Quantitative detection of drug dose and spatial distribution in the lung revealed by Cryoslicing Imaging

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.

Development of a dynamic in vitro stretch model of the alveolar interface with aerosol delivery

We describe the engineering design, computational modeling, and empirical performance of a moving air-liquid interface (MALI) bioreactor for the study of aerosol deposition on cells cultured on an elastic, porous membrane which mimics both air-liquid interface exposure conditions and mechanoelastic motion of lung tissue during breathing. The device consists of two chambers separated by a cell layer cultured on a porous, flexible membrane. The lower (basolateral) chamber is perfused with cell culture medium simulating blood circulation. The upper (apical) chamber representing the air compartment of the lung is interfaced to an aerosol generator and a pressure actuation system. By cycling the pressure in the apical chamber between 0 and 7 kPa, the membrane can mimic the periodic mechanical strain of the alveolar wall. Focusing on the engineering aspects of the system, we show that membrane strain can be monitored by measuring changes in pressure resulting from the movement of media in the basolateral chamber. Moreover, liquid aerosol deposition at a high dose delivery rate (>1 µl cm^-2  min^-1 ) is highly efficient (ca. 51.5%) and can be accurately modeled using finite element methods. Finally, we show that lung epithelial cells can be mechanically stimulated under air-liquid interface and stretch-conditions without loss of viability. The MALI bioreactor could be used to study the effects of aerosol on alveolar cells cultured at the air-liquid interface in a biodynamic environment or for toxicological or therapeutic applications.

Innovative preclinical models for pulmonary drug delivery research

Introduction: Pulmonary drug delivery is a complex field of research combining physics which drive aerosol transport and deposition and biology which underpins efficacy and toxicity of inhaled drugs. A myriad of preclinical methods, ranging from in-silico to in-vitro, ex-vivo and in-vivo, can be implemented.Areas covered: The present review covers in-silico mathematical and computational fluid dynamics modelization of aerosol deposition, cascade impactor technology to estimated drug delivery and deposition, advanced in-vitro cell culture methods and associated aerosol exposure, lung-on-chip technology, ex-vivo modeling, in-vivo inhaled drug delivery, lung imaging, and longitudinal pharmacokinetic analysis.Expert opinion: No single preclinical model can be advocated; all methods are fundamentally complementary and should be implemented based on benefits and drawbacks to answer specific scientific questions. The overall best scientific strategy depends, among others, on the product under investigations, inhalation device design, disease of interest, clinical patient population, previous knowledge. Preclinical testing is not to be separated from clinical evaluation, as small proof-of-concept clinical studies or conversely large-scale clinical big data may inform preclinical testing. The extend of expertise required for such translational research is unlikely to be found in one single laboratory calling for the setup of multinational large-scale research consortiums.

Multimodal Precision Imaging of Pulmonary Nanoparticle Delivery in Mice: Dynamics of Application, Spatial Distribution, and Dosimetry

Targeted delivery of nanomedicine/nanoparticles (NM/NPs) to the site of disease (e.g., the tumor or lung injury) is of vital importance for improved therapeutic efficacy. Multimodal imaging platforms provide powerful tools for monitoring delivery and tissue distribution of drugs and NM/NPs. This study introduces a preclinical imaging platform combining X-ray (two modes) and fluorescence imaging (three modes) techniques for time-resolved in vivo and spatially resolved ex vivo visualization of mouse lungs during pulmonary NP delivery. Liquid mixtures of iodine (contrast agent for X-ray) and/or (nano)particles (X-ray absorbing and/or fluorescent) are delivered to different regions of the lung via intratracheal instillation, nasal aspiration, and ventilator-assisted aerosol inhalation. It is demonstrated that in vivo propagation-based phase-contrast X-ray imaging elucidates the dynamic process of pulmonary NP delivery, while ex vivo fluorescence imaging (e.g., tissue-cleared light sheet fluorescence microscopy) reveals the quantitative 3D drug/particle distribution throughout the entire lung with cellular resolution. The novel and complementary information from this imaging platform unveils the dynamics and mechanisms of pulmonary NM/NP delivery and deposition for each of the delivery routes, which provides guidance on optimizing pulmonary delivery techniques and novel-designed NM for targeting and efficacy.

