Rapid identification of P-glycoprotein substrates and inhibitors

Repaglinide-Solid Lipid Nanoparticles in Chitosan Patches for Transdermal Application: Box-Behnken Design, Characterization, and In Vivo Evaluation

Background

Repaglinide (REP) is an antidiabetic drug with limited oral bioavailability attributable to its low solubility and considerable first-pass hepatic breakdown. This study aimed to develop a biodegradable chitosan-based system loaded with REP-solid lipid nanoparticles (REP-SLNs) for controlled release and bioavailability enhancement via transdermal delivery.

Methods

REP-SLNs were fabricated by ultrasonic hot-melt emulsification. A Box-Behnken design (BBD) was employed to explore and optimize the impacts of processing variables (lipid content, surfactant concentration, and sonication amplitude) on particle size (PS), and entrapment efficiency (EE). The optimized REP-SLN formulation was then incorporated within a chitosan solution to develop a transdermal delivery system (REP-SLN-TDDS) and evaluated for physicochemical properties, drug release, and ex vivo permeation profiles. Pharmacokinetic and pharmacodynamic characteristics were assessed using experimental rats.

Results

The optimized REP-SLNs had a PS of 249±9.8 nm and EE of 78%±2.3%. The developed REP-SLN-TDDS demonstrated acceptable characteristics without significant aggregation of REP-SLNs throughout the casting and drying processes. The REP-SLN-TDDS exhibited a biphasic release pattern, where around 36% of the drug load was released during the first 2 h, then the drug release was sustained at around 80% at 24 h. The computed flux across rat skin for the REP-SLN-TDDS was 2.481±0.22 μg/cm2/h in comparison to 0.696±0.07 μg/cm2/h for the unprocessed REP, with an enhancement ratio of 3.56. The REP-SLN-TDDS was capable of sustaining greater REP plasma levels over a 24 h period (p<0.05). The REP-SLN-TDDS also reduced blood glucose levels compared to unprocessed REP and commercial tablets (p<0.05) in experimental rats.

Conclusion

Our REP-SLN-TDDS can be considered an efficient therapeutic option for REP administration.

Repurposable Drugs for Immunotherapy and Strategies to Find Candidate Drugs

Conventional drug discovery involves significant steps, time, and expenses; therefore, novel methods for drug discovery remain unmet, particularly for patients with intractable diseases. For this purpose, the drug repurposing method has been recently used to search for new therapeutic agents. Repurposed drugs are mostly previously approved drugs, which were carefully tested for their efficacy for other diseases and had their safety for the human body confirmed following careful pre-clinical trials, clinical trials, and post-marketing surveillance. Therefore, using these approved drugs for other diseases that cannot be treated using conventional therapeutic methods could save time and economic costs for testing their clinical applicability. In this review, we have summarized the methods for identifying repurposable drugs focusing on immunotherapy.

Lipid-based solubilization technology via hot melt extrusion: promises and challenges

INTRODUCTION

Self-emulsifying drug delivery systems (SEDDS) are a promising strategy to improve the oral bioavailability of poorly water-soluble drugs (PWSD). The excipients of SEDDS enable permeation through the mucus and gastro-intestinal barrier, inhibiting efflux transporters (e.g. P-glycoprotein) of drugs. Poor drug loading capacity and formulation instability are the main setbacks of traditional SEDDS. The use of polymeric precipitation inhibitors was shown to create supersaturable SEDDS with increased drug payload, and their solidification can help to overcome the instability challenge. As an alternative to several existing SEDDS solidification technologies, hot melt extrusion (HME) holds the potential for lean and continuous manufacturing of supersaturable solid-SEDDS. Despite being ubiquitously applied in solid lipid and polymeric processing, HME has not yet been widely considered for the preparation of SEDDS.

AREAS COVERED

The review begins with the rationale why SEDDS as the preferred lipid-based delivery systems (LBDS) is suitable for the oral delivery of PWSD and discusses the common barriers to oral administration. The potential of LBDS to surmount them is discussed. SEDDS as the flagship of LBDS for PWSD is proposed with a special emphasis on solid-SEDDS. Finally, the opportunities and challenges of HME from the lipid-based excipient (LBE) processing and product performance standpoint are highlighted.

EXPERT OPINION

HME can be a continuous, solvent-free, cost-effective, and scalable technology for manufacturing solid supersaturable SEDDS. Several critical formulations and process parameters in successfully preparing SEDDS via HME are identified.

A Simple UPLC/MS-MS Method for Simultaneous Determination of Lenvatinib and Telmisartan in Rat Plasma, and Its Application to Pharmacokinetic Drug-Drug Interaction Study

Lenvatinib is a multi-targeted tyrosine kinase inhibitor that inhibits tumor angiogenesis, but hypertension is the most common adverse reaction. Telmisartan is an angiotensin receptor blocker used to treat hypertension. In this study, a simple ultra-performance liquid chromatography-tandem mass spectrometry method was developed for the simultaneous determination of lenvatinib and telmisartan, and it was applied to the pharmacokinetic drug interaction study. Plasma samples were treated with acetonitrile to precipitate protein. Water (containing 5 mM of ammonium acetate and 0.1% formic acid) and acetonitrile (0.1% formic acid) were used as the mobile phases to separate the analytes with gradient elution using a column XSelect HSS T3 (2.1 mm × 100 mm, 2.5 μm). Multiple reaction monitoring in the positive ion mode was used for quantification. The method was validated and the precision, accuracy, matrix effect, recovery, and stability of this method were reasonable. The determination of analytes was not interfered with by other substances in the blank plasma, and the calibration curves of lenvatinib and telmisartan were linear within the range of 0.2–1000 ng/mL and 0.1–500 ng/mL, respectively. The results indicate that lenvatinib decreased the systemic exposure of telmisartan. Potential drug interactions were observed between lenvatinib and telmisartan.

Drug-Drug Interactions in Vestibular Diseases, Clinical Problems, and Medico-Legal Implications

Peripheral vestibular disease can be treated with several approaches (e.g., maneuvers, surgery, or medical approach). Comorbidity is common in elderly patients, so polytherapy is used, but it can generate the development of drug-drug interactions (DDIs) that play a role in both adverse drug reactions and reduced adherence. For this reason, they need a complex kind of approach, considering all their individual characteristics. Physicians must be able to prescribe and deprescribe drugs based on a solid knowledge of pharmacokinetics, pharmacodynamics, and clinical indications. Moreover, full information is required to reach a real therapeutic alliance, to improve the safety of care and reduce possible malpractice claims related to drug-drug interactions. In this review, using PubMed, Embase, and Cochrane library, we searched articles published until 30 August 2021, and described both pharmacokinetic and pharmacodynamic DDIs in patients with vestibular disorders, focusing the interest on their clinical implications and on risk management strategies.

