Research ArticleParkinson’s Disease

LRRK2 inhibitors induce reversible changes in nonhuman primate lungs without measurable pulmonary deficits

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Science Translational Medicine  22 Apr 2020:
Vol. 12, Issue 540, eaav0820
DOI: 10.1126/scitranslmed.aav0820

Parsing the side effects of LRRK2 inhibitors

Preclinical studies have raised concerns about the safety of LRRK2 inhibitors—developed for treating Parkinson’s disease—specifically regarding lung function. Baptista et al. now report that several different LRRK2 inhibitors induce on-target histopathological changes in the lungs of nonhuman primates. However, they show that these morphological changes were reversible after drug withdrawal and had no effect on pulmonary function as demonstrated by a battery of lung function tests. These findings suggest that LRRK2 inhibitor–induced effects on lung tissue should not prevent the clinical testing of these compounds.

Abstract

The kinase-activating mutation G2019S in leucine-rich repeat kinase 2 (LRRK2) is one of the most common genetic causes of Parkinson’s disease (PD) and has spurred development of LRRK2 inhibitors. Preclinical studies have raised concerns about the safety of LRRK2 inhibitors due to histopathological changes in the lungs of nonhuman primates treated with two of these compounds. Here, we investigated whether these lung effects represented on-target pharmacology and whether they were reversible after drug withdrawal in macaques. We also examined whether treatment was associated with pulmonary function deficits. We conducted a 2-week repeat-dose toxicology study in macaques comparing three different LRRK2 inhibitors: GNE-7915 (30 mg/kg, twice daily as a positive control), MLi-2 (15 and 50 mg/kg, once daily), and PFE-360 (3 and 6 mg/kg, once daily). Subsets of animals dosed with GNE-7915 or MLi-2 were evaluated 2 weeks after drug withdrawal for lung function. All compounds induced mild cytoplasmic vacuolation of type II lung pneumocytes without signs of lung degeneration, implicating on-target pharmacology. At low doses of PFE-360 or MLi-2, there was ~50 or 100% LRRK2 inhibition in brain tissue, respectively, but histopathological lung changes were either absent or minimal. The lung effect was reversible after dosing ceased. Lung function tests demonstrated that the histological changes in lung tissue induced by MLi-2 and GNE-7915 did not result in pulmonary deficits. Our results suggest that the observed lung effects in nonhuman primates in response to LRRK2 inhibitors should not preclude clinical testing of these compounds for PD.

INTRODUCTION

Parkinson’s disease (PD) is the second most common age-related neurodegenerative disorder that is characterized by the loss of nigrostriatal dopaminergic neurons and accumulation of intracellular protein aggregates in cellular structures called Lewy bodies (1). With an aging population, the prevalence of PD worldwide and the associated health care burden is expected to increase exponentially (2). Currently available drugs primarily augment dopaminergic neurotransmission to treat motor symptoms of PD, but do not affect the progression of the disease. Thus, there remains an urgent need to develop disease-modifying therapies for PD.

Genetic studies have provided valuable insights into the pathogenesis of PD and suggested new drug targets (3). One such target is leucine-rich repeat kinase 2 (LRRK2), which has attracted much interest from the pharmaceutical industry for several reasons. First, point mutations in the LRRK2 gene represent the most common cause of genetic forms of PD (4). Second, these pathogenic mutations increase kinase activity, which is required for neuronal toxicity (5, 6). Third, common variants in the LRRK2 gene locus are risk factors for PD (7, 8), implicating a possible role for aberrant LRRK2 kinase activity in more common idiopathic forms of PD. Last, LRRK2 contains a kinase domain that offers a druggable pharmacological target for drug development. Concerns around potential safety of LRRK2-targeted therapies have emerged due to studies of rodent models of LRRK2 genetic deficiency, which show age-dependent emergence of pathological phenotypes in kidney and lung tissue (912). Furthermore, repeated dosing of nonhuman primates with two LRRK2 kinase inhibitors (GNE-7915 and GNE-0877) induced microscopic morphological changes in the lung similar to those observed in the rodent genetic models (13).

To investigate the implications of possible lung effects on therapeutic development of LRRK2 inhibitors, we designed a toxicology study and a pulmonary function study in nonhuman primates to answer several questions (fig. S1). First, we asked whether the observed lung effects were attributable to on-target LRRK2 kinase inhibition or to an off-target effect of the test compound. A previous study by Fuji et al. (13) tested two structurally similar LRRK2 inhibitors. Here, we compared the effects in nonhuman primates of GNE-7915 (positive control) with those of two additional LRRK2 inhibitors (MLi-2 and PFE-360) whose structures and off-target activities were distinct from each other and from GNE-7915 (fig. S1 and Table 1). Second, we sought to determine whether a safety margin for the lung effect could be observed. To address this, we tested MLi-2 and PFE-360 at two doses to determine whether a no-effect dose for the lung could be identified concurrently with adequate LRRK2 inhibition in brain tissue. Third, we asked whether the lung changes associated with LRRK2 inhibition were reversible by including a dose-free recovery arm for GNE-7915 and MLi-2. Last, we investigated whether the dosing regimen for GNE-7915 and MLi-2 that induced the lung phenotype also induced measurable functional deficits in a range of pulmonary function tests in nonhuman primates. The specific suite of pulmonary function tests selected was similar to those used in humans to assess lung function. The findings from the present study could inform the clinical safety monitoring of LRRK2 inhibitors in clinical trials. Of note, pulmonary safety and tolerability of an inhaled levodopa formulation, CPT-301, used a subset of the pulmonary function tests used here (14).

