Induction of P-glycoprotein expression and activity by ritonavir in bovine brain microvessel endothelial cells

Pharmacokinetics of Tenofovir Alafenamide With Boosted Protease Inhibitors in Pregnant and Postpartum Women Living With HIV: Results From IMPAACT P1026s

BACKGROUND

Tenofovir alafenamide (TAF) is a key component of HIV treatment, but pharmacokinetic data supporting the use of TAF during pregnancy are limited. In this study, we report pharmacokinetic, safety, and birth outcomes for TAF 25 mg with a boosted protease inhibitor in pregnant women living with HIV.

METHODS

IMPAACT P1026s was a multicenter, nonrandomized, open-label, phase IV prospective study. Pregnant women living with HIV receiving TAF 25 mg with a boosted protease inhibitor were eligible. Intensive pharmacokinetic assessments were performed during the second and third trimesters and 6-12 weeks postpartum. Maternal and cord blood samples were collected at delivery. Infant washout samples were collected through 5-9 days postbirth. Comparisons of paired pharmacokinetic data between pregnancy and postpartum were made using geometric mean ratios (GMR) [90% confidence intervals (CIs)] and Wilcoxon signed-rank tests with P < 0.10 considered significant.

RESULTS

Twenty-nine women were enrolled from the United States (median age 31 years and weight 84.5 kg during the third trimester; 48% Black, 45% Hispanic/Latina). TAF AUCtau did not significantly differ in the second [GMR 0.62 (90% CI: 0.29 to 1.34); P = 0.46] or third trimester [GMR 0.94 (90% CI: 0.63 to 1.39); P = 0.50] vs. postpartum and were comparable with historical data in nonpregnant adults. TAF was only quantifiable in 2/25 maternal delivery samples and below the limit of quantification in all cord blood and infant washout samples, likely because of the short half-life of TAF.

CONCLUSION

TAF AUCtau did not significantly differ between pregnancy and postpartum. These findings provide reassurance as TAF use during pregnancy continues to expand.

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.

In vitro Models of the Blood-Brain Barrier: Tools in Translational Medicine

Medical progress has historically depended on scientific discoveries. Until recently, science was driven by technological advancements that, once translated to the clinic, fostered new treatments and interventions. More recently, technology-driven medical progress has often outpaced laboratory research. For example, intravascular devices, pacemakers for the heart and brain, spinal cord stimulators, and surgical robots are used routinely to treat a variety of diseases. The rapid expansion of science into ever more advanced molecular and genetic mechanisms of disease has often distanced laboratory-based research from day-to-day clinical realities that remain based on evidence and outcomes. A recognized reason for this hiatus is the lack of laboratory tools that recapitulate the clinical reality faced by physicians and surgeons. To overcome this, the NIH and FDA have in the recent past joined forces to support the development of a "human-on-a-chip" that will allow research scientists to perform experiments on a realistic replica when testing the effectiveness of novel experimental therapies. The development of a "human-on-a-chip" rests on the capacity to grow in vitro various organs-on-a-chip, connected with appropriate vascular supplies and nerves, and our ability to measure and perform experiments on these virtually invisible organs. One of the tissue structures to be scaled down on a chip is the human blood-brain barrier. This review gives a historical perspective on in vitro models of the BBB and summarizes the most recent 3D models that attempt to fill the gap between research modeling and patient care. We also present a summary of how these in vitro models of the BBB can be applied to study human brain diseases and their treatments. We have chosen NeuroAIDS, COVID-19, multiple sclerosis, and Alzheimer's disease as examples of in vitro model application to neurological disorders. Major insight pertaining to these illnesses as a consequence of more profound understanding of the BBB can reveal new avenues for the development of diagnostics, more efficient therapies, and definitive clarity of disease etiology and pathological progression.

Nose to brain delivery of antiretroviral drugs in the treatment of neuroAIDS

NeuroAIDS (Neuro Acquired Immunodeficiency Syndrome) or HIV (Human Immunodeficiency Virus) associated neuronal abnormality is continuing to be a significant health issue among AIDS patients even under the treatment of combined antiretroviral therapy (cART). Injury and damage to neurons of the brain are the prime causes of neuroAIDS, which happens due to the ingress of HIV by direct permeation across the blood-brain barrier (BBB) or else via peripherally infected macrophage into the central nervous system (CNS). The BBB performs as a stringent barricade for the delivery of therapeutics drugs. The intranasal route of drug administration exhibits as a non-invasive technique to bypass the BBB for the delivery of antiretroviral drugs and other active pharmaceutical ingredients inside the brain and CNS. This method is fruitful for the drugs that are unable to invade the BBB to show its action in the CNS and thus erase the demand of systemic delivery and thereby shrink systemic side effects. Drug delivery from the nose to the brain/CNS takes very less time through both olfactory and trigeminal nerves. Intranasal delivery does not require the involvement of any receptor as it occurs by an extracellular route. Nose to brain delivery also involves nasal associated lymphatic tissues (NALT) and deep cervical lymph nodes. However, very little research has been done to explore the utility of nose to brain delivery of antiretroviral drugs in the treatment of neuroAIDS. This review focuses on the potential of nasal route for the effective delivery of antiretroviral nanoformulations directly from nose to the brain.

