Expression profiles of 50 xenobiotic transporter genes in humans and pre-clinical species: a resource for investigations into drug disposition

Lipids - two sides of the same coin in lung fibrosis

Idiopathic pulmonary fibrosis (IPF) is characterized by progressive extracellular matrix deposition in the lung parenchyma leading to the destruction of lung structure, respiratory failure and premature death. Recent studies revealed that the pathogenesis of IPF is associated with alterations in the synthesis and the activity of lipids, lipid regulating proteins and cell membrane lipid transporters and receptors in different lung cells. Furthermore, deregulated lipid metabolism was found to contribute to the profibrotic phenotypes of lung fibroblasts and alveolar epithelial cells. Consequently, several pharmacological agents, targeting lipids, lipid mediators, and lipoprotein receptors, was successfully tested in the animal models of lung fibrosis and entered early phase clinical trials. In this review, we highlight new therapeutic options to counteract disturbed lipid hemostasis in the maladaptive lung remodeling.

Genetic variation in the ATP binding cassette transporter ABCC10 is associated with neutropenia for docetaxel in Japanese lung cancer patients cohort

Background

Docetaxel is a widely used cytotoxic agent for treatments of various cancers. The ATP binding cassette (ABC) transporter / multidrug resistance protein (MRP) ABCC10/MRP7, involved in transporting taxanes, has been associated with resistance to these agents. Since genetic variation in drug transporters may affect clinical outcomes, we examined whether polymorphism of ABCC10 could affect clinical responses to docetaxel.

Methods

Using 18 NSCLC cell lines and CRISPR-based genome-edited HeLa cells, we analyzed whether genetic variants of ABCC10 (rs2125739, rs9349256) affected cytotoxicity to docetaxel. Subsequently, we analyzed genetic variants [ABCC10 (rs2125739), ABCB1 (C1236T, C3435T, G2677 T/A), ABCC2 (rs12762549), and SLCO1B3 (rs11045585)] in 69 blood samples of NSCLC patients treated with docetaxel monotherapy. Clinical outcomes were evaluated between genotype groups.

Results

In the cell lines, only one genetic variant (rs2125739) was significantly associated with docetaxel cytotoxicity, and this was confirmed in the genome-edited cell line. In the 69 NSCLC patients, there were no significant differences related to rs2125739 genotype in terms of RR, PFS, or OS. However, this SNP was associated with grade 3/4 neutropenia (T/C group 60% vs. T/T group 87%; P = 0.028). Furthermore, no patient with a T/C genotype experienced febrile neutropenia.

Conclusions

Our results indicate that genetic variation in the ABCC10 gene is associated with neutropenia for docetaxel treatment.

Evaluation of a Potential Clinical Significant Drug-Drug Interaction between Digoxin and Bupropion in Cynomolgus Monkeys

PURPOSE

A three-period digoxin-bupropion drug-drug interaction study was performed in cynomolgus monkeys to assess the effect of bupropion and its metabolites on digoxin disposition.

METHODS

Monkeys were administered either an i.v. infusion (0.1 mg/kg) or an oral dose of digoxin (0.2 mg/kg) as control. In single-dosing period, monkeys received an i.v. infusion of bupropion at 1.5 mg/kg together with an infusion or oral dosing of digoxin, respectively. During multiple-dosing period, bupropion was orally administered q.d. at 7.72 mg/kg for 12-day. Then it was co-administered with an i.v. infusion or oral dosing of digoxin, respectively. Renal expression of OATP4C1 and P-gp was examined.

RESULTS

Bupropion significantly increased i.v. digoxin CL_renal0-48h by 1 fold in single-dosing period. But it had no effect on the systemic disposition of digoxin. In multiple-dosing period, bupropion significantly increased oral digoxin CL_renal0-48h, CL_total0-48h, CL_{non-renal0-48h} and decreased its plasma exposure. Bupropion and its metabolites did not alter creatinine clearance. OATP4C1 was located at the basolateral membrane of proximal tubule cells, while P-gp was on the apical membrane.

CONCLUSIONS

The effect of multiple dosing with bupropion on the pharmacokinetics of digoxin is more pronounced. The magnitude of increase in digoxin CL_renal0-48h contributed to the decrease in AUC of digoxin in some extent, but certainly is not the major driving force. The lack of systemic exposure after a single dose but a significant decrease in exposure mediated by an increase in the digoxin CL_{non-renal0-48h} with repeated dosing is likely to be the more clinically relevant.

Comparison of uptake transporter functions in hepatocytes in different species to determine the optimal model for evaluating drug transporter activities in humans

A thorough understanding of species-dependent differences in hepatic uptake transporters is critical for predicting human pharmacokinetics (PKs) from preclinical data. In this study, the activities of organic anion transporting polypeptide (OATP/Oatp), organic cation transporter 1 (OCT1/Oct1), and sodium-taurocholate cotransporting polypeptide (NTCP/Ntcp) in cultured rat, dog, monkey and human hepatocytes were compared. The activities of hepatic uptake transporters were evaluated with respect to culture duration, substrate and species-dependent differences in hepatocytes. Longer culture duration reduced hepatic uptake transporter activities across species except for Oatp and Ntcp in rats. Comparable apparent Michaelis-Menten constant (K_m,app) values in hepatocytes were observed across species for atorvastatin, estradiol-17β-glucuronide and metformin. The K_m,app values for rosuvastatin and taurocholate were significantly different across species. Rat hepatocytes exhibited the highest Oatp percentage of uptake transporter-mediated permeation clearance (PS_inf,act) while no difference in %PS_inf,act of probe substrates were observed across species. The in vitro hepatocyte inhibition data in rats, monkeys and humans provided reasonable predictions of in vivo drug-drug interaction (DDIs) between atorvastatin/rosuvastatin and rifampin. These findings suggested that using human hepatocytes with a short culture time is the most robust preclinical model for predicting DDIs for compounds exhibiting active hepatic uptake in humans.

Interspecies comparison of putative ligand binding sites of human, rat and mouse P-glycoprotein

Prior to the clinical phases of testing, safety, efficacy and pharmacokinetic profiles of lead compounds are evaluated in animal studies. These tests are primarily performed in rodents, such as mouse and rats. In order to reduce the number of animal experiments, computational models that predict the outcome of these studies and thus aid in prioritization of preclinical candidates are heavily needed. However, although computational models for human off-target interactions with decent quality are available, they cannot easily be transferred to rodents due to lack of respective data. In this study, we assess the transferability of human P-glycoprotein activity data for development of in silico models to predict in vivo effects in rats and mouse using a structure-based approach. P-glycoprotein (P-gp) is an ATP-dependent efflux transporter that transports xenobiotic compounds such as toxins and drugs out of cells and has a broad substrate and inhibitor specificity. Being mostly expressed at barriers, it influences the bioavailability of drugs and thus contributes also to toxicity. Comparison of the binding site interaction profiles of human, rat and mouse P-gp derived from docking studies with a set of common inhibitors suggests that the inhibitors share potentially similar binding modes. These findings encourage the use of in vitro human P-gp data for predicting in vivo effects in rodents and thus contributes to the 3Rs (Replace, Reduce and Refine) of animal experiments.