Transporter-mediated drug-drug interactions: advancement in models, analytical tools, and regulatory perspective

Drug-drug interactions mediated by transporters are a serious clinical concern hence a tremendous amount of work has been done on the characterization of the transporter-mediated proteins in humans and animals. The underlying mechanism for the transporter-mediated drug-drug interaction is the induction or inhibition of the transporter which is involved in the cellular uptake and efflux of drugs. Transporter of the brain, liver, kidney, and intestine are major determinants that alter the absorption, distribution, metabolism, excretion profile of drugs, and considerably influence the pharmacokinetic profile of drugs. As a consequence, transporter proteins may affect the therapeutic activity and safety of drugs. However, mounting evidence suggests that many drugs change the activity and/or expression of the transporter protein. Accordingly, evaluation of drug interaction during the drug development process is an integral part of risk assessment and regulatory requirements. Therefore, this review will highlight the clinical significance of the transporter, their role in disease, possible cause underlying the drug-drug interactions using analytical tools, and update on the regulatory requirement. The recent in-silico approaches which emphasize the advancement in the discovery of drug-drug interactions are also highlighted in this review. Besides, we discuss several endogenous biomarkers that have shown to act as substrates for many transporters, which could be potent determinants to find the drug-drug interactions mediated by transporters. Transporter-mediated drug-drug interactions are taken into consideration in the drug approval process therefore we also provided the extrapolated decision trees from in-vitro to in-vivo, which may trigger the follow-up to clinical studies.

Masked Phenolic-Selenium Conjugates: Potent and Selective Antiproliferative Agents Overcoming P-gp Resistance

Cancer accounts for one of the most complex diseases nowadays due to its multifactorial nature. Despite the vast number of cytotoxic agents developed so far, good therapeutic approaches are not always reached. In recent years, multitarget drugs are gaining great attention against multifactorial diseases in contraposition to polypharmacy. Herein we have accomplished the conjugation of phenolic derivatives with an ample number of organochalcogen motifs with the aim of developing novel antiproliferative agents. Their antioxidant, and antiproliferative properties (against six tumour and one non-tumour cell lines) were analysed. Moreover, in order to predict P-gp-mediated chemoresistance, the P-glycoprotein assay was also conducted in order to determine whether compounds prepared herein could behave as substrates of that glycoprotein. Selenium derivatives were found to be significantly stronger antiproliferative agents than their sulfur isosters. Moreover, the length and the nature of the tether, together with the nature of the organoselenium scaffold were also found to be crucial features in the observed bioactivities. The lead compound, bearing a methylenedioxyphenyl moiety, and a diselenide functionality, showed a good activity (GI₅₀ = 0.88‒2.0 µM) and selectivity towards tumour cell lines (selectivity index: 14‒32); moreover, compounds considered herein were not substrates for the P-gp efflux pump, thus avoiding the development of chemoresistance coming from such mechanism, commonly found for widely-used chemotherapeutic agents.

A novel approach of targeting refractory epilepsy: Need of an hour

The refractory epilepsy adds to the global burden of epilepsy as about 25 % of all patients with epilepsy present drug-resistant epilepsy. The P-glycoprotein (P-gp) plays a vital role in the mechanism of resistance in epilepsy. The AED levels in the brain are regulated by the P-gp transport. The upregulation of P-gp results in low concentration of AEDs inside the brain parenchyma and thus leads to resistance. There are three main conditions which lead to decrease transport of AEDs in refractory epilepsy. First being AEDs as substrate of P-gp; secondly, the elevated expression of P-gp in patients with drug resistant epilepsy as compared to drug-responsive patients; thirdly, the low brain AED concentration in refractory epilepsy in comparison to drug-responsive epilepsy. Therefore, determination of P-gp substrate should be a criterion for the selection of new AED for management of refractory epilepsy. This review highlights various tools which help in identification of P-gp substrates and also illustrates a concept of using various novel non-P-gp substrates which can cross the blood brain barrier and leads to enhanced accumulation inside the brain. Hence, these non P-gp substrates can be used as an add on treatment for the management of resistant epilepsy.

Molecular pharmacokinetic mechanism of the drug-drug interaction between genistein and repaglinide mediated by P-gp

This study was devised to investigate if P-glycoprotein (P-gp) mediated the drug-drug interaction (DDI) between genistein and repaglinide. When genistein was added, the plasma concentrations of repaglinide in rats were increased. The maximum plasma concentration (Cmax) of repaglinide increased from 70.80 ± 7.98 ng/mL to 124.71 ± 9.02 ng/mL and the area under the plasma concentration-time curve (AUC) increased from 134.89 ± 13.65 μg·h/L to 245.95 ± 7.24 μg·h/L. Intestinal absorption of repaglinide was markedly enhanced by genistein or P-gp inhibitor verapamil (Ver), both in situ rat jejunal perfusion studies and in vitro transport assays using everted rat intestinal sac preparations. Furthermore, the accumulation of repaglinide in both Caco-2 cells and IEC-6 cells also increased significantly in the presence of genistein and Ver. The transepithelial transport rate of repaglinide from basolateral-to-apical in MDR1-MDCK cells was 3.6-fold higher than the apical-to-basolateral rate with a net efflux ratio of 1.92 compared with mock-MDCK cells, which was significantly decreased following co-administration with genistein or Ver. In an intracellular accumulation experiment using Rhodamine 123 as a P-gp substrate, genistein significantly increased the intracellular fluorescence of Rhodamine 123. These results indicated that genistein had an inhibitory effect on the efflux function of P-gp. Through molecular docking assays we further found that genistein could bind to the nucleotide-binding domains (NBD) in the cytoplasm of P-gp, thus affecting the functions of P-gp. In conclusion, genistein inhibited the efflux of repaglinide mediated by P-gp in rats and in vitro. The findings suggested that the DDI between genistein and repaglinide is mediated by P-gp, and a dosage adjustment may be needed when they are co-administered in a clinical setting.

Freely Accessible Chemical Database Resources of Compounds for In Silico Drug Discovery

BACKGROUND

In silico drug discovery has been proved to be a solidly established key component in early drug discovery. However, this task is hampered by the limitation of quantity and quality of compound databases for screening. In order to overcome these obstacles, freely accessible database resources of compounds have bloomed in recent years. Nevertheless, how to choose appropriate tools to treat these freely accessible databases is crucial. To the best of our knowledge, this is the first systematic review on this issue.

OBJECTIVE

The existed advantages and drawbacks of chemical databases were analyzed and summarized based on the collected six categories of freely accessible chemical databases from literature in this review.

RESULTS

Suggestions on how and in which conditions the usage of these databases could be reasonable were provided. Tools and procedures for building 3D structure chemical libraries were also introduced.

CONCLUSION

In this review, we described the freely accessible chemical database resources for in silico drug discovery. In particular, the chemical information for building chemical database appears as attractive resources for drug design to alleviate experimental pressure.

