The Use of Single Photon Emission Computed Tomography in Aerosol Medicine.

Imaging of radiolabeled aerosols provides useful in vivo data on both the initial site of deposition and its subsequent transport by mucociliary clearance and epithelial permeability. Single Photon Emission Computed Tomography (SPECT) uses a gamma camera with multiple rotating heads to produce three-dimensional (3D) images of inhaled radioaerosol labeled with technetium-99m. This enables total lung deposition and its 3D regional distribution to be quantified. Aligned 3D images of lung structure allow deposition data to be related to lung anatomy. Mucociliary clearance or epithelial permeability can be assessed from a time series of SPECT aerosol images. SPECT is slightly superior to planar imaging for measuring total lung deposition. However, it is more complex to use, and for studies where total lung deposition is the endpoint, planar imaging is recommended. However, SPECT has been shown to be clearly superior to planar imaging for assessing regional distribution of aerosol and is the method of choice for this purpose. It therefore has applications in studying the influence of regional deposition on clinical effectiveness and also in validating computer models of deposition. The inability to directly radiolabel drug molecules with 99mTc is a clear disadvantage of SPECT and limits its potential use for pharmacokinetic studies. SPECT provides a wealth of data on aerosol deposition, which has been relatively underused at present. Optimal methods of analyzing and interpreting the data need to be developed. SPECT can also, in principle, provide detailed information of mucociliary clearance and has the potential to significantly improve knowledge of this process and hence clarify the role of clearance as a biomarker.

Fine Particle Fraction: The Good and the Bad.

Fine particle fraction (FPF) is defined in general terms as the fraction or percentage of the drug mass contained in an aerosol cloud that may be small enough to enter the lungs and exert a clinical effect. An aerodynamic diameter of 5 µm represents the approximate border between "fine" and "coarse" particles, but there is no universally agreed upon definition of FPF in terms of an aerodynamic particle size range. FPF alone does not adequately describe a heterodisperse aerodynamic particle size distribution, and it needs to be combined with another measure or measures indicating the width of the distribution. When determined using techniques specified in United States and European Pharmacopeias, FPF is measured by cascade impactors that have straight-sided ninety degree inlets through which air is drawn at a constant rate. It is not the purpose of in vitro tests to predict in vivo behavior, and FPF is primarily a measure of aerosol quality. Despite this, FPF broadly predicts the amount of drug from an inhaler device depositing in the lungs, but it systematically overestimates whole lung deposition and may not correctly predict the relative lung depositions for two inhalers of different types. The relationship between FPF and both drug pharmacokinetics and clinical response is incompletely understood at the present time, and more studies are needed to investigate these relationships. Modifications to impactor technologies, including inlets that mimic the human extrathoracic airways and the use of realistic breathing patterns, would be expected to improve the predictive power of in vitro tests for drug delivery in vivo.

Assessment of in vitro kinetics and biological impact of nebulized trehalose on human bronchial epithelium.

Trehalose is added in drug formulations to act as fillers or improve aerosolization performance. Its characteristics as a carrier molecule have been explored; however, the fate of trehalose in human airway tissues has not been thoroughly investigated. Here, we investigated the fate of nebulized trehalose using in vitro human air-liquid bronchial epithelial cultures. First, a tracing experiment was conducted using 13C12-trehalose; we measured trehalose distribution in different culture compartments (apical surface liquid, epithelial culture, and basal side medium) at various time points following acute exposure to 13C12-labeled trehalose. We found that 13C12-trehalose was metabolized into 13C6-glucose. The data was then used to model the kinetics of trehalose disappearance from the apical surface of bronchial cultures. Secondly, we evaluated the potential adverse effects of nebulized trehalose on the bronchial cultures after they were acutely exposed to nebulized trehalose up to a level just below its solubility limit (50 g/100 g water). We assessed the ciliary beating frequency and histological characteristics. We found that nebulized trehalose did not lead to marked alteration in ciliary beating frequency and morphology of the epithelial cultures. The in vitro testing approach used here may enable the early selection of excipients for future development of inhalation products.

Bioequivalence assessment of pharmaceutical aerosol products through IVIVC.