New Frontiers: Approaches to Understand the Mechanistic Basis of Renal Toxicity

A scientific session entitled "New Frontiers: Approaches to Understand the Mechanistic Basis of Renal Toxicity" focused on novel biomarkers to monitor kidney injury both preclinically and clinically, as well as providing mechanistic insight of the induced injury. Further, the role and impact of kidney membrane transporters in drug-induced kidney toxicity provided additional considerations when understanding kidney injury and the complex role of drug transporters in either sensitivity or resistance to drug-induced injury. The onset of nephropathy in diabetic patients was also presented, focusing on the quest to discover novel biomarkers that would differentiate diabetic populations more susceptible to nephropathy and renal failure. The session highlighted exciting new research areas and novel biomarkers that will enhance our understanding of kidney injury and provide tools for ensuring patient safety clinically.

Metformin reduces liver glucose production by inhibition of fructose-1-6-bisphosphatase

Metformin is a first-line drug for the treatment of individuals with type 2 diabetes, yet its precise mechanism of action remains unclear. Metformin exerts its antihyperglycemic action primarily through lowering hepatic glucose production (HGP). This suppression is thought to be mediated through inhibition of mitochondrial respiratory complex I, and thus elevation of 5'-adenosine monophosphate (AMP) levels and the activation of AMP-activated protein kinase (AMPK), though this proposition has been challenged given results in mice lacking hepatic AMPK. Here we report that the AMP-inhibited enzyme fructose-1,6-bisphosphatase-1 (FBP1), a rate-controlling enzyme in gluconeogenesis, functions as a major contributor to the therapeutic action of metformin. We identified a point mutation in FBP1 that renders it insensitive to AMP while sparing regulation by fructose-2,6-bisphosphate (F-2,6-P2), and knock-in (KI) of this mutant in mice significantly reduces their response to metformin treatment. We observe this during a metformin tolerance test and in a metformin-euglycemic clamp that we have developed. The antihyperglycemic effect of metformin in high-fat diet-fed diabetic FBP1-KI mice was also significantly blunted compared to wild-type controls. Collectively, we show a new mechanism of action for metformin and provide further evidence that molecular targeting of FBP1 can have antihyperglycemic effects.

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.

Intrahepatic Sampling for the Elucidation of Antiviral Clinical Pharmacology

Although the importance of the liver in clinical pharmacology is widely recognized, little is known in humans concerning its function in vivo at the hepatocyte level and how pharmacological functions are altered in the setting of advanced liver disease. Several recent proof-of-principle studies with first-generation DAAs have demonstrated the feasibility of serial liver sampling for pharmacological studies. These studies have begun to describe the liver-to-plasma concentration ratio and how this ratio is altered in the setting of advanced liver disease. These data are particularly relevant to individuals with substance-use disorders because many have advanced liver disease as a consequence of long-standing viral hepatitis infection or continued use of hepatotoxins such as alcohol. Future research should attempt to develop standardized and reproducible methods to assess liver drug concentration, complex drug interactions, and pharmacogenomics in humans to permit elucidation of the clinical pharmacology within the liver.

Population Pharmacokinetic Modeling to Describe the Total Plasma and Free Brain Levels of Fluconazole in Healthy and Cryptococcus neoformans Infected Rats: How Does the Infection Impact the Drug's Levels on Biophase?

PURPOSE

The present work aimed to evaluate the influence of experimental meningitis caused by C. neoformans on total plasma and free brain concentrations of fluconazole (FLC) in Wistar rats.

METHOD

The infection was induced by the administration of 100 μL of inoculum (1.10⁵ CFU) through the tail vein. Free drug in the brain was assessed by microdialisys (μD). Blood and μD samples were collected at pre-determined time points up to 12 h after intravenous administration of FLC (20 mg/kg) to healthy and infected rats. The concentration-time profiles were analyzed by non-compartmental and population pharmacokinetics approaches.

RESULTS

A two-compartmental popPK model was able to simultaneously describe plasma and free drug concentrations in the brain for both groups investigated. Analysis of plasma and μD samples showed a better FLC distribution on the brain of infected than healthy animals (1.04 ± 0.31 vs 0.69 ± 0.14, respectively). The probability of target attainment was calculated by Monte Carlo simulations based on the developed popPK model for 125 mg/kg dose for rats and 400-2000 mg for humans.

CONCLUSIONS

FLC showed a limited use in monotherapy to the treatment of criptoccocosis in rats and humans to value of MIC >8 μg/mL.

Elucidating the Pharmacokinetics/Pharmacodynamics of Aerosolized Colistin against Multidrug-Resistant Acinetobacter baumannii and Klebsiella pneumoniae in a Mouse Lung Infection Model

The pharmacokinetics/pharmacodynamics (PK/PD) of aerosolized colistin was investigated against Acinetobacter baumannii and Klebsiella pneumoniae over 24 h in a neutropenic mouse lung infection model. Dose fractionation studies were performed over 2.64 to 23.8 mg/kg/day, and the data were fitted to a sigmoid inhibitory model. The area under the concentration-time curve over 24 h in the steady state divided by the MIC (AUC/MIC) in the epithelial lining fluid was the most predictive PK/PD index for aerosolized colistin against both pathogens. Our study provides important pharmacological information for optimizing aerosolized colistin.

The Differential Absorption of a Series of P-Glycoprotein Substrates in Isolated Perfused Lungs from Mdr1a/1b Genetic Knockout Mice can be Attributed to Distinct Physico-Chemical Properties: an Insight into Predicting Transporter-Mediated, Pulmonary Specific Disposition

PURPOSE

To examine if pulmonary P-glycoprotein (P-gp) is functional in an intact lung; impeding the pulmonary absorption and increasing lung retention of P-gp substrates administered into the airways. Using calculated physico-chemical properties alone build a predictive Quantitative Structure-Activity Relationship (QSAR) model distinguishing whether a substrate's pulmonary absorption would be limited by P-gp or not.

METHODS

A panel of 18 P-gp substrates were administered into the airways of an isolated perfused mouse lung (IPML) model derived from Mdr1a/Mdr1b knockout mice. Parallel intestinal absorption studies were performed. Substrate physico-chemical profiling was undertaken. Using multivariate analysis a QSAR model was established.

RESULTS

A subset of P-gp substrates (10/18) displayed pulmonary kinetics influenced by lung P-gp. These substrates possessed distinct physico-chemical properties to those P-gp substrates unaffected by P-gp (8/18). Differential outcomes were not related to different intrinsic P-gp transporter kinetics. In the lung, in contrast to intestine, a higher degree of non-polar character is required of a P-gp substrate before the net effects of efflux become evident. The QSAR predictive model was applied to 129 substrates including eight marketed inhaled drugs, all these inhaled drugs were predicted to display P-gp dependent pulmonary disposition.

