HIV-1 Alters Intestinal Expression of Drug Transporters and Metabolic Enzymes: Implications for Antiretroviral Drug Disposition

Efflux ABC transporters in drug disposition and their posttranscriptional gene regulation by microRNAs

ATP-binding cassette (ABC) transporters are transmembrane proteins expressed commonly in metabolic and excretory organs to control xenobiotic or endobiotic disposition and maintain their homeostasis. Changes in ABC transporter expression may directly affect the pharmacokinetics of relevant drugs involving absorption, distribution, metabolism, and excretion (ADME) processes. Indeed, overexpression of efflux ABC transporters in cancer cells or bacteria limits drug exposure and causes therapeutic failure that is known as multidrug resistance (MDR). With the discovery of functional noncoding microRNAs (miRNAs) produced from the genome, many miRNAs have been revealed to govern posttranscriptional gene regulation of ABC transporters, which shall improve our understanding of complex mechanism behind the overexpression of ABC transporters linked to MDR. In this article, we first overview the expression and localization of important ABC transporters in human tissues and their clinical importance regarding ADME as well as MDR. Further, we summarize miRNA-controlled posttranscriptional gene regulation of ABC transporters and effects on ADME and MDR. Additionally, we discuss the development and utilization of novel bioengineered miRNA agents to modulate ABC transporter gene expression and subsequent influence on cellular drug accumulation and chemosensitivity. Findings on posttranscriptional gene regulation of ABC transporters shall not only improve our understanding of mechanisms behind variable ADME but also provide insight into developing new means towards rational and more effective pharmacotherapies.

P-Glycoprotein and Organic Anion Transporter Polypeptide 1B/Breast Cancer Resistance Protein Drug Transporter Activity in Pregnant Women Living With HIV

This study evaluates the influence of pregnancy and HIV infection in conjunction with the use of raltegravir, lamivudine, and tenofovir disoproxil fumarate (combined antiretroviral therapy [cART]) on intestinal P-glycoprotein (P-gp) and hepatic organic anion transporter polypeptide (OATP) 1B1/1B3 and/or breast cancer resistance protein (BCRP) drug transporter activity using rosuvastatin (OATP1B/BCRP) and fexofenadine (P-gp) probes. Single oral doses of 5-mg rosuvastatin and 60-mg fexofenadine were administered to women living with HIV under cART in the third trimester of gestation (n = 15) and postpartum period (n = 10). A control group of 12 healthy nonpregnant women also was investigated. Pharmacokinetic parameters were estimated by using a noncompartmental method and evaluated by t test (P < .05). The rosuvastatin area under the plasma concentration-time curve from time 0 to the last quantifiable concentration (AUC_0-last ) value was higher in the third trimester of pregnancy (19.5 [95%CI, 16.8-22.3] ng • h/mL] when compared to postpartum (13.3 [95%CI, 9.3-17.5] ng • h/mL), while the fexofenadine AUC_0-last values did not differ between the third trimester of pregnancy (738.0 [95%CI, 611.4-864.6] ng • h/mL) and postpartum period (874.9 [95%CI, 408.2-1342.0] ng• h/mL). The rosuvastatin AUC_0-last values did not differ between healthy nonpregnant women (13.8 [95%CI, 10.0-17.6] ng • h/mL) and women living with HIV in the postpartum period (13.3 [95%CI, 9.3-17.5] ng • h/mL), and the fexofenadine AUC_0-last values did not differ between the 2 investigated groups (603.6 [95%CI, 467.5-739.7] ng • h/mL vs 874.9 [95%CI, 408.2-1342.0] ng • h/mL). It is suggested that gestation inhibits the hepatic OATP1B1/1B3 and/or BCRP activity but does not alter intestinal P-gp activity. The influence of HIV infection in conjunction with use of cART on OATP1B/BCRP and intestinal P-gp activity was not observed.

Irreversible depletion of intestinal CD4+ T cells is associated with T cell activation during chronic HIV infection

HIV infection in the human gastrointestinal (GI) tract is thought to be central to HIV progression, but knowledge of this interaction is primarily limited to cohorts within Westernized countries. Here, we present a large cohort recruited from high HIV endemic areas in South Africa and found that people living with HIV (PLWH) presented at a younger age for investigation in the GI clinic. We identified severe CD4⁺ T cell depletion in the GI tract, which was greater in the small intestine than in the large intestine and not correlated with years on antiretroviral treatment (ART) or plasma viremia. HIV-p24 staining showed persistent viral expression, particularly in the colon, despite full suppression of plasma viremia. Quantification of mucosal antiretroviral (ARV) drugs revealed no differences in drug penetration between the duodenum and colon. Plasma markers of gut barrier breakdown and immune activation were elevated irrespective of HIV, but peripheral T cell activation was inversely correlated with loss of gut CD4⁺ T cells in PLWH alone. T cell activation is a strong predictor of HIV progression and independent of plasma viral load, implying that the irreversible loss of GI CD4⁺ T cells is a key event in the HIV pathogenesis of PLWH in South Africa, yet the underlying mechanisms remain unknown.

Impact of in-utero antiretroviral drug exposure on expression of membrane-associated transporters in mouse placenta and fetal brain

OBJECTIVE

Although antiretroviral therapy (ART) during pregnancy is effective in limiting vertical HIV transmission, adverse outcomes persist amongst uninfected children exposed to antiretroviral drugs in utero. Membrane-associated drug transporters, metabolic enzymes, and tight junction proteins play important roles in adult antiretroviral drug disposition and toxicity; however, the fetal expression of these proteins in the context of ART, and their impact on in-utero antiretroviral drug distribution remain poorly understood. This study aimed to characterize the role of these proteins in modulating in-utero antiretroviral drug exposure.

METHODS

Pregnant mice were exposed to an ART regimen consisting of lamivudine, abacavir, atazanavir, and ritonavir, at clinically relevant doses. Fetal brain, liver, placenta amniotic fluid, and maternal plasma were collected on gestational day 18.5 and concentration of antiretroviral drugs in fetal tissues was measured by LC/MS/MS, whereas transporter expression was assessed by qPCR.

