Plasma Concentrations of Rosmarinic Acid in Patients on Antiretroviral Therapy: In Silico Exploration Based on Clinical Data

Rosmarinic acid (RA) is a phenolic compound with antiviral properties, often encountered in dietary supplements and herbal drugs. Data on the pharmacokinetics of RA are lacking in cases of the chronic use of supplements containing this compound, and only limited data on the metabolism and distribution of RA are available. The aim of the study was to investigate the plasma levels of RA after 12 weeks of use and determine potential interactions of RA and selected antiretroviral drugs. Patients infected with human immunodeficiency virus took a supplement containing RA for 12 weeks, after which the RA concentrations in the plasma samples were analyzed. A detailed in silico analysis was conducted in order to elucidate the potential interactions between RA and the drugs efavirenz, darunavir and raltegravir. It was found that RA can be detected in patients' plasma samples, mainly in the form of sulphoglucuronide. The potential interactions are suggested on the level of liver metabolizing enzymes and efflux P-glycoprotein, with RA competing with antiretroviral drugs as a substrate in metabolism and distribution systems. The present study suggests that the simultaneous use of RA and antiretroviral therapy (containing efavirenz, darunavir or raltegravir) may affect the plasma levels of RA after prolonged supplementation.

Coadministration of ABCB1/P-glycoprotein inhibitor elacridar improves tissue distribution of ritonavir-boosted oral cabazitaxel in mice

Developing an oral formulation for the chemotherapeutic cabazitaxel might improve its patient-friendliness, costs, and potentially exposure profile. Cabazitaxel oral availability is restricted by CYP3A-mediated first-pass metabolism, but can be substantially boosted with the CYP3A inhibitor ritonavir. We here tested whether adding the ABCB1/P-glycoprotein inhibitor elacridar to ritonavir-boosted oral cabazitaxel could further improve its tissue exposure using wild-type, CYP3A4-humanized and Abcb1a/b-/- mice. The plasma AUC0-2h of cabazitaxel was increased 2.3- and 1.9-fold in the ritonavir- and ritonavir-plus-elacridar groups of wild-type, and 10.5- and 8.8-fold in CYP3A4-humanized mice. Elacridar coadministration did not influence cabazitaxel plasma exposure. The brain-to-plasma ratio of cabazitaxel was not increased in the ritonavir group, 7.3-fold in the elacridar group and 13.4-fold in the combined booster group in wild-type mice. This was 0.4-, 4.6- and 3.6-fold in CYP3A4-humanized mice, illustrating that Abcb1 limited cabazitaxel brain exposure also during ritonavir boosting. Ritonavir itself was also a potent substrate for the Abcb1 efflux transporter, limiting its oral availability (3.3-fold) and brain penetration (10.6-fold). Both processes were fully reversed by elacridar. The tissue disposition of ritonavir-boosted oral cabazitaxel could thus be markedly enhanced by elacridar coadministration without affecting the plasma exposure. This approach should be verified in selected patient populations.

Knockout of ABC transporters by CRISPR/Cas9 contributes to reliable and accurate transporter substrate identification for drug discovery

It is essential to explore the relationship between drugs and transporters in the process of drug development. Strong background signals in nonhuman MDCK or LLC-PK1 cells and overlapping interference of inhibitors or RNAi in human Caco-2 cells mean that an ideal alternative could be to knock out specific transporter genes in Caco-2 cells. However, the application of gene knockout (KO) to Caco-2 cells is challenging because it is still inefficient to obtain rapidly growing Caco-2 subclones with double-allele KO through long-term monoclonal cultivation. Herein, CRISPR/Cas9, a low cost but more efficient and precise gene editing technology, was utilized to singly or doubly knockout the P-gp, BCRP, and MRP2 genes in Caco-2 cells. By combining this with single cell expansion, rapidly growing transporter-deficient subclones were successfully screened and established. Bidirectional transport assays with probe substrates and three protease inhibitors indicated that more reliable and detailed data could be drawn easily with these KO Caco-2 models. The six robust KO Caco-2 subclones could contribute to efficient in vitro drug transport research.

