Current Progress Toward a Better Understanding of Drug Disposition Within the Lungs: Summary Proceedings of the First Workshop on Drug Transporters in the Lungs

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.

The influence of SARS-CoV-2 infection on expression of drug-metabolizing enzymes and transporters in a hACE2 murine model

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and the resulting Coronavirus disease 2019 emerged in late 2019 and is responsible for significant morbidity and mortality worldwide. A hallmark of severe COVID-19 is exaggerated systemic inflammation, regarded as a "cytokine storm," which contributes to the damage of various organs, primarily the lungs. The inflammation associated with some viral illnesses is known to alter the expression of drug-metabolizing enzymes and transporters. These alterations can lead to modifications in drug exposure and the processing of various endogenous compounds. Here, we provide evidence to support changes in the mitochondrial ribonucleic acid expression of a subset of drug transporters (84 transporters) in the liver, kidneys, and lungs and metabolizing enzymes (84 enzymes) in the liver in a humanized angiotensin-converting enzyme 2 receptor mouse model. Specifically, three drug transporters (Abca3, Slc7a8, Tap1) and the pro-inflammatory cytokine IL-6 were upregulated in the lungs of SARS-CoV-2 infected mice. We also found significant downregulation of drug transporters responsible for the movement of xenobiotics in the liver and kidney. Additionally, expression of cytochrome P-450 2f2 which is known to metabolize some pulmonary toxicants, was significantly decreased in the liver of infected mice. The significance of these findings requires further exploration. Our results suggest that further research should emphasize altered drug disposition when investigating therapeutic compounds, whether re-purposed or new chemical entities, in other animal models and ultimately in individuals infected with SARS-CoV-2. Moreover, the influence and impact of these changes on the processing of endogenous compounds also require further investigation.

SARS-CoV-2 infection dysregulates the expression of clinically relevant drug metabolizing enzymes in Vero E6 cells and membrane transporters in human lung tissues

SARS-CoV-2-mediated interactions with drug metabolizing enzymes and membrane transporters (DMETs) in different tissues, especially lung, the main affected organ may limit the clinical efficacy and safety profile of promising COVID-19 drugs. Herein, we investigated whether SARS-CoV-2 infection could dysregulate the expression of 25 clinically relevant DMETs in Vero E6 cells and postmortem lung tissues from COVID-19 patients. Also, we assessed the role of 2 inflammatory and 4 regulatory proteins in modulating the dysregulation of DMETs in human lung tissues. We showed for the first time that SARS-CoV-2 infection dysregulates CYP3A4 and UGT1A1 at the mRNA level, as well as P-gp and MRP1 at the protein level, in Vero E6 cells and postmortem human lung tissues, respectively. We observed that at the cellular level, DMETs could potentially be dysregulated by SARS-CoV-2-associated inflammatory response and lung injury. We uncovered the pulmonary cellular localization of CYP1A2, CYP2C8, CYP2C9, and CYP2D6, as well as ENT1 and ENT2 in human lung tissues, and observed that the presence of inflammatory cells is the major driving force for the discrepancy in the localization of DMETs between COVID-19 and control human lung tissues. Because alveolar epithelial cells and lymphocytes are both sites of SARS-CoV-2 infection and localization of DMETs, we recommend further investigation of the pulmonary pharmacokinetic profile of current COVID-19 drug dosing regimen to improve clinical outcomes.

Imaging drug delivery to the lungs: Methods and applications in oncology

Direct delivery to the lung via inhalation is arguably one of the most logical approaches to treat lung cancer using drugs. However, despite significant efforts and investment in this area, this strategy has not progressed in clinical trials. Imaging drug delivery is a powerful tool to understand and develop novel drug delivery strategies. In this review we focus on imaging studies of drug delivery by the inhalation route, to provide a broad overview of the field to date and attempt to better understand the complexities of this route of administration and the significant barriers that it faces, as well as its advantages. We start with a discussion of the specific challenges for drug delivery to the lung via inhalation. We focus on the barriers that have prevented progress of this approach in oncology, as well as the most recent developments in this area. This is followed by a comprehensive overview of the different imaging modalities that are relevant to lung drug delivery, including nuclear imaging, X-ray imaging, magnetic resonance imaging, optical imaging and mass spectrometry imaging. For each of these modalities, examples from the literature where these techniques have been explored are provided. Finally the different applications of these technologies in oncology are discussed, focusing separately on small molecules and nanomedicines. We hope that this comprehensive review will be informative to the field and will guide the future preclinical and clinical development of this promising drug delivery strategy to maximise its therapeutic potential.