Synthesis and Evaluation of Pyrimidine Steroids as Antiproliferative Agents

A small and focused library of steroidal non-fused and fused pyrimidines was prepared from pregnenolone acetate and diosgenin, respectively. The key step was the cycloaddition reaction of nitrogen-containing 1,3-binucleophiles with the steroidal α,β-unsaturated ketone. Urea, thiourea and guanidine reacted in a similar manner and afforded the steroidal pyrimidines in good yields. The antiproliferative tests against human tumor cell lines gave GI₅₀ values in the micromolar range and had no effect on healthy fibroblasts. Additional experiments indicated that the compounds did not act as P-glycoprotein substrates, thus avoiding the rise of drug resistance. The fused steroidal pyrimidinethione was selected as drug lead for further testing due to its strong antiproliferative activities within the low micromolar range.

Interactions between artemisinin derivatives and P-glycoprotein

BACKGROUND

Artemisinin was isolated and identified in 1972, which was the starting point for a new era in antimalarial drug therapy. Furthermore, numerous studies have demonstrated that artemisinin and its derivatives exhibit considerable anticancer activity both in vitro, in vivo, and even in clinical Phase I/II trials. P-glycoprotein (P-gp) mediated multi-drug resistance (MDR) is one of the most serious causes of chemotherapy failure in cancer treatment. Interestingly, many artemisinin derivatives exhibit excellent ability to overcome P-gp mediated MDR and even show collateral sensitivity against MDR cancer cells. Furthermore, some artemisinin derivatives show P-gp-mediated MDR reversal activity. Therefore, the interaction between P-gp and artemisinin derivatives is important to develop novel combination treatment protocols with artemisinin derivatives and established anticancer drugs that are P-gp substrates.

PURPOSE

This systematic review provides an updated overview on the interaction between artemisinin derivatives and P-gp and the effect of artemisinin derivatives on the P-gp expression level.

RESULTS

Artemisinin derivatives exhibit multi-specific interactions with P-gp. The currently used artemisinin derivatives are not transported by P-gp. However, some of novel synthetized artemisinin derivatives exhibit P-gp substrate properties. Furthermore, many artemisinin derivatives act as P-gp inhibitors, which exhibit the potential to reverse MDR towards clinically used anticancer drugs.

CONCLUSION

Therefore, studies on the interaction between artemisinin derivatives and P-gp provide important information for the development of novel anti-cancer artemisinin derivatives to reverse P-gp mediated MDR and for the design of rational artemisinin-based combination therapies against cancer.

Selenocoumarins as new multitarget antiproliferative agents: Synthesis, biological evaluation and in silico calculations

Herein we report a straightforward preparation of new antiproliferative agents based on the hybridization of a coumarin skeleton and an organoselenium motif. Three families were obtained: isoselenocyanate, selenocarbamates and selenoureas. The main purpose of these hybrid structures is the development of new antiproliferative agents with a multitarget mode of action. A strong correlation between the nature of the organosenium scaffold and the antiproliferative activity was observed. Thus, whereas selenocarbamates proved to be inactive, or moderate antiproliferative agents, isoselenocyanate and most of the selenoureas behaved as strong antiproliferative agents, with GI₅₀ values within the low micromolar range. Interestingly, a good selectivity toward tumor cell lines was found for some of the compounds. Moreover, an increase in the ROS level was observed for tumor cells, and accordingly, these pro-oxidant species might be involved in their mode of action. Overall, title compounds were found not to be substrates for P-glycoprotein, which is overexpressed in many cancer cells as a way of detoxification, and thus, to develop drug resistance. In silico calculations revealed that the selenoderivatives prepared herein might undergo a strong interaction with the active site of HDAC8, and therefore, be potential inhibitors of histone deacetylase 8. In vitro assessment against HDAC8 revealed a strong inhibition of such enzyme exerted by selenoureas, particularly by symmetrical coumarin-containing selenourea. Two compounds showed good antiproliferative data and appear as plausible leads for further testings. The symmetrical coumarin 6 displays the best in vitro inhibition of HDAC8, but is affected by P-gp. In contrast, the N-butyl selenourea coumarin derivative 5a escapes P-gp resistance but has lower HDAC8 inhibition activity.

Selective Antiproliferative Withanolides from Species in the Genera Eriolarynx and Deprea

Four new withanolides (2-5), together with 4β,7β,20-trihydroxy-1-oxowitha-2,5,24-trienolide (1), were isolated from the aerial parts of Eriolarynx iochromoides. The antiproliferative activity of all compounds purified from E. iochromoides together with four withaphysalins and four physangulidines isolated previously from three Deprea species were evaluated against human solid tumor cell lines. Four withanolides showed antiproliferative activity comparable in potency to cisplatin. Selectivity toward cancer cells and interaction with P-glycoprotein of the active withanolides were evaluated.

Development of Simplified in Vitro P-Glycoprotein Substrate Assay and in Silico Prediction Models To Evaluate Transport Potential of P-Glycoprotein

For efficient drug discovery and screening, it is necessary to simplify P-glycoprotein (P-gp) substrate assays and to provide in silico models that predict the transport potential of P-gp. In this study, we developed a simplified in vitro screening method to evaluate P-gp substrates by unidirectional membrane transport in P-gp-overexpressing cells. The unidirectional flux ratio positively correlated with parameters of the conventional bidirectional P-gp substrate assay ( R² = 0.941) and in vivo K_p,brain ratio (mdr1a/1b KO/WT) in mice ( R² = 0.800). Our in vitro P-gp substrate assay had high reproducibility and required approximately half the labor of the conventional method. We also constructed regression models to predict the value of P-gp-mediated flux and three-class classification models to predict P-gp substrate potential (low-, medium-, and high-potential) using 2397 data entries with the largest data set collected under the same experimental conditions. Most compounds in the test set fell within two- and three-fold errors in the random forest regression model (71.3 and 88.5%, respectively). Furthermore, the random forest three-class classification model showed a high balanced accuracy of 0.821 and precision of 0.761 for the low-potential classes in the test set. We concluded that the simplified in vitro P-gp substrate assay was suitable for compound screening in the early stages of drug discovery and that the in silico regression model and three-class classification model using only chemical structure information could identify the transport potential of compounds including P-gp-mediated flux ratios. Our proposed method is expected to be a practical tool to optimize effective central nervous system (CNS) drugs, to avoid CNS side effects, and to improve intestinal absorption.