Differential Contribution of HIV-1 Subtypes B and C to Neurological Disorders: Mechanisms and Possible Treatments

With the introduction of combinatory antiretroviral therapy, patients infected with human immunodeficiency virus type 1 (HIV-1) can live much longer than before. However, the identification of HIV-associated neurocognitive disorder (HAND), especially HIV-associated dementia in 15-20% of patients infected with HIV-1, indicates additional complexity. These disorders turn out to be subtype dependent. Recently, many studies are ongoing trying to understand how the virus induces neuronal injury which could lead to neurological dysfunction. Most of these studies are focusing on the HIV-1 release of proteins such as Tat. However, the exact role of these proteins and their involvement in neuronal degeneration remains unidentified; this is especially true since viral proteins from different HIV-1 subtypes differ in their ability to cause neuronal damage. This review describes the role of different HIV-1 subtypes, identifies probable pathways involved in neuronal damage, the contribution of different HIV-1 subtypes to the progression of HAND, and potential treatments for HAND.

Comparing Various In Vitro Prediction Methods to Assess the Potential of a Drug to Inhibit P-glycoprotein (P-gp) Transporter In Vivo

The evaluation of potential of a new molecular entity (NME) to inhibit P-glycoprotein (P-gp) in vivo is an integral part of drug development and is recommended by regulatory agencies. In this study, we compared the performance of 5 prediction methods and their associated criteria (including those from the European Medicines Agency, the US Food and Drug Administration, and the Pharmaceuticals and Medical Devices Agency of Japan) for assessing the potential of an NME to inhibit P-gp in vivo based on in vitro assessment. We collected in vitro (eg, half-maximal inhibitory concentration [IC₅₀ ], fraction unbound to plasma protein) and in vivo (eg, dose, maximum concentration, change in maximum concentration or area under the plasma concentration-time curve of the substrate digoxin) data for 50 Food and Drug Administration-approved, orally administered drug products containing 53 NMEs, from the University of Washington Metabolism and Transport Drug Interaction Database, Drugs@FDA, and PubMed. All methods yielded similar accuracy with small differences in false-negative (FN) and false-positive (FP) predictions. In addition, use of ratio of the theoretical maximum gastrointestinal concentration to IC₅₀ is sufficient for a reasonable prediction for these orally administered drugs as potential P-gp inhibitors based on our dataset. The FN and FP rates varied depending on the cut-off value for the ratio of the theoretical maximum gastrointestinal concentration/IC₅₀ . Possible reasons underlying FP and FN results from different methods should be taken into consideration to predict in vivo P-gp inhibition.

Nose-to-Brain Delivery of Antiviral Drugs: A Way to Overcome Their Active Efflux?

Although several viruses can easily infect the central nervous system (CNS), antiviral drugs often show dramatic difficulties in penetrating the brain from the bloodstream since they are substrates of active efflux transporters (AETs). These transporters, located in the physiological barriers between blood and the CNS and in macrophage membranes, are able to recognize their substrates and actively efflux them into the bloodstream. The active transporters currently known to efflux antiviral drugs are P-glycoprotein (ABCB1 or P-gp or MDR1), multidrug resistance-associated proteins (ABCC1 or MRP1, ABCC4 or MRP4, ABCC5 or MRP5), and breast cancer resistance protein (ABCG2 or BCRP). Inhibitors of AETs may be considered, but their co-administration causes serious unwanted effects. Nasal administration of antiviral drugs is therefore proposed in order to overcome the aforementioned problems, but innovative devices, formulations (thermoreversible gels, polymeric micro- and nano-particles, solid lipid microparticles, nanoemulsions), absorption enhancers (chitosan, papaverine), and mucoadhesive agents (chitosan, polyvinilpyrrolidone) are required in order to selectively target the antiviral drugs and, possibly, the AET inhibitors in the CNS. Moreover, several prodrugs of antiretroviral agents can inhibit or elude the AET systems, appearing as interesting substrates for innovative nasal formulations able to target anti-Human Immunodeficiency Virus (HIV) agents into macrophages of the CNS, which are one of the most important HIV Sanctuaries of the body.

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.

In vitro models of the blood-brain barrier: An overview of commonly used brain endothelial cell culture models and guidelines for their use

The endothelial cells lining the brain capillaries separate the blood from the brain parenchyma. The endothelial monolayer of the brain capillaries serves both as a crucial interface for exchange of nutrients, gases, and metabolites between blood and brain, and as a barrier for neurotoxic components of plasma and xenobiotics. This "blood-brain barrier" function is a major hindrance for drug uptake into the brain parenchyma. Cell culture models, based on either primary cells or immortalized brain endothelial cell lines, have been developed, in order to facilitate in vitro studies of drug transport to the brain and studies of endothelial cell biology and pathophysiology. In this review, we aim to give an overview of established in vitro blood-brain barrier models with a focus on their validation regarding a set of well-established blood-brain barrier characteristics. As an ideal cell culture model of the blood-brain barrier is yet to be developed, we also aim to give an overview of the advantages and drawbacks of the different models described.

