CYP2B6*6 and CYP2B6*18 Predict Long-Term Efavirenz Exposure Measured in Hair Samples in HIV-Positive South African Women

Pharmacogenetics of Breast Cancer Treatments: A Sub-Saharan Africa Perspective

Breast cancer is the most frequent cause of cancer death in low- and middle-income countries, in particular among sub-Saharan African women, where response to available anticancer treatment therapy is often limited by the recurrent breast tumours and metastasis, ultimately resulting in decreased overall survival rate. This can also be attributed to African genomes that contain more variation than those from other parts of the world. The purpose of this review is to summarize published evidence on pharmacogenetic and pharmacokinetic aspects related to specific available treatments and the known genetic variabilities associated with metabolism and/or transport of breast cancer drugs, and treatment outcomes when possible. The emphasis is on the African genetic variation and focuses on the genes with the highest strength of evidence, with a close look on CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4/5, CYP19A1, UGT1A4, UGT2B7, UGT2B15, SLC22A16, SLC38A7, FcγR, DPYD, ABCB1, and SULT1A1, which are the genes known to play major roles in the metabolism and/or elimination of the respective anti-breast cancer drugs given to the patients. The genetic variability of their metabolism could be associated with different metabolic phenotypes that may cause reduced patients’ adherence because of toxicity or sub-therapeutic doses. Finally, this knowledge enhances possible personalized treatment approaches, with the possibility of improving survival outcomes in patients with breast cancer.

Hair Zidovudine Concentrations Predict Virologic Outcomes Among People Living with HIV/AIDS in China

BACKGROUND

Hair antiretroviral concentrations are an objective and non-invasive measure of adherence to long-term antiretroviral therapy (ART) and can further predict virologic outcomes among people living with HIV/AIDS (PLWH). Zidovudine, one of the mainstream antiretrovirals in China, has been verified to have high reliability in adherence assessment, especially for its hair concentrations. However, data are limited in its predicting virologic outcomes. Therefore, this study aimed to characterize whether hair zidovudine concentrations can predict virologic suppression among Chinese PLWH compared with hair lamivudine concentrations and two self-reported measures, the overall frequency of adherence behaviors and percentage adherence.

METHODS

This cross-sectional study randomly recruited 564 PLWH currently treated with zidovudine, lamivudine, and other ART agents (efavirenz, nevirapine, or lopinavir/ritonavir) in Guangxi, China. Hair antiretroviral concentrations were determined using the LC-ESI⁺-MS/MS method. Receiver operating characteristic (ROC) curves were used to estimate the optimal classification thresholds of hair concentrations of zidovudine and lamivudine, and the two self-reported measures. Based on those optimal classification thresholds, logistic regression was used to examine whether those four adherence measures can predict virologic suppression (HIV-1 RNA <200 copies/mL).

RESULTS

ROC curves demonstrated good classification performance for association with virologic suppression of zidovudine with the optimal threshold at 58 pg/mg and lamivudine at 255 pg/mg but no self-reported measures. PLWH with hair zidovudine concentrations >58 pg/mg had an adjusted odds ratio (aOR) of 43.191 (95% confidence interval (CI) = 10.171‒183.418, p < 0.001) for virologic suppression. Hair lamivudine concentrations were also associated with virologic suppression (aOR = 10.656, 95% CI = 3.670‒30.943, p < 0.001). However, two self-reported measures did not predict virologic suppression (aORs = 1.157 and 2.488, ps >0.149).

CONCLUSION

Hair zidovudine concentrations can be served as an alternative tool for clinically predicting virologic suppression among PLWH in China.

Factors influencing hair lamivudine concentration among people living with HIV in Guangxi, China

BACKGROUND

Hair antiretroviral concentration has served as an innovative and objective measure of antiretroviral adherence. However, some factors (for example, pharmacokinetics and hair characteristics) may contribute to the variability of hair antiretroviral concentration that may threaten the validity and reliability of the hair measure as a biomarker of adherence. This study aimed to examine the potential factors that may influence the measure of hair antiretroviral concentration.

METHODS

Hair samples from a cohort of 372 people living with HIV (PLHIV) receiving lamivudine (300 mg/day) in Guangxi, China. Lamivudine concentration was analysed using liquid chromatography-tandem mass spectrometry. Multivariable linear regression was used to evaluate the associations of hair lamivudine concentration with age, sex, ethnicity, height, weight, body mass index, duration of HIV diagnosis, duration of current regimen, dosing schedule, concomitant antiretroviral medications, frequency of hair washing, hair care products use, hair cosmetic treatment and self-reported adherence.