RESULTS

Abacavir and lamivudine were detected in fetal brain and amniotic fluid, whereas atazanavir and ritonavir were detected in amniotic fluid only. Robust mRNA expression of key transporters was observed in adult and fetal tissues, and sex differences were identified in the expression of Abcc1 and Slc29a1 in the placenta. Antiretroviral drug exposure was associated with a reduction in relative placental Abcg2, Abcc1, and Slc29a1 expression.

CONCLUSION

These findings identify a novel effect of fetal sex and antiretroviral drug treatment on the expression of placental transporters in a mouse model, and characterize the penetration of lamivudine and abacavir into fetal brain, uncovering a potential role of transporters in modulating fetal exposure to antiretroviral drugs.

No implication of HIV coinfection on the plasma exposure to rifampicin, pyrazinamide, and ethambutol in tuberculosis patients

There are contrasting findings regarding the effect of HIV on the pharmacokinetics of first‐line anti‐tubercular drugs (FLATDs) due to a lack of prospective controlled clinical studies, including patients with tuberculosis (TB) and patients with TB living with HIV. This study aims to assess the effect of HIV coinfection and antiviral therapy on the plasma exposure to FLATDs in patients with TB. HIV negative (TB‐HIV− group; n = 15) and HIV positive (TB‐HIV+ group; n = 18) adult patients with TB were enrolled during the second month of FLATDs treatment. All TB‐HIV+ patients were on treatment with lamivudine, tenofovir (or zidovudine), and raltegravir (or efavirenz). Serial blood sampling was collected over 24 h and FLATDs pharmacokinetic parameters were evaluated using noncompartmental methods. In the TB‐HIV+ patients, dose‐normalized plasma exposure area under the curve from zero to 24 h (nAUC_0–24; geometric mean and 95% confidence interval [CI]) values at steady‐state to rifampicin, pyrazinamide, and ethambutol were 18.38 (95% CI 13.74–24.59), 238.21 (95% CI 191.09–296.95), and 18.33 (95% CI 14.56–23.09) µg∙h/ml, respectively. Similar plasma exposure was found in the TB‐HIV− patients. The geometric mean and 90% CI of the ratios between TB‐HIV− and TB‐HIV+ groups suggest no significant pharmacokinetic interaction between the selected antivirals and FLATDs. Likewise, HIV coinfection itself does not appear to have any effect on the plasma exposure to FLATDs.

Clinical and Molecular Perspectives on Inflammation-Mediated Regulation of Drug Metabolism and Transport

Inflammation is a possible cause of variability in drug response and toxicity due to altered regulation in drug-metabolizing enzymes and transporters (DMETs) in humans. Here, we evaluate the clinical and in vitro evidence on inflammation-mediated modulation of DMETs, and the impact on drug metabolism in humans. Furthermore, we identify and discuss the gaps in our current knowledge. A systematic literature search on PubMed, Embase, and grey literature was performed in the period of February to September 2020. A total of 203 papers was included. In vitro studies in primary human hepatocytes revealed strong evidence that CYP3A4 is strongly downregulated by inflammatory cytokines IL-6 and IL-1β. CYP1A2, CYP2C9, CYP2C19, and CYP2D6 were downregulated to a lesser extent. In clinical studies, acute and chronic inflammatory diseases were observed to cause downregulation of CYP enzymes in a similar pattern. However, there is no clear correlation between in vitro studies and clinical studies, mainly because most in vitro studies use supraphysiological cytokine doses. Moreover, clinical studies demonstrate considerable variability in terms of methodology and inconsistencies in evaluation of the inflammatory state. In conclusion, we find inflammation and pro-inflammatory cytokines to be important factors in regulation of drug-metabolizing enzymes and transporters. The observed downregulation is clinically relevant, and we emphasize caution when treating patients in an inflammatory state with narrow therapeutic index drugs. Further research is needed to identify the full extent of inflammation-mediated changes in DMETs and to further support personalized medicine.

Antiretroviral Drug Transporters and Metabolic Enzymes in Circulating Monocytes and Monocyte-Derived Macrophages of ART-Treated People Living With HIV and HIV-Uninfected Individuals

ABSTRACT

Membrane-associated drug transport proteins and drug metabolic enzymes could regulate intracellular antiretroviral (ARV) drug concentrations in HIV-1 target cells such as myeloid cells. We investigated the expression of these transporters and enzymes in monocyte subsets and monocyte-derived macrophages (MDMs) isolated from peripheral blood mononuclear cells (PBMCs) of HIV-uninfected individuals (HIV-negative) and people living with HIV receiving viral suppressive antiretroviral therapy (ART; HIV+ART) and examined plasma and intracellular ARV concentrations. Monocytes were isolated from PBMCs of 12 HIV-negative and 12 HIV+ART donors and differentiated into MDMs. The mRNA and protein expression of drug transporters and metabolic enzymes were analyzed by quantitative real-time polymerase chain reaction and flow cytometry, respectively. ARV drug concentrations were quantified in plasma, PBMCs, monocytes, and MDMs by LC-MS/MS. The mRNA expression of relevant ARV transporters or metabolic enzymes, ABCB1/P-gp, ABCG2/BCRP, ABCC1/MRP1, ABCC4/MRP4, SLC22A1/OCT1, SLC29A2/ENT2, CYP2B6, CYP2D6, and UGT1A1, was demonstrated in monocytes and MDMs of 2 to 4 HIV-negative donors. P-gp, BCRP, and MRP1 proteins were differentially expressed in classical, intermediate, and nonclassical monocytes and MDMs of both HIV+ART and HIV-negative donors. Intracellular concentrations of ARVs known to be substrates of these transporters and metabolic enzymes were detected in monocytes of HIV+ART donors but were undetectable in MDMs. In this study, we demonstrated the expression of drug transporters and metabolic enzymes in monocytes and MDMs of HIV-negative and HIV+ART individuals, which could potentially limit intracellular concentrations of ARVs and contribute to residual HIV replication. Further work is needed to assess the role of these transporters in the penetration of ARVs in tissue macrophages.

