Affinity For P-glycoprotein Research Articles

Spice components as modulating agents of P-glycoprotein - An in silico study.

P-glycoprotein acts as a protective barrier against xenobiotics and cellular toxicants in the human body while playing an important role in drug transportation in many organs. Overexpression of p-glycoprotein can lead to a decrease in the absorption of many drugs. After screening, 33 phytochemicals from 25 spices were selected for docking with p-glycoprotein to detect some naturally occurring p-glycoprotein inhibitors to modulate multidrug resistance. Absorption, distribution, metabolism, excretion, and toxicity prediction and drug-like properties of those ligands were investigated from pkCSM, Molinspiration, and SwissADME software, followed by molecular docking study and molecular dynamic simulation on BIOVIA Discovery Studio. These 33 phytochemicals met the criteria of p-glycoprotein inhibitor as much as the reference drug verapamil. Pandamarilactone-31 showed the highest binding affinity for p-glycoprotein, acting as the lead p-glycoprotein inhibitor, followed by α-D-fructofuranoside methyl, sesamolinol, and nigellidine.

Search for immunomodulatory compounds with antiproliferative activity against melanoma

BackgroundMelanoma is a highly aggressive neoplasm with a high degree of malignancy and rapid acquisition of resistance by cancer cells. MethodsBiological studies of a series of isoxazole compounds with immunomodulatory properties were preceded by in silico analysis. The assay evaluated the viability of NHDF and A375 cell cultures after the administration of isoxazole compounds after a 24-hour incubation period in the MTT test. Analyzes of ROS and NO scavenging, P-glycoprotein activity, and properties were performed. The levels of Caspase 3 and Caspase 9 were measured using ELISA to assess which pathways induced apoptosis by the tested compounds. On the chip, the synergistic effect of doxorubicin and the most active compound from the MM9 series on cells of the A375 melanoma line was determined. ResultsAll tested N′-substituted derivatives of 5-amino-N,3-dimethyl-1,2-oxazole-4-carbohydrazide with immunomodulatory activity show multidirectional antitumor activity on A375 melanoma lines with an affinity for P-glycoprotein, induction of free radical formation and generation of DNA damage leading to the death of cancer cells, as well as formation of complexes with DNA Topoisomerase II. Most of the tested compounds show pro-apoptotic activity. The most active compound in the series induces apoptosis in three distinct pathways and acts synergistically with doxorubicin. ConclusionsThe most active compound with immunomodulatory properties showed multidirectional antitumor activity against cells of the A375 melanoma line and also had a synergistic pro-apoptotic effect with doxorubicin, which may result in a reduction of this cytostatic dose with increased effectiveness.

A Comprehensive Evaluation of Sdox, a Promising H2S-Releasing Doxorubicin for the Treatment of Chemoresistant Tumors.

Sdox is a hydrogen sulfide (H2S)-releasing doxorubicin effective in P-glycoprotein-overexpressing/doxorubicin-resistant tumor models and not cytotoxic, as the parental drug, in H9c2 cardiomyocytes. The aim of this study was the assessment of Sdox drug-like features and its absorption, distribution, metabolism, and excretion (ADME)/toxicity properties, by a multi- and transdisciplinary in silico, in vitro, and in vivo approach. Doxorubicin was used as the reference compound. The in silico profiling suggested that Sdox possesses higher lipophilicity and lower solubility compared to doxorubicin, and the off-targets prediction revealed relevant differences between Dox and Sdox towards several cancer targets, suggesting different toxicological profiles. In vitro data showed that Sdox is a substrate with lower affinity for P-glycoprotein, less hepatotoxic, and causes less oxidative damage than doxorubicin. Both anthracyclines inhibited CYP3A4, but not hERG currents. Unlike doxorubicin, the percentage of zebrafish live embryos at 72 hpf was not affected by Sdox treatment. In conclusion, these findings demonstrate that Sdox displays a more favorable drug-like ADME/toxicity profile than doxorubicin, different selectivity towards cancer targets, along with a greater preclinical efficacy in resistant tumors. Therefore, Sdox represents a prototype of innovative anthracyclines, worthy of further investigations in clinical settings.