CONCLUSIONS

Lung P-gp can affect the pulmonary kinetics of a subset of P-gp substrates. Physico-chemical relationships determining the significance of P-gp to absorption in the lung are different to those operative in the intestine. Our QSAR framework may assist profiling of inhaled drug discovery candidates that are also P-gp substrates. The potential for P-gp mediated pulmonary disposition exists in the clinic.

Multiple organic cation transporters contribute to the renal transport of sulpiride

Sulpiride, a selective dopamine D2 receptor blocker, is used widely for the treatment of schizophrenia, depression and gastric/duodenal ulcers. Because the great majority of sulpiride is positively charged at physiological pH 7.4, and ~70% of the dose recovered in urine is in the unchanged form after human intravenous administration of sulpiride, it is believed that transporters play an important role in the renal excretion of sulpiride. The aim of the present study was to explore which transporters contribute to the renal disposition of sulpiride. The results demonstrated that sulpiride was a substrate of human carnitine/organic cation transporter 1 (hOCTN1) and 2 (hOCTN2), human organic cation transporter 2 (hOCT2), human multidrug and toxin efflux extrusion protein 1 (hMATE1) and 2-K (hMATE2-K). Sulpiride accumulation from the basolateral (BL) to the apical (AP) side in MDCK-hOCT2/pcDNA3.1 cell monolayers was much greater than that in MDCK-hOCT2/hMATE1 cells, and cimetidine dramatically reduced the intracellular accumulation of sulpiride from BL to AP. In addition, the accumulation of sulpiride in mouse primary renal tubular cells (mPRTCs) was markedly reduced by inhibitors of Oct2 and Octns. The results implied that OCTN1, OCTN2, OCT2, MATE1 and MATE2-K probably contributed to the renal transfer of sulpiride, in which OCT2 mediated the uptake of sulpiride from the bloodstream to the proximal tubular cells, while MATEs contributed to the sulpiride efflux from the proximal tubular cells to the renal lumen, and OCTNs participated in both renal secretion and reabsorption.

Oligopeptide Transport in Rat Lung Alveolar Epithelial Cells is Mediated by Pept2

PURPOSE

Studies were conducted in primary cultured rat alveolar epithelial cell monolayers to characterize peptide transporter expression and function.

METHODS

Freshly isolated rat lung alveolar epithelial cells were purified and cultured on permeable support with and without keratinocyte growth factor (KGF). Messenger RNA and protein expression of Pept1 and Pept2 in alveolar epithelial type I- and type II-like cell monolayers (±KGF, resp.) were examined by RT-PCR and Western blotting. ³H-Glycyl-sarcosine (³H-gly-sar) transmonolayer flux and intracellular accumulation were evaluated in both cell types.

RESULTS

RT-PCR showed expression of Pept2, but not Pept1, mRNA in both cell types. Western blot analysis revealed presence of Pept2 protein in type II-like cells, and less in type I-like cells. Bi-directional transmonolayer ³H-gly-sar flux lacked asymmetry in transport in both types of cells. Uptake of ³H-gly-sar from apical fluid of type II-like cells was 7-fold greater than that from basolateral fluid, while no significant differences were observed from apical vs. basolateral fluid of type I-like cells.

CONCLUSIONS

This study confirms the absence of Pept1 from rat lung alveolar epithelium in vitro. Functional Pept2 expression in type II-like cell monolayers suggests its involvement in oligopeptide lung disposition, and offers rationale for therapeutic development of di/tripeptides, peptidomimetics employing pulmonary drug delivery.

Acetyl-coenzyme A carboxylase inhibition reduces de novo lipogenesis in overweight male subjects: A randomized, double-blind, crossover study

NDI-010976, an allosteric inhibitor of acetyl-coenzyme A carboxylases (ACC) ACC1 and ACC2, reduces hepatic de novo lipogenesis (DNL) and favorably affects steatosis, inflammation, and fibrosis in animal models of fatty liver disease. This study was a randomized, double-blind, placebo-controlled, crossover trial evaluating the pharmacodynamic effects of a single oral dose of NDI-010976 on hepatic DNL in overweight and/or obese but otherwise healthy adult male subjects. Subjects were randomized to receive either NDI-010976 (20, 50, or 200 mg) or matching placebo in period 1, followed by the alternate treatment in period 2; and hepatic lipogenesis was stimulated with oral fructose administration. Fractional DNL was quantified by infusing a stable isotope tracer, [1-¹³ C]acetate, and monitoring ¹³ C incorporation into palmitate of circulating very low-density lipoprotein triglyceride. Single-dose administration of NDI-010976 was well tolerated at doses up to and including 200 mg. Fructose administration over a 10-hour period stimulated hepatic fractional DNL an average of 30.9 ± 6.7% (mean ± standard deviation) above fasting DNL values in placebo-treated subjects. Subjects administered single doses of NDI-010976 at 20, 50, or 200 mg had significant inhibition of DNL compared to placebo (mean inhibition relative to placebo was 70%, 85%, and 104%, respectively). An inverse relationship between fractional DNL and NDI-010976 exposure was observed with >90% inhibition of fractional DNL associated with plasma concentrations of NDI-010976 >4 ng/mL.

CONCLUSION

ACC inhibition with a single dose of NDI-010976 is well tolerated and results in a profound dose-dependent inhibition of hepatic DNL in overweight adult male subjects. Therefore, NDI-010976 could contribute considerable value to the treatment algorithm of metabolic disorders characterized by dysregulated fatty acid metabolism, including nonalcoholic steatohepatitis. (Hepatology 2017;66:324-334).

Transporters Involved in Metformin Pharmacokinetics and Treatment Response

Metformin, widely used as first-line treatment for type 2 diabetes, exists primarily as a hydrophilic cation at physiological pHs. As such, membrane transporters play a substantial role in its absorption, tissues distribution, and renal elimination. Multiple organic cation transporters are determinants of the pharmacokinetics of metformin, and many of them are important in its pharmacological action, as mediators of metformin entry into target tissues. Furthermore, a recent genome-wide association study in a large multi-ethnic population implicated polymorphisms in SLC2A2, encoding the glucose transporter, GLUT2, as important determinants of response to metformin. Here, we describe the key transporters associated with metformin pharmacokinetics and response.

Effect of Liver Disease on Hepatic Transporter Expression and Function

Liver disease can alter the disposition of xenobiotics and endogenous substances. Regulatory agencies such as the Food and Drug Administration and the European Medicines Evaluation Agency recommend, if possible, studying the effect of liver disease on drugs under development to guide specific dose recommendations in these patients. Although extensive research has been conducted to characterize the effect of liver disease on drug-metabolizing enzymes, emerging data have implicated that the expression and function of hepatobiliary transport proteins also are altered in liver disease. This review summarizes recent developments in the field, which may have implications for understanding altered disposition, safety, and efficacy of new and existing drugs. A brief review of liver physiology and hepatic transporter localization/function is provided. Then, the expression and function of hepatic transporters in cholestasis, hepatitis C infection, hepatocellular carcinoma, human immunodeficiency virus infection, nonalcoholic fatty liver disease and nonalcoholic steatohepatitis, and primary biliary cirrhosis are reviewed. In the absence of clinical data, nonclinical information in animal models is presented. This review aims to advance the understanding of altered expression and function of hepatic transporters in liver disease and the implications of such changes on drug disposition.