The impact of quantity of lipid based formulations with different compositions on the oral absorption of ritonavir: A trade-off between apparent solubility and permeability

In this study, the effect of the quantity of lipid-based formulations (LBFs) on the oral absorption of ritonavir (RTV), a model for poorly water-soluble drugs, was investigated. Two types of LBFs, comprising short- and medium-chain lipids (LBF-SMC) and long-chain lipids (LBF-LC) loaded with different masses of RTV, were prepared. Then, the respective LBFs were dispersed in distilled water at concentrations of 1.0, 2.0, and 3.0% w/w, which provided the same drug concentration for all formulations. When 1.0% LBF-SMC and LBF-LC were orally administered to rats, the oral absorption was significantly improved compared with that of the suspension (a reference formulation) because of enhanced solubilization of RTV in the gastrointestinal tract; however, this improvement was lower for LBF-LC than for LBF-SMC. The oral absorption decreased with increasing LBF concentration for both LBF-SMC and LBF-LC. The in vitro permeation in sequence with in vitro digestion revealed that this phenomenon was caused by a reduction in the free drug concentration in the gastrointestinal tract. Moreover, the effect of decreasing the free concentration was more remarkable for LBF-LC than for LBF-SMC because of the greater solubilization capacity of LC digestion products. These findings may be useful for designing improved drug delivery systems.

Disease-drug and drug-drug interaction in COVID-19: Risk and assessment

COVID-19 is announced as a global pandemic in 2020. Its mortality and morbidity rate are rapidly increasing, with limited medications. The emergent outbreak of COVID-19 prompted by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) keeps spreading. In this infection, a patient's immune response plays pivotal role in the pathogenesis. This inflammatory factor was shown by its mediators that, in severe cases, reach the cytokine at peaks. Hyperinflammatory state may sparks significant imbalances in transporters and drug metabolic machinery, and subsequent alteration of drug pharmacokinetics may result in unexpected therapeutic response. The present scenario has accounted for the requirement for therapeutic opportunities to relive and overcome this pandemic. Despite the diminishing developments of COVID-19, there is no drug still approved to have significant effects with no side effect on the treatment for COVID-19 patients. Based on the evidence, many antiviral and anti-inflammatory drugs have been authorized by the Food and Drug Administration (FDA) to treat the COVID-19 patients even though not knowing the possible drug-drug interactions (DDI). Remdesivir, favipiravir, and molnupiravir are deemed the most hopeful antiviral agents by improving infected patient’s health. Dexamethasone is the first known steroid medicine that saved the lives of seriously ill patients. Some oligopeptides and proteins have also been using. The current review summarizes medication updates to treat COVID-19 patients in an inflammatory state and their interaction with drug transporters and drug-metabolizing enzymes. It gives an opinion on the potential DDI that may permit the individualization of these drugs, thereby enhancing the safety and efficacy.

Characterization of P-Glycoprotein Inhibitors for Evaluating the Effect of P-Glycoprotein on the Intestinal Absorption of Drugs

For developing oral drugs, it is necessary to predict the oral absorption of new chemical entities accurately. However, it is difficult because of the involvement of efflux transporters, including P-glycoprotein (P-gp), in their absorption process. In this study, we conducted a comparative analysis on the inhibitory activities of seven P-gp inhibitors (cyclosporin A, GF120918, LY335979, XR9576, WK-X-34, VX-710, and OC144-093) to evaluate the effect of P-gp on drug absorption. GF120918, LY335979, and XR9576 significantly decreased the basal-to-apical transport of paclitaxel, a P-gp substrate, across Caco-2 cell monolayers. GF120918 also inhibited the basal-to-apical transport of mitoxantrone, a breast cancer resistance protein (BCRP) substrate, in Caco-2 cells, whereas LY335979 hardly affected the mitoxantrone transport. In addition, the absorption rate of paclitaxel after oral administration in wild-type mice was significantly increased by pretreatment with LY335979, and it was similar to that in mdr1a/1b knockout mice. Moreover, the absorption rate of topotecan, a BCRP substrate, in wild-type mice pretreated with LY335979 was similar to that in mdr1a/1b knockout mice but significantly lower than that in bcrp knockout mice. These results indicate that LY335979 has a selective inhibitory activity for P-gp, and would be useful for evaluating the contribution of P-gp to drug absorption.