Interactions between Rhodamine Dyes and Model Membrane Systems-Insights from Molecular Dynamics Simulations.

Background: rhodamines are dyes widely used as fluorescent tags in cell imaging, probing of mitochondrial membrane potential, and as P-glycoprotein model substrates. In all these applications, detailed understanding of the interaction between rhodamines and biomembranes is fundamental. Methods: we combined atomistic molecular dynamics (MD) simulations and fluorescence spectroscopy to characterize the interaction between rhodamines 123 and B (Rh123 and RhB, respectively) and POPC bilayers. Results: while the xanthene moiety orients roughly parallel to the membrane plane in unrestrained MD simulations, variations on the relative position of the benzoic ring (below the xanthene for Rh123, above it for RhB) were observed, and related to the structure of the two dyes and their interactions with water and lipids. Subtle distinctions were found among different ionization forms of the probes. Experimentally, RhB displayed a lipid/water partition coefficient more than two orders of magnitude higher than Rh123, in agreement with free energy profiles obtained from umbrella sampling MD. Conclusions: this work provided detailed insights on the similarities and differences in the behavior of bilayer-inserted Rh123 and RhB, related to the structure of the probes. The much higher affinity of RhB for the membranes increases the local concentration and explains its higher apparent affinity for P-glycoprotein reconstituted in model membranes.

Enzyme-responsive polymeric micelles of cabazitaxel for prostate cancer targeted therapy

Cabazitaxel, a novel tubulin inhibitor with poor affinity for P-glycoprotein, is a second-generation taxane holding great promise for the treatment of metastatic castration-resistant prostate cancer. However, its poor solubility and lack of target-ability limit its therapeutic applications. Herein, we develop a biodegradable, enzyme-responsive, and targeted polymeric micelle for cabazitaxel. The micelle is formed from two amphiphilic block copolymers. The first block copolymer consists of PEG, an enzyme-responsive peptide, and cholesterol; whereas the second block copolymer consists of a targeting ligand, PEG and cholesterol. The enzyme-responsive peptide is cleavable in the presence of matrixmetaloproteinase-2 (MMP-2), which is overexpressed in the tumor microenvironment of prostate cancer. The micelle showed a very low critical micelle concentration (CMC), high drug loading, and high entrapment efficiency. Release of cabazitaxel from the micelle is dependent on the cleavage of the enzyme-responsive peptide. Moreover, the micelle showed dramatically higher cellular uptake in prostate cancer cells compared to free cabazitaxel. Importantly, the ligand-coupled polymeric micelle demonstrated better inhibition of tumor growth in mice bearing prostate cancer xenografts compared to unmodified micelle and free cabazitaxel. Taken together, these findings suggest that the enzyme-responsive cabazitaxel micelle is a potent and promising drug delivery system for advanced prostate cancer therapy. Statement of SignificanceHerein, we develop a biodegradable, enzyme-responsive, and actively targeted polymer micelle for cabazitaxel, which is a novel tubulin inhibitor with poor affinity for P-glycoprotein. Despite cabazitaxel’s great promise for metastatic castration-resistant prostate cancer, its poor solubility, lack of target-ability, and high systemic toxicity limit its therapeutic applications, and therefore a targeted delivery system is highly needed for cabazitaxel. Our results demonstrate the importance of active targeting in targeted prostate cancer therapy. Encapsulating cabazitaxel in the micelle increases its activity and is expected to reduce its systemic toxicity, which is a major hurdle in its clinical applications. Moreover, the polymeric micelle may servers as a promising nanoscale platform for the targeted delivery of other chemotherapeutic agents to prostate cancer.

