➡ Developing new (inhalational) anti-infective strategies for the clinical application is a very lengthy and difficult process. For a fast and predictive non-clinical development we established a integrative test-platform for evaluation of inhalational drug candidates In this platform we integrate state of the art human ex vivo methods like PCLS with the rat ex vivo isolated perfused lung system and in vitro cell-based inhalation assay in order to address different questions highly relevant for the assessment of safety and efficacy of new drugs. In this case we used Nafamostat, a repurposing drug with excellent anti-viral efficacy against SARS Cov-2 that is already is approved for systemic use against pancreatitis in Japan.
➡ In a highly integrative approach, we used state of the art in vitro/ex vivo and in vivo methods to determine the safety and efficacy of inhalational Nafamostat. First, using the Fraunhofer ITEM developed PRIT ExpoCube human epithelial cells were exposed to nebulized Nafamostat in order to define the NOAEL. For human proof of concept and to define a therapeutic window a Precision Cut Lung Slice (PCLS) model was used as an ex vivo organotypic infection model for investigation of the host-pathogen interaction in situ. The Isolated Perfused Rat Lung (IPL) providing a fully intact organ system with cellular, structural and functional integrity was established to investigate local organotoxic effects as well as for pharmacokinetic studies. In addition, a classical GLP 28-day regulatory inhalation toxicological study was performed in rats. Data integration was conducted using the Multiple-Path Particle Dosimetry (MPPD) model and the PBKit inhalation-focused PBK model developed by the Fh ITEM.
Results and Conclusion:
➡ In-vitro inhalation studies with A549 cells indicate at a LOAEL value for Nafamostat Mesylate of ~2 µg/ cm2. For Nafamostat, a dose dependent efficacy could be demonstrated in Precision-Cut-Lung Slice infection models (SARS-CoV-2). Efficacy has been shown for 0.5 µM in PCLS, which is in a similar range with the assumed therapeutic range reported in the literature (30 – 240 nM). Determination of local toxicity revealed an excellent therapeutic window with efficacy being a factor of more than 100 lower than the toxic level. In Isolated Perfused Lungs, a LOAEL of 0.2 mg/kg bw was observed in an inhalation dose-escalation protocol with adverse effects observed in the upper airways only. Applying the MPPD-model for detailed dosimetry, a corresponding surface specific LOAEL of ~ 7 µg/cm2 was derived. In a 28-day in vivo inhalation study, animals showed adverse effects for a 0.3 mg/kg body weight dose in the larynx and upper airways (ulcer, necrosis) with locally deposited doses up to ~ 30 µg/cm2, while effects in the pulmonary region were smaller with locally deposited doses ≤ 2 µm/cm2. No toxicity was found in histopathological analysis of the nasal area though a high head deposited dose. Thus, in vitro/ex vivo and in vivo data point towards comparable LOAEL values. Furthermore, integration of IPL derived absorption parameters into the PBKit inhalation-focused PBK model supports a favorable lung concentration profile for inhalational application.
As shown for Nafamostat, application and combination of different methods can provide data, that can be incorporated into the non-clinical development of inhaled drug candidates. Therefore, these studies can contribute to a faster and more effective early pre-clinical development and can help to refine regulatory studies by e.g. supporting dose selection.