Spatial expression and functionality of drug transporters in the intact lung: objectives for further research

Insights into Inhalation Drug Disposition: The Roles of Pulmonary Drug-Metabolizing Enzymes and Transporters

The past five decades have witnessed remarkable advancements in the field of inhaled medicines targeting the lungs for respiratory disease treatment. As a non-invasive drug delivery route, inhalation therapy offers numerous benefits to respiratory patients, including rapid and targeted exposure at specific sites, quick onset of action, bypassing first-pass metabolism, and beyond. Understanding the characteristics of pulmonary drug transporters and metabolizing enzymes is crucial for comprehending efficient drug exposure and clearance processes within the lungs. These processes are intricately linked to both local and systemic pharmacokinetics and pharmacodynamics of drugs. This review aims to provide a comprehensive overview of the literature on lung transporters and metabolizing enzymes while exploring their roles in exogenous and endogenous substance disposition. Additionally, we identify and discuss the principal challenges in this area of research, providing a foundation for future investigations aimed at optimizing inhaled drug administration. Moving forward, it is imperative that future research endeavors to focus on refining and validating in vitro and ex vivo models to more accurately mimic the human respiratory system. Such advancements will enhance our understanding of drug processing in different pathological states and facilitate the discovery of novel approaches for investigating lung-specific drug transporters and metabolizing enzymes. This deeper insight will be crucial in developing more effective and targeted therapies for respiratory diseases, ultimately leading to improved patient outcomes.

Nuclear medicine imaging methods as novel tools in the assessment of pulmonary drug disposition

INTRODUCTION

Drugs for the treatment of respiratory diseases are commonly administered by oral inhalation. Yet surprisingly little is known about the pulmonary pharmacokinetics of inhaled molecules. Nuclear medicine imaging techniques (i.e. planar gamma scintigraphy, single-photon emission computed tomography [SPECT] and positron emission tomography [PET]) enable the noninvasive dynamic measurement of the lung concentrations of radiolabeled drugs or drug formulations. This review discusses the potential of nuclear medicine imaging techniques in inhalation biopharmaceutical research.

AREAS COVERED

(i) Planar gamma scintigraphy studies with radiolabeled inhalation formulations to assess initial pulmonary drug deposition; (ii) imaging studies with radiolabeled drugs to assess their intrapulmonary pharmacokinetics; (iii) receptor occupancy studies to quantify the pharmacodynamic effect of inhaled drugs.

EXPERT OPINION

Imaging techniques hold potential to bridge the knowledge gap between animal models and humans with respect to the pulmonary disposition of inhaled drugs. However, beyond the mere assessment of the initial lung deposition of inhaled formulations with planar gamma scintigraphy, imaging techniques have rarely been employed in pulmonary drug development. This may be related to several technical challenges encountered with such studies. Considering the wealth of information that can be obtained with imaging studies their use in inhalation biopharmaceutics should be further investigated.

Impact of P-gp and BCRP on pulmonary drug disposition assessed by PET imaging in rats

P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are two efflux transporters which are expressed in the apical (i.e. airway lumen-facing) membranes of lung epithelial cells. To assess the influence of P-gp and BCRP on the pulmonary disposition of inhaled drugs, we performed positron emission tomography (PET) imaging in rats after intratracheal aerosolization of two model P-gp/BCRP substrate radiotracers (i.e. [¹¹C]erlotinib and [¹¹C]tariquidar). We studied rat groups in which both transporters were active (i.e. wild-type rats), either of the two transporters was inactive (Abcb1a/b^(-/-) and Abcg2^(-/-) rats) or both transporters were inactive (Abcg2^(-/-) rats in which pulmonary P-gp activity was inhibited by treatment with unlabeled tariquidar). PET-measured lung distribution data were compared with brain-to-plasma radioactivity concentration ratios measured in a gamma counter at the end of the PET scan. For [¹¹C]erlotinib, lung exposure (AUC_lungs) was moderately but not significantly increased in Abcb1a/b^(-/-) rats (1.6-fold) and Abcg2^(-/-) rats (1.5-fold), and markedly (3.6-fold, p < 0.0001) increased in tariquidar-treated Abcg2^(-/-) rats, compared to wild-type rats. Similarly, the brain uptake of [¹¹C]erlotinib was substantially (4.5-fold, p < 0.0001) increased when both P-gp and BCRP activities were impaired. For [¹¹C]tariquidar, differences in AUC_lungs between groups pointed into a similar direction as for [¹¹C]erlotinib, but were less pronounced and lacked statistical significance. Our study demonstrates functional P-gp and BCRP activity in vivo in the lungs and further suggests functional redundancy between P-gp and BCRP in limiting the pulmonary uptake of a model P-gp/BCRP substrate, analogous to the blood-brain barrier. Our results suggest that pulmonary efflux transporters are important for the efficacy and safety of inhaled drugs and that their modulation may be exploited in order to improve the pharmacokinetic and pharmacodynamic performance of pulmonary delivered drugs.