Pharmacogenetics of the safety of phenazepam in alcohol withdrawal syndrome: haplotype and combinatorial analyses of polymorphic variants in the pharmacokinetic factor genes

Phenazepam is a benzodiazepine tranquilizer that is widely used in Russia. The drug is metabolized by cytochrome P450 3A (CYP3A) isozymes. Since their substrates have an affinity for P-glycoprotein, the polymorphic variants in the ABCB1 gene may affect the safety of this drug. Objective: to analyze associations between the CYP3A5, CYP2C9, CYP2C19, CYP2D6 and ABCB1 gene polymorphisms and the safety of phenazepam treatment for alcohol withdrawal syndrome (AWS). Patients and methods. The investigation enrolled 102 patients diagnosed with uncomplicated AWS (IDC-10 code F10.30). All the patients were followed up for 6 days within which they took phenazepam. 5-ml venous blood samples were collected from each patient for genotyping. The carriage of CYP3A4*22, CYP3A5*3, CYP2C19*2, CYP2C19*17, CYP2C9*2, ABCB1 3435C>T, 1236C>T, and 2677G>T/A polymorphic variants was determined by a real-time polymerase chain reaction assay. Therapy safety was evaluated using the UKU Side-Effect Rating Scale on day 6. Statistical analysis was carried out with SPSS Statistics 21.0. Haplotype and combinatorial analyses were performed using SNPStats. Results and discussion. The greater subjective severity of adverse reactions (ARs) was shown for the homozygotes of ABCB1 1236C>T CC (odds ratio (OR), 2.154; 95% confidence interval (CI), 1.271–3.650; p=0.014) and ABCB1 2677G>T GG (OR, 2.154; 95% CI, 1.271–3.650; p=0.014). On the contrary, a combinatorial analysis revealed the role of ABCB1 3435C>T, 1236C>T, and 2677G>T polymorphic alleles as predictors for the greater subjective severity of ARs. The following statistically significant polymorphic variant combinations were ABCB1 3435-1236–2677 and T-T-T-CYP3A5*3 isozymes (OR=5.03; 95% CI, 1.65–15.34; p=0.0056); T-T-T-CYP2C9*1 (OR=3.61; 95% CI, 1.31–9.92; p=0.015); T-T-T-CYP2C19*1 (OR=2.52; 95% CI, 1.05–6.08; p=0.042). Attention disorders were also established to be associated with the carriage of T-T-T-CYP2D6*1 (OR=2.58; 95 CI, 1.08–6.13; p=0.035). Conclusion. The carriage of ABCB1 3435-2677-1236 (T-T-T) haplotype is significantly associated with the greater severity of ARs in phenazepam-treated patients with AWS.

Current Development of Oral Taxane Formulations: A Review.

In this review, we describe the advances in oral drug delivery approaches for taxanes for successful therapeutic outcome. Taxanes (paclitaxel and docetaxel) have unwanted pharmacokinetic profiles when they are given in their current dosage forms. Taxanes have low bioavailability, are extensively metabolized by CYP3A, and have a high affinity for P-glycoprotein. Regardless of dosage schedule, the overall docetaxel or paclitaxel dose that a patient can tolerate at a given interval remains similar. Currently, there are no commercially available oral taxane nanoformulations, and there are still several challenges to overcome. Nano-based formulations may offer the best solutions to problems involving the safety and effectiveness of taxane delivery. Thus, further research is necessary before such taxane nanoformulations can be manufactured for clinical use.

Possible Role of P-Glycoprotein in Cyclosporine -Acitretin Drug Interaction

P-glycoprotein, an efflux transporter prevents intracellular accumulation of xenobiotics. Cyclosporine A and acitretin are used to treat psoriasis. The present research work aims to investigate the possible role of P-glycoprotein in Cyclosporine- Acitretin drug interaction due to evidence of both drugs having affinity for P-glycoprotein.The study has three different objective namely to assess apparent permeability coefficient of cyclosporine in presence of acitretin by non-everted sac technique, to study the intestinal permeation and absorption kinetics of cyclosporine in presence of acitretin by single pass intestinal perfusion (SPIP) technique and to study the influence of acitretin on oral bioavailability of cyclosporine in Wistar rats.The result of ex vivo, in situ and in vivo study showed that cyclosporine level increased in a time dependent manner. As the dose of acitretin increases the cyclosporine concentration in all three methods tend to increase and was statistically significant. The improvement in absorption of cyclosporine may be due to the inhibition of P-glycoprotein transporter in the intestine by acitretin. Thus acitretin may enhance the oral pharmacokinetics of cyclosporine. Hence this combination may require close monitoring for better therapeutic outcome. Our study confirmed the inhibitory role of acitretin on P-glycoprotein leading to increase concentration of cyclosporine.