Three-Dimensional Quantitative Co-Mapping of Pulmonary Morphology and Nanoparticle Distribution with Cellular Resolution in Nondissected Murine Lungs

Deciphering biodistribution, biokinetics, and biological effects of nanoparticles (NPs) in entire organs with cellular resolution remains largely elusive due to the lack of effective imaging tools. Here, light sheet fluorescence microscopy in combination with optical tissue clearing was validated for concomitant three-dimensional mapping of lung morphology and NP biodistribution with cellular resolution in nondissected ex vivo murine lungs. Tissue autofluorescence allowed for label-free, quantitative morphometry of the entire bronchial tree, acinar structure, and blood vessels. Co-registration of fluorescent NPs with lung morphology revealed significant differences in pulmonary NP distribution depending on the means of application (intratracheal instillation and ventilator-assisted aerosol inhalation under anesthetized conditions). Inhalation exhibited a more homogeneous NP distribution in conducting airways and acini indicated by a central-to-peripheral (C/P) NP deposition ratio of unity (0.98 ± 0.13) as compared to a 2-fold enhanced central deposition (C/P = 1.98 ± 0.37) for instillation. After inhalation most NPs were observed in the proximal part of the acini as predicted by computational fluid dynamics simulations. At cellular resolution patchy NP deposition was visualized in bronchioles and acini, but more pronounced for instillation. Excellent linearity of the fluorescence intensity-dose response curve allowed for accurate NP dosimetry and revealed ca. 5% of the inhaled aerosol was deposited in the lungs. This single-modality imaging technique allows for quantitative co-registration of tissue architecture and NP biodistribution, which could accelerate elucidation of NP biokinetics and bioactivity within intact tissues, facilitating both nanotoxicology studies and the development of nanomedicines.

Predicting drug delivery efficiency into tumor tissues through molecular simulation of transport in complex vascular networks

Efficient delivery of anticancer drugs into tumor tissues at maximally effective and minimally toxic concentrations is vital for therapeutic success. At present, no method exists that can predict the spatial and temporal distribution of drugs into a target tissue after administration of a specific dose. This prevents accurate estimation of optimal dosage regimens for cancer therapy. Here we present a new method that predicts quantitatively the time-dependent spatial distribution of drugs in tumor tissues at sub-micrometer resolution. This is achieved by modeling the diffusive flow of individual drug molecules through the three-dimensional network of blood-vessels that vascularize the tumor, and into surrounding tissues, using molecular mechanics techniques. By evaluating delivery into tumors supplied by a series of blood-vessel networks with varying degrees of complexity, we show that the optimal dose depends critically on the precise vascular structure. Finally, we apply our method to calculate the optimal dosage of the cancer drug doxil into a section of a mouse ovarian tumor, and demonstrate the enhanced delivery of liposomally administered doxorubicin when compared to free doxorubicin. Comparison with experimental data and a multiple-compartment model show that the model accurately recapitulates known pharmacokinetics and drug-load predictions. In addition, it provides, for the first time, a detailed picture of the spatial dependence of drug uptake into tissues surrounding tumor vasculatures. This approach is fundamentally different to current continuum models, and reveals that the target tumor vascular topology is as important for therapeutic success as the transport properties of the drug delivery platform itself. This sets the stage for revisiting drug dosage calculations.

In vivo Dynamic Phase-Contrast X-ray Imaging using a Compact Light Source

We describe the first dynamic and the first in vivo X-ray imaging studies successfully performed at a laser-undulator-based compact synchrotron light source. The X-ray properties of this source enable time-sequence propagation-based X-ray phase-contrast imaging. We focus here on non-invasive imaging for respiratory treatment development and physiological understanding. In small animals, we capture the regional delivery of respiratory treatment, and two measures of respiratory health that can reveal the effectiveness of a treatment; lung motion and mucociliary clearance. The results demonstrate the ability of this set-up to perform laboratory-based dynamic imaging, specifically in small animal models, and with the possibility of longitudinal studies.

Applicability of avidin protein coated mesoporous silica nanoparticles as drug carriers in the lung

Mesoporous silica nanoparticles (MSNs) exhibit unique drug delivery properties and are thus considered as promising candidates for next generation nano-medicines. In particular, inhalation into the lungs represents a direct, non-invasive delivery route for treating lung disease. To assess MSN biocompatibility in the lung, we investigated the bioresponse of avidin-coated MSNs (MSN-AVI), as well as aminated (uncoated) MSNs, after direct application into the lungs of mice. We quantified MSN distribution, clearance rate, cell-specific uptake, and inflammatory responses to MSNs within one week after instillation. We show that amine-functionalized (MSN-NH2) particles are not taken up by lung epithelial cells, but induced a prolonged inflammatory response in the lung and macrophage cell death. In contrast, MSN-AVI co-localized with alveolar epithelial type 1 and type 2 cells in the lung in the absence of sustained inflammatory responses or cell death, and showed preferential epithelial cell uptake in in vitro co-cultures. Further, MSN-AVI particles demonstrated uniform particle distribution in mouse lungs and slow clearance rates. Thus, we provide evidence that avidin functionalized MSNs (MSN-AVI) have the potential to serve as versatile biocompatible drug carriers for lung-specific drug delivery.