The impact of SLCO1B1 polymorphisms on the plasma concentration of lopinavir and ritonavir in HIV-infected men

The Farnesoid X Receptor as a Master Regulator of Hepatotoxicity

The nuclear receptor farnesoid X receptor (FXR, NR1H4) is a bile acid (BA) sensor that links the enterohepatic circuit that regulates BA metabolism and elimination to systemic lipid homeostasis. Furthermore, FXR represents a real guardian of the hepatic function, preserving, in a multifactorial fashion, the integrity and function of hepatocytes from chronic and acute insults. This review summarizes how FXR modulates the expression of pathway-specific as well as polyspecific transporters and enzymes, thereby acting at the interface of BA, lipid and drug metabolism, and influencing the onset and progression of hepatotoxicity of varying etiopathogeneses. Furthermore, this review article provides an overview of the advances and the clinical development of FXR agonists in the treatment of liver diseases.

Frequency of functional exonic single-nucleotide polymorphisms and haplotype distribution in the SLCO1B1 gene across genetic ancestry groups in the Qatari population

Organic anion transporting polypeptides (OATP), which are encoded by SLCO genes, participate in the hepatic elimination of drugs and xenobiotics. SLCO1B1 is an important pharmacogenomic gene (encoding OATP1B1) associated with response to the uptake of endogenous compounds, such as statin and bilirubin. Ethnicity of the patient modulates the response to these drugs; the frequency and haplotype data for SLCO1B1 genetic variants in the Arab population is lacking. Therefore, we determined the frequencies of two well-characterized SLCO1B1 single nucleotide polymorphisms (SNP) and haplotypes that affect the OATP1B1 drugs transportation activity in Qatari population. Genotyping data for two SLCO1B1 SNPs (c.388A > G, c.521 T > C) were extracted from whole exome data of 1050 Qatari individuals, who were divided into three ancestry groups, namely Bedouins, Persians/South Asians, and Africans. By way of using Fisher's exact and Chi-square tests, we evaluated the differences in minor allele frequency (MAF) of the two functional SNPs and haplotype frequencies (HF) among the three ancestry groups. The OATP1B1 phenotypes were assigned according to their function by following the guidelines from the Clinical Pharmacogenetics Implementation Consortium for SLCO1B1 and Simvastatin-Induced Myopathy.The MAF of SLCO1B1:c.388A > G was higher compared to that of SLCO1B1:c.521 T > C in the study cohort. It was significantly high in the African ancestry group compared with the other two groups, whereas SLCO1B1:c.521 T > C was significantly low in the African ancestry group compared with the other two groups. The SLCO1B1 *15 haplotype had the highest HF, followed by *1b, *1a, and *5. Only the SLCO1B1 *5 haplotype showed no significant difference in frequency across the three ancestry groups. Furthermore, we observed that the OATP1B1 normal function phenotype accounted for 58% of the Qatari individuals, the intermediate function phenotype accounted for 35% with significant differences across the ancestry groups, and the low function phenotype accounted for 6% of the total Qatari individuals with a higher trend observed in the Bedouin group.The results indicate that the phenotype frequencies of the OATP1B1 intermediate and low function in the Qatari population appear at the higher end of the frequency range seen worldwide. Thus, a pharmacogenetic screening program for SLCO1B1 variants may be necessary for the Qatari population.

Pharmacogenetics research in Brazil: a systematic review

Aim: Pharmacogenomics (PGx) is a rising scientific area in many countries, such as Brazil. Objectives: To identify biomarkers, therapeutic areas, probe drugs and regions/ethnicities most studied in the country in order to guide future studies. Materials & methods: Systematic review of 1060 studies (from 1968 to 2020) comprising 80 genes, six probe drugs and 3,819,233 individuals. Results: MTHFR and HLA-A/B were the most studied genes and metoprolol and dextromethorphan the most studied probe drugs. Oncology was the most studied therapeutic area considering PGx biomarkers. The country’s regions and ethnic groups were studied unevenly, with south/southeast and White people over-represented in respect to their demographic relevance, in detriment of the center-west/northeast/north and Black/mixed individuals. Conclusion: Many of the gaps and possible paths to be covered to reach even PGx data are pointed out by this review.

Pharmacogenetics of HIV therapy: State of the art in Latin American countries

The use of combined antiretroviral therapy (cART) has resulted in a remarkable reduction in morbidity and mortality of people living with HIV worldwide. Nevertheless, interindividual variations in drug response often impose a challenge to cART effectiveness. Although personalized therapeutic regimens may help overcome incidence of adverse reactions and therapeutic failure attributed to host factors, pharmacogenetic studies are often restricted to a few populations. Latin American countries accounted for 2.1 million people living with HIV and 1.4 million undergoing cART in 2020-21. The present review describes the state of art of HIV pharmacogenetics in this region and highlights that such analyses remain to be given the required relevance. A broad analysis of pharmacogenetic markers in Latin America could not only provide a better understanding of genetic structure of these populations, but might also be crucial to develop more informative dosing algorithms, applicable to non-European populations.

The role of pharmacogenetics in Efficacy and safety of protease inhibitor based therapy in human immunodeficiency virus type (HIV) infection

Antiretroviral therapy has markedly reduced morbidity and mortality for persons living with human immunodeficiency virus (HIV). HIV can now be classified as a chronic disease; until a cure is found, patients are likely to require life-long therapy. However, despite these undoubted advances, there are many issues that need to be resolved, including the problems associated with long-term efficacy and toxicity. Moreover, pharmacotherapy of patients infected with HIV is challenging because a great number of comorbidities increase polypharmacy and the risk for drug-drug interactions. There is considerable interindividual variability in patient outcomes in terms of drug disposition, drug efficacy and adverse events. The basis of these differences is multifactorial, but host genetics are believed to play a significant part. HIV-infected population consists of ethnically diverse individuals on complex and potentially toxic antiretroviral regimens on a long-term basis. These individuals would benefit greatly from predictive tests that identify the most durable regimens. Pharmacogenetics holds that promise. Thus, detailed understanding of the metabolism and transport of antiretrovirals and the influence of genetics on these pathways is important. To this end, this review provides an up-to-date overview of the metabolism of antiHIV therapeutics of the protease inhibitors Lopinavir and Ritonavir and the impact of genetic variation in drug metabolism and transport on the treatment of HIV.

Pharmacogenomic landscape of COVID-19 therapies from Indian population genomes

Aim: Numerous drugs are being widely prescribed for COVID-19 treatment without any direct evidence for the drug safety/efficacy in patients across diverse ethnic populations. Materials & methods: We analyzed whole genomes of 1029 Indian individuals (IndiGen) to understand the extent of drug–gene (pharmacogenetic), drug–drug and drug–drug–gene interactions associated with COVID-19 therapy in the Indian population. Results: We identified 30 clinically significant pharmacogenetic variants and 73 predicted deleterious pharmacogenetic variants. COVID-19-associated pharmacogenes were substantially overlapped with those of metabolic disorder therapeutics. CYP3A4, ABCB1 and ALB are the most shared pharmacogenes. Fifteen COVID-19 therapeutics were predicted as likely drug–drug interaction candidates when used with four CYP inhibitor drugs. Conclusion: Our findings provide actionable insights for future validation studies and improved clinical decisions for COVID-19 therapy in Indians.

Influence of CYP3A5 and SLCO1B1 polymorphisms on atazanavir/r concentrations in Thai HIV-infected patients

Aim: To evaluate the influence of genetic polymorphisms on plasma trough concentrations of atazanavir (ATV) and ritonavir (RTV). Patients & methods: The concentration-to-dose ratios were compared between different genotype groups of CYP3A5, ABCB1, SLCO1B1 and NR1I2 in 490 patients. Multiple regression analysis was used to examine the association between genetic and clinical factors and log-transformed concentration-to-dose ratio of ATV and RTV. Results: Higher concentrations of ATV and RTV were significantly associated with CYP3A5 6986 GG and SLCO1B1 521 TC or CC. Female patients had significantly higher ATV plasma concentration than male patients. Conclusion: Genetic polymorphisms and gender are factors affecting the variability of ATV and RTV concentrations in the Thai population. Thus, genetic testing is worth considering when atazanavir + low dose ritonavir is prescribed.