Quantitative Benefit-Risk Assessment of P-gp-Mediated Drug-Drug Interactions of Dabigatran Coadministered With Pharmacokinetic Enhancers in Patients With Renal Impairment

Drug-drug interactions (DDIs) between dabigatran and ritonavir/cobicistat are of major concern in people living with HIV, particularly in those with impaired renal function, because they can result in increased dabigatran exposure and thus an increased risk of major bleeding events. However, the extent of this interaction and subsequent need for dose adjustment in subjects with varying degrees of renal function is currently not yet fully understood. To close this knowledge gap, we conducted an integrated population physiologically-based pharmacokinetic/pharmacodynamic analysis linking changes in dabigatran exposure due to DDIs and varying degrees of renal function to the probability of experiencing an ischemic stroke or major bleeding event within 1 year. The results of our analysis suggest that coadministration of dabigatran etexilate (dabigatran prodrug) and ritonavir/cobicistat should be avoided in subjects with severe renal impairment. A 2-hour dose separation or dabigatran etexilate dose reduction to 110 mg b.i.d. (twice daily) should be considered in subjects with moderate renal impairment when coadministered with ritonavir, while the dabigatran etexilate dose should be further reduced to 75 mg b.i.d. when coadministered with cobicistat. No dabigatran etexilate dose adjustment is needed in subjects with normal renal function receiving ritonavir, but dabigatran etexilate dose reduction to 110 mg b.i.d. should be considered when coadministered with cobicistat.

Brief Report: Higher Peripheral Monocyte Activation Markers Are Associated With Smaller Frontal and Temporal Cortical Volumes in Women With HIV

BACKGROUND

Persistent inflammation is a life-long complication of HIV infection, even in virally suppressed individuals. Elevated plasma concentrations of soluble(s) CD14 and CD163 have been established as biomarkers of chronic inflammation, conferring higher risk for cognitive, neurovascular, and structural abnormalities.

METHODS

Structural magnetic resonance imaging (frontal and temporal regions) as well as plasma inflammatory biomarkers of monocyte activation (sCD14 and sCD163), general inflammation (plasma C-reactive protein, interleukin[IL]-6), and gut microbial translocation (plasma intestinal fatty acid-binding protein) were available on 38 women (25 with HIV) from the Chicago Women's Interagency HIV Study site. Partial least-squares models adjusting for relevant covariates (eg, age, education, and race) were conducted to evaluate the relationship between inflammatory biomarkers and brain volume in the overall sample and among women with HIV (WWH).

RESULTS

In the total sample, higher plasma sCD14 was associated with smaller volumes in multiple frontal and temporal lobe regions. In the WWH-only sample, sCD163 was associated with smaller volumes only in one region of the left frontal lobe. C-reactive protein, IL-6, and intestinal fatty acid-binding protein were not associated with brain volumes for either group of women.

CONCLUSIONS

Of the inflammatory monocyte markers evaluated, sCD14 was associated with smaller frontal and temporal cortical volume in the overall and WWH-only samples, while plasma sCD163 was only associated with smaller left caudal middle frontal gyrus in the WWH-only group. Validating these monocyte proteins as neurological biomarkers of structural brain deficits in a larger sample is critical for understanding HIV-associated neurobiological complications.

Tenofovir disoproxil fumarate associated nephrotoxicity: a retrospective cohort study at two referral hospitals in Namibia

INTRODUCTION

The incidence and risk factors of tenofovir disoproxil fumarate (TDF)-related renal impairment (RI) in Namibia are unknown where TDF-containing ART regimens are used as the first line for HIV.

METHODOLOGY

A retrospective cohort study among HIV-infected patients at two intermediate hospitals. A decline in estimated glomerular filtration rate (eGFR) was significant if it was ≥25% and included a change to a lower eGFR stage. New-onset RI was defined as an eGFR <50 mL/min/1.73m² .

RESULTS

10 387 patients were included: 11.4% (n = 1182) experienced the decline in eGFR. Of these, 0.6% (n = 62) migrated to eGFR stages IV and V. The incidence was 4.5 (95% CI: 4.3-4.8) per 100 patient years. RI developed in 400 patients for an incidence rate of 2.4 (95% CI: 2.2-2.6) cases per 100 patient years. Risk factors with effect sizes >2.0, for decline-in-eGFR were baseline eGFR >60 (aHR = 15.6); hyperfiltration (aHR = 5.0); and pregnancy (aHR = 2.4); while for RI, they were hyperfiltration (aHR = 4.1) and pregnancy (aHR = 29).

CONCLUSION

The incidence of decline-in-eGFR was higher than in other sub-SSA countries, but not RI. A high baseline eGFR had the greatest risk for the decline, and hyperfiltration for the RI.

HIV-1 Sanctuary Sites-the Role of Membrane-Associated Drug Transporters and Drug Metabolic Enzymes

Despite significant advances in the treatment of human immunodeficiency virus-1 (HIV) infection with highly active antiretroviral drug therapy, the persistence of the virus in cellular and anatomic reservoirs is a major obstacle preventing total HIV eradication. Viral persistence could result from a variety of contributing factors including, but not limited to, non-adherence to treatment and adverse drug reactions, latently infected cells carrying replication-competent virus, drug-drug interactions, and inadequate antiretroviral drug (ARV) concentrations reached in several anatomic sites such as the brain, testis, and gut-associated lymphoid tissues. The distribution of ARVs at specific sites of infection is primarily dependent on drug physicochemical properties and drug plasma protein binding, as well as drug efflux, influx, and metabolic processes. A thorough understanding of the functional roles of drug transporters and metabolic enzymes in the disposition of ARVs in immune cell types and tissues that are characterized as HIV reservoirs and sanctuaries is critical to overcome the challenge of suboptimal drug distribution at sites of persistent HIV infection. This review summarizes the current knowledge related to the expression and function of drug transporters and metabolic enzymes in HIV cellular and anatomic reservoirs, and their potential contribution to drug-drug interactions and insufficient drug concentration at these sites.

An update on drug-drug interactions between antiretroviral therapies and drugs of abuse in HIV systems

INTRODUCTION

While considerable progress has been made in the fight against HIV/AIDS, to date there has not been a cure, and millions of people around the world are currently living with HIV/AIDS. People living with HIV/AIDS have substance abuse disorders at higher rates than non-infected individuals, which puts them at an increased risk of drug-drug interactions.

AREAS COVERED

Potential drug-drug interactions are reviewed for a variety of potential drugs of abuse, both licit and illicit. These drugs include alcohol, cigarettes or other nicotine delivery systems, methamphetamine, cocaine, opioids, and marijuana. Potential interactions include decreased adherence, modulation of drug transporters, or modulation of metabolic enzymes. We also review the relative incidence of the use of these drugs of abuse in People living with HIV/AIDS.