Table 1 Dosing regimens for LRRK2 inhibitors and associated plasma exposures.

The dosing regimen for each compound was selected on the basis of PK-PD studies conducted by the pharmaceutical companies. Expected versus observed exposure multiples for each test compound are shown.

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RESULTS

Dose selection for three different LRRK2 inhibitors

The three LRRK2 inhibitors we tested have varying potencies and pharmacokinetics (PK) in nonhuman primates (fig. S1 and Table 1). To be able to directly compare their toxicological effects, we selected dosing regimens targeted to produce unbound plasma exposures in the nonhuman primates that were a fixed multiple of the in vivo potency of each compound for inhibition of LRRK2 kinase activity in the mouse brain. The in vivo potency was based on inhibition of phosphorylation of serine residue 935 (Ser935) in the mouse brain, a commonly used marker of LRRK2 activity (15). Thus, PK data in nonhuman primates generated by each of the companies providing the three LRRK2 inhibitors and unbound plasma exposures associated with the half maximal inhibitory concentration (IC50) for mouse brain pSer935-LRRK2 inhibition (fig. S1) were used to predict exposure multiples at a specific dose using the following equation: predicted nonhuman primate unbound plasma area under the curve (AUC) over 24 hours divided by the unbound concentration equal to IC50 for pS935-LRRK2 inhibition in the mouse brain × 24 hours. Dosing regimens (Table 1) targeted 1× and 10× plasma exposure multiples at the low and high doses, for both MLi-2 and PFE360. The dose regimen for the GNE-7915 positive control was the same as that used in Fuji et al. (13).

Both MLi-2 and PFE-360 showed dose-related increases in plasma AUC in male and female cynomolgus macaques (Table 1). For PFE-360, the observed unbound plasma AUC resulted in calculated exposure multiples of 1 to 1.2× and 8.1 to 10.2× for the 3- and 6-mg/kg dose groups, which was close to the targets of 1 and 10×, respectively. In contrast, the observed unbound plasma AUCs for MLi-2 resulted in higher than the 1 and 10× multiples targeted (Table 1). Thus, MLi-2 produced plasma exposure multiples of 9.5 to 16.9× at the low dose and 45.5 to 64.8× at the high dose. In preparation for this study, scientists at Merck conducted several single-dose PK studies of MLi-2 in nonhuman primates, exploring various vehicle formulations with the goal of identifying a dose and formulation that would achieve the target exposures. Unfortunately, these PK experiments showed inter-animal variability in plasma exposures, and a decision was made to move forward with the planned study using 15 and 50 mg/kg to minimize the risk of a failed study due to underexposure of drug in plasma. For GNE-7915, the observed plasma exposure multiple was 2 to 3.2×, which was higher than the targeted 1× exposure multiple (Table 1).

Repeat-dose toxicological assessments in macaques

All compounds were well tolerated, and clinical observations in the GNE-7915–treated animals were similar to those previously reported (13). Lungs of animals administered GNE-7915 [30 mg/kg per dose; oral administration (PO), twice daily (BID)] or higher doses of MLi-2 [50 mg/kg; PO, once daily (QD)] and PFE-360 (6 mg/kg; PO, QD) showed slight increases in cytoplasmic vacuolation of type II lung pneumocytes (Fig. 1). This lysosomal effect in type II lung pneumocytes was consistent with the effect previously seen with GNE-7915 (13). None of the animals treated with lower doses of MLi-2 (15 mg/kg; QD) or PFE-360 (3 mg/kg; QD) showed the lung phenotype in this study (Fig. 1). Two weeks after the cessation of GNE-7915 dosing, type II pneumocyte vacuolation returned to baseline, indicating that the type II pneumocyte phenotype was reversible (Fig. 1). Our study established no-effect doses for both MLi-2 and PFE-360. Importantly, neither kidney nor brain tissue showed any histopathological or macroscopic changes in response to the three LRRK2 inhibitors (table S1). Notably, amounts of total and unbound compound were similar in the kidneys and lungs (table S2), but histological changes were not seen in the kidneys within the time frame of this study. Although the unbound compound concentrations in the brain were lower than those in the lungs and kidneys, they met or exceeded the targeted exposure multiples for each compound (Table 1).

Fig. 1 LRRK2 inhibitors induce a reversible phenotype in macaque lung pneumocytes.