Influence of SLCO1B1 polymorphisms on lopinavir Ctrough in Serbian HIV/AIDS patients

AIMS

Lopinavir (LPV) is not a first-line regimen. According to recent WHO data, LPV usage in low- and middle-income countries accounted for approximately 52% of the adult and 23% of the paediatric protease inhibitor market in 2017. Since LPV is a substrate for the SLCO1B1 (OATP1B1) transporter, the aim of this study was to assess the impact of SLCO1B1 polymorphisms (rs11045819, rs4149032 and rs4149056) on LPV trough plasma concentrations (C_trough ) in Serbian patients.

METHODS

Plasma samples from 104 HIV/AIDS Caucasians were collected. LPV C_trough was quantified using liquid-chromatography-mass spectrometry. Genotyping was carried out using real-time-PCR-based allelic discrimination. One-way analysis of variance, t test and linear regression were used for data analysis.

RESULTS

The overall mean (SD) LPV C_trough was 5885 ± 2755 ng/mL. Significant differences were between patients with different rs11045819 genotypes: CC (LPV median C_trough = 6072 ng/mL, interquartile range (IQR) = 4318-7617 ng/mL), CA (LPV median C_trough = 4987 ng/mL, IQR = 4300-6295 ng/mL) and AA (LPV median C_trough = 3648 ng/mL, IQR = 1949-4072 ng/mL) (P = .005). Significant differences were also observed according to rs4149032 genotype: CC (LPV median C_trough = 6027 ng/mL, IQR =4548-8250 ng/mL), CT (LPV median C_trough = 5553 ng/mL, IQR = 4300-6888 ng/mL) and TT (LPV median C_trough = 4408 ng/mL, IQR = 3361-5233 ng/mL) (P = .007). For rs4149056 a statistically significant difference between T-homozygotes (LPV median C_trough = 5434 ng/mL, IQR = 3855-6830 ng/mL), heterozygotes (LPV median C_trough = 6707 ng/mL, IQR = 5088-8063 ng/mL) and C-homozygotes (LPV median C_trough = 13906 ng/mL, IQR = 12946-14866 ng/mL) was observed (P = .002). In multivariate regression analysis, only the SLCO1B1 rs4149056 polymorphism was independently associated with higher LPV C_trough (β = 2834.5 [1442-4226.9] ng/mL [P = .001]).

CONCLUSIONS

Our results demonstrate a statistically significant influence of the SLCO1B1 rs4149056 polymorphism on higher LPV C_trough in Caucasian HIV/AIDS patients.

microRNA-206 modulates the hepatic expression of the organic anion-transporting polypeptide 1B1

BACKGROUND & AIMS

The organic anion-transporting polypeptide 1B1 (OATP1B1) is an anion exchanger expressed at the hepatocyte sinusoidal membrane, which mediates the uptake of several endogenous metabolites and drugs. OATP1B1 expression level and activity are major sources of inter-patient variability of pharmacokinetics and pharmacodynamics of several drugs. Besides the genotype, factors that contribute to the inter-individual variability in OATP1B1 expression level are practically unknown. The aim of this work was to uncover novel epigenetic mechanisms of OATP1B1 regulation.

METHODS

A functional screening strategy to assess the effect of microRNAs on the uptake of estrone-3-sulphate, an OATP1B1 substrate, into human hepatocellular carcinoma (Huh-7) cells was used. microRNA-206 (miR-206) expression in human liver tissues was measured by real-time RT-PCR. OATP1B1 expression in Huh-7 and in human liver tissues was assessed by real-time RT-PCR, Western blotting and immunostaining. The mRNA-miRNA interaction was assessed by reporter assay.

RESULTS

miR-206 mimic repressed mRNA and protein expression of OATP1B1 in Huh-7 cells. The intracellular accumulation of estrone-3-sulphate was reduced by 30% in cells overexpressing miR-206. The repressive effect of miR-206 on the activity of the firefly luciferase gene 2 under the control of the OATP1B1 3' untranslated region was lost upon deletion of the predicted miR-206 binding site. Hepatic miR-206 level negatively correlated with OATP1B1 mRNA and protein levels extracted from normal human liver tissues.

CONCLUSIONS

miR-206 exerts a suppressive effect on OATP1B1 expression by an epigenetic mechanism. Individuals with high hepatic levels of miR-206 appear to display lower level of OATP1B1.

SLCO1B1 c.388A > G variant incidence and the severity of hyperbilirubinemia in Indonesian neonates

OBJECTIVE

It has been established that genetic factors play a substantial role in the development of neonatal hyperbilirubinemia. The population of Indonesia and other Southeast Asian countries has similar, yet different genetic makeup compared to the rest of Asia. Aside from UGT1A1, variants of SLCO1B1 have also been known to contribute to the severity of neonatal hyperbilirubinemia in Asian populations. Since there has been no report on SLCO1B1 polymorphism in relation with hyperbilirubinemia in Indonesia, this study aims to explore incidence of SLCO1B1*1B polymorphism in Indonesia based on 3 hospitals from different provinces and population, and their association with hyperbilirubinemia severity.

METHODS

Our study included 88 neonates with mild and moderate-severe hyperbilirubinemia from 3 NICU in hospitals representing homogenous and heterogenous populations: Biak General Hospital Papua, Cipto Mangunkusumo Hospital (Jakarta), and M Yunus Hospital (Bengkulu). We collected samples between November 2016 and September 2017. DNA was obtained from existing samples of the patients from previous studies and were subjected to Polymerase Chain Reaction - Restriction Fragment Length Polymorphism (PCR-RFLP). We analyzed the *1B variant located in exon 5 of SLCO1B1 with TaqI restriction endonuclease. Clinical, demographic, and laboratory data was also collected from medical records and parents' interviews.

RESULTS

The most dominant variant of SLCO1B1*1B in our population is the homozygous G/G (68.18%), followed by heterozygous A/G (26.14%), and wild type A/A (5.68%). The heterozygous A/G had an Odds Ratio (OR) of 0.73 (95% CI 0.10-5.2) and homozygous G/G with OR of 0.51 (95%CI 0.08-3.27), both were not significant. Genotypic distribution across the different centers were also similar and not significant. The significant risk factors for moderate-severe hyperbilirubinemia were the population the neonate originated from (p = < 0.001) and the delivery location (p = 0.001), while SLCO1B1*1B was not associated with the different severity of hyperbilirubinemia.

CONCLUSIONS

SLCO1B1*1B is not associated with higher bilirubin levels among neonates with hyperbilirubinemia in Indonesia. Further study is needed to find other potentially important genetic polymorphisms in the development of severe hyperbilirubinemia in Indonesia.

The dawn of precision medicine in HIV: state of the art of pharmacotherapy

INTRODUCTION

Combination antiretroviral therapy (ART) reduces viral load to under the limit of detection, successfully decreasing HIV-related morbidity and mortality. Due to viral mutations, complex drug combinations and different patient response, there is an increasing demand for individualized treatment options for patients.

AREAS COVERED

This review first summarizes the pharmacokinetic and pharmacodynamic profile of clinical first-line drugs, which serves as guidance for antiretroviral precision medicine. Factors which have influential effects on drug efficacy and thus precision medicine are discussed: patients' pharmacogenetic information, virus mutations, comorbidities, and immune recovery. Furthermore, strategies to improve the application of precision medicine are discussed.

