P-glycoprotein and MRP1 expression and reduced ritonavir and saquinavir accumulation in HIV-infected individuals

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.

Modulation of Multidrug Resistance Protein 1-mediated Transport Processes by the Antiviral Drug Ritonavir in Cultured Primary Astrocytes

The Multidrug Resistance Protein 1 (Mrp1) is an ATP-dependent efflux transporter and a major facilitator of drug resistance in mammalian cells during cancer and HIV therapy. In brain, Mrp1-mediated GSH export from astrocytes is the first step in the supply of GSH precursors to neurons. To reveal potential mechanisms underlying the drug-induced modulation of Mrp1-mediated transport processes, we investigated the effects of the antiviral drug ritonavir on cultured rat primary astrocytes. Ritonavir strongly stimulated the Mrp1-mediated export of glutathione (GSH) by decreasing the Km value from 200 nmol/mg to 28 nmol/mg. In contrast, ritonavir decreased the export of the other Mrp1 substrates glutathione disulfide (GSSG) and bimane-glutathione. To give explanation for these apparently contradictory observations, we performed in silico docking analysis and molecular dynamics simulations using a homology model of rat Mrp1 to predict the binding modes of ritonavir, GSH and GSSG to Mrp1. The results suggest that ritonavir binds to the hydrophilic part of the bipartite binding site of Mrp1 and thereby differently affects the binding and transport of the Mrp1 substrates. These new insights into the modulation of Mrp1-mediated export processes by ritonavir provide a new model to better understand GSH-dependent detoxification processes in brain cells.

Potential herb‒drug interactions between anti-COVID-19 drugs and traditional Chinese medicine

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread worldwide. Effective treatments against COVID-19 remain urgently in need although vaccination significantly reduces the incidence, hospitalization, and mortality. At present, antiviral drugs including Nirmatrelvir/Ritonavir (PaxlovidTM), Remdesivir, and Molnupiravir have been authorized to treat COVID-19 and become more globally available. On the other hand, traditional Chinese medicine (TCM) has been used for the treatment of epidemic diseases for a long history. Currently, various TCM formulae against COVID-19 such as Qingfei Paidu decoction, Xuanfei Baidu granule, Huashi Baidu granule, Jinhua Qinggan granule, Lianhua Qingwen capsule, and Xuebijing injection have been widely used in clinical practice in China, which may cause potential herb-drug interactions (HDIs) in patients under treatment with antiviral drugs and affect the efficacy and safety of medicines. However, information on potential HDIs between the above anti-COVID-19 drugs and TCM formulae is lacking, and thus this work seeks to summarize and highlight potential HDIs between antiviral drugs and TCM formulae against COVID-19, and especially pharmacokinetic HDIs mediated by metabolizing enzymes and/or transporters. These well-characterized HDIs could provide useful information on clinical concomitant medicine use to maximize clinical outcomes and minimize adverse and toxic effects.

Impact of P-glycoprotein on intracellular drug concentration in peripheral blood mononuclear cells and K562 cells

P-glycoprotein (P-gp) expression in lymphocytes is variable and 2-fold higher in rheumatoid arthritis (RA) patients with treatment resistance than in healthy subjects. To date the information on P-gp-mediated drug interaction in lymphocyte is limited. We analyzed the importance on P-gp in lymphocytes using peripheral blood mononuclear cells (PBMCs) together with K562, K562/Adr, and K562/Vin cells, which have various P-gp levels, as cell models, and dexamethasone, nintedanib and apafant as weak to good P-gp substrates. P-gp levels in K562, K562/Adr, and K562/Vin cells were 0.3-, 20-, and 106-fold of healthy PBMCs, respectively. While cell accumulation of apafant and nintedanib decreased in all cells with increasing P-gp levels, dexamethasone accumulation in K562/Adr was comparable to that in healthy PBMCs and K562 cells. Cell accumulations of substrates in cells with low P-gp expression were not significantly changed by the P-gp inhibitors at therapeutic concentrations. However, accumulation increased to 1.4-fold at highest in K562/Adr cells with higher P-gp expression than in PBMCs of the RA patients. These results suggest P-gp controls the cellular concentration of P-gp substrates in PBMCs or K562 cells but cellular concentration of a weak P-gp substrate would not be apparently affected even in cells with a sufficient P-gp expression.

Dysfunction of ABC transporters at the blood-brain barrier: Role in neurological disorders

ABC (ATP-binding cassette) transporters represent one of the largest and most diverse superfamily of proteins in living species, playing an important role in many biological processes such as cell homeostasis, cell signaling, drug metabolism and nutrient uptake. Moreover, using the energy generated from ATP hydrolysis, they mediate the efflux of endogenous and exogenous substrates from inside the cells, thereby reducing their intracellular accumulation. At present, 48 ABC transporters have been identified in humans, which were classified into 7 different subfamilies (A to G) according to their phylogenetic analysis. Nevertheless, the most studied members with importance in drug therapeutic efficacy and toxicity include P-glycoprotein (P-gp), a member of the ABCB subfamily, the multidrug-associated proteins (MPRs), members of the ABCC subfamily, and breast cancer resistance protein (BCRP), a member of the ABCG subfamily. They exhibit ubiquitous expression throughout the human body, with a special relevance in barrier tissues like the blood-brain barrier (BBB). At this level, they play a physiological function in tissue protection by reducing or limiting the brain accumulation of neurotoxins. Furthermore, dysfunction of ABC transporters, at expression and/or activity level, has been associated with many neurological diseases, including epilepsy, multiple sclerosis, Alzheimer's disease, and amyotrophic lateral sclerosis. Additionally, these transporters are strikingly associated with the pharmacoresistance to central nervous system (CNS) acting drugs, because they contribute to the decrease in drug bioavailability. This article reviews the signaling pathways that regulate the expression and activity of P-gp, BCRP and MRPs subfamilies of transporters, with particular attention at the BBB level, and their mis-regulation in neurological disorders.