RESULTS

Multivariable models revealed that frequency of hair washing (β=-0.221, P=0.001), dosing schedule (β=0.141, P=0.036) and self-reported adherence (β=0.160, P=0.002) were associated with hair lamivudine concentration.

CONCLUSIONS

We observed that, among those potential factors, hair lamivudine concentration was influenced by frequency of hair washing and dosing schedule. Therefore, frequency of hair washing and dosing schedule should be considered in future research using hair lamivudine concentration as a measure of lamivudine exposure and biomarker of adherence.

Association of CYP2B6 Genetic Variation with Efavirenz and Nevirapine Drug Resistance in HIV-1 Patients from Botswana

Purpose

CYP2B6 liver enzyme metabolizes the two non-nucleoside reverse transcriptase inhibitors Efavirenz (EFV) and Nevirapine (NVP) used in the antiretroviral therapy (ART) regimens for HIV-infected individuals. Polymorphisms of the CYP2B6 gene influence drug levels in plasma and possibly virological outcomes. The aim of this study was to explore the potential impact of CYP2B6 genotype and haplotype variation on the risk of developing EFV/NVP drug resistance mutations (DRMs) in HIV-1 patients receiving EFV-/NVP-containing regimens in Botswana.

Patients and Methods

Participants were a sub-sample of a larger study (Tshepo study) conducted in Gaborone, Botswana, among HIV-infected individuals taking EFV/NVP containing ART. Study samples were retrieved and assigned to cases (with DRMs) and controls (without DRMs). Four single-nucleotide polymorphisms (SNPs) in the CYP2B6 gene (−82T>C; 516G>T; 785A>G; 983T>C) were genotyped, the haplotypes reconstructed, and the metabolic score assigned. The possible association between drug resistance and several independent factors (baseline characteristics and CYP2B6 genotypes) was assessed by Binary Logistic Regression (BLR) analysis. EFV/NVP resistance status and CYP2B6 haplotypes were also analyzed using Z-test, chi-square and Fisher’s exact test statistics.

Results

Two hundred and twenty-seven samples were analysed (40 with DRMs, 187 without DRMs). BLR analysis showed an association between EFV/NVP resistance and CYP2B6 516G allele (OR: 2.26; 95% CI: 1.27–4.01; P=0.005). Moreover, haplotype analysis revealed that the proportion of EFV/NVP-resistant infections was higher among CYP2B6 fast than extensive/slow metabolizers (30.8% vs 16.8%; P=0.035), with the 516G allele more represented in the haplotypes of fast than extensive/slow metabolizers (100.0% vs 53.8%; P<0.001).

Conclusion

We demonstrated that the CYP2B6 516G allele, and even more when combined in fast metabolic haplotypes, is associated with the presence of EFV/NVP resistance, strengthening the need to assess the CYP2B6 genetic profiles in HIV-infected patients in order to improve the virologic outcomes of NNRTI containing ART.

PharmVar GeneFocus: CYP2B6

The Pharmacogene Variation Consortium (PharmVar) catalogs star (*) allele nomenclature for the polymorphic human CYP2B6 gene. Genetic variation within the CYP2B6 gene locus impacts the metabolism or bioactivation of clinically important drugs. Of particular importance are efficacy and safety concerns regarding: efavirenz, which is used for the treatment of HIV type-1 infection; methadone, a mainstay in the treatment of opioid use disorder and as an analgesic; ketamine, used as an antidepressant and analgesic; and bupropion, which is prescribed to treat depression and for smoking cessation. This GeneFocus provides a comprehensive overview and summary of CYP2B6 and describes how haplotype information catalogued by PharmVar is utilized by the Pharmacogenomics Knowledgebase (PharmGKB) and the Clinical Pharmacogenetics Implementation Consortium (CPIC).

Potential challenges to sustained viral load suppression in the HIV treatment programme in South Africa: a narrative overview

Background

South Africa, with one of the highest HIV prevalences in the world, introduced the universal test and treat (UTT) programme in September 2016. Barriers to sustained viral suppression may include drug resistance in the pre-treated population, non-adherence, acquired resistance; pharmacokinetics and pharmacodynamics, and concurrent use of alternative treatments.

Objective

The purpose of this review is to highlight potential challenges to achieving sustained viral load suppression in South Africa (SA), a major expectation of the UTT initiative.

Methodology

Through the PRISMA approach, published articles from South Africa on transmitted drug resistance; adherence to ARV; host genetic factors in drug pharmacokinetics and pharmacodynamics, and interactions between ARV and herbal medicine were searched and reviewed.