Trafficking and other regulatory mechanisms for organic anion transporting polypeptides and organic anion transporters that modulate cellular drug and xenobiotic influx and that are dysregulated in disease

Organic anion transporters (OATs) and organic anion-transporting polypeptides (OATPs), encoded by a number of solute carrier (SLC)22A and SLC organic anion (SLCO) genes, mediate the absorption and distribution of drugs and other xenobiotics. The regulation of OATs and OATPs is complex, comprising both transcriptional and post-translational mechanisms. Plasma membrane expression is required for cellular substrate influx by OATs/OATPs. Thus, interest in post-translational regulatory processes, including membrane targeting, endocytosis, recycling and degradation of transporter proteins, is increasing because these are critical for plasma membrane expression. After being synthesized, transporters undergo N-glycosylation in the endoplasmic reticulum and Golgi apparatus and are delivered to the plasma membrane by vesicular transport. Their expression at the cell surface is maintained by de novo synthesis and recycling, which occurs after clathrin- and/or caveolin-dependent endocytosis of existing protein. Several studies have shown that phosphorylation by signalling kinases is important for the internalization and recycling processes, although the transporter protein does not appear to be directly phosphorylated. After internalization, transporters that are targeted for degradation undergo ubiquitination, most likely on intracellular loop residues. Epigenetic mechanisms, including methylation of gene regulatory regions and transcription from alternate promoters, are also significant in the regulation of certain SLC22A/SLCO genes. The membrane expression of OATs/OATPs is dysregulated in disease, which affects drug efficacy and detoxification. Several transporters are expressed in the cytoplasmic subcompartment in disease states, which suggests that membrane targeting/internalization/recycling may be impaired. This article focuses on recent developments in OAT and OATP regulation, their dysregulation in disease and the significance for drug therapy.

The Role of HIV Infection in Neurologic Injury

The central nervous system (CNS) is a very challenging HIV-1 sanctuary, in which HIV-1 replication is established early on during acute infection and can persist despite potent antiretroviral treatments. HIV-1 infected macrophages play a pivotal role acting as vehicles for HIV-1 to spread into the brain, and can be the major contributor of an early compartmentalization. HIV-1 infection in CNS may lead to a broad spectrum of neurological syndromes, such as dementia, mild neurocognitive disorders, and asymptomatic impairment. These clinical manifestations are caused by the release of neurotoxins from infected cells (mainly macrophages), and also by several HIV-1 proteins, able to activate cell-signaling involved in the control of cellular survival and apoptosis. This review is aimed at highlighting the virological aspects associated with the onset of neurocognitive disorders and at addressing the novel therapeutic approaches to stop HIV-1 replication in this critical sanctuary.

Inflammation and pharmacokinetics: potential implications for HIV-infection

INTRODUCTION

The physiological changes accompanying inflammation may alter the pharmacokinetics (PK) of certain medications. Individuals infected with HIV have chronically elevated inflammatory markers despite viral suppression following effective antiretroviral therapy (ART), as well as age-related inflammation. Understanding the potential clinical implications of inflammation on the PK of medications is important for understanding dose-response relationships and necessitates future research. Areas covered: An extensive literature search was carried out using PubMed and associated bibliographies to summarize the current state of knowledge regarding altered PK in response to inflammation and its application to the field of HIV. Expert opinion: Preclinical and clinical studies show that inflammation leads to a downregulation of certain drug metabolizing enzymes and both up and down regulation of transporters depending on the transporter and cell type. Decreased gastric acidity, fluid shifts, and plasma protein alterations also occur with inflammation, leading to potential absorption, distribution, and clearance changes. More research is needed including controlled PK studies to address the clinical relevance of these observations, especially in the aging HIV-infected population. Results from future studies will enable us to better predict drug concentrations in individuals with inflammation, in line with efforts to provide personalized pharmacotherapy in our healthcare system.

Estrone Sulfate Transport and Steroid Sulfatase Activity in Colorectal Cancer: Implications for Hormone Replacement Therapy

Hormone replacement therapy (HRT) affects the incidence and potential progression of colorectal cancer (CRC). As HRT primarily consists of estrone sulfate (E₁S), understanding whether this conjugated estrogen is transported and metabolized in CRC will define its potential effect in this malignancy. Here, we show that a panel of CRC cell lines (Colo205, Caco2, HCT116, HT-29) have steroid sulfatase (STS) activity, and thus can hydrolyze E₁S. STS activity is significantly higher in CRC cell lysate, suggesting the importance of E₁S transport in intracellular STS substrate availability. As E₁S transport is regulated by the expression pattern of certain solute carrier organic anion transporter polypeptides, we show that in CRC OATP4A1 is the most abundantly expressed transporter. All four CRC cell lines rapidly transported E₁S into cells, with this effect significantly inhibited by the competitive OATP inhibitor BSP. Transient knockdown of OATP4A1 significantly disrupted E₁S uptake. Examination of estrogen receptor status showed ERα was present in Colo205 and Caco2 cells. None of the cells expressed ERβ. Intriguingly, HCT116 and HT29 cells strongly expressed the G protein coupled estrogen receptor (GPER), and that stimulation of this receptor with estradiol (E₂) and G1, a GPER agonist, significantly (p < 0.01) increased STS activity. Furthermore, tamoxifen and fulvestrant, known GPER agonist, also increased CRC STS activity, with this effect inhibited by the GPER antagonist G15. These results suggest that CRC can take up and hydrolyze E₁S, and that subsequent GPER stimulation increases STS activity in a potentially novel positive feedback loop. As elevated STS expression is associated with poor prognosis in CRC, these results suggest HRT, tamoxifen and fulvestrant may negatively impact CRC patient outcomes.

Allometric Scaling of Clearance in Paediatric Patients: When Does the Magic of 0.75 Fade?