In vitro characterization of ritonavir formulations and correlation to in vivo performance in dogs

Ritonavir (RTV) is a weakly basic drug with a pH-dependent solubility. In vitro characterization of dissolution and supersaturation behaviors of three PEG-8000 based amorphous solid dispersions (ASD) and a physical blend (PB) with crystalline drug were performed in the biomimetic media (e.g., FaSSGF, FaSSIF, FaSSIF-V2). A two-stage dissolution test and a biphasic dissolution-partition test at the small scale (referred as to biphasic test) were employed with intention to examine the in vitro and in vivo relationship (IVIVR) with retrospective PK data in dog model. The two-stage dissolution test revealed a high degree of supersaturation of RTV from these ASDs accompanied by the occurrence of liquid-liquid phase separation (LLPS) in the biomimetic media. A rapid decrease of apparent RTV concentrations of these ASDs was associated with significant precipitation upon the pH shift of the dissolution medium, revealing the important role of "the gastric stage". In comparison, the biphasic test revealed a lower degree of supersaturation of RTV that is attributed to removal of RTV through partition into octanol, acting as "the absorption compartment". These two dissolution tests provide characterization of the supersaturation state with a complex, dynamic interplay among dissolution, precipitation and partition processes. Results of both in vitro dissolution tests are in good agreement with in vivo results in dogs. In addition, three commercial generic RTV drug products were examined by the biphasic test. Agreement was also obtained between the RTV concentrations in octanol at 3 h from these generic drug products and their corresponding relative bioavailability in dogs.

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.

Emerging Role of Proteases in the Pathogenesis of Chronic Rhinosinusitis with Nasal Polyps

Chronic rhinosinusitis with nasal polyps (CRSwNP) is a heterogeneous upper airway disease with multiple etiologies. Clinically, CRSwNP can be classified into either eosinophilic or non-eosinophilic subtypes. The eosinophilic phenotype of CRSwNP is widely thought to be highly associated with recurrence of nasal polyps or surgical failure. Epithelial cells have a crucial role in the development of Th2-biased airway diseases. Recent studies have shown that a wide range of external stimuli such as allergens and microorganisms can elicit the release of epithelial-derived Th2-driving cytokines and chemokines. Protease activity is a feature common to these multiple environmental insults and there is growing evidence for the concept that an imbalance of proteases and protease inhibitors in the epithelial barrier leads to both the initiation and maintenance of chronic eosinophilic airway inflammation. In this review, we analyze recent work on the role of proteases in the development of the sinonasal mucosal type 2 immune response with an emphasis on the molecular pathways promoting adaptive Th2 cell immunity.

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

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

ABC transporters and neuroblastoma

Neuroblastoma is the most common cancer of infancy and accounts for 15% of all pediatric oncology deaths. Survival rates of high-risk neuroblastoma remain less than 50%, with amplification of the MYCN oncogene the most important aberration associated with poor outcome. Direct transcriptional targets of MYCN include a number of ATP-binding cassette (ABC) transporters, of which ABCC1 (MRP1), ABCC3 (MRP3), and ABCC4 (MRP4) are the best characterized. These three transporter genes have been shown to be strongly prognostic of neuroblastoma outcome in primary untreated neuroblastoma. In addition to their ability to efflux a number of chemotherapeutic drugs, evidence suggests that these transporters also contribute to neuroblastoma outcome independent of any role in cytotoxic drug efflux. Endogenous substrates of ABCC1 and ABCC4 that may be potential candidates affecting neuroblastoma biology include molecules such as prostaglandins and leukotrienes. These bioactive lipid mediators have the ability to influence biological processes contributing to cancer initiation and progression, such as angiogenesis, cell signaling, inflammation, proliferation, and migration and invasion. ABCC1 and ABCC4 are thus potential targets for therapeutic suppression in high-risk neuroblastoma, and recently developed small-molecule inhibitors may be an effective strategy in treating aggressive forms of this cancer, as well as other cancers that express high levels of these transporters.

A pilot study of leukocyte expression patterns for drug metabolizing enzyme and transporter transcripts in autoimmune glomerulonephritis

OBJECTIVE

Leukocyte mRNA expression patterns of drug metabolizing enzyme genes and transporter genes that are relevant for the disposition of cyclophosphamide and mycophenolate were studied. The relationships between expression and patient-level data and pharmacokinetics were evaluated.

METHODS

The study included patients with glomerulonephritis secondary to lupus nephritis (SLE, n = 36), small vessel vasculitis (SVV, n = 35), healthy controls (HC, n = 10), and disease controls (VC, n = 5; LC, n = 5). Transcript assays targeted metabolizing enzymes (UGT1A7, UGT1A9, UGT2B7, CYP3A4, CYP2C9, CYP2B6) and transporters (ABCB1, ABCC2, ABCG2, SLCO1A2). Genotyping for specific variants was conducted. Group transcript fold-changes were evaluated. Patient level data was evaluated for transcript foldchange and disease, treatment, gender, race, and genotype.

RESULTS

Significant differences were noted in expression of UGT1A7, ABCB1, and ABCC2; for UGT1A7, SVV (0.17 ± 0.42; p < 0.05) and SLE (0.03 ± 0.1; p < 0.05) groups had lower expression than HC (0.79 ± 2.02). For ABCB1, SLE had a lower expression (0.33 ± 0.21; p < 0.05) than HCs (1 ± 0.82). For ABCG2, SVV group had a lower expression (0.17 ± 0.14; p < 0.05) than HCs (1 ± 1.82). Differences in expression of ABCC2 approached statistical significance with VC patients (2.02 ± 1.13) exhibiting higher expression than SVV patients (1.06 ± 1.11; p = 0.05). The relationships between transcript expression and patient-level data demonstrated; ABCC2 expression was different by race (1.26 ± 1.82 Caucasian versus 1.37 ± 0.86 non-Caucasian; p = 0.049) and CYP2B6 expression was different by treatment (2.07 ± 2.94 cyclophosphamide versus 0.45 ± 0.5 mycophenolate; p = 0.01).

CONCLUSIONS

The current study showed differential expression of drug metabolizing enzyme and transporter transcripts and contributes to the literature on transcript expression of drug transporters in leukocytes. The implications of altered local metabolism and transport in leukocytes may be important in autoimmune diseases and transplant patients where treatment is targeted to leukocytes.