The role of glucuronidation in drug resistance

The final therapeutic effect of a drug candidate, which is directed to a specific molecular target strongly depends on its absorption, distribution, metabolism and excretion (ADME). The disruption of at least one element of ADME may result in serious drug resistance. In this work we described the role of one element of this resistance: phase II metabolism with UDP-glucuronosyltransferases (UGTs). UGT function is the transformation of their substrates into more polar metabolites, which are better substrates for the ABC transporters, MDR1, MRP and BCRP, than the native drug. UGT-mediated drug resistance can be associated with (i) inherent overexpression of the enzyme, named intrinsic drug resistance or (ii) induced expression of the enzyme, named acquired drug resistance observed when enzyme expression is induced by the drug or other factors, as food-derived compounds. Very often this induction occurs via ligand binding receptors including AhR (aryl hydrocarbon receptor) PXR (pregnane X receptor), or other transcription factors. The effect of UGT dependent resistance is strengthened by coordinate action and also a coordinate regulation of the expression of UGTs and ABC transporters. This coupling of UGT and multidrug resistance proteins has been intensively studied, particularly in the case of antitumor treatment, when this resistance is "improved" by differences in UGT expression between tumor and healthy tissue. Multidrug resistance coordinated with glucuronidation has also been described here for drugs used in the management of epilepsy, psychiatric diseases, HIV infections, hypertension and hypercholesterolemia. Proposals to reverse UGT-mediated drug resistance should consider the endogenous functions of UGT.

Modulation of P-glycoprotein efflux pump: induction and activation as a therapeutic strategy

P-glycoprotein (P-gp) is an ATP-dependent efflux pump encoded by the MDR1 gene in humans, known to mediate multidrug resistance of neoplastic cells to cancer therapy. For several decades, P-gp inhibition has drawn many significant research efforts in an attempt to overcome this phenomenon. However, P-gp is also constitutively expressed in normal human epithelial tissues and, due to its broad substrate specificity, to its cellular polarized expression in many excretory and barrier tissues, and to its great efflux capacity, it can play a crucial role in limiting the absorption and distribution of harmful xenobiotics, by decreasing their intracellular accumulation. Such a defense mechanism can be of particular relevance at the intestinal level, by significantly reducing the intestinal absorption of the xenobiotic and, consequently, avoiding its access to the target organs. In this review, the current knowledge on this important efflux pump is summarized, and a new focus is brought on the therapeutic interest of inducing and/or activating P-gp for limiting the toxicity caused by its substrates. Several in vivo and in vitro studies validating the use of such a therapeutic strategy are discussed. An extensive literature search for reported P-gp inducers/activators and for the experimental models used in their characterization was conducted. Those studies demonstrate that effective antidotal pathways can be achieved by efficiently promoting the P-gp-mediated efflux of deleterious xenobiotics, resulting in a significant reduction in their intracellular levels and, consequently, in a significant reduction of their toxicity.

Induction of P-glycoprotein by antiretroviral drugs in human brain microvessel endothelial cells

The membrane-associated drug transporter P-glycoprotein (P-gp) plays an essential role in drug efflux from the brain. Induction of this protein at the blood-brain barrier (BBB) could further affect the ability of a drug to enter the brain. At present, P-gp induction mediated by antiretroviral drugs at the BBB has not been fully investigated. Since P-gp expression is regulated by ligand-activated nuclear receptors, i.e., human pregnane X receptor (hPXR) and human constitutive androstane receptor (hCAR), these receptors could represent potential pathways involved in P-gp induction by antiretroviral drugs. The aims of this study were (i) to determine whether antiretroviral drugs currently used in HIV pharmacotherapy are ligands for hPXR or hCAR and (ii) to examine P-gp function and expression in human brain microvessel endothelial cells treated with antiretroviral drugs identified as ligands of hPXR and/or hCAR. Luciferase reporter gene assays were performed to examine the activation of hPXR and hCAR by antiretroviral drugs. The hCMEC/D3 cell line, which is known to display several morphological and biochemical properties of the BBB in humans, was used to examine P-gp induction following 72 h of exposure to these agents. Amprenavir, atazanavir, darunavir, efavirenz, ritonavir, and lopinavir were found to activate hPXR, whereas abacavir, efavirenz, and nevirapine were found to activate hCAR. P-gp expression and function were significantly induced in hCMEC/D3 cells treated with these drugs at clinical concentrations in plasma. Together, our data suggest that P-gp induction could occur at the BBB during chronic treatment with antiretroviral drugs identified as ligands of hPXR and/or hCAR.