Pulmonary inflammation caused by cigarette smoke combined with lipopolysaccharide up-regulated OATP2B1 in rat lung tissue and pulmonary epithelial cells

Organic anion transport polypeptide 2B1 (OATP2B1), as an uptake transporter, is involved in the transport of many related substrate drugs and endogenous substances in the lungs. A large amount of data shows that cigarette smoke plays an important role in the occurrence and development of lung diseases such as chronic obstructive pulmonary disease (COPD), asthma and bronchitis. However, the effect of cigarette smoke combined with lipopolysaccharide-induced pulmonary inflammation on the expression of OATP2B1 is not clear. In this study, we used cigarette smoke combined with lipopolysaccharide to establish a lung inflammation model in vivo and in vitro to explore the effect of inflammation on the expression of OATP2B1. Our study found that cigarette smoke combined with lipopolysaccharide-induced pulmonary inflammation upregulated the mRNA and protein expression of OATP2B1 and related inflammatory factors, and the expression level of related proteins was higher with the aggravation of inflammation. The experimental results of animals in vivo were consistent with those of cells in vitro. In summary, these findings provide a model and basis for a follow-up study of the mechanism of OATP2B1 in pulmonary inflammation.

PET imaging to assess the impact of P-glycoprotein on pulmonary drug delivery in rats

Several drugs approved for inhalation for the treatment of pulmonary diseases are substrates of the adenosine triphosphate-binding cassette (ABC) transporter P-glycoprotein (P-gp). P-gp is expressed in the apical membrane of pulmonary epithelial cells and could play a role in modulating the pulmonary absorption and distribution of inhaled drugs, thereby potentially contributing to variability in therapeutic response and/or systemic side effects. We developed a new in vivo experimental approach to assess the functional impact of P-gp on the pulmonary delivery of inhaled drugs in rats. By using positron emission tomography (PET) imaging, we measured the intrapulmonary pharmacokinetics of the model P-gp substrates (R)-[¹¹C]verapamil ([¹¹C]VPM) and [¹¹C]-N-desmethyl-loperamide ([¹¹C]dLOP) administered by intratracheal aerosolization in three rat groups: wild-type, Abcb1a/b^(-/-) and wild-type treated with the P-gp inhibitor tariquidar. Lung exposure (AUC_{lung_right}) to [¹¹C]VPM was 64% and 50% lower (p < 0.05) in tariquidar-treated and in Abcb1a/b^(-/-) rats, respectively, compared to untreated wild-type rats. For [¹¹C]dLOP, AUC_{lung_right} was 59% and 34% lower (p < 0.05) in tariquidar-treated and in Abcb1a/b^(-/-) rats, respectively. Our results show that P-gp can affect the pulmonary disposition of inhaled P-gp substrates, whereby a decrease in P-gp activity may lead to lower lung exposure and potentially to a decrease in therapeutic efficacy. Our study highlights the potential of PET imaging with intratracheally aerosolized radiotracers to assess the impact of membrane transporters on pulmonary drug delivery, in rodents and potentially also in humans.

NovoSpaRc: flexible spatial reconstruction of single-cell gene expression with optimal transport

Single-cell RNA-sequencing (scRNA-seq) technologies have revolutionized modern biomedical sciences. A fundamental challenge is to incorporate spatial information to study tissue organization and spatial gene expression patterns. Here, we describe a detailed protocol for using novoSpaRc, a computational framework that probabilistically assigns cells to tissue locations. At the core of this framework lies a structural correspondence hypothesis, that cells in physical proximity share similar gene expression profiles. Given scRNA-seq data, novoSpaRc spatially reconstructs tissues based on this hypothesis, and optionally, by including a reference atlas of marker genes to improve reconstruction. We describe the novoSpaRc algorithm, and its implementation in an open-source Python package ( https://pypi.org/project/novosparc ). NovoSpaRc maps a scRNA-seq dataset of 10,000 cells onto 1,000 locations in <5 min. We describe results obtained using novoSpaRc to reconstruct the mouse organ of Corti de novo based on the structural correspondence assumption and human osteosarcoma cultured cells based on marker gene information, and provide a step-by-step guide to Drosophila embryo reconstruction in the Procedure to demonstrate how these two strategies can be combined.