EXPERT OPINION

Despite considerable improvements in outcomes, disparities in outcomes between PLWHA who use drugs of abuse, vs those who do not still exist. It is of critical necessity to improve outcomes in these patients and to work with them to stop abusing drugs of abuse.

Gene Expression: the Key to Understanding HIV-1 Infection?

Gene expression profiling of the host response to HIV infection has promised to fill the gaps in our knowledge and provide new insights toward vaccine and cure. However, despite 20 years of research, the biggest questions remained unanswered. A literature review identified 62 studies examining gene expression dysregulation in samples from individuals living with HIV. Changes in gene expression were dependent on cell/tissue type, stage of infection, viremia, and treatment status. Some cell types, notably CD4+ T cells, exhibit upregulation of cell cycle, interferon-related, and apoptosis genes consistent with depletion. Others, including CD8+ T cells and natural killer cells, exhibit perturbed function in the absence of direct infection with HIV. Dysregulation is greatest during acute infection. Differences in study design and data reporting limit comparability of existing research and do not as yet provide a coherent overview of gene expression in HIV. This review outlines the extraordinarily complex host response to HIV and offers recommendations to realize the full potential of HIV host transcriptomics.

Profiling of Drug-Metabolizing Enzymes and Transporters in Human Tissue Biopsy Samples: A Review of the Literature

Within the drug pharmacokinetics (PK)-absorption, distribution, metabolism, and excretion (ADME) research community, investigators regularly generate in vitro data sets using appropriately vendor-sourced and processed human tissue. Such data enable drug screening, the generation of kinetic parameters, extrapolation of in vitro to in vivo, as well as the modeling and simulation of drug PK. Although there are large numbers of manuscripts describing studies with deceased organ donor tissue, relatively few investigators have published studies utilizing living donor tissue biopsy samples. After a review of the available literature, it was possible to find publications describing the use of tissue biopsy samples to determine enzyme inhibition ex vivo, the study of genotype-phenotype associations, the evaluation of tissue expression profiling following an inducer, and assessment of correlations between tissue expression profiles and in vivo-derived trait measures (e.g., biomarker plasma levels and probe drug PK). Some reports described multiple single-tissue biopsies, whereas others described single multiple-organ biopsies. It is concluded that biopsy-derived data can support modeling exercises (as input data and when validating models) and enable the assessment of organ-specific changes in enzyme and transporter profiles resulting from drug interactions, disease (e.g., metabolic disease, fibrosis, inflammation, cancer, infection), age, pregnancy, organ impairment, and genotype. With the emergence of multiorgan axes (e.g., microbiome-gut-liver-kidney) and interest in remote sensing (interorgan communication), it is envisioned that there will be increased demand for single- and multiorgan tissue biopsy data to support hypothesis testing and PK-ADME model building. SIGNIFICANCE STATEMENT: Based on a review of the literature, it is apparent that profiling of human tissue biopsy samples is useful in support of pharmacokinetics (PK)-absorption, distribution, metabolism, and excretion (ADME)-related studies. With conventional tissue biopsy as precedent, it is envisioned that researchers will turn to less invasive "liquid biopsy" methods in support of ADME-related studies (e.g., profiling of plasma-derived tissue-specific nanovesicles). Generation of such multiorgan liquid biopsy data in larger numbers of subjects and at multiple study time points will provide a rich data set for modeling purposes.

In Vivo Modulation of Cervicovaginal Drug Transporters and Tissue Distribution by Film-Released Tenofovir and Darunavir for Topical Prevention of HIV-1

Clinical trials have demonstrated partial protection against HIV-1 infection by vaginal microbicide formulations based on antiretroviral (ARV) drugs. Improved formulations that will maintain sustained drug concentrations at viral target sites in the cervicovaginal mucosa are needed. We have previously demonstrated that treatment of cervicovaginal cell lines with ARV drugs can alter gene expression of drug transporters, suggesting that the mucosal disposition of ARV drugs delivered vaginally can be modulated by drug transporters. This study aimed to investigate in vivo modulation of drug transporter expression in a nonhuman primate model by tenofovir and darunavir released from film formulations. Cervicovaginal tissues were collected from drug-naïve macaques and from macaques vaginally treated with film formulations of tenofovir or darunavir. Drug release in vaginal fluid as well as drug absorption in cervicovaginal tissues and lymph nodes were verified by mass spectrometry. The effects of exposure to drugs on the expression of transporters relevant to ARV drugs were evaluated by quantitative PCR. We showed expression in cervicovaginal tissue of drug-naïve macaques of transporters important for distribution of ARV drugs, albeit at lower levels compared to human tissue for key transporters including P-glycoprotein. Concentrations of tenofovir and darunavir well above the EC₅₀ values determined in vitro were detected in vaginal fluid and vaginal tissues of macaques treated with drug-dissolving films over 24 h and were also comparable to those shown previously to modulate drug transporter expression. Accordingly, Multidrug Resistance associated Protein 2 (MRP2) in cervicovaginal tissue was upregulated by both tenofovir and darunavir. The two drugs also differentially induced and/or inhibited expression of key uptake transporters for reverse transcriptase inhibitors and protease inhibitors. The lower expression of key transporters in macaques may result in increased retention of ARV drugs at the simian cervicovaginal mucosa compared to the human mucosa and has implications for translation of preclinical data. Modulation of drug transporter expression by tenofovir and darunavir points to the potential benefit of MRP2 inhibition to increase ARV drug penetration through the cervicovaginal epithelium.

Raltegravir pharmacokinetics before and during treatment with ombitasvir, paritaprevir/ritonavir plus dasabuvir in adults with human immunodeficiency virus-1 and hepatitis C virus coinfection: AIDS Clinical Trials Group sub-study A5334s

AIMS

AIDS Clinical Trials Group study A5334s evaluated the pharmacokinetics of raltegravir before and during combined administration of ombitasvir, paritaprevir/ritonavir, plus dasabuvir (OBV/PTV/r + DSV) and weight-based ribavirin in human immunodeficiency virus (HIV) and hepatitis C virus (HCV) coinfected adults. The pharmacokinetics of OBV/PTV/r + DSV during raltegravir coadministration were also characterized.

