In vitro and in vivo characterisation of the novel neutrophil elastase inhibitor BI 1323495

Abstract

Background: Excess activity of neutrophil elastase (NE) in the lung of COPD patients results in the degradation of extracellular matrix (ECM) proteins and an increased activation of other proteases, leading to the destruction of alveolar septa and, ultimately, emphysema development. Direct inhibition of NE is expected to reduce lung parenchyma destruction, emphysema formation and progression in patients with COPD. Aim: We investigated the in vitro and in vivo profile of the novel NE inhibitor BI 1323495. Methods: Inhibition of human NE and the related proteases cathepsin G and proteinase 3 was determined in enzymatic assays using purified enzymes. In addition, inhibition of NE in plasma from zymosan-stimulated human whole blood was measured. An acute lung injury model in mice was used to monitor the in vivo inhibition of NE in the lung by BI 1323495. Lung injury was induced by intratracheal application of 25 µg human NE and haemoglobin concentration as a read-out for lung injury, and neutrophil counts as a read-out for inflammation were measured in bronchioalveolar lavage fluid after 4 hours. Results: BI 1323495 blocked NE in vitro with an IC50 of 0.4 nM and demonstrated a > 4000-fold selectivity versus related proteases cathepsin G and proteinase 3. BI 1323495 fully inhibited the activity of NE released by zymosan-stimulated human neutrophils with a mean IC50 of 1 nM. Treatment of mice with an oral formulation of BI 1323495 attenuated lung damage and inflammation induced by intratracheal instillation of human recombinant NE with an ED50 of 1.9 mg/kg. Conclusions: BI 1323495 is a very potent and highly selective inhibitor of human NE with in vivo efficacy.