Acute regulation of apical ABC transporters in the gut. Potential influence on drug bioavailability

The extensive intestinal surface offers an advantage regarding nutrient, ion and water absorptive capacity but also brings along a high exposition to xenobiotics, including drugs of therapeutic use and food contaminants. After absorption of these compounds by the enterocytes, apical ABC transporters play a key role in secreting them back to the intestinal lumen, hence acting as a transcellular barrier. Rapid and reversible modulation of their activity is a subject of increasing interest for pharmacologists. On the one hand, a decrease in transporter activity may result in increased absorption of therapeutic agents given orally. On the other hand, an increase in transporter activity would decrease their absorption and therapeutic efficacy. Although of less relevance, apical ABC transporters also contribute to disposition of drugs systemically administered. This review article summarizes the present knowledge on the mechanisms aimed to rapidly regulate the activity of the main apical ABC transporters of the gut: multidrug resistance protein 1 (MDR1), multidrug resistance-associated protein 2 (MRP2) and breast cancer resistance protein (BCRP). Regulation of these mechanisms by drugs, drug delivery systems, drug excipients and nutritional components are particularly considered. This information could provide the basis for controlled regulation of bioavailability of therapeutic agents and at the same time would help to prevent potential drug-drug interactions.

Anti-HIV and Anti-Hepatitis C Virus Drugs Inhibit P-Glycoprotein Efflux Activity in Caco-2 Cells and Precision-Cut Rat and Human Intestinal Slices

P-glycoprotein (ABCB1), an ATP-binding-cassette efflux transporter, limits intestinal absorption of its substrates and is a common site of drug-drug interactions (DDIs). ABCB1 has been suggested to interact with many antivirals used to treat HIV and/or chronic hepatitis C virus (HCV) infections. Using bidirectional transport experiments in Caco-2 cells and a recently established ex vivo model of accumulation in precision-cut intestinal slices (PCIS) prepared from rat ileum or human jejunum, we evaluated the potential of anti-HIV and anti-HCV antivirals to inhibit intestinal ABCB1. Lopinavir, ritonavir, saquinavir, atazanavir, maraviroc, ledipasvir, and daclatasvir inhibited the efflux of a model ABCB1 substrate, rhodamine 123 (RHD123), in Caco-2 cells and rat-derived PCIS. Lopinavir, ritonavir, saquinavir, and atazanavir also significantly inhibited RHD123 efflux in human-derived PCIS, while possible interindividual variability was observed in the inhibition of intestinal ABCB1 by maraviroc, ledipasvir, and daclatasvir. Abacavir, zidovudine, tenofovir disoproxil fumarate, etravirine, and rilpivirine did not inhibit intestinal ABCB1. In conclusion, using recently established ex vivo methods for measuring drug accumulation in rat- and human-derived PCIS, we have demonstrated that some antivirals have a high potential for DDIs on intestinal ABCB1. Our data help clarify the molecular mechanisms responsible for reported increases in the bioavailability of ABCB1 substrates, including antivirals and drugs prescribed to treat comorbidity. These results could help guide the selection of combination pharmacotherapies and/or suitable dosing schemes for patients infected with HIV and/or HCV.

Application of the MechPeff model to predict passive effective intestinal permeability in the different regions of the rodent small intestine and colon

A major component of physiologically based pharmacokinetic (PBPK) models is the prediction of the rate and extent of absorption of orally dosed drugs for which knowledge of effective passive intestinal permeability (P_eff ) is essential. Single-pass intestinal perfusion (SPIP) studies are used to establish effective permeability in vivo but are difficult to perform in rodents, while mechanistic models to predict drug P_eff in rat and mouse have not been published. This work evaluates the predictive performance of the 'MechPeff' model to predict P_eff in the rodent intestine based upon knowledge of regional gut physiology and drug-specific physicochemical parameters. The 'MechPeff' model, built-in to the Simcyp Rat and Mouse Simulators, predicts transcellular, paracellular and mucus layer permeabilities and combines these to give the overall P_eff . The jejunal and/or ileal P_eff was predicted for 12 (4) acidic, 13 (12) basic, 10 (8) neutral and 2 (0) ampholytic drugs in the rat (mouse), spanning a wide range of MW and logP_o:w , and compared with experimental P_eff obtained using SPIP. A key input is the intrinsic transcellular permeability (P_trans,0 ) which can be derived from modelling of appropriate in vitro permeability experiments or predicted from physicochemical properties. The P_eff predictions were reasonably good when experimentally derived P_trans,0 was used; from 42 P_eff,rat values, 24 (57%) were within 3-fold, and of 19 P_eff,mouse values, 12 (63%) were within 3-fold, of observed P_eff . Considering the lack of alternative models to predict P_eff in preclinical species, and the minimal drug-specific inputs required, this model provides a valuable tool within drug discovery and development programmes. Copyright © 2017 John Wiley & Sons, Ltd.