(A to G) Shown are representative images of hematoxylin and eosin (H&E)–stained sections of macaque lung obtained 4 hours after the last treatment: (A) vehicle control, (B) GNE-7915 (30 mg/kg, BID), (C) GNE-7915 treatment followed by a 2-week recovery, (D) low-dose MLi-2 (15 mg/kg, QD), (E) high-dose MLi-2 (50 mg/kg, QD), (F) low-dose PFE-360 (3 mg/kg, QD), and (G) high-dose PFE-360 (6 mg/kg, QD). Black arrows indicate abundant vacuolated cytoplasm of type II lung pneumocytes in H&E-stained lung sections from macaques treated with GNE-7915 (B), or high-dose MLi-2 (E) or PFE-360 (G), compared to vehicle control (A). In lung sections from vehicle control–treated animals, type II pneumocytes (black arrows) exhibited relatively small amounts of cytoplasm and lacked large vacuoles. The appearance of pneumocytes in vehicle control–treated lung was comparable to that seen in lung sections from animals treated with low-dose MLi-2 (D) or PFE-360 (F) or GNE-7915 (30 mg/kg, BID) with a 2-week recovery. Scale bars, 30 μm (A to G). (H and I) Shown are representative transmission electron microscopic ultrastructural images of type II pneumocytes in lung sections from a vehicle-treated control macaque (H) and an animal treated with high-dose MLi-2 (50 mg/kg, QD) (I). A qualitative increase in size and number of lamellar bodies (black arrows) was found in lung pneumocytes of the drug-treated macaque. Scale bars, 1 μm (H and I).

To further characterize the lung changes in response to drug treatment, we examined tissues from a subset of animals by transmission electron microscopy. We examined tissues from a total of five animals: one male from the vehicle control group and one male plus one female each from the high-dose PFE-360 and high-dose MLi-2 groups. In the vehicle-treated animal (Fig. 1H), type II lung pneumocytes exhibited a typical ultrastructural appearance with the presence of cytoplasmic lamellar bodies characterized by membrane-bound vacuoles containing concentric laminations of electron-dense membranous material (16). Similar to the findings with hematoxylin and eosin (H&E) staining of lung tissue (Fig. 1, A to G), animals treated with MLi-2 at 50 mg/kg or PFE-360 at 6 mg/kg showed a qualitative increase in the number and size of lamellar bodies in type II pneumocytes (Fig. 1, E and G, and table S1). Despite this prominent morphological finding, there were no ultrastructural results indicative of lung degeneration. Thus, the ultrastructural data confirmed the light microscopic observation of increased vacuolation in type II pneumocytes after treatment with the higher doses of MLi-2 and PFE-360.

Target inhibition of LRRK2 in macaque lung, brain, and peripheral blood mononuclear cells

All three compounds tested were able to inhibit LRRK2 kinase activity in macaque lung and brain tissue ex vivo and in macaque peripheral blood mononuclear cells (PBMCs), as assessed by a reduction in the ratio of pSer935-LRRK2 to total LRRK2 (Fig. 2, A to C, and data file S1). In the macaque lung and PBMCs, LRRK2 kinase activity was completely inhibited by GNE-7915, MLi-2, and PFE-360 at all doses tested (Fig. 2, A and B). In the brain, GNE-7915 and MLi-2 (15 and 50 mg/kg, QD) and PFE-360 (6 mg/kg, QD) reduced the ratio of pSer935-LRRK2 to total LRRK2, but only a partial reduction in this ratio was seen at the low dose of PFE-360 (3 mg/kg, QD) (Fig. 2C). After a 2-week withdrawal of GNE-7915, the amount of pSer935-LRRK2 in the lung, PBMCs, and brain returned to levels comparable to those of the vehicle-treated control group (Fig. 2, A to C). Treatment with all three LRRK2 kinase inhibitors produced variable but statistically significant reductions in total LRRK2 in the brain and PBMCs but not in the lungs (Fig. 2, D to F; P < 0.05).

Fig. 2 Effect of LRRK2 inhibitors on pSer935-LRRK2 in macaque lung, PBMCs, and brain.

(A to F) The ratio of pSer935-LRRK2 to total LRRK2 and the ratio of total LRRK2 to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were measured 4 hours after the last drug treatment to evaluate LRRK2 inhibition. Shown is the ratio of pSer935-LRRK2 to total LRRK2 (A to C) and total LRRK2 to GAPDH (D to F) for macaque lung, PBMCs, and brain after 15 days of dosing with vehicle, GNE-7915 (30 mg/kg, BID), MLi-2 (15 and 50 mg/kg, QD), or PFE-360 (3 and 6 mg/kg, QD). (G to I) Representative Western blots are shown for macaque lung (G), PBMCs (H), and brain (I) after treatment with vehicle, GNE-7915 (30 mg/kg, BID, with or without a 2-week recovery), MLi-2 (15 or 50 mg/kg, QD), or PFE-360 (3 or 6 mg/kg, QD). The loading order is different for (H). Data are mean ± SEM; n = 4 to 8 animals per treatment group. *P < 0.05, **P < 0.01, ***P < 0.001 compared to vehicle-treated control animals [one-way analysis of variance (ANOVA) followed by Dunnett’s multiple comparison test].