METHODS

Adults living with HIV/HCV coinfection receiving steady-state raltegravir (400 mg twice daily) with 2 nucleos(t)ide analogues were enrolled. Pharmacokinetics of raltegravir were assessed prior to HCV therapy, and 4 weeks later following initiation of OBV/PTV/r (25/150/100 mg) once daily + DSV (250 mg) twice daily. Geometric mean ratios (GMRs) and 90% confidence intervals (CIs) were used to compare the following: raltegravir pharmacokinetics with HCV therapy (week 4) vs before HCV therapy (week 0); OBV/PTV/r and DSV pharmacokinetics vs historical healthy controls; raltegravir pharmacokinetics at week 0 vs historical control adults living with HIV.

RESULTS

Eight of 11 participants had decreased raltegravir exposures after initiation of HCV therapy. The GMRs (90% CI) for maximum concentration and area under the concentration-time curve of raltegravir with vs without HCV therapy were 0.68 (0.38-1.19) and 0.82 (0.58-1.17), respectively. Comparing OBV/PTV/r pharmacokinetics in healthy controls, A5334s study participants demonstrated generally lower maximum concentration and area under the concentration-time curve values by 41-82% and 4-73%, respectively. Raltegravir exposures tended to be higher in A5334s study participants compared to adults living with HIV.

CONCLUSIONS

The majority of participants' plasma raltegravir exposures were lower after initiation of HCV therapy in coinfected adults; however, confidence intervals were wide.

PPARα-targeted mitochondrial bioenergetics mediate repair of intestinal barriers at the host-microbe intersection during SIV infection

Our study has identified that impaired peroxisome proliferator-activated receptor-α (PPARα) signaling and associated mitochondrial dysfunction is an important underlying mechanism for prolonged leaky gut barriers in HIV and Simian immunodeficiency virus (SIV) infections despite antiretroviral therapy. Using the intestinal loop model in SIV-infected rhesus macaques, we found rapid repair of gut epithelial barriers within 5 h of administering Lactobacillus plantarum into virally inflamed gut. The rapid recovery was driven by PPARα activation and occurred independent of mucosal CD4⁺ T cell recovery, highlighting a metabolic repair pathway that can be targeted for epithelial repair prior to complete immune recovery. Our findings provide translational insights into restoring gut mucosal immunity and function, both of which are essential to enable HIV cure efforts.

Chronic gut inflammatory diseases are associated with disruption of intestinal epithelial barriers and impaired mucosal immunity. HIV-1 (HIV) causes depletion of mucosal CD4⁺ T cells early in infection and disruption of gut epithelium, resulting in chronic inflammation and immunodeficiency. Although antiretroviral therapy (ART) is effective in suppressing viral replication, it is incapable of restoring the “leaky gut,” which poses an impediment for HIV cure efforts. Strategies are needed for rapid repair of the epithelium to protect intestinal microenvironments and immunity in inflamed gut. Using an in vivo nonhuman primate intestinal loop model of HIV/AIDS, we identified the pathogenic mechanism underlying sustained disruption of gut epithelium and explored rapid repair of gut epithelium at the intersection of microbial metabolism. Molecular, immunological, and metabolomic analyses revealed marked loss of peroxisomal proliferator-activated receptor-α (PPARα) signaling, predominant impairment of mitochondrial function, and epithelial disruption both in vivo and in vitro. To elucidate pathways regulating intestinal epithelial integrity, we introduced probiotic Lactobacillus plantarum into Simian immunodeficiency virus (SIV)-inflamed intestinal lumen. Rapid recovery of the epithelium occurred within 5 h of L. plantarum administration, independent of mucosal CD4⁺ T cell recovery, and in the absence of ART. This intestinal barrier repair was driven by L. plantarum-induced PPARα activation and restoration of mitochondrial structure and fatty acid β-oxidation. Our data highlight the critical role of PPARα at the intersection between microbial metabolism and epithelial repair in virally inflamed gut and as a potential mitochondrial target for restoring gut barriers in other infectious or gut inflammatory diseases.

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.

Tobacco and Antiretrovirals Modulate Transporter, Metabolic Enzyme, and Antioxidant Enzyme Expression and Function in Polarized Macrophages

BACKGROUND

Cigarette smoking increases systemic oxidative stress, inflammation, and viral replication in individuals with HIV. Macrophages are infected during HIV infection and serve as an important reservoir throughout the process. Macrophages exist in two phenotypes, the classically activated M1 macrophage and alternatively activated M2 macrophage. The expression of drug efflux transporters and metabolic enzymes, which have direct effects on intracellular drug concentrations, differ between the pro-inflammatory M1 macrophage and the anti-inflammatory M2 macrophage.

OBJECTIVE

To further explain the role of tobacco use in worsened outcomes in the HIV + population receiving antiretroviral therapy.

METHODS

Western blotting was used to examine macrophage polarization and expression of drug efflux transporters, CYP enzymes, and antioxidant enzymes. The arginase assay was used to measure arginase activity. Cytokine production was measured using the human multiplex inflammatory cytokine assay kit. The 8-OHdG DNA Damage Quantification Direct Kit was used to quantify DNA damage. Viral replication under the influence of tobacco and antiretroviral drug use was measured by p24 Elisa.

RESULTS

We observed phenotypic shifts from M1 to M2 with both individual and combination treatments with cigarette smoke condensate and the protease inhibitor antiretroviral drug lopinavir. These shifts lead to changes in cytokine production, the expression of CYP enzymes, anti-oxidant enzymes, and drug efflux transporters, as well as changes in viral replication.

CONCLUSION

This data suggest a mechanism by which tobacco use impairs HIV antiretroviral therapy to increase intracellular drug concentrations in this important cellular reservoir.