Drivers of absolute systemic bioavailability after oral pulmonary inhalation in humans

There are few studies in humans dealing with the relationship between physico-chemical properties of drugs and their systemic bioavailability after administration via oral inhalation route (Fpulm). Getting further insight in the determinants of Fpulm after oral pulmonary inhalation could be of value for drugs considered for a systemic delivery as a result of poor oral bioavailability, as well as for drugs considered for a local delivery to anticipate their undesirable systemic effects. To better delineate the parameters influencing the systemic delivery after oral pulmonary inhalation in humans, we studied the influence of physico-chemical and permeability properties obtained in silico on the rate and extent of Fpulm in a series of 77 compounds with or without marketing approval for pulmonary delivery, and intended either for local or for systemic delivery. Principal component analysis (PCA) showed mainly that Fpulm was positively correlated with Papp and negatively correlated with %TPSA, without a significant influence of solubility and ionization fraction, and no apparent link with lipophilicity and drug size parameters. As a result of the small sample set, the performance of the different models as predictive of Fpulm were quite average with random forest algorithm displaying the best performance. As a whole, the different models captured between 50 and 60% of the variability with a prediction error of less than 20%. Tmax data suggested a significant positive influence of lipophilicity on absorption rate while charge apparently had no influence. A significant linear relationship between Cmax and dose (R² = "0.79) highlighted that Cmax was primarily dependent on dose and absorption rate and could be used to estimate Cmax in humans for new inhaled drugs.

Present Situation and Future Progress of Inhaled Lung Cancer Therapy: Necessity of Inhaled Formulations with Drug Delivery Functions

Inhaled lung cancer therapy is promising because of direct and noninvasive drug delivery to the lungs with low potential for severe systemic toxicity. Thus chemotherapeutic drugs have been administered clinically by nebulization of solution or suspension formulations, which demonstrated their limited pulmonary absorption and relatively mild systemic toxicity. In all these clinical trials, however, there was no obviously superior anticancer efficacy in lung cancer patients even at the maximum doses of drugs limited by pulmonary toxicity. Therefore methods that deliver both higher anticancer efficacy and lower pulmonary toxicity are strongly desired. In addition to the worldwide availability of pressured metered dose inhalers (pMDIs) and dry powder inhalers (DPIs) to treat local respiratory diseases, recent innovations in medicines and technologies are encouraging next steps toward effective inhaled lung cancer therapy with new therapeutic or drug delivery concepts. These include the discovery of target cells/molecules and drug candidates for novel cancer therapy, the development of high-performance inhalation devices for effective pulmonary drug delivery, and the establishment of manufacturing technologies for functional nanoparticles/microparticles. This review highlights the present situation and future progress of inhaled drugs for lung cancer therapy, including an overview of available inhalation devices, pharmacokinetics, and outcomes in clinical trials so far and some novel formulation strategies based on drug delivery systems to achieve enhanced anticancer efficacy and attenuated pulmonary toxicity.

The conjugation of rhodamine B enables carrier-free mitochondrial delivery of functional proteins

The development of protein-based therapeutics faces many challenges, for example, carrier-dependence, safety concerns, endocytosis-dependence, and uncertain in vivo therapeutic outcomes. Small molecules are rarely used for intracellular organelle-targeting and disease tissue-specific carrier-independent delivery of therapeutic proteins. Here, we report that rhodamine B, after modification with proteins, is able to guide carrier-free delivery into mitochondria and tissue-dependent distributions of functional proteins through organic cation transporters (OCTs). The enrichment of the modified catalase in the cancer tissue efficiently suppresses xenograft human lung tumor in mice. This carrier-free delivery platform of proteins may emerge as a simple yet powerful approach for cancer treatment.

Suitability and functional characterization of two Calu-3 cell models for prediction of drug permeability across the airway epithelial barrier

The Calu-3 cell line has been largely investigated as a physiological and pharmacological model of the airway epithelial barrier. Its suitability for prediction of drug permeability across the airway epithelia, however, has not been yet evaluated by using large enough set of model drugs. We evaluated two Calu-3 cell models (air-liquid and liquid-liquid) for drug permeability prediction based on the recent regulatory guidelines on showing suitability of in vitro permeability methods for drug permeability classification. Bidirectional permeability assays using 22 model drugs and several zero permeability markers, as well as using ABC transporter substrates were conducted. Functional activity of P-gp, but not of BCRP was revealed. The potential of the Calu-3 cells to be used as a model of the nasal epithelial barrier, despite their different anatomical origin, has been demonstrated by the obtained excellent correlation with the fully differentiated 3D human nasal epithelial model (MucilAir™) for 11 model drugs, as well as by the good correlation obtained with the human nasal epithelial cell line RPMI 2650. In addition, the permeability values determined in the two Calu-3 models correlated well with the intestinal permeability model Caco-2.

Organic Cation Transporters (OCTs) in EpiAirway™, A Cellular Model of Normal Human Bronchial Epithelium

Organic cation transporters (OCTs) and novel organic cation transporters (OCTNs) are responsible for drug delivery in the intestine and kidney; in the lung, OCTs mediate inhaled drugs’ transport, although their physiological role in airways remains poorly understood. The studies addressing OCTs/OCTNs in human airways were mostly performed in immortal or transformed cell lines; here, we studied OCTs in EpiAirway™, a recently developed in vitro model of normal bronchial epithelium. Calu-3 monolayers were used for comparison. The activity of OCTs was evaluated by measuring the uptake of 1-methyl-4-phenylpyridinium (MPP⁺) at the apical and basolateral side of monolayers and protein expression through Western Blot analysis. OCTs and OCTNs expression, along with that of Amino acid Transporter B^0,+ (ATB^0,+)transporter, was determined by measuring the number of mRNA molecules through quantitative Polymerase Chain Reaction (qPCR). The interaction of the transporters with bronchodilators was also assessed. Results highlight significant differences between Calu-3 cells and EpiAirway™, since, in the latter, OCTs are active only on the basolateral membrane where they interact with the bronchodilator ipratropium. No activity of OCTs is detectable at the apical side; there, the most abundant carrier is, instead, SLC6A14/ATB^0,+, that can thus be potentially listed among organic cation transporters responsible for drug delivery in the lung.