Cabazitaxel: A novel taxane for metastatic castration-resistant prostate cancer-current implications and future prospects

Recent advances in the management of prostate cancer have shown considerable development with time and many novel therapeutic agents have been approved over the past years. For patients with metastatic castration-resistant prostate cancer (mCRPC), initially docetaxel was the standard chemotherapy but once they became refractory to docetaxel, no treatment improved survival. This scenario changed in June 2010 when the US Food and Drug Administration (FDA) approved Cabazitaxel as a new therapeutic option for patients with mCRPC resistant to docetaxel. Cabazitaxel, being a novel tubulin-binding taxane with poor affinity for P-glycoprotein, decreases the chances of resistance. It has shown antitumor activity in preclinical, phase I, II and III clinical studies in docetaxel-resistant tumors. This article summarises the background, pharmacodynamic, kinetics and clinical development of cabazitaxel for the treatment of castration-resistant prostate cancer. Future development and rational use of this drug in other tumors is under therapeutic investigation.

Nowe trendy w leczeniu raka jajnika

Ovarian cancer is the fifth most lethal malignancy in women. The standard treatment of this disease is chemotherapy which is, however, often inefficient. The failure of chemotherapy is due to the developing multidrug resistance and the presence of cancer stem cells. This article describes research on new drugs, which can overcome these limitations. Some of the substances which are effective in cancer cells resistant to the standard approach are bisintercalating anthracyclines and epothilones. One of the bisanthracyclines is WP 631, which is more effective than commonly used first-generation anthracyclines, even on cells resistant to cisplatin or doxorubicin. In turn, epothilones have a similar mechanism of action as taxanes. They stabilize microtubules and consequently perturb mitosis. Both WP 631 and epothilones appear to be hopeful candidates to break multidrug resistance because of their low affinity for P-glycoprotein – the efflux pump for drugs. Substances, which effectively eliminate cancer stem cells include metformin, Mullerian inhibiting substance, and salinomycin. Metformin has a proapoptotic activity and exhibits synergism with cisplatin – a chemotherapeutic agent used in ovarian cancer treatment. Mullerian inhibiting substance perturbs the cell cycle, while salinomycin inhibits proliferation and induces apoptosis in the ovarian cancer cells. The search for new drugs effective in the ovarian cancer treatment, especially in cases resistant to current forms of therapy, remains a challenging priority.

Microtubule-Targeting Drugs and Personalization of Cancer Treatment

dose-limiting toxicities. Myelosuppression is a common feature for most chemotherapeutic agents owing to the high proliferation rate in bone marrow. The peripheral neuropathy, observed for many of these drugs, seems to be related to the crucial role of b-tubulins in neurons. In fact, germline mutations in isotypes IIb and III have recently been shown to result in severe neurologic defects [2,3]. The lack of toxicity of these drugs in the CNS can be explained by the high affinity for P-glycoprotein, an efflux pump highly expressed at the brain–blood barrier. The efficacy and adverse drug reactions of the different microtubule-targeting drugs also vary widely among patients treated with the same drugs and using the same schemes. This is the reason why the search for pharmaco genetic markers able to predict the clinical effects of these drugs has been given so much attention as of late.

Cabazitaxel: a novel second-line treatment for metastatic castration-resistant prostate cancer