EXPERT OPINION

Precision medicine for ART requires comprehensive information on the drug, virus, and clinical data from the patients. The clinically available genetic tests are a good starting point. To better apply precision medicine, deeper knowledge of drug concentrations, HIV reservoirs, and efficacy associated genes, such as polymorphisms of drug transporters and metabolizing enzymes, are required. With advanced computer-based prediction systems which integrate more comprehensive information on pharmacokinetics, pharmacodynamics, pharmacogenomics, and the clinically relevant information of the patients, precision medicine will lead to better treatment choices and improved disease outcomes.

Pharmacokinetic Changes during Pregnancy According to Genetic Variants: a Prospective Study in HIV-Infected Patients Receiving Atazanavir-Ritonavir

Atazanavir-ritonavir concentrations change over time during pregnancy in HIV-positive patients; the impact of genetic variants is unknown. Twenty patients were enrolled in this study; plasma and intracellular concentrations of antiretrovirals were measured, in addition to single-nucleotide polymorphisms in transport-related genes. Linear logistic regression showed that genetic variants in organic-anion-transporter-1B1- and pregnane-X-receptor-encoding genes affected third-trimester atazanavir exposure. In this prospective study, genetic variants partially explained the observed interpatient variability in third-trimester exposure to antiretrovirals.

Intrahepatic Sampling for the Elucidation of Antiviral Clinical Pharmacology

Although the importance of the liver in clinical pharmacology is widely recognized, little is known in humans concerning its function in vivo at the hepatocyte level and how pharmacological functions are altered in the setting of advanced liver disease. Several recent proof-of-principle studies with first-generation DAAs have demonstrated the feasibility of serial liver sampling for pharmacological studies. These studies have begun to describe the liver-to-plasma concentration ratio and how this ratio is altered in the setting of advanced liver disease. These data are particularly relevant to individuals with substance-use disorders because many have advanced liver disease as a consequence of long-standing viral hepatitis infection or continued use of hepatotoxins such as alcohol. Future research should attempt to develop standardized and reproducible methods to assess liver drug concentration, complex drug interactions, and pharmacogenomics in humans to permit elucidation of the clinical pharmacology within the liver.

Regulation of Organic Anion Transporting Polypeptides (OATP) 1B1- and OATP1B3-Mediated Transport: An Updated Review in the Context of OATP-Mediated Drug-Drug Interactions

Organic anion transporting polypeptides (OATP) 1B1 and OATP1B3 are important hepatic transporters that mediate the uptake of many clinically important drugs, including statins from the blood into the liver. Reduced transport function of OATP1B1 and OATP1B3 can lead to clinically relevant drug-drug interactions (DDIs). Considering the importance of OATP1B1 and OATP1B3 in hepatic drug disposition, substantial efforts have been given on evaluating OATP1B1/1B3-mediated DDIs in order to avoid unwanted adverse effects of drugs that are OATP substrates due to their altered pharmacokinetics. Growing evidences suggest that the transport function of OATP1B1 and OATP1B3 can be regulated at various levels such as genetic variation, transcriptional and post-translational regulation. The present review summarizes the up to date information on the regulation of OATP1B1 and OATP1B3 transport function at different levels with a focus on potential impact on OATP-mediated DDIs.

Mapping SLCO1B1 Genetic Variation for Global Precision Medicine in Understudied Regions in Africa: A Focus on Zulu and Cape Admixed Populations

The U.S. President Barack Obama has announced, in his State of the Union address on January 20, 2015, the Precision Medicine Initiative, a US$215-million program. For global precision medicine to become a reality, however, biological and environmental "variome" in previously understudied populations ought to be mapped and catalogued. Chief among the molecular targets that warrant global mapping is the organic anion-transporting polypeptide 1B1 (OATP1B1), encoded by solute carrier organic anion transporter family member 1B1 (SLCO1B1), a hepatic uptake transporter predominantly expressed in the basolateral side of hepatocytes. Human OATP1B1 plays a crucial role in the transport of a wide variety of substrates. This includes endogenous compounds such as bile salts as well as medicines, including benzylpenicillin, methotrexate, pravastatin, and rifampicin, and natural toxins microcystin and phalloidin. Genetic variations observed in the SLCO1B1 gene have been associated with altered in vitro and in vivo OATP1B1 transport activity, and consequently influencing patients' response to medicines, toxins, and susceptibility to common complex diseases. Well-characterized haplotypes, *5 (RS4149056C) and *15 (RS4149056T), have been associated with a strikingly reduced uptake of multiple OATP1B1 substrates, including estrone-3-sulfate, estradiol-17β-d-glucuronide, atorvastatin, cerivastatin, pravastatin, and rifampicin. In particular, RS4149056C is observed in 60% of the Cape admixed (CA) population and is associated with increased plasma concentrations of many statins as well as fexofenadine and repaglinide. We designed and optimized a SNaPshot minisequencing panel to characterize the variants of relevance for precision medicine in the clinic. We report here the first study on allele and genotype frequencies for 10 nonsynonymous, 4 synonymous, and 6 intronic single-nucleotide polymorphisms of SLCO1B1 in the Zulu and CA populations of South Africa. These variants are further contextualized here, in relation to their potential clinical relevance. These observations collectively contribute to current efforts to advance global precision medicine in understudied populations and resource-limited regions of the world.

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.

Impact of Single Nucleotide Polymorphisms on Plasma Concentrations of Efavirenz and Lopinavir/Ritonavir in Chinese Children Infected with the Human Immunodeficiency Virus

Single nucleotide polymorphisms (SNPs) in the genes that encode the cytochrome P450 (CYP) drug metabolizing enzymes and drug transporters have been reported to influence antiretroviral drug pharmacokinetics. Although primarily metabolized by CYP2B6 and -3A, efavirenz (EFV) and lopinavir/ritonavir (LPV/r) are substrates of P-glycoprotein and the solute carrier organic (SLCO) anion transporter, respectively. We investigated the association between SNPs and efavirenz (EFV) or lopinavir/ritonavir (LPV/r) concentrations in Chinese children infected with the human immunodeficiency virus (HIV). Genotyping was performed on CYP2B6 516G→T, -1459C→T, and -983T→C, ABCB1 3435C→T, and SLCO1B1 521T→C in 229 HIV-infected Chinese pediatric patients (age range 4.0 to 17.5 yrs). Plasma concentrations of EFV and LPV/r were measured using validated high-performance liquid chromatography coupled with the mass spectrum method among 39 and 69 children who received EFV- and LPV/r-containing regimens, respectively. The frequencies of CYP2B6 516G→T in the study participants were 71%, 25%, and 4% for the G/G, G/T, and T/T genotypes, respectively. Among the children under therapeutic drug monitoring, 21% and 39% experienced EFV and LPV concentrations, respectively, above the upper threshold of the therapeutic window. CYP2B6 516G→T was significantly associated with EFV concentrations (p<0.001). Older children (older than 10 yrs) were more likely to have significantly higher EFV concentrations than the younger ones (p=0.0314). CYP2B6 genotyping and EFV concentration monitoring may help optimize antiretroviral therapy in pediatric patients who initiate an EFV-based regimen.

Role of vitamin D pathway gene polymorphisms on rifampicin plasma and intracellular pharmacokinetics

AIM

We retrospectively evaluate the pharmacogenetic role of single nucleotide polymorphisms involved in rifampicin transport (SLCO1B1, MDR1 and PXR genes) and vitamin D (VDR, CYP24A1 and CYP27B1 genes) metabolism and activity on drug plasma and intracellular concentrations.

PATIENTS & METHODS

Rifampicin C_max and C_trough were measured at weeks 2 and 4 using Ultra-Performance Liquid Chromatography-tandem mass spectroscopy methods. Allelic discrimination was performed by real-time polymerase chain reaction.

