Drug uptake transporters in antiretroviral therapy

Emerging drugs for the treatment of herpetic keratitis

INTRODUCTION

Herpes simplex keratitis stands as a prominent factor contributing to infectious blindness among developed nations. On a global scale, over 60% of the population tests positive for herpes simplex virus type-1 (HSV-1). Despite these statistics, there is currently no vaccine available for the virus. Moreover, the conventional nucleoside drugs prescribed to patients are proving ineffective in addressing issues related to drug resistance, recurrence, latency, and the escalating risk of vision loss. Hence, it is imperative to continually explore all potential avenues to restrict the virus. This review article centers on the present treatment methods for HSV-1 keratitis (HSK), highlighting the ongoing clinical trials. It delves into the emerging drugs, their mode-of-action and future therapeutics.

AREAS COVERED

The review focuses on the significance of a variety of small molecules targeting HSV-1 lifecycle at multiple steps. Peer-reviewed articles and abstracts were searched in MEDLINE, PubMed, Embase, and clinical trial websites.

EXPERT OPINION

The exploration of small molecules that target specific pathways within the herpes lifecycle holds the potential for substantial impact on the antiviral pharmaceutical market. Simultaneously, the pursuit of disease-specific biomarkers has the capacity to usher in a transformative era in diagnostics within the field.

The synergy between nucleotide biosynthesis inhibitors and antiviral nucleosides: New opportunities against viral infections?

5'-Phosphorylated nucleoside derivatives are molecules that can be found in all living organisms and viruses. Over the last century, the development of structural analogs that could disrupt the transcription and translation of genetic information culminated in the development of clinically relevant anticancer and antiviral drugs. However, clinically effective broad-spectrum antiviral compounds or treatments are lacking. This viewpoint proposes that molecules that inhibit nucleotide biosynthesis may sensitize virus-infected cells toward direct-acting antiviral nucleosides. Such potentially synergistic combinations might allow the repurposing of drugs, leading to the development of new combination therapies.

Nanocarrier Drug Delivery Systems: Characterization, Limitations, Future Perspectives and Implementation of Artificial Intelligence

There has been an increasing demand for the development of nanocarriers targeting multiple diseases with a broad range of properties. Due to their tiny size, giant surface area and feasible targetability, nanocarriers have optimized efficacy, decreased side effects and improved stability over conventional drug dosage forms. There are diverse types of nanocarriers that have been synthesized for drug delivery, including dendrimers, liposomes, solid lipid nanoparticles, polymersomes, polymer-drug conjugates, polymeric nanoparticles, peptide nanoparticles, micelles, nanoemulsions, nanospheres, nanocapsules, nanoshells, carbon nanotubes and gold nanoparticles, etc. Several characterization techniques have been proposed and used over the past few decades to control and predict the behavior of nanocarriers both in vitro and in vivo. In this review, we describe some fundamental in vitro, ex vivo, in situ and in vivo characterization methods for most nanocarriers, emphasizing their advantages and limitations, as well as the safety, regulatory and manufacturing aspects that hinder the transfer of nanocarriers from the laboratory to the clinic. Moreover, integration of artificial intelligence with nanotechnology, as well as the advantages and problems of artificial intelligence in the development and optimization of nanocarriers, are also discussed, along with future perspectives.

A Critical Review on Advancement in Analytical Strategies for the Quantification of Clinically Relevant Biological Transporters

Success of a drug discovery program is highly dependent on rapid scientific advancement and periodic inclusion of sensitive and specific analytical techniques. Biological membrane transporters can significantly alter the bioavailability of a molecule in its actual site of action. Expression of transporter proteins responsible for drug transport is extremely low in the biological system. Therefore, proper scientific planning in selection of their quantitative analytical technique is essential. This article discusses critical advancement in the analytical strategies for quantification of clinically relevant biological transporters for the drugs. Article cross-talked key planning and execution strategies concerning analytical quantification of the transporters during drug discovery programs.

Substrates and Inhibitors of Organic Cation Transporters (OCTs) and Plasma Membrane Monoamine Transporter (PMAT) and Therapeutic Implications

The gene products of the SLC22A gene family (hOCT1, hOCT2, and hOCT3) and of the SLC29A4 gene (hPMAT or hENT4) are all polyspecific organic cation transporters. Human OCTs (including hPMAT) are expressed in peripheral tissues such as small intestine, liver, and kidney involved in the pharmacokinetics of drugs. In the human brain, all four transporters are expressed at the blood-brain barrier (BBB), hOCT2 is additionally expressed in neurons, and hOCT3 and hPMAT in glia. More than 40% of the presently used drugs are organic cations. This chapter lists and discusses all known drugs acting as substrates or inhibitors of these four organic cation transporters, independently of whether the transporter is expressed in the central nervous system (CNS) or in peripheral tissues. Of interest is their involvement in drug absorption, distribution, and excretion as well as potential OCT-associated drug-drug interactions (DDIs), with a focus on drugs that act in the CNS.

Antiretroviral Penetration and Drug Transporter Concentrations in the Spleens of Three Preclinical Animal Models and Humans

Adequate antiretroviral (ARV) concentrations in lymphoid tissues are critical for optimal antiretroviral therapy (ART). While the spleen contains 25% of the body's lymphocytes, there are minimal data on ARV penetration in this organ. This study quantified total and protein-unbound splenic ARV concentrations and determined whether drug transporters, sex, or infection status were modifiers of these concentrations in animal models and humans. Two humanized mice models (hu-HSC-Rag [n = 36; 18 HIV-positive (HIV⁺) and 18 HIV-negative (HIV^-)] and bone marrow-liver-thymus [n = 13; 7 HIV⁺ and 6 HIV^-]) and one nonhuman primate (NHP) model (rhesus macaque [n = 18; 10 SHIV⁺ and 8 SHIV^-]) were dosed to steady state with ARV combinations. HIV⁺ human spleens (n = 14) from the National NeuroAIDS Tissue Consortium were analyzed postmortem (up to 24 h postdose). ARV concentrations were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS), drug transporter concentrations were measured with LC-MS proteomics, and protein binding in NHP spleens was determined by rapid equilibrium dialysis. Mice generally had the lowest splenic concentrations of the three species. Protein binding in splenic tissue was 6 to 96%, compared to 76 to 99% in blood plasma. NHPs had quantifiable Mrp4, Bcrp, and Ent1 concentrations, and humans had quantifiable ENT1 concentrations. None significantly correlated with tissue ARV concentrations. There was also no observable influence of infection status or sex. With these dosing strategies, NHP splenic penetration most closely resembled that of humans. These data can inform tissue pharmacokinetic scaling to humans to target HIV reservoirs by identifying important species-related differences.