Given that pSer935 does not represent a direct phosphorylation site of LRRK2, we also evaluated pThr73 Rab10, a bona fide substrate for LRRK2 (17). All three LRRK2 inhibitors reduced pThr73 Rab10 as assessed by a protein phosphorylation assay that specifically traps phosphorylated proteins (Phos-tag) in the lung without affecting total Rab10 (fig. S2 and data file S1). Notably, both low and high doses of MLi-2 and PFE-360 produced similar reductions in pThr73 Rab10 in lung tissue (fig. S2 and data file S1). As with LRRK2 pSer935, we saw recovery of pThr73 Rab10 to levels seen in vehicle-treated control animal lung tissue 2 weeks after withdrawal of GNE-7915 (fig. S2).

Correlating unbound drug plasma concentrations with IC50 for pSer935-LRRK2 inhibition in mouse brain

Neither the observed drug plasma exposures at multiple doses (Table 1) nor the target inhibition data (Fig. 2 and fig. S2) completely explained the observation that the lung effect was seen only in the GNE-7915 group and high-dose MLi-2 and PFE-360 groups. To investigate whether lung changes could be due to the duration of LRRK2 inhibition during the dosing cycle, we examined the relationship between unbound plasma exposure–time profiles to the unbound plasma IC50 for pSer935-LRRK2 inhibition in mouse brain for each compound (Fig. 3 and data file S2). These data show that the minimum unbound plasma concentration (Cmin) in the nonhuman primates for GNE-7915 remained above its IC50 for brain target inhibition (pS935-LRRK2) over the course of 24 hours. In contrast, regression analyses of toxicokinetic data indicated that the time during which unbound drug plasma exposures remained at or above the IC50 for the low doses of MLi-2 (15 mg/kg, QD) and PFE-360 (3 mg/kg, QD) was 17 and 8.5 hours, respectively. Notably, animal #105235 in the high-dose MLi-2 group did not show a lung effect and had drug plasma exposures that appeared to fall below its IC50 of 0.8 nM at a time point under 17 hours (Fig. 3). Considering the shape of the concentration-time profiles in the terminal phase of drug treatment (Fig. 3), the 17-hour threshold may be an overestimate of the actual time at which the free plasma concentration of drug fell below the IC50. These data led us to hypothesize that the lung effect of the three LRRK2 inhibitors was likely to be mediated by Cmin and its relationship to the IC50 for brain target inhibition.

Fig. 3 Correlation of unbound drug concentration in macaque plasma and IC50 for pSer935-LRRK2 inhibition in mouse brain.

The drug concentration–time profile (mean ± SEM) for unbound drug concentration in macaque plasma is shown for GNE-7915 (A), MLi-2 (B), and PFE-60 (C) after 15, 14, and 14 days of treatment, respectively. The closed symbols represent data from n = 4 animals for all groups except for the MLi-2 15 mg/kg (B) data point at 24 hours, which is n = 1. For both doses of PFE-360 (C), the plasma drug concentration at the zero time point was below the level of quantification. Dotted lines and open symbols represent extrapolated values using log-linear regression of the observed drug concentration data from 2 to 7 hours. Regression analysis was applied because the majority of animals in these groups had plasma drug concentrations less than the lower limit of quantification at 24 hours of dosing. For GNE-7915 treatment, (A) the drug plasma exposure modeling took into account PK data from day 8. The dashed line in each panel represents the unbound IC50 for pSer935-LRRK2 in mouse brain for each of the three compounds. (D) shows an unbound drug plasma concentration–time profile for four individual animals treated with QD MLi-2 (50 mg/kg). Note that animal #I05235 (orange line) did not exhibit vacuolation of type II lung pneumocytes and showed the shortest duration (18 hours) during which MLi-2 plasma exposures were above the IC50 for pSer935-LRRK2 in mouse brain. The 18-hour threshold was estimated by log-linear regression from 7 to 24 hours. Considering the shape of the concentration-time profile, 18 hours is likely to be an overestimate of the actual time during which the free plasma drug concentration fell below the IC50.

Di-22:6-bis(monoacylglycerol)phosphate concentrations in macaque biofluids and tissues

Previous studies (13) showed that genetic deletion of LRRK2 or pharmacological inhibition of LRRK2 kinase activity by GNE-7915 reduced the amount of the phospholipid di-22:6-bis(monoacylglycerol)phosphate (di-22:6-BMP) in the urine of nonhuman primates. BMPs are phospholipids localized exclusively in the inner membranes of late endosomes where they play a central role in the degradation of lipids and membranes by lysosomes (18). BMP production is altered in lysosomal storage disorders (19), suggesting that BMP species could serve as markers of lysosomal function.

Consistent with the previous study (13), we observed a decrease in di-22:6-BMP in the urine of nonhuman primates treated with GNE-7915 compared to animals treated with vehicle control. Similarly, in the high-dose groups of PFE-360 and MLi-2, di-22:6 BMP was decreased compared to the vehicle control group at the end of the dosing period (Fig. 4 and data file S3). Following the 2-week dose-free interval for animals administered GNE-7915, di-22:6-BMP returned to baseline ranges, indicating that the decrease was reversible. In contrast to urine, di-22:6-BMP amounts in plasma, brain, lung, and kidney tissues were highly variable and failed to show a consistent pattern of changes induced by LRRK2 inhibitor treatment (data file S3).

Fig. 4 Concentration of di-22:6-BMP in macaque urine.

