Characterization of P-glycoprotein mediated transport of K02, a novel vinylsulfone peptidomimetic cysteine protease inhibitor, across MDR1-MDCK and Caco-2 cell monolayers

Organic Cation Transporter 1 and 3 Contribute to the High Accumulation of Dehydrocorydaline in the Heart

Dehydrocorydaline (DHC), one of the main active components of Corydalis yanhusuo, is an important remedy for the treatment of coronary heart disease. Our previous study revealed a higher unbound concentration of DHC in the heart than plasma of mice after oral administration of C. yanhusuo extract or DHC, but the underlying uptake mechanism remains unelucidated. In our investigations, we studied the transport mechanism of DHC in transgenic cells, primary neonatal rat cardiomyocytes, and animal experiments. Using quantitative real-time polymerase chain reaction and Western blotting, we found that uptake transporters expressed in the mouse heart include organic cation transporter 1/3 (OCT1/3) and carnitine/organic cation transporter 1/2 (OCTN1/2). The accumulation experiments in transfected cells showed that DHC was a substrate of OCT1 and OCT3, with K _m of 11.29 ± 3.3 and 8.96 ± 3.7 μM, respectively, but not a substrate of OCTN1/2. Additionally, a higher efflux level (1.71-fold of MDCK-mock) of DHC was observed in MDCK-MDR1 cells than in MDCK-mock cells. Therefore, DHC is a weak substrate for MDR1. Studies using primary neonatal rat cardiomyocytes showed that OCT1/3 inhibitors (quinidine, decynium-22, and levo-tetrahydropalmatine) prevented the accumulation of DHC, whereas OCTN2 inhibitors (mildronate and l-carnitine) did not affect its accumulation. Moreover, the coadministration of OCT1/3 inhibitors (levo-tetrahydropalmatine, THP) decreased the concentration of DHC in the mouse heart. Based on these findings, DHC may be accumulated partly by OCT1/3 transporters and excreted by MDR1 in the heart. THP could alter the distribution of DHC in the mouse heart. SIGNIFICANCE STATEMENT: We reported the cardiac transport mechanism of dehydrocorydaline, highly distributed to the heart after oral administration of Corydalis yanhusuo extract or dehydrocorydaline only. Dehydrocorydaline (an OCT1/3 and MDR1 substrate) accumulation in primary cardiomyocytes may be related to the transport activity of OCT1/3. This ability, hampered by selective inhibitors (levo-tetrahydropalmatine, an inhibitor of OCT1/3), causes a nearly 40% reduction in exposure of the heart to dehydrocorydaline. These results suggest that OCT1/3 may contribute to the uptake of dehydrocorydaline in the heart.

P-Glycoprotein-Mediated Efflux Using a Rapidly Maturing Caco2 Clone (CLEFF4) in Only 5 Days without Requiring Modified Growth Medium

In drug discovery it is essential that one of the parameters tested for any new chemical entity is its affinity for human efflux systems, most notably P-glycoprotein (P-gp). These efflux systems affect not only rates of oral absorption but also rates of excretion through the liver, blood-brain barrier, and accumulation in potential target cells that upregulate efflux systems. Current methods to determine drugs' P-gp transport potential include in vitro bidirectional transport studies, and the two most common cell lines used are Caco2 and MDR1-transfected MDCK models. Caco2 cells are human but slow growing and require more than 3 weeks to mature, while MDCK cells are canine, but when transfected with human P-gp become a rapid model of P-gp affinity. Our laboratory has generated a Caco2 subclone called CLEFF4 that is fully human, yet now approaches the rapid nature of the MDCK model. No special medium is required. We have shown, in as little as 5 days postseeding, high transepithelial electrical resistance values of more than 1000 Ω·cm² plus P-gp expression more than threefold higher than that of 21-day-old cells. Currently tested drugs included rhodamine 123 (Rh123), vinblastine, and doxorubicin, and all drugs exhibited P-gp-mediated efflux that was inhibited by PSC833. By day 6, bidirectional transport of Rh123 was as potent as that of mature Caco2 cells, for use in comparative P-gp affinity studies. We now have a human P-gp model that is rapid and works without any need for special accelerating medium. We believe this could be a welcome addition to the testing regime of new chemical entities.

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.

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

BACKGROUND

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

METHODOLOGY AND PRINCIPAL FINDINGS

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

CONCLUSION AND SIGNIFICANCE

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

PET study on mice bearing human colon adenocarcinoma cells using [11C]GF120918, a dual radioligand for P-glycoprotein and breast cancer resistance protein

OBJECTIVE

To evaluate the functions of P-glycoprotein (Pgp) and breast cancer resistance protein (BCRP) in human colon adenocarcinoma (Caco-2), we carried out an in-vitro study and a small animal positron emission tomography (PET) study using [C]GF120918 (elacridar).

