifampin and isoniazid with levonorgestrel emergency contraception during treatment of HIV or tuberculosis

OBJECTIVE

In AIDS Clinical Trials Group study A5375, a pharmacokinetic trial of levonorgestrel emergency contraception, double-dose levonorgestrel (3 mg, versus standard dose 1.5 mg) offset the induction effects of efavirenz or rifampin on plasma levonorgestrel exposure over 8 h post-dose (AUC 0-8h ). We characterized the pharmacogenetics of these interactions.

METHODS

Cisgender women receiving efavirenz- or dolutegravir-based HIV therapy, or on isoniazid-rifampin for tuberculosis, were followed after a single oral dose of levonorgestrel. Linear regression models, adjusted for BMI and age, characterized associations of CYP2B6 and NAT2 genotypes (which affect plasma efavirenz and isoniazid exposure, respectively) with levonorgestrel pharmacokinetic parameters.

RESULTS

Of 118 evaluable participants, 17 received efavirenz/levonorgestrel 1.5 mg, 35 efavirenz/levonorgestrel 3 mg, 34 isoniazid-rifampin/levonorgestrel 3 mg, and 32 (control group) dolutegravir/levonorgestrel 1.5 mg. There were 73 Black and 33 Asian participants. Regardless of genotype, women on efavirenz and isoniazid-rifampin had higher levonorgestrel clearance. In the efavirenz/levonorgestrel 3 mg group, CYP2B6 normal/intermediate metabolizers had levonorgestrel AUC 0-8h values similar to controls, while CYP2B6 poor metabolizers had AUC 0-8h values of 40% lower than controls. In the isoniazid-rifampin group, NAT2 rapid/intermediate acetylators had levonorgestrel AUC 0-8h values similar to controls, while NAT2 slow acetylators had AUC 0-8h values 36% higher than controls.

CONCLUSION

CYP2B6 poor metabolizer genotypes exacerbate the efavirenz-levonorgestrel interaction, likely by increased CYP3A induction with higher efavirenz exposure, making the interaction more difficult to overcome. NAT2 slow acetylator genotypes attenuate the rifampin-levonorgestrel interaction, likely by increased CYP3A inhibition with higher isoniazid exposure.

Association of CYP3A5*3, CYP3A4*18 & CYP2B6*6 polymorphisms with imatinib treatment outcome in Azerbaijani chronic myeloid leukaemia patients

Background & objectives

Imatinib mesylate (IM) is a reliable first line treatment for chronic myeloid leukaemia (CML). Nevertheless, despite promising results, a considerable proportion of patients develop resistance to the drug. Cytochrome P450 (CYP) enzymes play a crucial role in IM metabolism. Thus, point mutations in CYP genes may modify IM enzyme activity resulting in insufficient treatment response. This investigation was aimed to identify the functional impact of CYP3A5*3, CYP3A4*18 and CYP2B6*6 polymorphisms on the IM response in patients with CML in Azerbaijan.

Methods

Genotyping of CYP3A5*3, CYP3A4*18 and CYP2B6*6 was performed in 153 patients (102 IM non-responders and 51 IM responders) with CML by the PCR-restriction fragment length polymorphism (RFLP) assays. The odds ratios (ORs) with 95 per cent confidence intervals (CIs) were applied to assess the association between allelic variants and IM therapy outcome. The results were validated by sequencing.

Results

The frequency of the CYP3A4*18 allele was considerably lower in the responder's group (97.1 vs. 100%; P=0.036). For CYP3A5*3, the allelic frequency was slightly higher among the IM responders (100 vs. 99.02%) with no significant difference. Although patients heterozygous (TC) for CYP2B6*6 demonstrated a higher risk of acquiring resistance (OR 1.04; 95% CI: 0.492-2.218), differences were not significant (P=0.909). In addition, the homozygous genotype (TT) demonstrated a lower risk of unresponsiveness (OR 0.72; 95% CI: 0.283-1.836), but associations were not significant (P=0.491).

Interpretation & conclusions

Our results demonstrated that CYP3A4*18 was significantly associated with IM treatment response in patients with CML in Azerbaijan, whereas rather common CYP3A5*3 was identified to have no such association.

Association between CYP2B6 genetic variability and cyclophosphamide therapy in pediatric patients with neuroblastoma

Cyclophosphamide, an oxazaphosphorine prodrug is frequently used in treatment of neuroblastoma, which is one of the most prevalent solid organ malignancies in infants and young children. Cytochrome P450 2B6 (CYP2B6) is the major catalyst and CYP2C19 is the minor enzyme in bioactivation and inactivation pathways of cyclophosphamide. CYP-mediated metabolism may contribute to the variable pharmacokinetics of cyclophosphamide and its toxic byproducts leading to insufficient response to the therapy and development of clinically significant side effects. The aim of the study was to reveal the contribution of pharmacogenetic variability in CYP2B6 and CYP2C19 to the treatment efficacy and cyclophosphamide-induced side effects in pediatric neuroblastoma patients under cyclophosphamide therapy (N = 50). Cyclophosphamide-induced hematologic toxicities were pivotal in all patients, whereas only moderate hepatorenal toxicity was developed. The patients' CYP2B6 metabolizer phenotypes were associated with the occurrence of lymphopenia, thrombocytopenia, and monocytopenia as well as of liver injury, but not with kidney or urinary bladder (hemorrhagic cystitis) toxicities. Furthermore, the patients' age (< 1.5 years, P = 0.03) and female gender (P ≤ 0.02), but not CYP2B6 or CYP2C19 metabolizer phenotypes appeared as significant prognostic factors in treatment outcomes. Our results may contribute to a better understanding of the impact of CYP2B6 variability on cyclophosphamide-induced side effects.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2D6, CYP2C19, CYP2B6, SLC6A4, and HTR2A Genotypes and Serotonin Reuptake Inhibitor Antidepressants

Serotonin reuptake inhibitor antidepressants, including selective serotonin reuptake inhibitors (SSRIs; i.e., citalopram, escitalopram, fluoxetine, fluvoxamine, paroxetine, and sertraline), serotonin and norepinephrine reuptake inhibitors (i.e., desvenlafaxine, duloxetine, levomilnacipran, milnacipran, and venlafaxine), and serotonin modulators with SSRI-like properties (i.e., vilazodone and vortioxetine) are primary pharmacologic treatments for major depressive and anxiety disorders. Genetic variation in CYP2D6, CYP2C19, and CYP2B6 influences the metabolism of many of these antidepressants, which may potentially affect dosing, efficacy, and tolerability. In addition, the pharmacodynamic genes SLC6A4 (serotonin transporter) and HTR2A (serotonin-2A receptor) have been examined in relation to efficacy and side effect profiles of these drugs. This guideline updates and expands the 2015 Clinical Pharmacogenetics Implementation Consortium (CPIC) guideline for CYP2D6 and CYP2C19 genotypes and SSRI dosing and summarizes the impact of CYP2D6, CYP2C19, CYP2B6, SLC6A4, and HTR2A genotypes on antidepressant dosing, efficacy, and tolerability. We provide recommendations for using CYP2D6, CYP2C19, and CYP2B6 genotype results to help inform prescribing these antidepressants and describe the existing data for SLC6A4 and HTR2A, which do not support their clinical use in antidepressant prescribing.

Relating CYP2B6 genotype and efavirenz resistance among post-partum women living with HIV with high viremia in Uganda: a nested cross-sectional study

BACKGROUND

We investigated the association between CYP2B6 polymorphisms and efavirenz drug resistance among women living with HIV who started on antiretroviral therapy during pregnancy and with high viremia during post-partum.

METHODS

This was a cross-sectional study of women with viral loads greater than 1000 copies/ml who were at least 6 weeks postpartum. Sanger sequencing was used to detect resistant mutations, as well as host genotyping, and efavirenz resistance was compared among the metabolizer genotypes.

RESULTS

Over the course of one year (July 2017-July 2018), 322 women were screened, with 110 (34.2%) having viral loads of 1000 copies/ml and 62 having whole blood available for genotyping. Fifty-nine of these women had both viral resistance and human host genotypic results. Efavirenz resistance according to metabolizer genotype was; 47% in slow, 34% in extensive and 28% in intermediate metabolizers, but the difference was not statistically significant due to the small sample size.