Bleomycin Induces Drug Efflux in Lungs. A Pitfall for Pharmacological Studies of Pulmonary Fibrosis

ATP-binding cassette (ABC) transporters are evolutionarily conserved membrane proteins that pump a variety of endogenous substrates across cell membranes. Certain subfamilies are known to interact with pharmaceutical compounds, potentially influencing drug delivery and treatment efficacy. However, the role of drug resistance-associated ABC transporters has not been examined in idiopathic pulmonary fibrosis (IPF) or its animal model: the bleomycin (BLM)-induced murine model. Here, we investigate the expression of two ABC transporters, P-gp (permeability glycoprotein) and BCRP (breast cancer resistance protein), in human IPF lung tissue and two different BLM-induced mouse models of pulmonary fibrosis. We obtained human IPF specimens from patients during lung transplantation and administered BLM to male C57BL/6J mice either by oropharyngeal aspiration (1 U/kg) or subcutaneous osmotic infusion (100 U/kg over 7 d). We report that P-gp and BCRP expression in lungs of patients with IPF was comparable to controls. However, murine lungs expressed increased levels of P-gp and BCRP after oropharyngeal and subcutaneous BLM administration. We localized this upregulation to multiple pulmonary cell types, including alveolar fibroblasts, endothelial cells, and type 2 epithelial cells. Functionally, this effect reduced murine lung exposure to nintedanib, a U.S. Food and Drug Administration-approved IPF therapy known to be a P-gp substrate. The study reveals a discrepancy between IPF pathophysiology and the common animal model of lung fibrosis. BLM-induced drug efflux in the murine lungs may present an uncontrolled confounding variable in the preclinical study of IPF drug candidates, and these findings will facilitate disease model validation and enhance new drug discoveries that will ultimately improve patient outcomes.

LPS-induced inflammation delays the transportation of ASP+ due to down-regulation of OCTN1/2 in alveolar epithelial cells

Organic cation transporters (OCTNs) can significantly affect drug disposition in alveolar epithelial cells (A549), but this process is not well understood. We investigated the expression and function of OCTN1/2 in A549 cells under different inflammatory status to examine pulmonary drug distribution. This experiment used lipopolysaccharide (LPS)-treated A549 cells to mimic inflammation in alveolar epithelial cells, and the expression of OCTN1/2, interleukin-6 (IL6), IL18, IL1β and tumour necrosis factor-alpha (TNF-α) was investigated by western blot and quantitative real-time PCR (qRT-PCR). The fluorescent compound 4-(4-(dimethylamino)styryl)-N-methylpyridinium iodide (ASP⁺) was chosen as a probe to study the activity of OCTN1/2. OCTN1/2 down-regulation induced by LPS was more pronounced than that in normal control (NC) groups. Experiments further detected the release of inflammatory factors that revealed a negative correlation between OCTN1/2 expression and inflammation secretion in human alveolar epithelial cells exposed to different concentrations of LPS. The Michaelis constant (K_m) and apparent permeability coefficient (P_app) of ASP⁺ were also decreased significantly. Our results thus show that LPS-induced inflammation could inhibit the expression and activity of OCTN1/2 in vitro and reduce the distribution of inhaled medicine in pulmonary diseases.

Population pharmacokinetic modeling to establish the role of P-glycoprotein on ciprofloxacin distribution to lung and prostate following intravenous and intratracheal administration to Wistar rats

Ciprofloxacin (CIP) is indicated for clinical treatment of urinary and respiratory tract infections. Poor infection site penetration and consequent insufficient exposure to the antimicrobial agent may be the reason for some therapeutic failures. Ciprofloxacin is reported as a substrate for efflux transporters, such as P-glycoprotein, which could be related to the presence of sub-therapeutic drug concentration at the infection site. In the present work we evaluated CIP pharmacokinetics (PK) in plasma and lung and prostate tissues of Wistar rats after intravenous (i.v.) and intratracheal (i.t.) dosing (7 mg/Kg) in the presence and absence of P-gp inhibitor tariquidar (TAR, 15 mg/Kg). Microdialysis was applied to determine free tissue concentration-time profiles and the obtained data were analyzed by non-compartmental and population PK (popPK) analysis. A sequential strategy was used to develop the popPK model: characterization of CIP PK in tissues (Tissue model) was performed subsequently to CIP PK modeling in plasma (Plasma model). Two and three compartmental models were used to simultaneously characterize plasma concentrations after i.t. and i.v. dosing; the distribution model was developed by separating the central compartment into venous and arterial compartment and by adding lung and prostate; TAR was identified as a significant covariate for clearance and volume of distribution of central compartment as well as for inter-compartmental clearance. Our results indicate an impact of P-gp on plasma PK, likely by acting on renal active secretion of CIP. Regarding CIP exposure in lung and prostate tissues, our results suggest a complex interplay between drug transporters; P-gp inhibition by TAR was likely counterbalanced by the activity of other efflux/influx transporters, which could not be fully characterized by our model.