Pharmacokinetic considerations to optimize clinical outcomes for COVID-19 drugs

The development of clinically effective drugs that could complement existing vaccines is urgently needed to reduce the morbidity and mortality associated with COVID-19. Drug-metabolizing enzymes, membrane-associated drug transporters, and inflammatory responses can partly determine the safety and efficacy of COVID-19 drugs by controlling their concentrations in both the systemic circulation and in peripheral tissues. It is still unknown how these factors affect how well COVID-19 drugs work in the clinic. We explore how drug metabolism and transport, as well as SARS-CoV-2-associated inflammatory response at disease target sites, may affect the clinical outcomes of COVID-19 drugs. In addition, we provide expert opinion on potential strategies for overcoming the clinical pharmacology and pathophysiological obstacles to improve COVID-19 drug effectiveness.

Predicting Regional Respiratory Tissue and Systemic Concentrations of Orally Inhaled Drugs through a Novel PBPK Model

Oral inhalation (OI) of drugs is the route of choice to treat respiratory diseases or for recreational drug use (e.g., cannabis). After OI, the drug is deposited in and systemically absorbed from various regions of the respiratory tract. Measuring regional respiratory tissue drug concentrations at the site of action is important for evaluating the efficacy and safety of orally inhaled drugs (OIDs). Because such a measurement is routinely not possible in humans, the only alternative is to predict these concentrations, for example by physiologically based pharmacokinetic (PBPK) modeling. Therefore, we developed an OI-PBPK model to integrate the interplay between regional respiratory drug deposition and systemic absorption to predict regional respiratory tissue and systemic drug concentrations. We validated our OI-PBPK model by comparing the simulated and observed plasma concentration-time profiles of two OIDs, morphine and nicotine. Furthermore, we performed sensitivity analyses to quantitatively demonstrate the impact of key parameters on the extent and pattern of regional respiratory drug deposition, absorption, and the resulting regional respiratory tissue and systemic plasma concentrations. Our OI-PBPK model can be applied to predict regional respiratory tissue and systemic drug concentrations to optimize OID formulations, delivery systems, and dosing regimens. Furthermore, our model could be used to establish the bioequivalence of generic OIDs for which systemic plasma concentrations are not measurable or are not a good surrogate of the respiratory tissue drug concentrations. SIGNIFICANCE STATEMENT: Our OI-PBPK model is the first comprehensive model to predict regional respiratory deposition, as well as systemic and regional tissue concentrations of OIDs, especially at the drug's site of action, which is difficult to measure in humans. This model will help optimize OID formulations, delivery systems, dosing regimens, and bioequivalence assessment of generic OID. Furthermore, this model can be linked with organs-on-chips, pharmacodynamic and quantitative systems pharmacology models to predict and evaluate the safety and efficacy of OID.

Developing inhaled drugs for respiratory diseases: A medicinal chemistry perspective

Despite the devastating impact of many lung diseases on human health, there is still a significant unmet medical need in respiratory diseases, for which inhaled delivery represents a crucial strategy. More guidance on how to design and carry out multidisciplinary inhaled projects is needed. When designing inhaled drugs, the medicinal chemist must carefully balance the physicochemical properties of the molecule to achieve optimal target engagement in the lung. Although the medicinal chemistry strategy is unique for each project, and will change depending on multiple factors, such as the disease, target, systemic risk, delivery device, and formulation, general guidelines aiding inhaled drug design can be applied and are summarised in this review.

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.

Pharmacokinetic/pharmacodynamic approaches to drug delivery design for inhalation drugs

Introduction: Inhaled drugs are important in the treatment of many lung pathologies, but to be therapeutically effective they must reach unbound concentrations at their effect site in the lung that are adequate to interact with their pharmacodynamic properties (PD) and exert the pharmacological action over an appropriate dosing interval. Therefore, the evaluation of pharmacokinetic (PK)/PD relationship is critical to predict their possible therapeutic effect.Areas covered: We review the approaches used to assess the PK/PD relationship of the major classes of inhaled drugs that are prescribed to treat pulmonary pathologies.Expert opinion: There are still great difficulties in producing data on lung concentrations of inhaled drugs and interpreting them as to their ability to induce the desired therapeutic action. The structural complexity of the lungs, the multiplicity of processes involved simultaneously and the physical interactions between the lungs and drug make any PK/PD approach to drug delivery design for inhalation medications extremely challenging. New approaches/methods are increasing our understanding about what happens to inhaled drugs, but they are still not ready for regulatory purposes. Therefore, we must still rely on plasma concentrations based on the axiom that they reflect both the extent and the pattern of deposition within the lungs.