In-vitro investigation regarding the effects of Gelucire® 44/14 and Labrasol® ALF on the secretory intestinal transport of P-gp substrates

In this present study, the secretory transport of P-gp substrates, rhodamine 123 and digoxin, was evaluated using a Caco-2/HT29-MTX co-culture characterized by an efflux mechanism and a paracellular permeability closer to the human intestinal barrier compared to the Caco-2 monolayer gold standard. The influence of simulated intestinal fluids termed FeSSIF and FaSSIF on the intestinal absorption was also assessed in comparison with a conventional saline buffer. Labrasol^® ALF and Gelucire^® 44/14 in saline buffer significantly decreased to 83% and 62%, the P-gp-mediated transport of rhodamine 123 across the co-culture, respectively. The effects of Gelucire^® 44/14 were much more exacerbated with the Caco-2 monolayer model with a reduced permeability to 34% but they were partially reversed in the co-culture with FeSSIF. The modulation by the lipid excipients of digoxin secretory transport across the Caco-2 monolayer and the co-culture was reduced compared with the rhodamine 123. This work also emphasizes the numerous parameters that have to be considered for predicting accurately the effects of potential P-gp inhibitors including the in-vitro model, the incubation media and the intrinsic properties of P-gp substrates.

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.

Therapeutic Drug Monitoring of Anti-human Immunodeficiency Virus Drugs in a Patient with Short Bowel Syndrome

An elderly woman with human immunodeficiency virus-1 infection developed short bowel syndrome as a result of extensive intestinal resection. Considering the possibility of poor absorption of antiretroviral drugs (ARVs), therapeutic drug monitoring (TDM) was performed. A single-dose test of 6 ARVs (darunavir, ritonavir, lopinavir, etravirine, maraviroc, and raltegravir) did not provide information on the appropriate ARV, and repeated TDM under continuous antiretroviral therapy resulted in viral suppression below 50 copies/mL, which was considered to be treatment success. These assessments suggest the importance of TDM in the steady state for the successful treatment of individuals with impaired gastrointestinal function using ARVs.

Intestinal solubility and absorption of poorly water soluble compounds: predictions, challenges and solutions

We have explored for which type of compounds biorelevant dissolution profiling in simulated intestinal fluids would accurately predict solubility in human intestinal fluid. In total, 474 solubility values in simulated and aspirated human intestinal fluid for 78 drugs were compiled and analyzed. Significant solubilization in the colloidal structures was obtained in fasted and fed state fluids for drug compounds with a logD(oct)>3. Highly lipophilic compounds with high melting points (Tm > 200 °C) could also be significantly solubilized, but typically such compounds had solubility values in the lower µg/ml range also in the presence of the colloidal structures. On the basis of our analysis, compounds with a logD(oct)>3 should be explored in biorelevant dissolution media to better predict in vivo performance after oral dosing.

Intestinal permeability study of minoxidil: assessment of minoxidil as a high permeability reference drug for biopharmaceutics classification

The purpose of this study was to evaluate minoxidil as a high permeability reference drug for Biopharmaceutics Classification System (BCS). The permeability of minoxidil was determined in in situ intestinal perfusion studies in rodents and permeability studies across Caco-2 cell monolayers. The permeability of minoxidil was compared with that of metoprolol, an FDA reference drug for BCS classification. In rat perfusion studies, the permeability of minoxidil was somewhat higher than that of metoprolol in the jejunum, while minoxidil showed lower permeability than metoprolol in the ileum. The permeability of minoxidil was independent of intestinal segment, while the permeability of metoprolol was region-dependent. Similarly, in mouse perfusion study, the jejunal permeability of minoxidil was 2.5-fold higher than that of metoprolol. Minoxidil and metoprolol showed similar permeability in Caco-2 study at apical pH of 6.5 and basolateral pH of 7.4. The permeability of minoxidil was independent of pH, while metoprolol showed pH-dependent transport in Caco-2 study. Minoxidil exhibited similar permeability in the absorptive direction (AP-BL) in comparison with secretory direction (BL-AP), while metoprolol had higher efflux ratio (ER > 2) at apical pH of 6.5 and basolateral pH of 7.4. No concentration-dependent transport was observed for either minoxidil or metoprolol transport in Caco-2 study. Verapamil did not alter the transport of either compounds across Caco-2 cell monolayers. The permeability of minoxidil was independent of both pH and intestinal segment in intestinal perfusion studies and Caco-2 studies. Caco-2 studies also showed no involvement of carrier mediated transport in the absorption process of minoxidil. These results suggest that minoxidil may be an acceptable reference drug for BCS high permeability classification. However, minoxidil exhibited higher jejunal permeability than metoprolol and thus to use minoxidil as a reference drug would raise the permeability criteria for BCS high permeability classification.