Understanding Membrane Protein Drug Targets in Computational Perspective

Membrane proteins play crucial physiological roles in vivo and are the major category of drug targets for pharmaceuticals. The research on membrane protein is a significant part in the drug discovery. The biological process is a cycled network, and the membrane protein is a vital hub in the network since most drugs achieve the therapeutic effect via interacting with the membrane protein. In this review, typical membrane protein targets are described, including GPCRs, transporters and ion channels. Also, we conclude network servers and databases that are referring to the drug, drug-target information and their relevant data. Furthermore, we chiefly introduce the development and practice of modern medicines, particularly demonstrating a series of state-of-the-art computational models for the prediction of drug-target interaction containing network-based approach and machine-learningbased approach as well as showing current achievements. Finally, we discuss the prospective orientation of drug repurposing and drug discovery as well as propose some improved framework in bioactivity data, created or improved predicted approaches, alternative understanding approaches of drugs bioactivity and their biological processes.

Dietary supplement with nucleotides in the form of uridine monophosphate or uridine stimulate intestinal development and promote nucleotide transport in weaned piglets

BACKGROUND

Nucleotides are key constituents of milk, where they are utilized in cell replication, although there are limited studies for weaned piglets. This study evaluated the effects of uridine monophosphate (UMP) with uridine (UR) feed supplementation on the intestinal development and nucleotide transport in weaned piglets.

RESULTS

Supplementation with UMP significantly increased (P < 0.05) plasma glucose, and UR supplementation significantly reduced (0.05 < P < 0.10) the plasma total cholesterol (TC) of piglets when compared with that of the control group, although non-significant difference (P > 0.05) in growth performance was observed among three groups. Piglets fed supplementary UR exhibited greater (P < 0.05) crypt depth in the duodenum and ileum when compared with those in the supplementary UMP and control groups. Real-time quantitative polymerase chain reaction (RT-qPCR) results revealed that UR supplementation increased (P < 0.05) the relative mRNA levels of genes encoding the transmembrane proteins ZO-1 and occludin in the duodenum mucosa, and ZO-1 in the jejunum mucosa (P < 0.05). Similarly, UR supplementation increased (P < 0.05) expression of solute carriers SLC28A1 and SLC29A1 in the duodenum mucosa. Conversely, claudin-1 expression in the duodenum mucosa was inhibited (P < 0.05) by dietary supplementation with UMP or UR.

CONCLUSION

Collectively, our data indicated that dietary supplementation with UMP or UR was conducive to stimulating intestinal development and promoting nucleotide transport in weaned piglets. © 2019 Society of Chemical Industry.

Drug-drug interactions when treating HIV-related metabolic disorders

Introduction: Drug-drug interactions (DDI) between antiretroviral drugs and drugs for the treatment of metabolic disturbances in people living with human immunodeficiency virus (HIV) (PLWH) have represented a problem of paramount importance in the recent times. The problem has been mainly driven by sharing common metabolizing pathways. This problem has classically been worsened by the frequent use of pharmacokinetic boosters to enhance protease inhibitors and some integrase inhibitors plasma levels. Areas covered: This article focuses on the interactions between antiretroviral drugs and those drugs used to treat metabolic disturbances which frequently appear in PLWH. These include dyslipidemia, diabetes mellitus, hyperuricemia, and finally, drugs for the treatment of overweight and clinical obesity. References from PubMed, Embase, or Web of Science, among others, were reviewed. Expert opinion: The advent of safer drugs, in terms of DDI, in the antiretroviral and the metabolic field,such as non-boosted antiretrovirals and drugs with divergent metabolizing paths. Besides, learning by the caregivers on how to decrease and manage DDI, together with the extensive use of online updated DDI databases, has undoubtedly minimized the problem. The foreseeable increase in the burden of HIV-associated comorbidities and their associated treatments anticipates further complexities in the management of DDI in PLWH.

Antiretroviral Drug Concentrations in Lymph Nodes: A Cross-Species Comparison of the Effect of Drug Transporter Expression, Viral Infection, and Sex in Humanized Mice, Nonhuman Primates, and Humans

In a "kick and kill" strategy for human immunodeficiency virus (HIV) eradication, protective concentrations of antiretrovirals (ARVs) in the lymph node are important to prevent vulnerable cells from further HIV infection. However, the factors responsible for drug distribution and concentration into these tissues are largely unknown. Although humanized mice and nonhuman primates (NHPs) are crucial to HIV research, ARV tissue pharmacology has not been well characterized across species. This study investigated the influence of drug transporter expression, viral infection, and sex on ARV penetration within lymph nodes of animal models and humans. Six ARVs were dosed for 10 days in humanized mice and NHPs. Plasma and lymph nodes were collected at necropsy, 24 hours after the last dose. Human lymph node tissue and plasma from deceased patients were collected from tissue banks. ARV, active metabolite, and endogenous nucleotide concentrations were measured by liquid chromatography-tandem mass spectrometry, and drug transporter expression was measured using quantitative polymerase chain reaction and quantitative targeted absolute proteomics. In NHPs and humans, lymph node ARV concentrations were greater than or equal to plasma, and tenofovir diphosphate/deoxyadenosine triphosphate concentration ratios achieved efficacy targets in lymph nodes from all three species. There was no effect of infection or sex on ARV concentrations. Low drug transporter expression existed in lymph nodes from all species, and no predictive relationships were found between transporter gene/protein expression and ARV penetration. Overall, common preclinical models of HIV infection were well suited to predict human ARV exposure in lymph nodes, and low transporter expression suggests primarily passive drug distribution in these tissues. SIGNIFICANCE STATEMENT: During human immunodeficiency virus (HIV) eradication strategies, protective concentrations of antiretrovirals (ARVs) in the lymph node prevent vulnerable cells from further HIV infection. However, ARV tissue pharmacology has not been well characterized across preclinical species used for HIV eradication research, and the influence of drug transporters, HIV infection, and sex on ARV distribution and concentration into the lymph node is largely unknown. Here we show that two animal models of HIV infection (humanized mice and nonhuman primates) were well suited to predict human ARV exposure in lymph nodes. Additionally, we found that drug transporter expression was minimal and-along with viral infection and sex-did not affect ARV penetration into lymph nodes from any species.

Advancement in the development of heterocyclic nucleosides for the treatment of cancer - A review

Cancer diseases are widely recognised as an important medical problem and killing millions of people in a year. Chemotherapeutic drugs are successful against cancer in many cases and different compounds, including the analogues of natural substances, may be used for anticancer agents. Nucleoside analogues also have become a necessity for the treatment of cancer diseases. Nucleoside, nucleotide and base analogues have been utilised for decades for the treatment of viral pathogens, neoplasms and in anticancer chemotherapy. This review focuses on the different types of nucleosides and their potential role as anticancer agents. It also discusses the nucleoside analogues approved by FDA and in process of approval. The effect of the substitution on the nucleoside analogues and their pharmacological role is also discussed in the review. Owing to the advances in computational chemistry, it concludes with the future advancement and possible outcome of the nucleoside analogues. Also, it depicts the development of heterocyclic nucleoside analogues, explores the QSAR of the synthesised compounds and discusses the 3 D QSAR pharmacophore modelling in order to examine their potential anti-cancer activities.

Enhancement of saquinavir absorption and accumulation through the formation of solid drug nanoparticles

Background

Nanotechnology is now considered a promising drug delivery method for orally administered hydrophobic drugs to their sites of action. The effect of nanodispersion on cellular transport and accumulation of saquinavir (SQV) was investigated.