Pharmacokinetic interactions between 20(S)-ginsenoside Rh2 and the HIV protease inhibitor ritonavir in vitro and in vivo

AIM

20(S)-Ginsenoside Rh2 (Rh2) has shown potent inhibition on P-glycoprotein (P-gp), while most HIV protease inhibitors are both substrates and inhibitors of P-gp and CYP3A4. The aim of this study was to investigate the potential pharmacokinetic interactions between Rh2 and the HIV protease inhibitor ritonavir.

METHODS

The effects of Rh2 on the cellular accumulation and transepithelial transport of ritonavir were studied in Caco-2 and MDCK-MDR1 cells. Male rats were administered Rh2 (25 or 60 mg/kg, po) or Rh2 (5 mg/kg, iv), followed by ritonavir (25 mg/kg, po). The P-gp inhibitors verapamil (20 mg/kg, po) or GF120918 (5 mg/kg, po) were used as positive controls. The concentrations of ritonavir in plasma, bile, urine, feces and tissue homogenates were analyzed using LC-MS.

RESULTS

Rh2 (10 μmol/L) significantly increased the accumulation and inhibited the efflux of ritonavir in Caco-2 and MDCK-MDR1 cells, as verapamil did. But Rh2 did not significantly alter ritonavir accumulation or transport in MDCK-WT cells. Intravenous Rh2 significantly increased the plasma exposure of ritonavir while reducing its excretion in the bile, and oral verapamil or GF120918 also increased plasma exposure of ritonavir but without changing its excretion in the bile. Interestingly, oral Rh2 at both doses did not significantly change the plasma profile of ritonavir. Moreover, oral Rh2 (25 mg/kg) significantly elevated the ritonavir concentration in the hepatic portal vein, and markedly increased its urinary excretion and tissue distribution, which might counteract the elevated absorption of ritonavir.

CONCLUSION

Rh2 inhibits the efflux of ritonavir through P-gp in vitro. The effects of Rh2 on ritonavir exposure in vivo depend on the administration route of Rh2: intravenous, but not oral, administration of Rh2 significantly increased the plasma exposure of ritonavir.

Determination of P-glycoprotein surface expression and functional ability after in vitro treatment with darunavir or raltegravir in lymphocytes of healthy donors

It has been shown that P-glycoprotein (P-gp) can greatly affect the cell uptake of antiretroviral drugs, thus hampering their access to HIV-1 replication sites. Lymphocytes are important sites of replication of HIV and target of other drugs, modification on these cells of P-gp could have an effect on pharmacokinetic of antiretrovirals and drug substrates. Blood samples from 16 healthy volunteers were used to determine the expression of P-gp on total, T and T helper lymphocytes after exposure to darunavir, a second generation protease inhibitor, and raltegravir, the first approved integrase inhibitor. Moreover, the effect of the drugs on P-gp functional activity was also studied by the rhodamine-123 efflux test. Darunavir, but not raltegravir, exposure caused a moderate, dose-dependent increment in P-gp expression in total, T and T helper lymphocytes, as demonstrated by the relative frequency of P-gp+ cells and by the amount of P-gp molecules present on cell surface. Functionally, incubation with darunavir led to a marked inhibition of P-gp activity measured by the efflux of rhodamine-123 similar to that observed by verapamil, a specific P-gp inhibitor. Raltegravir was not able to modify the efflux of rhodamine-123 level. Data show that darunavir, unlike raltegravir, may modify the expression and functionality of P-gp on human lymphocytes, thus leading to potential changes in intracellular concentrations of darunavir in patients treated with other drugs substrate of P-gp and vice versa. Our study highlights the need for studies on drug interactions via the P-gp modulation mechanism, especially with the current multi-drug regimens.

Microglial activation decreases retention of the protease inhibitor saquinavir: implications for HIV treatment

Background

Active HIV infection within the central nervous system (CNS) is confined primarily to microglia. The glial cell compartment acts as a viral reservoir behind the blood-brain barrier. It provides an additional roadblock to effective pharmacological treatment via expression of multiple drug efflux transporters, including P-glycoprotein. HIV/AIDS patients frequently suffer bacterial and viral co-infections, leading to deregulation of glial cell function and release of pro-inflammatory mediators including cytokines, chemokines, and nitric oxide.

Methods

To better define the role of inflammation in decreased HIV drug accumulation into CNS targets, accumulation of the antiretroviral saquinavir was examined in purified cultures of rodent microglia exposed to the prototypical inflammatory mediator lipopolysaccharide (LPS).

Results

[³H]-Saquinavir accumulation by microglia was rapid, and was increased up to two-fold in the presence of the specific P-glycoprotein inhibitor, PSC833. After six or 24 hours of exposure to 10 ng/ml LPS, saquinavir accumulation was decreased by up to 45%. LPS did not directly inhibit saquinavir transport, and did not affect P-glycoprotein protein expression. LPS exposure did not alter RNA and/or protein expression of other transporters including multidrug resistance-associated protein 1 and several solute carrier uptake transporters.

Conclusions

The decrease in saquinavir accumulation in microglia following treatment with LPS is likely multi-factorial, since drug accumulation was attenuated by inhibitors of NF-κβ and the MEK1/2 pathway in the microglia cell line HAPI, and in primary microglia cultures from toll-like receptor 4 deficient mice. These data provide new pharmacological insights into why microglia act as a difficult-to-treat viral sanctuary site.

HIV protease inhibitors disrupt lipid metabolism by activating endoplasmic reticulum stress and inhibiting autophagy activity in adipocytes

BACKGROUND

HIV protease inhibitors (PI) are core components of Highly Active Antiretroviral Therapy (HAART), the most effective treatment for HIV infection currently available. However, HIV PIs have now been linked to lipodystrophy and dyslipidemia, which are major risk factors for cardiovascular disease and metabolic syndrome. Our previous studies have shown that HIV PIs activate endoplasmic reticulum (ER) stress and disrupt lipid metabolism in hepatocytes and macrophages. Yet, little is known on how HIV PIs disrupt lipid metabolism in adipocytes, a major cell type involved in the pathogenesis of metabolic syndrome.