Results

The level of drug resistance in the pre-treated population in South Africa has increased over the years, although it is heterogeneous across and within Provinces. At least one study has documented a pre-treated population with moderate (> 5%) or high (> 15%) levels of drug resistance in eight of the nine Provinces. The concurrent use of ARV and medicinal herbal preparation is fairly common in SA, and may be impacting negatively on adherence to ARV. Only few studies have investigated the association between the genetically diverse South African population and pharmacokinetics and pharmacodynamics of ARVs.

Conclusion

The increasing levels of drug resistant viruses in the pre-treated population poses a threat to viral load suppression and the sustainability of first line regimens. Drug resistance surveillance systems to track the emergence of resistant viruses, study the burden of prior exposure to ARV and the parallel use of alternative medicines, with the goal of minimizing resistance development and virologic failure are proposed for all the Provinces of South Africa. Optimal management of the different drivers of drug resistance in the pre-treated population, non-adherence, and acquired drug resistance will be beneficial in ensuring sustained viral suppression in at least 90% of those on treatment, a key component of the 90-90-90 strategy.

The atorvastatin metabolic phenotype shift is influenced by interaction of drug-transporter polymorphisms in Mexican population: results of a randomized trial

Atorvastatin (ATV) is a blood cholesterol-lowering drug used to prevent cardiovascular events, the leading cause of death worldwide. As pharmacokinetics, metabolism and response vary among individuals, we wanted to determine the most reliable metabolic ATV phenotypes and identify novel and preponderant genetic markers that affect ATV plasma levels. A controlled, randomized, crossover, single-blind, three-treatment, three-period, and six-sequence clinical study of ATV (single 80-mg oral dose) was conducted among 60 healthy Mexican men. ATV plasma levels were measured using high-performance liquid chromatography mass spectrometry. Genotyping was performed by real-time PCR with TaqMan probes. Four ATV metabolizer phenotypes were found: slow, intermediate, normal and fast. Six gene polymorphisms, SLCO1B1-rs4149056, ABCB1-rs1045642, CYP2D6-rs1135840, CYP2B6-rs3745274, NAT2-rs1208, and COMT- rs4680, had a significant effect on ATV pharmacokinetics (P < 0.05). The polymorphisms in SLCO1B1 and ABCB1 seemed to have a greater effect and were especially important for the shift from an intermediate to a normal metabolizer. This is the first study that demonstrates how the interaction of genetic variants affect metabolic phenotyping and improves understanding of how SLCO1B1 and ABCB1 variants that affect statin metabolism may partially explain the variability in drug response. Notwithstanding, the influence of other genetic and non-genetic factors is not ruled out.

Antiretroviral Concentration in Hair as a Measure for Antiretroviral Medication Adherence: A Systematic Review of Global Literature

This review aims to validate hair antiretroviral concentration (HAC) as a measure for antiretroviral medication adherence. This review included 31 studies that analyzed a total of 11 ARV drugs in four different drug classes. The associations between HAC and non-pharmacokinetic measures were generally lower than the association between HAC and other pharmacokinetic measures: the correlation coefficients (r) ranged from - 0.20 to 0.38 for self-report or pill counts and 0.20 to 0.85 for electronic drug monitoring; HAC and other pharmacokinetic measures were positively correlated with the correlation coefficients (r) ranging from 0.20 to 0.72, 0.34 to 0.86, 0.50 to 0.85 for antiretroviral concentration in plasma, peripheral blood mononuclear cells, and dried blood spots, respectively. HAC was one of the strongest independent predictors of virologic responses. HAC of tenofovir was significantly associated with renal toxicity in large sample studies. This review suggests that HAC is a valid biomarker of antiretroviral medication adherence.

Efavirenz Metabolism: Influence of Polymorphic CYP2B6 Variants and Stereochemistry