Role of nuclear receptors in the regulation of drug transporters in the brain

ATP-binding cassette membrane-associated drug efflux transporters and solute carrier influx transporters, expressed at the blood-brain barrier, blood-cerebrospinal fluid barrier, and in brain parenchyma, are important determinants of drug disposition in the central nervous system. Targeting the regulatory pathways that govern the expression of these transporters could provide novel approaches to selectively alter drug permeability into the brain. Nuclear receptors are ligand-activated transcription factors which regulate the gene expression of several metabolic enzymes and drug efflux/influx transporters. Although efforts have primarily been focused on investigating these regulatory pathways in peripheral organs (i.e., liver and intestine), recent findings demonstrate their significance in the brain. This review addresses the role of nuclear receptors in the regulation of drug transporter functional expression in the brain. An in-depth understanding of these pathways could guide the development of novel pharmacotherapy with either enhanced efficacy in the central nervous system or minimal associated neurotoxicity.

Inhibition of P-glycoprotein by HIV protease inhibitors increases intracellular accumulation of berberine in murine and human macrophages

BACKGROUND

HIV protease inhibitor (PI)-induced inflammatory response in macrophages is a major risk factor for cardiovascular diseases. We have previously reported that berberine (BBR), a traditional herbal medicine, prevents HIV PI-induced inflammatory response through inhibiting endoplasmic reticulum (ER) stress in macrophages. We also found that HIV PIs significantly increased the intracellular concentrations of BBR in macrophages. However, the underlying mechanisms of HIV PI-induced BBR accumulation are unknown. This study examined the role of P-glycoprotein (P-gp) in HIV PI-mediated accumulation of BBR in macrophages.

METHODOLOGY AND PRINCIPAL FINDINGS

Cultured mouse RAW264.7 macrophages, human THP-1-derived macrophages, Wild type MDCK (MDCK/WT) and human P-gp transfected (MDCK/P-gp) cells were used in this study. The intracellular concentration of BBR was determined by HPLC. The activity of P-gp was assessed by measuring digoxin and rhodamine 123 (Rh123) efflux. The interaction between P-gp and BBR or HIV PIs was predicated by Glide docking using Schrodinger program. The results indicate that P-gp contributed to the efflux of BBR in macrophages. HIV PIs significantly increased BBR concentrations in macrophages; however, BBR did not alter cellular HIV PI concentrations. Although HIV PIs did not affect P-gp expression, P-gp transport activities were significantly inhibited in HIV PI-treated macrophages. Furthermore, the molecular docking study suggests that both HIV PIs and BBR fit the binding pocket of P-gp, and HIV PIs may compete with BBR to bind P-gp.

CONCLUSION AND SIGNIFICANCE

HIV PIs increase the concentration of BBR by modulating the transport activity of P-gp in macrophages. Understanding the cellular mechanisms of potential drug-drug interactions is critical prior to applying successful combinational therapy in the clinic.

Anti-AIDS agents 89. Identification of DCX derivatives as anti-HIV and chemosensitizing dual function agents to overcome P-gp-mediated drug resistance for AIDS therapy

In this study, 19 dicamphanoyl-dihydropyranochromone (DCP) and dicamphanoyl-dihydropyranoxanthone (DCX) derivatives, previously discovered as novel anti-HIV agents, were evaluated for their potential to reverse multi-drug resistance (MDR) in a cancer cell line over-expressing P-glycoprotein (P-gp). Seven compounds fully reversed resistance to vincristine (VCR) at 4 μM, a 20-fold enhancement compared to the first generation chemosensitizer, verapamil (4 μM). The mechanism of action of DCPs and DCXs was also resolved, since the most active compounds (3, 4, and 7) significantly increased intracellular drug accumulation due, in part, to inhibiting the P-gp mediated drug efflux from cells. We conclude that DCPs (3 and 4) and DCXs (7, 11, and 17) can exhibit polypharmacologic behavior by acting as dual inhibitors of HIV replication and chemoresistance mediated by P-gp. As such, they may be useful in combination therapy to overcome P-gp-associated drug resistance for AIDS treatment.

Looking at the blood-brain barrier: molecular anatomy and possible investigation approaches

The blood-brain barrier (BBB) is a dynamic and complex interface between blood and the central nervous system that strictly controls the exchanges between the blood and brain compartments, therefore playing a key role in brain homeostasis and providing protection against many toxic compounds and pathogens. In this review, the unique properties of brain microvascular endothelial cells and intercellular junctions are examined. The specific interactions between endothelial cells and basement membrane as well as neighboring perivascular pericytes, glial cells and neurons, which altogether constitute the neurovascular unit and play an essential role in both health and function of the central nervous system, are also explored. Some relevant pathways across the endothelium, as well as mechanisms involved in the regulation of BBB permeability, and the emerging role of the BBB as a signaling interface are addressed as well. Furthermore, we summarize some of the experimental approaches that can be used to monitor BBB properties and function in a variety of conditions and have allowed recent advances in BBB knowledge. Elucidation of the molecular anatomy and dynamics of the BBB is an essential step for the development of new strategies directed to maintain or restore BBB integrity and barrier function and ultimately preserve the delicate interstitial brain environment.