CONCLUSIONS

There was no statistically significant difference in EFV resistance between EFV metabolizer genotypes in women who started antiretroviral therapy during pregnancy and had high viremia in the postpartum period. However, a numerical trend was discovered, which calls for confirmation in a large, well-designed, statistically powered study.

Multidisciplinary Insights into the Structure-Function Relationship of the CYP2B6 Active Site

Cytochrome P450 2B6 (CYP2B6) is a highly polymorphic human enzyme involved in the metabolism of many clinically relevant drugs, environmental toxins, and endogenous molecules with disparate structures. Over the last 20-plus years, in silico and in vitro studies of CYP2B6 using various ligands have provided foundational information regarding the substrate specificity and structure-function relationship of this enzyme. Approaches such as homology modeling, X-ray crystallography, molecular docking, and kinetic activity assays coupled with CYP2B6 mutagenesis have done much to characterize this originally neglected monooxygenase. However, a complete understanding of the structural details that make new chemical entities substrates of CYP2B6 is still lacking. Surprisingly little in vitro data has been obtained about the structure-function relationship of amino acids identified to be in the CYP2B6 active site. Since much attention has already been devoted to elucidating the function of CYP2B6 allelic variants, here we review the salient findings of in silico and in vitro studies of the CYP2B6 structure-function relationship with a deliberate focus on the active site. In addition to summarizing these complementary approaches to studying structure-function relationships, we note gaps/challenges in existing data such as the need for more CYP2B6 crystal structures, molecular docking results with various ligands, and data coupling CYP2B6 active site mutagenesis with kinetic parameter measurement under standard expression conditions. Harnessing in silico and in vitro techniques in tandem to understand the CYP2B6 structure-function relationship will likely offer further insights into CYP2B6-mediated metabolism. SIGNIFICANCE STATEMENT: The apparent importance of cytochrome P450 2B6 (CYP2B6) in the metabolism of various xenobiotics and endogenous molecules has grown since its discovery with many in silico and in vitro studies offering a partial description of its structure-function relationship. Determining the structure-function relationship of CYP2B6 is difficult but may be aided by thorough biochemical investigations of the CYP2B6 active site that provide a more complete pharmacological understanding of this important enzyme.

Human Cytochrome P450 1, 2, 3 Families as Pharmacogenes with Emphases on Their Antimalarial and Antituberculosis Drugs and Prevalent African Alleles

Precision medicine gives individuals tailored medical treatment, with the genotype determining the therapeutic strategy, the appropriate dosage, and the likelihood of benefit or toxicity. Cytochrome P450 (CYP) enzyme families 1, 2, and 3 play a pivotal role in eliminating most drugs. Factors that affect CYP function and expression have a major impact on treatment outcomes. Therefore, polymorphisms of these enzymes result in alleles with diverse enzymatic activity and drug metabolism phenotypes. Africa has the highest CYP genetic diversity and also the highest burden of malaria and tuberculosis, and this review presents current general information on CYP enzymes together with variation data concerning antimalarial and antituberculosis drugs, while focusing on the first three CYP families. Afrocentric alleles such as CYP2A6*17, CYP2A6*23, CYP2A6*25, CYP2A6*28, CYP2B6*6, CYP2B6*18, CYP2C8*2, CYP2C9*5, CYP2C9*8, CYP2C9*9, CYP2C19*9, CYP2C19*13, CYP2C19*15, CYP2D6*2, CYP2D6*17, CYP2D6*29, and CYP3A4*15 are implicated in diverse metabolic phenotypes of different antimalarials such as artesunate, mefloquine, quinine, primaquine, and chloroquine. Moreover, CYP3A4, CYP1A1, CYP2C8, CYP2C18, CYP2C19, CYP2J2, and CYP1B1 are implicated in the metabolism of some second-line antituberculosis drugs such as bedaquiline and linezolid. Drug-drug interactions, induction/inhibition, and enzyme polymorphisms that influence the metabolism of antituberculosis, antimalarial, and other drugs, are explored. Moreover, a mapping of Afrocentric missense mutations to CYP structures and a documentation of their known effects provided structural insights, as understanding the mechanism of action of these enzymes and how the different alleles influence enzyme function is invaluable to the advancement of precision medicine.

Detection of Transgene Location in the CYP2A13/2B6/2F1-transgenic Mouse Model using Optical Genome Mapping Technology

Most transgenic mouse models are generated through random integration of the transgene. The location of the transgene provides valuable information for assessing potential effects of the transgenesis on the host and for designing genotyping protocols that can amplify across the integration site, but it is challenging to identify. Here, we report the successful utility of optical genome mapping technology to identify the transgene insertion site in a CYP2A13/2B6/2F1-transgenic mouse model, which produces three human cytochrome P450 (P450) enzymes (CYP2A13, CYP2B6, and CYP2F1) that are encoded by neighboring genes on human chromosome 19. These enzymes metabolize many drugs, respiratory toxicants, and chemical carcinogens. Initial efforts to identify candidate insertion sites by whole genome sequencing was unsuccessful, apparently because the transgene is located in a region of the mouse genome that contains highly repetitive sequences. Subsequent utility of the optical genome mapping approach, which compares genome-wide marker distribution between the transgenic mouse genome and a reference mouse (GRCm38) or human (GRCh38) genome, localized the insertion site to mouse chromosome 14, between two marker positions at 4451324 base pair and 4485032 base pair. A transgene-mouse genome junction sequence was further identified through long-polymerase chain reaction amplification and DNA sequencing at GRCm38 Chr.14:4484726. The transgene insertion (∼2.4 megabase pair) contained 5-7 copies of the human transgenes, which replaced a 26.9-33.4 kilobase pair mouse genomic region, including exons 1-4 of Gm3182, a predicted and highly redundant gene. Finally, the sequencing results enabled the design of a new genotyping protocol that can distinguish between hemizygous and homozygous CYP2A13/2B6/2F1-transgenic mice. SIGNIFICANCE STATEMENT: This study characterizes the genomic structure of, and provides a new genotyping method for, a transgenic mouse model that expresses three human P450 enzymes, CYP2A13, CYP2B6, and CYP2F1, that are important in xenobiotic metabolism and toxicity. The demonstrated success in applying the optical genome mapping technology for identification of transgene insertion sites should encourage others to do the same for other transgenic models generated through random integration, including most of the currently available human P450 transgenic mouse models.

Artemisia extracts differ from artemisinin effects on human hepatic CYP450s 2B6 and 3A4 in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

The Chinese medicinal herb, Artemisia annua L., has been used for >2,000 yr as traditional tea infusions to treat a variety of infectious diseases including malaria, and its use is spreading globally (along with A. afra Jacq. ex Willd.) mainly through grassroots efforts.

AIM OF THE STUDY

Artemisinin is more bioavailable delivered from the plant, Artemisia annua L. than the pure drug, but little is known about how delivery via a hot water infusion (tea) alters induction of hepatic CYP2B6 and CYP3A4 that metabolize artemisinin.

MATERIALS AND METHODS

HepaRG cells were treated with 10 μM artemisinin or rifampicin (positive control), and teas (10 g/L) of A. annua SAM, and A. afra SEN and MAL with 1.6, 0.05 and 0 mg/g DW artemisinin in the leaves, respectively; qPCR and Western blots were used to measure CYP2B6 and CYP3A4 responses. Enzymatic activity of these P450s was measured using human liver microsomes and P450-Glo assays.

RESULTS

All teas inhibited activity of CYP2B6 and CYP3A4. Artemisinin and the high artemisinin-containing tea infusion (SAM) induced CYP2B6 and CYP3A4 transcription, but artemisinin-deficient teas, MAL and SEN, did not. Artemisinin increased CYP2B6 and CYP3A4 protein levels, but none of the three teas did, indicating a post-transcription inhibition by all three teas.

CONCLUSIONS

This study showed that Artemisia teas inhibit activity and artemisinin autoinduction of CYP2B6 and CYP3A4 post transcription, a response likely the effect of other phytochemicals in these teas. Results are important for understanding Artemisia tea posology.