In situ perfusion in rodents to explore intestinal drug absorption: challenges and opportunities

The in situ intestinal perfusion technique in rodents is a very important absorption model, not only because of its predictive value, but it is also very suitable to unravel the mechanisms underlying intestinal drug absorption. This literature overview covers a number of specific applications for which the in situ intestinal perfusion set-up can be applied in favor of established in vitro absorption tools, such as the Caco-2 cell model. Qualities including the expression of drug transporters and metabolizing enzymes relevant for human intestinal absorption and compatibility with complex solvent systems render the in situ technique the most designated absorption model to perform transporter-metabolism studies or to evaluate the intestinal absorption from biorelevant media. Over the years, the in situ intestinal perfusion model has exhibited an exceptional ability to adapt to the latest challenges in drug absorption profiling. For instance, the introduction of the mesenteric vein cannulation allows determining the appearance of compounds in the blood and is of great use, especially when evaluating the absorption of compounds undergoing intestinal metabolism. Moreover, the use of the closed loop intestinal perfusion set-up is interesting when compounds or perfusion media are scarce. Compatibility with emerging trends in pharmaceutical profiling, such as the use of knockout or transgenic animals, generates unparalleled possibilities to gain mechanistic insight into specific absorption processes. Notwithstanding the fact that the in situ experiments are technically challenging and relatively time-consuming, the model offers great opportunities to gain insight into the processes determining intestinal drug absorption.

Prediction of drug-drug interactions between various antidepressants and efavirenz or boosted protease inhibitors using a physiologically based pharmacokinetic modelling approach

BACKGROUND AND OBJECTIVE

The rate of depression in patients with HIV is higher than in the general population. The use of antidepressants can have a beneficial effect, improving antiretroviral therapy adherence and consequently their efficacy and safety. Efavirenz and protease inhibitor boosted with ritonavir are major components of the antiretroviral therapy and are inducers and/or inhibitors of several cytochrome P450 (CYP) isoforms. Although antidepressants are prescribed to a significant proportion of patients treated with antiretrovirals, there are limited clinical data on drug-drug interactions. The aim of this study was to predict the magnitude of drug-drug interactions among efavirenz, boosted protease inhibitors and the most commonly prescribed antidepressants using an in vitro-in vivo extrapolation (IVIVE) model simulating virtual clinical trials.

METHODS

In vitro data describing the chemical characteristics, and absorption, distribution, metabolism and elimination (ADME) properties of efavirenz, boosted protease inhibitors and the most commonly prescribed antidepressants were obtained from published literature or generated by standard methods. Pharmacokinetics and drug-drug interaction were simulated using the full physiologically based pharmacokinetic model implemented in the Simcyp™ ADME simulator. The robustness of our modeling approach was assessed by comparing the magnitude of simulated drug-drug interactions using probe drugs to that observed in clinical studies.

RESULTS

Simulated pharmacokinetics and drug-drug interactions were in concordance with available clinical data. Although the simulated drug-drug interactions with antidepressants were overall weak to moderate according to the classification of the US FDA, fluoxetine and venlafaxine represent better candidates from a pharmacokinetic standpoint for patients on efavirenz and venlafaxine or citalopram for patients on boosted protease inhibitors.

CONCLUSION

The modest magnitude of interaction could be explained by the fact that antidepressants are substrates of multiple isoforms and thus metabolism can still occur through CYPs that are weakly impacted by efavirenz or boosted protease inhibitors. These findings indicate that IVIVE is a useful tool for predicting drug-drug interactions and designing prospective clinical trials, giving insight into the variability of exposure, sample size and time-dependent induction or inhibition.

