Lack of difference in pulmonary absorption of digoxin, a P-glycoprotein substrate, in mdr1a-deficient and mdr1a-competent mice

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

This commentary provides a background appraising evidence in the intact lung on the spatial expression of drug transporters and, where available, evidence in the intact lung of the impact, or otherwise, that such transporters can have upon pulmonary drug absorption and disposition. Ultimately drug discovery and development scientists will wish to identify in a 'pulmonary' context the effect of disease upon transporter function, the potential for drug transporters to contribute to drug-drug interactions and to inter-individual variation in drug handling and response. The rate and extent of lung epithelial permeation of drugs involve an interplay between the dose and the deposition site of drug within the lung and physiological variables operational at the epithelial-luminal interface. Amongst the latter variables is the potential impact of active transporter processes which may well display regio-selective characteristics along the epithelial tract. In pulmonary tissues the spatial pattern of drug transporter expression is generally poorly defined and the functional significance of transporters within the intact lung is explored in only a limited manner. Active transporters in the lung epithelium may affect airway residence times of drug, modulate access of drug to intracellular targets and to submucosal lung tissue, and potentially influence airway to systemic drug absorption profiles. Transporters in the lung tissue may also have the capacity to mediate uptake of drug from the systemic circulation resulting in drug accumulation in the lung. Transporters have physiological roles and new drug candidates while not necessarily serving as transport substrates may modulate transporter activity and hence physiology. The commentary highlights a series of recommendations for further work in pulmonary drug transporter research.

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.

Nanoparticles attenuate P-glycoprotein/MDR1 function in A549 human alveolar epithelial cells

P-glycoprotein/MDR1 (P-gp) is a well-characterised membrane transporter relevant in drug disposition and multi-drug resistance. In this study, we aimed to investigate how far nanoparticulates impair the function of the P-gp transport system and which particle properties govern these interactions. Expression and function of P-gp was confirmed in A549 cell monolayers. Rhodamine 123 (Rh123) release studies were carried out in the presence of known inhibitors of P-gp function (i.e., cyclosporine A and verapamil), under ATP depletion (NaN(3)/DOG) and after acute exposure to nanoparticles (NPs) with different surface modifications, ζ-potentials and sizes (plain, carboxylated, and amine- and sulphate-modified). The cytotoxic potential of NPs on A549 monolayers was evaluated by MTT assay. The effects on P-gp protein level, after incubation with NPs, were investigated by Western blot analysis of A549 cell lysate and supernatant. Cellular retention of Rh123 was significantly (P<0.05) increased in the presence of carboxylated (100 nm), amine- and sulphate-modified NPs. A slight, but not significant, decrease in Rh123 release was also observed for plain latex and carboxylated (500 nm) NPs. The MTT assay demonstrated that most NPs caused only marginal levels of cytotoxicity (78-88% cell viability); the positively charged amine-NPs, however, were considerably more cytotoxic. Western blot showed that NPs did not cause any cell membrane disruption. Our findings suggest that nanomaterials can attenuate membrane transporter function depending on their size and surface properties and hence might influence the disposition of xenobiotics as well as endogenous substrates.