Many pharmaceutical developers of generic orally inhaled products (OIPs) are facing significant issues in passing the regulatory requirement to show pharmacokinetic (PK) bioequivalence (BE) to the originator product. The core of the issue is that no reliable in vitro-in vivo correlation (IVIVC) is available to guide their development. In this paper, several issues are identified and means to improve the data used for developing an IVIVC are discussed. The article also presents an "IVIVC-free" approach for developing a formulation matching the originator's PK performance.

Inhalation delivery technology for genome-editing of respiratory diseases.

The clustered regulatory interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (CRISPR/Cas9) system has significant therapeutic potentials for lung congenital diseases such as cystic fibrosis, as well as other pulmonary disorders like lung cancer and obstructive diseases. Local administration of CRISPR/Cas9 therapeutics through inhalation can achieve high drug concentration and minimise systemic exposure. While the field is advancing with better understanding on the biological functions achieved by CRISPR/Cas9 systems, the lack of progress in inhalation formulation and delivery of the molecule may impede their clinical translation efficiently. This forward-looking review discussed the current status of formulations and delivery for inhalation of relevant biologics such as genes (plasmids and mRNAs) and proteins, emphasising on their design strategies and preparation methods. By adapting and optimising formulation strategies used for genes and proteins, we envisage that development of inhalable CRISPR/Cas9 liquid or powder formulations for inhalation administration can potentially be fast-tracked in near future.

Aerosol Inhalation Delivery of Triazavirin in Mice: Outlooks for Advanced Therapy Against Novel Viral Infections.

Under pandemic-caused emergency, evaluation of the potential of existing antiviral drugs for the treatment of COVID-19 is relevant. Triazavirin, an antiviral drug developed in Russia for per-oral administration, is involved in clinical trials against SARS-CoV-2 coronavirus. This virus has affinity to epithelial cells in respiratory tract, so drug delivery directly in lungs may enhance therapeutic effect and reduce side effects for stomach, liver, kidneys. We elaborated ultrasonic method of triazavirin aerosol generation and investigated the inhalation delivery of this drug in mice. Mean particle size and number concentration of aerosol used in inhalation experiments are 560 nm and 4 × 105 cm-3, respectively. Aerosol mass concentration is 1.6 × 10-4 mg/cm3. Inhalation for 20 min in a nose-only chamber resulted in 2 mg/kg body delivered dose and 2.6 µg/mL triazavirin concentration in blood plasma. Elimination rate constant determined in aerosol administration experiments was ke = 0.077 min-1, which agrees with the value measured after intravenous delivery, but per-oral administration resulted in considerably lower apparent elimination rate constant of pseudo-first order, probably due to non-linear dependence of absorption rate on triazavirin concentration in gastrointestinal tract. The bioavailability of triazavirin aerosol is found to be 85%, which is about four times higher than for per-oral administration.

Nebulised Gadolinium-Based Nanoparticles for a Multimodal Approach: Quantitative and Qualitative Lung Distribution Using Magnetic Resonance and Scintigraphy Imaging in Isolated Ventilated Porcine Lungs.

PURPOSE: This study aims at determining lung distribution of gadolinium-based polysiloxane nanoparticles, AGuIX® (small rigid platform - SRP), as a potential theranostic approach by the pulmonary route. METHODS: First, the aerodynamic size distribution and the aerosol output rate were thoroughly characterized. Then, a multimodal approach using magnetic resonance (MR) and gamma-camera (GC) imaging allows to assess the deposition of the aerosolised nanoparticles in the respiratory tract using isolated ventilated porcine lungs. RESULTS: The SRP has proven to be radiolabelled by radioisotope with a good yield. Crude SRP or radiolabelled ones showed the same aerodynamic size distribution and output as a conventional molecular tracer, as sodium fluoride. With MR and GC imaging approaches, the nebulised dose represented about 50% of the initial dose of nanoparticles placed in the nebuliser. Results expressed as proportions of the deposited aerosol showed approximately a regional aerosol deposition of 50% of the deposited dose in the lungs and 50% in the upper airways. Each technique assessed a homogeneous pattern of deposited nanoparticles in Lungs. MR observed a strong signal enhancement with the SRP, similar to the one obtained with a commonly used MRI contrast agent, gadoterate meglumine. CONCLUSION: As a known theranostic approach by intravenous administration, SRP appeared to be easily aerosolised with a conventional nebuliser. The present work proves that pulmonary administration of SRP is feasible in a human-like model and allows multimodal imaging with MR and GC imaging. This work presents the proof of concept of SRP nebulisation and aims to generate preclinical data for the potential clinical transfer of SRP for pulmonary delivery.