Suppression of P-glycoprotein by cigarette smoke extract in human lung-derived A549/P-gp cells

Effect of long-term treatment with cigarette smoke extract (CSE) on the function and expression of P-glycoprotein (P-gp) in lung alveolar epithelial cells was examined using A549/P-gp cell line expressing P-gp. CSE treatment suppressed P-gp activity in a concentration- and treatment time-dependent manner. The suppression of P-gp activity by CSE was irreversible for at least 96 h after removal of CSE. In addition, CSE treatment suppressed the expression of P-gp mRNA and protein. In order to understand the mechanisms underlying P-gp suppression by CSE, the role of reactive oxygen species (ROS) was examined. CSE treatment increased intracellular ROS level, and suppressed catalase activity. α-Tocopherol suppressed ROS production by CSE, and ameliorated the suppression of P-gp activity by CSE, suggesting that ROS is involved in CSE-induced suppression of P-gp. The role of intracellular signaling pathways such as the nuclear factor κB and mitogen-activated protein kinase pathways was also examined. Among these pathways, the involvement of extracellular signal-regulated kinase (ERK) pathway was suggested. Taken together, long-term CSE treatment may suppress P-gp via modulation of ROS level and ERK pathway in alveolar epithelial cells.

Induction of multidrug resistance-associated protein 3 expression by diesel exhaust particle extract in human bronchial epithelial BEAS-2B cells

Diesel exhaust particles (DEPs) are common environmental air pollutants known to impair expression and activity of drug detoxifying proteins, including hepatic ATP-binding cassette (ABC) drug transporters. The present study was designed to determine whether organic DEP extract (DEPe) may also target ABC drug transporters in bronchial cells. DEPe (10 μg/mL) was demonstrated to induce mRNA and protein expression of the multidrug resistance-associated protein (MRP) 3 in cultured bronchial epithelial BEAS-2B cells, whereas mRNA levels of other MRPs, multidrug resistance gene 1 or breast cancer resistance protein were unchanged, reduced or not detected. DEPe also increased MRP3 mRNA expression in normal human bronchial epithelial cells. Inhibition of the aryl hydrocarbon receptor (AhR) pathway by AhR antagonist or AhR silencing, as well as the silencing of nuclear-factor-E2-related factor 2 (Nrf2) repressed DEPe-mediated MRP3 induction. This underlines the implication of the AhR and Nrf2 signaling cascades in DEPe-mediated MRP3 regulation. DEPe was additionally demonstrated to directly inhibit MRP activity in BEAS-2B cells, in a concentration-dependent manner. Taken together, these data indicate that DEPs may impair expression and activity of MRPs, notably MRP3, in human bronchial cells, which may have consequences in terms of lung barrier and toxicity for humans exposed to diesel pollution.

Advances in experimental and mechanistic computational models to understand pulmonary exposure to inhaled drugs

Prediction of local exposure following inhalation of a locally acting pulmonary drug is central to the successful development of novel inhaled medicines, as well as generic equivalents. This work provides a comprehensive review of the state of the art with respect to multiscale computer models designed to provide a mechanistic prediction of local and systemic drug exposure following inhalation. The availability and quality of underpinning in vivo and in vitro data informing the computer based models is also considered. Mechanistic modelling of local exposure has the potential to speed up and improve the chances of successful inhaled API and product development. Although there are examples in the literature where this type of modelling has been used to understand and explain local and systemic exposure, there are two main barriers to more widespread use. There is a lack of generally recognised commercially available computational models that incorporate mechanistic modelling of regional lung particle deposition and drug disposition processes to simulate free tissue drug concentration. There is also a need for physiologically relevant, good quality experimental data to inform such modelling. For example, there are no standardized experimental methods to characterize the dissolution of solid drug in the lungs or measure airway permeability. Hence, the successful application of mechanistic computer models to understand local exposure after inhalation and support product development and regulatory applications hinges on: (i) establishing reliable, bio-relevant means to acquire experimental data, and (ii) developing proven mechanistic computer models that combine: a mechanistic model of aerosol deposition and post-deposition processes in physiologically-based pharmacokinetic models that predict free local tissue concentrations.

A Comparison of Drug Transport in Pulmonary Absorption Models: Isolated Perfused rat Lungs, Respiratory Epithelial Cell Lines and Primary Cell Culture

PURPOSE

To evaluate the ability of human airway epithelial cell layers and a simple rat isolated perfused lung (IPL) model to predict pulmonary drug absorption in rats in vivo.

METHOD

The permeability of seven compounds selected to possess a range of lipophilicity was measured in two airway cell lines (Calu-3 and 16HBE14o-), in normal human bronchial epithelial (NHBE) cells and using a simple isolated perfused lungs (IPL) technique. Data from the cell layers and ex vivo lungs were compared to published absorption rates from rat lungs measured in vivo.

RESULTS

A strong relationship was observed between the logarithm of the in vivo absorption half-life and the absorption half-life in the IPL (r = 0.97; excluding formoterol). Good log-linear relationships were also found between the apparent first-order absorption rate in vivo and cell layer permeability with correlation coefficients of 0.92, 0.93, 0.91 in Calu-3, 16HBE14o- and NHBE cells, respectively.

CONCLUSION

The simple IPL technique provided a good prediction of drug absorption from the lungs, making it a useful method for empirical screening of drug absorption in the lungs. Permeability measurements were similar in all the respiratory epithelial cell models evaluated, with Calu-3 having the advantage for routine permeability screening purposes of being readily availability, robust and easy to culture.