Marco A.S. Baptista¹, Kalpana M. Merchant¹, Sakshi Bharghava², Diane Bryce³, Michael Ellis³, Anthony A. Estrada⁴, Matthew Fell³, Reina N. Fuji⁴, Paul Galatsis², Sue Hill³, Warren D. Hirst², Christopher Houle², Matthew Kennedy³, Xingrong Liu⁴, Matthew Maddess³, Carrie Markgraf³, Hong Mei³, Elie Needle², Stefan Steyn², Zhizhang Yi³, Honghsi Yu³, Brian K. Fiske¹, and Todd B. Sherer¹

¹MJFF^{, 2}Pfizer^{, 3}Merck^{, 4}Genentech

Leucine-rich repeat kinase 2 (LRRK2) mutations are the most common cause of genetic Parkinson's disease (PD), accounting for 1-2% of all cases and up to 40% in some ethnic groups. Several mutations in LRRK2 increase kinase activity and have been shown to be neurotoxic, hence the interest in the discovery and development of drugs that inhibit the kinase activity of LRRK2 to slow the progression of PD. To this end, Fuji et al. (2015) recently undertook and reported the results of toxicology studies of two LRRK2 kinase inhibitors (GNE-7915 and GNE-0877) in non-human primates (NHPs). Abnormal accumulations of lamellar bodies in type II pneumocytes were seen with both inhibitors after 7- and/or 29 days of daily dosing. The present study was undertaken with two major aims: (a) to confirm that the lung effect was not chemotype-specific and therefore mediated by inhibition of LRRK2 kinase activity, by testing LRRK2 kinase inhibitors of very distinct structural classes (PFE-360 and MLi-2), and (b) to assess the reversibility of the lung finding by evaluating NHP lungs after 2 weeks off dosing of GNE-7915. PFE-360 and MLi-2 were administered to cohorts at two dose levels for two weeks. GNE-7915 was administered at one dose level for two weeks as positive control, with one cohort evaluated after a 2-week dose-free period. The low doses of PFE-360 and MLi-2 targeted kinase inhibition similar to that reported for the GNE-7915 dose, and the high doses targeted 10x kinase inhibition. All three LRRK2 kinase inhibitors reduced pSer935 in the lungs by >90% at all doses tested (at Cmax). However, the same mild type II pneumocyte change was only observed at the high doses of PFE-360 and MLi-2. GNE-7915 also induced the effect as expected; importantly, absence of the lung change was seen after two weeks off dosing. Overall, these data indicate that the lung pathology is an on-target effect of LRRK2 kinase inhibition, but reversible. Encouragingly, we also observed that it was possible to inhibit brain LRRK2 kinase activity with the lower doses of PFE-360 and MLi-2 without producing the lung effect. Currently, we are investigating whether the abnormal lung morphology is associated with pulmonary functional deficits as this information is essential in assessing respiratory system risk and in informing the monitoring of this potential lung safety liability in patients.