Polymorphisms of SLCO1B1 rs4149056 and SLC22A1 rs2282143 are associated with responsiveness to acitretin in psoriasis patients

Acitretin is widely used to treat psoriasis, but the efficacy varies significantly among individuals. To explore the association between polymorphisms and acitretin efficacy, we enrolled 46 and 105 Chinese Han psoriasis vulgaris patients for discovery and validation phases, respectively. The patients were treated with acitretin (30 mg/day) and calcipotriol ointment for at least 8 weeks, and their genotypes were detected. The wild-type genes and variants were transfected into HEK293 cells, which were then incubated with acitretin. The cellular acitretin concentration was measured by liquid chromatography-mass spectrometry. We found that the polymorphisms rs4149056 in the SLCO1B1 gene and rs2282143 in the SLC22A1 gene were associated with efficacy, both in the discovery (P = 0.013 and P = 0.002) and validation phases (P = 0.028 and P = 0.014), based on a 50% reduction from before to after treatment of the psoriasis area severity index (PASI50). When the PASI75 was used as an efficacy cutoff, a similar conclusion was drawn. The uptake of acitretin was lower with the rs4149056C (P = 0.002) and rs2282143T alleles (P = 0.038) than the wild-type alleles. Our results imply that the rs4149056C and rs2282143T variants decrease the acitretin uptake, and significantly associated with clinical effective responsiveness.

Challenges with the precise prediction of ABC-transporter interactions for improved drug discovery

INTRODUCTION

Given that membrane efflux transporters can influence a drug's pharmacokinetics, efficacy and safety, identifying potential substrates and inhibitors of these transporters is a critical element in the drug discovery and development process. Additionally, it is important to predict the inhibition potential of new drugs to avoid clinically significant drug interactions. The goal of preclinical studies is to characterize a new drug as a substrate or inhibitor of efflux transporters. Areas covered: This article reviews preclinical systems that are routinely utilized to determine whether a new drug is substrate or inhibitor of efflux transporters including in silico models, in vitro membrane and cell assays, and animal models. Also included is an examination of studies comparing in vitro inhibition data to clinical drug interaction outcomes. Expert opinion: While a number of models are employed to classify a drug as an efflux substrate or inhibitor, there are challenges in predicting clinical drug interactions. Improvements could be made in these predictions through a tier approach to classify new drugs, validation of preclinical assays, and refinement of threshold criteria for clinical interaction studies.

Cholecalciferol-PEG Conjugate Based Nanomicelles of Doxorubicin for Treatment of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is the leading cancer in women. Chemotherapeutic agents used for TNBC are mainly associated with dose-dependent toxicities and development of resistance. Hence, novel strategies to overcome resistance and to offer dose reduction are warranted. In this study, we designed a novel dual-functioning agent, conjugate of cholecalciferol with PEG2000 (PEGCCF) which can self-assemble into micelles to encapsulate doxorubicin (DOX) and act as a chemosensitizer to improve the therapeutic potential of DOX. DOX-loaded PEGCCF (PEGCCF-DOX) micelles have particle size, polydispersity index (PDI), and zeta potential of 40 ± 8.7 nm, 0.180 ± 0.051, and 2.39 ± 0.157 mV, respectively. Cellular accumulation studies confirmed that PEGCCF was able to concentration-dependently enhance the cellular accumulation of DOX and rhodamine 123 in MDA-MB-231 cells through its P-glycoprotein (P-gp) inhibition activity. PEGCCF-DOX exhibited 1.8-, 1.5-, and 2.9-fold enhancement in cytotoxicity of DOX in MDA-MB-231, MDA-MB-468, and MDA-MB-231DR (DOX-resistant) cell lines, respectively. Western blot analyses showed that PEGCCF-DOX caused significant reduction in tumor markers including mTOR, c-Myc, and antiapoptotic marker Bcl-xl along with upregulation of preapoptotic marker Bax. Further, reduction in mTOR activity by PEGCCF-DOX indicates reduced P-gp activity due to P-gp downregulation as well and, hence, PEGCCF causes enhanced chemosensitization and induces apoptosis. Substantially enhanced apoptotic activity of DOX (10-fold) in MDA-MB-231(DR) cells confirmed apoptotic potential of PEGCCF. Conclusively, PEGCCF nanomicelles are promising delivery systems for improving anticancer activity of DOX in TNBC, thereby reducing its side effects and may act as a potential carrier for other chemotherapeutic agents.

The prototypical proton-coupled oligopeptide transporter YdgR from Escherichia coli facilitates chloramphenicol uptake into bacterial cells

Chloramphenicol (Cam) is a broad-spectrum antibiotic used to combat bacterial infections in humans and animals. Cam export from bacterial cells is one of the mechanisms by which pathogens resist Cam's antibacterial effects, and several different proteins are known to facilitate this process. However, to date no report exists on any specific transport protein that facilitates Cam uptake. The proton-coupled oligopeptide transporter (POT) YdgR from Escherichia coli is a prototypical member of the POT family, functioning in proton-coupled uptake of di- and tripeptides. By following bacterial growth and conducting LC-MS-based assays we show here that YdgR facilitates Cam uptake. Some YdgR variants displaying reduced peptide uptake also exhibited reduced Cam uptake, indicating that peptides and Cam bind YdgR at similar regions. Homology modeling of YdgR, Cam docking, and mutational studies suggested a binding mode that resembles that of Cam binding to the multidrug resistance transporter MdfA. To our knowledge, this is the first report of Cam uptake into bacterial cells mediated by a specific transporter protein. Our findings suggest a specific bacterial transporter for drug uptake that might be targeted to promote greater antibiotic influx to increase cytoplasmic antibiotic concentration for enhanced cytotoxicity.

Machine learning and docking models for Mycobacterium tuberculosis topoisomerase I

There is a shortage of compounds that are directed towards new targets apart from those targeted by the FDA approved drugs used against Mycobacterium tuberculosis. Topoisomerase I (Mttopo I) is an essential mycobacterial enzyme and a promising target in this regard. However, it suffers from a shortage of known inhibitors. We have previously used computational approaches such as homology modeling and docking to propose 38 FDA approved drugs for testing and identified several active molecules. To follow on from this, we now describe the in vitro testing of a library of 639 compounds. These data were used to create machine learning models for Mttopo I which were further validated. The combined Mttopo I Bayesian model had a 5 fold cross validation receiver operator characteristic of 0.74 and sensitivity, specificity and concordance values above 0.76 and was used to select commercially available compounds for testing in vitro. The recently described crystal structure of Mttopo I was also compared with the previously described homology model and then used to dock the Mttopo I actives norclomipramine and imipramine. In summary, we describe our efforts to identify small molecule inhibitors of Mttopo I using a combination of machine learning modeling and docking studies in conjunction with screening of the selected molecules for enzyme inhibition. We demonstrate the experimental inhibition of Mttopo I by small molecule inhibitors and show that the enzyme can be readily targeted for lead molecule development.