METHODS

[C]GF120918 was synthesized by reacting the desmethyl precursor with [C]CH3I. An in-vitro study using [C]GF120918 was carried out in Caco-2 and Madin-Darby canine kidney cells in the presence or absence of a transporter inhibitor (cyclosporine A and unlabeled GF120918). The biodistribution of radioactivity after the injection of [C]GF120918 was determined in Caco-2-bearing mice using a small animal PET scanner.

RESULTS

In Caco-2 cells expressing Pgp and BCRP, coincubation with unlabeled GF120918 caused an approximately two-fold increase in [C]GF120918 uptake compared with that of the control ([C]GF120918 only). In Caco-2-bearing mice, PET results indicated that [C]GF120918 uptake in the tumor was low, but was significantly increased by treatment with unlabeled GF120918. In metabolite analysis, the radioactive component in the tumor almost corresponded to intact [C]GF120918.

CONCLUSION

A PET study combining the administration of [C]GF120918 with unlabeled GF120918 may be a useful tool for evaluating the functions of Pgp and BCRP in tumors.

Is Ciprofloxacin a Substrate of P-glycoprotein?

Introduction

Studies using MDCKII and LLC-PK1 cells transfected with MDR1 cDNA indicate that ciprofloxacin is not a substrate of P-glycoprotein. However, our data has shown that transport studies done using different P-gp overexpressing cell lines (MDCKI-MDR1, MDCKII-MDR1 and L-MDR1), could lead to contradictory conclusion on whether a compound is a substrate of P-gp. The aim of our study was to determine if ciprofloxacin is indeed not a P-glycoprotein substrate using MDCKI cells transfected with human MDR1 cDNA.

Methods

Semi-quantitative RT-PCR was used to determine the mRNA level of MDR1 while Western blot was performed to determine the protein expression level of P-gp, MRP1 and MRP2 in various cells. Ciprofloxacin bidirectional transport studies were performed in MDCKI, MDCKI-MDR1, MDCKII, MDCKII-MDR1, MDCKII-MRP2, LLC-PK1, L-MRP1 and L-MDR1 cells.

Results

Ciprofloxacin showed net secretion in MDCKI-MDR1 but net absorption in MDCKI cells. Various P-gp inhibitors decreased the B to A and increased the A to B transport of ciprofloxacin in MDCKI-MDR1 cells while having no effect in MDCKI cells. The B to A transport of ciprofloxacin in MDCKI-MDR1 cells was not affected by non-P-gp inhibitors. In the presence of indomethacin, ciprofloxacin showed net secretion instead of net absorption in MDCKI cells while in the presence of probenecid and sulfinpyrazone, there was no net secretion and absorption. There was no difference in ciprofloxacin transport between MDCKII and MDCKII-MDR1, LLC-PK1 and L-MDR1, LLC-PK1 and L-MRP1 and MDCKII and MDCKII-MRP2.

Conclusions

Transport data in MDCKI and MDCKI-MDR1 cells indicate that ciprofloxacin is a substrate of P-gp but data from MDCKII, MDCKII-MDR1, LLC-PK1 and L-MDR1 cells indicate that ciprofloxacin is not a substrate of P-gp. Vinblastine, a well-known P-gp substrate, also did not show differences between LLC-PK1 and L-MDR1 cells. Further studies need to be performed to characterize these P-gp overexpressing cell lines and the transport of ciprofloxacin.

N-(3,4-dimethoxyphenethyl)-4-(6,7-dimethoxy-3,4-dihydroisoquinolin-2[1H]-yl)-6,7-dimethoxyquinazolin-2-amine (CP-100,356) as a "chemical knock-out equivalent" to assess the impact of efflux transporters on oral drug absorption in the rat

The utility of the diaminoquinazoline derivative CP-100,356 as an in vivo probe to selectively assess MDR1/BCRP-mediated drug efflux was examined in the rat. CP-100,356 was devoid of inhibition (IC(50) >50 microM) against major human P450 enzymes including P4503A4. In human MDR1-transfected MDCKII cells, CP-100,356 inhibited acetoxymethyl calcein (calcein-AM) uptake (IC(50) approximately 0.5 +/- 0.07 microM) and digoxin transport (IC(50) approximately 1.2 +/- 0.1 microM). Inhibition of prazosin transport (IC(50) approximately 1.5 +/- 0.3 microM) in human BCRP-transfected MDCKII cells by CP-100,356 confirmed the dual MDR1/BCRP inhibitory properties. CP-100,356 was a weak inhibitor of OATP1B1 (IC(50) approximately 66 +/- 1.1 microM) and was devoid of MRP2 inhibition (IC(50) >15 microM). In vivo inhibitory effects of CP-100,356 in rats were examined after coadministration with MDR1 substrate fexofenadine and dual MDR1/BCRP substrate prazosin. Coadministration with increasing doses of CP-100,356 resulted in dramatic increases in systemic exposure of fexofenadine (36- and 80-fold increase in C(max) and AUC at a CP-100,356 dose of 24 mg/kg). Significant differences in prazosin pharmacokinetics were also discernible in CP-100,356-pretreated rats as reflected from a 2.6-fold increase in AUC. Coadministration of CP-100,356 and P4503A substrate midazolam did not result in elevations in systemic exposure of midazolam in the rat. The in vivo methodology should have utility in drug discovery in selective and facile assessment of the role of MDR1 and BCRP efflux transporters in oral absorption of new drug candidates.

