Evaluation of novel LOXL2-selective inhibitors in models of pulmonary fibrosis

Background: Increased tissue stiffness is a consequence and a driver of fibrosis. Tissue stiffness is modulated by the lysyl oxidase (LOX) family of enzymes, which cross-link collagen and elastin fibres. Increased expression of LOX-like-2 (LOXL2) is associated with the development of fibrosis and therefore a therapeutic target. We have profiled novel orally bioavailable LOXL2-selective small molecule inhibitors in in vitro and in vivo models of lung fibrosis. Methods: In the in vitro model, lung fibroblasts from IPF patients were cultured under optimised conditions for mature collagen matrix deposition. Following TGF-β1 treatment, multicellular foci formed which were histochemically similar in organization to fibroblastic foci in vivo (Jones et al., AJRCCM 191;2015:A4912). Transient overexpression of active TGF-β1 by adenovector gene transfer in rat lungs results in severe progressive fibrosis (Sime et al JCI 1997;100:768–776). The effects of treatment with a LOXL2-selective inhibitor (days 2-28) on histology and lung function were assessed at day 28. Results: Treatment with LOXL2-selective inhibitors dose-dependently reduced cross-link formation, altered the organisation of collagen matrix and reduced matrix stiffness (assessed by parallel plate compression) in the in-vitro model. In vivo, treatment at 15 or 30 mg/kg significantly lowered lung elastance compared to vehicle control from 2.2 (0.39) to 1.7 (0.31) or 1.6 (0.31) respectively (mean (SD) cmH2O/ml; p<0.05/0.01) and reduced Ashcroft fibrosis score (p<0.01). Conclusions The results suggest that inhibition of LOXL2 using these novel inhibitors has the potential to improve lung function in patients with lung fibrosis by reducing tissue stiffness.