The Pharmacokinetics of Beraprost Sodium Following Single Oral Administration to Subjects With Impaired Kidney Function

The purpose of the present study was to evaluate the pharmacokinetics of beraprost sodium (BPS) and its active enantiomer, BPS-314d, in Japanese subjects with impaired kidney function. The plasma and urine concentrations of BPS and BPS-314d were measured following the single oral administration of 120 μg of BPS as the sustained-release tablet, TRK-100STP, under fasting conditions to 18 subjects with impaired kidney function (stage 2, 3, and 4 chronic kidney disease [CKD] as categorized by the estimated glomerular filtration rate) and to 6 age-, body weight-, and gender-matched subjects with normal kidney function (stage 1 CKD). The C_max values (mean ± SD) of BPS in stage 1, 2, 3, and 4 CKD, respectively, were 84.9 ± 22.9, 119.8 ± 36.4, 190.6 ± 137.3, and 240.2 ± 110.5 pg/mL; its AUC_0-48h were 978 ± 226, 1252 ± 427, 1862 ± 964, and 1766 ± 806 pg·h/mL, respectively, and its cumulative urinary excretion rates were 0.704 ± 0.351%, 0.638 ± 0.292%, 0.485 ± 0.294%, and 0.159 ± 0.136%. The C_max values of BPS-314d were 22.4 ± 6.4, 30.8 ± 8.5, 46.7 ± 30.6, and 54.4 ± 25.2 pg/mL, its AUC_0-48h were 155 ± 56, 226 ± 67, 341 ± 176, and 329 ± 143 pg·h/mL, and its cumulative urinary excretion rates were 0.428 ± 0.242%, 0.349 ± 0.179%, 0.356 ± 0.270%, and 0.096 ± 0.099%, respectively. Adverse events were reported in 2 subjects with stage 2 CKD and 1 subject with stage 4 CKD. The C_max and AUC_0-48h of BPS and BPS-314d were higher based on the severity of impaired kidney function. No relationship was observed between the incidence of adverse events and the severity, and tolerability was confirmed. We consider that dose adjustment is not necessary, but BPS is more carefully treated in patients with impaired kidney function.

Patient Variables Associated with Nafcillin Plasma Concentrations and Toxicity

OBJECTIVES

PRIMARY OBJECTIVE

To retrospectively review nafcillin plasma concentrations (CNAF ) and determine nafcillin clearance (CLNAF ) in a diverse sample of patients treated with nafcillin administered as a continuous infusion.

SECONDARY OBJECTIVE

To identify clinical variables associated with CLNAF and nafcillin-related adverse drug reactions (ADRs).

METHODS

Retrospective chart review of patients receiving nafcillin via continuous infusion at University of Utah Health Care from 2006 to 2013 who had at least one steady-state CNAF measured. CLNAF was determined by dividing the nafcillin rate of infusion by CNAF . Adverse drug reactions (ADRs) were defined using the National Institutes of Health, Division of Microbiology and Infectious Diseases criteria and scored for probability of association with nafcillin by using Naranjo criteria. Multivariate models were constructed to identify independent variables associated with CLNAF and ADRs.

MAIN RESULTS

Seventy-six CNAF from 54 patients were included. Median CLNAF was 13.9 L/hour (range ≤ 4.2 to 36.9 L/hr). Congestive heart failure (p=0.007), hyperbilirubinemia (p<0.0001), and serum creatinine (p<0.0001) were associated with reduced CLNAF , and Hispanic race (p=0.002) was associated with increased CLNAF by multivariate analysis. Twenty patients (37.0%) experienced an ADR. CNAF were significantly higher between patients that experienced an ADR and those that did not (66.0 vs 25.5 mg/L, p<0.001). Individual ADRs associated with CNAF included hepatotoxicity (62.8 vs 27.0 mg/L, p=0.001), nausea/vomiting (80.0 vs 28.5 mg/L, p=0.01), and diarrhea (66.5 vs 26.5 mg/L, p<0.001). Multivariate analysis identified CNAF as being independently associated with ADRs. A putative toxicity relationship between CNAF and predicted probability of ADR was established.

CONCLUSIONS

Several patient variables were associated with impaired CLNAF , and elevated CNAF were associated with ADRs. Additional studies assessing the utility of nafcillin therapeutic drug monitoring to minimize toxicity are warranted.

Machine learning-, rule- and pharmacophore-based classification on the inhibition of P-glycoprotein and NorA

The efflux pumps P-glycoprotein (P-gp) in humans and NorA in Staphylococcus aureus are of great interest for medicinal chemists because of their important roles in multidrug resistance (MDR). The high polyspecificity as well as the unavailability of high-resolution X-ray crystal structures of these transmembrane proteins lead us to combining ligand-based approaches, which in the case of this study were machine learning, perceptual mapping and pharmacophore modelling. For P-gp inhibitory activity, individual models were developed using different machine learning algorithms and subsequently combined into an ensemble model which showed a good discrimination between inhibitors and noninhibitors (acctrain-diverse = 84%; accinternal-test = 92% and accexternal-test = 100%). For ligand promiscuity between P-gp and NorA, perceptual maps and pharmacophore models were generated for the detection of rules and features. Based on these in silico tools, hit compounds for reversing MDR were discovered from the in-house and DrugBank databases through virtual screening in an attempt to restore drug sensitivity in cancer cells and bacteria.

Jatrophane diterpenes and cancer multidrug resistance - ABCB1 efflux modulation and selective cell death induction

BACKGROUND

Modulation of P-glycoprotein (ABCB1) and evaluation of the collateral sensitivity effect are among the most promising approaches to overcome multidrug resistance (MDR) in cancer. In a previous study, two rare 12,17-cyclojatrophanes (1-2) and other novel jatrophanes (3-4), isolated from Euphorbia welwitschii, were screened for collateral sensitivity effect. Herein, the isolation of another jatrophane (5) is presented, being the broader goal of this work to investigate the role of euphowelwitschines A (1) and B (2), welwitschene (3), epoxywelwitschene (4) and esulatin M (5) as ABCB1 modulators and/or collateral sensitivity agents.

METHODS

Compounds 1-5 were evaluated for ABCB1 modulation ability through combination of transport and chemosensitivity assays, using a mouse T-lymphoma MDR1-transfected cell model. Moreover, the nature of interaction of compound 4 with ABCB1 was studied, using an ATPase assay. The MDR-selective antiproliferative activity of compound 5 was evaluated against gastric (EPG85-257) and pancreatic (EPP85-181) human cancer cells and their drug-selected counterparts (EPG85-257RDB, EPG85-257RNOV, EPP85-181RDB, EPP85-181RNOV). The drug induced cell death was investigated for compounds 4 and 5, using the annexin V/PI staining and the active caspase-3 assay.