RESULTS

Twenty-four patients were enrolled. At week 2, OATP1B1 521TT and CYP27B1 +2838CC/CT considering plasma and BsmIAA for intraperipheral blood mononuclear cells C_max, remained in regression analysis. Concerning week 4, TaqITC/CC and CYP24A1 22776CT/TT were retained in plasma C_max regression model.

CONCLUSION

This study confirms the role of SLCO1B1 and it suggests the involvement of vitamin D pathway gene polymorphisms in rifampicin pharmacokinetics.

Prediction of area under the concentration-time curve for lopinavir from peak or trough lopinavir concentrations in patients receiving lopinavir-ritonavir therapy

PURPOSE

A "single time point" strategy for predicting the area under the concentration-time curve (AUC) for lopinavir in patients receiving ritonavir-boosted lopinavir therapy was investigated.

METHODS

Linear regression equations describing the relationships of lopinavir peak and trough concentrations to lopinavir AUC values were established using pharmacokinetic data from published studies of patients or healthy subjects receiving lopinavir and ritonavir at standard dosages. The resulting "trough-AUC model" and "peak-AUC model" were used to predict lopinavir AUC values in the evaluated study populations (total n = 479); those values were then compared with reported AUC values.

RESULTS

Lopinavir peak or trough concentrations were strongly correlated with lopinavir AUC values (r = 0.9947 and r = 0.9541, respectively). For about 94% of calculations using the peak-AUC model and 87% of calculations using the trough-AUC model, differences between predicted and observed AUC values were in the range of 0.76-1.5 fold; the associated r values were 0.9514 (p < 0.001) and 0.9345 (p < 0.001), respectively. The mean absolute predictive error was less than 6% with the use of either the peak-AUC model or the trough-AUC model, with corresponding values for root-mean-square error of 17.6% and 23.5%, respectively.

CONCLUSION

Equations incorporating lopinavir peak and trough concentrations were found to satisfactorily predict lopinavir AUC values in data sets describing patients receiving lopinavir with ritonavir boosting. Variability in predictions was higher with use of the trough-AUC model.

New treatment strategies for HIV-positive cancer patients undergoing antiblastic chemotherapy

INTRODUCTION

The introduction of Highly Active Antiretroviral Therapy (HAART) into clinical practice has dramatically changed the outcome of HIV-infected patients by prolonging their survival. The increase in life expectancy has led to an increased risk of non-AIDS-related mortality and morbidity, including cardiovascular diseases, neurocognitive diseases, neuroendocrine dysfunctions and cancer. Areas covered: The GICAT (Italian Cooperation Group on AIDS and Tumors) has demonstrated that patients who receive a multidisciplinary approach with the combination of anticancer agents (AC) and HAART can achieve better responses and survival rates than patients who receive AC alone. The first obstacle for the oncologist to plan treatment for cancer HIV-patients is the preliminary evaluation of drug-drug interactions between AC and HAART. Recent progress in pharmacogenomics could provide a new approach for personalized treatments. The rationale of this review is to summarize the existing data on the impact of HAART on the clinical management of cancer patients with HIV/AIDS and DDIs between antiretrovirals and AC. In addition, to maximize the efficacy of both concomitant therapy and to minimize the risk of DDIs, a currently useful list of pharmacogenomic markers of key metabolic enzymes is provided. Expert opinion: In this scenario, the importance of cooperation between oncologists and other health specialists (i.e., infectivologists, pharmacists, genetics and lab specialists) must not be underestimated in the management of these patients with the aim of planning an individual treatment strategy.

Single Nucleotide Polymorphisms in Cellular Drug Transporters Are Associated with Intolerance to Antiretroviral Therapy in Brazilian HIV-1 Positive Individuals

Adverse reactions are the main cause of treatment discontinuation among HIV+ individuals. Genes related to drug absorption, distribution, metabolism and excretion (ADME) influence drug bioavailability and treatment response. We have investigated the association between single nucleotide polymorphisms (SNPs) in 29 ADME genes and intolerance to therapy in a case-control study including 764 individuals. Results showed that 15 SNPs were associated with intolerance to nucleoside and 11 to non-nucleoside reverse transcriptase inhibitors (NRTIs and NNRTIs), and 8 to protease inhibitors (PIs) containing regimens under alpha = 0.05. After Bonferroni adjustment, two associations remained statistically significant. SNP rs2712816, at SLCO2B1 was associated to intolerance to NRTIs (OR_GA/AA = 2.37; p = 0.0001), while rs4148396, at ABCC2, conferred risk of intolerance to PIs containing regimens (OR_CT/TT = 2.64; p = 0.00009). Accordingly, haplotypes carrying rs2712816A and rs4148396T alleles were also associated to risk of intolerance to NRTIs and PIs, respectively. Our data reinforce the role of drug transporters in response to HIV therapy and may contribute to a future development of personalized therapies.

Role and modulation of drug transporters in HIV-1 therapy

Current treatment of human immunodeficiency virus type-1 (HIV-1) infection involves a combination of antiretroviral drugs (ARVs) that target different stages of the HIV-1 life cycle. This strategy is commonly referred to as highly active antiretroviral therapy (HAART) or combined antiretroviral therapy (cART). Membrane-associated drug transporters expressed ubiquitously in mammalian systems play a crucial role in modulating ARV disposition during HIV-1 infection. Members of the ATP-binding cassette (ABC) and solute carrier (SLC) transporter superfamilies have been shown to interact with ARVs, including those that are used as part of first-line treatment regimens. As a result, the functional expression of drug transporters can influence the distribution of ARVs at specific sites of infection. In addition, pathological factors related to HIV-1 infection and/or ARV therapy itself can alter transporter expression and activity, thus further contributing to changes in ARV disposition and the effectiveness of HAART. This review summarizes current knowledge on the role of drug transporters in regulating ARV transport in the context of HIV-1 infection.

Pharmacogenetics of unboosted atazanavir in HIV-infected individuals in resource-limited settings: a sub-study of the AIDS Clinical Trials Group (ACTG) PEARLS study (NWCS 342)

OBJECTIVES

The multinational PEARLS (ACTG A5175) study, conducted mainly in resource-limited settings, identified an increased treatment failure rate among HIV-infected individuals randomized to once-daily unboosted atazanavir, didanosine-EC, and emtricitabine compared with efavirenz-based regimens. We evaluated associations between selected human genetic polymorphisms and atazanavir pharmacokinetics in PEARLS.

METHODS

Polymorphisms in CYP3A5, ABCB1, SLCO1B1 and NR1I2 were genotyped in PEARLS participants randomized to atazanavir plus didanosine-EC plus emtricitabine in Peru, South Africa and the USA, who also consented to genetic analysis. Non-linear mixed-effects population pharmacokinetic modelling was used to predict atazanavir oral clearance (CL/F) and concentration at 24 h (C24). Atazanavir mono-oxidation metabolites M1 and M2 were quantified from the same single-point plasma sample used to quantify the parent drug. Data were log10 transformed for statistical analysis using unpaired t-tests and one-way ANOVA and are presented as geometric mean (95% CI).

RESULTS

Eighty-four HIV-infected participants were genotyped, including 44 Black Africans or African Americans and 28 women. Median age was 34 years. We identified 56 CYP3A5 expressers and 28 non-expressers. Atazanavir CL/F and C24 did not differ between CYP3A5 expressers and non-expressers: 13.2 (12.1-14.4) versus 12.7 L/h (11.7-13.9), P = 0.61, and 75.3 (46.1-123.0) versus 130.9 ng/mL (86.9-197.2), P = 0.14, respectively. M1/atazanavir and M2/atazanavir ratios were higher in expressers than in non-expressers: 0.0083 (0.0074-0.0094) versus 0.0063 (0.0053-0.0075), P = 0.008, and 0.0065 (0.0057-0.0073) versus 0.0050 (0.0042-0.0061), P = 0.02, respectively.