Methadone pharmacogenetics in vitro and in vivo: Metabolism by CYP2B6 polymorphic variants and genetic variability in paediatric disposition

AIMS

Methadone metabolism and clearance are determined principally by polymorphic cytochrome P4502B6 (CYP2B6). Some CYP2B6 allelic variants affect methadone metabolism in vitro and disposition in vivo. We assessed methadone metabolism by CYP2B6 minor variants in vitro. We also assessed the influence of CYP2B6 variants, and P450 oxidoreductase (POR) and CYP2C19 variants, on methadone clearance in surgical patients in vivo.

METHODS

CYP2B6 and P450 oxidoreductase variants were coexpressed with cytochrome b5 . The metabolism of methadone racemate and enantiomers was measured at therapeutic concentrations and intrinsic clearances were determined. Adolescents receiving methadone for surgery were genotyped for CYP2B6, CYP2C19 and POR, and methadone clearance and metabolite formation clearance were determined.

RESULTS

In vitro, CYP2B6.4 was more active than wild-type CYP2B6.1. CYPs 2B6.5, 2B6.6, 2B6.7, 2B6.9, 2B6.17, 2B6.19 and 2B6.26 were less active. CYPs 2B6.16 and 2B6.18 were inactive. CYP2B6.1 expressed with POR variants POR.28, POR.5 and P228L had lower rates of methadone metabolism than wild-type reductase. In vivo, methadone clinical clearance decreased linearly with the number of CYP2B6 slow metabolizer alleles, but was not different in CYP2C19 slow or rapid metabolizer phenotypes, or in carriers of the POR*28 allele.

CONCLUSIONS

Several CYP2B6 and POR variants were slow metabolizers of methadone in vitro. Polymorphisms in CYP2B6, but not CYP2C19 or P450 reductase, affected methadone clearance in vivo. CYP2B6 polymorphisms 516G>T and 983T>C code for canonical loss of function variants and should be assessed when considering genetic influences on clinical methadone disposition. These complementary translational in vitro and in vivo results inform on pharmacogenetic variability affecting methadone disposition in patients.

CYP2B6 SINGLE NUCLEOTIDE POLYMORPHISMS IN AN AZERBAIJANI POPULATION

Despite being one of the less-characterized human isoforms, cytochrome P450 2B6 is already known for its participation in the metabolism of many drugs and several environmental carcinogens. It has been studied in different populations, but ethnicity is a crucial variable to account for interindividual variability. ; This study aimed to investigate the genotype and allelic frequencies of CYP2B6 c.516G>T SNP in an Azerbaijani population, as the determination of SNP's prevalence will be helpful in further pharmacogenetics research and optimization of personalized drug therapy in Azerbaijan. ; Identification of CYP2B6*6 allelic and genotype frequencies in 100 volunteers was performed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique. The obtained results were confirmed by next-generation sequencing. ; The frequency of the *6 allele was 0.275, with the *1 allele frequency being 0.725. The frequency of the CYP2B6*1/*1, CYP2B6*1/*6 and CYP2B6*6/*6 genotypes were 0.55, 0.35, 0.1, respectively. ; This is the first investigation to report the frequencies of CYP2B6*/6 alleles in the Azerbaijani population. The results of this study suggest that genetic polymorphisms in the CYP2B6 gene are abundantly present among Azerbaijani individuals.

Genetic variants in CYP2B6 and HSD17B12 associated with risk of squamous cell carcinoma of the head and neck

Polycyclic aromatic hydrocarbons (PAH) and tobacco-specific nitrosamines (TSNA) metabolism-related genes play an important role in the development of cancers. We assessed the associations of genetic variants in genes involved in the metabolism of PAHs and TSNA with risk of squamous cell carcinoma of the head and neck (SCCHN) in European populations using two published genome-wide association study datasets. In the single-locus analysis, we identified two SNPs (rs145533669 and rs35246205) in CYP2B6 to be associated with risk of SCCHN (P = 1.57 × 10-4 and .004, respectively), two SNPs (EPHX1 rs117522494 and CYP2B6 rs145533669) to be associated with risk of oropharyngeal cancer (P = .001 and .004, respectively), and one SNP (rs4359199 in HSD17B12) to be associated with risk of oral cancer (P = .006). A significant interaction effect was found between rs4359199 and drinking status on risks of SCCHN and oropharyngeal cancer (P < .05). eQTL and sQTL analyzes revealed that two SNPs (CYP2B6 rs35246205 and HSD17B12 rs4359199) were correlated with alternative splicing or mRNA expression levels of the corresponding genes in liver cells (P < .05 for both). In silico functional annotation suggested that these two SNPs may regulate mRNA expression by affecting the binding of transcription factors. Results from phenome-wide association studies presented significant associations between these genes and risks of other cancers, smoking behavior and alcohol dependence (P < .05). Thus, our study provided some insight into the underlying genetic mechanism of head and neck cancer, which warrants future functional validation.

Influence of CYP2B6 and CYP3A4 polymorphisms on the virologic and immunologic responses of patients treated with efavirenz-containing regimen

OBJECTIVES

The main objective of this study was to evaluate the effect of CYP2B6 and CYP3A4 polymorphisms on the virological and immunologic responses of HIV patients. A total of 153 HIV-positive patients were enlisted for the study.

PATIENTS AND METHODS

Viral load and median CD4 T cell counts were evaluated at baseline and month 6 (M6). Samples were identified using TaqMan genotyping assays.

RESULTS

The AG in CYP2B6 rs2279343 was associated with VLS compared to homozygous AA. In the dominant model, the AG/GG genotypes were associated with VLS compared to the AA genotype. Moreover, in overdominant model, the AG genotype was associated with VLS compared to AA/GG. Regarding immunological response, only the AG in SNP rs2279343 CYP2B6 was associated with an increase in CD4 cell count between baseline and M6. In CYP2B6 rs3745274, the CD4 cell count at M6 was higher than that of baseline for GG carriers and for GT carriers. In CYP3A4 rs2740574, the TC carriers showed a higher median CD4 count at M6 compared to that of the baseline count, as well as for CC carriers. The best genotypes combination associated with CD4 cell count improvement were AA/AG in SNP rs2279343 and GG/GT in SNP rs3745274.

CONCLUSION

Our findings support the fact that CYP2B6 rs2279343 could help in the prediction of VLS and both SNPs rs3745274 and rs2279343 in CYP2B6 and CYP3A4 rs2740574 were associated with immune recovery in Malian HIV-positive patients.

Plasma levels of efavirenz and frequency of the CYP2B6 516G>T polymorphism in people living with HIV-1 in Mexico

Efavirenz (EFV) is a widely used antiretroviral, due to its safety, efficacy, and low cost. However, plasma concentrations have been related with an increased risk of virological failure and the appearance of serious adverse reactions. EFV is metabolized by Cytochrome P450, the main isoenzyme involved is CYP2B6 and the most relevant genetic polymorphisms found in several populations has been the CYP2B6 516G> T. The aim of this study was to identify the frequency of the CYP2B6 516G>T polymorphism and its effect on the plasma concentration of efavirenz (EFV) in a group of people living with HIV (PLWH) and undergoing EFV treatment in Morelos, Mexico. Ninety-six PLWH undergoing EFV treatment, at a daily dose of 600 mg orally in combination with other antiretrovirals (ARVs), were included in this study. The CYP2B6 516G>T polymorphism was detected using PCR-RFLP. The plasma concentrations of EFV were evaluated by high-resolution liquid chromatography coupled to a mass-mass detector, using a protein precipitation method. The median plasma EFV concentration was 4.6 μg/mL (IQR = 4.64) and 64.6% of the subjects had concentrations above the therapeutic range. The CYP2B6 516G>T genotype findings were as follows: 46.9% of the population presented the wild-type genotype (GG), while 45.8 % and 7.3 % showed the heterozygote (GT) and the polymorphic homozygote (TT) genotype, respectively. The homozygote G had the lowest plasma concentrations of EFV (median = 4.1 μg/mL and IQR = 1.7 μg/mL), followed by those with the GT genotype (median = 5.1 μg/mL and IQR = 3.0 μg/mL). Participants with the homozygous T genotype had the highest EFV concentrations (median = 9.7 μg/mL and IQR = 5.8 μg/mL). In conclusion, the CYP2B6 516G>T polymorphism was associated with plasma levels of EFV in PLWH undergoing ARV treatment. EFV plasma concentrations at 600mg doses were outside the therapeutic range in most subjects.