Heterogeneous antiretroviral drug distribution and HIV/SHIV detection in the gut of three species

HIV replication within tissues may increase in response to a reduced exposure to antiretroviral drugs. Traditional approaches to measuring drug concentrations in tissues are unable to characterize a heterogeneous drug distribution. Here, we used mass spectrometry imaging (MSI) to visualize the distribution of six HIV antiretroviral drugs in gut tissue sections from three species (two strains of humanized mice, macaques, and humans). We measured drug concentrations in proximity to CD3+ T cells that are targeted by HIV, as well as expression of HIV or SHIV RNA and expression of the MDR1 drug efflux transporter in gut tissue from HIV-infected humanized mice, SHIV-infected macaques, and HIV-infected humans treated with combination antiretroviral drug therapy. Serial 10-μm sections of snap-frozen ileal and rectal tissue were analyzed by MSI for CD3+ T cells and MDR1 efflux transporter expression by immunofluorescence and immunohistochemistry, respectively. The tissue slices were analyzed for HIV/SHIV RNA expression by in situ hybridization and for antiretroviral drug concentrations by liquid chromatography-mass spectrometry. The gastrointestinal tissue distribution of the six drugs was heterogeneous. Fifty percent to 60% of CD3+ T cells did not colocalize with detectable drug concentrations in the gut tissue. In all three species, up to 90% of HIV/SHIV RNA was found to be expressed in gut tissue with no exposure to drug. These data suggest that there may be gut regions with little to no exposure to antiretroviral drugs, which may result in low-level HIV replication contributing to HIV persistence.

Disease-Associated Changes in Drug Transporters May Impact the Pharmacokinetics and/or Toxicity of Drugs: A White Paper From the International Transporter Consortium

Drug transporters are critically important for the absorption, distribution, metabolism, and excretion (ADME) of many drugs and endogenous compounds. Therefore, disruption of these pathways by inhibition, induction, genetic polymorphisms, or disease can have profound effects on overall physiology, drug pharmacokinetics, drug efficacy, and toxicity. This white paper provides a review of changes in transporter function associated with acute and chronic disease states, describes regulatory pathways affecting transporter expression, and identifies opportunities to advance the field.

HIV RNA persists in rectal tissue despite rapid plasma virologic suppression with dolutegravir-based therapy

OBJECTIVES

Despite plasma virologic suppression with antiretroviral therapy (ART), HIV persists in gut tissue. The objectives of this study were to compare plasma and rectal tissue HIV RNA dynamics and to assess relationships with dolutegravir (DTG) plasma and tissue concentrations.

DESIGN

A longitudinal cohort study of HIV-infected treatment-naïve individuals initiating DTG-based ART was conducted over 12 weeks with plasma and rectal tissue sampling (Clinicaltrials.gov:NCT02924389).

METHODS

HIV RNA and DTG concentrations were quantified in plasma and rectal tissue samples collected pre-ART (baseline) and post-ART at weeks 2, 6, and 12 using Abbott Real-Time HIV-1 assays and high-performance liquid chromatography tandem mass spectroscopy, respectively. Relationships between rectal tissue RNA and DTG concentrations were modeled using binary logistic regression, controlling for repeated measures.

RESULTS

Twelve participants were enrolled: six (50.0%) women, nine (75.0%) black, median age 42.0 years (Q1 31.2, Q3 52.0). All attained plasma virologic suppression by week 6. 11 of 12 (91.7%) had detectable rectal tissue HIV RNA at baseline, and only three of 11 (27.3%) achieved rectal tissue virologic suppression at any time-point. Compared with rectal tissue nonsuppressors, three of three (100.0%) of rectal tissue suppressors were women, had higher BMI, 35.9 kg/m (range 24.9-38.5) versus 20.6 (17.7-29.9), P = 0.05, and lower baseline log plasma HIV RNA: 3.7 copies/ml (range 3.6-4.4) versus 4.7 (3.8-5.4), P = 0.02. No significant relationships between rectal tissue RNA suppression and DTG concentrations were seen.

CONCLUSION

Rectal tissue HIV RNA persisted in most participants and was not predicted by DTG concentrations. Impact of host factors, particularly sex, on tissue HIV viral dynamics warrants further exploration.

No Clinical Impact of CYP3A5 Gene Polymorphisms on the Pharmacokinetics and/or Efficacy of Maraviroc in Healthy Volunteers and HIV-1-Infected Subjects

Maraviroc is a C-C chemokine receptor type-5 antagonist approved for the treatment of HIV-1. Previous studies show that cytochrome P450 3A5 (CYP3A5) plays a role in maraviroc metabolism. CYP3A5 is subject to a genetic polymorphism. The presence of 2 functional alleles (CYP3A5*1/*1) confers the extensive metabolism phenotype, which is rare in whites but common in blacks. The effect of CYP3A5 genotype on maraviroc and/or metabolite pharmacokinetics was evaluated in 2 clinical studies: a post hoc analysis from a phase 2b/3 study (NCT00098293) conducted in 494 HIV-1-infected subjects (study 1) in which the impact on maraviroc efficacy in 303 subjects was also assessed, and a study conducted in 47 healthy volunteers (study 2). In study 2 (NCT02625207), extensive metabolizers had 26% to 37% lower mean area under the concentration-time curve compared with poor metabolizers (no CYP3A5*1 alleles). This effect diminished to 17% in the presence of potent CYP3A inhibition. The effect of CYP3A5 genotype was greatest in the formation of the metabolite (1S,2S)-2-hydroxymaraviroc. In study 1, the CYP3A5*1/*1 genotype unexpectedly had higher maraviroc area under the curve predictions (20%) compared with those with no CYP3A5*1 alleles. The reason for this disparity remains unclear. The proportions of subjects with viral loads <50 and <400 copies/mL for maraviroc were comparable among all 3 CYP3A5 genotypes. In both studies maraviroc exposures were in the range of near-maximal viral inhibition in the majority of subjects. These results demonstrate that although CYP3A5 contributes to the metabolism of maraviroc, CYP3A5 genotype does not affect the clinical response to maraviroc in combination treatment of HIV-1 infection at approved doses.

Potential neuroprotective role of astroglial exosomes against smoking-induced oxidative stress and HIV-1 replication in the central nervous system

INTRODUCTION

HIV-1-infected smokers are at risk of oxidative damage to neuronal cells in the central nervous system by both HIV-1 and cigarette smoke. Since neurons have a weak antioxidant defense system, they mostly depend on glial cells, particularly astrocytes, for protection against oxidative damage and neurotoxicity. Astrocytes augment the neuronal antioxidant system by supplying cysteine-containing products for glutathione synthesis, antioxidant enzymes such as SOD and catalase, glucose for antioxidant regeneration via the pentose-phosphate pathway, and by recycling of ascorbic acid. Areas covered: The transport of antioxidants and energy substrates from astrocytes to neurons could possibly occur via extracellular nanovesicles called exosomes. This review highlights the neuroprotective potential of exosomes derived from astrocytes against smoking-induced oxidative stress, HIV-1 replication, and subsequent neurotoxicity observed in HIV-1-positive smokers. Expert opinion: During stress conditions, the antioxidants released from astrocytes either via extracellular fluid or exosomes to neurons may not be sufficient to provide neuroprotection. Therefore, we put forward a novel strategy to combat oxidative stress in the central nervous system, using synthetically developed exosomes loaded with antioxidants such as glutathione and the anti-aging protein Klotho.