CONCLUSIONS

Expression of CYP3A5 appears to be associated with increased M1 and M2 atazanavir metabolite formation, without significantly affecting parent compound pharmacokinetics.

Drug-Drug Interactions Based on Pharmacogenetic Profile between Highly Active Antiretroviral Therapy and Antiblastic Chemotherapy in Cancer Patients with HIV Infection

The introduction of Highly Active Antiretroviral Therapy (HAART) into clinical practice has dramatically changed the natural approach of HIV-related cancers. Several studies have shown that intensive antiblastic chemotherapy (AC) is feasible in HIV-infected patients with cancer, and that the outcome is similar to that of HIV-negative patients receiving the same AC regimens. However, the concomitant use of HAART and AC can result in drug accumulation or possible toxicity with consequent decreased efficacy of one or both classes of drugs. In fact, many AC agents are preferentially metabolized by CYP450 and drug-drug interactions (DDIs) with HAART are common. Therefore, it is important that HIV patients with cancer in HAART receiving AC treatment at the same time receive an individualized cancer management plan based on their liver and renal functions, their level of bone marrow suppression, their mitochondrial dysfunction, and their genotype profile. The rationale of this review is to summarize the existing data on the impact of HAART on the clinical management of cancer patients with HIV/AIDS and DDIs between antiretrovirals and AC. In addition, in order to maximize the efficacy of antiblastic therapy and minimize the risk of drug-drug interaction, a useful list of pharmacogenomic markers is provided.

A pharmacist’s role in the individualization of treatment of HIV patients

The pharmacological treatment of HIV is complex and varies considerably among patients, as does the response of patients to therapy, requiring treatment plans that are closely tailored to individual needs. Pharmacists can take an active role in individualizing care by employing their knowledge of pharmacokinetics and pharmacogenetics and by interacting directly with patients in counseling sessions. These strategies promote the following: maintenance of plasma concentrations of antiretroviral agents within therapeutic ranges, prediction of pharmacological response of patients with certain genetic characteristics, and clinical control of HIV through the correct use of antiretroviral treatments. Together, these strategies can be used to tailor antiretroviral therapy to individual patients, thus improving treatment efficacy and safety.

Maraviroc: a review of its use in HIV infection and beyond

The human immunodeficiency virus-1 (HIV-1) enters target cells by binding its envelope glycoprotein gp120 to the CD4 receptor and/or coreceptors such as C-C chemokine receptor type 5 (CCR5; R5) and C-X-C chemokine receptor type 4 (CXCR4; X4), and R5-tropic viruses predominate during the early stages of infection. CCR5 antagonists bind to CCR5 to prevent viral entry. Maraviroc (MVC) is the only CCR5 antagonist currently approved by the United States Food and Drug Administration, the European Commission, Health Canada, and several other countries for the treatment of patients infected with R5-tropic HIV-1. MVC has been shown to be effective at inhibiting HIV-1 entry into cells and is well tolerated. With expanding MVC use by HIV-1-infected humans, different clinical outcomes post-approval have been observed with MVC monotherapy or combination therapy with other antiretroviral drugs, with MVC use in humans infected with dual-R5- and X4-tropic HIV-1, infected with different HIV-1 genotype or infected with HIV-2. This review discuss the role of CCR5 in HIV-1 infection, the development of the CCR5 antagonist MVC, its pharmacokinetics, pharmacodynamics, drug–drug interactions, and the implications of these interactions on treatment outcomes, including viral mutations and drug resistance, and the mechanisms associated with the development of resistance to MVC. This review also discusses available studies investigating the use of MVC in the treatment of other diseases such as cancer, graft-versus-host disease, and inflammatory diseases.

Perspectives on pharmacogenomics of antiretroviral medications and HIV-associated comorbidities

PURPOSE OF REVIEW

To summarize current knowledge and provide perspective on relationships between human genetic variants, antiretroviral medications, and aging-related complications of HIV-1 infection.

RECENT FINDINGS

Human genetic variants have been convincingly associated with interindividual variability in antiretroviral toxicities, drug disposition, and aging-associated complications in HIV-1 infection. Screening for HLA-B5701 to avoid abacavir hypersensitivity reactions has become a routine part of clinical care, and has markedly improved drug safety. There are well established pharmacogenetic associations with other agents (efavirenz, nevirapine, atazanavir, dolutegravir, and others), but this knowledge has yet to have substantial impact on HIV-1 clinical care. As metabolic complications including diabetes mellitus, dyslipidemia, osteoporosis, and cardiovascular disease are becoming an increasing concern among individuals who are aging with well controlled HIV-1 infection, human genetic variants that predispose to these complications also become more relevant in this population.

SUMMARY

Pharmacogenetic knowledge has already had considerable impact on antiretroviral prescribing. With continued advances in the field of human genomics, the impact of pharmacogenomics on HIV-1 clinical care and research is likely to continue to grow in importance and scope.

CYP3A4 polymorphism and lopinavir toxicity in an HIV-infected pregnant woman

Cytochrome P450 (CYP) 3A4 has been considered to be the most important enzyme system for metabolism of lopinavir/ritonavir (LPV/r), a widely used HIV protease inhibitor (PI) recommended during pregnancy. Herein we present a clinical case of a pregnant HIV-infected woman who was taking standard doses of LPV/r, 400/100 mg twice daily. The trough plasma concentrations for LPV were fourfold above that recommended for PI-pretreated patients and toxicity associated with LPV/r and PI regimens was observed. These high concentrations continued after delivery in spite of a dosage reduction. The pharmacogenetic analysis revealed a genetic polymorphism in the CYP3A4 gene that encodes a non-functional protein. The pharmacokinetic study could indicate the occurrence of a phenomenon of non-linear pharmacokinetics which would justify why dosage reduction after pregnancy did not proportionally affect the patient's degree of exposure to the drug. In addition, an increment in CYP3A activity during pregnancy could explain lower LPV/r exposure during this period compared to postpartum, despite the impaired activity of CYP3A4 caused by the polymorphism.

Pharmacogenomics of antimicrobial agents

Antimicrobial efficacy and toxicity varies between individuals owing to multiple factors. Genetic variants that affect drug-metabolizing enzymes may influence antimicrobial pharmacokinetics and pharmacodynamics, thereby determining efficacy and/or toxicity. In addition, many severe immune-mediated reactions have been associated with HLA class I and class II genes. In the last two decades, understanding of pharmacogenomic factors that influence antimicrobial efficacy and toxicity has rapidly evolved, leading to translational success such as the routine use of HLA-B*57:01 screening to prevent abacavir hypersensitivity reactions. This article examines recent advances in the field of antimicrobial pharmacogenomics that potentially affect treatment efficacy and toxicity, and challenges that exist between pharmacogenomic discovery and translation into clinical use.

Class-specific relative genetic contribution for key antiretroviral drugs

OBJECTIVES

Antiretroviral pharmacokinetics is defined by numerous factors affecting absorption, distribution, metabolism and elimination. Biological processes underpinning drug distribution are only partially characterized and multiple genetic factors generate cumulative or antagonistic interactions, which complicates the implementation of pharmacogenetic markers. The aim of this study was to assess the degree to which heredity influences pharmacokinetics through the quantification of the relative genetic contribution (rGC) for key antiretrovirals.

METHODS

A total of 407 patients receiving lopinavir/ritonavir, atazanavir/ritonavir, atazanavir, efavirenz, nevirapine, etravirine, maraviroc, tenofovir or raltegravir were included. Intra-patient variability (SDw) and inter-patient (SDb) variability were measured in patients with plasma concentrations available from more than two visits. The rGC was calculated using the following equation: 1 - (1 / F) where F = SDb(2) / SDw(2).