Regional Deposition: Deposition Models.

Modeling particle deposition in the human lung requires information about the morphology of the lung in terms of simple geometric units, e.g., characterizing bronchial airways by straight cylindrical tubes. Five different regional deposition models are discussed in this section with respect to morphometric lung models and related mathematical modeling techniques: 1) one-dimensional cross-section or "trumpet" model, 2) deterministic symmetric generation or "single-path" model, 3) deterministic asymmetric generation or "multiple-path" model, 4) stochastic asymmetric generation or "multiple-path" model, and 5) single-path computational fluid and particle dynamics (CFPD) model. Current deposition models can predict the following regional deposition quantities relevant for the administration of medical aerosols: 1) regional bronchial and alveolar deposition, 2) generational lung deposition, 3) lobar deposition, 4) generational lobar deposition, and 5) generational surface deposition. Although deposition fractions predicted by the different models depend on the selection of a specific morphometric lung model and a specific set of analytical deposition equations, all models predict the same trends as functions of particle diameter and breathing parameters. In general, the overall agreement between the modeling predictions obtained by the various deposition models and the available experimental evidence indicates that current deposition models correctly predict regional and generational deposition.

In vitro, ex vivo and in vivo methods of lung absorption for inhaled drugs.

The assessment and prediction of lung absorption and disposition are an increasingly essential preclinical task for successful discovery and product development of inhaled drugs for both local and systemic delivery. Hence, in vitro, ex vivo and in vivo preclinical methods of lung absorption continue to evolve with several technical, methodological and analytical refinements. As in vitro lung epithelial cell monolayer models, the air-liquid interface (ALI)-cultured Calu-3 cells have most frequently been used, but the NCI-H441 and hAELVi cells have now been proposed as the first immortalized human alveolar epithelial cells capable of forming highly-restricted monolayers. The primary ALI-cultured three-dimensional (3D) human lung cell barriers have also become available; efforts to incorporate aerosol drug deposition into the in vitro lung cell models continue; and stem cell-derived lung epithelial cells and "lung-on-a-chip" technology are emerging. The ex vivo isolated perfused rat lung (IPRL) methods have increasing been used, as they enable the kinetic determination of tissue/organ-level diffusive and membrane protein-mediated absorption and competing non-absorptive loss; the assessment of "pre-epithelial" aerosol biopharmaceutical events in the lung, such as dissolution and release; and the ex vivo-to-in vivo extrapolation and prediction. Even so, in vivo small rodent-based methods have been of mainstay use, while large animal-based methods find an additional opportunity to study region-dependent lung absorption and disposition. It is also exciting that human pharmacokinetic (PK) profiles and systemic exposures for inhaled drugs/molecules may be able to be predicted from these in vivo rodent PK data following lung delivery using kinetic modeling approach with allometric scaling. Overall, the value of these preclinical assessments appears to have shifted more to their translational capability of predicting local lung and systemic exposure in humans, in addition to rationalizing optimal inhaled dosage form and delivery system for drugs/molecules in question. It is critically important therefore to make appropriate selection and timely exploitation of the best models at each stage of drug discovery and development program for efficient progress toward product approval and clinical use.

Correlation and clinical relevance of animal models for inhaled pharmaceuticals and biopharmaceuticals.

Nonclinical studies are fundamental for the development of inhaled drugs, as for any drug product, and for successful translation to clinical practice. They include in silico, in vitro, ex vivo and in vivo studies and are intended to provide a comprehensive understanding of the inhaled drug beneficial and detrimental effects. To date, animal models cannot be circumvented during drug development programs, acting as surrogates of humans to predict inhaled drug response, fate and toxicity. Herein, we review the animal models used during the different development stages of inhaled pharmaceuticals and biopharmaceuticals, highlighting their strengths and limitations.

Emerging trends in inhaled drug delivery.