Lack of association of CYP2B6 pharmacogenetics with cyclophosphamide toxicity in patients with cancer

PURPOSE

Cyclophosphamide is a commonly used cancer agent that is metabolically activated by polymorphic enzymes. This study aims to investigate the association between predicted activity of candidate pharmacogenes with severe toxicity during cyclophosphamide treatment.

METHODS

Genome-wide genetic data was collected from an institutional genetic data repository for CYP2B6, CYP3A4, CYP2C9, CYP2C19, GSTA1, GSTP1, ALDH1A1, ALDH3A1, ABCC1, ABCB1, and ERCC1. Treatment and toxicity data were retrospectively collected from the patient's medical record. The a priori selected primary hypothesis was that patients who have CYP2B6 reduced metabolizer activity (poor or intermediate (PM/IM) vs. normal (NM) metabolizer) have lower risk of severe toxicity or cyclophosphamide treatment modification due to toxicity.

RESULTS

In the primary analysis of 510 cyclophosphamide-treated patients with available genetic data, there was no difference in the odds of severe toxicity or treatment modification due to toxicity in CYP2B6 PM/IM vs. NM (odds ratio = 0.97, 95% Confidence Interval: 0.62-1.50, p = 0.88). In an exploratory, statistically uncorrected secondary analysis, carriers of the ALDH1A1 rs8187996 variant had a lower risk of the primary toxicity endpoint compared with wild-type homozygous patients (odds ratio = 0.31, 95% Confidence Interval: 0.09-0.78, p = 0.028). None of the other tested phenotypes or genotypes was associated with the primary or secondary endpoints in unadjusted analysis (all p > 0.05).

CONCLUSION

The finding that patients who carry ALDH1A1 rs8187996 may have a lower risk of cyclophosphamide toxicity than wild-type patients contradicts a prior finding for this variant and should be viewed with skepticism. We found weak evidence that any of these candidate pharmacogenetic predictors of cyclophosphamide toxicity may be useful to personalize cyclophosphamide dosing to optimize therapeutic outcomes in patients with cancer.

The role of CYP2B6 516G>T polymorphism on efavirenz/nevirapine toxicity. Implications on treatment outcomes: Lessons from Botswana

The two non-nucleoside reverse transcriptase inhibitors (NNRTIs), efavirenz (EFV) and nevirapine (NVP), are currently the core antiretroviral drugs for treatment of HIV in sub-Saharan Africa including Botswana. The drugs are metabolized by Cytochrome P450 2B6 (CYP2B6) liver enzyme. The CYP2B6 gene that encodes for metabolism of these drugs is known to be highly polymorphic. One of the polymorphism in the CYP2B6 gene, 516G>T, particularly the 516T allele, is known to confer poor metabolism of EFV and NVP. This may lead to high levels of plasma drug concentrations and development of treatment toxicities, like central nervous system toxicities, and cutaneous and hepatic toxicities, for EFV and NVP, respectively. The CYP2B6 516G allele on the other hand is associated with an extensive metabolism of the two NNRTIs drugs. We sought to establish association between possible developments of NNRTIs toxicities with CYP2B6 516G>T variation in Botswana.A total of 316 peripheral blood mononuclear cells samples were used in a retrospective view. All the samples were from participants on EFV/NVP-containing regimen with known toxicity output. TaqMan Real-Time PCR approach was applied for assessing CYP2B6 516 allele variation in cases with treatment toxicity and those without. Analysis was performed by chi-square statistics and logistic regression analysis.The rate of poor metabolizers among participants with toxicity and those without toxicity was 18.4% and 15.1%, respectively. The CYP2B6 516 genotype distribution comparisons between the participants with toxicity and those without were not statistically different (chi-square = .326; P = .568).CYP2B6 516 variation was not associated with NNRTI toxicity. No other factors were associated with toxicity when considering age, baseline body mass index, baseline CD4, baseline HIV viral load and adherence. The results were discussed in the context of all the studies done in Botswana to date.

Impact of CYP2B6 genotype, tuberculosis therapy, and formulation on efavirenz pharmacokinetics in infants and children under 40 months of age

OBJECTIVE

Dosing efavirenz (EFV) in children less than 3 years of age is challenging due to large variability in drug levels. This study evaluated differences in pharmacokinetics with tuberculosis (TB) therapy, formulation, age, and CYP2B6 genotype.

DESIGN

Pharmacokinetic data from three IMPAACT/PACTG studies (P382, P1021, and P1070) for children initiating therapy less than 40 months of age were evaluated.

METHODS

Pharmacokinetic data were combined in a population pharmacokinetic model. Exposure from the 2-week pharmacokinetic visit was compared with changes in viral RNA between the Week 0 and Week 4 visits.

RESULTS

The model included 103 participants (19 on TB therapy). CYP2B6 516 genotype information was available for 82 participants (TT: 15, GT: 28, GG: 39). Median age at the first pharmacokinetic visit was 17.0 months (range: 2.0-39.0 months). Liquid formulation led to a 42% decrease in bioavailability compared with opened capsules. TB therapy (isoniazid and rifampin) led to a 29% decreased clearance, however Monte Carlo simulations demonstrated the majority of participants on TB therapy receiving standard EFV dosing to be in the target area under the curve range. Clearance was 5.3-fold higher for GG than TT genotype and 3.3-fold higher for GT than TT genotype. Age did not have a significant effect on clearance in the final model. Initial viral RNA decay was lower for patients in the lowest quartile of exposures (area under the curves) than for higher quartiles (P = 0.013).

CONCLUSION

EFV dosing should account for CYP2B6 516 genotype and formulation, but does not require adjustment for concurrent TB therapy.

Implications of OPRM1 and CYP2B6 variants on treatment outcomes in methadone-maintained patients in Ontario: Exploring sex differences

Genetic variants in the OPRM1 and CYP2B6 genes, respectively coding for an opioid receptor and methadone metabolizers, have been linked to negative treatment outcomes in patients undergoing methadone maintenance treatment, with little consensus on their effect. This study aims to test the associations between pre-selected SNPs of OPRM1 and CYP2B6 and outcomes of continued opioid use, relapse, and methadone dose. It also aims to observe differences in associations within the sexes. 1,172 participants treated with methadone (nMale = 666, nFemale = 506) were included in this study. SNPs rs73568641 and rs7451325 from OPRM1 and all the tested CYP2B6 SNPs were detected to be in high linkage disequilibrium. Though no associations were found to be significant, noteworthy differences were observed in associations of OPRM1 rs73568641 and CYP2B6 rs3745274 with treatment outcomes between males and females. Further research is needed to determine if sex-specific differences are present.

CYP2B6 Genotype and Weight Gain Differences Between Dolutegravir and Efavirenz

BACKGROUND

Dolutegravir is associated with more weight gain than efavirenz. Loss-of-function polymorphisms in CYP2B6 result in higher efavirenz concentrations, which we hypothesized would impair weight gain among people living with human immunodeficiency virus (HIV; PLWH) starting efavirenz-based antiretroviral therapy (ART).

METHODS

We studied ART-naive participants from the ADVANCE study randomized to the efavirenz /emtricitabine/tenofovir disoproxil fumarate (TDF) and dolutegravir/emtricitabine/TDF arms. We compared changes in weight and regional fat on DXA from baseline to week 48 between CYP2B6 metabolizer genotypes in the efavirenz arm, and with the dolutegravir arm.

RESULTS

There were 342 participants in the dolutegravir arm and 168 in the efavirenz arm who consented to genotyping. Baseline characteristics were similar. Weight gain was greater in women than men. In the efavirenz arm CYP2B6 metaboliser genotype was associated with weight gain (P = .009), with extensive metabolizers gaining the most weight, and with changes in regional fat in women, but not in men. Weight gain was similar in CYP2B6 extensive metabolizers in the efavirenz arm and in the dolutegravir arm (P = .836). The following variables were independently associated with weight gain in all participants: baseline CD4 count, baseline human immunodeficiency virus type 1 (HIV-1) RNA, and CYP2B6 metaboliser genotype.