The concentration of di-22:6-BMP in urine is shown for 28 macaques before dosing (blue circles) and after 15 days of dosing (red squares) with vehicle, GNE-7915 (30 mg/kg, BID), PFE-360 (3 and 6 mg/kg, QD), and MLi-2 (15 and 50 mg/kg, QD). In the GNE-7915–treated group and high-dose PFE-360– and MLi-2–treated groups, di-22:6 BMP in urine was decreased compared to the vehicle control group. The urine concentration of di-22:6-BMP returned to baseline after a 2-week dose-free recovery interval for the GNE-7915–treated group (purple triangles). Unpaired t test, **P < 0.01 and *P < 0.05.

Effects of MLi-2 and GNE-7915 on lung morphology and function

In a separate cohort of cynomolgus macaques, we administered high and low doses of MLi-2 (15 and 50 mg/kg, QD) daily for 15 days and evaluated the effects of drug treatment on lung function during the dosing phase and after a 2-week recovery phase (fig. S3).

On day 15, a subset of eight animals (four per group) was analyzed for lung histopathology. All four animals treated with high doses of MLi-2 (50 mg/kg) showed a widespread increase in cytoplasmic vacuolation of type II lung pneumocytes similar to the changes observed in our earlier studies (table S3) (13). Pathological examination graded these alterations as minimal in three animals and mild in one animal. In contrast, two out of the four animals administered low doses of MLi-2 (15 mg/kg) showed cytoplasmic vacuolation of type II pneumocytes (table S3). After the 13-day recovery period, histological examinations of lungs of each animal in both the high- and low-dose groups were unremarkable, indicating complete recovery from the lung effect, as was reported in previous studies with GNE-7915 (13). Minimal to mild vacuolation of type II pneumocytes was observed in all eight GNE-7915–dosed animals, as expected (table S3).

Lung function tests were conducted at four different time points: baseline (day 0), day 7 and day 15 of dosing, and day 28, which was 2 weeks after treatment withdrawal. Neither dose of MLi-2 affected DLCO or elasticity of the lung, as determined by quasi-static lung compliance (Cqs) in the insufflation pressure range of 0 to 10 cm H2O (Cqs10) (Fig. 5, A and B, and data file S4). Similarly, MLi-2 treatment did not affect forced vital capacity (FVC), forced expiratory volume (FEV), forced expiratory flow, or mean mid-expiratory flow (MMEF) (Fig. 5C and data file S4). MLi-2 treatment also had no apparent effect on ventilator capacity as determined by forced expiratory flow testing given the lack of change over time and that ventilator capacity values in treated animals generally fell within the range of variability (data file S4). We also tested GNE-7915 (30 mg/kg, BID) at baseline and day 7 and day 15 of treatment. As with MLi-2 treatment, animals treated with GNE-7915 did not differ from the vehicle control group in any of the tests administered (data file S4).

Fig. 5 Lung function tests in macaques treated with MLi-2.

Thirty-six macaques were treated with two doses of MLi-2 (15 and 50 mg/kg) (green and blue) or vehicle control (black) for 15 days, and lung function tests were performed at days 7, 15, and 28. (A) Shown is the lung diffusion capacity for carbon monoxide (DLCO) test. (B) Shown is lung elasticity determined by Cqs in the insufflation pressure range of 0 to 10 cm H2O (Cqs10). (C) Shown is forced vital capacity (FVC), the lung volume obtained from a forced expiratory maneuver.

Effects of MLi-2 and GNE-7915 on phosphatidylcholine in bronchoalveolar lavage fluid

The amount of alveolar phosphatidylcholine in lung provides an index of surfactant secretion (20). Hence, we measured this phospholipid in bronchoalveolar lavage of treated animals. The amount of phosphatidylcholine did not differ between MLi-2–treated and vehicle-treated control animals, suggesting that the compound did not alter surfactant release in the lung (Fig. 6 and data file S5). MLi-2 treatment had no effect on nucleated cell counts in bronchoalveolar lavage fluid, suggesting that there was no inflammatory response. Although some variability in phosphatidylcholine amounts was noted at the low dose (15 mg/kg) of MLi-2, the absence of a dose-response relationship indicated that it was not due to LRRK2 inhibition.

Fig. 6 Effect of MLi-2 on phosphatidylcholine in macaque bronchoalveolar lavage fluid.

Bronchoalveolar lavage (BAL) fluid was collected from 36 macaques at baseline (day 0 of drug treatment), at days 7 and 15 of drug treatment, and from 24 macaques on day 28 (2 weeks after drug withdrawal). Total phosphatidylcholine in BAL fluid at baseline (n = 12 per group), day 7 (n = 12 per group), day 15 (n = 12 per group), and day 28 (n = 8 per group) is shown as mean ± SEM, *P < 0.05; **P < 0.01; two-way ANOVA and Bonferroni’s multiple comparison test.

Toxicokinetic and target inhibition data from macaques subjected to lung function tests

For both MLi-2 and GNE-7915, exposure multiples were calculated using the observed unbound AUC at 0 to 8 hours and unbound IC50 for pSer935-LRRK2 over 8 hours. Consistent with the toxicokinetic data from the histology study (Table 1), MLi-2 and GNE-7915 exposures measured on day 8 exceeded the targeted exposures and were within the range of those seen in the histology study. Thus, the unbound AUC for MLi-2 was 20× at low dose and 35× at the high dose. For GNE-7915, the observed AUC for unbound drug in the plasma resulted in the exposure multiple of 2×.