Ideally, inhaled therapy is driven by the needs of specific disease management. Lung biology interfaces with inhaler performance to allow optimal delivery of therapeutic agent for disease treatment. Inhalation aerosol products consist of the therapeutic agent, formulation, and device. The manufacturing specifications on each of the components, and their combination, allow accurate and reproducible control of measures of quality and in-vitro performance. These product variables in combination with patient variables, including co-ordination skill during inhaler use, intrinsic lung biology, disease and consequent pulmonary function, contribute to drug safety and efficacy outcomes. Due to the complexity of pulmonary drug delivery, predicting biological outcomes from first principles has been challenging. Ongoing research appears to offer new insights that may allow accurate prediction of drug behavior in the lungs. Disruptive innovations were characteristic of research and development in inhaled drug delivery at the end of the last century. Although there were relatively few new inhaled products launched in the first decade of the new millennium it was evident that the earlier years of exploration resulted in maturation of commercially successful technologies. A significant increase in new and generic products has occurred in the last decade and technical, regulatory and disease management trends are emerging. Some of these developments can trace their origins to earlier periods of creativity in the field while others are a reflection of advances in other areas of basic and computer, sciences and engineering. Select biological and technical advances are highlighted with reflections on the potential to impact future clinical and regulatory considerations.

In vitro-in vivo correlations (IVIVCs) of deposition for drugs given by oral inhalation.

Conventional in vitro tests to assess the aerodynamic particle size distribution (APSD) from inhaler devices use simple right-angle inlets ("mouth-throats", MTs) to cascade impactors, and air is drawn through the system at a fixed flow for a fixed time. Since this arrangement differs substantially from both human oropharyngeal airway anatomy and the patterns of air flow when patients use inhalers, the ability of in vitro tests to predict in vivo deposition of pharmaceutical aerosols has been limited. MTs that mimic the human anatomy, coupled with simulated breathing patterns, have yielded estimates of lung dose from in vitro data that closely match those from in vivo gamma scintigraphic or pharmacokinetic studies. However, different models of MTs do not always yield identical data, and selection of an anatomical MT and representative inhalation profiles remains challenging. Improved in vitro - in vivo correlations (IVIVCs) for inhaled drug products could permit increased reliance on in vitro data when developing new inhaled drug products, and could ultimately result in accelerated drug product development, together with reduced research and development spending.

Deposition Mechanisms.

The success of inhalation therapy is not only dependent upon the pharmacology of the drugs being inhaled but also upon the site and extent of deposition in the respiratory tract. Similarly, the toxicity of environmental and industrial particulate matter is affected not only by the nature of the dust but also by the amount and spatial distribution of deposited particles in the lung. Aerosol deposition is primarily governed by the mechanisms of inertial impaction, gravitational sedimentation, Brownian diffusion, and, to a lesser extent, by turbulence, electrostatic precipitation, and interception. The relative contribution of these different mechanisms is a function of the physical characteristics of the particles, the lung structure, and the flow patterns. Large particles (>5 µm) tend to deposit mainly in the upper and large airways, limiting the amount of aerosols that can be delivered to the lung. Small particles (<2 µm) deposit mainly in the alveolar region, whereas particles in the size range 2-5 µm deposit preferentially in the central and small airways.

Spray-dried raloxifene submicron particles for pulmonary delivery: Development and in vivo pharmacokinetic evaluation in rats.

Raloxifene hydrochloride (RH) is a selective oestrogen receptor modulator used for the treatment of osteoporosis. Even though 60% of an oral dose is quickly absorbed via the gastrointestinal tract, the absolute bioavailability of RH is only 2-3% in humans due to extensive first-pass metabolism. Various approaches to improve RH bioavailability have been reported over the past few years; however, none have focused on the development of products for pulmonary administration. Therefore, in this study, submicron particles containing RH were produced for pulmonary administration with the aim to limit first-pass metabolism. Powders were produced by vibrational atomisation spray drying with a high process yield (>80%). The drug content was between 440 and 890 mg·g-1, and powders had a high encapsulation efficiency (>95%), mean particle size of 400-700 nm, low residual moisture (<2%) and spherical shape. These powders showed an improved drug dissolution rate compared to the raw RH material. Moreover, they presented high dose uniformity (95-100%), a high in vitro respirable fraction (>55%) and adequate mass median aerodynamic diameter for pulmonary delivery (<5 µm). The pharmacokinetic study in male Wistar rats demonstrated an absolute bioavailability of 47.20% after pulmonary administration of the particles. Therefore, these submicron-sized powders are promising for pulmonary RH delivery as a dry powder medicine.