METHODOLOGY AND PRINCIPAL FINDINGS

Cultured and primary mouse adipocytes and human adipocytes were used to examine the effect of frequently used HIV PIs in the clinic, lopinavir/ritonavir, on adipocyte differentiation and further identify the underlying molecular mechanism of HIV PI-induced dysregulation of lipid metabolism in adipocytes. The results indicated that lopinavir alone or in combination with ritonavir, significantly activated the ER stress response, inhibited cell differentiation, and induced cell apoptosis in adipocytes. In addition, HIV PI-induced ER stress was closely linked to inhibition of autophagy activity. We also identified through the use of primary adipocytes of CHOP(-/-) mice that CHOP, the major transcriptional factor of the ER stress signaling pathway, is involved in lopinavir/ritonavir-induced inhibition of cell differentiation in adipocytes. In addition, lopinavir/ritonavir-induced ER stress appears to be associated with inhibition of autophagy activity in adipocytes.

CONCLUSION AND SIGNIFICANCE

Activation of ER stress and impairment of autophagy activity are involved in HIV PI-induced dysregulation of lipid metabolism in adipocytes. The key components of ER stress and autophagy signaling pathways are potential therapeutic targets for HIV PI-induced metabolic side effects in HIV patients.

Impact of food administration on lopinavir-ritonavir bioequivalence studies

A bioequivalence study in 16 Caucasian healthy volunteers (eight male, eight female), comparing plasma drug concentrations after a single oral dose of lopinavir and ritonavir (400 and 100mg, respectively), was carried out following a two-period, two-sequence, two-treatment, randomized crossover design. Formulations were given 15 min after a moderate-fat breakfast in order to diminish both the intrinsic highly-variable performance and the sex differences observed in bioequivalence trials under fasting conditions. Ninety percent confidence intervals for the Test/Reference (T/R) ratio of geometric means for area under concentration-time curve (AUC) and maximum concentration (C(MAX)), either for lopinavir or ritonavir, were within the range of 0.80-1.25. Coprandial administration of formulations not only reduced the number of subjects required for bioequivalence assessment, reducing both ethical and economic cost of the trial, but also the sex differences in the T/R ratio of means.

Expression of ATP-binding cassette membrane transporters in rodent and human sertoli cells: relevance to the permeability of antiretroviral therapy at the blood-testis barrier

The blood-testis barrier (BTB), composed primarily of Sertoli cells, is responsible for protecting developing germ cells from xenobiotic exposure. ATP-binding cassette (ABC) membrane-associated drug efflux transporters, P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and the multidrug resistance-associated proteins (Mrps), have been shown to restrict antiretroviral drug permeability at blood-tissue barriers such as the blood-brain barrier. However, it remains unclear whether these transporters are functional at the level of Sertoli cells and can regulate anti-HIV drug permeability at the BTB. This study investigated the functional expression of ABC transporters in a mouse Sertoli cell line system (TM4) and in primary cultures of human Sertoli cells (HSECs). Expression of multidrug resistance Mdr1a/1b/MDR1/P-gp, Mrp1/MRP1, and Mrp4/MRP4 is confirmed by quantitative polymerase chain reaction and immunoblotting analysis in TM4 cells and HSECs. Immunofluorescence studies revealed plasma membrane localization of P-gp, Mrp1/MRP1, and Mrp4/MRP4 in both cell systems. However, Bcrp expression and localization was only detected in rodent cells. Accumulation of 1) rhodamine-6G (R-6G), a fluorescent P-gp substrate, 2) [³H]atazanavir, a HIV protease inhibitor and known P-gp substrate, 3) 2'7'-bis-(2-carboxyethyl)-5-(and-6)carboxyfluorescein (BCECF), a fluorescent Mrp substrate, and 4) [³H]mitoxantrone, a BCRP substrate, by TM4 monolayer cells in the presence of established inhibitors demonstrates that these transporters are functional. In addition, several anti-HIV drugs significantly enhance the accumulation of R-6G, [³H]atazanavir, BCECF, and [³H]mitoxantrone by TM4 cells. This study provides the first evidence of ABC transporter expression and activity in Sertoli cells and suggests that these transporters could play an important role in restricting antiretroviral drug permeability at the BTB.

Drug transporter expression in human macrophages

Macrophages represent major cellular targets of various drugs, especially antibiotics and anti-viral drugs. Factors that may govern intracellular accumulation of drugs in these cells, especially those related to activity of drug transporters, are consequently likely important to consider. The present study was therefore designed to extensively characterize expression of solute carrier (SLC) and ATP-binding cassette (ABC) transporters in primary human macrophages generated from blood monocytes. Using quantitative polymerase chain reaction assays, these cells were found to exhibit very high or high levels of mRNA expression of concentrative nucleoside transporter (CNT) 3, equilibrative nucleoside transporter 3, monocarboxylate transporter (MCT) 1, MCT4, peptide/histidine transporter (PHT) 1, PHT2, organic anion transporting polypeptide transporter 2B1 and ABC pumps multidrug resistance protein (MRP) 1/ABCC1 and MRP3/ABCC3. By contrast, other transporters, including the efflux pump ABCB1/P-glycoprotein, were found at lower levels or were not expressed. Concomitantly, human macrophages displayed notable uptake of the MCT substrate lactate and of the CNT substrate uridine and also exhibited cellular efflux of the MRP substrate carboxy-2',7'-dichlorofluorescein. Such a functional expression of these transporters has likely to be considered with respect to cellular pharmacokinetics of drugs targeting macrophages.