Regulation of P-glycoprotein and other ABC drug transporters at the blood-brain barrier

ATP-binding cassette (ABC) transporters are important selective elements of the blood-brain barrier. They line the luminal plasma membrane of the brain capillary endothelium, facing the vascular space, and both protect the central nervous system from entry of neurotoxicants and limit the access of therapeutic drugs to the brain parenchyma. Recent studies highlight the multiple signaling pathways through which the expression and activity of P-glycoprotein and other ABC transporters are modulated in response to xenobiotics, stress and disease. The results show that increased transporter expression occurs in response to signals that activate specific transcription factors, including pregnane-X receptor, constitutive androstane receptor, nuclear factor-kappaB and activator protein-1, and that reduced transporter activity occurs rapidly and reversibly in response to signaling through Src kinase, protein kinase C and estrogen receptors. A detailed understanding of such regulation can provide the basis for improved neuroprotection and enhanced therapeutic drug delivery to the brain.

Reversal of P-glycoprotein-mediated multidrug resistance in vitro by doramectin and nemadectin

Objectives

Multidrug resistance (MDR) is a serious obstacle encountered in cancer treatment. This study was performed to explore the reversal of MDR by doramectin from the avermectin family and nemadectin belonging to the milbemycin family.

Methods

The MTT assay was used to evaluate the abilities of the two compounds to reverse drug resistance in adriamycin-resistant human breast carcinoma cells (MCF-7/adr). Intracellular accumulation of adriamycin was determined by HPLC. The effects of the two compounds on inhibiting P-glycoprotein (P-gp) efflux was demonstrated by accumulation of rhodamine 123 in MCF-7/adr cells. To investigate the mechanism of reversal by the two compounds, the expressions of P-gp and the MDR1 gene encoding P-gp were tested by flow cytometry and reverse-transcriptase PCR.

Key findings

Doramectin and nemadectin at the high dose of 8 μmol/l significantly increased the sensitivity of MCF-7/adr cells to adriamycin by 49.35- and 23.97-fold, respectively. They also increased the intracellular accumulation of adriamycin and rhodamine 123 in MCF-7/adr cells in a dose-dependent manner. Expression of both P-gp and MDR1 were down-regulated.

Conclusions

Doramectin and nemadectin are promising agents for overcoming MDR in cancer therapy. Doramectin was more potent in reversing MDR.

Impact of ATP-binding cassette transporters on human immunodeficiency virus therapy

Even though potent antiretrovirals are available against human immunodeficiency virus (HIV)-1 infection, therapy fails in a significant fraction of patients. Among the most relevant reasons for treatment failure are drug toxicity and side effects, but also the development of viral resistance towards the drugs applied. Efflux by ATP-binding cassette (ABC-) transporters represents one major mechanism influencing the pharmacokinetics of antiretroviral drugs and particularly their distribution, thus modifiying the concentration within the infected cells, that is, at the site of action. Moreover, drug-drug interactions may occur at the level of these transporters and modulate their activity or expression thus influencing the efficacy and toxicity of the substrate drugs. This review summarizes current knowledge on the interaction of antiretrovirals used for HIV-1 therapy with ABC-transporters and highlights the impact of ABC-transporters for cellular resistance and therapeutic success. Moreover, the suitability of different cell models for studying the interaction of antiretrovirals with ABC-transporters is discussed.

Concentration-dependent effects and intracellular accumulation of HIV protease inhibitors in cultured CD4 T cells and primary human lymphocytes

BACKGROUND

The intracellular and plasma concentrations of HIV protease inhibitors (HPIs) vary widely in vivo. It is unclear whether there is a concentration-dependent effect of HPIs such that at increasing concentration they may either block their own efflux (leading to 'autoboosting') or influx (leading to saturability/decreased intracellular accumulation).

METHOD

The effects of various concentrations (0-30 microM) of lopinavir, saquinavir, ritonavir and atazanavir on the accumulation of [(14)C]lopinavir, [(3)H]saquinavir, [(3)H]ritonavir and [(3)H]atazanavir, respectively, were investigated in CEM(parental), CEM(VBL) [P-glycoprotein (ABCB1) overexpressing], CEM(E1000) (MRP1 overexpressing) and in peripheral blood mononuclear cells (PBMCs). We also investigated the effects of inhibitors of ABCB1/ABCG2 (tariquidar), ABCC (MK571) and ABCC1/2 (frusemide), singly and in combination with HPIs, on cellular accumulation.

RESULTS

In all the cell lines, with increasing concentration of lopinavir, saquinavir and ritonavir, there was a significant increase in the cellular accumulation of [(14)C]lopinavir, [(3)H]saquinavir and [(3)H]ritonavir. Tariquidar, MK571 and frusemide (alone and in combination with lopinavir, saquinavir and ritonavir) significantly increased the accumulation of [(14)C]lopinavir, [(3)H]saquinavir and [(3)H]ritonavir. Ritonavir (alone or in combination with tariquidar) decreased the intracellular accumulation of [(3)H]ritonavir in PBMCs. Atazanavir decreased the accumulation of [(3)H]atazanavir in a concentration-dependent manner in all of the cells tested.