The Confusing World of Dry Powder Inhalers: It Is All About Inspiratory Pressures, Not Inspiratory Flow Rates.

Dry powder inhalers (DPIs) all have the ability to aerosolize dry powders, but they each offer different operating mechanisms and resistances to inhaled airflow. This variety has resulted in both clinician and patient confusion concerning DPI performance, use, and effectiveness. Particularly, there is a growing misconception that a single peak inspiratory flow rate (PIFR) can determine a patient's ability to use a DPI effectively, regardless of its design or airflow resistance. For this review article, we have sifted through the relevant literature concerning DPIs, inspiratory pressures, and inspiratory flow rates to provide a comprehensive and concise discussion and recommendations for DPI use. We ultimately clarify that the controlling parameter for DPI performance is not the PIFR but the negative pressure generated by the patient's inspiratory effort. A pressure drop ∼≥1 kPa (∼10 cm H2O) with any DPI is a reasonable threshold above which a patient should receive an adequate lung dose. Overall, we explore the underlying factors controlling inspiratory pressures, flow rates and dispensing, and dispersion characteristics of the various DPIs to clarify that inspiratory pressures, not flow rates, limit and control a patient's ability to generate sufficient flow for effective DPI use.

Aerosol delivery during invasive mechanical ventilation: development of a preclinical ex vivo respiratory model for aerosol regional deposition.

In intensive care units, nebulization is a usual route for drug administration to patients under mechanical ventilation (MV). The effectiveness of inhalation devices as well as depositions sites of aerosols for ventilated patients remain poorly documented. In vivo human inhalation studies are scarce due to ethical restrictions because imaging techniques require radioaerosols to assess regional aerosol deposition. Thus, we developed an ex vivo respiratory model under invasive MV for preclinical aerosol deposition studies. The model was composed of ex vivo porcine respiratory tracts. MV was achieved thanks to a tracheal intubation and a medical ventilator under controlled conditions. Respiratory features were studied using analogical sensors. Then regional homogeneity of gas-ventilation was assessed with 81mKrypton scintigraphies. Finally, a proof of concept study for aerosol deposition was performed. Obtained respiratory features as well as gamma-imaging techniques, which demonstrated a homogenous regional ventilation and about 18% ± 4% of the nebulized dose deposited the respiratory tract, were in good agreement with human data available in the literature. This original ex vivo respiratory model provides a feasible, reproducible and cost-effective preclinical tool to achieve aerosol deposition studies under MV.

Development of an ex vivo preclinical respiratory model of idiopathic pulmonary fibrosis for aerosol regional studies.

Idiopathic pulmonary fibrosis is a progressive disease with unsatisfactory systemic treatments. Aerosol drug delivery to the lungs is expected to be an interesting route of administration. However, due to the alterations of lung compliance caused by fibrosis, local delivery remains challenging. This work aimed to develop a practical, relevant and ethically less restricted ex vivo respiratory model of fibrotic lung for regional aerosol deposition studies. This model is composed of an Ear-Nose-Throat replica connected to a sealed enclosure containing an ex vivo porcine respiratory tract, which was modified to mimic the mechanical properties of fibrotic lung parenchyma - i.e. reduced compliance. Passive respiratory mechanics were measured. 81mKr scintigraphies were used to assess the homogeneity of gas-ventilation, while regional aerosol deposition was assessed with 99mTc-DTPA scintigraphies. We validated the procedure to induce modifications of lung parenchyma to obtain aimed variation of compliance. Compared to the healthy model, lung respiratory mechanics were modified to the same extent as IPF-suffering patients. 81mKr gas-ventilation and 99mTc-DTPA regional aerosol deposition showed results comparable to clinical studies, qualitatively. This ex vivo respiratory model could simulate lung fibrosis for aerosol regional deposition studies giving an interesting alternative to animal experiments, accelerating and facilitating preclinical studies before clinical trials.

Radiation Dosimetry of Inhaled Radioactive Aerosols: CFPD and MCNP Transport Simulations of Radionuclides in the Lung.