Lipopolysaccharide increases the expression of multidrug resistance-associated protein 1 (MRP1) in RAW 264.7 macrophages

Multidrug resistance-associated protein 1 (MRP-1) is a ubiquitously expressed member of the ATP-binding cassette transporter family. MRP-1 is one of the primary transporters of glutathione and glutathione conjugates. This protein also transports antiretroviral therapeutics, such as HIV-1 protease inhibitors (PI). We hypothesized that inflammatory mediators that activate macrophages would modify the expression and activity of MRP-1 in macrophages. Real-time PCR assays, western blots, and calcein efflux assays were used to show that exposure of macrophage cell line RAW 264.7 to lipopolysaccharide (LPS) increased expression of MRP-1 at the levels of mRNA, protein, and functional activity. Treatment of macrophages with LPS resulted in 2-fold increases of MRP-1 expression or functional activity. LPS-mediated increases in calcein efflux were repressed by the MRP-specific inhibitor MK-571. These results suggest that the effectiveness of HIV-1 PI therapy may be compromised by the presence of opportunistic infections.

Impact of drug transporters on cellular resistance towards saquinavir and darunavir

OBJECTIVES

Highly active antiretroviral therapy is complicated by drug-drug interactions and the development of viral resistance. Drug interactions involve transporters that may critically affect the pharmacokinetics of many antiretroviral drugs and contribute to the formation of functional sanctuary sites. We therefore investigated the effect of saquinavir and darunavir on drug transporter expression and functional consequences for cellular resistance towards these compounds.

METHODS

Induction of transporters was investigated in LS180 cells over a period of 4 weeks by means of RT-PCR, and for some transporters also at the protein and functional levels. Cellular resistance was measured by growth inhibition assays.

RESULTS

Incubation with 10 µM darunavir for 1 week significantly increased mRNA expression of P-glycoprotein (P-gp/MDR1/ABCB1) 3.8-fold and of organic anion-transporting polypeptide 2B1 (SLCO2B1) 1.9-fold. In contrast, 10 µM saquinavir significantly increased mRNA expression of P-gp 5.7-fold, multidrug resistance-associated protein 1 (MRP1/ABCC1) 2.3-fold, MRP2/ABCC2 4.5-fold, MRP3/ABCC3 2.0-fold, MRP4/ABCC4 1.8-fold, MRP5/ABCC5 3.8-fold, breast cancer resistance protein (BCRP/ABCG2) 4.1-fold, SLCO1B1 4.6-fold, SLCO2B1 1.8-fold and SLCO3A1 1.8-fold. P-gp induction was also confirmed at the protein and functional levels. Induction by darunavir caused an increase in cellular resistance towards this compound, as measured in growth inhibition assays; however, saquinavir treatment did not cause reduced sensitivity of cells, indicating unchanged intracellular concentration. Hence, induction by darunavir increased drug efflux and might therefore lead to a suboptimal intracellular concentration of darunavir.

CONCLUSIONS

The study revealed substantial induction of several drug transporters by saquinavir and darunavir, possibly leading to decreased efficacy of antiretrovirals and drugs used to treat co-morbidity.

Darunavir/ritonavir and efavirenz exert differential effects on MRP1 transporter expression and function in healthy volunteers

BACKGROUND

The efflux transporter MRP1 actively transports antiretrovirals and reduces intracellular accumulation in peripheral blood mononuclear cells (PBMCs). We studied MRP1 expression and function in healthy volunteers treated with darunavir/ritonavir and efavirenz.

METHODS

Seven healthy HIV-negative volunteers were recruited. PBMCs were collected at baseline, 9 days after administration of darunavir (900 mg) and ritonavir (100 mg) once daily, 9 days after coadministration of darunavir/ritonavir and efavirenz (600 mg) once daily and 13 days after administration of efavirenz alone. MRP1 expression was measured in PBMCs using flow cytometry with fluorescein isothiocyanate-conjugated antibody against MRP1m6. MRP1 expression was also measured in CD4(+) T-cells with a phycoerythrin-conjugated antibody against CD4. MRP1 efflux function was assessed by incubating PBMCs with carboxyfluorescein diacetate (CFDA) and comparing CFDA fluorescence with and without the modulators MK571 and probenecid.

RESULTS

MRP1 expression was reduced after darunavir/ritonavir administration (geometric mean ratio [GMR] 0.58, 95% confidence interval [95% CI] 0.51-0.65; P<0.001) and darunavir/ritonavir plus efavirenz coadministration (GMR 0.74, 95% CI 0.64-0.84; P=0.001), but not after efavirenz administration alone (GMR 0.82, 95% CI 0.64-1.06; P=0.10). MRP1 protein expression was 41% higher in CD4(+) T-cells. MRP1 efflux function was increased after efavirenz administration (GMR 3.13, 95% CI 2.73-3.59; P<0.001) and darunavir/ritonavir plus efavirenz coadministration (GMR 4.35, 95% CI 3.35-5.68; P<0.001), but not after darunavir/ritonavir administration (GMR 1.06, 95% CI 0.80-1.42; P=0.42).

CONCLUSIONS

Darunavir/ritonavir and efavirenz treatment exerted differential effects on MRP1 expression and function. These effects could potentially alter antiviral activity, especially in CD4(+) T-cells.

ABC transporters in human lymphocytes: expression, activity and role, modulating factors and consequences for antiretroviral therapies

IMPORTANCE OF THE FIELD

ATP-binding cassette (ABC) transporters are a superfamily of efflux pumps that transport numerous compounds across cell membranes. These transporters are located in various human tissues including peripheral blood cells, in particular lymphocytes, and present a high variability of expression and activity. This variability may affect the intracellular concentrations and efficacy of drugs acting within lymphocytes, such as antiretroviral drugs.

AREAS COVERED IN THIS REVIEW

This review focuses on the current knowledge about the expression, activity, roles and variability of ABC drug transporters in human lymphocytes. The identified modulating factors and their impact on the intracellular pharmacokinetics and efficacy of antiretroviral drugs are also detailed.

WHAT THE READER WILL GAIN

Controversial data regarding the expression, activity and sources of variability of ABC transporters in lymphocytes are discussed. The modulating factors and their pharmacological consequences regarding antiretroviral therapies are also provided.

TAKE HOME MESSAGE

Numerous studies have reported conflicting results regarding the expression and activity of ABC drug transporters in lymphocytes. Despite these discrepancies, which may partly result from heterogeneous analytical methods, ABCC1 appears to have the highest expression in lymphocytes and may thus play a predominant role in the resistance to antiretroviral drugs, particularly to protease inhibitors.