Using a phospho-specific antibody, we assessed the amount of pThr73 Rab10 in lung tissue from animals dosed with vehicle or GNE-7915 (30 mg/kg) twice daily for 15 days. The amount of pThr73 Rab10 was decreased in lung samples from GNE-7915–dosed animals compared to vehicle-treated control animals, whereas the amount of total Rab10 was comparable between the two groups (Fig. 7 and data file S6). These data demonstrate inhibition of LRRK2 activity in animals dosed with GNE-7915 and demonstrate that pThr73 Rab10 could be useful as a pharmacodynamic readout of LRRK2 activity in vivo.

Fig. 7 GNE-7915 decreases pThr73 Rab10 in macaque lung.

(A) Western blot analysis of macaque lung was performed using a phospho-specific antibody against pThr73 Rab10. pThr73 Rab10 was assessed in cultured A549 cells [wild type (wt), Rab8a knockout and Rab10 knockout] to show specificity of the anti–pThr73 Rab10 antibody. Lysate from human embryonic kidney 293T cells co-expressing hemagglutinin-tagged Rab10 and FLAG-tagged LRRK2-R1441C were used as a positive control (Ctrl). β-Actin was the loading control. (B to D) pThr73 Rab10, total Rab10, and β-actin were quantified and normalized to the signal measured in vehicle control samples. Shown is quantification of pThr73 Rab10 relative to β-actin (B), pThr73 Rab10 relative to total Rab10 (C), and total Rab10 relative to β-actin (D) for 6 to 8 macaques treated twice daily with vehicle control (n = 6) or GNE-7915 (30 mg/kg; n = 8). Mean ± S.E.M., ****P < 0.0001, Student’s t test.

DISCUSSION

Our study described here represents an exploratory toxicological evaluation in nonhuman primates of three structurally distinct LRRK2 inhibitors with distinct off-target activity profiles, with a focus on lung effects that have been previously reported (13). The overarching aim was to provide further clarity on the potential lung safety risks and functional implications associated with clinical development of compounds targeting LRRK2. Here, we demonstrate that 2-week dosing with three different LRRK2 inhibitors induced a similar response in the lungs of cynomolgus macaques. The lung effect was characterized by a minimal to mild increase in vacuolation of type II lung pneumocytes that correlated ultrastructurally with an increase in size and number of cytoplasmic lamellar bodies in the absence of any associated lung degenerative findings. These data confirm previous studies (13) and support the notion that this lung effect is a consequence of LRRK2 inhibition. Several additional sets of data further clarify the potential safety risk of LRRK2 inhibitors. First, kidney tissue from treated animals did not show any histopathological or macroscopic changes in response to any of the compounds administered, in contrast to what has been reported in Lrrk2-deficient mice (12) and in rats treated with the PFE-360 LRRK2 inhibitor (21). Notably, no changes were observed in brain tissue, indicating that the lung is the most sensitive target organ in nonhuman primates treated with LRRK2 inhibitors. Second, we identified a clear no-effect dose of PFE-360 by demonstrating that PFE-360 inhibited LRRK2 activity by ~50% in the nonhuman primate brain without producing changes in the lung. This effect was achieved at unbound drug plasma exposures in the range of the in vivo IC50 for pSer935-LRRK2 inhibition in mouse brain. We also observed a no-effect dose in the first cohort of MLi-2–treated animals. However, the second cohort of MLi-2–treated animals showed that the low dose may be at the threshold of the no-effect dose because two of the four macaques showed evidence of lung pneumocyte vacuolation. However, the low dose of MLi-2 produced a >20× plasma exposure multiple, which exceeded the intended target of 1×. In addition, the low dose of MLi-2 produced complete inhibition of pSer935-LRRK2 in macaque brain, suggesting that at lower doses of MLi-2, brain LRRK2 inhibition may be achievable without the lung effect. Although the amount of LRRK2 inhibition in the brain required to produce clinically meaningful effects remains unknown, the ability to show the potential for a margin of safety at doses that inhibit brain LRRK2 kinase activity has important implications for ongoing and future clinical trials. Third, a 2-week withdrawal from treatment with either GNE-7915 or MLi-2 resulted in recovery from the type II pneumocyte vacuolation effect. Last, a battery of clinically relevant pulmonary function tests in nonhuman primates treated with MLi-2 or GNE-7915 at doses that produced the vacuolation changes in lung had no impact on pulmonary function or surfactant secretion. Together, these data provide additional characterization of the potential mechanism-based liability of LRRK2 kinase inhibitors and should help to guide the preclinical and clinical development path for this class of compounds.