Despite extensive efforts in studying radioactive aerosols, including the transmission of radionuclides in different chemical matrices throughout the body, the internal organ-specific radiation dose due to inhaled radioactive aerosols has largely relied on experimental deposition data and simplified human phantoms. Computational fluid-particle dynamics (CFPD) has proven to be a reliable tool in characterizing aerosol transport in the upper airways, while Monte Carlo based radiation codes allow accurate simulation of radiation transport. The objective of this study is to numerically assess the radiation dosimetry due to particles decaying in the respiratory tract from environmental radioactive exposures by coupling CFPD with Monte Carlo N-Particle code, version 6 (MCNP6). A physiologically realistic mouth-lung model extending to the bifurcation generation G9 was used to simulate airflow and particle transport within the respiratory tract. Polydisperse aerosols with different distributions were considered, and deposition distribution of the inhaled aerosols on the internal airway walls was quantified. The deposition mapping of radioactive aerosols was then registered to the respiratory tract of an image-based whole-body adult male model (VIP-Man) to simulate radiation transport and energy deposition. Computer codes were developed for geometry visualization, spatial normalization, and source card definition in MCNP6. Spatial distributions of internal radiation dosimetry were compared for different radionuclides (131I, 134,137Cs, 90Sr-90Y, 103Ru and 239,240Pu) in terms of the radiation fluence, energy deposition density, and dose per decay.

The Influence of Aerosol Density and Shape Factor on the Assessment of Internal Exposure to 239Pu.

Internal exposure due to inhalation of aerosols depends on the ratio of aerodynamic shape factor (χ) to aerosol mass density (ρ). Inhaled aerosol parameters may differ from the default ρ and χ values provided by the International Commission on Radiological Protection, which are adopted for the assessment of internal exposures. This paper focuses on the influences of χ/ρ on the assessment of internal exposure to Pu for reference workers. Regional deposition fractions are found to decrease with increasing χ/ρ, and larger decreases are observed with smaller activity median aerodynamic diameter aerosols, while the slow clearance fractions (fs) in the tracheobronchial region are more sensitive for larger activity median aerodynamic diameter aerosols. Results from biokinetics calculations reveal that both the time-dependent content (excretion) and cumulative activities are determined mainly for particles initially deposited in the alveolar-interstitial region, while fs affects the local cumulative activities in the tracheobronchial region. χ/ρ is proven to have different influences for aerosols with different activity median aerodynamic diameters. The default χ/ρ values can be used when activity median aerodynamic diameters are greater than 1 µm, while one should pay attention to the value of χ/ρ when activity median aerodynamic diameters are less than 1 µm, where significant influence may be anticipated.

Comparison of Tissue and Blood Concentrations of Oxaliplatin Administrated by Different Modalities of Intraperitoneal Chemotherapy.

BACKGROUND: Pressurized intraperitoneal aerosol chemotherapy (PIPAC) is a new technology for delivering intraperitoneal chemotherapy. It is generally assumed that with PIPAC, the ratio of peritoneal to systemic drug concentration is superior to liquid hyperthermic intraperitoneal chemotherapy (HIPEC). To date, no direct comparative data are available supporting such an assumption. MATERIALS AND METHODS: Twelve 65-day-old pigs were randomly separated into three groups of four pigs each, all of which received intraperitoneal chemotherapy using the following administration methods: PIPAC with oxaliplatin 92 mg in 150 ml dextrose 5% (Group 1); PIPAC with electrostatic aerosol precipitation (ePIPAC; Group 2); or laparoscopic HIPEC (L-HIPEC) with oxaliplatin 400 mg in 4 L dextrose 5% at 42 °C (Group 3). Serial blood and peritoneal tissue concentrations of oxaliplatin were determined by spectrometry. RESULTS: In all three groups, the maximum concentration of oxaliplatin in blood was detected 50-60 min after onset of the chemotherapy experiments, with no significant differences among the three groups (p = 0.7994). Blood oxaliplatin concentrations (0-30 min) were significantly higher in the L-HIPEC group compared with the ePIPAC group (p < 0.05). No difference was found for the overall systemic oxaliplatin absorption (area under the curve). Overall concentrations in the peritoneum were not different among the three groups (p = 0.4725), but were significantly higher in the visceral peritoneum in the PIPAC group (p = 0.0242). CONCLUSIONS: Blood and tissue concentrations were comparable between all groups; however, depending on the intraperitoneal area examined and the time points of drug delivery, the concentrations differed significantly between the three groups.