P-glycoprotein related drug interactions: clinical importance and a consideration of disease states

IMPORTANCE OF THE FIELD

P-glycoprotein (P-gp) is the most characterized drug transporter in terms of its clinical relevance for pharmacokinetic disposition and interaction with other medicines. Clinically significant P-gp related drug interactions appear restricted to digoxin. P-gp may act as a major barrier to current and effective drug treatment in a number of diseases including cancer, AIDS, Alzheimer's and epilepsy due to its expression in tumors, lymphocytes, cell membranes of brain capillaries and the choroid plexus.

AREAS COVERED IN THIS REVIEW

This review summarizes the current understanding of P-gp structure/function, clinical importance of P-gp related drug interactions and the modulatory role this transporter may contribute towards drug efficacy in disease states such as cancer, AIDS, Alzheimer's and epilepsy.

WHAT THE READER WILL GAIN

The reader will gain an understanding that the clinical relevance of P-gp in drug interactions is limited. In certain disease states, P-gp in barrier tissues can modulate changes in regional distribution.

TAKE HOME MESSAGE

P-gp inhibition in isolation will not result in clinically important alterations in systemic exposure; however, P-gp transport may be of significance in barrier tissues (tumors, lymphocytes, brain) resulting in attenuated efficacy.

Protease inhibitors atazanavir, lopinavir and ritonavir are potent blockers, but poor substrates, of ABC transporters in a broad panel of ABC transporter-overexpressing cell lines

OBJECTIVES

A possible mechanism for HIV therapy failure is the efflux of HIV drugs from viral target cells or certain body compartments by ATP-binding cassette (ABC) transporters, allowing ongoing viral replication. Here, we investigated the interaction between protease inhibitors (PIs) and ABC transporters.

METHODS

To explore the potential blocking capacity of PIs, we exposed cells overexpressing multidrug resistance 1 P-glycoprotein (MDR1 P-gp), multidrug resistance protein 1 (MRP1) and breast cancer resistance protein (BCRP) to established cytotoxic substrates with or without one of the PIs atazanavir, lopinavir or ritonavir. Furthermore, to assess whether PIs serve as substrates, cell growth-inhibitory effects of these PIs were evaluated on cells overexpressing 1 of 11 ABC transporters and their parental counterparts.

RESULTS

Atazanavir, lopinavir and ritonavir were highly effective in reversing resistance against established substrates in cells overexpressing MDR1 P-gp and MRP1, and, to a lesser extent, BCRP. Concurrently, however, PIs appeared to be relatively poor substrates for ABC transporters. Only a moderate level of resistance to atazanavir was observed in cells overexpressing MRP6 and MRP9 [resistance factor (RF): 2.0-2.6]. Cells overexpressing MDR1 P-gp, MRP3, MRP4 and MRP5 displayed low levels of resistance to atazanavir (RF: 1.3-1.7); MRP7- and MRP9-overexpressing cells to lopinavir (RF: 1.4-1.5); and MRP9-overexpressing cells to ritonavir (RF: 1.4).

CONCLUSIONS

PIs can act as potent blockers of MDR1 P-gp, MRP1 and BCRP, but they are poor substrates for 11 ABC transporters. Consequently, ABC transporters are unlikely to play a major role in PI failure, but still may contribute to drug-specific adverse events and drug-drug interactions.

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.

The complexities of antiretroviral drug-drug interactions: role of ABC and SLC transporters

Treatment of human immunodeficiency virus (HIV) infection involves a combination of several antiviral agents belonging to different pharmacological classes. This combination is referred to as highly active antiretroviral therapy (HAART). This treatment has proved to be very effective in suppressing HIV replication, but antiretroviral drugs have complex pharmacokinetic properties involving extensive drug metabolism and transport by membrane-associated drug carriers. Combination drug therapy often introduces complex drug-drug interactions that can result in toxic or sub-therapeutic drug concentrations, compromising treatment. This review focuses on the role of ATP-binding cassette (ABC) membrane-associated efflux transporters and solute carrier (SLC) uptake transporters in antiretroviral drug disposition, and identifies clinically important antiretroviral drug-drug interactions associated with changes in drug transport.

P-glycoprotein mediates efflux transport of darunavir in human intestinal Caco-2 and ABCB1 gene-transfected renal LLC-PK1 cell lines

Darunavir (DRV) is a nonpeptidic protease inhibitor (PI) approved for the treatment of human immunodeficiency virus (HIV) infection. DRV displays potent activity against HIV strains resistant to other available PIs. Coadministration with ritonavir (RTV) improves the oral bioavailability of DRV. Inhibition of cytochrome P450 by RTV has been proposed as a mechanism for enhanced DRV bioavailability. However, interaction of these drugs with intestinal transporters has not been elucidated. This study was performed to explore the involvement of P-glycoprotein in transcellular DRV transport in monolayers of human intestinal Caco-2 and in ABCB1 multidrug resistance 1, (MDR1) gene-transfected renal LLC-PK1 (L-MDR1) cell lines. Transepithelial transport of DRV in Caco-2 cell monolayers was 2-fold greater in the basal-to-apical direction compared to that in the opposite direction. RTV had a significant inhibitory effect on the efflux transport of DRV in Caco-2 cells. The apical-to-basal DRV transport was enhanced by P-glycoprotein inhibitors, cyclosporin A and verapamil, as well as multidrug resistance-related protein (MRP/ABCC) inhibitors, probenecid and MK571. Using the L-MDR1 cell line, basal-to-apical DRV transport was much greater than in the opposite direction. Furthermore, cyclosporin A markedly inhibited the basal-to-apical DRV transport. RTV significantly increased the apical-to-basal transport of DRV in L-MDR1 cells, but reduced transport in the opposite direction. DRV inhibited P-glycoprotein-mediated efflux of calcein-acetoxymethyl ester in L-MDR1 cells with the inhibitory potency of 121 microM. These findings suggest that DRV is a substrate of P-glycoprotein and MRP, most likely MRP2. RTV appeared to inhibit P-glycoprotein, thereby enhancing the absorptive transport of DRV.