RESULTS

The jatrophanes 1-5 were able to modulate the efflux activity of ABCB1, and at 2µM, 3-5 maintained the strong modulator profile. Structure activity results indicated that high conformational flexibility of the twelve-membered ring of compounds 3-5 favored ABCB1 modulation, in contrast to the tetracyclic scaffold of compounds 1 and 2. The effects of epoxywelwitschene (4) on the ATPase activity of ABCB1 showed it to interact with the transporter and to be able to reduce the transport of a second subtrate. Drug combination experiments also corroborated the anti-MDR potential of these diterpenes due to their synergistic interaction with doxorubicin (combination index <0.7). Esulatin M (5) showed a strong MDR-selective antiproliferative activity against EPG85-257RDB and EPP85-181RDB cells, with IC50 of 1.8 and 4.8 µM, respectively. Compounds 4 and 5 induced apoptosis via caspase-3 activation. A significant discrimination was observed between the resistant cell lines and parental cells.

CONCLUSIONS

This study strengthens the role of jatrophane diterpenes as lead candidates for the development of MDR reversal agents, higlighting the action of compounds 4 and 5.

Enhancing Activity of Anticancer Drugs in Multidrug Resistant Tumors by Modulating P-Glycoprotein through Dietary Nutraceuticals

Multidrug resistance is a principal mechanism by which tumors become resistant to structurally and functionally unrelated anticancer drugs. Resistance to chemotherapy has been correlated with overexpression of p-glycoprotein (p-gp), a member of the ATP-binding cassette (ABC) superfamily of membrane transporters. P-gp mediates resistance to a broad-spectrum of anticancer drugs including doxorubicin, taxol, and vinca alkaloids by actively expelling the drugs from cells. Use of specific inhibitors/blocker of p-gp in combination with clinically important anticancer drugs has emerged as a new paradigm for overcoming multidrug resistance. The aim of this paper is to review p-gp regulation by dietary nutraceuticals and to correlate this dietary nutraceutical induced-modulation of p-gp with activity of anticancer drugs.

Role of Human Breast Cancer Related Protein versus P-Glycoprotein as an Efflux Transporter for Benzylpenicillin: Potential Importance at the Blood-Brain Barrier

While the blood-brain barrier (BBB) protects the brain by controlling the access of solutes and toxic substances to brain, it also limits drug entry to treat central nervous system disorders. Many drugs are substrates for ATP-binding cassette (ABC) transporters at the BBB that limit their entry into the brain. The role of those transporters in limiting the entry of the widely prescribed therapeutic, benzylpenicillin, has produced conflicting results. This study investigated the possible potential involvement of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), two ABC transporters, in benzylpenicillin transport at BBB in human using MDCKII cells overexpressing those transporters as well as pharmacological inhibition. MDCKII cells overexpressing human BCRP (MDCKII-BCRP) but not those overexpressing human P-gp (MDCKII-MDR cells) had reduced [3H]benzylpenicillin uptake. Similarly, inhibiting BCRP increased [3H]benzylpenicillin uptake in MDCKII-BCRP cells, while inhibiting P-gp in MDCKII-MDR cells had no effect on uptake although there was evidence that benzylpenicillin is a substrate for canine P-gp. While inhibiting BCRP affected [3H]benzylpenicillin cell concentrations it did not affect transepithelial flux in MDCKII-BCRP cells. In summary, the results indicate that human BCRP and not human P-gp is involved in benzylpenicillin transport. However, targeting BCRP alone was not sufficient to alter transepithelial flux in MDCKII cells. Whether it would be sufficient to alter blood-to-brain flux at the human BBB remains to be investigated.

Simotinib as a modulator of P-glycoprotein: substrate, inhibitor, or inducer?

As a new antitumor drug, simotinib hydrochloride is prescribed for prolonged periods, often to patients with comorbidities. Therefore, the risk for developing drug resistance and drug-drug interactions between simotinib and other agents has to be taken into consideration. As P-glycoprotein (P-gp) is an efflux transporter, which plays a significant role in drug resistance and influences the pharmacological properties and toxicities of the drugs it interacts with, the interactions between simotinib and P-gp were investigated. Cytotoxicity was measured using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assay. Intracellular drug concentrations were detected by high-performance liquid chromatography, fluorescence-activated cell sorting and using a fluorescence reader. P-gp ATPase activity was measured using the Pgp-Glo assay, and intracellular pH was assessed using the fluorescent probe 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl. The expression and transcription of P-gp were detected by western blotting and the luciferase assay. Simotinib has no cross-resistance to P-gp substrates, and its efflux rate was independent of either the P-gp expression or the coadministered P-gp substrate. Simotinib reversed chemotherapeutic agent resistance in a short time by increasing the intracellular concentration of the chemotherapeutic agent and blocked rhodamine 123 efflux. Further studies demonstrated that simotinib inhibited P-gp activity by modulating its ATPase activity and the intracellular pH. Although simotinib induced P-gp expression after extended treatment, the induced expression of P-gp had little impact on drug resistance. Simotinib is not a substrate of P-gp. As a modulator, it functions mainly as an inhibitor of P-gp by modulating the intracellular pH and ATPase activity, although it also induces P-gp expression after extended treatment.

The comparative efficacy and safety of the angiotensin receptor blockers in the management of hypertension and other cardiovascular diseases

All national guidelines for the management of hypertension recommend angiotensin receptor blockers (ARBs) as an initial or add-on antihypertensive therapy. The eight available ARBs have variable clinical efficacy when used for control of hypertension. Additive blood pressure-lowering effects have been demonstrated when ARBs are combined with thiazide diuretics or dihydropyridine calcium channel blockers, augmenting hypertension control. Furthermore, therapeutic use of ARBs goes beyond their antihypertensive effects, with evidence-based benefits in heart failure and diabetic renal disease particularly among angiotensin-converting enzyme inhibitor-intolerant patients. On the other hand, combining renin-angiotensin system blocking agents, a formerly common practice among medical subspecialists focusing on the management of hypertension, has ceased, as there is not only no evidence of cardiovascular benefit but also modest evidence of harm, particularly with regard to renal dysfunction. ARBs are very well tolerated as monotherapy, as well as in combination with other antihypertensive medications, which improve adherence to therapy and have become a mainstay in the treatment of stage 1 and stage 2 hypertension.

Anti-tubercular drug development: computational strategies to identify potential compounds

InhA is an attractive target to combat tuberculosis (TB), which is targeted by many pro-drugs (isoniazid, etc.) and drugs such as triclosan. However, triclosan is less useful as an antitubercular drug due to its low bioavailability and therefore, in order to overcome this difficulty, many derivatives of triclosan were prepared. Here, we have combined various computational techniques to virtually screen out four potential triclosan derivatives. Molecular docking methods have been employed to screen out 32 out of 62 triclosan derivatives considering the mode of binding and the top re-rank scores. A comparative study on the chemical properties of triclosan and some of its derivatives has been performed using density functional theory (DFT) calculations. DFT based global reactivity descriptors (GRD), such as hardness, chemical potential, chemical softness, electrophilicity index, Fukui function, and local philicity calculated at the optimized geometries were used to investigate the usefulness of these descriptors for understanding the reactive nature and sites of the molecules. QSAR equations were built using these descriptors considering these 32 compounds. Four common compounds showing the best correlation and the best docking scores were considered for the ADMET property calculations and their dynamical movements have been studied using molecular dynamics simulations. Our results showed that these four compounds are chemically more active than triclosan and have the potential to inhibit the Mycobacterium tuberculosis enoyl acyl carrier protein reductase. This work shows that combination of different computational techniques may help to screen out potential drug candidates from a list of possible ones.