Role of P-glycoprotein in the distribution of the HIV protease inhibitor atazanavir in the brain and male genital tract

The blood-testis barrier and blood-brain barrier are responsible for protecting the male genital tract and central nervous system from xenobiotic exposure. In HIV-infected patients, low concentrations of antiretroviral drugs in cerebrospinal fluid and seminal fluid have been reported. One mechanism that may contribute to reduced concentrations is the expression of ATP-binding cassette drug efflux transporters, such as P-glycoprotein (P-gp). The objective of this study was to investigate in vivo the tissue distribution of the HIV protease inhibitor atazanavir in wild-type (WT) mice, P-gp/breast cancer resistance protein (Bcrp)-knockout (Mdr1a-/-, Mdr1b-/-, and Abcg2-/- triple-knockout [TKO]) mice, and Cyp3a-/- (Cyp) mice. WT mice and Cyp mice were pretreated with a P-gp/Bcrp inhibitor, elacridar (5 mg/kg of body weight), and the HIV protease inhibitor and boosting agent ritonavir (2 mg/kg intravenously [i.v.]), respectively. Atazanavir (10 mg/kg) was administered i.v. Atazanavir concentrations in plasma (Cplasma), brain (Cbrain), and testes (Ctestes) were quantified at various times by liquid chromatography-tandem mass spectrometry. In TKO mice, we demonstrated a significant increase in atazanavir Cbrain/Cplasma (5.4-fold) and Ctestes/Cplasma (4.6-fold) ratios compared to those in WT mice (P<0.05). Elacridar-treated WT mice showed a significant increase in atazanavir Cbrain/Cplasma (12.3-fold) and Ctestes/Cplasma (13.5-fold) ratios compared to those in vehicle-treated WT mice. In Cyp mice pretreated with ritonavir, significant (P<0.05) increases in atazanavir Cbrain/Cplasma (1.8-fold) and Ctestes/Cplasma (9.5-fold) ratios compared to those in vehicle-treated WT mice were observed. These data suggest that drug efflux transporters, i.e., P-gp, are involved in limiting the ability of atazanavir to permeate the rodent brain and genital tract. Since these transporters are known to be expressed in humans, they could contribute to the low cerebrospinal and seminal fluid antiretroviral concentrations reported in the clinic.

PXR/CYP3A4-humanized mice for studying drug-drug interactions involving intestinal P-glycoprotein

Rodent models are less suitable for predicting drug-drug interactions at the level of the human intestinal mucosa, especially when nuclear receptors such as pregnane X receptor (PXR) are involved. Recently, a transgenic mouse model, expressing both human PXR and CYP3A4, was developed and shown to be a better predictor of CYP3A4 induction by xenobiotics in humans as compared to wild-type mice. In the present study, we tested the hypothesis that this mouse model can also predict PXR-mediated induction of intestinal P-gp in humans. By use of the in situ intestinal perfusion technique with mesenteric blood sampling, the effect of oral rifampicin treatment on intestinal permeability for the HIV protease inhibitor darunavir, a dual CYP3A4/P-gp substrate, was investigated. Rifampicin treatment lowered the intestinal permeability for darunavir by 50% compared to that in nontreated mice. The P-gp inhibitor GF120918 increased the permeability for darunavir by 400% in rifampicin-treated mice, whereas this was only 56% in mice that were not treated, thus indicating P-gp induction by rifampicin. The nonspecific P450 inhibitor aminobenzotriazole (100 μM) did not affect the permeability for darunavir. Quantitative Western blot analysis of the intestinal tissue showed that rifampicin treatment induced intestinal P-gp levels 4-fold, while CYP3A4 levels remained unchanged. Oral co-administration of rifampicin with the phytochemical sulforaphane for 3 days increased the permeability for darunavir by 50% compared to that with rifampicin treatment alone. These data show that PXR/CYP3A4-humanized mice can be used to study the inducing effects of xenobiotics on intestinal P-gp.