Methods

The transport of five solid drug nanoparticle (SDN) SQV formulations along Caco-2 cell monolayers (CCM) was compared to that of standard SQV. The SDNs were prepared using SQV mesylate (20%), Pluronic F127 (10%) plus five other excipients (HPMC, PVP, PVA, Lecithin S75 and Span 80) in different proportions. Cellular accumulation in CEM parental and CEMVBL (P-gp overexpressing) cells was conducted to ascertain the effect of nanodispersion on P-gp mediated efflux of SQV. All SDN formulations were dissolved in water, whereas SQV in DMSO to improve solubility. Quantification was via HPLC.

Results

From transport results, an SDN sample composed of SQV mesylate/Pluronic F127 plus HPMC (70%) and had a 24% increase in apparent absorption compared to standard SQV, largely driven by a 38% reduction in basolateral to apical permeation. Additionally, the formulation and two others (SQV mesylate/Pluronic F127 alone; and + HPMC (65%)/Lecithin [5%]) accumulated more significantly in CEM cells, suggesting enhanced delivery to these cells. Moreover, accumulation and transport of the three SDNs compared well to that of SQV despite being dissolved in water, suggestive of improved dissolution. The inclusion of PVA resulted in increased efflux.

Conclusion

The use of HPMC and Pluronic F127 produced SQV SDNs with improved permeation in Caco-2 cells and improved accumulation in CEM cells, but negative effects with PVA.

Pharmacogenetic variation influences sensory neuropathy occurrence in Southern Africans treated with stavudine-containing antiretroviral therapy

BACKGROUND

The use of the HIV antiretroviral drug stavudine (d4T), a thymidine analogue, is associated with the development of mitochondrial toxicities such as sensory neuropathy (SN). Genetic variation in genes relating to d4T transport and metabolism, as well as genetic variation in the thymidine synthesis pathway, could influence occurrence of d4T-related toxicity.

METHODS

We examined this hypothesis in a cohort of HIV-positive South African adults exposed to d4T, including 143 cases with SN and 120 controls without SN. Ten SNPs in four genes associated with stavudine transport, and 16 SNPs in seven genes of the thymidine synthesis / phosphorylation pathway were genotyped using Agena mass spectrometry methods. Associations between sensory neuropathy and genetic variants were evaluated using PLINK by univariate and multivariable analyses.

RESULTS

Age and height were significantly associated with SN occurrence. Using logistic regression with age and height as covariates, and uncorrected empirical p-values, genetic variation in SLC28A1, SAMHD1, MTHFR and RRM2B was associated with SN in South Africans using d4T.

CONCLUSION

Variation in genes relating to d4T transport and metabolism, as well as genetic variation in the thymidine synthesis pathway may influence occurrence of d4T-related SN. These data contribute to the characterisation of African pharmacogenetic variation and its role in adverse response to antiretroviral therapy.

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.

Who Is Who in Adenosine Transport

Extracellular adenosine concentrations are regulated by a panel of membrane transporters which, in most cases, mediate its uptake into cells. Adenosine transporters belong to two gene families encoding Equilibrative and Concentrative Nucleoside Transporter proteins (ENTs and CNTs, respectively). The lack of appropriate pharmacological tools targeting every transporter subtype has introduced some bias on the current knowledge of the role of these transporters in modulating adenosine levels. In this regard, ENT1, for which pharmacology is relatively well-developed, has often been identified as a major player in purinergic signaling. Nevertheless, other transporters such as CNT2 and CNT3 can also contribute to purinergic modulation based on their high affinity for adenosine and concentrative capacity. Moreover, both transporter proteins have also been shown to be under purinergic regulation via P1 receptors in different cell types, which further supports its relevance in purinergic signaling. Thus, several transporter proteins regulate extracellular adenosine levels. Moreover, CNT and ENT proteins are differentially expressed in tissues but also in particular cell types. Accordingly, transporter-mediated fine tuning of adenosine levels is cell and tissue specific. Future developments focusing on CNT pharmacology are needed to unveil transporter subtype-specific events.

Precision medicine for HIV: where are we?

To date, antiretroviral therapy is highly effective in HIV-affected patients, but the individualization of such a life-long therapy may be advised. This review briefly summarizes the main factors involved in the potential personalization of antiretroviral treatment. Relevant articles in English were identified by PubMed and recent congresses’ abstracts. Foremost influences concerning pharmacodynamics, therapeutic drug monitoring, pharmacogenetics, comorbidities, immune recovery and viral characteristics affecting the healthcare of HIV-positive patients are listed here. Furthermore, pharmacoeconomic aspects are mentioned. Applying pharmacokinetic and pharmacogenetic knowledge may be informative and guide the better choice of treatment in order to achieve long-term efficacy and avoid adverse events. Randomized investigations of the clinical relevance of tailored antiretroviral regimens are needed in order to obtain a better management of HIV/AIDS-affected patients.

Population Pharmacokinetic Model Linking Plasma and Peripheral Blood Mononuclear Cell Concentrations of Efavirenz and Its Metabolite, 8-Hydroxy-Efavirenz, in HIV Patients

The objectives of this study were to characterize the population pharmacokinetics (PK) of efavirenz (EFV) and 8-hydroxy-efavirenz (8OHEFV) in plasma and peripheral blood mononuclear cells (PBMCs) and to explore covariates affecting the PK parameters. Fifty-one patients had steady-state 0-to-24-h concentrations of EFV and 8OHEFV in plasma with corresponding concentrations in PBMCs, while 261 patients had one or two sparse concentrations at 16 ± 1 h postdose at weeks 4 and/or 16. The pharmacogenetic markers CYP2B6*6, CYP3A5*3, CYP3A5*6, UGT2B7*2, ABCB1 (3435C→T, 3842A→G), OATP1B1*1B, and OATP1B1*5, the presence of a rifampin-based antituberculosis (anti-TB) regimen, baseline body weight and organ function values, and demographic factors were explored as covariates. EFV concentration data were well described by a two-compartment model with first-order absorption (K_a ) and absorption lag time (A_lag) (K_a = 0.2 h^-1; A_lag = 0.83 h; central compartment clearance [CL_c/F] for CYP2B6*1/*1 = 18 liters/h, for CYP2B6*1/*6 = 14 liters/h, and for CYP2B6*6/*6 = 8.6 liters/h) and PBMCs as a peripheral compartment. EFV transfer from plasma to PBMCs was first order (CL_p/F = 32 liters/h), followed by capacity-limited return (V_max = 4,400 ng/ml/h; K_m = 710 ng/ml). Similarly, 8OHEFV displayed a first-order elimination and distribution to PBMCs, with a capacity-limited return to plasma. No covariate relationships resulted in a significant explanation of interindividual variability (IIV) on the estimated PK parameters of EFV and 8OHEFV, except for CYP2B6*6 genotypes, which were consistent with prior evidence. Both EFV and 8OHEFV accumulated to higher concentrations in PBMCs than in plasma and were well described by first-order input and Michaelis-Menten kinetics removal from PBMCs. CYP2B6*6 genotype polymorphisms were associated with decreased EFV and 8OHEFV clearance.