Expression of MATE1, P-gp, OCTN1 and OCTN2, in epithelial and immune cells in the lung of COPD and healthy individuals

Background

Several inhaled drugs are dependent on organic cation transporters to cross cell membranes. To further evaluate their potential to impact on inhaled drug disposition, the localization of MATE1, P-gp, OCTN1 and OCTN2 were investigated in human lung.

Methods

Transporter proteins were analysed by immunohistochemistry in lung tissue from healthy subjects and COPD patients. Transporter mRNA was analysed by qPCR in lung tissue and in bronchoalveolar lavage (BAL) cells from smokers and non-smokers.

Results

We demonstrate for the first time MATE1 protein expression in the lung with localization to the apical side of bronchial and bronchiolar epithelial cells. Interestingly, MATE1 was strongly expressed in alveolar macrophages as demonstrated both in lung tissue and in BAL cells, and in inflammatory cells including CD3 positive T cells. P-gp, OCTN1 and OCTN2 were also expressed in the alveolar epithelial cells and in inflammatory cells including alveolar macrophages. In BAL cells from smokers, MATE1 and P-gp mRNA expression was significantly lower compared to cells from non-smokers whereas no difference was observed between COPD patients and healthy subjects. THP-1 cells were evaluated as a model for alveolar macrophages but did not reflect the transporter expression observed in BAL cells.

Conclusions

We conclude that MATE1, P-gp, OCTN1 and OCTN2 are expressed in pulmonary lung epithelium, in alveolar macrophages and in other inflammatory cells. This is important to consider in the development of drugs treating pulmonary disease as the transporters may impact drug disposition in the lung and consequently affect pharmacological efficacy and toxicity.

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0760-9) contains supplementary material, which is available to authorized users.

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.

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.

Development of a Novel Quantitative Structure-Activity Relationship Model to Accurately Predict Pulmonary Absorption and Replace Routine Use of the Isolated Perfused Respiring Rat Lung Model

Purpose

We developed and tested a novel Quantitative Structure-Activity Relationship (QSAR) model to better understand the physicochemical drivers of pulmonary absorption, and to facilitate compound design through improved prediction of absorption. The model was tested using a large array of both existing and newly designed compounds.

Methods

Pulmonary absorption data was generated using the isolated perfused respiring rat lung (IPRLu) model for 82 drug discovery compounds and 17 marketed drugs. This dataset was used to build a novel QSAR model based on calculated physicochemical properties. A further 9 compounds were used to test the model’s predictive capability.

Results

The QSAR model performed well on the 9 compounds in the “Test set” with a predicted versus observed correlation of R² = 0.85, and >65% of compounds correctly categorised. Calculated descriptors associated with permeability and hydrophobicity positively correlated with pulmonary absorption, whereas those associated with charge, ionisation and size negatively correlated.

Conclusions

The novel QSAR model described here can replace routine generation of IPRLu model data for ranking and classifying compounds prior to synthesis. It will also provide scientists working in the field of inhaled drug discovery with a deeper understanding of the physicochemical drivers of pulmonary absorption based on a relevant respiratory compound dataset.

Maternal bile acid transporter deficiency promotes neonatal demise

Intrahepatic cholestasis of pregnancy (ICP) is associated with adverse neonatal survival and is estimated to impact between 0.4 and 5% of pregnancies worldwide. Here we show that maternal cholestasis (due to Abcb11 deficiency) produces neonatal death among all offspring within 24 h of birth due to atelectasis-producing pulmonary hypoxia, which recapitulates the neonatal respiratory distress of human ICP. Neonates of Abcb11-deficient mothers have elevated pulmonary bile acids and altered pulmonary surfactant structure. Maternal absence of Nr1i2 superimposed on Abcb11 deficiency strongly reduces maternal serum bile acid concentrations and increases neonatal survival. We identify pulmonary bile acids as a key factor in the disruption of the structure of pulmonary surfactant in neonates of ICP. These findings have important implications for neonatal respiratory failure, especially when maternal bile acids are elevated during pregnancy, and highlight potential pathways and targets amenable to therapeutic intervention to ameliorate this condition.

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.