Induction of multiple drug transporters by efavirenz

Efavirenz, an important component of human immunodeficiency virus 1 (HIV-1) therapy, causes substantial drug interactions as an inducer of cytochromes and the transporter ABCB1. So far its effect on the expression of other transporters is unknown. We therefore investigated the effect of long-term exposure of cells to efavirenz on expression of a large number of important drug transporters and on cell proliferation as a surrogate of intracellular availability. LS180 cells were used as a surrogate for the major site of drug interactions and Jurkat cells were used as a surrogate for the main target cells of HIV therapy. Cells were treated with efavirenz over 4 weeks and mRNA expression of drug transporters was repeatedly quantified. After 4 weeks, efavirenz significantly up-regulated the mRNA of ABCB1, ABCG2, ABCC2, ABCC3, ABCC5, and SLCO3A1 in LS180 cells and ABCG2, ABCC1, ABCC4, ABCC5, and SLCO2B1 in Jurkat cells. However these changes in transporter expression did not influence cell proliferation indicating that intracellular efavirenz concentrations were likely not altered. Efavirenz induces mRNA expression of several drug transporters critically modulating the kinetics of other drugs. While these expressional changes will most likely not influence the efficiency of efavirenz itself, they might change the effect of other co-administered drugs.

MRP (ABCC) transporters-mediated efflux of anti-HIV drugs, saquinavir and zidovudine, from human endothelial cells

The constituents of highly active anti-retroviral therapy (HAART) include HIV-1 protease inhibitors (HPIs) and nucleoside reverse transcriptase inhibitors (NRTIs). Endothelial cell (EC) barriers, especially the blood-brain-barrier (BBB) suppresses the entry of HAART drugs to subendothelial HIV-1 reservoirs. The ATP binding cassette (ABC) transporter family members, multidrug resistant-1 (MDR-1) and multidrug resistance-associated proteins (MRPs) can efflux both HPIs and NRTIs from intracellular compartments. Using brain derived ECs from non-human sources, previous studies suggested a dominant role for MDR-1 in HAART efflux from the BBB. However, due to species variations in ABC-transporter expression, drug-efflux functions using human brain ECs need to be investigated. Furthermore, roles of ABC-transporters in drug-efflux from systemic EC barriers need to be studied. We monitored the expression of ABC-transporters in primary human ECs obtained from brain (HBMVECs), aorta (HAECs), pulmonary-artery (HPAECs), dermal-microvessel (HDMVECs) and umbilical vein (HUVECs). Gene expression for MDR-1 and MRPs (MRP-1 to MRP-5) were analyzed by reverse transcriptase polymerase chain reaction (RT-PCR). Drug efflux functions were determined by calcein retention assays. Intracellular accumulation of both 3H-saquinavir (an HPI) and 3H-zidovudine (an NRTI) were also monitored in HAECs and HBMVECs. Both assays were carried out in presence of verapamil (20-60 microM) or MK-571 (12.5-50 microM) inhibitors of MDR-1 and MRPs, respectively in presence of verapamil or MK-571. The HBMVECs expressed higher levels of MRPs than MDR-1 and only MK-571 significantly (P<0.01) suppressed calcein efflux from these cells. However, both HAECs and HPAECs showed MDR-1 and MRP expression and calcein efflux was inhibited by both verapamil and MK-571. Both inhibitors suppressed 3H-saqubinavir efflux from HAECs, but only MK-571 suppressed saquinavir efflux from HBMVECs. In both ECs, 3H-zidovudine efflux was only suppressed by MK-571. Thus, primary human ECs, especially brain derived ECs, predominantly express MRPs and their specific inhibition may enhance HAART efficacy in subendothelial HIV-1 reservoirs.

Biopharmaceutical challenges associated with drugs with low aqueous solubility--the potential impact of lipid-based formulations

The percentage of new chemical entities synthesised with low aqueous solubility and high therapeutic efficacy is growing, this presents major challenges for the drug delivery scientists. The role of physicochemical properties in identification of suitable drug candidates for oral lipid-based delivery systems is discussed. A knowledge of the interplay of physicochemical and biopharmaceutical drug properties with the physiological environment of the gastro-intestinal tract (GIT), as a prerequisite to successful formulation design, is reviewed. The importance of excipient selection with an emphasis on bioactive excipients is stressed. The need for more examples of in vitro-in vivo correlations as a means of maximizing the development potential and commercial future for lipid-based formulations, and, promoting confidence within the industry for these delivery systems is highlighted.

Transient viremia, plasma viral load, and reservoir replenishment in HIV-infected patients on antiretroviral therapy

When antiretroviral therapy (ART) is administered for long periods to HIV-1-infected patients, most achieve viral loads that are "undetectable" by standard assay methods (ie, HIV-1 RNA <50 copies/mL). Despite sustaining viral loads lower than the level of detection, a number of patients experience unexplained episodes of transient viremia or viral "blips." We propose that transient activation of the immune system by infectious agents may explain these episodes of viremia. Using 2 different mathematical models, one in which blips arise because of target cell activation and subsequent infection and another in which latent cell activation generates blips, we establish a nonlinear (power law) relationship between blip amplitude and viral load (under ART) that suggest blips should be of lower amplitude, and thus harder to detect, as increasingly potent therapy is used. This effect can be more profound than is predicted by simply lowering the baseline viral load from which blips originate. Finally, we suggest that sporadic immune activation may elevate the level of chronically infected cells and replenish viral reservoirs, including the latent cell reservoir, providing a mechanism for recurrent viral blips and low levels of viremia under ART.