CONCLUSIONS

There are complex and variable drug-specific rather than class-specific effects of the HPIs on their own accumulation.

Up-regulation of P-glycoprotein by HIV protease inhibitors in a human brain microvessel endothelial cell line

A major concern regarding the chronic administration of antiretroviral drugs is the potential for induction of drug efflux transporter expression (i.e., P-glycoprotein, P-gp) at tissue sites that can significantly affect drug distribution and treatment efficacy. Previous data have shown that the inductive effect of human immunodeficiency virus protease inhibitors (PIs) is mediated through the human orphan nuclear receptor, steroid xenobiotic receptor (SXR or hPXR). The objectives of this study were to investigate transport and inductive properties on efflux drug transporters of two PIs, atazanavir and ritonavir, at the blood-brain barrier by using a human brain microvessel endothelial cell line, hCMEC/D3. Transport properties of PIs by the drug efflux transporters P-gp and multidrug resistance protein 1 (MRP1) were assessed by measuring the cellular uptake of (3)H-atazanavir or (3)H-ritonavir in P-gp and MRP1 overexpressing cells as well as hCMEC/D3. Whereas the P-gp inhibitor, PSC833, increased atazanavir and ritonavir accumulation in hCMEC/D3 cells by 2-fold, the MRP inhibitor MK571 had no effect. P-gp, MRP1, and hPXR expression and localization were examined by Western blot analysis and immunogold cytochemistry at the electron microscope level. Treatment of hCMEC/D3 cells for 72 hr with rifampin or SR12813 (two well-established hPXR ligands) or PIs (atazanavir or ritonavir) resulted in an increase in P-gp expression by 1.8-, 6-, and 2-fold, respectively, with no effect observed for MRP1 expression. In hCMEC/D3 cells, cellular accumulation of these PIs appears to be primarily limited by P-gp efflux activity. Long-term exposure of atazanavir or ritonavir to brain microvessel endothelium may result in further limitations in brain drug permeability as a result of the up-regulation of P-gp expression and function.

Mechanism of ritonavir changes in methadone pharmacokinetics and pharmacodynamics: I. Evidence against CYP3A mediation of methadone clearance

Ritonavir diminishes methadone plasma concentrations, an effect attributed to CYP3A induction, but the actual mechanisms are unknown. We determined ritonavir effects on stereoselective methadone pharmacokinetics and clinical effects (pupillary miosis) in healthy human immunodeficiency virus-negative volunteers. Subjects received intravenous plus oral (deuterium-labeled) racemic methadone after no ritonavir, short-term (3-day) ritonavir, and steady-state ritonavir. Acute and steady-state ritonavir, respectively, caused 1.5- and 2-fold induction of systemic and apparent oral R- and S-methadone clearances. Ritonavir increased renal clearance 40-50%, and stereoselectively (S > R) increased hepatic methadone N-demethylation 50-80%, extraction twofold, and clearance twofold. Bioavailability was unchanged despite significant inhibition of intestinal P-glycoprotein. Intestinal and hepatic CYP3A was inhibited > 70%. Ritonavir shifted methadone plasma concentration-miosis curves leftward and upward. Rapid ritonavir induction of methadone clearance results from increased renal clearance and induced hepatic metabolism. Induction of methadone metabolism occurred despite profound CYP3A inhibition, suggesting no role for CYP3A in clinical methadone metabolism and clearance. Ritonavir may alter methadone pharmacodynamics.

Interactions of pluronic block copolymers on P-gp efflux activity: experience with HIV-1 protease inhibitors

The objective was to examine the influence of Pluronic block-copolymers on the interaction between the drug efflux transporter, P-glycoprotein and HIV-1 protease inhibitors (PIs). The ATPase assay determined the effect of various Pluronics on PI-stimulated P-gp ATPase activity. Cellular accumulation studies were conducted using MDCKII and LLC-PK1 cells transfected with human MDR1 to assess Pluronic modulation of PI efflux. Pluronic P85 inhibited both basal and nelfinavir-stimulated P-gp ATPase activity, while Pluronic F127 had no effect. In cell accumulation studies, Pluronic P85 restored the accumulation of nelfinavir in MDCKII-MDR1 cells while Pluronic F127 and F88 had no effect. Pluronic P85 increased saquinavir accumulation in wild-type and MDR1-transfected cells in both the MDCKII and LLC-PK1 cell models, suggesting inhibition of multiple transporters, including MRPs. In conclusion, this study provides evidence that a block-copolymer, Pluronic P85, effectively inhibits the interaction of P-gp with nelfinavir and saquinavir. These data indicate that effective inhibition of HIV-1 PI efflux by Pluronic P85 may influence the distribution of antiretroviral agents to sites protected by efflux mechanisms, such as the blood-brain barrier, and possibly increase the brain exposure of these drugs resulting in suppression of viral replication and reduction in the incidence of drug resistant mutants.