PFE-360, MLi-2, and GNE-7915 are chemically distinct LRRK2 inhibitors that have minimal overlap in their off-target activity (fig. S1) (15, 2225). Thus, a comparison of these three compounds offered us an opportunity to assess whether the lung phenotype might be mediated through LRRK2 inhibition or other compound-specific off-target pharmacology. The in vivo IC50 drug plasma concentrations required for inhibition of LRRK2 phosphorylation on serine-935 in wild-type mouse brain were 98, 0.8, and 3.0 nM, respectively, for GNE-7915, MLi-2, and PFE-360 (after correcting for protein binding). There is indirect evidence that pSer935-LRRK2 phosphorylation reflects LRRK2 kinase activity (26). Hence, we selected doses and a dosing regimen for MLi-2 and PFE-360 that were projected from data from nonhuman primate PK studies to achieve drug exposures in plasma that were either 1 to 2× (low dose) or 8 to 10× (high dose) the in vivo IC50 for reduction of pSer935-LRRK2 in mouse brain. GNE-7915 was used as an experimental positive control for this study with dosing similar to that previously reported (13). Toxicokinetic analyses demonstrated that the observed plasma exposures of PFE-360 and GNE-7915 were close to the targeted plasma exposure multiples, whereas those of MLi-2 were much higher. To directly assess whether the drug exposures in plasma achieved were sufficient for LRRK2 inhibition in the brain, pSer935-LRRK2 and total LRRK2 were examined by immunoblotting of striatal lysates from the macaque brain. All three compounds reduced pS935-LRRK2 in the macaque striatum, with the smallest reduction (~50%) observed for the low dose of PFE-360. Small and somewhat variable reduction in total LRRK2 was also observed for animals treated with all three compounds, with greater reductions at higher doses of PFE-360 and MLi-2. Similarly, nonhuman primate lung and PBMCs also showed >90% inhibition of LRRK2 kinase activity in all treatment groups. Thus, the selected dosing regimens resulted in tissue exposures sufficient for LRRK2 inhibition at all doses for all three compounds.

Histopathology of lung tissue from the two macaque cohorts examined here demonstrated replication of the previously observed mild effect on lung in the form of accumulation of lamellar bodies in type II lung pneumocytes in animals treated with GNE-7915 (30 mg/kg) (13). Similar microscopic changes in the type II pneumocytes were observed in nonhuman primates treated with high doses of PFE-360 (6 mg/kg, QD) and MLi-2 (50 mg/kg, QD). These data indicate that the observed effects in lung may be attributable to the on-target (i.e., LRRK2 kinase inhibition) pharmacology of the three compounds. In contrast to the high-dose effect, lower doses of MLi-2 and PFE-360 at plasma exposures that inhibited LRRK2 kinase activity in the nonhuman primate brain produced minimal to no effect in the lungs. These data are consistent with previous findings (13), demonstrating that a lower dose of GNE-7915 did not produce the lung phenotype despite inhibiting LRRK2 kinase activity in the nonhuman primate brain. Thus, it appears that a safety margin for this lung effect would be achievable with brain-penetrant LRRK2 inhibitors.

The observed dose-dependent effects of MLi-2 and PFE-360 on lung histology concurrent with a >90% reduction in pSer935-LRRK2 in the lung at both high and low doses of these compounds raise the question of whether pSer935-LRRK2 is an adequate marker of LRRK2 inhibition. This concern is especially critical given that Ser935 phosphorylation is not induced directly by LRRK2 (26). To circumvent this issue, we assessed a recently identified LRRK2 target (17), Rab10, for phosphorylation on threonine-73 in the lung tissue of treated macaques (brain tissue was not examined as the available antibody was not able to detect brain pThr73 Rab10 at sufficient sensitivity and specificity). Both low and high doses of MLi-2 and PFE-360 produced similar reductions in pThr73 Rab10 in the lungs without affecting total Rab10. These data indicate that target inhibition at a single time point cannot explain the lack of morphological changes observed in the lungs at low doses of MLi-2 and PFE-360. Hence, we investigated whether the duration over which the compound exposures were maintained above their individual in vivo IC50 values correlated with the observed lung changes. This analysis showed that whereas GNE-7915 concentrations in plasma remained above its IC50 for brain target inhibition for 24 hours, the times the concentrations were over the IC50 for the low doses of MLi-2 and PFE-360 were 17 and 8.5 hours, respectively. The argument for the time period over which drug plasma concentrations were greater than the IC50 was further bolstered by the observation that a single animal in the high-dose MLi-2 group achieved lower drug exposure in plasma and also failed to exhibit lung changes. These data raise the question of whether designing a dosing regimen that produces partial inhibition of LRRK2 in the lungs may be a viable strategy to avoid the induction of the cytoplasmic vacuolation in the type II pneumocytes. Of course, it is imperative to demonstrate that this strategy could produce the desired target inhibition and efficacy-predicting endpoints in the brain. It is also noteworthy that pathogenic mutations in LRRK2 increase kinase activity and that emerging data indicate that LRRK2 kinase activity may be higher in individuals with idiopathic PD (27, 28). Thus, restoration of LRRK2 kinase activity to physiological levels rather than more robustly inhibiting its activity may provide a viable therapeutic strategy with the potential of a better margin of safety.