Until recently, patients with castration-resistant prostate cancer (CRPC) had limited therapeutic options once they became refractory to docetaxel chemotherapy, and no treatments improved survival. This changed in June 2010 when the Food and Drug Administration (FDA) approved cabazitaxel as a new option for patients with CRPC whose disease progresses during or after docetaxel treatment. For most of these patients, cabazitaxel will now replace mitoxantrone (a drug that was FDA-approved because of its palliative effects) as the treatment of choice for docetaxel-refractory disease. The approval of cabazitaxel was based primarily on the TROPIC trial, a large (n = 755) randomized Phase III study showing an overall median survival benefit of 2.4 months for men with docetaxel-pretreated metastatic CRPC receiving cabazitaxel (with prednisone) compared to mitoxantrone (with prednisone). Cabazitaxel is a novel tubulin-binding taxane that differs from docetaxel because of its poor affinity for P-glycoprotein (P-gp), an ATP-dependent drug efflux pump. Cancer cells that express P-gp become resistant to taxanes, and the effectiveness of docetaxel can be limited by its high substrate affinity for P-gp. Preclinical and early clinical studies show that cabazitaxel retains activity in docetaxel-resistant tumors, and this was confirmed by the TROPIC study. Common adverse events with cabazitaxel include neutropenia (including febrile neutropenia) and diarrhea, while neuropathy was rarely observed. Thus, the combination of cabazitaxel and prednisone is an important new treatment option for men with docetaxel-refractory metastatic CRPC, but this agent should be administered cautiously and with appropriate monitoring (especially in men at high risk of neutropenic complications).

Sigma Receptors in Oncology: Therapeutic and Diagnostic Applications of Sigma Ligands

Sigma receptors (subtypes sigma-1 and sigma-2) are a unique class of binding sites expressed throughout the mammalian body. The endogenous ligand for these sites has not been identified, but steroid hormones (particularly progesterone), sphingolipid-derived amines and N,N-dimethyltryptamine can bind with fairly high affinity. Sigma receptors are overexpressed in rapidly proliferating cells, like cancer cells. Particularly the sigma-2 subtype is upregulate when cells divide and down regulated when they become quiescent. Sigma ligands, especially sigma-2 agonists, can inhibit proliferation and induce apoptosis by a mechanism involving changes in cytosolic Ca(2+), ceramide and sphingolipid levels. Tumor cells are much more sensitive to such treatment than cells from their tissue of origin. Sigma ligands induce apoptosis not only in drug-sensitive but also in drug-resistant cancer cells (e.g., cells with p53 mutations, or caspase dysfunction). Moreover, sigma ligands may abrogate P-glycoprotein-mediated drug resistance and at subtoxic doses, they can potentiate the effect of conventional cytostatics. Thus, sigma-2 agonists may be developed as antineoplastic agents for the treatment of drug-resistant tumors. A large number of radiolabeled sigma ligands has been prepared for SPECT (single-photon emission computed tomography) and PET (positron emission tomography) imaging. Such radiopharmaceuticals can be used for tumor detection, tumor staging, and evaluation of anti-tumor therapy. There is still a need for the development of ligands with (1) high selectivity for the sigma-2 subtype, (2) defined action (agonist or antagonist) and (3) optimal pharmacokinetics (low affinity for P-glycoprotein, high and specific tumor uptake, and rapid washout from non-target tissues).

Population pharmacokinetics of intravenously and orally administered docetaxel with or without co‐administration of ritonavir in patients with advanced cancer

Docetaxel has a low oral bioavailability due to affinity for P-glycoprotein and cytochrome P450 (CYP) 3A4 enzymes. Inhibition of the CYP3A4 enzymes by ritonavir resulted in increased oral bioavailability. The aim of this study was to develop a population pharmacokinetic (PK) model and to evaluate and quantify the influence of ritonavir on the PK of docetaxel. Data from two clinical trials were included in the data analysis, in which docetaxel (75 mg m(-2) or 100 mg) had been administered intravenously or orally (10 mg or 100 mg) with or without co-administration of oral ritonavir (100 mg). Population modelling was performed using non-linear mixed effects modelling. A three-compartment model was used to describe the i.v. data. PK data after oral administration, with or without co-administration of ritonavir, were incorporated into the model. Gut bioavailability of docetaxel increased approximately two-fold from 19 to 39% (CV 13%) with ritonavir co-administration. The hepatic extraction ratio and the elimination rate of docetaxel were best described by estimating the intrinsic clearance. Ritonavir was found to inhibit in a concentration dependent manner the intrinsic clearance of docetaxel, which was described by an inhibition constant of 0.028 microg ml(-1) (CV 36%). A maximum inhibition of docetaxel clearance of more then 90% was reached. A PK model describing both the PK of orally and intravenously administered docetaxel in combination with ritonavir, was successfully developed. Co-administration of ritonavir lead to increased oral absorption and reduced elimination rate of docetaxel.