CONCLUSIONS

CYP2B6 metaboliser genotype was associated with weight gain in PLWH starting efavirenz-based ART. Weight gain was similar between CYP2B6 extensive metabolizers in the efavirenz arm and in the dolutegravir arm, suggesting that impaired weight gain among CYP2B6 slow or intermediate metabolizers could explain the increased weight gain on dolutegravir compared with efavirenz observed in ADVANCE and other studies.

Associations between efavirenz concentrations, pharmacogenetics and neurocognitive performance in people living with HIV in Nigeria

OBJECTIVE

Efavirenz (EFV) use is associated with neuropsychiatric side effects, which may include poor neurocognitive performance. We evaluated single nucleotide polymorphisms in genes that contribute to EFV pharmacokinetics and examined them in association with EFV concentrations in plasma and hair, as well as neurocognitive performance.

DESIGN

Cross-sectional study in which adults with HIV receiving 600-mg EFV for at least 2 months were recruited and paired hair and dried blood spots (DBS) samples collected.

METHODS

Participants (N = 93, 70.3% female) were genotyped for seven single nucleotide polymorphisms in CYP2B6, NRII3 and ABCB1 using DBS. EFV was quantified in DBS and hair using validated liquid-chromatography-tandem-mass-spectrometry methods, with plasma EFV concentrations derived from DBS levels. Participants were also administered a neurocognitive battery of 10 tests (seven domains) that assessed total neurocognitive functioning.

RESULTS

Strong correlation (r = 0.66, P < 0.001) was observed between plasma and hair EFV concentrations. The median (interquartile range) hair EFV concentration was 6.85 ng/mg (4.56-10.93). CYP2B6 516G>T, (P < 0.001) and CYP2B6 983T>C (P = 0.001) were each associated with hair EFV concentrations. Similarly, 516G>T (P < 0.001) and 983T>C (P = 0.009) were significantly associated with plasma EFV concentration. No other genetic associations were observed. Contrary to other studies, total neurocognitive performance was significantly associated with plasma EFV concentrations (r = 0.23, P = 0.043) and 983T>C genotype (r = 0.38, P < 0.0005).

CONCLUSION

This study demonstrated approximately three-fold and two-fold higher EFV plasma and hair concentrations, respectively, among CYP2B6 516TT compared with 516GG. Higher EFV concentrations were associated with better neurocognitive performance, requiring further study to elucidate the relationships between adherence, adverse effects and outcomes.

Association between CYP2B6 c.516G >T variant and acute leukaemia: A protocol for systematic review and meta-analysis

BACKGROUND

Acute leukemia (AL) is a kind of malignant tumor of hematopoietic system. A number of studies have suggested that Single Nucleotide Polymorphisms are significantly associated with risk of AL. Present study performs meta-analysis to evaluate the association between CYP2B6 c.516G>T variant and AL risk.

METHODS

Databases including PubMed, EMBASE, Chinese National Knowledge Infrastructure (CNKI), and Wanfang were searched for literatures to September 30, 2019, both in English and Chinese. Relative risk and its 95% confidence intervals were used to assess the associations. Statistical analyses of this meta-analysis were conducted by using STATA 13.0. software.

RESULTS

A total of 7 studies, including 1038 cases and 1648 controls, were analyzed. Our results indicated that CYP2B6 c.516G>T variant was significantly related to an increased the risk of AL under dominant model, recessive model, homozygote model, and allelic model. In addition, subgroup analyses were also performed by disease classification, country, and study design. No significant associations were obtained between CYP2B6 c.516G>T variant and the risk of AL under the recessive model in the design of hospital-based (relative risk = 0.98; 95% confidence interval: 0.95-1.01; P  = 0.118).

CONCLUSION

Our meta-analysis indicated that the CYP2B6 variant is significantly associated with AL risk, in which CYP2B6 c.516G>T is related to an increased risk of AL.

Distribution of alleles, genotypes and haplotypes of the CYP2B6 (rs3745274; rs2279343) and CYP3A4 (rs2740574) genes in the Malian population: Implication for pharmacogenetics

Cytochrome P450 enzymes play a central role in the phase I biotransformation process of a wide range of compounds, including xenobiotics, drugs, hormones and vitamins. It is noteworthy that these enzymes are highly polymorphic and, depending on the genetic makeup, an individual may have impaired enzymatic activity. Therefore, the identification of genetic variants in these genes could facilitate the implementation of pharmacogenetic studies and genetic predisposition to multifactorial diseases. We have established the frequencies of CYP2B6 (rs3745274; rs2279343) and CYP3A4 (rs2740574) alleles and genotypes in 209 healthy Malian subjects using TaqMan drug metabolism genotyping assays for allelic discrimination. Allele frequencies were 37% for CYP2B6 rs3745274; 38% for CYP2B6 rs2279343; and 75% for CYP3A4 rs2740574 respectively. Overall, the frequencies observed in Mali are statistically comparable to those reported across Africa except North Africa. The major haplotypes in CYP2B6 rs3745274 and CYP2B6 rs2279343 were represented by GA (60.24%) followed by TG (35.36%). We noted a strong linkage disequilibrium between CYP2B6 rs3745274 and CYP2B6 rs2279343 with D' = 0.91 and r2 = 0.9. The frequencies of the genotypic combinations were 43.5% (GT/AG), 37.3% (GG/AA) and 11.5% (TT/GG) in the combination of CYP2B6-rs3745274 and CYP2B6-rs2279343; 26.8% (GT/CC), 25.4%, (GT/CT), 17.2% and GG/CT in the combination CYP2B6-rs3745274-CYP3A4-rs2740574; 26.8% (AG/CC), 23.9% (AA/CC), 19.1% (AG/CT), and 11% (AA/CT) in the combination CYP2B6-rs2279343-CYP3A4-rs2740574, respectively. The most common triple genotype was GT/AG/CC with 24.9%, followed by GG/AA/CC with 23.9%, GT/AG/CT with 16.7%, and GG/AA/CT with 10%. Our results provide new insights into the distribution of these pharmacogenetically relevant genes in the Malian population. Moreover, these data will be useful for studies of individual genetic variability to drugs and genetic predisposition to diseases.

Increased toxicity and retention of perflourooctane sulfonate (PFOS) in humanized CYP2B6-Transgenic mice compared to Cyp2b-null mice is relieved by a high-fat diet (HFD)

PFOS is a persistent, fluorosurfactant used in multiple products. Murine Cyp2b's are induced by PFOS and high-fat diets (HFD) and therefore we hypothesized that human CYP2B6 may alleviate PFOS-induced steatosis. Cyp2b-null and hCYP2B6-Tg mice were treated with 0, 1, or 10 mg/kg/day PFOS by oral gavage for 21-days while provided a chow diet (ND) or HFD. Similar to murine Cyp2b10, CYP2B6 is inducible by PFOS. Furthermore, three ND-fed hCYP2B6-Tg females treated with 10 mg/kg/day PFOS died during the exposure period; neither Cyp2b-null nor HFD-fed mice died. hCYP2B6-Tg mice retained more PFOS in serum and liver than Cyp2b-null mice presumably causing the observed toxicity. In contrast, serum PFOS retention was reduced in the HFD-fed hCYP2B6-Tg mice; the opposite trend observed in HFD-fed Cyp2b-null mice. Hepatotoxicity biomarkers, ALT and ALP, were higher in PFOS-treated mice and repressed by a HFD. However, PFOS combined with a HFD exacerbated steatosis in all mice, especially in the hCYP2B6-Tg mice with significant disruption of key lipid metabolism genes such as Srebp1, Pparg, and Hmgcr. In conclusion, CYP2B6 is induced by PFOS but does not alleviate PFOS toxicity presumably due to increased retention. CYP2B6 protects from PFOS-mediated steatosis in ND-fed mice, but increases steatosis when co-treated with a HFD.