Allometric scaling on the basis of bodyweight raised to the power of 0.75 (AS0.75) is frequently used to scale size-related changes in plasma clearance (CLp) from adults to children. A systematic assessment of its applicability is undertaken for scenarios considering size-related changes with and without maturation processes. A physiologically-based pharmacokinetic (PBPK) simulation workflow was developed in R for 12,620 hypothetical drugs. In scenario one, only size-related changes in liver weight, hepatic blood flow, and glomerular filtration were included in simulations of 'true' paediatric CLp. In a second scenario, maturation in unbound microsomal intrinsic clearance (CLint,mic), plasma protein concentration, and haematocrit were also included in these simulated 'true' paediatric CLp values. For both scenarios, the prediction error (PE) of AS0.75-based paediatric CLp predictions was assessed, while, for the first scenario, an allometric exponent was also estimated based on 'true' CLp. In the first scenario, the PE of AS0.75-based paediatric CLp predictions reached up to 278 % in neonates, and the allometric exponent was estimated to range from 0.50 to 1.20 depending on age and drug properties. In the second scenario, the PE sensitivity to drug properties and maturation was higher in the youngest children, with AS0.75 resulting in accurate CLp predictions above 5 years of age. Using PBPK principles, there is no evidence for one unique allometric exponent in paediatric patients, even in scenarios that only consider size-related changes. As PE is most sensitive to the allometric exponent, drug properties and maturation in younger children, AS0.75 leads to increasingly worse predictions with decreasing age.

Is the unbound concentration of atazanavir of interest in therapeutic drug monitoring?

To date, therapeutic drug monitoring (TDM) is carried out with antiretrovirals and is usually based on total concentrations (C_t ). However, for some patients, TDM does not reflect efficacy or the avoidance of toxicity as is the case for atazanavir (ATV), a HIV protease inhibitor. As the unbound concentration (C_u ) is the pharmacological active form, the aim of the study was to evaluate the value of C_u and the unbound fraction (f_u , f_u = C_u /C_t ) for the TDM of ATV. The variability of C_u and the corresponding f_u of ATV was explored in 43 patients treated with ATV for an average of 13.5 months. C_u was determined by coupling ultrafiltration and liquid chromatography. As ATV is highly bound to alpha-1 acid glycoprotein (AAG), the correlation between f_u and AAG was also evaluated. The viral load was monitored to evaluate the patients' virologic response, while total plasma bilirubin and unconjugated plasma bilirubin were used as biomarkers of ATV toxicity. Median trough C_u and C_t were 37.9 μg/L (Interquartile range (IQR) 20.6-94.9 μg/L) and 628.6 μg/L (IQR 362.7-1078.1 μg/L), respectively. f_u , C_u and C_t showed high variability, but the f_u variability was not correlated with the AAG level. The unbound concentration and fraction were unrelated to the virologic response (P = 0.21 and P = 0.65 for C_u and f_u , respectively) nor to the unconjugated bilirubin (Pearson correlation coefficient (ρ), ρ = 0.22; P = 0.17 for C_u ). Neither total nor unbound concentrations of ATV fully explained hyperbilirubinaemia or virologic failure. From this study, we conclude that unbound ATV did not appear to be more relevant than C_t .

Allele frequency and genotype distribution of a common variant in the 3´-untranslated region of the SLC22A3 gene in patients with type 2 diabetes: Association with response to metformin

Background:

Organic cation transporter 3 (OCT3) is an excellent transporter for metformin, which is used as first-line therapy for type 2 diabetes (T2D). OCT3 genetic variants may influence the clinical response to metformin. This study aimed to determine the genotype and allele frequency of OCT3-564G>A (rs3088442) variant and its role in the glycemic response to metformin in patients with newly diagnosed T2D.

Materials and Methods:

Based on the response to metformin, 150 patients were classified into two groups: Sixty-nine responders (decrease in glycated hemoglobin [HbA1c] values by more than 1% from the baseline) and 81 nonresponders (decrease in HbA1c values <1% from the baseline). HbA1c levels were determined by chromatography. The variant OCT3-564G>A was genotyped using polymerase chain reaction - based restriction fragment length polymorphism.

Results:

The genotypes frequencies were 51.3% GG, 36% AG, and 12.7% AA. Allele frequency of major allele (G) and minor allele (A) in OCT3-564G>A variant was found to be 0.69 and 0.31, respectively. Fasting glucose, HbA1c, body mass index, and lipid profile in both GG genotypes and GA + AA group decreased significantly after 3 months of metformin therapy compared with baseline (P < 0.05). In both responders and nonresponders, HbA1c and fasting glucose levels were lower in patients with the GA + AA genotype than in those with the GG genotype; however, the differences were not statistically significant (P > 0.05).

Conclusion:

The A allele frequency (which may be a protective allele against coronary heart disease) in the Iranian diabetic patients was lower than Iranian, Caucasian and Japanese healthy populations. Metformin is useful in improving the lipid profile, in addition to its impacts in glycemic control, and these effects are regardless of OCT3-564G>A variant.

Multiple Drug Transporters Are Involved in Renal Secretion of Entecavir

Entecavir (ETV) is a first-line antiviral agent for the treatment of chronic hepatitis B virus infection. Renal excretion is the major elimination path of ETV, in which tubular secretion plays the key role. However, the secretion mechanism has not been clarified. We speculated that renal transporters mediated the secretion of ETV. Therefore, the aim of our study was to elucidate which transporters contribute to the renal disposition of ETV. Our results revealed that ETV (50 μM) remarkably reduced the accumulation of probe substrates in MDCK cells stably expressing human multidrug and toxin efflux extrusion proteins (hMATE1/2-K), organic cation transporter 2 (hOCT2), and carnitine/organic cation transporters (hOCTNs) and increased the substrate accumulation in cells transfected with multidrug resistance-associated protein 2 (hMRP2) or multidrug resistance protein 1 (hMDR1). Moreover, ETV was proved to be a substrate of the above-described transporters. In transwell studies, the transport of ETV in MDCK-hOCT2-hMATE1 showed a distinct directionality from BL (hOCT2) to AP (hMATE1), and the cellular accumulation of ETV in cells expressing hMATE1 was dramatically lower than that of the mock-treated cells. The accumulation of ETV in mouse primary renal tubular cells was obviously affected by inhibitors of organic anion transporter 1/3 (Oat1/3), Oct2, Octn1/2, and Mrp2. Therefore, the renal uptake of ETV is likely mediated by OAT1/3 and OCT2 while the efflux is mediated by MATEs, MDR1, and MRP2, and OCTN1/2 may participate in both renal secretion and reabsorption.

Application of RPMI 2650 nasal cell model to a 3D printed apparatus for the testing of drug deposition and permeation of nasal products

The aim of this study was to incorporate an optimized RPMI2650 nasal cell model into a 3D printed model of the nose to test deposition and permeation of drugs intended for use in the nose. The nasal cell model was optimized for barrier properties in terms of permeation marker and mucus production. RT-qPCR was used to determine the xenobiotic transporter gene expression of RPMI 2650 cells in comparison with primary nasal cells. After 14days in culture, the cells were shown to produce mucus, and to express TEER (define) values and sodium fluorescein permeability consistent with values reported for excised human nasal mucosa. In addition, good correlation was found between RPMI 2650 and primary nasal cell transporter expression values. The purpose-built 3D printed model of the nose takes the form of an expansion chamber with inserts for cells and an orifice for insertion of a spray drug delivery device. This model was validated against the FDA glass chamber with cascade impactors that is currently approved for studies of nasal products. No differences were found between the two apparatus. The apparatus including the nasal cell model was used to test a commercial nasal product containing budesonide (Rhinocort, AstraZeneca, Australia). Drug deposition and transport studies on RPMI 2650 were successfully performed. The new 3D printed apparatus that incorporates cells can be used as valid in vitro model to test nasal products in conditions that mimic the delivery from nasal devices in real life conditions.