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

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

Primary hepatocytes: current understanding of the regulation of metabolic enzymes and transporter proteins, and pharmaceutical practice for the use of hepatocytes in metabolism, enzyme induction, transporter, clearance, and hepatotoxicity studies

This review brings you up-to-date with the hepatocyte research on: 1) in vitro-in vivo correlations of metabolism and clearance; 2) CYP enzyme induction, regulation, and cross-talk using human hepatocytes and hepatocyte-like cell lines; 3) the function and regulation of hepatic transporters and models used to elucidate their role in drug clearance; 4) mechanisms and examples of idiosyncratic and intrinsic hepatotoxicity; and 5) alternative cell systems to primary human hepatocytes. We also report pharmaceutical perspectives of these topics and compare methods and interpretations for the drug development process.

Decrease in intracellular concentration causes the shift in Km value of efflux pump substrates

Passive permeability and active efflux are parallel processes in transcellular flux. Therefore, the observed kinetics of a transporter substrate depends on both of these factors. The transporter expression has been shown to affect both the apparent K(m) and V(max) values. Kinetic parameters can be obtained from various experimental settings, but these do not necessarily reflect the situation in transcellular flux. Kinetic absorption models need reliable estimates of saturable kinetics when accurate in silico predictions are to be made. The effect of increasing P-glycoprotein expression on apparent transport kinetics was studied using quinidine and digoxin as model compounds. The intracellular concentrations of drugs during the transport process were also measured. A dynamic simulation model was constructed to study the observed data. The apparent K(m) and V(max) values increased as the P-glycoprotein expression increased. Simulations reproduced the shift in both kinetic parameters as a function of efflux pump expression. In addition, the apparent K(m) value showed a strong inverse relationship to the passive permeability. In contrast, the apparent V(max) value reached a maximum at intermediate passive permeability and declined above and below this passive permeability. The true V(max) and K(m) values were never reached. The shift in K(m) was assigned to a decrease in intracellular concentration at the P-glycoprotein interaction site with both experimental and simulation data. In conclusion, the apparent kinetic parameters in transcellular permeability assays depend on passive permeability and efflux pump activity. Therefore, parameters that are obtained from in vitro assays should be cautiously applied to in vivo predictions.

The road map to oral bioavailability: an industrial perspective

Optimisation of oral bioavailability is a continuing challenge for the pharmaceutical and biotechnology industries. The number of potential drug candidates requiring in vivo evaluation has significantly increased with the advent of combinatorial chemistry. In addition, drug discovery programmes are increasingly forced into more lipophilic and lower solubility chemical space. To aid in the use of in vitro and in silico tools as well as reduce the number of in vivo studies required, a team-based discussion tool is proposed that provides a 'road map' to guide the selection of profiling assays that should be considered when optimising oral bioavailability. This road map divides the factors that contribute to poor oral bioavailability into two interrelated categories: absorption and metabolism. This road map provides an interface for cross discipline discussions and a systematic approach to the experimentation that drives the drug discovery process towards a common goal - acceptable oral bioavailability using minimal resources in an acceptable time frame.

Ischemia/Reperfusion Injury in the Monolayers of Human Intestinal Epithelial Cell Line Caco-2 and Its Recovery by Antioxidants

We previously established a in vitro system for assessing early ischemia/reperfusion injury using monolayers of human intestinal epithelial cell line Caco-2, in which lipid peroxidation caused by tertiary-butylhydroperoxide (t-BuOOH), a lipid peroxidation inducer, acts as a trigger of the injury. By now, we have shown that superoxide anion participates in the opening of tight junctions (TJ) induced by reoxygenation following the induction of lipid peroxidation by t-BuOOH at a low concentration. The present objectives are to elucidate the dysfunction of P-glycoprotein (P-gp) in addition to the opening of TJ by t-BuOOH at a high concentration condition using rhodamine123 (Rho123) as a P-gp substrate and cyclosporine A (CyA) as a P-gp inhibitor. Also, we compared the inhibition effect of lutein and other compounds such as biliverdin as a radical scavenger on the opening of TJ and the dysfunction of P-gp. t-BuOOH at a high concentration increased the permeability of Rho123 in the apical to basal direction and decreased basal to apical direction when compared with control conditions. t-BuOOH at a high concentration showed no significant difference between directional transport of Rho123 and no inhibition was observed in the permeability of both directions by CyA. The staining intensity of Western blot was decreased by t-BuOOH at a high concentration. Although lutein and the other compounds had recovery effects on the opening of TJ and P-gp dysfunction induced by t-BuOOH, lutein is more advantageous than other compounds since it has effective effects at the lower concentration. In conclusion, the barrier dysfunction such as the inhibition of P-gp in addition to the opening of TJ was induced by t-BuOOH at a high concentration condition. The above two barrier dysfunctions was ameliorated by antioxidant such as lutein and biliverdin.