The transport of anti-HIV drugs across blood-CNS interfaces: summary of current knowledge and recommendations for further research

The advent of highly active antiretroviral therapy (HAART), which constitutes HIV protease inhibitors, nucleoside reverse transcriptase inhibitors, non-nucleoside reverse transcriptase inhibitors and nucleotide reverse transcriptase inhibitors, has dramatically reduced the morbidity and mortality associated with human immunodeficiency virus (HIV) infection in resource-rich countries. However, this disease still kills several million people each year. Though the reason for therapeutic failure is multi-factorial, an important concern is the treatment and control of HIV within the central nervous system (CNS). Due to the restricted entry of anti-HIV drugs, the brain is thought to form a viral sanctuary site. This not only results in virological resistance, but also is often associated with the development of complications such as HIV-associated dementia. The CNS delivery of anti-HIV drugs is limited by the blood–brain and blood–CSF interfaces due to a combination of restricted paracellular movement, powerful metabolic enzymes and numerous transporters including members of the ATP binding cassette (ABC) and solute carrier (SLC) superfamilies. A better appreciation of the transporters present at the brain barriers will prove a valuable milestone in understanding the limited brain penetration of anti-HIV drugs in HIV and also aid the development of new anti-HIV drugs and drug combinations, with enhanced efficacy in the CNS. This review aims to summarise current knowledge on the transport of anti-HIV drugs across the blood–brain barrier and the choroid plexus, as well as provide recommendations for future research.

Pregnane X receptor (PXR) regulates P-glycoprotein at the blood-brain barrier: functional similarities between pig and human PXR

Pharmacotherapy of central nervous system (CNS) disorders is impaired by the drug efflux transporter, P-glycoprotein, which limits drug penetration across the blood-brain barrier into the CNS. One strategy to increase brain drug levels is to modulate P-glycoprotein regulation. This approach requires understanding of the mechanisms that control transporter expression and function. One mechanism through which P-glycoprotein is regulated is the nuclear receptor, pregnane X receptor (PXR). Xenobiotics including drugs activate PXR and induce P-glycoprotein, which potentially affects pharmacokinetics/pharmacodynamics of coadministered drugs. Because rodent models are not suitable to predict xenobiotic interactions with human PXR, in a porcine model, we studied functional similarities between pig and human PXR. We used brain capillary endothelial cells from pig to study the effect of PXR activation on P-glycoprotein. To activate PXR, we used the PXR ligands, rifampicin, hyperforin, and pregnenolone-16alpha-carbonitrile (PCN), and measured abcb1 mRNA with quantitative polymerase chain reaction, P-glycoprotein expression with Western blotting, and P-glycoprotein transport activity with a calcein assay. We provide first proof of principle that the human PXR ligands, rifampicin and hyperforin, but not the rodent PXR ligand, PCN, activate pig PXR at the blood-brain barrier and induce mRNA, protein expression, and transport activity of P-glycoprotein. Our data indicate functional similarities between human and pig PXR that suggest the pig model could be useful for predicting xenobiotic-PXR interactions in humans. Because PXR is crucial in controlling drug efflux transporters, our findings will contribute to a better understanding of the regulation of blood-brain barrier function, which could potentially have important clinical implications for the treatment of CNS disorders.

Comparison of ABC transporter modulation by atazanavir in lymphocytes and human brain endothelial cells: ABC transporters are involved in the atazanavir-limited passage across an in vitro human model of the blood-brain barrier

Efflux pumps, P-glycoprotein (P-gp), multidrug resistance-associated proteins (MRPs), and breast cancer resistance protein (BCRP) have been shown to extrude HIV protease inhibitors from cells. These transporters are present on many barrier sites such as the blood-brain barrier (BBB) and on many circulating cells such as lymphocytes, and could reduce protease inhibitor concentration in sanctuary or HIV-1 target sites. This study compares the potential of the antiretroviral drug atazanavir to modulate P-gp and MRP expression and function in total lymphocytes and in human fetal brain endothelial cells (HBMECs). We address the question of atazanavir transport across the human BBB. Following incubation with atazanavir, P-gp and MRP1 expression was determined by direct immunofluorescence. Transporter function was assessed by measuring fluorescent dye efflux, either with or without specific inhibitors. Atazanavir substrate properties were determined by transport quantification through a validated in vitro human BBB model. Our results show that in contrast to HBMECs, in lymphocytes, atazanavir has no effect on MRP1 and P-gp expression. However, there were overall changes in P-gp function increasing its activity in lymphocytes and HBMECs. Using the in vitro human BBB model, we confirm the interaction of atazanavir with P-gp, MRPs, and BCRP in preventing its passage across this barrier and thus its entry into the central nervous system.