Pokharkar V. Understanding peroral absorption: regulatory aspects and contemporary approaches to tackling solubility and permeability hurdles

Oral drug absorption is a process influenced by the physicochemical and biopharmaceutical properties of the drug and its inter-relationship with the gastrointestinal tract. Drug solubility, dissolution and permeability across intestinal barrier are the key parameters controlling absorption. This review provides an overview of the factors that affect drug absorption and the classification of a drug on the basis of solubility and permeability. The biopharmaceutical classification system (BCS) was introduced in early 90׳s and is a regulatory tool used to predict bioavailability problems associated with a new entity, thereby helping in the development of a drug product. Strategies to combat solubility and permeability issues are also discussed.

Loss of amplitude of accommodation in pre-presbyopic HIV and AIDS patients under treatment with antiretrovirals

Background: The prevalence of HIV and AIDS is causing an enormous public health burden. Its manifestations spare no organ. Ocular complications are mainly attributed to various opportunistic infections which are directly or indirectly caused by immune deficiency.Purpose and aim: The purpose of this study was to determine the effect of HIV and AIDS on subjective amplitude of accommodation of patients under treatment with antiretrovirals and then to compare their results to those of control subjects.Methods: The study took place over a period of 10 months. A quantitative study was carried out on 58 subjects (29 ± 5.5 years) with HIV and AIDS and 35 (28.67 ± 4.6 years) controls of similar age. Amplitude of accommodation was measured using the subjective Royal Air Force push-up method. The influence of CD4+ cell count was also recorded.Results: People with HIV and AIDS had lower mean amplitude of accommodation (5.69 ± 0.88 D) compared to controls (8.53 ± 1.2 D). The decrease in amplitude of accommodation did not show any correlation with the CD4+ cell count. Lower amplitude of accommodation exists in people living with HIV and AIDS when compared with age-related healthy people.Conclusion: The results suggest that patients with HIV and AIDS on antiretroviral drugs (ARVs) have reduced amplitude of accommodation and might experience presbyopia earlier in life than participants without HIV and AIDS. The reduced amplitude of accommodation could be the initial presentation of HIV infection before the systemic manifestation. The possible causes could be the direct neuronal infection by HIV-1, ARVs use, pathological changes of the lens and ciliary muscle or the sensory component of the visual system. It is unknown whether the reduced amplitude of accommodation occurred prior to antiretroviral therapy or represents an ongoing injury to the eye and visual system by the HIV.

Expression, regulation, and function of drug transporters in cervicovaginal tissues of a mouse model used for microbicide testing

P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and multidrug resistance protein 4 (MRP4) are three efflux transporters that play key roles in the pharmacokinetics of antiretroviral drugs used in the pre-exposure prophylaxis of HIV sexual transmission. In this study, we investigated the expression, regulation, and function of these transporters in cervicovaginal tissues of a mouse model. Expression and regulation were examined using real-time RT-PCR and immunohistochemical staining, in the mouse tissues harvested at estrus and diestrus stages under natural cycling or after hormone synchronization. The three transporters were expressed at moderate to high levels compared to the liver. Transporter proteins were localized in various cell types in different tissue segments. Estrous cycle and exogenous hormone treatment affected transporter mRNA and protein expression, in a tissue- and transporter-dependent manner. Depo-Provera-synchronized mice were dosed vaginally or intraperitoneally with (3)H-TFV, with or without MK571 co-administration, to delineate the function of cervicovaginal Mrp4. Co-administration of MK571 significantly increased the concentration of vaginally-administered TFV in endocervix and vagina. MK571 increased the concentration of intraperitoneally-administered TFV in the cervicovaginal lavage and vagina by several fold. Overall, P-gp, Bcrp, and Mrp4 were positively expressed in mouse cervicovaginal tissues, and their expression can be regulated by the estrous cycle or by exogenous hormones. In this model, the Mrp4 transporter impacted TFV distribution in cervicovaginal tissues.

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.

Cytotoxic chemotherapy and the evolution of cellular and viral resistance to antiretroviral therapy in HIV- infected individuals with lymphoma

BACKGROUND

The use of combination antiretroviral therapy (cART) and cytotoxic chemotherapy for HIV-associated lymphoma runs the risks of inducing HIV drug resistance. This study examined two possible mechanisms: altered expression of membrane drug transporter protein (MTP) and acquisition of mutations in pro-viral DNA.

METHODS

Expression levels of MTP and pro-viral DNA resistance mutation analysis were performed on peripheral blood mononuclear cells (PBMC) before, during, and after chemotherapy.

RESULTS

Twenty nine patients completed the three time point estimations. There were no significant variations before, during, and after chemotherapy in the expression of four MTPs: ABCB1, ABCC1, ABCC2, and SLCO3A1 (OATP3A1). Pro-viral DNA sequencing revealed that only one patient developed a new nucleos/tide reverse transcriptase inhibitor-associated mutation (184V) during the course of the study, giving a mutation rate of 0.0027 per person per year.

CONCLUSIONS

In conclusion, concomitant administration of cytotoxic chemotherapy and cART does not induce expression of MTP. Furthermore, no significant changes in viral resistance were observed pre- and post-chemotherapy, suggesting mutagenic cytotoxic chemotherapy seems not to induce mutations in HIV pro-viral DNA.

P-glycoprotein (ABCB1) activity decreases raltegravir disposition in primary CD4+P-gphigh cells and correlates with HIV-1 viral load

Objectives

To evaluate the role of P-glycoprotein (P-gp) and multidrug-resistant-protein 1 (MRP1) on raltegravir intracellular drug disposition in CD4+ T cells, investigate the effect of HIV-1 infection on P-gp expression and correlate HIV-1 viraemia with P-gp activity in primary CD4+ T cell subsets.

Methods

The cellular accumulation ratio of [³H]raltegravir was quantified in CD4+ T cell lines overexpressing either P-gp (CEM-P-gp) or MRP1 (CEM-MRP1) and in primary CD3+CD4+ T cells with high (P-gp^high) and low P-gp activity (P-gp^low); inhibition of efflux transporters was confirmed by the intracellular retention of calcein-AM. The correlation of P-gp activity with HIV-1 viraemia was assessed in naive and memory T cell subsets from 21 HIV-1-infected treatment-naive subjects.

Results

[³H]Raltegravir cellular accumulation ratio decreased in CEM-P-gp cells (P < 0.0001). XR9051 (a P-gp inhibitor) and HIV-1 PIs reversed this phenomenon. Primary CD4+P-gp^high cells accumulated less raltegravir (38.4% ± 9.6%) than P-gp^low cells, whereas XR9051 also reversed this effect. In vitro HIV-1 infection of PBMCs and stimulation of CD4+ T cells increased P-gp mRNA and P-gp activity, respectively, while primary CD4+P-gp^high T cells sustained a higher HIV-1 replication than P-gp^low cells. A significant correlation between HIV-1 viraemia and P-gp activity was found in different CD4+ T cell subsets, particularly memory CD4+ T cells (r = 0.792, P < 0.0001).