Investigation of CYP2B6, 3A4 and β-esterase interactions of Withania somnifera (L.) dunal in human liver microsomes and HepG2 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Withania somnifera (L.) Dunal (Solanaceae) is a traditional herb, used in African indigenous systems of medicine for the treatment of various diseases (including HIV/AIDS and tuberculosis). The relevance of clinically significant interactions of Withania with ARVs and anti-TB drugs needs to be investigated.

AIM OF THE STUDY

This study evaluated the effects of its roots on cytochromes P450 (CYPs) 2B6, 3A4, and rifampicin metabolism pathway, using methanol, ethanol, aqueous, and ethyl acetate solvent extractions.

MATERIALS AND METHODS

The extracts were tested on human liver microsomes (HLM) for CYP inhibition, mRNA expression in HepG2 cells for CYP induction. Biochemical qualitative tests and LC-MS/MS methodology were used to determine active phytoconstituents.

RESULTS

The methanolic and ethyl acetate extracts inhibited CYP2B6 with IC₅₀s 79.16 and 57.96 μg/ml respectively, while none of the extracts had any effect on rifampicin metabolism or showed time-dependant inhibition (TDI). All extracts were moderate inducers of CYP3A4; the aqueous extract exhibited 38%-fold shift induction of CYP3A4 compared to the control. The methanolic extract had the lowest CTC₅₀ (50% of cytotoxicity inhibition) (67.13 ± 0.83 μg/ml). LC-MS/MS-PDA full scans were consistent with the presence of flavone salvigenin (m/z 327), alkaloid isopelletierine (m/z 133), steroidal lactone 2,3-dihydrowithaferin-A (m/z 472), and other withanolides including withaperuvin I (m/z 533), withaferin derivative (m/z 567), some of these compounds likely being responsible for the observed CYP2B6 inhibition and CYP3A4 induction. The putative gastrointestinal tract (GIT) concentration for the active extracts was 1800 μg/ml and the hepatic circulation concentrations were estimated at about 220 μg/ml and 13.5 μg/ml for the methanolic and ethyl acetate extracts, respectively. The extrapolated in vivo percentage of inhibition was at 85% for the methanolic extract against CYP2B6.

CONCLUSIONS

The findings reported in this study suggest that W. somnifera extracts have the potential of causing clinically significant herb-drug interactions (HDI) as moderate inducer of CYP3A4 and inhibitor of CYP2B6 metabolism pathway (methanol and ethyl acetate extracts).

Prevalence of Cytochrome P450 2B6 Single Nucleotide Polymorphism in an HIV-Positive Cohort in Jos, Nigeria: Implication for HIV Therapy

BACKGROUND

Africans exhibit great diversity in cytochrome P450 2B6 isoenzyme (CYP2B6), the major enzyme in efavirenz metabolism.

AIM

We examined the frequency of two functional single nucleotide polymorphisms (SNPs) of the CYP2B6 pharmacogene in HIV-infected Nigerians on efavirenz-based antiretroviral therapy. The potential implications of the SNPs for HIV therapy were discussed.

MATERIALS AND METHODS

A cross-sectional study conducted from July 2018 to December 2018 in a tertiary health facility in Nigeria. A random sample of a clinic cohort of HIV-infected adult Nigerians of different ethnicities was characterized for two key SNPs; CYP2B6:516G>, and CYP2B6:983T > C, defining the alleles CYP2B6*6 and CYP2B6*18, respectively. Hardy-Weinberg equilibrium was calculated to evaluate the genotype frequency distribution.

RESULTS

Genotyping was successful for 262 (83%) of the 316 study participants. Of those with genotype results, mean age was 41 ± 8 years and 182 (69.5%) were female. The CYP2B6:516 G/G (extensive metabolizers), CYP2B6:516 G/T (intermediate metabolizers), and CYP2B6:516 T/T (poor metabolizers) genotype frequency was 35.9%, 46.6%, and 17.6%, respectively. Also, 88.9% and 11.1% of participants were carriers of the CYP2B6:983 T/T and CYP2B6:983 T/C (poor metabolizers) genotypes, respectively. There were no gender or age-related differences in the genotype distribution. The CYP2B6:516G >T allele frequencies showed no significant deviations from the Hardy-Weinberg equilibrium (P = 0.66).

CONCLUSIONS

The intermediate metabolizer genotype was more common than the extensive and poor metabolizer genotypes in our study sample. We recommended further studies to investigate the risk of efavirenz underexposure and overexposure in carries of the extensive and poor metabolizer genotypes respectively in our patient population.

Meta-analysis of the effect of CYP2B6, CYP2A6, UGT2B7 and CAR polymorphisms on efavirenz plasma concentrations

BACKGROUND

Efavirenz primary metabolism is catalysed by CYP2B6 with minor involvement of CYP2A6. Subsequently, phase I metabolites are conjugated by UGT2B7, and constitutive androstane receptor (CAR) has been shown to transcriptionally regulate many relevant enzymes and transporters. Several polymorphisms occurring in the genes coding for these proteins have been shown to impact efavirenz pharmacokinetics in some but not all studies.

OBJECTIVES

A meta-analysis was performed to assess the overall effect of CYP2B6 rs3745274, CYP2A6 (rs28399454, rs8192726 and rs28399433), UGT2B7 (rs28365062 and rs7439366) and NR1I3 (rs2307424 and rs3003596) polymorphisms on mid-dose efavirenz plasma concentrations.

METHODS

Following a literature review, pharmacokinetic parameters were compiled and a meta-analysis for these variants was performed using Review Manager and OpenMetaAnalyst. A total of 28 studies were included.

RESULTS

Unsurprisingly, the analysis confirmed that individuals homozygous for the T allele for CYP2B6 rs3745274 had significantly higher efavirenz concentrations than those homozygous for the G allele [weighted standard mean difference (WSMD) = 2.98; 95% CI 2.19-3.76; P < 0.00001]. A subgroup analysis confirmed ethnic differences in frequency but with a similar effect size in each ethnic group (P = 0.96). Associations with CYP2A6 and UGT2B7 variants were not statistically significant, but T homozygosity for CAR rs2307424 was associated with significantly lower efavirenz concentrations than in C homozygotes (WSMD = -0.32; 95% CI -0.59 to -0.06; P = 0.02).

CONCLUSIONS

This meta-analysis provides the overall effect size for the impact of CYP2B6 rs3745274 and NR1I3 rs2307424 on efavirenz pharmacokinetics. The analysis also indicates that some previous associations were not significant when interrogated across studies.

Tyrosine Nitration Contributes to Nitric Oxide-Stimulated Degradation of CYP2B6

Human cytochrome P450 (P450) CYP2B6 undergoes nitric oxide (NO)-dependent proteasomal degradation in response to the NO donor dipropylenetriamine NONOate (DPTA) and biologic NO in HeLa and HuH7 cell lines. CYP2B6 is also downregulated by NO in primary human hepatocytes. We hypothesized that NO or derivative reactive nitrogen species may generate adducts of tyrosine and/or cysteine residues, causing CYP2B6 downregulation, and selected Tyr and Cys residues for mutation based on predicted solvent accessibility. CYP2B6V5-Y317A, -Y380A, and -Y190A mutant proteins expressed in HuH7 cells were less sensitive than wild-type (WT) enzyme to degradation evoked by DPTA, suggesting that these tyrosines are targets for NO-dependent downregulation. The Y317A or Y380A mutants did not show increases in high molecular mass (HMM) species after treatment with DPTA or bortezomib + DPTA, in contrast to the WT enzyme. Carbon monoxide-releasing molecule 2 treatment caused rapid suppression of 2B6 enzyme activity, significant HMM species generation, and ubiquitination of CYP2B6 protein but did not stimulate CYP2B6 degradation. The CYP2B6 inhibitor 4-(4-chlorophenyl)imidazole blocked NO-dependent CYP2B6 degradation, suggesting that NO access to the active site is important. Molecular dynamics simulations predicted that tyrosine nitrations of CYP2B6 would cause significant destabilizing perturbations of secondary structure and remove correlated motions likely required for enzyme function. We propose that cumulative nitrations of Y190, Y317, and Y380 by reactive nitrogen species cause destabilization of CYP2B6, which may act synergistically with heme nitrosylation to target the enzyme for degradation. SIGNIFICANCE STATEMENT: This work provides novel insight into the mechanisms by which nitric oxide, which is produced in hepatocytes in response to inflammation, triggers the ubiquitin-dependent proteasomal degradation of the cytochrome P450 (P450) enzyme CYP2B6. Our data demonstrate that both nitration of specific tyrosine residues and interaction of nitric oxide (NO) with the P450 heme are necessary for NO to trigger ubiquitination and protein degradation.