RESULTS

Mean (95% CI) rGC was calculated to be 0.81 (0.72-0.88) for efavirenz, 0.74 (0.61-0.84) for nevirapine, 0.67 (0.49-0.78) for etravirine, 0.65 (0.41-0.79) for tenofovir, 0.59 (0.38-0.74) for atazanavir, 0.47 (0.27-0.60) for atazanavir/ritonavir, 0.36 (0.01-0.48) for maraviroc, 0.15 (0.01-0.44) for lopinavir/ritonavir and 0 (0-0.33) for raltegravir.

CONCLUSIONS

The rank order for genetic contribution to variability in plasma concentrations for the study drugs was efavirenz > nevirapine > etravirine > tenofovir > atazanavir > atazanavir/ritonavir > maraviroc > lopinavir/ritonavir > raltegravir, indicating that class-specific differences exist. The rGC strategy represents a useful tool to rationalize future investigations as drugs with higher rGC scores may represent better candidates for pharmacogenetic-pharmacokinetic studies.

Intestinal and hepatic drug transporters: pharmacokinetic, pathophysiological, and pharmacogenetic roles

The efficacy and safety of pharmacotherapies are determined by the complex processes involved in the interactions between drugs with the human body, including pharmacokinetic aspects. Among pharmacokinetic factors, it has been recognized that drug transporters play critical roles for absorption, distribution and excretion of drugs, regulating the membrane transport of drugs. The vast amounts of information on drug transporters collected in the past 20 years have been organized according to biochemical, molecular, genetic, and clinical analyses. Novel technologies, public databases, and regulatory guidelines have advanced the use of such information in drug development and clinical practice. In this review, we selected some clinically important drug transporters expressed in the intestine and liver, and introduced the research history and current knowledge of their pharmacokinetic, pathophysiological, and pharmacogenetic implications.

Genomewide association study of atazanavir pharmacokinetics and hyperbilirubinemia in AIDS Clinical Trials Group protocol A5202

BACKGROUND

Atazanavir-associated hyperbilirubinemia can cause premature discontinuation of atazanavir and avoidance of its initial prescription. We used genomewide genotyping and clinical data to characterize determinants of atazanavir pharmacokinetics and hyperbilirubinemia in AIDS Clinical Trials Group protocol A5202.

METHODS

Plasma atazanavir pharmacokinetics and indirect bilirubin concentrations were characterized in HIV-1-infected patients randomized to atazanavir/ritonavir-containing regimens. A subset had genomewide genotype data available.

RESULTS

Genomewide assay data were available from 542 participants, of whom 475 also had data on estimated atazanavir clearance and relevant covariates available. Peak bilirubin concentration and relevant covariates were available for 443 participants. By multivariate analysis, higher peak on-treatment bilirubin levels were found to be associated with the UGT1A1 rs887829 T allele (P=6.4×10(-12)), higher baseline hemoglobin levels (P=4.9×10(-13)), higher baseline bilirubin levels (P=6.7×10(-12)), and slower plasma atazanavir clearance (P=8.6×10(-11)). For peak bilirubin levels greater than 3.0 mg/dl, the positive predictive value of a baseline bilirubin level of 0.5 mg/dl or higher with hemoglobin concentrations of 14 g/dl or higher was 0.51, which increased to 0.85 with rs887829 TT homozygosity. For peak bilirubin levels of 3.0 mg/dl or lower, the positive predictive value of a baseline bilirubin level less than 0.5 mg/dl with a hemoglobin concentration less than 14 g/dl was 0.91, which increased to 0.96 with rs887829 CC homozygosity. No polymorphism predicted atazanavir pharmacokinetics at genomewide significance.

CONCLUSION

Atazanavir-associated hyperbilirubinemia is best predicted by considering UGT1A1 genotype, baseline bilirubin level, and baseline hemoglobin level in combination. Use of ritonavir as a pharmacokinetic enhancer may have abrogated genetic associations with atazanavir pharmacokinetics.

Potential role of organic anion transporting polypeptide 1B1 (OATP1B1) in the selective hepatic uptake of hematoporphyrin monomethyl ether isomers

AIM

Hematoporphyrin monomethyl ether (HMME), which consists of equal amounts of isomers HMME-1 and HMME-2, is a novel porphyrin-related drug for photodynamic therapy. This study was aimed to investigate the uptake transporter-mediated selective uptake of HMME into the liver and to identify the major uptake transporter isoforms involved.

METHODS

Adult SD rats were intravenously injected with a single dose of HMME (5 mg/kg) with or without rifampicin (an inhibitor of organic anion transporting polypeptides OATP1B1 and OATP1B3, 25 mg/kg). Blood samples were collected, and HMME concentrations were measured using LC-MS/MS. Rat hepatocytes, human hepatocytes and HEK293 cells expressing OATP1B1, OATP1B3, or OATP2B1 were used to investigate the uptake of HMME or individual isomers in vitro.

RESULTS

Co-administration of rifampicin significantly increased the exposure of HMME isomers, and decreased the AUC ratio of HMME-1 to HMME-2 from 1.98 to 1.56. The uptake of HMME-2 into human hepatocytes and the HEK293 cells expressing OATP1B1 or OATP2B1 in vitro was 2-7 times greater than that of HMME-1, whereas OATP1B3 mediated a higher HMME-1 uptake. OATP1B1 exhibited a higher affinity for HMME-2 than for HMME-1 (the Km values were 0.63 and 5.61 μmol/L, respectively), which were similar to those in human hepatocytes. By using telmisartan (a non-specific OATP inhibitor) and rifampicin, OATP2B1 was demonstrated to account for <20% of hepatic HMME uptake.

CONCLUSION

OATP1B1 is the major transporter involved in the rapid hepatic uptake of HMME, and the greater uptake of HMME-2 by OATP1B1 may lead to a lower exposure of HMME-2 than HMME-1 in humans.

Intracellular accumulation of atazanavir/ritonavir according to plasma concentrations and OATP1B1, ABCB1 and PXR genetic polymorphisms

OBJECTIVES

The rate of accumulation of atazanavir and ritonavir within cells is still debated due to methodological limitations. Our aim was to measure peripheral blood mononuclear cell (PBMC) concentrations of atazanavir and ritonavir and investigate whether single-nucleotide polymorphisms of OATP, ABCB1, CYP3A4 and PXR genes are involved in intracellular drug penetration.

METHODS

HIV-positive patients administered 300 mg of atazanavir/100 mg of ritonavir were enrolled. Blood sampling was performed at the end of the dosing interval (Ctrough). PBMC-associated and plasma atazanavir and ritonavir concentrations were measured by validated HPLC coupled with a single mass detector (HPLC-MS) and HPLC-photodiode array (PDA) methods, respectively. Cell count and mean cellular volume were determined using a Coulter counter. Genotyping was conducted using real-time PCR.

RESULTS

Thirty-five patients were enrolled. Median atazanavir and ritonavir intracellular concentrations were 1844 and 716 ng/mL, respectively. Median plasma concentrations were 645 ng/mL for atazanavir and 75 ng/mL for ritonavir, while median intracellular/plasma concentration ratios were 2.4 and 9.2, respectively. Median ritonavir intracellular concentrations were higher for OATP1B1 521 T→C TC or CC carriers and for PXR 44477 A→G AG or GG carriers. Atazanavir intracellular/plasma concentration ratios were higher in patients GG for the ABCB1 2677 G→T single-nucleotide polymorphism (SNP) compared with GT and TT groups.

CONCLUSIONS

Our study showed a higher intracellular ritonavir accumulation than previously reported. Ritonavir intracellular concentrations were associated with OATP1B1 521 and PXR 44477 SNPs while intracellular atazanavir exposure was associated with the ABCB1 2677 SNP. Further clinical studies are necessary in order to confirm these data.