TAT-conjugated nanoparticles for the CNS delivery of anti-HIV drugs

We have shown that nanoparticles (NPs) conjugated to trans-activating transcriptor (TAT) peptide bypass the efflux action of P-glycoprotein and increase the transport of the encapsulated ritonavir, a protease inhibitor (PI), across the blood-brain-barrier (BBB) to the central nervous system (CNS). A steady increase in the drug parenchyma/capillary ratio over time without disrupting the BBB integrity suggests that TAT-conjugated NPs are first immobilized in the brain vasculature prior to their transport into parenchyma. Localization of NPs in the brain parenchyma was further confirmed with histological analysis of the brain sections. The brain drug level with conjugated NPs was 800-fold higher than that with drug in solution at two weeks. Drug clearance was seen within four weeks. In conclusion, TAT-conjugated NPs enhanced the CNS bioavailability of the encapsulated PI and maintained therapeutic drug levels in the brain for a sustained period that could be effective in reducing the viral load in the CNS, which acts as a reservoir for the replicating HIV-1 virus.

Modulation of P-glycoprotein at the blood-brain barrier: opportunities to improve central nervous system pharmacotherapy

Pharmacotherapy of central nervous system (CNS) disorders (e.g., neurodegenerative diseases, epilepsy, brain cancer, and neuro-AIDS) is limited by the blood-brain barrier. P-glycoprotein, an ATP-driven, drug efflux transporter, is a critical element of that barrier. High level of expression, luminal membrane location, multispecificity, and high transport potency make P-glycoprotein a selective gatekeeper of the blood-brain barrier and thus a primary obstacle to drug delivery into the brain. As such, P-glycoprotein limits entry into the CNS for a large number of prescribed drugs, contributes to the poor success rate of CNS drug candidates, and probably contributes to patient-to-patient variability in response to CNS pharmacotherapy. Modulating P-glycoprotein could therefore improve drug delivery into the brain. Here we review the current understanding of signaling mechanisms responsible for the modulation of P-glycoprotein activity/expression at the blood-brain barrier with an emphasis on recent studies from our laboratories. Using intact brain capillaries from rats and mice, we have identified multiple extracellular and intracellular signals that regulate this transporter; several signaling pathways have been mapped. Three pathways are triggered by elements of the brain's innate immune response, one by glutamate, one by xenobiotic-nuclear receptor (pregnane X receptor) interactions, and one by elevated beta-amyloid levels. Signaling is complex, with several pathways sharing common signaling elements [tumor necrosis factor (TNF) receptor 1, endothelin (ET) B receptor, protein kinase C, and nitric-oxide synthase), suggesting a regulatory network. Several pathways include autocrine/paracrine elements, involving release of the proinflammatory cytokine, TNF-alpha, and the polypeptide hormone, ET-1. Finally, several steps in signaling are potential therapeutic targets that could be used to modulate P-glycoprotein activity in the clinic.

Alterations in the Notch4 pathway in cerebral endothelial cells by the HIV aspartyl protease inhibitor, nelfinavir

Background

Aspartyl protease inhibitors (PIs) used to treat HIV belong to an important group of drugs that influence significantly endothelial cell functioning and angiogenic capacity, although specific mechanisms are poorly understood. Recently, PIs, particularly Nelfinavir, were reported to disrupt Notch signaling in the HIV-related endothelial cell neoplasm, Kaposi's sarcoma. Given the importance of maintaining proper cerebral endothelial cell signaling at the blood brain barrier during HIV infection, we considered potential signaling pathways such as Notch, that may be vulnerable to dysregulation during exposure to PI-based anti-retroviral regimens. Notch processing by γ-secretase results in cleavage of the notch intracellular domain that travels to the nucleus to regulate expression of genes such as vascular endothelial cell growth factor and NFκB that are critical in endothelial cell functioning. Since, the effects of HIV PIs on γ-secretase substrate pathways in cerebral endothelial cell signaling have not been addressed, we sought to determine the effects of HIV PIs on Notch and amyloid precursor protein.

Results

Exposure to reported physiological levels of Saquinavir, Indinavir, Nelfinavir and Ritonavir, significantly increased reactive oxygen species in cerebral endothelial cells, but had no effect on cell survival. Likewise, PIs decreased Notch 4-protein expression, but had no effect on Notch 1 or amyloid precursor protein expression. On the other hand, only Nelfinavir increased significantly Notch 4 processing, Notch4 intracellular domain nuclear localization and the expression of notch intracellular domain targets NFκB and matrix metalloproteinase 2. Pre-treatment with the antioxidant Vitamin E prevented PI-induced reactive oxygen species generation and partially prevented Nelfinavir-induced changes in both Notch 4 processing, and cellular localization patterns. Moreover, in support of increased expression of pro-angiogenic genes after Nelfinavir treatment, Nelfinavir did not inhibit angiogenic capacity.

Conclusion

Nelfinavir affects Notch 4 processing that results in induction of expression of the pro-angiogenic genes NFκB and matrix metalloproteinase 2 in cerebral endothelial cells.