A Comparison of Pharmacokinetics between Humans and Monkeys

To verify the availability of pharmacokinetic parameters in cynomolgus monkeys, hepatic availability (Fh) and the fraction absorbed multiplied by intestinal availability (FaFg) were evaluated to determine their contributions to absolute bioavailability (F) after intravenous and oral administrations. These results were compared with those for humans using 13 commercial drugs for which human pharmacokinetic parameters have been reported. In addition, in vitro studies of these drugs, including membrane permeability, intrinsic clearance, and p-glycoprotein affinity, were performed to classify the drugs on the basis of their pharmacokinetic properties. In the present study, monkeys had a markedly lower F than humans for 8 of 13 drugs. Although there were no obvious differences in Fh between humans and monkeys, a remarkable species difference in FaFg was observed. Subsequently, we compared the FaFg values for monkeys with the in vitro pharmacokinetic properties of each drug. No obvious FaFg differences were observed between humans and monkeys for drugs that undergo almost no in vivo metabolism. In contrast, low FaFg were observed in monkeys for drugs that undergo relatively high metabolism in monkeys. These results suggest that first-pass intestinal metabolism is greater in cynomolgus monkeys than in humans, and that bioavailability in cynomolgus monkeys after oral administration is unsuitable for predicting pharmacokinetics in humans. In addition, a rough correlation was also observed between in vitro metabolic stability and Fg in humans, possibly indicating the potential for Fg prediction in humans using only in vitro parameters after slight modification of the evaluation system for in vitro intestinal metabolism.

A multicenter phase II study of XRP6258 administered as a 1-h i.v. infusion every 3 weeks in taxane-resistant metastatic breast cancer patients

BackgroundXRP6258 is a novel taxoid with a low affinity for P-glycoprotein. This multicenter phase II study assessed the activity of XRP6258 in the treatment of taxane-resistant metastatic breast cancer (MBC). Patients and methodsXRP6258 was administered as a 1-h i.v. infusion every 3 weeks at 20 mg/m2 (then, in the absence of severe toxicity, at 25 mg/m2 from cycle 2). The primary end point was the objective response rate (ORR) assessed according to response evaluation criteria in solid tumours (RECIST) guidelines. ResultsSeventy-one patients were enrolled. The median relative dose intensity was 0.98. The ORR was 14% (two complete, eight partial responses). Eighteen patients (25%) had stable disease of >3 months duration. At a median follow-up of 20.0 months, the median time to progression was 2.7 months, and the median overall survival 12.3 months. The most common grade 3/4 adverse events (AEs) were neutropenia (73%) and leucopenia (55%), with a low febrile neutropenia rate (3%) and infrequent grade 3/4, treatment-related, non-hematological AEs (<5% patients for any AE). Two deaths were reported, one related to study drug and one to unknown cause. ConclusionsXRP6258 was active and well tolerated in this group of MBC patients with taxane-resistant disease. These results support the further clinical development of this agent.

Sertraline and Its Metabolite Desmethylsertraline, but not Bupropion or Its Three Major Metabolites, Have High Affinity for P-Glycoprotein

The ATP-binding cassette (ABC) transporter protein subfamily B1 line (ABCB1) transporter P-glycoprotein (P-gp) plays an important role in the blood-brain barrier limiting a broad spectrum of substrates from entering the central nervous system. In the present study, the transport activity of P-gp for sertraline, desmethylsertraline, bupropion, and the major metabolites of bupropion, threo-amino alcohol (TB), erythro-amino alcohol (EB), and hydroxy metabolite (HB) was studied using an ATPase assay in expressed human P-gp membranes by measuring concentrations of inorganic P(i) in expressed human P-gp membranes. Verapamil was included as a positive control. The Michaelis-Menten equation was used for characterizing the kinetic data. Sertraline and desmethylsertraline showed high affinity for P-gp. The V(max)/K(m) values of sertraline (1.6 min(-1) x 10(-3)) and desmethylsertraline (1.4 min(-1) x 10(-3)) were comparable with that of verapamil (1.7 min(-1) x 10(-3)). Bupropion and its three metabolites showed very weak affinity for P-gp, with V(max)/K(m) values lower than 0.01 min(-1) x 10(-3). The results of the present study indicate that sertraline and desmethylsertraline have high affinity for P-gp, whereas bupropion and its three major metabolites TB, EB, and HB have very weak affinity for P-gp. These findings may help to explain observed drug-drug interactions among antidepressants.