SPECIES DIFFERENCES IN THE DISPOSITION OF THE CCR5 ANTAGONIST, UK-427,857, A NEW POTENTIAL TREATMENT FOR HIV

UK-427,857 (4, 4-difluoro-N-[(1S)-3-[exo-3-(3-isopropyl-5-methyl-4H-1,2,4-triazol-4-yl)-8-azabicyclo[3.2.1]oct-8-yl]-1-phenylpropyl]cyclohexanecarboxamide) is a novel CCR5 antagonist undergoing investigation for use in the treatment of human immunodeficiency virus (HIV) infection. Pharmacokinetic and metabolism studies have been performed in mouse, rat, dog, and human after single and multiple administration by oral and intravenous routes. The compound has physicochemical properties that are borderline for good pharmacokinetics, being moderately lipophilic (log D(7.4) 2.1) and basic (pK(a) 7.3), possessing a number of H-bonding functionalities, and with a molecular weight of 514. The compound was incompletely absorbed in rat (approximately 20-30%) but well absorbed in dog (>70%). Based on in vitro studies in Caco-2 cells, UK-427,857 has relatively poor membrane permeability, and transcellular flux is enhanced in the presence of inhibitors of P-glycoprotein. Further evidence for the involvement of P-glycoprotein in restricting the oral absorption of UK-427,857 was obtained in P-glycoprotein null mice (mdr1a/mdr1b knockout). In these animals, AUC after oral administration was 3-fold higher than in control animals. In oral dose escalation studies in humans, the compound demonstrated nonlinear pharmacokinetics, with increased dose-normalized exposure with increased dose size, consistent with saturation of P-glycoprotein. The oral dose-exposure relationship of UK-427,857 in humans was not reflected in either rat or dog. In animal species and humans, UK-427,857 undergoes some metabolism, with parent compound the major component present in the systemic circulation and excreta. Elimination of radioactive dose was primarily via the feces. In rat, parent compound was secreted via bile and directly into the gastrointestinal tract. Metabolites were products of oxidative metabolism and showed a high degree of structural consistency across species.

[High throughput screening of pharmacokinetics and metabolism in drug discovery (I)--establishment of assessment system for absorption to compounds with a wide diversity of physical properties]

The application of combinatorial chemistry and high-throughput screening to biological targets has led to efficient identification of lead compounds in wide therapeutic areas. However, the physicochemical properties of some lead compounds are lipophilic with low water soluble. Since these parameters determine in vivo absorption, we established robust screening methods for solubility and Caco-2 membrane permeability which are applicable to our screening strategy based on the structure-pharmacokinetic parameter relationship (SPR). Of test compounds with different core structures, turbidimetric solubility and apparent solubility as determined by HPLC-UV analysis after dilution of aqueous media from DMSO stock solution was overestimated in comparison with the corresponding thermodynamic solubility obtained using a traditional shake-flask method. A new powder-dissolution method providing thermodynamic solubility similar to that in the traditional method was developed using 96-well plates for equilibrium dialysis. The throughput of the method was the almost the same as that using the apparent solubility method. In a conventional Caco-2 assay, membrane permeability (P(app)) of some lipophilic compounds was underestimated due to low solubility in the apical site and adhesion to the device, resulting in a poor relationship between the in vivo absorption fraction and the P(app) values. The addition of 0.1% Gelucire 44/14 into the apical site and 4% bovine serum albumin into the basolateral site improved the relationship. These newly developed methods are therefore useful to optimize lead compounds with less water solubility and high lipophilicity on the basis of SPR.