Ultra rapidly dissolving repaglinide nanosized crystals prepared via bottom-up and top-down approach: influence of food on pharmacokinetics behavior

The present work was undertaken with the objectives of improving the dissolution velocity, related oral bioavailability, and minimizing the fasted/fed state variability of repaglinide, a poorly water-soluble anti-diabetic active by exploring the principles of nanotechnology. Nanocrystal formulations were prepared by both top-down and bottom-up approaches. These approaches were compared in light of their ability to provide the formulation stability in terms of particle size. Soluplus® was used as a stabilizer and Kolliphor™ E-TPGS was used as an oral absorption enhancer. In vitro dissolution profiles were investigated in distilled water, fasted and fed state simulated gastric fluid, and compared with the pure repaglinide. In vivo pharmacokinetics was performed in both the fasted and fed state using Wistar rats. Oral hypoglycemic activity was also assessed in streptozotocin-induced diabetic rats. Nanocrystals TD-A and TD-B showed 19.86 and 25.67-fold increase in saturation solubility, respectively, when compared with pure repaglinide. Almost 10 (TD-A) and 15 (TD-B)-fold enhancement in the oral bioavailability of nanocrystals was observed regardless of the fasted/fed state compared to pure repaglinide. Nanocrystal formulations also demonstrated significant (p < 0.001) hypoglycemic activity with faster onset (less than 30 min) and prolonged duration (up to 8 h) compared to pure repaglinide (after 60 min; up to 4 h, respectively).

In silico methods for predicting drug-drug interactions with cytochrome P-450s, transporters and beyond

Drug-drug interactions (DDIs) are associated with severe adverse effects that may lead to the patient requiring alternative therapeutics and could ultimately lead to drug withdrawal from the market if they are severe. To prevent the occurrence of DDI in the clinic, experimental systems to evaluate drug interaction have been integrated into the various stages of the drug discovery and development process. A large body of knowledge about DDI has also accumulated through these studies and pharmacovigillence systems. Much of this work to date has focused on the drug metabolizing enzymes such as cytochrome P-450s as well as drug transporters, ion channels and occasionally other proteins. This combined knowledge provides a foundation for a hypothesis-driven in silico approach, using either cheminformatics or physiologically based pharmacokinetics (PK) modeling methods to assess DDI potential. Here we review recent advances in these approaches with emphasis on hypothesis-driven mechanistic models for important protein targets involved in PK-based DDI. Recent efforts with other informatics approaches to detect DDI are highlighted. Besides DDI, we also briefly introduce drug interactions with other substances, such as Traditional Chinese Medicines to illustrate how in silico modeling can be useful in this domain. We also summarize valuable data sources and web-based tools that are available for DDI prediction. We finally explore the challenges we see faced by in silico approaches for predicting DDI and propose future directions to make these computational models more reliable, accurate, and publically accessible.

The putative P-gp inhibitor telmisartan does not affect the transcellular permeability and cellular uptake of the calcium channel antagonist verapamil in the P-glycoprotein expressing cell line MDCK II MDR1

Verapamil is used in high doses for the treatment of cluster headache. Verapamil has been described as a P-glycoprotein (P-gp, ABCB1) substrate. We wished to evaluate in vitro whether co administration of a P-gp inhibitor with verapamil could be a feasible strategy for increasing CNS uptake of verapamil. Fluxes of radiolabelled verapamil across MDCK II MDR1 monolayers were measured in the absence and presence of the putative P-gp inhibitor telmisartan (a clinically approved drug compound). Verapamil displayed a vectorial basolateral-to-apical transepithelial efflux across the MDCK II MDR1 monolayers with a permeability of 5.7 × 10(-5) cm sec(-1) compared to an apical to basolateral permeability of 1.3 × 10(-5) cm sec(-1). The efflux could be inhibited with the P-gp inhibitor zosuquidar. Zosuquidar (0.4 μmol/L) reduced the efflux ratio (PB-A/PA-B) for verapamil 4.6-1.6. The presence of telmisartan, however, only caused a slight reduction in P-gp-mediated verapamil transport to an efflux ratio of 3.4. Overall, the results of the present in vitro approach indicate, that clinical use of telmisartan as a P-gp inhibitor may not be an effective strategy for increasing brain uptake of verapamil by co-administration with telmisartan.

HZ08 reverse P-glycoprotein mediated multidrug resistance in vitro and in vivo

Background

Multidrug efflux transporter P-glycoprotein (P-gp) is highly expressed on membrane of tumor cells and is implicated in resistance to tumor chemotherapy. HZ08 is synthesized and studied in order to find a novel P-gp inhibitor.

Methods

MDCK-MDR1 monolayer transport, calcein-AM P-gp inhibition and P-gp ATPase assays were used to confirm the P-gp inhibition capability of HZ08. Furthermore, KB-WT and KB-VCR cells were used to evaluate the P-gp inhibitory activity of HZ08 both in vitro and in vivo.

Results

Results showed that HZ08 was more potent than verapamil in MDCK-MDR1 monolayer transportation model. Meanwhile, P-gp ATPase assay and calcein-AM P-gp inhibition assay confirmed that HZ08 inhibited P-gp ATPase with a calcein-AM IC50 of 2.44±0.31μM. In addition, significantly greater in vitro multidrug resistance reversing effects were observed when vincristine or paclitaxel was used in combination with 10μM HZ08 compared with 10μM verapamil. Moreover, HZ08 could significantly enhance the sensitivity of vincristine with a similar effect like verapamil in both KB-WT and KB-VCR tumor xenograft models.

Conclusions

The novel structure HZ08 could be a potent P-gp inhibitor.

Novel non-substrate modulators of the transmembrane efflux pump P-glycoprotein (ABCB1)

Novel non-substrate modulators of the transmembrane efflux pump P-gp have been profiled as nontoxic and mdr reversing agents.