Efavirenz (more specifically the S-enantiomer) is a cornerstone antiretroviral therapy for treatment of HIV infection. The major primary metabolite is S-8-hydroxyefavirenz, which does not have antiretroviral activity but is neurotoxic. Cytochrome P450 2B6 (CYP2B6) is the major enzyme catalyzing S-8-hydroxyefavirenz formation. CYP2B6 genetics and drug interactions are major determinants of clinical efavirenz disposition and dose adjustment. In addition, as a prototypic CYP2B6 substrate, S-efavirenz and analogs can inform on the structure, activity, catalytic mechanisms, and stereoselectivity of CYP2B6. Metabolism of R-efavirenz by CYP2B6 remains unexplored. This investigation assessed S-efavirenz metabolism by clinically relevant CYP2B6 genetic variants. This investigation also evaluated R-efavirenz hydroxylation by wild-type CYP2B6.1 and CYP2B6 variants. S-Efavirenz 8-hydroxylation by wild-type CYP2B6.1 and variants exhibited positive cooperativity and apparent cooperative substrate inhibition. On the basis of Cl_max values, relative activities for S-efavirenz 8-hydroxylation were in the order CYP2B6.4 > CYP2B6.1 ≈ CYP2B6.5 ≈ CYP2B6.17 > CYP2B6.6 ≈ CYP2B6.7 ≈ CYP2B6.9 ≈ CYP2B6.19 ≈ CYP2B6.26; CYP2B6.16 and CYP2B6.18 showed minimal activity. Rates of R-efavirenz metabolism were approximately 1/10 those of S-efavirenz for wild-type CYP2B6.1 and variants. On the basis of Cl_max values, there was 14-fold enantioselectivity (S > R-efavirenz) for wild-type CYP2B6.1, and 5- to 22-fold differences for other CYP2B6 variants. These results show that both CYP2B6 516G > T (CYP2B6*6 and CYP2B6*9) and 983T > C (CYP2B6*16 and CYP2B6*18) polymorphisms cause canonical diminishment or loss-of-function variants for S-efavirenz 8-hydroxylation, provide a mechanistic basis for known clinical pharmacogenetic differences in efavirenz disposition, and may predict additional clinically important variant alleles. Efavirenz is the most stereoselective CYP2B6 drug substrate yet identified and may be a useful probe for the CYP2B6 active site and catalytic mechanisms. SIGNIFICANCE STATEMENT: Clinical disposition of the antiretroviral S-efavirenz is affected by CYP2B6 polymorphisms. Expressed CYP2B6 with 516G>T (CYP2B6*6 and CYP2B6*9), and 983T>C (CYP2B6*16 and CYP2B6*18) polymorphisms had a diminishment or loss of function for efavirenz 8-hydroxylation. This provides a mechanistic basis for efavirenz clinical pharmacogenetics and may predict additional clinically important variant alleles. Efavirenz metabolism showed both cooperativity and cooperative substrate inhibition. With greater than 10-fold enantioselectivity (S- vs. R- metabolism), efavirenz is the most stereoselective CYP2B6 drug substrate yet identified. These findings may provide mechanistic insights.

Correlation of hair and plasma efavirenz concentrations in HIV-positive South Africans

BACKGROUND

Antiretroviral concentrations in hair provide a longer window of drug detection and are useful for measuring longer-term drug exposure. Efavirenz is an important component of first-line treatment in resource-limited settings, but its concentrations in hair have not been well studied.

METHODS

This study is a supplementary to a randomised controlled trial of an adherence intervention using an electronic adherence measuring device. Hair and plasma samples were collected from human immunodeficiency virus-positive patients in Cape Town, South Africa. Previously validated liquid chromatography tandem mass spectrometry methods were used to measure efavirenz concentrations in the collected hair and plasma samples. CYP2B6 genotyping of participants was also performed. Data analysis was performed using descriptive and comparative statistics as well as regression modelling.

RESULTS

Hair samples were collected from 59% of patients enrolled in the parent study. Results indicated that hair efavirenz concentrations were significantly influenced by participants' CYP2B6 metaboliser status. Median efavirenz concentrations for extensive, intermediate and slow metaboliser genotypes were 3.54 ng/mg, 5.11 ng/mg and 10.66 ng/mg, respectively. A strong correlation was observed between the efavirenz concentrations measured in hair and plasma samples (Spearman's correlation coefficients, 0.672-0.741, p < 0.0001). No relationship between hair efavirenz concentrations and virological failure or adherence measured using an electronic adherence was shown.

CONCLUSION

The results from this study provide further insight into the potential of using hair as a matrix for measuring antiretroviral concentrations. However, challenges experienced in collecting hair samples suggest that this adherence measure may have limited utility in an African population.