Large-scale multiplex absolute protein quantification of drug-metabolizing enzymes and transporters in human intestine, liver, and kidney microsomes by SWATH-MS: Comparison with MRM/SRM and HR-MRM/PRM

The purpose of the present study was to examine simultaneously the absolute protein amounts of 152 membrane and membrane-associated proteins, including 30 metabolizing enzymes and 107 transporters, in pooled microsomal fractions of human liver, kidney, and intestine by means of SWATH-MS with stable isotope-labeled internal standard peptides, and to compare the results with those obtained by MRM/SRM and high resolution (HR)-MRM/PRM. The protein expression levels of 27 metabolizing enzymes, 54 transporters, and six other membrane proteins were quantitated by SWATH-MS; other targets were below the lower limits of quantitation. Most of the values determined by SWATH-MS differed by less than 50% from those obtained by MRM/SRM or HR-MRM/PRM. Various metabolizing enzymes were expressed in liver microsomes more abundantly than in other microsomes. Ten, 13, and eight transporters listed as important for drugs by International Transporter Consortium were quantified in liver, kidney, and intestinal microsomes, respectively. Our results indicate that SWATH-MS enables large-scale multiplex absolute protein quantification while retaining similar quantitative capability to MRM/SRM or HR-MRM/PRM. SWATH-MS is expected to be useful methodology in the context of drug development for elucidating the molecular mechanisms of drug absorption, metabolism, and excretion in the human body based on protein profile information.

A mutation in SLC22A4 encoding an organic cation transporter expressed in the cochlea strial endothelium causes human recessive non-syndromic hearing loss DFNB60

The high prevalence/incidence of hearing loss (HL) in humans makes it the most common sensory defect. The majority of the cases are of genetic origin. Non-syndromic hereditary HL is extremely heterogeneous. Genetic approaches have been instrumental in deciphering genes that are crucial for auditory function. In this study, we first used NADf chip to exclude the implication of known North-African mutations in HL in a large consanguineous Tunisian family (FT13) affected by autosomal recessive non-syndromic HL (ARNSHL). We then performed genome-wide linkage analysis and assigned the deafness gene locus to ch:5q23.2-31.1, corresponding to the DFNB60 ARNSHL locus. Moreover, we performed whole exome sequencing on FT13 patient DNA and uncovered amino acid substitution p.Cys113Tyr in SLC22A4, a transporter of organic cations, cosegregating with HL in FT13 and therefore the cause of ARNSHL DFNB60. We also screened a cohort of small Tunisian HL families and uncovered an additional deaf proband of consanguineous parents that is homozygous for p.Cys113Tyr carried by the same microsatellite marker haplotype as in FT13, indicating that this mutation is ancestral. Using immunofluorescence, we found that Slc22a4 is expressed in stria vascularis (SV) endothelial cells of rodent cochlea and targets their apical plasma membrane. We also found Slc22a4 transcripts in our RNA-seq library from purified primary culture of mouse SV endothelial cells. Interestingly, p.Cys113Tyr mutation affects the trafficking of the transporter and severely alters ergothioneine uptake. We conclude that SLC22A4 is an organic cation transporter of the SV endothelium that is essential for hearing, and its mutation causes DFNB60 form of HL.

Cynomolgus Monkey as a Clinically Relevant Model to Study Transport Involving Renal Organic Cation Transporters: In Vitro and In Vivo Evaluation

Organic cation transporter (OCT) 2, multidrug and toxin extrusion protein (MATE) 1, and MATE2K mediate the renal secretion of various cationic drugs and can serve as the loci of drug-drug interactions (DDI). To support the evaluation of cynomolgus monkey as a surrogate model for studying human organic cation transporters, monkey genes were cloned and shown to have a high degree of amino acid sequence identity versus their human counterparts (93.7, 94.7, and 95.4% for OCT2, MATE1, and MATE2K, respectively). Subsequently, the three transporters were individually stably expressed in human embryonic kidney (HEK) 293 cells and their properties (substrate selectivity, time course, pH dependence, and kinetics) were found to be comparable to the corresponding human form. For example, six known human cation transporter inhibitors, including pyrimethamine (PYR), showed generally similar IC50 values against the monkey transporters (within sixfold). Consistent with the in vitro inhibition of metformin (MFM) transport by PYR (IC50 for cynomolgus OCT2, MATE1, and MATE2K; 1.2 ± 0.38, 0.17 ± 0.04, and 0.25 ± 0.04 µM, respectively), intravenous pretreatment of monkeys with PYR (0.5 mg/kg) decreased the clearance (54 ± 9%) and increased in the area under the plasma concentration-time curve of MFM (AUC ratio versus control = 2.23; 90% confidence interval of 1.57 to 3.17). These findings suggest that the cynomolgus monkey may have some utility in support of in vitro-in vivo extrapolations (IVIVEs) involving the inhibition of renal OCT2 and MATEs. In turn, cynomolgus monkey-enabled IVIVEs may inform human DDI risk assessment.

The small molecule tyrosine kinase inhibitor NVP-BHG712 antagonizes ABCC10-mediated paclitaxel resistance: a preclinical and pharmacokinetic study

Paclitaxel exhibits clinical activity against a wide variety of solid tumors. However, resistance to paclitaxel significantly attenuates the response to chemotherapy. The ABC transporter subfamily C member 10 (ABCC10), also known as multi-drug resistance protein 7 (MRP7) efflux transporter, is a major mediator of paclitaxel resistance. Here, we determine the effect of NVP-BHG712, a specific EphB4 receptor inhibitor, on 1) paclitaxel resistance in HEK293 cells transfected with ABCC10, 2) the growth of tumors in athymic nude mice that received NVP-BHG712 and paclitaxel systemically and 3) the pharmacokinetics of paclitaxel in presence or absence of NVP-BHG712. NVP-BHG712 (0.5 μM), in HEK293/ABCC10 cells, significantly enhanced the intracellular accumulation of paclitaxel by inhibiting the efflux activity of ABCC10 without altering the expression level of the ABCC10 protein. Furthermore, NVP-BHG712 (25 mg/kg, p.o., q3d x 6), in combination with paclitaxel (15 mg/kg, i.p., q3d x 6), significantly inhibited the growth of ABCC10-expressing tumors in athymic nude mice. NVP-BHG712 administration significantly increased the levels of paclitaxel in the tumors but not in plasma compared to paclitaxel alone. The combination of NVP-BHG712 and paclitaxel could serve as a novel and useful therapeutic strategy to attenuate paclitaxel resistance mediated by the expression of the ABCC10 transporter.