Comparison of the permeability of metoprolol and labetalol in rat, mouse, and Caco-2 cells: use as a reference standard for BCS classification

The purpose of this study was to investigate labetalol as a potential high permeability reference standard for the application of Biopharmaceutics Classification Systems (BCS). Permeabilities of labetalol and metoprolol were investigated in animal intestinal perfusion models and Caco-2 cell monolayers. After isolating specific intestinal segments, in situ single-pass intestinal perfusions (SPIP) were performed in rats and mice. The effective permeabilities (Peff) of labetalol and metoprolol, an FDA standard for the low/high Peff class boundary, were investigated in two different segments of rat intestine (proximal jejunum and distal ileum) and in the proximal jejunum of mouse. No significant difference was found between Peff of metoprolol and labetalol in the jejunum and ileum of rat (0.33 ± 0.11 × 10(-4) vs 0.38 ± 0.06 × 10(-4) and 0.57 ± 0.17 × 10(-4) vs 0.64 ± 0.30 × 10(-4) cm/s, respectively) and in the jejunum of mouse (0.55 ± 0.05 × 10(-4) vs 0.59 ± 0.13 × 10(-4) cm/s). However, Peff of metoprolol and labetalol were 1.7 and 1.6 times higher in the jejunum of mouse, compared to the jejunum of rat, respectively. Metoprolol and labetalol showed segmental-dependent permeability through the rat intestine, with increased Peff in the distal ileum in comparison to the proximal jejunum. Most significantly, Peff of labetalol was found to be concentration-dependent. Decreasing concentrations of labetalol in the perfusate resulted in decreased Peff compared to Peff of metoprolol. The intestinal epithelial permeability of labetalol was lower than that of metoprolol in Caco-2 cells at both apical pH 6.5 and 7.5 (5.96 ± 1.96 × 10(-6) vs 9.44 ± 3.44 × 10(-6) and 15.9 ± 2.2 × 10(-6) vs 23.2 ± 7.1 × 10(-6) cm/s, respectively). Labetalol exhibited higher permeability in basolateral to apical (BL-AP) compared to AP-BL direction in Caco-2 cells at 0.1 times the highest dose strength (HDS) (46.7 ± 6.5 × 10(-6) vs 14.2 ± 1.5 × 10(-6) cm/s). The P-gp inhibitor, verapamil, significantly increased AP-BL and decreased BL-AP direction transport of labetalol. Overall, labetalol showed high Peff in rat and mouse intestinal perfusion models similar to metoprolol at a concentration based on HDS. However, the concentration-dependent permeability of labetalol in mice due to P-gp and the inhibition study with verapamil in Caco-2 cells indicated that labetalol is not an ideal reference standard for BCS classification.

The effect of ABCB1 genetic variants on chemotherapy response in HIV and cancer treatment

Despite their clearly distinct pathophysiologies, HIV and cancer are diseases whose response to chemotherapy treatment varies substantially amongst patients, in particular for those with prior drug exposure. This has been attributed, in part, to elevated expression of the ABCB1 drug transporter in some patients, which results in reduced drug accumulation in target tissues. Many mechanisms have been identified for this elevated expression of ABCB1, including variations in the sequence of the gene coding for the transporter (ABCB1). Over 50 SNPs within ABCB1 have been identified. Associations have been made between the presence of specific ABCB1 SNPs/haplotypes and both ABCB1 expression and the efficacy or toxicity of certain chemotherapy regimens. If these associations are strong and reproducibly demonstrated, then this would greatly aid in the development of individualized therapy regimes for specific cancer or HIV patients, based on their ABCB1 genotypes. This article highlights the significant recent progress made in this direction, but cautions that the utility of ABCB1 gene variants as biomarkers of chemotherapy drug response remains unclear to date.

Influence of drug transport proteins on the pharmacokinetics and drug interactions of HIV protease inhibitors

Protease inhibitors, a class of antiretroviral agents frequently used in the treatment of HIV infection, interact with numerous transport proteins resulting in clinically significant drug-drug interactions (DDIs). This review focuses on the proteins that transport protease inhibitors and directly influence the pharmacokinetics of these drugs, as well as the transport proteins that are inhibited or induced by protease inhibitors. Clinically relevant DDIs involving drug transporters and protease inhibitors, either as "victim" drugs or as "perpetrator" drugs, and the pharmacokinetic consequences of such interactions are highlighted. A summary of transporter-mediated processes underlying the toxicity of protease inhibitors is provided. Finally, the effect of HIV infection or co-infection on drug transport proteins, and the implications for protease inhibitor pharmacokinetics is discussed. Transport proteins significantly influence the pharmacokinetics, efficacy and toxicity profiles of this important class of drugs.