EFFECTS OF UREMIC TOXINS ON HEPATIC UPTAKE AND METABOLISM OF ERYTHROMYCIN

Hepatic clearance of erythromycin (Ery) is significantly reduced in patients with end stage renal disease. Since Ery is primarily eliminated via excretion of unchanged drug in the bile, we suspect that this change could be due to the effect of uremic toxins on hepatic uptake and/or efflux transporters. Using rat hepatocytes and microsomes as model proof of concept systems, we examined six uremic toxins, 3-carboxy-4-methyl-5-propyl-2-furan-propanoic acid (CMPF), indoxyl sulfate (IS), hippuric acid (HA), indole acetic acid (IA), guanidinosuccinic acid (GSA), and indoxyl-beta-D-glucuronide (IG), for their effects on Ery uptake and metabolism. Ery and the metabolite N-demethyl-Ery were measured by liquid chromatography/tandem mass spectrometry. The uptake of Ery by rat hepatocytes was markedly inhibited by rifampin and digoxin, but not by quinidine, suggesting that Oatp2 plays a major role in the uptake of Ery. At 50 microM, CMPF significantly (p < 0.05) reduced hepatocyte accumulation of Ery and N-demethyl-Ery. At higher concentrations (>200 microM), CMPF appears to also inhibit the enzymatic metabolism of Ery. In contrast, IS did not significantly inhibit the hepatocyte uptake of Ery, even at the highest concentration (800 microM) tested, but reduced metabolite generation (p < 0.001). The other uremic toxins, HA, IA, IG, and GSA, did not affect either hepatic uptake or microsomal metabolism of Ery. CMPF, IS, and HA were shown not to inhibit differential P-glycoprotein transport of Ery in cellular systems. Our results suggest that CMPF can directly inhibit the uptake of Ery by inhibiting Oatp2, whereas IS is more likely to inhibit the enzymatic metabolism of Ery.

Classification analysis of P-glycoprotein substrate specificity

Prediction of P-glycoprotein substrate specificity (S(PGP)) can be viewed as a constituent part of a compound's "pharmaceutical profiling" in drug design. This task is difficult to achieve due to several factors that raised many contradictory opinions: (i) the disparity between the S(PGP) values obtained in different assays, (ii) the confusion between Pgp substrates and inhibitors, (iii) the confusion between lipophilicity and amphiphilicity of Pgp substrates, and (iv) the dilemma of describing class-specific relationships when Pgp has no binding sites of high ligand specificity. In this work, we compiled S(PGP) data for 1000 compounds. All data were represented in a binary format, assigning S(PGP) = 1 for substrates and S(PGP) = 0 for non-substrates. Each value was ranked according to the reliability of experimental assay. Two data sets were considered. Set 1 included 220 compounds with S(PGP) from polarized transport across MDR1 transfected cell monolayers. Set 2 included the entire list of 1000 compounds, with S(PGP) values of generally lower reliability. Both sets were analysed using a stepwise classification structure-activity relationship (C-SAR) method, leading to derivation of simple rules for crude estimation of S(PGP) values. The obtained rules are based on the following factors: (i) compound's size expressed through molar weight or volume, (ii) H-accepting given by the Abraham's beta (that can be crudely approximated by the sum of O and N atoms), and (iii) ionization given by the acid and base pKa values. Very roughly, S(PGP) can be estimated by the "rule of fours". Compounds with (N + O) > or = 8, MW > 400 and acid pKa > 4 are likely to be Pgp substrates, whereas compounds with (N + O) < or = 4, MW < 400 and base pKa < 8 are likely to be non-substrates. The obtained results support the view that Pgp functioning can be compared to a complex "mini-pharmacokinetic" system with fuzzy specificity. This system can be described by a probabilistic version of Abraham's solvation equation, suggesting a certain similarity between Pgp transport and chromatographic retention. The chromatographic model does not work in the case of "marginal" compounds with properties close to the "global" physicochemical cut-offs. In the latter case various class-specific rules must be considered. These can be associated with the "amphiphilicity" and "biological similarity" of compounds. The definition of class-specific effects entails construction of the knowledge base that can be very useful in ADME profiling of new drugs.

Multidrug Resistance Gene G1199A Polymorphism Alters Efflux Transport Activity of P-Glycoprotein

The significance of the human multidrug resistance gene (MDR1) G1199A polymorphism, resulting in a Ser400Asn modification in P-glycoprotein (P-gp), remains unclear. We have developed stable recombinant LLC-PK1 epithelial cells expressing either MDR1wt or MDR11199 to evaluate functional consequences of G1199A [N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide]. P-gp activity observed in MDR1wt and MDR11199 cells was completely inhibited in the presence of the specific P-gp inhibitor GF120918. Comparable expression of mRNA and protein in the MDR1-expressed cells and correct localization of P-gp in the apical membrane of recombinant cells was verified. Mean intracellular rhodamine-123 (R123) accumulation, measured by flow cytometry, was approximately 4.75-fold higher in MDR11199 recombinant cells than MDR1wt cells. Cytotoxicity studies have shown that MDR1wt and MDR11199 cells exhibited similar resistance, as measured by EC50 values, to doxorubicin (155 +/- 68 versus 120 +/- 32 nM); however, MDR11199 cells were more resistant to vinblastine (1.41 +/- 0.51 versus 15.7 +/- 4.0 nM; p < 0.001) and vincristine (1.18 +/- 0.56 versus 3.41 +/- 1.47 nM; p < 0.05). The apparent transepithelial permeability ratios of R123 in MDR1wt and MDR11199 cells were 3.54 +/- 0.94 and 2.02 +/- 0.51 (p < 0.05), respectively. Therefore, the G1199A polymorphism alters the efflux and transepithelial permeability of a fluorescent substrate and sensitivity to select cytotoxic agents, which may influence drug disposition and therapeutic efficacy of some P-gp substrates.