Phase I safety, pharmacokinetics, and pharmacogenetics study of the antituberculosis drug PA-824 with concomitant lopinavir-ritonavir, efavirenz, or rifampin

There is an urgent need for new antituberculosis (anti-TB) drugs, including agents that are safe and effective with concomitant antiretrovirals (ARV) and first-line TB drugs. PA-824 is a novel antituberculosis nitroimidazole in late-phase clinical development. Cytochrome P450 (CYP) 3A, which can be induced or inhibited by ARV and antituberculosis drugs, is a minor (∼20%) metabolic pathway for PA-824. In a phase I clinical trial, we characterized interactions between PA-824 and efavirenz (arm 1), lopinavir/ritonavir (arm 2), and rifampin (arm 3) in healthy, HIV-uninfected volunteers without TB disease. Participants in arms 1 and 2 were randomized to receive drugs via sequence 1 (PA-824 alone, washout, ARV, and ARV plus PA-824) or sequence 2 (ARV, ARV with PA-824, washout, and PA-824 alone). In arm 3, participants received PA-824 and then rifampin and then both. Pharmacokinetic sampling occurred at the end of each dosing period. Fifty-two individuals participated. Compared to PA-824 alone, plasma PA-824 values (based on geometric mean ratios) for maximum concentration (Cmax), area under the concentration-time curve from 0 to 24 h (AUC0-24), and trough concentration (Cmin) were reduced 28%, 35%, and 46% with efavirenz, 13%, 17%, and 21% with lopinavir-ritonavir (lopinavir/r) and 53%, 66%, and 85% with rifampin, respectively. Medications were well tolerated. In conclusion, lopinavir/r had minimal effect on PA-824 exposures, supporting PA-824 use with lopinavir/r without dose adjustment. PA-824 exposures, though, were reduced more than expected when given with efavirenz or rifampin. The clinical implications of these reductions will depend upon data from current clinical trials defining PA-824 concentration-effect relationships. (This study has been registered at ClinicalTrials.gov under registration no. NCT01571414.).

Different interaction profiles of direct-acting anti-hepatitis C virus agents with human organic anion transporting polypeptides

Simeprevir (SMV), asunaprevir (ASV), daclatasvir (DCV), and sofosbuvir (SFV), which are newly developed direct-acting antiviral agents (DAAs) against hepatitis C virus (HCV) infection, are among the key components of anti-HCV regimens. Preclinical studies have identified inhibitory properties for some of these DAAs against organic anion transporting polypeptide 1B (OATP1B) functions. However, their details remain mostly uncharacterized. Because OATP1B1 and OATP1B3 play determinant roles in the pharmacokinetics of various drugs via their uptake into human hepatocytes, it is plausible that the inhibition of these OATP1Bs by a DAA would create a potential risk of drug-drug interaction, which has been an emerging concern in anti-HCV therapy. Accordingly, in the present study, we intended to clarify the inhibitory characteristics of newly developed DAAs toward OATP1B1 and -1B3 functions. The results of our coincubation inhibition assays have shown that all tested DAAs could inhibit OATP1B1 functions and that SMV, ASV, and DCV (to a lesser extent), but not SFV, exhibited long-lasting preincubation inhibitory effects on OATP1B1 functions. It was also found that the preincubation inhibitory effects of SMV and ASV could augment their coincubation inhibition potency. Furthermore, significant, but differential, inhibitory effects of the DAAs on the OATP1B3 function were identified. To summarize, our results clearly show that the newly developed DAAs are newly identified OATP1B1 and OATP1B3 inhibitors with distinctive interaction properties. It is believed that these inhibition profiles will provide essential information to all concerned parties with respect to the clinical significance of DAA-mediated inhibition of OATP1Bs in anti-HCV therapy.

Discordant associations between SLCO1B1 521T→C and plasma levels of ritonavir-boosted protease inhibitors in AIDS clinical trials group study A5146

OBJECTIVE

Among HIV-positive patients prescribed ritonavir-boosted lopinavir, SLCO1B1 521T→C (rs4149056) is associated with increased plasma lopinavir exposure. Protease inhibitors (PIs) are also substrates for cytochrome P450 (CYP) 3A and ABCB1, which are induced by NR1I2. We characterized relationships between ABCB1, CYP3A4, CYP3A5, NR1I2, and SLCO1B1 polymorphisms and trough PI concentrations among AIDS Clinical Trials Group study A5146 participants.

METHODS

At study entry, subjects with virologic failure on PI-containing regimens initiated new ritonavir-boosted PI regimens. We studied associations between week 2 PI plasma trough concentrations and 143 polymorphisms in these genes, including 4 targeted polymorphisms.

RESULTS

Among 275 subjects with both drug concentrations and genetic data, allelic frequencies of SLCO1B1 521T→C were 15%, 1%, and 8% in whites, blacks, and Hispanics, respectively. Further analyses were limited to 268 white, black, or Hispanic subjects who initiated ritonavir-boosted lopinavir (n = 98), fosamprenavir (n = 69), or saquinavir (n = 99). Of targeted polymorphisms, SLCO1B1 521T→C tended to be associated with higher lopinavir concentrations, with a 1.38-fold increase in the mean per C allele (95% confidence interval, 0.97-1.96; n = 98; P = 0.07). With fosamprenavir, SLCO1B1 521T→C was associated with lower amprenavir concentrations, with a 35% decrease in the mean per C allele (geometric mean ratio 0.65; 95% confidence interval, 0.44-0.94; n = 69; adjusted P = 0.02). There was no significant association with saquinavir concentrations, and none of the remaining 139 exploratory polymorphisms were statistically significant after correcting for multiple comparisons.

CONCLUSIONS

With ritonavir-boosted PIs, a SLCO1B1 polymorphism that predicts higher lopinavir trough concentrations seems to predict lower amprenavir trough concentrations. The mechanism underlying this discordant association is uncertain.

A population pharmacokinetic-pharmacogenetic analysis of atazanavir

Atazanavir is a first-line HIV protease inhibitor commonly co-dosed with ritonavir. Ritonavir inhibits atazanavir metabolism, decreasing variability and increasing plasma concentrations. However, ritonavir use results in higher costs and increased drug-related adverse events. Elucidating atazanavir pharmacokinetics might allow for individualized ritonavir boosting. We previously demonstrated that genetically determined CYP3A5 nonexpression was associated with slower atazanavir clearance CL/F and higher trough concentrations. This effect was prominent in non-African-American men but absent in African-Americans. The present study considers additional genetic predictors of atazanavir CL/F with a focus on race differences. Nine polymorphisms in CYP3A4, ABCG2, NR1I2 (PXR), and SLCO1B1 were evaluated; 330 plasma samples from 30 HIV-negative volunteers, balanced by sex, race, and CYP3A5 expressor status, were available. Analyses were performed using nonlinear mixed-effects modeling (NONMEM). The following factors were univariately associated with atazanavir CL/F (% effect) : African-American race (decreased 35%), female sex (decreased 25%), older age (decreased 1.7%/year), CYP3A5 nonexpressors (decreased 26%), ABCB1 CGC haplotype carriers (1236C/2677G/3435C) (decreased 33%), and CYP3A4*1B carriers (decreased 31%). However, an independent genetic explanation for the differential race effect could not be identified. An interaction was observed with PXR 63396 C>T and CYP3A5 expressor status (p=0.0002). CYP3A5 nonexpressors with a PXR 63396 CC genotype had 37% slower CL/F versus those with CT or TT genotypes. For CYP3A5 expressors, those with a PXR 63396 CC genotype had 63% faster CL/F versus those with CT or TT genotypes. Although this study has as its main limitation a small overall sample size, these results nonetheless provide new leads and impetus to evaluate ways to individualize the need for ritonavir boosting using demographic and genetic predictors of atazanavir pharmacokinetics.

UGT1A1, SLCO1B1, and SLCO1B3 polymorphisms vs. neonatal hyperbilirubinemia: is there an association?