"Target-Site" Drug Metabolism and Transport

The recent symposium on "Target-Site" Drug Metabolism and Transport that was sponsored by the American Society for Pharmacology and Experimental Therapeutics at the 2014 Experimental Biology meeting in San Diego is summarized in this report. Emerging evidence has demonstrated that drug-metabolizing enzyme and transporter activity at the site of therapeutic action can affect the efficacy, safety, and metabolic properties of a given drug, with potential outcomes including altered dosing regimens, stricter exclusion criteria, or even the failure of a new chemical entity in clinical trials. Drug metabolism within the brain, for example, can contribute to metabolic activation of therapeutic drugs such as codeine as well as the elimination of potential neurotoxins in the brain. Similarly, the activity of oxidative and conjugative drug-metabolizing enzymes in the lung can have an effect on the efficacy of compounds such as resveratrol. In addition to metabolism, the active transport of compounds into or away from the site of action can also influence the outcome of a given therapeutic regimen or disease progression. For example, organic anion transporter 3 is involved in the initiation of pancreatic β-cell dysfunction and may have a role in how uremic toxins enter pancreatic β-cells and ultimately contribute to the pathogenesis of gestational diabetes. Finally, it is likely that a combination of target-specific metabolism and cellular internalization may have a significant role in determining the pharmacokinetics and efficacy of antibody-drug conjugates, a finding which has resulted in the development of a host of new analytical methods that are now used for characterizing the metabolism and disposition of antibody-drug conjugates. Taken together, the research summarized herein can provide for an increased understanding of potential barriers to drug efficacy and allow for a more rational approach for developing safe and effective therapeutics.

Functional Expression of PEPT2 in the Human Distal Lung Epithelial Cell Line NCl-H441

PURPOSE

The peptide transporter PEPT2 is expressed in alveolar type II epithelial cells. So far, however, no appropriate alveolar epithelial cell line for studying PEPT2 function has been known. In this study, we examined the functional expression of PEPT2 in the human distal lung epithelial cell line NCl-H441 (H441).

METHODS

Expression of PEPT2 mRNA and protein was examined in H441 cells. Transport function of PEPT2 was studied using glycylsarcosine (Gly-Sar) as a substrate.

RESULTS

Lamellar bodies were well developed in H441 cells and mRNA expression of type II cell markers and PEPT2 increased during time in culture. PEPT2 protein expression was confirmed in H441 cells, but not in A549 cells, by immunostaining and Western blotting. The uptake of Gly-Sar in H441 cells was inhibited by cefadroxil, and the cefadroxil-sensitive uptake was pH-dependent and peaked at pH 6.5. Gly-Sar uptake in H441 cells showed saturation kinetics with a Km value of 112.5 μM. In addition, apical-to-basal, but not basal-to-apical, transport of cephalexin across H441 cell monolayers was sensitive to cefadroxil.

CONCLUSIONS

PEPT2 is functionally expressed in H441 cells, making the cell line a good in vitro model to study PEPT2 function and its regulation in human distal lung.

In Vitro Testing for Orally Inhaled Products: Developments in Science-Based Regulatory Approaches

This article is part of a series of reports from the "Orlando Inhalation Conference-Approaches in International Regulation" which was held in March 2014, and coorganized by the University of Florida and the International Pharmaceutical Aerosol Consortium on Regulation and Science (IPAC-RS). The goal of the conference was to foster the exchange of ideas and knowledge across the global scientific and regulatory community in order to identify and help move towards strategies for internationally harmonized, science-based regulatory approaches for the development and marketing approval of inhalation medicines, including innovator and second entry products. This article provides an integrated perspective of case studies and discussion related to in vitro testing of orally inhaled products, including in vitro-in vivo correlations and requirements for in vitro data and statistical analysis that support quality or bioequivalence for regulatory applications.

Functional characterization of the organic cation transporters (OCTs) in human airway pulmonary epithelial cells

Organic cation transporters (OCT1-3) mediate the transport of organic cations including inhaled drugs across the cell membrane, although their role in lung epithelium hasn't been well understood yet. We address here the expression and functional activity of OCT1-3 in human airway epithelial cells A549, Calu-3 and NCl-H441. Kinetic and inhibition analyses, employing [(3)H]1-methyl-4-phenylpyridinium (MPP+) as substrate, and the compounds quinidine, prostaglandine E2 (PGE2) and corticosterone as preferential inhibitors of OCT1, OCT2, and OCT3, respectively, have been performed. A549 cells present a robust MPP+ uptake mediated by one high-affinity component (Km~50μM) which is identifiable with OCT3. Corticosterone, indeed, completely inhibits MPP+ transport, while quinidine and PGE2 are inactive and SLC22A3/OCT3 silencing with siRNA markedly lowers MPP+ uptake. Conversely, Calu-3 exhibits both a high (Km<20μM) and a low affinity (Km>0.6mM) transport components, referable to OCT3 and OCT1, respectively, as demonstrated by the inhibition analysis performed at proper substrate concentrations and confirmed by the use of specific siRNA. These transporters are active also when cells are grown under air-liquid interface (ALI) conditions. Only a very modest saturable MPP+ uptake is measurable in NCl-H441 cells and the inhibitory effect of quinidine points to OCT1 as the subtype functionally involved in this model. Finally, the characterization of MPP+ transport in human bronchial BEAS-2B cells suggests that OCT1 and OCT3 are operative. These findings could help to identify in vitro models to be employed for studies concerning the specific involvement of each transporter in drug transportation.