Targeting Mycobacterium tuberculosis topoisomerase I by small-molecule inhibitors

We describe inhibition of Mycobacterium tuberculosis topoisomerase I (MttopoI), an essential mycobacterial enzyme, by two related compounds, imipramine and norclomipramine, of which imipramine is clinically used as an antidepressant. These molecules showed growth inhibition of both Mycobacterium smegmatis and M. tuberculosis cells. The mechanism of action of these two molecules was investigated by analyzing the individual steps of the topoisomerase I (topoI) reaction cycle. The compounds stimulated cleavage, thereby perturbing the cleavage-religation equilibrium. Consequently, these molecules inhibited the growth of the cells overexpressing topoI at a low MIC. Docking of the molecules on the MttopoI model suggested that they bind near the metal binding site of the enzyme. The DNA relaxation activity of the metal binding mutants harboring mutations in the DxDxE motif was differentially affected by the molecules, suggesting that the metal coordinating residues contribute to the interaction of the enzyme with the drug. Taken together, the results highlight the potential of these small molecules, which poison the M. tuberculosis and M. smegmatis topoisomerase I, as leads for the development of improved molecules to combat mycobacterial infections. Moreover, targeting metal coordination in topoisomerases might be a general strategy to develop new lead molecules.

Trantinterol, a novel β2-adrenoceptor agonist, noncompetitively inhibits P-glycoprotein function in vitro and in vivo

P-glycoprotein (P-gp)-mediated drug-drug interactions are important factors causing adverse effects of drugs in clinical use. The aim of this study was to determine whether trantinterol (also known as SPFF), a novel β2-adrenoceptor agonist, was a P-gp inhibitor or substrate. The results showed that trantinterol was not a substrate of P-gp but increased rhodamine 123 (Rho 123) uptake by MDCK-MDR1 cells and decreased the efflux transport of both Rho 123 and cyclosporine A (CsA) in bidirectional transport studies across MDCK-MDR1 cell monolayers. This suggested that trantinterol was a P-gp inhibitor but not a P-gp substrate. The mechanism of inhibition was investigated in the P-gp-Glo assay system, where it was found that trantinterol inhibited P-gp ATPase activity in a dose-dependent manner. A subsequent study using the antibody binding assay with the conformation-sensitive P-gp-specific antibody UIC2 confirmed that trantinterol decreased UIC2 binding at 10 μM in contrast to the competitive inhibitor, verapamil. This suggested that trantinterol was a noncompetitive inhibitor of P-gp. Finally, a pharmacokinetic study in rat showed that trantinterol significantly increased the area under the plasma concentration-time curve (AUC) and maximum plasma concentration (Cmax) of digoxin and paclitaxel (PAC), and the Cmax of cyclosporine A (CsA). In summary, trantinterol is a potent noncompetitive P-gp inhibitor which may increase the bioavailability of other P-gp substrate drugs coadministered with it.

Effects of nifedipine on the pharmacokinetics of repaglinide in rats: possible role of CYP3A4 and P-glycoprotein inhibition by nifedipine

BACKGROUND

The aim of this study was to investigate the effects of nifedipine on the bioavailability and pharmacokinetics of repaglinide in rats.

METHODS

The effect of nifedipine on P-glycoprotein (P-gp) and cytochrome P450 (CYP) 3A4 activity was evaluated. The pharmacokinetic parameters of repaglinide and blood glucose concentrations were also determined in rats after oral (0.5 mg/kg) and intravenous (0.2 mg/kg) administration of repaglinide to rats in the presence and absence of nifedipine (1 and 3 mg/kg).

RESULTS

Administration of nifedipine resulted in inhibition CYP3A4 activity with an IC50 value of 7.8 μM, and nifedipine significantly inhibited P-gp activity in a concentration-dependent manner. Compared to the oral control group, nifedipine significantly increased the area under the plasma concentration-time curve (AUC0-∞) and the peak plasma concentration (Cmax) of repaglinide by 49.3 and 25.5%, respectively. Nifedipine significantly decreased the total body clearance (CL/F) of repaglinide by 22.0% compared to the oral control group. Nifedipine also increased the absolute bioavailability (AB) of repaglinide by 50.0% compared to the oral control group (33.6%). In addition, the relative bioavailability (RB) of repaglinide was 1.16- to 1.49-fold greater than that of the control group. Compared to the intravenous control, nifedipine significantly increased AUC0-∞ of repaglinide. Blood glucose concentrations had significant differences compared to the oral control groups.

CONCLUSION

Nifedipine enhanced the oral bioavailability of repaglinide, which may be mainly attributable to inhibition of CYP3A4-mediated metabolism of repaglinide in the small intestine and/or in the liver and to inhibition of the P-gp efflux transporter in the small intestine and/or reduction of total body clearance by nifedipine. The current study has raised awareness of potential drug interactions by concomitant use of repaglinide with nifedipine.

Activation of the constitutive androstane receptor inhibits gluconeogenesis without affecting lipogenesis or fatty acid synthesis in human hepatocytes

OBJECTIVE

Accumulating evidence suggests that activation of mouse constitutive androstane receptor (mCAR) alleviates type 2 diabetes and obesity by inhibiting hepatic gluconeogenesis, lipogenesis, and fatty acid synthesis. However, the role of human (h) CAR in energy metabolism is largely unknown. The present study aims to investigate the effects of selective hCAR activators on hepatic energy metabolism in human primary hepatocytes (HPH).

METHODS

Ligand-based structure-activity models were used for virtual screening of the Specs database (www.specs.net) followed by biological validation in cell-based luciferase assays. The effects of two novel hCAR activators (UM104 and UM145) on hepatic energy metabolism were evaluated in HPH.

RESULTS

Real-time PCR and Western blotting analyses reveal that activation of hCAR by UM104 and UM145 significantly repressed the expression of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase, two pivotal gluconeogenic enzymes, while exerting negligible effects on the expression of genes associated with lipogenesis and fatty acid synthesis. Functional experiments show that UM104 and UM145 markedly inhibit hepatic synthesis of glucose but not triglycerides in HPH. In contrast, activation of mCAR by 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene, a selective mCAR activator, repressed the expression of genes associated with gluconeogenesis, lipogenesis, and fatty acid synthesis in mouse primary hepatocytes, which were consistent with previous observations in mouse model in vivo.

CONCLUSION

Our findings uncover an important species difference between hCAR and mCAR in hepatic energy metabolism, where hCAR selectively inhibits gluconeogenesis without suppressing fatty acid synthesis.

IMPLICATIONS

Such species selectivity should be considered when exploring CAR as a potential therapeutic target for metabolic disorders.

In vivo imaging of multidrug resistance using a third generation MDR1 inhibitor

Cellular up-regulation of multidrug resistance protein 1 (MDR1) is a common cause for resistance to chemotherapy; development of third generation MDR1 inhibitors-several of which contain a common 6,7-dimethoxy-2-phenethyl-1,2,3,4-tetrahydroisoquinoline substructure-is underway. Efficacy of these agents has been difficult to ascertain, partly due to a lack of pharmacokinetic reporters for quantifying inhibitor localization and transport dynamics. Some of the recent third generation inhibitors have a pendant heterocycle, for example, a chromone moiety, which we hypothesized could be converted to a fluorophore. Following synthesis and teasing of a small set of analogues, we identified one lead compound that can be used as a cellular imaging agent that exhibits structural similarity and behavior akin to the latest generation of MDR1 inhibitors.