Pharmacogenetics of Antiretroviral Drug Response and Pharmacokinetic Variations in Indigenous South African Populations

Interindividual and interethnic differences in response to antiretroviral drugs (ARVs) are influenced by genetic variation. The few genomic studies conducted among African-Americans and African ethnic groups do not reflect the extensive genetic diversity within African populations. ARVs are widely used in Africa. Therefore, genomic characterization of African populations is required before genotype-guided dosing becomes possible. The aim of this study was to determine and report on the frequency of genetic variants in genes implicated in metabolism and transport of ARVs in South African populations. The study comprised 48 self-reported South African Colored (SAC) and 296 self-reported Black African (BA) individuals. Allele and genotype frequency distributions for 93 variants contributing to metabolism and transport of ARVs were compared between groups, and other global populations. Fifty-three variants had significant differences in allele and genotype frequencies when comparing SAC and BA groups. Thirteen of these have strong clinical annotations, affecting efavirenz and tenofovir pharmacokinetics. This study provides a summary of the genetic variation within genes implicated in metabolism and transport of ARVs in indigenous South African populations. The observed differences between indigenous population groups, and between these groups and global populations, demonstrate that data generated from specific African populations cannot be used to infer genetic diversity within other populations on the continent. These results highlight the need for comprehensive characterization of genetic variation within indigenous African populations, and the clinical utility of these variants in ARV dosing for global precision medicine. Population pharmacogenetics is a nascent field of global health and warrants further research and education.

A validated liquid chromatography/tandem mass spectrometry method for the analysis of efavirenz in 0.2 mg hair samples from human immunodeficiency virus infected patients

RATIONALE

Drug levels in hair provide a longer window of detection, compared to plasma drug levels, and therefore hair analysis has the advantage of assessing adherence over a longer period of time. No methods for the analysis of antiretroviral drugs in hair currently exist in South Africa, and worldwide there is only one validated method for the determination of efavirenz in hair that has been published.

METHODS

Efavirenz was extracted from 0.2 mg of hair through a simultaneous pulverization and extraction step. Separation was achieved on an Agilent Poroshell C18 column using an isocratic elution with a total run time of 3 min. A triple quadrupole mass spectrometer set to electrospray ionization in positive multiple reaction monitoring mode was used for detection. The method was validated over the concentration range 0.625-40 ng/mg.

RESULTS

Using ten times less hair than in a previously published method, the lower limit of quantitation was validated at 0.625 ng/mg. The interday and intraday assay precision, expressed as the percentage coefficient of variation (CV), for spiked calibration standards and quality control samples was lower than 7% and accuracy ranged from 97 to 110%. For quality controls prepared from authentic hair the CV was less than 12%. The extraction efficiency for authentic quality control samples was determined to be 83% after repeated extractions of the same samples.

CONCLUSIONS

This paper reports the first quantitative method for the determination of efavirenz in hair to be developed in South Africa. The validated method allowed for the successful monitoring of efavirenz in hair collected from HIV-infected patients as part of a clinical study.

Genetic Polymorphisms Affecting the Pharmacokinetics of Antiretroviral Drugs

BACKGROUND

Antiretroviral treatment is highly effective in enhancing HIV-positive patients' survival and quality of life. Despite an increased tolerability in recent years, a substantial amount of patients experience side effects. Antiretrovirals' efficacy and tolerability have been associated with plasma concentrations and single nucleotide polymorphisms in selected genes involved in drug disposition.

OBJECTIVE

Our aim was to review the current knowledge in genetic polymorphisms affecting plasma, intracellular or compartmental concentrations of antiretrovirals.

METHODS

A search of the PubMed database was conducted to identify relevant articles, using the following terms: 'pharmacogenetics' or 'pharmacogenomics' or 'single nucleotide polymorphisms' or 'genetic/allelic variants' and 'pharmacokinetics' or 'concentrations' and 'HIV' or 'antiretroviral'. Abstracts from the main HIV conferences during 2015 and 2016 were also searched using the same keywords. Abstracts were manually checked and, if relevant, full papers were obtained. Only articles published in English were selected.

RESULTS

Several genetic polymorphisms in genes coding enzymes involved in drug metabolism (cytochrome P450 isoenzymes and uridine diphosphate glucuronosyltransferases) and transport (P-glycoprotein, anionic and cationic transporters, other transporters), as well as nuclear receptors (pregnane X receptor and the constitutive androstane receptor), have been associated with concentrations of antiretrovirals. The extent of such influence, the conflicting data, and the potential clinical relevance are discussed in the main section of this article.

CONCLUSION

Genetic polymorphisms may affect antiretroviral disposition, as well as both efficacy and toxicity. Despite a large amount of data, such precious knowledge has seldom been applied in patients. Studies on the clinical relevance and cost effectiveness of tailoring antiretroviral regimens to patients' genetic assets are lacking, but their importance may grow with the increasing age and complexity of persons living with HIV/AIDS.