Conclusions

Raltegravir is a substrate of P-gp in CD4+ T cells. Primary CD4+P-gp^high T cells eliminate intracellular raltegravir more readily than P-gp^low cells and HIV-1 viraemia correlates with P-gp overall activity. Specific CD4+P-gp^high T cell subsets could facilitate the persistence of viral replication in vivo and ultimately promote the appearance of drug resistance.

Polyspecific organic cation transporters and their impact on drug intracellular levels and pharmacodynamics

Most drugs are intended to act on molecular targets residing within a specific tissue or cell type. Therefore, the drug concentration within the target tissue or cells is most relevant to its pharmacological effect. Increasing evidences suggest that drug transporters not only play a significant role in governing systemic drug levels, but are also an important gate keeper for intra-tissue and intracellular drug concentrations. This review focuses on polyspecific organic cation transporters, which include the organic cation transporters 1-3 (OCT1-3), the multidrug and toxin extrusion proteins 1-2 (MATE1-2) and the plasma membrane monoamine transporter (PMAT). Following an overview of the tissue distribution, transport mechanisms, and functional characteristics of these transporters, we highlight the studies demonstrating the ability of locally expressed OCTs to impact intracellular drug concentrations and directly influence their pharmacological and toxicological activities. Specifically, OCT1-mediated metformin access to its site of action in the liver is impacted by genetic polymorphisms and chemical inhibition of OCT1. The impact of renal OCT2 and MATE1/2-K in cisplatin intrarenal accumulation and nephrotoxicity is reviewed. New data demonstrating the role of OCT3 in salivary drug accumulation and secretion is discussed. Whenever possible, the pharmacodynamic response and toxicological effects is presented and discussed in light of intra-tissue and intracellular drug exposure. Current challenges, knowledge gaps, and future research directions are discussed. Understanding the impact of transporters on intra-tissue and intracellular drug concentrations has important implications for rational-based optimization of drug efficacy and safety.

Antitubercular Agent Delamanid and Metabolites as Substrates and Inhibitors of ABC and Solute Carrier Transporters

Delamanid (Deltyba, OPC-67683) is the first approved drug in a novel class of nitro-dihydro-imidazooxazoles developed for the treatment of multidrug-resistant tuberculosis. Patients with tuberculosis require treatment with multiple drugs, several of which have known drug-drug interactions. Transporters regulate drug absorption, distribution, and excretion; therefore, the inhibition of transport by one agent may alter the pharmacokinetics of another, leading to unexpected adverse events. Therefore, it is important to understand how delamanid affects transport activity. In the present study, the potencies of delamanid and its main metabolites as the substrates and inhibitors of various transporters were evaluated in vitro Delamanid was not transported by the efflux ATP-binding cassette (ABC) transporters P-glycoprotein (P-gp; MDR1/ABCB1) and breast cancer resistance protein (BCRP/ABCG2), solute carrier (SLC) transporters, organic anion-transporting polypeptides, or organic cation transporter 1. Similarly, metabolite 1 (M1) was not a substrate for any of these transporters except P-gp. Delamanid showed no inhibitory effect on ABC transporters MDR1, BCRP, and bile salt export pump (BSEP; ABCB11), SLC transporters, or organic anion transporters. M1 and M2 inhibited P-gp- and BCRP-mediated transport but did so only at the 50% inhibitory concentrations (M1, 4.65 and 5.71 μmol/liter, respectively; M2, 7.80 and 6.02 μmol/liter, respectively), well above the corresponding maximum concentration in plasma values observed following the administration of multiple doses in clinical trials. M3 and M4 did not affect the activities of any of the transporters tested. These in vitro data suggest that delamanid is unlikely to have clinically relevant interactions with drugs for which absorption and disposition are mediated by this group of transporters.

Entecavir Interacts with Influx Transporters hOAT1, hCNT2, hCNT3, but Not with hOCT2: The Potential for Renal Transporter-Mediated Cytotoxicity and Drug-Drug Interactions

Entecavir (ETV) is one of the most potent agents for the treatment of the hepatitis B viral infection. The drug is principally eliminated by the kidney. The goal of this study was to investigate the potential of ETV to interact in vitro with the renal SLC transporters hOAT1, hOCT2, hCNT2 and hCNT3. Potential drug–drug interactions of ETV at the renal transporters with antiviral drugs known to be excreted by the kidney (adefovir, tenofovir, cidofovir) as well as transporter-dependent cytotoxicity were also examined. Interactions with the selected transporters along with cytotoxicity were studied in several transiently transfected cellular models using specific substrates and inhibitors. ETV was found to be both a substrate and inhibitor of hOAT1 (IC₅₀ = 175.3 μM), hCNT2 (IC₅₀ = 241.9 μM) and hCNT3 (IC₅₀ = 278.4 μM) transporters, although it interacted with the transporters with relatively low affinities. ETV inhibited the cellular uptake of adefovir, tenofovir, and cidofovir by hOAT1; however, effective inhibition was shown at ETV concentrations exceeding therapeutic levels. In comparison with adefovir, tenofovir, and cidofovir, ETV displayed no transporter-mediated cytotoxicity in cells transfected with hOAT1, hCNT2, and hCNT3. No significant interaction of ETV with hOCT2 was detected. The study demonstrates interactions of ETV with several human renal transporters. For the first time, an interaction of ETV with the hCNTs was proved. We show that the potency of ETV to cause nephrotoxicity and/or clinically significant drug-drug interactions related to the tested transporters is considerably lower than that of adefovir, tenofovir, and cidofovir.

Drug transporters in tissues and cells relevant to sexual transmission of HIV: Implications for drug delivery

Efflux and uptake transporters of drugs are key regulators of the pharmacokinetics of many antiretroviral drugs. A growing body of literature has revealed the expression and functionality of multiple transporters in female genital tract (FGT), colorectal tissue, and immune cells. Drug transporters could play a significant role in the efficacy of preventative strategies for HIV-1 acquisition. Pre-exposure prophylaxis (PrEP) is a promising strategy, which utilizes topically (vaginally or rectally), orally or other systemically administered antiretroviral drugs to prevent the sexual transmission of HIV to receptive partners. The drug concentration in the receptive mucosal tissues and target immune cells for HIV is critical for PrEP effectiveness. Hence, there is an emerging interest in utilizing transporter information to explain tissue disposition patterns of PrEP drugs, to interpret inter-individual variability in PrEP drug pharmacokinetics and effectiveness, and to improve tissue drug exposure through modulation of the cervicovaginal, colorectal, or immune cell transporters. In this review, the existing literature on transporter expression, functionality and regulation in the transmission-related tissues and cells is summarized. In addition, the relevance of transporter function for drug delivery and strategies that could exploit transporters for increased drug concentration at target locales is discussed. The overall goal is to facilitate an understanding of drug transporters for PrEP optimization.