Pharmacokinetic Considerations for Combining Antiretroviral Therapy, Direct-Acting Antiviral Agents for Hepatitis C Virus, and Addiction Treatment Medications

There are many factors that can affect the pharmacokinetics (PK) of drugs. Pathophysiological changes from disease states can alter the mechanisms that control the PK of antiretrovirals (ARVs), direct-acting antivirals (DAAs), and addiction treatment medications. Drug-drug interaction pathways of certain ARVs and DAAs can be very complex, with agents being substrates, inhibitors, or inducers of multiple metabolic and transporter pathways. Buprenorphine and methadone may be used in HIV- and hepatitis C virus (HCV)-infected patients and may also be affected by drug interactions. Current research is focused on novel PK analyses, which aim to describe the PK of agents within organs that host the infection of interest, such as within hepatocytes during treatment for HCV. Modeling techniques allow for the prediction of drug PK in specific organs and the plasma compartment. This review will provide a summary of these areas while exploring PK considerations for ARVs, DAAs, and addiction treatment medications.

Inflammation investigated as a source of pharmacokinetic variability of atazanavir in AIDS Clinical Trials Group protocol A5224s

BACKGROUND

Inflammation is associated with the downregulation of drug metabolizing enzymes and transporters. Thus, we investigated the chronic inflammatory state associated with HIV infection as a source of pharmacokinetic variability of atazanavir. We also explored the association of total bilirubin concentrations with markers of inflammation and endothelial activation.

METHODS

Apparent oral clearance (CL/F) of atazanavir was estimated from plasma samples collected from participants in AIDS Clinical Trials Group Study A5202. Several inflammatory and endothelial activation biomarkers were measured at baseline and weeks 24 and 96 as part of metabolic substudy A5224s: high-sensitivity C-reactive protein (hsCRP), interleukin-6, tumour necrosis factor-α and its soluble receptors, soluble vascular cellular and intracellular adhesion molecules and total bilirubin. Statistical analysis was performed by a matrix of correlation coefficients between atazanavir CL/F and biomarker concentrations measured at week 24. The correlation between atazanavir clearance and percentage change in bilirubin from baseline to weeks 24 and 96, and between biomarkers and bilirubin concentrations at each week were also evaluated.

RESULTS

Among 107 participants, there were no significant correlations observed between atazanavir CL/F and inflammatory and endothelial activation biomarkers measured at week 24 (P≥0.24). As expected, bilirubin increased with increasing exposure to atazanavir (rho=-0.25, P=0.01). Bilirubin concentrations were inversely correlated (P<0.01) with each of the biomarkers except hsCRP.

CONCLUSIONS

Atazanavir CL/F did not correlate with the inflammatory biomarkers changes. Inflammatory-mediated inhibition of cytochrome P450 3A may have been attenuated due to atazanavir-associated increases of bilirubin, which has known anti-inflammatory properties.

Differential Influence of the Antiretroviral Pharmacokinetic Enhancers Ritonavir and Cobicistat on Intestinal P-Glycoprotein Transport and the Pharmacokinetic/Pharmacodynamic Disposition of Dabigatran

Dabigatran etexilate (DE) is a P-glycoprotein (P-gp) probe substrate, and its active anticoagulant moiety, dabigatran, is a substrate of the multidrug and toxin extrusion protein-1 (MATE-1) transporter. The antiretroviral pharmacokinetic enhancers, ritonavir and cobicistat, inhibit both these transporters. Healthy volunteers received single doses of DE at 150 mg alone, followed by ritonavir at 100 mg or cobicistat at 150 mg daily for 2 weeks. DE was then given 2 h before ritonavir or cobicistat. One week later, DE was given simultaneously with ritonavir or cobicistat. No significant increases in dabigatran pharmacokinetic (PK) exposure or thrombin time (TT) measures were observed with the simultaneous administration of ritonavir. Separated administration of ritonavir resulted in a mean decrease in dabigatran PK exposure of 29% (90% confidence interval [CI], 18 to 40%) but did not significantly change TT measures. However, cobicistat increased dabigatran PK exposure (area under the concentration-versus-time curve from time zero to infinity and maximum plasma concentration) by 127% each (90% CI, 81 to 173% and 59 to 196%, respectively) and increased TT measures (33% for the area-under-the-effect curve from time zero to 24 h [90% CI, 22 to 44%] and 51% for TT at 24 h [90% CI, 22 to 78%]) when given simultaneously with dabigatran. Similar increases were observed when cobicistat was administered separately by 2 h from the administration of dabigatran. In all comparisons, no significant increase in the dabigatran elimination half-life was observed. Therefore, it is likely safe to coadminister ritonavir with DE, while there is a potential need for reduced dosing and prudent clinical monitoring with the coadministration of cobicistat due to the greater net inhibition of intestinal P-gp transport and increased bioavailability. (This study has been registered at ClinicalTrials.gov under identifier NCT01896622.).

Decreased Absorption of Dolutegravir and Tenofovir Disoproxil Fumarate, But Not Emtricitabine, in an HIV-Infected Patient Following Oral and Jejunostomy-Tube Administration

The use of enteral feeding tubes to administer antiretroviral medications is necessary in certain patients with human immunodeficiency virus (HIV) infection. However, adequacy of drug exposures after these administration routes are largely unknown, making dosing recommendations and the attainment of viral suppression challenging in this patient population. This report describes a patient with advanced HIV infection and a complicated medical history including long-term intractable nausea/vomiting necessitating antiretroviral medication administration via a Roux-en-Y jejunostomy (J)-tube. Pharmacokinetic assessments were performed to compare differences in antiretroviral drug absorption and plasma exposure following oral and J-tube administration of dolutegravir, tenofovir disoproxil fumarate, and emtricitabine. Results were also compared with published pharmacokinetic data in HIV-infected individuals. Exposure to dolutegravir and tenofovir were similar between J-tube and oral administration routes, whereas emtricitabine exposure was 38% lower when administered via J-tube. However, in comparison with reference data in HIV-infected individuals taking these medications orally, exposure to dolutegravir and tenofovir was 75-76% and 55-61% lower, respectively, following both routes of administration. Emtricitabine exposure was similar to and 71% higher than reference data following J-tube and oral administration, respectively. This report highlights the importance of performing pharmacokinetic assessments in patients with the potential for impaired drug absorption to ensure antiretroviral treatment success.