Five genetic polymorphisms of cytochrome P450 enzymes in the Czech non-Roma and Czech Roma population samples

Objectives Cytochromes P450 play a role in human drugs metabolic pathways and their genes are among the most variable in humans. The aim of this study was to analyze genotype frequencies of five common polymorphisms of cytochromes P450 in Roma/Gypsy and Czech (non-Roma) population samples with Czech origin. Methods Roma/Gypsy (n=302) and Czech subjects (n=298) were genotyped for CYP1A2 (rs762551), CYP2A6 (rs4105144), CYP2B6 (rs3745274) and CYP2D6 (rs3892097; rs1065852) polymorphisms using PCR-RFLP or Taqman assay. Results We found significant allelic/genotype differences between ethnics in three genes. For rs3745274 polymorphism, there was increased frequency of T allele carriers in Roma in comparison with Czech population (53.1 vs. 43.7%; p=0.02). For rs4105144 (CYP2A6) there was higher frequency of T allele carriers in Roma in comparison with Czech population (68.7 vs. 49.8%; p<0.0001). For rs3892097 (CYP2D6) there was more carriers of the A allele between Roma in comparison with Czech population (39.2 vs. 38.2%; p=0.048). Genotype/allelic frequencies of CYP2D6 (rs1065852) and CYP1A2 (rs762551) variants did not significantly differ between the ethnics. Conclusions There were significant differences in allelic/genotype frequencies of some, but not all cytochromes P450 polymorphisms between the Czech Roma/Gypsies and Czech non-Roma subjects.

Precision therapeutic opioid dosing implications from genetic biomarkers and craving score

Determining the clinically optimal dose in methadone maintenance therapy (MMT) is a time-consuming procedure, which considers clinical signs and symptoms.To perform a quantitative trait locus association for identifying genetic variants for MMT dosage that underlie heroin addiction and methadone metabolism and then integrate several genotypic and phenotypic factors are potential predictors for clinically optimal MMT dose for personalized prescription.In total, 316 heroin-dependent patients undergoing MMT were recruited at the Addiction Center of the China Medical University Hospital. A multinomial logistic regression model was used to assess associations between genetic polymorphisms and MMT dosing. The data were randomly separated into training and testing sets. In order to enhance the prediction accuracy and the reliability of the prediction model, we used areas under the receiver operating characteristic curves to evaluate optimal MMT dose in both training and testing sets.Four single nucleotide polymorphisms, namely rs806368 in CNR1, s1386493 in TPH2, s16974799 in CYP2B6, and rs2229205 in OPRL1, were significantly associated with the maximum MMT dose (P < .05). The genetic risk score (GRS) was associated with maximum MMT dose, and after adjustments for age, sex, and body mass index, the GRS remained independently associated with the maximum MMT dose. The area under the receiver operating characteristic curve of the combined GRS and craving score was 0.77 for maximum MMT dose, with 75% sensitivity and 60% specificity.Integrating the GRS and craving scores may be useful in the evaluation of individual MMT dose requirements at treatment initiation. Optimal dose prediction allows clinicians to tailor MMT to each patient's needs.

Pharmacogenomics of Nicotine Metabolism: Novel CYP2A6 and CYP2B6 Genetic Variation Patterns in Alaska Native and American Indian Populations

INTRODUCTION

Alaska Native and American Indian (AN/AI) populations have higher tobacco use prevalence than other ethnic/racial groups. Pharmacogenetic testing to tailor tobacco cessation treatment may improve cessation rates. This study characterized polymorphic variations among AN/AI people in genes associated with metabolism of nicotine and drugs used for tobacco cessation.

METHODS

Recruitment of AN/AI individuals represented six subgroups, five geographic subgroups throughout Alaska and a subgroup comprised of AIs from the lower 48 states living in Alaska. We sequenced the CYP2A6 and CYP2B6 genes to identify known and novel gain, reduced, and loss-of-function alleles, including structural variation (eg, gene deletions, duplications, and hybridizations).

RESULTS

Variant allele frequencies differed substantially between AN/AI subgroups. The gene deletion CYP2A6*4 and reduced function CYP2A6*9 alleles were found at high frequency in Northern/Western subgroups and in Lower 48/Interior subgroups, respectively. The reduced function CYP2B6*6 allele was observed in all subgroups and a novel, predicted reduced function CYP2B6 variant was found at relatively high frequency in the Southeastern subgroup.

CONCLUSIONS

Diverse CYP2A6 and CYP2B6 variation among the subgroups highlight the need for comprehensive pharmacogenetic testing to guide tobacco cessation therapy for AN/AI populations.

IMPLICATIONS

Nicotine metabolism is largely determined by CYP2A6 genotype, and variation in CYP2A6 activity has altered the treatment success in other populations. These findings suggest pharmacogenetic-guided smoking cessation drug treatment could provide benefit to this unique population seeking tobacco cessation therapy.

Dosage Optimization of Efavirenz Based on a Population Pharmacokinetic-Pharmacogenetic Model of HIV-infected Patients in Thailand

PURPOSE

Efavirenz exhibits high interindividual variability in plasma concentrations, leading to unpredictable efficacy and toxicity. Polymorphism of CYP2B6 516G > T has been found to predominantly contribute to efavirenz variability. However, dosage recommendations incorporating CYP2B6 516G > T polymorphism have not been investigated in the Thai population. This study aimed to develop a population model of the pharmacokinetic properties of efavirenz, and to investigate the impact of patients' characteristics and CYP2B6 516G > T polymorphism on the pharmacokinetic properties of efavirenz. Model-based simulations were performed to provide genotype-based dosage optimization in a Thai population.

METHODS

Plasma efavirenz concentrations measured at 12 h post-dose in 360 Thai HIV-infected patients with and without tuberculosis were analyzed by the nonlinear mixed-effects modeling approach. A 1-compartment model with first-order absorption and elimination was used for describing the pharmacokinetic properties of efavirenz.

FINDINGS

The allele frequency of CYP2B6 516G > T was 34.17%. The efavirenz oral clearance were 11.9, 8.0, and 2.8 L/h in patients weighing 57 kg and having the CYP2B6 516 GG, 516 GT, and 516 TT genotypes, respectively. The use of rifampicin increased efavirenz oral clearance by 28%. The results from the simulations suggest that efavirenz dosages of 400, 300, and 100 mg once daily in Thai HIV mono-infected patients, and 800, 600, and 200 mg once daily in HIV/tuberculosis co-infected patients carrying CYP2B6 516 GG, 516 GT, and 516 TT, respectively.

IMPLICATION

The results from this study provide a rationale for efavirenz dose adjustment based on CYP2B6 516G > T polymorphism in Thai HIV-infected patients, which could help to improve treatment outcomes in this population. ClinicalTrials.gov identifier: NCT01138267.

Toward precision prescribing for methadone: Determinants of methadone deposition

BACKGROUND

Despite the World Health Organization listing methadone as an essential medication, effective dose selection is challenging, especially in racial and ethnic minority populations. Subtherapeutic doses can result in withdrawal symptoms while supratherapeutic doses can result in overdose and death. Although CYP3A4 was conventionally considered the principal methadone metabolizing enzyme, more recent data have identified CYP2B6 as the principal enzyme. CYP2B6 has ethnically-associated polymorphisms that affect the metabolic rate. Our objective was to investigate the effects of genetic and nongenetic factors on methadone metabolism.