Preclinical assessment of the interactions between the antiretroviral drugs, ritonavir and efavirenz, and the tyrosine kinase inhibitor erlotinib

PURPOSE

Prevalence of non-AIDS-defining cancers (NADCs) has increased in the era of potent antiretroviral treatments. Incidence rates of NADCs now exceed AIDS-defining cancers in HIV-positive patients. Treatment of NADCs may be complicated by interactions between antiretrovirals and chemotherapy mostly via inhibition or induction of CYP3A4. Erlotinib is used to treat non-small cell lung and pancreatic cancer and is primarily metabolized by CYP3A4 into multiple products including the active metabolite (OSI-420). Preclinical in vivo assessment was performed to gain a better understanding of CYP3A4-mediated interactions between antiretrovirals and erlotinib.

METHODS

Erlotinib (50 mg/kg p.o.) was administered to male FVB mice in the presence and absence of dexamethasone (10 mg/kg p.o. QDx4), efavirenz (25 mg/kg p.o. QDx4), ketoconazole (50 mg/kg p.o.), or ritonavir (12.5 mg/kg p.o.). Blood samples were collected to characterize exposure (AUC).

RESULTS

Administration of erlotinib with CYP3A4 inducers (dexamethasone) and inhibitors (ketoconazole and ritonavir) resulted in significant alterations in erlotinib exposure. Ketoconazole and ritonavir resulted in a 1.7- and 3.0-fold increase in erlotinib AUC, respectively, while dexamethasone results in a 0.6-fold decrease in erlotinib AUC. The CYP3A4 inducer efavirenz did not have a significant effect on erlotinib exposure.

CONCLUSION

CYP3A4 inducers and inhibitors altered the exposure of erlotinib. Until a definitive clinical trial is performed, erlotinib should be used with caution in patients on a ritonavir-containing antiretroviral regimen, while standard doses may be appropriate for patients on an efavirenz-containing antiretroviral regimen.

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.

Nucleoside transporters and human organic cation transporter 1 determine the cellular handling of DNA-methyltransferase inhibitors

BACKGROUND AND PURPOSE

Inhibitors of DNA methyltransferases (DNMTs), such as azacytidine, decitabine and zebularine, are used for the epigenetic treatment of cancer. Their action may depend upon their translocation across the plasma membrane. The aim of this study was to identify transporter proteins contributing to DNMT inhibitor action.

EXPERIMENTAL APPROACH

Drug interactions with selected hCNT and hENT proteins were studied in transiently transfected HeLa and MDCK cells. Interaction with human organic cation transporters (hOCTs) was assessed in transiently transfected HeLa cells and Xenopus laevis oocytes.

KEY RESULTS

Zebularine uptake was mediated by hCNT1, hCNT3 and hENT2. Decitabine interacted with but was not translocated by any nucleoside transporter (NT) type. hCNT expression at the apical domain of MDCK cells promoted net vectorial flux of zebularine. Neither hOCT1 nor hOCT2 transported decitabine, but both were involved in the efflux of zebularine, suggesting these proteins act as efflux transporters. hOCT1 polymorphic variants, known to alter function, decreased zebularine efflux.

CONCLUSIONS AND IMPLICATIONS

This study highlights the influence of human NTs and hOCTs on the pharmacokinetics and pharmacodynamics of selected DNMT inhibitors. As hOCTs may also behave as efflux transporters, they could contribute either to chemoresistance or to chemosensitivity, depending upon the nature of the drug or combination of drugs being used in cancer therapy.

Drug interactions and antiretroviral drug monitoring

Owing to the improved longevity afforded by combination antiretroviral therapy (cART), HIV-infected individuals are developing several non-AIDS-related comorbid conditions. Consequently, medical management of the HIV-infected population is increasingly complex, with a growing list of potential drug-drug interactions (DDIs). This article reviews some of the most relevant and emerging potential interactions between antiretroviral medications and other agents. The most common DDIs are those involving protease inhibitors or non-nucleoside reverse transcriptase inhibitors, which alter the cytochrome P450 enzyme system and/or drug transporters such as p-glycoprotein. Of note are the new agents for the treatment of chronic hepatitis C virus infection. These new classes of drugs and others drugs that are increasingly used in this patient population represent a significant challenge with regard to achieving the goals of effective HIV suppression and minimization of drug-related toxicities. Awareness of DDIs and a multidisciplinary approach are imperative in reaching these goals.

Nucleoside transporter proteins as biomarkers of drug responsiveness and drug targets

Nucleoside and nucleobase analogs are currently used in the treatment of solid tumors, lymphoproliferative diseases, viral infections such as hepatitis and AIDS, and some inflammatory diseases such as Crohn. Two gene families are implicated in the uptake of nucleosides and nucleoside analogs into cells, SCL28 and SLC29. The former encodes hCNT1, hCNT2, and hCNT3 proteins. They translocate nucleosides in a Na⁺ coupled manner with high affinity and some substrate selectivity, being hCNT1 and hCNT2 pyrimidine- and purine-preferring, respectively, and hCNT3 a broad selectivity transporter. SLC29 genes encode four members, being hENT1 and hENT2 the only two which are unequivocally implicated in the translocation of nucleosides and nucleobases (the latter mostly via hENT2) at the cell plasma membrane. Some nucleoside-derived drugs can also interact with and be translocated by members of the SLC22 gene family, particularly hOCT and hOAT proteins. Inter-individual differences in transporter function and perhaps, more importantly, altered expression associated with the disease itself might modulate the transporter profile of target cells, thereby determining drug bioavailability and action. Drug transporter pharmacology has been periodically reviewed. Thus, with this contribution we aim at providing a state-of-the-art overview of the clinical evidence generated so far supporting the concept that these membrane proteins can indeed be biomarkers suitable for diagnosis and/or prognosis. Last but not least, some of these transporter proteins can also be envisaged as drug targets, as long as they can show “transceptor” functions, in some cases related to their role as modulators of extracellular adenosine levels, thereby providing a functional link between P1 receptors and transporters.

Human organic cation transporter 1 (hOCT1) as a mediator of bendamustine uptake and cytotoxicity in chronic lymphocytic leukemia (CLL) cells

Bendamustine is used in the treatment of chronic lymphocytic leukemia (CLL). Routes for bendamustine entry into target cells are unknown. This study aimed at identifying transporter proteins implicated in bendamustine uptake. Our results showed that hOCT1 is a bendamustine transporter, as bendamustine could cis-inhibit the uptake of a canonical hOCT1 substrate, with a Ki in the micromolar range, consistent with the EC50 values of the cytotoxicity triggered by this drug in HEK293 cells expressing hOCT1. hOCT1 polymorphic variants determining impaired bendamustine-transporter interaction, consistently reduced bendamustine cytotoxicity in HEK293 cells stably expressing them. Exome genotyping of the SLC22A1 gene, encoding hOCT1, was undertaken in a cohort of 241 CLL patients. Ex vivo cytotoxicity to bendamustine was measured in a subset of cases and shown to correlate with SLC22A1 polymorphic variants. In conclusion, hOCT1 is a suitable bendamustine transporter, thereby contributing to its cytotoxic effect depending upon the hOCT1 genetic variants expressed.