HIV Persistence in Gut-Associated Lymphoid Tissues: Pharmacological Challenges and Opportunities

An increasing amount of evidence suggests that HIV replication persists in gut-associated lymphoid tissues (GALT), despite treatment with combination antiretroviral therapy (cART). Residual replication in this compartment may propagate infection at other sites in the body and contribute to sustained immune dysregulation and delayed immune recovery. Therefore, it is important to focus efforts on eliminating residual replication at this site. There are several challenges to accomplishing this goal, including low antiretroviral (ARV) exposure at specific tissue locations within GALT, which might be overcome by using the tools of clinical pharmacology. Here, we summarize the evidence for GALT as a site of residual HIV replication, highlight the consequences of persistent infection in tissues, identify current pharmacologic knowledge of drug exposure in GALT, define the challenges that hinder eradication from this site, and propose several avenues for pharmacologic intervention.

Effect of Liver Disease on Hepatic Transporter Expression and Function

Liver disease can alter the disposition of xenobiotics and endogenous substances. Regulatory agencies such as the Food and Drug Administration and the European Medicines Evaluation Agency recommend, if possible, studying the effect of liver disease on drugs under development to guide specific dose recommendations in these patients. Although extensive research has been conducted to characterize the effect of liver disease on drug-metabolizing enzymes, emerging data have implicated that the expression and function of hepatobiliary transport proteins also are altered in liver disease. This review summarizes recent developments in the field, which may have implications for understanding altered disposition, safety, and efficacy of new and existing drugs. A brief review of liver physiology and hepatic transporter localization/function is provided. Then, the expression and function of hepatic transporters in cholestasis, hepatitis C infection, hepatocellular carcinoma, human immunodeficiency virus infection, nonalcoholic fatty liver disease and nonalcoholic steatohepatitis, and primary biliary cirrhosis are reviewed. In the absence of clinical data, nonclinical information in animal models is presented. This review aims to advance the understanding of altered expression and function of hepatic transporters in liver disease and the implications of such changes on drug disposition.

Inflammation and pharmacokinetics: potential implications for HIV-infection

INTRODUCTION

The physiological changes accompanying inflammation may alter the pharmacokinetics (PK) of certain medications. Individuals infected with HIV have chronically elevated inflammatory markers despite viral suppression following effective antiretroviral therapy (ART), as well as age-related inflammation. Understanding the potential clinical implications of inflammation on the PK of medications is important for understanding dose-response relationships and necessitates future research. Areas covered: An extensive literature search was carried out using PubMed and associated bibliographies to summarize the current state of knowledge regarding altered PK in response to inflammation and its application to the field of HIV. Expert opinion: Preclinical and clinical studies show that inflammation leads to a downregulation of certain drug metabolizing enzymes and both up and down regulation of transporters depending on the transporter and cell type. Decreased gastric acidity, fluid shifts, and plasma protein alterations also occur with inflammation, leading to potential absorption, distribution, and clearance changes. More research is needed including controlled PK studies to address the clinical relevance of these observations, especially in the aging HIV-infected population. Results from future studies will enable us to better predict drug concentrations in individuals with inflammation, in line with efforts to provide personalized pharmacotherapy in our healthcare system.

Mechanisms of HIV persistence in HIV reservoirs

The establishment and maintenance of HIV reservoirs that lead to persistent viremia in patients on antiretroviral drugs remains the greatest challenge of the highly active antiretroviral therapy era. Cellular reservoirs include resting memory CD4+ T lymphocytes, implicated as the major HIV reservoir, having a half-life of approximately 44 months while this is less than 6 hours for HIV in plasma. In some individuals, persistent viremia consists of invariant HIV clones not detected in circulating resting CD4+ T lymphocytes suggesting other possible sources of residual viremia. Some anatomical reservoirs that may harbor such cells include the brain and the central nervous system, the gastrointestinal tract and the gut-associated lymphoid tissue and other lymphoid organs, and the genital tract. The presence of immune cells and other HIV susceptible cells, occurring in differing compositions in anatomical reservoirs, coupled with variable and poor drug penetration that results in suboptimal drug concentrations in some sites, are all likely factors that fuel the continued low-level replication and persistent viremia during treatment. Latently, HIV-infected CD4+ T cells harboring replication-competent virus, HIV cell-to-cell spread, and HIV-infected T cell homeostatic proliferation due to chronic immune activation represent further drivers of this persistent HIV viremia during highly active antiretroviral therapy.

ABCG2/BCRP: Specific and Nonspecific Modulators

Multidrug resistance (MDR) in cancer cells is the development of resistance to a variety of structurally and functionally nonrelated anticancer drugs. This phenomenon has become a major obstacle to cancer chemotherapy seriously affecting the clinical outcome. MDR is associated with increased drug efflux from cells mediated by an energy-dependent mechanism involving the ATP-binding cassette (ABC) transporters, mainly P-glycoprotein (ABCB1), the MDR-associated protein-1 (ABCC1), and the breast cancer resistance protein (ABCG2). The first two transporters have been widely studied already and reviews summarized the results. The ABCG2 protein has been a subject of intense study since its discovery as its overexpression has been detected in resistant cell lines in numerous types of human cancers. To date, a long list of modulators of ABCG2 exists and continues to increase. However, little is known about the clinical consequences of ABCG2 modulation. This makes the design of novel, potent, and nontoxic inhibitors of this efflux protein a major challenge to reverse MDR and thereby increase the success of chemotherapy. The aim of the present review is to describe and highlight specific and nonspecific modulators of ABCG2 reported to date based on the selectivity of the compounds, as many of them are effective against one or more ABC transport proteins.

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.