Beta-2 Adrenergic Agonists Are Substrates and Inhibitors of Human Organic Cation Transporter 1

Beta-2-adrenergic agonists are first line therapeutics in the treatment of asthma and chronic obstructive pulmonary disease (COPD). Upon inhalation, bronchodilation is achieved after binding to β2-receptors, which are primarily localized on airway smooth muscle cells. Given that β2-adrenergic agonists chemically are bases, they carry net positive charge at physiologic pH value in the lungs (i.e., pH 7.4). Here, we studied whether β2-agonists interact with organic cation transporters (OCT) and whether this interaction exerted an influence on their passage across the respiratory epithelium to their target receptors. [14C]-TEA uptake into proximal (i.e., Calu-3) and distal (i.e., A549 and NCI-H441) lung epithelial cells was significantly reduced in the presence of salbutamol sulfate, formoterol fumarate, and salmeterol xinafoate in vitro. Expression of all five members of the OCT/N family has been confirmed in human pulmonary epithelial cells in situ and in vitro, which makes the identification of the transporter(s) responsible for the β2-agonist interaction challenging. Thus, additional experiments were carried out in HEK-293 cells transfected with hOCT1-3. The most pronounced inhibition of organic cation uptake by β2-agonists was observed in hOCT1 overexpressing HEK-293 cells. hOCT3 transfected HEK-293 cells were affected to a lesser extent, and in hOCT2 transfectants only marginal inhibition of organic cation uptake by β2-agonists was observed. Bidirectional transport studies across confluent NCI-H441 cell monolayers revealed a net absorptive transport of [3H]-salbutamol, which was sensitive to inhibition by the OCT1 modulator, verapamil. Accordingly, salbutamol uptake into hOCT1 overexpressing HEK-293 cells was time- and concentration-dependent and could be completely blocked by decynium-22. Taken together, our data suggest that β2-agonists are specific substrates and inhibitors of OCT1 in human respiratory epithelial cells and that this transporter might play a role in the pulmonary disposition of drugs of this class.

Carrier interactions with the biological barriers of the lung: advanced in vitro models and challenges for pulmonary drug delivery

In recent years significant progress has been made to improve particle deposition in the lung. However, the development of strategies to overcome the air-blood lung barrier is still needed. The combination of complex in vitro models and sophisticated particulate carriers is promising as a strategy by which that goal could be achieved. In this review we discuss currently available in vitro lung models, including some recent tissue-engineering approaches, as well as the challenges associated to implement such complex in vitro systems. Furthermore, we discuss available carrier technologies, often based on nanotechnology, to target specific regions of the lungs and to overcome the respective biological barriers, ideally resulting in safe and effective delivery to the desired pulmonary destination.

Biopharmaceutical in vitro characterization of CPZEN-45, a drug candidate for inhalation therapy of tuberculosis

BACKGROUND

The caprazamycin derivative, CPZEN-45 has previously demonstrated antitubercular activity against Mycobacterium tuberculosis H37Rv. Here, the authors report a basic biopharmaceutical characterization of the compound focusing on in vitro permeability and cytotoxicity, with respect to the suitability of CPZEN-45 hydrochloride for inhalation treatment of tuberculosis.

RESULTS

MTT assays confirmed that CPZEN-45 HCl had no acute cytotoxic effects up to 3 mg/ml. In transport studies, apparent permeability coefficients of CPZEN-45 HCl across Calu-3 monolayers in absorptive and secretive directions were 0.43 ± 0.20 × 10(-6) cm/s and 0.38 ± 0.12 × 10(-6) cm/s, respectively. Across ATI-like monolayers, apparent permeability values were 12.10 ± 4.31 × 10(-6) cm/s and 8.50 ± 1.83 × 10(-6) cm/s. CPZEN-45 HCl formed colloidal complexes at concentrations above 0.38 mg/ml; however, these complexes were not micelles, as assessed by Orange OT encapsulation assay.

CONCLUSION

CPZEN-45 is an interesting new drug candidate with potential to be used in aerosol therapy of tuberculosis.