What do drug transporters really do?

Potential drug-drug interactions mediated by the ATP-binding cassette (ABC) transporter and solute carrier (SLC) transporter families are of clinical and regulatory concern. However, the endogenous functions of these drug transporters are not well understood. Discussed here is evidence for the roles of ABC and SLC transporters in the handling of diverse substrates, including metabolites, antioxidants, signalling molecules, hormones, nutrients and neurotransmitters. It is suggested that these transporters may be part of a larger system of remote communication ('remote sensing and signalling') between cells, organs, body fluid compartments and perhaps even separate organisms. This broader view may help to clarify disease mechanisms, drug-metabolite interactions and drug effects relevant to diabetes, chronic kidney disease, metabolic syndrome, hypertension, gout, liver disease, neuropsychiatric disorders, inflammatory syndromes and organ injury, as well as prenatal and postnatal development.

Expression and localization of p-glycoprotein, multidrug resistance protein 4, and breast cancer resistance protein in the female lower genital tract of human and pigtailed macaque

Antiretroviral drug absorption and disposition in cervicovaginal tissue is important for the effectiveness of vaginally or orally administered drug products in preexposure prophylaxis (PrEP) of HIV-1 sexual transmission to women. Therefore, it is imperative to understand critical determinants of cervicovaginal tissue pharmacokinetics. This study aimed to examine the mRNA expression and protein localization of three efflux transporters, P-glycoprotein (P-gp), multidrug resistance-associated protein 4 (MRP4), and breast cancer resistance protein (BCRP), in the lower genital tract of premenopausal women and pigtailed macaques. Along the human lower genital tract, the three transporters were moderately to highly expressed compared to colorectal tissue and liver, as revealed by real-time reverse transcriptase polymerase chain reaction (RT-PCR). In a given genital tract segment, the transporter with the highest expression level was either BCRP or P-gp, while MRP4 was always expressed at the lowest level among the three transporters tested. The immunohistochemical staining showed that P-gp and MRP4 were localized in multiple cell types including epithelial cells and vascular endothelial cells. BCRP was predominantly localized in the vascular endothelial cells. Differences in transporter mRNA level and localization were observed among endocervix, ectocervix, and vagina. Compared to human tissues, the macaque cervicovaginal tissues displayed comparable expression and localization patterns of the three transporters, although subtle differences were observed between the two species. The role of these cervicovaginal transporters in drug absorption and disposition warrants further studies. The resemblance between human and pigtailed macaque in transporter expression and localization suggests the utility of the macaque model in the studies of human cervicovaginal transporters.

Downregulation of duodenal SLC transporters and activation of proinflammatory signaling constitute the early response to high altitude in humans

Solute carrier (SLC) transporters mediate the uptake of biologically active compounds in the intestine. Reduced oxygenation (hypoxia) is an important factor influencing intestinal homeostasis. The aim of this study was to investigate the pathophysiological consequences of hypoxia on the expression and function of SLCs in human intestine. Hypoxia was induced in human intestinal epithelial cells (IECs) in vitro (0.2; 1% O2 or CoCl2). For human in vivo studies, duodenal biopsies and serum samples were obtained from individuals (n = 16) acutely exposed to 4,554 meters above sea levels. Expression of relevant targets was analyzed by quantitative PCR, Western blotting, or immunofluorescence. Serum levels of inflammatory mediators and nucleosides were determined by ELISA and LC/MS-MS, respectively. In the duodenum of volunteers exposed to high altitude we observed decreased mRNA levels of apical sodium-dependent bile acid transporter (ASBT), concentrative nucleoside transporters 1/2 (CNT1/2), organic anion transporting polypeptide 2B1 (OATP2B1), organic cation transporter 2 (OCTN2), peptide transporter 1 (PEPT1), serotonin transporter (SERT), and higher levels of IFN-γ, IL-6, and IL-17A. Serum levels of IL-10, IFN-γ, matrix metalloproteinase-2 (MMP-2), and serotonin were elevated, whereas the levels of uridine decreased upon exposure to hypoxia. Hypoxic IECs showed reduced levels of equilibrative nucleoside transporter 2 (ENT2), OCTN2, and SERT mRNAs in vitro, which was confirmed on the protein level and was accompanied by activation of ERK1/2, increase of hypoxia-inducible factor (HIF) proteins, and production of IL-8 mRNA. Costimulation with IFN-γ and IL-6 during hypoxia further decreased the expression of SERT, ENT2, and CNT2 in vitro. Reduced oxygen supply affects the expression pattern of duodenal SLCs that is accompanied by changes in serum levels of proinflammatory cytokines and biologically active compounds demonstrating that intestinal transport is affected during systemic exposure to hypoxia in humans.

Age-related differences in reporting of drug-associated liver injury: data-mining of WHO Safety Report Database

BACKGROUND/AIMS

Age-differences in the frequency and manifestations of drug-induced liver injury are not fully characterized. Data-mining analyses were performed to assess the impact of age on liver event reporting frequency with different phenotypes and agents.

METHODS

236 drugs associated with hepatotoxicity were evaluated using the Empirical Bayes Geometric Mean (EBGM) of the relative reporting ratio with 90% confidence interval (EB05 and EB95) calculated for the age groups: 0-17, 18-64, and⩾65years (or elderly), for overall, serious (acute liver failure), hepatocellular, and cholestatic liver injury, using the WHO Safety Report Database.

RESULTS

Overall, cases of age 0-17, 18-64, and 65years or older comprised 6%, 62%, and 32% of liver event reports. Acute liver failure and hepatocellular injury were more frequently reported among children compared to adults and the elderly while reports with cholestatic injury were more frequent among the elderly (p<0.00001). A potential to cause mitochondrial dysfunction was more prevalent among the drugs with increased pediatric reporting frequency while high lipophilicity and biliary excretion were more common among the drugs associated with higher reporting frequency in the elderly.

CONCLUSION

Age-specific phenotypes and potential drug properties associated with age-specific hepatotoxicity were identified in reported liver events; further analyses are warranted.