Characterization of Dexloxiglumide in vitro Biopharmaceutical Properties and Active Transport

The objective of this work was to characterize dexloxiglumide biopharmaceutical properties in vitro and relate these characteristics to its in vivo absorption performance, and to assess dexloxiglumide interaction with P-glycoprotein (P-gp) and MRP1 to anticipate its drug interaction potential. Dexloxiglumide aqueous solubility was moderate and pH dependent. Dexloxiglumide exhibited moderate Caco-2 permeability that was polarized, concentration dependent, and pH dependent. The apical-to-basolateral (AP-BL) permeability at pH 5 [14.5 (+/-1.8) x 10(-6) cm/s] was 2-fold higher than at pH 7.5 [7.24 (+/-0.27) x 10(-6) cm/s]. Neutral and ionized dexloxiglumide species displayed permeabilities of 30.8 (+/-8.4) x 10(-6) cm/s and 9.03 (+/-1.31) x 10(-6) cm/s, respectively. The transport of dexloxiglumide across MDR1-MDCK (P-gp overexpressing Madine Darby canine kidney cells) monolayers was polarized, with a BL-AP/AP-BL permeability ratio of 9.35 (+/-0.73), which was reduced to 1.03 (+/-0.03) by P-gp inhibition. Rhodamine 123 efflux was reduced by dexloxiglumide from 4.06 (+/-0.34) to 2.84 (+/-0.15) across Caco-2 monolayers, and from 17.3 (+/-0.9) to 8.26 (+/-1.38) across MDR1-MDCK monolayers, further indicating dexloxiglumide interaction with P-gp. Additionally, P-gp ATPase activity increased with dexloxiglumide concentration. Dexloxiglumide was effluxed from MRP1-NIH3T3 cells (NIH-3T3 cells expressing the multidrug resistance-associated protein 1). Dexloxiglumide increased MRP1-substrate fluorescein uptake 4-fold, and fluorescein increased dexloxiglumide uptake 1.8-fold. Overall, in vitro transport studies indicate dexloxiglumide to be moderately soluble and moderately permeable, which is in agreement with the incomplete oral absorption of dexloxiglumide. In vitro, dexloxiglumide was moderately modulated by P-gp and MRP1, which provides a rationale for the design of drug interaction studies.

Impact of drug transporter studies on drug discovery and development

Drug transporters are expressed in many tissues such as the intestine, liver, kidney, and brain, and play key roles in drug absorption, distribution, and excretion. The information on the functional characteristics of drug transporters provides important information to allow improvements in drug delivery or drug design by targeting specific transporter proteins. In this article we summarize the significant role played by drug transporters in drug disposition, focusing particularly on their potential use during the drug discovery and development process. The use of transporter function offers the possibility of delivering a drug to the target organ, avoiding distribution to other organs (thereby reducing the chance of toxic side effects), controlling the elimination process, and/or improving oral bioavailability. It is useful to select a lead compound that may or may not interact with transporters, depending on whether such an interaction is desirable. The expression system of transporters is an efficient tool for screening the activity of individual transport processes. The changes in pharmacokinetics due to genetic polymorphisms and drug-drug interactions involving transporters can often have a direct and adverse effect on the therapeutic safety and efficacy of many important drugs. To obtain detailed information about these interindividual differences, the contribution made by transporters to drug absorption, distribution, and excretion needs to be taken into account throughout the drug discovery and development process.

Novel experimental parameters to quantify the modulation of absorptive and secretory transport of compounds by P-glycoprotein in cell culture models of intestinal epithelium

PURPOSE

The purpose of this work was to elucidate the asymmetric effect of P-gp on modulation of absorptive and secretory transport of compounds across polarized epithelium, to develop experimental parameters to quantify P-gp-mediated modulation of absorptive and secretory transport, and to elucidate how P-gp-mediated modulation of transport is affected by passive diffusion properties, interaction of the substrate with P-gp, and P-gp expression.

METHODS

The permeability of a set of P-gp substrates was determined in absorptive and secretory directions in Madine-Darby Canine kidney (MDCK), Caco-2, and MDR-MDCK monolayers. The transport was also determined in the presence of GW918, a non-competitive P-gp inhibitor, to quantify the permeability without the influence of P-gp. From these two experimental permeability values in each direction, two new parameters, absorptive quotient (AQ) and the secretory quotient (SQ), were defined to express the functional activity of P-gp during absorptive and secretory transport, respectively. Western blot analysis was used to quantify P-gp expression in these monolayers and in normal human intestinal.