Mechanisms of absorption and elimination of drugs administered by inhalation

Pulmonary drug delivery is an effective route for local or systemic drug administration. However, compared with other routes of administration, there is a scarcity of information on how drugs are absorbed from the lung. The different cell composition lining the airways and alveoli makes this task extremely complicated. Lung cell lines and primary culture cells are useful in studying the absorption mechanisms. However, it is imperative that these cell cultures express essential features required to study these mechanisms such as intact tight junctions and transporters. In vivo, the drug has to face defensive physical and immunological barriers such as mucociliary clearance and alveolar macrophages. Knowledge of the physicochemical properties of the drug and aerosol formulation is required. All of these factors interact together leading to either successful drug deposition followed by absorption or drug elimination. These aspects concerning drug transport in the lung are addressed in this review.

Selectivity in the impact of P-glycoprotein upon pulmonary absorption of airway-dosed substrates: a study in ex vivo lung models using chemical inhibition and genetic knockout

P-glycoprotein (P-gp) mediated efflux is recognised to alter the absorption and disposition of a diverse range of substrates. Despite evidence showing the presence of P-gp within the lung, relatively little is known about the transporter's effect upon the absorption and distribution of drugs delivered via the pulmonary route. Here, we present data from an intact isolated rat lung model, alongside two isolated mouse lung models using either chemical or genetic inhibition of P-gp. Data from all three models show inhibition of P-gp increases the extent of absorption of a subset of P-gp substrates (e.g. rhodamine 123 and loperamide) whose physico-chemical properties are distinct from those whose pulmonary absorption remained unaffected (e.g. digoxin and saquinavir). This is the first study showing direct evidence of P-gp mediated efflux within an intact lung, a finding that should warrant consideration as part of respiratory drug discovery and development as well as in the understanding of pulmonary pharmacokinetic (PK)-pharmacodynamic (PD) relationships.

Inhaled biopharmaceutical drug development: nonclinical considerations and case studies

Biopharmaceuticals are complex molecules often manufactured from living systems and their specificity and novelty holds great promise for the treatment of chronic diseases for which there are currently no cures. The inhalation route of biopharmaceutical drug delivery is attractive because the large surface area of the lung, and close proximity of the alveolar and vascular systems, maximizes the potential for drug delivery to the lung and/or systemic circulation. In addition, costs of delivery to the patient are potentially much reduced, in comparison with parental administration, since inhalation is non-invasive and likely to promote patient compliance. However, in comparison with small molecule drug development, developing an inhaled biopharmaceutical that is effective and safe for human use is associated with many challenges. This review considers some general principles of drug delivery to lung and issues associated with the translation of proof of concept studies to toxicology safety studies (e.g. aerosol generation, species selection, exaggerated pharmacology, and immunogenicity). This review also presents a summary of nonclinical and clinical data from inhaled biopharmaceuticals which are either marketed for human use or in Phase II clinical trials (e.g. DNase, insulin, human growth hormone, vaccines, therapeutic plasmid DNA complexes).

Organic cation transporters in the blood-air barrier: expression and implications for pulmonary drug delivery

Studies concerning the impact that hepatic, renal and intestinal transporters have on drug disposition have been frequently reported in the literature. Surprisingly, however, little is known regarding the distribution and function of drug-transporter proteins of the lung epithelium. Many drugs (delivered to the lung) have a net positive charge and, thus, are potential substrates of organic cation transporters; currently marketed compounds (e.g., bronchodilators), as well as novel drug candidates in development, are such substrates. It is the aim of this review to summarize the current state of organic cation-transporter expression analysis in the lung and in in vitro models of bronchial and alveolar barriers. Moreover, activity of selected transporters in lung epithelium in situ and in vitro will be highlighted, and their potential role in pulmonary drug disposition will be addressed. One example included here is the transporter-dependent absorption of beta2-agonists in respiratory epithelial cells.

Challenges in inhaled product development and opportunities for open innovation

Dosimetry, safety and the efficacy of drugs in the lungs are critical factors in the development of inhaled medicines. This article considers the challenges in each of these areas with reference to current industry practices for developing inhaled products, and suggests collaborative scientific approaches to address these challenges. The portfolio of molecules requiring delivery by inhalation has expanded rapidly to include novel drugs for lung disease, combination therapies, biopharmaceuticals and candidates for systemic delivery via the lung. For these drugs to be developed as inhaled medicines, a better understanding of their fate in the lungs and how this might be modified is required. Harmonized approaches based on 'best practice' are advocated for dosimetry and safety studies; this would provide coherent data to help product developers and regulatory agencies differentiate new inhaled drug products. To date, there are limited reports describing full temporal relationships between pharmacokinetic (PK) and pharmacodynamic (PD) measurements. A better understanding of pulmonary PK and PK/PD relationships would help mitigate the risk of not engaging successfully or persistently with the drug target as well as identifying the potential for drug accumulation in the lung or excessive systemic exposure. Recommendations are made for (i) better industry-academia-regulatory co-operation, (ii) sharing of pre-competitive data, and (iii) open innovation through collaborative research in key topics such as lung deposition, drug solubility and dissolution in lung fluid, adaptive responses in safety studies, biomarker development and validation, the role of transporters in pulmonary drug disposition, target localisation within the lung and the determinants of local efficacy following inhaled drug administration.