METHODS

We measured trough plasma methadone levels in 100 participants with opioid use disorder. We assessed methadone metabolism by calculating the metabolite ratio (major metabolite: 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine [EDDP] divided by methadone concentration). We assessed hepatic fibrosis and steatosis by transient elastography and CYP2B6 alleles, principally responsible for methadone metabolism. Mixed effects models modeled the data in 97 participants.

RESULTS

Participants were largely male (58%), minority (61% African American) and non-Hispanic (68%). Forty percent were HCV mono-infected, 40% were uninfected, and 20% were HCV/HIV co-infected. Female sex had significant effects on (R)- and (S)-methadone metabolism (p = 0.016 and p = 0.044, respectively). CYP2B6 loss of function (LOF) alleles significantly affected (S)-methadone metabolism (p = 0.012). Body mass index (BMI) significantly affected (R)-methadone metabolism (p = 0.034). Methadone metabolism appeared to be lower in males, in individuals with LOF alleles, and elevated BMI.

CONCLUSIONS

Genetic analysis, especially in minority populations, is essential to delivering individualized treatments. Although the principal methadone metabolizing enzyme remains controversial, our results suggest that sex, CYP2B6 genotype, and BMI should be incorporated into multivariate models to create methadone dosing algorithms. Methadone dosing algorithms should facilitate medication delivery, improve patient satisfaction, and diminish overdose potential.

A randomized placebo-controlled trial of bupropion for Cancer-related fatigue: Study design and procedures

BACKGROUND

Cancer-related fatigue is a significant problem and is associated with poor quality of life. Behavioral interventions include exercise and cognitive-behavioral therapy, which survivors may be unwilling or unable to adopt. Pharmacologic interventions (e.g., selective serotonin reuptake inhibitors) have been disappointing. One potential therapy is the antidepressant bupropion, a norepinephrine-dopamine reuptake inhibitor that targets both inflammation and the hypothalamic-pituitary-adrenal axis. The current study is intended to provide a rigorous test of the efficacy and tolerability of bupropion for cancer-related fatigue.

METHODS

A randomized, double-blind, placebo-controlled trial will examine the effects of bupropion on cancer-related fatigue. The trial will be conducted nationwide through the University of Rochester Medical Center (URMC) National Cancer Institute Community Oncology Research Program (NCORP). Disease-free breast cancer survivors (n = 422) who completed chemotherapy and/or radiotherapy 12-60 months previously and report significant fatigue will be randomized 1:1 to receive bupropion (300 mg/day) or placebo. Outcomes will be assessed at baseline and the 12-week follow-up. The primary outcome, fatigue, will be measured with the Functional Assessment of Chronic Illness Therapy - Fatigue (FACIT-F). Secondary outcomes include quality of life, depression, and drug tolerability. Exploratory outcomes include cognition and symptomatology. Potential biological mechanisms and genetic moderators of cancer-related fatigue will also be explored.

DISCUSSION

This study is the first placebo-controlled trial to our knowledge to evaluate bupropion for cancer-related fatigue. Positive results could revolutionize the treatment of cancer-related fatigue, as bupropion is safe, inexpensive, widely-available, and may be more tolerable and acceptable for many patients than current, limited treatment options.

Retention of polybrominated diphenyl ethers and hydroxylated metabolites in paired human serum and milk in relation to CYP2B6 genotype

Polybrominated diphenyl ethers (PBDEs) and their hydroxylated metabolites (OH-BDEs) are endocrine disrupting compounds prevalent in human serum and breast milk. Retention of PBDEs and OH-BDEs in humans may be affected by differences in PBDE metabolism due to variants in cytochrome P450 2B6 (CYP2B6). The objectives of this study are to assess the partitioning profiles of PBDEs and OH-BDEs in forty-eight paired human serum and milk samples, and to evaluate the relationship between variants in CYP2B6 genotype and PBDE and OH-BDE accumulation in humans. Results show that the geometric mean (GM) concentrations of PBDEs are similar in serum (GM = 43.4 ng/g lipid) and milk samples (GM = 52.9 ng/g lipid), while OH-BDEs are retained primarily in serum (GM = 2.31 ng/g lipid), compared to milk (GM = 0.045 ng/g lipid). Participants with CYP2B6*6 genotype had a greater relative retention of PBDEs in serum and milk, and significant relationships (p <  0.05) were also observed for PBDE-47, 5-OH-BDE-47 and 6-OH-BDE-47 concentrations relative to CYP2B6*5 and CYP2B6*6 genotypes. These results are the first to show that CYP2B6 genotype is significantly related to the relative retention of PBDEs in humans, which may have direct implications for variability in the susceptibility of individuals to the potential adverse effects of these contaminants.

CYP2B6*6 Genotype Specific Differences in Artemether-Lumefantrine Disposition in Healthy Volunteers

Cytochrome P450 2B6 (CYP2B6) is involved in the metabolism of the antimalarial drugs artemether and lumefantrine. Here we investigated the effect of CYP2B6*6 on the plasma pharmacokinetics of artemether, lumefantrine, and their metabolites in healthy volunteers. Thirty healthy and previously genotyped adult volunteers-15 noncarriers (CYP2B6*1/*1) and 15 homozygote carriers (CYP2B6*6/*6)-selected from a cohort of 150 subjects from the Ilorin metropolitan area were administered the complete 3-day course of artemether and lumefantrine (80 and 480 mg twice daily, respectively). Intensive pharmacokinetic sampling was conducted at different time points before and after the last dose. Plasma concentrations of artemether, lumefantrine, dihydroartemisinin, and desbutyllumefantrine were quantified using validated liquid chromatography-mass spectrometric methods. Pharmacokinetic parameters were evaluated using noncompartmental analysis. Artemether clearance of CYP2B6*6/*6 volunteers was nonsignificantly lower by 26% (ratios of geometric mean [90% CI]; 0.74 [0.52-1.05]), and total exposure (the area under the plasma concentration-time curve from time 0 to infinity [AUC0-∞ ]) was greater by 35% (1.35 [0.95-1.93]) when compared with those of *1/*1 volunteers. Similarly, assuming complete bioconversion from artemether, the dihydroartemisinin AUC0-∞ was 22% lower. On the contrary, artemether-to-dihydroartemisinin AUC0-∞ ratio was 73% significantly higher (1.73 [1.27-2.37]). Comparison of lumefantrine exposure and lumefantrine-to-desbutyllumefantrine metabolic ratio of *6/*6 with corresponding data from *1/*1 volunteers showed no differences. The increased artemether-to-dihydroartemisinin metabolic ratio of *6/*6 volunteers is unlikely to result in differences in artemether-lumefantrine efficacy and treatment outcomes. This is the first study in humans to associate CYP2B6*6 genotype with artemether disposition.

CYP2B6 Genotype-Dependent Inhibition of CYP1A2 and Induction of CYP2A6 by the Antiretroviral Drug Efavirenz in Healthy Volunteers

We investigated the effect of efavirenz on the activities of cytochrome P450 (CYP)1A2, CYP2A6, xanthine oxidase (XO), and N-acetyltransferase 2 (NAT2), using caffeine as a probe. A single 150 mg oral dose of caffeine was administered to healthy volunteers (n = 58) on two separate occasions; with a single 600 mg oral dose of efavirenz and after treatment with 600 mg/day efavirenz for 17 days. Caffeine and its metabolites in plasma and urine were quantified using liquid chromatography/tandem-mass spectrometry. DNA was genotyped for CYP2B6*4 (785A>G), CYP2B6*9 (516G>T), and CYP2B6*18 (983T>C) alleles using TaqMan assays. Relative to single-dose efavirenz treatment, multiple doses of efavirenz decreased CYP1A2 (by 38%) and increased CYP2A6 (by 85%) activities (P < 0.05); XO and NAT2 activities were unaffected. CYP2B6*6*6 genotype was associated with lower CYP1A2 activity following both single and multiple doses of efavirenz. No similar association was noted for CYP2A6 activity. This is the first report showing that efavirenz reduces hepatic CYP1A2 and suggesting chronic efavirenz exposure likely enhances the elimination of CYP2A6 substrates. This is also the first to report the extent of efavirenz-CYP1A2 interaction may be efavirenz exposure-dependent and CYP2B6 genotype-dependent.