Characterization of the Onset, Progression, and Reversibility of Morphological Changes in Mouse Lung after Pharmacological Inhibition of Leucine-Rich Kinase 2 Kinase Activity.

Gain-of-function mutations in leucine-rich kinase 2 (LRRK2) are associated with increased incidence of Parkinson disease (PD); thus, pharmacological inhibition of LRRK2 kinase activity is postulated as a disease-modifying treatment of PD. Histomorphological changes in lungs of nonhuman primates (NHPs) treated with small-molecule LRRK2 kinase inhibitors have brought the safety of this treatment approach into question. Although it remains unclear how LRRK2 kinase inhibition affects the lung, continued studies in NHPs prove to be both cost- and resource-prohibitive. To develop a tractable alternative animal model platform, we dosed male mice in-diet with the potent, highly selective LRRK2 kinase inhibitor MLi-2 and induced histomorphological changes in lung within 1 week. Oral bolus dosing of MLi-2 at a frequency modeled to provide steady-state exposure equivalent to that achieved with in-diet dosing induced type II pneumocyte vacuolation, suggesting pulmonary changes require sustained LRRK2 kinase inhibition. Treating mice with MLi-2 in-diet for up to 6 months resulted in type II pneumocyte vacuolation that progressed only modestly over time and was fully reversible after withdrawal of MLi-2. Immunohistochemical analysis of lung revealed a significant increase in prosurfactant protein C staining within type II pneumocytes. In the present study, we demonstrated the kinetics for onset, progression, and rapid reversibility of chronic LRRK2 kinase inhibitor effects on lung histomorphology in rodents and provide further evidence for the derisking of safety and tolerability concerns for chronic LRRK2 kinase inhibition in PD. SIGNIFICANCE STATEMENT: We have defined a mouse model by which the on-target lung effects of leucine-rich kinase 2 (LRRK2) kinase inhibition can be monitored, whereas previous in vivo testing relied solely on nonhuman primates. Data serve to derisk long-term treatment with LRRK2 kinase inhibitors, as all lung changes were mild and readily reversible.