The Potential of Minipigs in the Development of Anticancer Therapeutics: Species Comparison and Examples of Special Applications

Minipigs are increasingly being used as an alternative to dog or monkey in nonclinical safety testing of pharmaceuticals since they share similar anatomical and physiological characteristics to humans. Integrative assessment of pharmacodynamic and pharmacokinetic data sets of drug candidates fromin silico,in vitro, andin vivoinvestigations form the basis for selecting the most relevant nonrodent species for toxicology studies. Developing anticancer therapeutics represents a special challenge for species selection due to their effects on multiple organ systems. The toxicological profile of anticancer drugs can be associated with steep dose-response curves, especially due to dose-limiting toxicity on the alimentary, hematopoietic, and immune systems. Selection of an appropriate species for toxicology studies is of importance to avoid an inappropriately low (without benefit for the late-stage cancer patient) or high clinical starting dose (with a risk of unexpected adverse reactions). Although the minipig has been the preferred species to develop drugs applied topically, it is only rarely used in anticancer drug development compared to dog and monkey. In this context, we discuss the potential of minipigs in anticancer drug development with examples of programs for oral and dermal administration, intravascular application in drug-eluting stents, and local chemotherapy (chemoembolization).

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

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

Human organic anion transporter 2 is distinct from organic anion transporters 1 and 3 with respect to transport function

Phylogentically, organic anion transporter (OAT)1 and OAT3 are closely related, whereas OAT2 is more distant. Experiments with human embryonic kidney-293 cells stably transfected with human OAT1, OAT2, or OAT3 were performed to compare selected transport properties. Common to OAT1, OAT2, and OAT3 is their ability to transport cGMP. OAT2 interacted with prostaglandins, and cGMP uptake was inhibited by PGE2 and PGF2α with IC50 values of 40.8 and 12.7 μM, respectively. OAT1 (IC50: 23.7 μM), OAT2 (IC50: 9.5 μM), and OAT3 (IC50: 1.6 μM) were potently inhibited by MK571, an established multidrug resistance protein inhibitor. OAT2-mediated cGMP uptake was not inhibited by short-chain monocarboxylates and, as opposed to OAT1 and OAT3, not by dicarboxylates. Consequently, OAT2 showed no cGMP/glutarate exchange. OAT1 and OAT3 exhibited a pH and a Cl− dependence with higher substrate uptake at acidic pH and lower substrate uptake in the absence of Cl−, respectively. Such pH and Cl− dependencies were not observed with OAT2. Depolarization of membrane potential by high K+ concentrations in the presence of the K+ ionophore valinomycin left cGMP uptake unaffected. In addition to cGMP, OAT2 transported urate and glutamate, but cGMP/glutamate exchange could not be demonstrated. These experiments suggest that OAT2-mediated cGMP uptake does not occur via exchange with monocarboxylates, dicarboxylates, and hydroxyl ions. The counter anion for electroneutral cGMP uptake remains to be identified.

Role of SLC22A1 polymorphic variants in drug disposition, therapeutic responses, and drug-drug interactions

The SCL22A1 gene encodes the broad selectivity transporter hOCT1. hOCT1 is expressed in most epithelial barriers thereby contributing to drug pharmacokinetics. It is also expressed in different drug target cells, including immune system cells and others. Thus, this membrane protein might also contribute to drug pharmacodynamics. Up to 1000 hOCT1 polymorphisms have been identified so far, although only a small fraction of those have been mechanistically studied. A paradigm in the field of drug transporter pharmacogenetics is the impact of hOCT1 gene variability on metformin clinical parameters, affecting area under the concentration-time curve, Cmax and responsiveness. However, hOCT1 also mediates the translocation of a variety of drugs used as anticancer, antiviral, anti-inflammatory, antiemetic agents as well as drugs used in the treatment of neurological diseases among. This review focuses exclusively on those drugs for which some pharmacogenetic data are available, and aims at highlighting the need for further clinical research in this area.

Clinical pharmacology of tenofovir clearance: a pharmacokinetic/pharmacogenetic study on plasma and urines

The HIV virus and hepatitis B virus nucleotide reverse transcriptase inhibitor tenofovir has been associated with proximal tubular toxicity; the latter was found to be predicted by plasma concentrations and with single-nucleotide polymorphisms in transporters-encoding genes. A cross-sectional analysis in adult HIV-positive patients with estimated creatinine clearance >60 ml min^-1 was performed. Twelve-hour plasma and urinary tenofovir concentrations and single-nucleotide polymorphisms in several transporter-encoding genes were analysed. In 289 patients 12-h tenofovir plasma, urinary and urinary to plasma ratios were 69 ng ml^-1 (interquartile range 51.5-95), 24.3 mg ml^-1 (14.3-37.7) and 384 (209-560). At multivariate analysis estimated creatinine clearance, protease inhibitors co-administration and SLC28A2 CT/TT genotypes were independently associated with plasma tenofovir exposure; ABCC10 GA/AA genotypes and protease inhibitor co-administration were independently associated with the urinary to plasma tenofovir ratio. Tenofovir clearance was associated with genetic polymorphisms in host genes and with co-administered drugs: if confirmed by ongoing studies these data may inform treatment tailoring and/or dose reductions.

Cross-Species Differences in the Preclinical Pharmacokinetics of CT7758, an α4β1/α4β7 Integrin Antagonist

CT7758, a carboxylate containing α4β1/α4/β7 integrin antagonist, was characterized for its pharmacokinetic profile in various in vitro and in vivo assays in support of clinical development. The oral bioavailability of CT7758 was 4% in mice, 2% in rats, 7-55% in dogs, and 0.2% in cynomolgus monkeys. The low bioavailability in rodents and monkey results from low intestinal absorption as evidenced by a low fraction absorbed in the rat portal vein model (3%), low-to-medium permeability in Caco-2 cells (≤1.3 × 10(-6) cm/s) with evidences of polarized efflux, and high polar surface area (104 Å). In rodents and cynomolgus monkeys, the total plasma clearance was moderate to high (≥50% hepatic blood flow QH) and associated with a short elimination half-life (≤1 hour). This contrast with the dog data which showed a much lower clearance (6% QH) and a longer t1/2 (2.4 hours). The volume of distribution (Vz) also varied significantly across species with value of 5.5, 2.8, 0.24, and 0.93 l/kg in mouse, rat, dog, and cynomolgus monkey, respectively. In vitro assays demonstrated that active hepatic uptake accounted for most of the in vivo clearance and was the source of the large species variability. In vitro uptake assays predicted a total plasma clearance in humans in the low range (33% QH), a finding subsequently confirmed in the clinic. Assays in OAPT1B1-transfected cells demonstrated active uptake transport through this transporter. The prospect of limited absorption in human prompted the synthesis an ethyl ester prodrug, CDP323, which demonstrated higher in vitro permeability, increased oral bioavailability, as well as efficient in vivo release of its active moiety CT7758.