BACKGROUND

Jaundice is a physiological phenomenon; however, severe hyperbilirubinemia occurs in only 5 to 6% of the healthy newborn population. It has been suggested that genetic variation could enhance the risk of hyperbilirubinemia when coexpressed with other icterogenic conditions.

METHODS

The study included newborns with a gestational age of greater than 35 wk and weights greater than 2,000 g with indications for phototherapy. The polymorphisms from UGT1A1 (rs8175347), SLCO1B1 (rs4149056 and rs2306283), and SLCO1B3 (rs17680137 and rs2117032) were analyzed by capillary electrophoresis and hydrolysis probes.

RESULTS

A total of 167 hyperbilirubinemic infants and 247 control subjects were enrolled. The gender, ABO incompatibility, birth weight, and gestational age differed between the groups, but the allelic and genotypic frequency of the polymorphisms from SLCO1B genes did not. In logistic regression, the ABO incompatibility, gestational age, and polymorphic T allele of rs2117032 remained in the model. The presence of this polymorphism seemed to provide protection from hyperbilirubinemia. The individuals who were homozygous for the G allele of rs2306283 and who were glucose 6-phosphate-dehydrogenase deficient were more frequent among the cases.

CONCLUSION

Although genetic variation accounts for a good part of this condition, the association between different polymorphisms and environmental factors has yet to be explained.

Organic anion transporting polypeptides OATP1B1 and OATP1B3 and their genetic variants influence the pharmacokinetics and pharmacodynamics of raloxifene

Background

Raloxifene, a selective estrogen receptor modulator, exhibits quite large and unexplained interindividual variability in pharmacokinetics and pharmacodynamics. The aim of this study was to determine the role of organic-anion transporting polypeptides OATP1B1 and OATP1B3 and their genetic variants in the pharmacokinetics and pharmacodynamics of raloxifene.

Methods

To test the role of OATP1B1 and OATP1B3 transporters on hepatic uptake of raloxifene and its metabolites an in vitro model of Chinese Hamster Ovary cells expressing OATP1B1 or OATP1B3 was employed. The influence of OATP1B1 and OATP1B3 genetic variants on in vivo pharmacokinetics and pharmacodynamics was evaluated in 53 osteoporotic postmenopausal women treated with raloxifene.

Results

Our in vitro results showed that raloxifene and two of the three metabolites, raloxifene-4'-β-glucuronide (M2) and raloxifene-6,4'-diglucuronide (M3), interact with OATP1B1 and OATP1B3. Higher M3 and total raloxifene serum concentrations in patients correlated with lower serum levels of bone resorption marker, serum C-terminal telopeptide fragments of type I collagen, indicating a higher antiresorptive effect of raloxifene. Higher concentrations of M2 correlated with higher increase of lumbar spine bone mineral density supporting the raloxifene vertebral fracture specific protection effect. Finally, raloxifene, M3 and total raloxifene serum concentrations were significantly higher in patients with SLCO1B1 c.388A > G polymorphism and *1b haplotype implicating a considerable genetic effect on pharmacokinetics and pharmacodynamics of raloxifene.

Conclusions

These findings indicate that SLCO1B1 c.388A > G polymorphism could play an important role in pharmacokinetics and pharmacodynamics of raloxifene.

Estimation of the effect of SLCO1B1 polymorphisms on lopinavir plasma concentration in HIV-infected adults

BACKGROUND

The organic anion transporting polypeptides (OATP)/SLCO family represents an important class of hepatic drug uptake transporters that mediate the sodium independent transport of a diverse range of amphipathic organic compounds, including the protease inhibitors. The SLCO1B1 521T>C (rs4149056) single nucleotide polymorphism (SNP) has been consistently associated with reduced transport activity in vivo, and we previously showed an association of this polymorphism with lopinavir plasma concentrations. The aim of this study was to develop a population pharmacokinetic (PK) model to quantify the impact of 521T>C.

METHODS

A population PK analysis was performed with 594 plasma samples from 375 patients receiving lopinavir/ritonavir. Non-linear mixed effects modelling was applied to explore the effects of SLCO1B1 521T>C and patient demographics. Simulations of the lopinavir concentration profile were performed with different dosing regimens considering the different alleles.

RESULTS

A one-compartment model with first-order absorption best described the data. Population clearance was 5.67 l/h with inter-patient variability of 37%. Body weight was the only demographic factor influencing clearance, which increased 0.5 l/h for every 10 kg increase. Homozygosity for the C allele was associated with a 37% lower clearance, and 14% for heterozygosity, which were statistically significant.

CONCLUSIONS

These data show an association between SLCO1B1 521T>C and lopinavir clearance. The association is likely to be mediated through reduced uptake by hepatocytes leading to higher plasma concentrations of lopinavir. Further studies are now required to confirm the association and to assess the influence of other polymorphisms in the SLCO family on lopinavir PK.

[New strategies in the optimisation of lopinavir/ritonavir doses in human immunodeficiency virus-infected patients]

Lopinavir/ritonavir (LPV/r) has demonstrated virological and immunological efficacy in the combined antiretroviral treatment (cART), in both naïve and experienced patients. Furthermore, LPV/r showed a high barrier to the development of resistance. Although generally well tolerated, adverse gastrointestinal side effects and metabolic disorders are frequent. The different tools used to optimise the cART with this drug combination in the daily clinical practice, emphasising the therapeutic drug monitoring (TDM) of LPV/r and the genetic analysis of the main enzymes responsible for the metabolism and transport, are reviewed. The relationship between phenotype and genotype, established through TDM, could be useful for the physician to improve the clinical management of the HIV infection, due to the possibility of individualising the dose with this drug. Monotherapy is also reviewed as a new strategy used in the simplification of the treatment with this drug, which could increase safety and reduce costs.

CYP3A5, ABCB1, and SLCO1B1 polymorphisms and pharmacokinetics and virologic outcome of lopinavir/ritonavir in HIV-infected children

OBJECTIVE

CYP3A5, MDR1 (ABCB1), and OATP1 (SLCO1B1) polymorphisms have been associated with variability in the pharmacokinetics (PK) of protease inhibitors. The aim of this study was to investigate the influence of CYP3A5 A6986G, ABCB1 (C3435T and G2677T), and SLCO1B1 (T521C and A388AG) polymorphisms on the PK and virologic outcome of lopinavir/ritonavir (LPV/RTV) in HIV-infected children.

DESIGN AND METHODS

We conducted a prospective cohort study in children (4-18 years old) on stable antiretroviral therapy with LPV/RTV. CYP3A5, ABCB1, and SLCO1B1 genotypes were determined using polymerase chain reaction amplification with allelic discrimination assays. The 12-hour plasma area under the concentration-time curves (AUC) and clearances (CL) of LPV and RTV were estimated using noncompartmental models. HIV RNA viral load was evaluated every 12 weeks for a total study period of 52 weeks. Analysis of covariance models with adjustment for age and adherence and allometric adjustment of CL were used to assess associations between studied polymorphisms and AUC, CL, and HIV RNA.

RESULTS

Fifty children (median age 11.2 years) were enrolled. Allele frequencies of the genotypes studied were in Hardy-Weinberg equilibrium. There was no statistically significant association between LPV or RTV AUC or CL, and CYP3A5, ABCB1, or SLCO1B1 A388G polymorphisms. There was a significant association between SLCO1B1 T521C genotype and increased LPV AUC (P = 0.042) and a nearly significant association with decreased LPV CL (P = 0.063). None of the studied polymorphisms, including SLCO1B1 T521C, were associated with virologic outcome during 52 weeks of study follow-up.

CONCLUSIONS

There was no statistically significant influence of the CYP3A5, ABCB1, or SLCO1B1 A388AG polymorphisms on the PK and virologic outcome of LPV/RTV in HIV-infected children. SLCO1B1 T521C polymorphism was significantly associated with an increase in LPV AUC but was not associated with undetectable HIV RNA during the study period.