RESULTS

P-gp expression in Caco-2 and MDR-MDCK monolayers was comparable to that in normal intestine, and much less in MDCK cells. For all models, the substrates encompassed a wide range of apparent permeability due to passive diffusion (PPD). The parameters AQ and SQ, calculated for all compounds, assessed the attenuation in absorptive and enhancement of secretory transport, respectively, normalized to the permeability due to passive diffusion. Analysis of these parameters showed that 1) P-gp affected absorptive and secretory transport differentially and 2) compounds could be stratified into distinct groups with respect to the modulation of their absorptive and secretory transport by P-gp. Compounds could be identified whose absorptive transport was either strongly affected or poorly affected by changes in P-gp expression. For certain compounds, AQ values showed parabolic relationship with respect to passive diffusivity, and for others AQ was unaffected by changes in passive diffusivity.

CONCLUSIONS

The relationship between attenuation of absorptive transport and enhancement of secretory transport of compounds by P-gp is asymmetric, and different for different sets of compounds. The relationship between attenuation of absorption by P-gp and passive diffusivity of compounds, their interaction potential with P-gp, and levels of P-gp expression is complex; however, compounds can be classified into sets based on these relationships. A classification system that describes the functional activity of P-gp with respect to modulation of absorptive and secretory transport was developed from these results.

Endogenous drug transporters in in vitro and in vivo models for the prediction of drug disposition in man

The epithelial canine and porcine kidney cell lines MDCK, MDCKII and LLC-PK1, respectively are employed to establish recombinant models of drug transport. Endogenous drug carriers in these cells may contribute to the activities of recombinant drug transporters, thus making it difficult to assess their properties. We analysed the expression of endogenous transporters in these cell lines by RT-PCR and by determining drug transporter activities. Concerning drug efflux, multidrug resistance protein 1 (MDR1) and MRP1 mRNAs were found in all lines. MRP2 mRNA was expressed in all cell lines except MDCK. Transepithelial transport of vinblastine and its modulation by a MDR1-specific inhibitor or by the MDR1- and MRP-inhibitor verapamil, indicated that MDCKII cells have, in comparisons to the other cell lines, relatively high levels of functional MDR1 while vinblastine transport in MDCK cells is likely to be mediated more by MRP1. Notably, LLC-PK1 cells displayed little activity attributable to either MDR1 and MRP1, thus making them suitable for the expression of these efflux pumps. Of the drug uptake carriers, OATP-A mRNA was only expressed in MDCK cells. OATP-C mRNA was barely detectable in MDCK cells and absent in MDCKII and LLC-PK1 cells. In agreement with transcriptional profiling, the OATP-mediated uptake of either estradiol-glucuronide or estrone-sulfate was either absent or barely detectable in all cell lines thus implying that they are suitable to establish recombinant models for human OATP's. Transcriptional profiling was also performed on porcine and canine tissues and revealed that MRP1 was expressed in canine but not in human or porcine liver, whereas surprisingly OATP-C was expressed in canine kidney but only in human and porcine liver. The findings presented are relevant to the use of porcine and canine models for drug disposition.

Can the enhanced renal clearance of antibiotics in cystic fibrosis patients be explained by P-glycoprotein transport?

PURPOSE

To investigate in vitro if P-glycoprotein (P-gp) transport can differentiate between antibiotic drugs exhibiting increased active renal clearance (CL(r)) in cystic fibrosis (CF) patients (i.e., dicloxacillin, trimethoprim) and drugs that do not exhibit this phenomenon (i.e.. cefsulodin, sulfamethoxazole).

METHODS

Transport studies were carried out in MDCK (wild type) and MDR1-MDCK (P-gp overexpressing) cells that were grown to confluence on Transwell inserts. [14C]-mannitol transport and transepithelial electrical resistance (TEER) were measured to validate the integrity of the cells. Drug concentrations were analyzed using HPLC.

RESULTS

Dicloxacillin and trimethoprim are substrates of P-gp (B-->A/A-->B ratios in MDR1-MDCK cells are 32 and 50, respectively). P-gp inhibitors (i.e., GG918, cyclosporine, ketoconazole, vinblastine) decreased the B-->A transport of dicloxacillin and trimethoprim and increased the A-->B transport of trimethoprim while non-P-gp inhibitors (e.g., PAH) had no effect. In contrast, cefsulodin and sulfamethoxazole are not substrates of P-gp (B-->sA/A-->B values in MDCK and MDR1-MDCK cells are -1).

CONCLUSIONS

Our in vitro studies suggest that P-glycoprotein may play a role in increasing renal clearance of drug substrates in CF patients. Dicloxacillin and trimethoprim. which are both substrates of P-gp, show increased active renal clearance in CF patients while cefsulodin and sulfamethoxazole, which are not P-gp substrates, do not show increased active renal clearance in CF patients.