Drug-drug interactions between HMG-CoA reductase inhibitors (statins) and antiviral protease inhibitors

The HMG-CoA reductase inhibitors are a class of drugs also known as statins. These drugs are effective and widely prescribed for the treatment of hypercholesterolemia and prevention of cardiovascular morbidity and mortality. Seven statins are currently available: atorvastatin, fluvastatin, lovastatin, pitavastatin, pravastatin, rosuvastatin and simvastatin. Although these drugs are generally well tolerated, skeletal muscle abnormalities from myalgia to severe lethal rhabdomyolysis can occur. Factors that increase statin concentrations such as drug-drug interactions can increase the risk of these adverse events. Drug-drug interactions are dependent on statins' pharmacokinetic profile: simvastatin, lovastatin and atorvastatin are metabolized through cytochrome P450 (CYP) 3A, while the metabolism of the other statins is independent of this CYP. All statins are substrate of organic anion transporter polypeptide 1B1, an uptake transporter expressed in hepatocyte membrane that may also explain some drug-drug interactions. Many HIV-infected patients have dyslipidemia and comorbidities that may require statin treatment. HIV-protease inhibitors (HIV PIs) are part of recommended antiretroviral treatment in combination with two reverse transcriptase inhibitors. All HIV PIs except nelfinavir are coadministered with a low dose of ritonavir, a potent CYP3A inhibitor to improve their pharmacokinetic properties. Cobicistat is a new potent CYP3A inhibitor that is combined with elvitegravir and will be combined with HIV-PIs in the future. The HCV-PIs boceprevir and telaprevir are both, to different extents, inhibitors of CYP3A. This review summarizes the pharmacokinetic properties of statins and PIs with emphasis on their metabolic pathways explaining clinically important drug-drug interactions. Simvastatin and lovastatin metabolized through CYP3A have the highest potency for drug-drug interaction with potent CYP3A inhibitors such as ritonavir- or cobicistat-boosted HIV-PI or the hepatitis C virus (HCV) PI, telaprevir or boceprevir, and therefore their coadministration is contraindicated. Atorvastatin is also a CYP3A substrate, but less potent drug-drug interactions have been reported with CYP3A inhibitors. Non-CYP3A-dependent statin concentrations are also affected although to a lesser extent when coadministered with HIV or HCV PIs, mainly through interaction with OATP1B1, and treatment should start with the lowest available statin dose. Effectiveness and occurrence of adverse effects should be monitored at regular time intervals.

Combination antiretroviral therapy (cART) component ritonavir significantly alters docetaxel exposure

PURPOSE

Non-AIDS-defining cancers (NADCs) now exceed rates of AIDS-defining cancers in HIV-positive patients. Treatment of NADCs may be complicated by drug-drug interactions between antiretrovirals and chemotherapy. Docetaxel is a widely used anticancer agent that is primarily metabolized by CYP3A4 enzymes and used to treat NADCs. A preclinical in vivo assessment was performed to gain a better understanding of CYP3-mediated drug-drug interactions between antiretrovirals and docetaxel, as well as to assess any alterations in gene expression with these combinations.

METHODS

Docetaxel (20 mg/kg i.v.) was administered to male FVB mice in the presence and absence of dexamethasone (10 mg/kg p.o. ×4d), efavirenz (25 mg/kg p.o. ×4d), ketoconazole (50 mg/kg p.o.), or ritonavir (12.5 mg/kg p.o.). At various time points, plasma and liver tissue were harvested. Docetaxel concentrations were determined by LC/MS/MS. Pharmacokinetic parameters were calculated. Liver tissue RNA was used to evaluate alterations in Cyp3a11 and Abcb1a gene expression.

RESULTS

Docetaxel exposure was altered by CYP3A4 inhibitors but not by inducers. The CYP3A4 inducers efavirenz and dexamethasone did not have a significant effect on docetaxel exposure (AUC). However, the CYP3A4 inhibitors ritonavir and ketoconazole resulted in a 6.9- and 3.1-fold increase in AUC, respectively. Alterations in gene expression did not account for the altered docetaxel exposure.

CONCLUSIONS

Docetaxel exposure was significantly altered by CYP3A4 inhibitors. Until a definitive clinical trial is performed, docetaxel should be used with caution in patients on a ritonavir-containing antiretroviral regimen or an alternative antineoplastic therapy or antiretroviral regimen should be considered.

A computational study identifies HIV progression-related genes using mRMR and shortest path tracing

Since statistical relationships between HIV load and CD4+ T cell loss have been demonstrated to be weak, searching for host factors contributing to the pathogenesis of HIV infection becomes a key point for both understanding the disease pathology and developing treatments. We applied Maximum Relevance Minimum Redundancy (mRMR) algorithm to a set of microarray data generated from the CD4+ T cells of viremic non-progressors (VNPs) and rapid progressors (RPs) to identify host factors associated with the different responses to HIV infection. Using mRMR algorithm, 147 gene had been identified. Furthermore, we constructed a weighted molecular interaction network with the existing protein-protein interaction data from STRING database and identified 1331 genes on the shortest-paths among the genes identified with mRMR. Functional analysis shows that the functions relating to apoptosis play important roles during the pathogenesis of HIV infection. These results bring new insights of understanding HIV progression.

Short communication: expression of transporters and metabolizing enzymes in the female lower genital tract: implications for microbicide research

Topical vaginal microbicides have been considered a promising option for preventing the male-to-female sexual transmission of HIV; however, clinical trials to date have not clearly demonstrated robust and reproducible effectiveness results. While multiple approaches may help enhance product effectiveness observed in clinical trials, increasing the drug exposure in lower genital tract tissues is a compelling option, given the difficulty in achieving sufficient drug exposure and positive correlation between tissue exposure and microbicide efficacy. Since many microbicide drug candidates are substrates of transporters and/or metabolizing enzymes, there is emerging interest in improving microbicide exposure and efficacy through local modulation of transporters and enzymes in the female lower genital tract. However, no systematic information on transporter/enzyme expression is available for ectocervical and vaginal tissues of premenopausal women, the genital sites most relevant to microbicide drug delivery. The current study utilized reverse transcriptase polymerase chain reaction (RT-PCR) to examine the mRNA expression profile of 22 transporters and 19 metabolizing enzymes in premenopausal normal human ectocervix and vagina. Efflux and uptake transporters important for antiretroviral drugs, such as P-gp, BCRP, OCT2, and ENT1, were found to be moderately or highly expressed in the lower genital tract as compared to liver. Among the metabolizing enzymes examined, most CYP isoforms were not detected while a number of UGTs such as UGT1A1 were highly expressed. Moderate to high expression of select transporters and enzymes was also observed in mouse cervix and vagina. The implications of this information on microbicide research is also discussed, including microbicide pharmacokinetics, the utilization of the mouse model in microbicide screening, as well as the in vivo functional studies of cervicovaginal transporters and enzymes.

The SLC22 family with transporters of organic cations, anions and zwitterions

The SLC22 family contains 13 functionally characterized human plasma membrane proteins each with 12 predicted α-helical transmembrane domains. The family comprises organic cation transporters (OCTs), organic zwitterion/cation transporters (OCTNs), and organic anion transporters (OATs). The transporters operate as (1) uniporters which mediate facilitated diffusion (OCTs, OCTNs), (2) anion exchangers (OATs), and (3) Na(+)/zwitterion cotransporters (OCTNs). They participate in small intestinal absorption and hepatic and renal excretion of drugs, xenobiotics and endogenous compounds and perform homeostatic functions in brain and heart. Important endogeneous substrates include monoamine neurotransmitters, l-carnitine, α-ketoglutarate, cAMP, cGMP, prostaglandins, and urate. It has been shown that mutations of the SLC22 genes encoding these transporters cause specific diseases like primary systemic carnitine deficiency and idiopathic renal hypouricemia and are correlated with diseases such as Crohn's disease and gout. Drug-drug interactions at individual transporters may change pharmacokinetics and toxicities of drugs.