Expression of adenosine triphosphate-binding cassette (ABC) drug transporters in peripheral blood cells: relevance for physiology and pharmacotherapy

Adenosine triphosphate-binding cassette (ABC)-type transport proteins were initially described for their ability to reduce intracellular concentrations of anticancer compounds, thereby conferring drug resistance. In recent years, expression of this type of proteins has also been reported in numerous cell types under physiological conditions; here, these transporters are often reported to alter systemic and local drug disposition (e.g. in the brain or the gastrointestinal tract). In this context, peripheral blood cells have also been found to express several ABC-type transporters. While erythrocytes mainly express multidrug resistance protein (MRP) 1, MRP4 and MRP5, which are discussed with regard to their involvement in glutathione homeostasis (MRP1) and in the efflux of cyclic nucleotides (MRP4 and MRP5), leukocytes also express P-glycoprotein and breast cancer resistance protein. In the latter cell types, the main function of efflux transporters may be protection against toxins, as these cells demonstrate a very high turnover rate. In platelets, only two ABC transporters have been described so far. Besides MRP1, platelets express relatively high amounts of MRP4 not only in the plasma membrane but also in the membrane of dense granules, suggesting relevance for mediator storage. In addition to its physiological function, ABC transporter expression in these structures can be of pharmacological relevance since all systemic drugs reach their targets via circulation, thereby enabling interaction of the therapeutic agent with peripheral blood cells. Moreover, both intended effects and unwanted side effects occur in peripheral blood cells, and intracellular micropharmacokinetics can be affected by these transport proteins. The present review summarises the data available on expression of ABC transport proteins in peripheral blood cells.

Antiviral activity of HIV type 1 protease inhibitors nelfinavir and indinavir in vivo is not influenced by P-glycoprotein activity on CD4+ T cells

P-glycoprotein (P-gp) can compromise the antiretroviral effect of a protease inhibitor (PI)-containing regimen for HIV-1, but can also reduce HIV-1 replication. We studied the net effect of P-gp on the intracellular HIV-1 RNA and DNA load in vivo. CD4(+) T cells were isolated from 27 HIV-1 patients (13 without and 14 with a PI-containing regimen) and subsequently sorted in CD45RO(-) (naive) and CD45RO(+) (memory) subsets with either high (P-gp(high)) or low (P-gp(low)) P-gp activity. Unspliced HIV-1 RNA and HIV-1 DNA load were determined. For each patient P-gp(high) and P-gp(low) subsets were compared. In patients on a PI-containing regimen, intracellular unspliced HIV-1 RNA was significantly lower in P-gp(high)-naive CD4(+) cells compared to P-gp(low)-naive CD4(+) cells (p = 0.04). The same trend was seen in naive CD4(+) cells of treatment naive patients. In both treated and untreated patients HIV-1 DNA levels were significantly lower in P-gp(high) than in P-gp(low) memory CD4(+) cells (p = 0.02 and p = 0.04). High cellular P-gp activity coincided with a reduced intracellular HIV-1 load in vivo, both in therapy-naive and in PI-treated patients. Therefore we conclude that the potential efflux function of P-gp on PIs may be clinically less relevant than the effect of P-gp on intracellular HIV-1 replication.

Monitoring of lopinavir and ritonavir in peripheral blood mononuclear cells, plasma, and ultrafiltrate using a selective and highly sensitive LC/MS/MS assay

For the determination of the HIV protease inhibitors lopinavir and ritonavir in human plasma, plasma ultrafiltrate, and peripheral blood mononuclear cells (PBMCs) a highly sensitive and selective method has been developed, validated, and applied to samples of a healthy volunteer. BD Vacutainer CPT and Amicon Centriplus centrifugal filter devices were used for separation of PBMCs and for ultrafiltrate generation, respectively. After liquid/liquid-extraction extracts were chromatographed isocratically within 6 min on a Jupiter Proteo column. The drugs were quantified using 2H5-saquinavir as internal standard and electrospray tandem mass spectrometry in the selected reaction monitoring mode. Limits of quantification for both analytes were 4.0 ng/mL in plasma, 0.2 ng/mL in ultrafiltrate, and 0.1 ng/cell pellet (approximately 3 x 10(6) cells) in PBMCs. The calibration ranges were linear over more than three logs with an over-all accuracy varying between 98.7% and 111.5% and an over-all precision ranging from 6.2% to 14.0% (SD batch-to-batch). After a regular oral dose of Kaletra (400 mg lopinavir, 100 mg ritonavir) analyte concentrations were detectable over a full dosing interval in plasma, ultrafiltrate, and PBMCs. The method is well suited for monitoring of free and total plasma, and intracellular lopinavir/ritonavir concentrations in samples from clinical trials.

Exon sequencing and high resolution haplotype analysis of ABC transporter genes implicated in drug resistance

BACKGROUND

The ATP-binding cassette (ABC) proteins are a superfamily of efflux pumps implicated as a mechanism for multidrug resistance in cytotoxic chemotherapy, immunosuppressive therapy, HIV and epilepsy. Genetic variation in P-glycoprotein, the product of the ABCB1 gene, is proposed to mediate de novo drug resistance, but associations between polymorphisms in ABCB1 and pharmacoresistance have produced conflicting results. Potential explanations for the inconsistency of results include inadequate characterization of gene structure, variation and linkage disequilibrium (LD) in ABCB1, as well as overlap in substrate specificity between ABCB1 and the various other drug transporters.

METHODS AND RESULTS

We undertook a fundamental analysis of gene structure, variation and LD in ABCB1 and four other drug transporter genes implicated in pharmacoresistance: ABCC1, ABCC2, ABCC5 and ABCB4. Manual annotation of the five genes revealed nine shorter alternative transcripts with new untranslated regions and one novel region of coding sequence, demonstrating that on-line annotations are incomplete. Sequencing of exons in 47 Caucasian individuals identified 75 novel single nucleotide polymorphisms (SNPs) previously undescribed in any public database, including 14 new coding sequence SNPs. Genotyping of 502 SNPs in 842 Caucasian individuals across the five genes revealed large blocks of high LD, and low haplotype diversity across all five genes that could be characterized by between 67 and 114 tagging SNPs, depending on the tagging criteria.

CONCLUSION

The study illustrates that publicly available data resources on genomic organization of genes and common variation can have important gaps and limitations, and establishes a comprehensive set of tagging SNPs for future association studies in pharmacoresistance.