Organic cation transporter function in different in vitro models of human lung epithelium

Organic cation transporters (OCT) encoded by members of the solute carrier (SLC) 22 family of genes are involved in the disposition of physiological substrates and xenobiotics, including drugs used in the treatment of chronic obstructive lung diseases and asthma. The aim of this work was to identify continuously growing epithelial cell lines that closely mimic the organic cation transport of freshly isolated human alveolar type I-like epithelial cells (ATI) in primary culture, and which consequently, can be utilised as in vitro models for the study of organic cation transport at the air-blood barrier. OCT activity was investigated by measuring [(14)C]-tetraethylammonium (TEA) uptake into monolayers of Calu-3, NCI-H441 and A549 lung epithelial cell lines in comparison to ATI-like cell monolayers in primary culture. Levels of time-dependent TEA uptake were highest in A549 and ATI-like cells. In A549 cells, TEA uptake had a saturable and a non-saturable component with Km=528.5±373.1μM, Vmax=0.3±0.1nmol/min/mg protein and Kd=0.02μl/min/mg protein. TEA uptake into Calu-3 and NCI-H441 cells did not reach saturation within the concentration range studied. RNAi experiments in A549 cells confirmed that TEA uptake was mainly facilitated by OCT1 and OCT2. Co-incubation studies using pharmacological OCT modulators suggested that organic cation uptake pathways share several similarities between ATI-like primary cells and the NCI-H441 cell line, whereas more pronounced differences exist between primary cells and the A549 and Calu-3 cell lines.

Permeation of Therapeutic Drugs in Different Formulations across the Airway Epithelium In Vitro

BACKGROUND

Pulmonary drug delivery is characterized by short onset times of the effects and an increased therapeutic ratio compared to oral drug delivery. This delivery route can be used for local as well as for systemic absorption applying drugs as single substance or as a fixed dose combination. Drugs can be delivered as nebulized aerosols or as dry powders. A screening system able to mimic delivery by the different devices might help to assess the drug effect in the different formulations and to identify potential interference between drugs in fixed dose combinations. The present study evaluates manual devices used in animal studies for their suitability for cellular studies.

METHODS

Calu-3 cells were cultured submersed and in air-liquid interface culture and characterized regarding mucus production and transepithelial electrical resistance. The influence of pore size and material of the transwell membranes and of the duration of air-liquid interface culture was assessed. Compounds were applied in solution and as aerosols generated by MicroSprayer IA-1C Aerosolizer or by DP-4 Dry Powder Insufflator using fluorescein and rhodamine 123 as model compounds. Budesonide and formoterol, singly and in combination, served as examples for drugs relevant in pulmonary delivery.

RESULTS AND CONCLUSIONS

Membrane material and duration of air-liquid interface culture had no marked effect on mucus production and tightness of the cell monolayer. Co-application of budesonide and formoterol, applied in solution or as aerosol, increased permeation of formoterol across cells in air-liquid interface culture. Problems with the DP-4 Dry Powder Insufflator included compound-specific delivery rates and influence on the tightness of the cell monolayer. These problems were not encountered with the MicroSprayer IA-1C Aerosolizer. The combination of Calu-3 cells and manual aerosol generation devices appears suitable to identify interactions of drugs in fixed drug combination products on permeation.

Solute Carrier Family of the Organic Anion-Transporting Polypeptides 1A2- Madin-Darby Canine Kidney II: A Promising In Vitro System to Understand the Role of Organic Anion-Transporting Polypeptide 1A2 in Blood-Brain Barrier Drug Penetration

Organic anion-transporting polypeptide (OATP) 1A2 has the potential to be a target for central nervous system drug delivery due to its luminal localization at the human blood-brain barrier and broad substrate specificity. We found OATP1A2 mRNA expression in the human brain to be comparable to breast cancer resistance protein and OATP2B1 and much higher than P-glycoprotein (P-gp), and confirmed greater expression in the brain relative to other tissues. The goal of this study was to establish a model system to explore OATP1A2-mediated transcellular transport of substrate drugs and the interplay with P-gp. In vitro (human embryonic kidney 293 cells stably expressing Oatp1a4, the closest murine isoform) and in vivo (naïve and Oatp1a4 knock-out mice) studies with OATP1A2 substrate triptan drugs demonstrated that these drugs were not Oatp1a4 substrates. This species difference demonstrates that the rodent is not a good model to investigate the active brain uptake of potential OATP1A2 substrates. Thus, we constructed a novel OATP1A2 expressing Madin-Darby canine kidney (MDCK) II wild type and an MDCKII-multidrug resistance protein 1 (MDR1) system using BacMam virus transduction. The spatial expression pattern of OATP1A2 after transduction in MDCKII-MDR1 cells was superimposed to P-gp, confirming apical membrane localization. OATP1A2-mediated uptake of zolmitriptan, rosuvastatin, and fexofenadine across monolayers increased with increasing OATP1A2 protein expression. OATP1A2 counteracted P-gp efflux for cosubstrates zolmitriptan and fexofenadine. A three-compartment model incorporating OATP1A2-mediated influx was used to quantitatively describe the time- and concentration-dependent apical-to-basolateral transcellular transport of rosuvastatin across OATP1A2 expressing the MDCKII monolayer. This novel, simple and versatile experimental system is useful for understanding the contribution of OATP1A2-mediated transcellular transport across barriers, such as the blood-brain barrier.

Dosing time-dependent changes in the analgesic effect of pregabalin on diabetic neuropathy in mice

Patients with diabetes often develop peripheral nerve complications, including numbness and pain in the extremities. Diabetes-induced peripheral neuropathic pain is characterized by hypersensitivity to innocuous stimuli, known as tactile allodynia. Pregabalin (PGN) is currently used to treat diabetes-induced peripheral neuropathy and alleviates allodynia. In the present study, we demonstrated that the antiallodynic effect of PGN on diabetic mice was modulated by circadian changes in its intestinal absorption. A single intraperitoneal administration of 200 mg/kg streptozotocin (STZ) to mice induced type I diabetic pathologic changes that were accompanied by tactile allodynia. The intensity of tactile allodynia in STZ-induced diabetic mice was alleviated by the oral administration of PGN; however, the antiallodynic effect varied according to its dosing time. The analgesic effect of PGN was enhanced by its administration at the times of day when its intestinal absorption was accelerated. Organic cation transporter novel type 1 (Octn1) mediated the uptake of PGN into intestinal epithelial cells. The expression of Octn1 in the small intestine of STZ-induced diabetic mice oscillated in a circadian time-dependent manner. This oscillation in Octn1 appeared to cause the time of day-dependent changes in the intestinal absorption of PGN. Similar dosing time dependencies of the antiallodynic effect of PGN and oscillation in Octn1 expression were also detected in type II diabetic db/db mice. These results suggested that the dosing time-dependent differences in the analgesic effect of PGN were attributable to circadian oscillations in the intestinal expression of Octn1 and also that optimizing its dosing schedule may assist in achieving rational pharmacotherapy for diabetes-induced peripheral neuropathic pain.