Interactions of attention-deficit/hyperactivity disorder therapeutic agents with the efflux transporter P-glycoprotein

The objective of this study was to assess the potential interactions of the drug transporter P-glycoprotein with attention-deficit/hyperactivity disorder (ADHD) therapeutic agents atomoxetine — and the individual isomers of methylphenidate, amphetamine, and modafinil utilizing established in vitro assay. An initial ATPase assay indicated that both d- and l-methylphenidate have weak affinity for P-glycoprotein. The intracellular accumulation of P-glycoprotein substrates doxorubicin and rhodamine123 in the P-glycoprotein overexpressing cell line LLC-PK1/MDR1 was determined to evaluate potential inhibitory effects on P-glycoprotein. The results demonstrated that all compounds, except both modafinil isomers, significantly increased doxorubicin and rhodamine123 accumulation in LLC-PK1/MDR1 cells at higher concentrations. To investigate the P-glycoprotein substrate properties, the intracellular concentrations of the tested compounds in LLC-PK1/MDR1 and P-glycoprotein negative LLC-PK1 cells were measured in the presence and absence of the P-glycoprotein inhibitor PSC833. The results indicate that the accumulation of d-methylphenidate in LLC-PK1 cells was 32.0% higher than in LLC-PK1/MDR1 cells. Additionally, coadministration of PSC833 leads to 52.9% and 45.6% increases in d-modafinil and l-modafinil accumulation, respectively, in LLC-PK1/MDR1 cells. Further studies demonstrated that l-modafinil transport across LLC-PK1/MDR1 cell monolayers in the basolateral-to-apical (B–A) direction was significantly higher than in the apical-to-basolateral (A–B) direction. PSC833 treatment significantly decreased the transport of l-modafinil in B–A direction. In conclusion, our results suggest that all tested agents with the exception of modafinil isomers are relatively weak P-glycoprotein inhibitors. Furthermore, P-glycoprotein may play a minor role in the transport of d-methylphenidate, d-modafinil, and l-modafinil.

Transport of a new erectogenic udenafil in caco-2 cells

P-glycoprotein, an ATP-dependent efflux pump, is a membrane transporter that influences the absorption and excretion of drugs. There is a striking overlap between the substrates for CYP3A4 and P-glycoprotein. This study was designed to assess whether udenafil, a substrate of CYP3A4, is also a P-glycoprotein substrate. Udenafil stimulated P-glycoprotein ATPase activity, a putative measure of P-glycoprotein affinity, although with lower affinity than a proven substrate, verapamil. Bidirectional transport studies of udenafil using Caco-2 cell monolayers showed that its efflux (15.9-22.8 x 10(-6) cm/s) was significantly higher than its influx (3.7-9.1 x 10(-6) cm/s). P-glycoprotein inhibitors such as cyclosporine, tariquidar and verapamil significantly increased the influx of udenafil and decreased the efflux of udenafil. These results indicate that udenafil is a substrate for P-glycoprotein. The low bioavailability, variable absorption and drug-drug interactions of udenafil may be related to the variability of CYP3A4 and P-glycoprotein expression and to possible CYP3A4 and P-glycoprotein interactions.

PI-35Sertraline and its metabolite desmethylsertraline, but not bupropion or its major metabolites, have high affinity for P-glycoprotein

PI-35Sertraline and its metabolite desmethylsertraline, but not bupropion or its major metabolites, have high affinity for P-glycoprotein