Contributions of saturable active secretion, passive transcellular, and paracellular diffusion to the overall transport of furosemide across adenocarcinoma (Caco-2) cells

Furosemide permeation across Caco-2 cells was investigated to determine if previously reported directional differences in transport rates are due to a saturable, energy dependent process. In addition, studies were carried out to determine the route of permeation for this drug. By comparing apical (A) to basolateral (B) and B to A directional transport across Caco-2 cells, a saturable, nonlinear component to furosemide transport was observed. Transport in the secretory direction was fit to yield the following apparent parameters K(m) = 63 +/- 28 microM, V(max) = 436 +/- 137 pmol/cm(2)h, and P(app) = 3.7 +/- 0.9 x 10(-7) cm/s. Evidence of energy dependence was demonstrated using both metabolic inhibition, and transport against a diffusion gradient methods. Disruption of tight junctions by use of the calcium chelator, EGTA, caused a significant increase in furosemide transport (twofold and 12-fold increases in B to A and A to B, respectively) indicating the importance of the paracellular route. We conclude that furosemide secretion from Caco-2 cells is the result of saturable active transport and passive diffusion that has a significant paracellular component.

Retroviral transfection of Madin-Darby canine kidney cells with human MDR1 results in a major increase in globotriaosylceramide and 10(5)- to 10(6)-fold increased cell sensitivity to verocytotoxin. Role of p-glycoprotein in glycolipid synthesis

Retroviral infection of the Madin-Darby canine kidney (MDCK) renal cell line with human MDR1 cDNA, encoding the P-glycoprotein (P-gp) multidrug resistance efflux pump, induces a major accumulation of the glycosphingolipid (GSL), globotriaosylceramide (Galalpha1-4Galbeta1-4glucosylceramide-Gb(3)), the receptor for the E. coli-derived verotoxin (VT), to effect a approximately million-fold increase in cell sensitivity to VT. The shorter chain fatty acid isoforms of Gb(3) (primarily C16 and C18) are elevated and VT is internalized to the endoplasmic reticulum/nuclear envelope as we have reported for other hypersensitive cell lines. P-gp (but not MRP) inhibitors, e.g. ketoconazole or cyclosporin A (CsA) prevented the increased Gb(3) and VT sensitivity, concomitant with increased vinblastine sensitivity. Gb(3) synthase was not significantly elevated in MDR1-MDCK cells and was not affected by CsA. In MDR1-MDCK cells, synthesis of fluorescent N-[7-(4-nitrobenzo-2-oxa-1,3-diazole)]-aminocaproyl (NBD)-lactosylceramide (LacCer) and NBD-Gb(3) via NBD-glucosylceramide (GlcCer) from exogenous NBD-C(6)-ceramide, was prevented by CsA. We therefore propose that P-gp can mediate GlcCer translocation across the bilayer, from the cytosolic face of the Golgi to the lumen, to provide increased substrate for the lumenal synthesis of LacCer and subsequently Gb(3). These results provide a molecular mechanism for the observed increased sensitivity of multidrug-resistant tumors to VT and emphasize the potential of verotoxin as an antineoplastic. Two strains (I and II) of MDCK cells, which differ in their glycolipid profile, have been described. The original MDR1-MDCK parental cell was not specified, but the MDR1-MDCK GSL phenotype and glycolipid synthase activities indicate MDCK-I cells. However, the partial drug resistance of MDCK-I cells precludes their being the parental cell. We speculate that the retroviral transfection per se, or the subsequent selection for drug resistance, selected a subpopulation of MDCK-I cells in the parental MDCK-II cell culture and that drug resistance in MDR1-MDCK cells is thus a result of both MDR1 expression and a second, previously unrecognized, component, likely the high level of GlcCer synthesis in these cells.

Active transport of the angiotensin-II antagonist losartan and its main metabolite EXP 3174 across MDCK-MDR1 and caco-2 cell monolayers

1. We studied the functional interaction between transport and metabolism by comparing the transport of losartan and its active metabolite EXP 3174 (EXP) across cell monolayers. 2. Epithelial layers of Caco-2 cells as well as MDR1, MRP-1 and MRP-2 overexpressing cells, in comparison to the respective wildtypes, were used to characterize the transcellular transport of losartan and EXP. 3. Losartan transport in MDCK-MDR1 and Caco-2 cells was saturable and energy-dependent with a significantly greater basolateral-to-apical (B/A) than apical-to-basolateral (A/B) flux (ratio=31+/-1 in MDCK-MDR1 and ratio 4+/-1 in Caco-2 cells). The B/A flux of losartan was inhibited by cyclosporine and vinblastine, inhibitors of P-glycoprotein and MRP. In contrast, no active losartan transport was observed in MRP-1 or MRP-2 overexpressing cells. 4. The metabolite was only transported in Caco-2 cells with a B/A-to-A/B ratio of 5+/-1, while lacking active transport in the MDR1, MRP-1 or MRP-2 overexpressing cells. The B/A flux of EXP was significantly inhibited by cyclosporine and vinblastine. 5. In conclusion, losartan is transported by P-glycoprotein and other intestinal transporters, that do not include MRP-1 and MRP-2. In contrast, the carboxylic acid metabolite is not a P-glycoprotein substrate, but displays considerably higher affinity for other transporters than losartan, that again most probably do not include MRP-1 and MRP-2.