It is critical to note two major weaknesses of the current study. These weaknesses preclude us from reaching firm conclusions regarding the hypothesis that the lung effect may be mediated by the amount of time the drug plasma concentration remained over the IC50 and its implications for dosing regimens. First, this study was principally designed as a toxicological study and was not powered to ask this question robustly. Second, the lung effect was studied only at a single time point (4 hours after the last dose) after daily dosing for 2 weeks. Thus, the time course of the lung effect, associated target inhibition, and drug exposures in plasma at different time points were not studied. Unfortunately, even the PBMCs were collected from animals at that same single time point, precluding the ability to model a PK-PD relationship in the peripheral blood compartment. Although an adequately powered time-course study is important, it is outside the scope of the present study and will require a large number of nonhuman primates, which may be ethically more appropriate for testing a clinical drug candidate rather than the tool compounds tested here.

In addition to the possibility of attaining a margin of safety for the lung effect through careful dosing, we demonstrate here that a relatively short (13 to 14 days) recovery phase results in amelioration of lamellar body accumulation in type II lung pneumocytes induced by GNE-7915 or MLi-2. Future studies will need to investigate the time course of lung recovery from drug-induced changes upon cessation of treatment with LRRK2 inhibitors. It is also noteworthy that kidney tissues were free of any pathological changes, as reported previously (13).

We explored the use of di-22:6-BMP as a marker of LRRK2 inhibitor–induced lung changes. Di-22:6-BMP is a phospholipid localized in the internal membranes of lysosomes and late endosomes where it is thought to participate in the lysosomal degradation pathway (18). Di-22:6-BMP concentrations in the plasma is currently a U.S. Food and Drug Administration–approved biomarker of cationic amphiphilic drug–induced phospholipidosis. We hypothesized that given the similarity of the LRRK2 inhibition–induced lamellar body changes in lung pneumocytes to that induced by iatrogenic phospholipidosis di-22:6-BMP may be useful for monitoring the lung changes in LRRK2 inhibitor–treated macaques. We found no changes in di-22:6-BMP concentrations in plasma, but found a decrease in urine of LRRK2 inhibitor treated animals. The changes in urinary di-22:6-BMP concentrations appeared to reflect an LRRK2 inhibition–driven effect on lysosomal biology. Di-22:6-BMP concentrations in the animal group treated with GNE-7915 that underwent a 2-week dose-free recovery period were within the range of vehicle-treated control animals, providing further evidence that the lysosomal effects in lung due to LRRK2 inhibition were reversible. To demonstrate the utility of di-22:6-BMP as a marker of lung histopathology, additional well-powered studies with multiple drug doses and time courses will be required.

A major objective of our study was to go beyond histopathological analyses and investigate the functional effects of the observed lung changes. Using a comprehensive battery of pulmonary function tests, we showed that LRRK2 inhibition by GNE-7915 or MLi-2 at doses that induced an increase in size or number of lamellar bodies in type II pneumocytes did not disrupt pulmonary function. It is important to point out that the tests used here have clinical correlates that could be used to monitor lung function in clinical studies of LRRK2 inhibitors. However, given the consistency of the lung effect produced by all LRRK2 inhibitors, it would be important to evaluate the involvement of LRRK2 in lung homeostasis on a molecular and cellular level (29).

Our study demonstrated that LRRK2 kinase inhibition produced a minimal to mild nondegenerative, reversible lung phenotype in nonhuman primates after 2 weeks of drug treatment. These changes in the lung were not associated with functional consequences. A safety margin for this effect appeared to be achievable given the demonstration of no-effect doses even with LRRK2 inhibition in the brain. These data suggest that the on-target morphological changes in the lungs of nonhuman primates treated with LRRK2 inhibitors do not preclude advancing LRRK2 inhibitors to the next stage of drug development, including clinical evaluation in individuals with PD. However, the current study does not rule out the potential for other on-target safety issues of LRRK2 kinase inhibition. LRRK2 inhibitors will require further testing in carefully conducted preclinical and clinical studies.

MATERIALS AND METHODS

Study design

A total of 66 cynomolgus (Macaca fascicularis) macaques were used for this study. Animals had free access to water and were fed Certified Primate Diet #2055C (Harlan Laboratories Inc.) one or two times daily and given various cage-enrichment devices and fruits, vegetables, or dietary enrichment for the duration of the study. All procedures performed on animals were in accordance with regulations and established guidelines and were reviewed and approved by an Institutional Animal Care and Use Committee.

The histopathology and toxicology studies were conducted at Covance Laboratories Inc. (Madison, WI) and used 28 macaques (14 males and 14 females, Asian origin, Covance Research Products). Three LRRK2 inhibitors GNE-7915 (Genentech), PFE-360 (Pfizer), and MLi-2 (Merck & Co.) were tested in these histology studies. The independent review of the histology was conducted by four toxicology groups (Covance, Merck & Co., Pfizer, and Genentech), who were not blinded to treatment group but were blinded to each other’s analyses; the groups all independently came to the same conclusions. No data generated from the animals were excluded.

The lung function tests were conducted at the Lovelace Respiratory Research Institute (Albuquerque, NM) using 38 macaques (all females, Chinese origin, Charles River). Only the MLi-2 (Merck & Co.) and GNE-7915 (Genentech) compounds were tested in these studies. For testing of the MLi-2 compound, 36 macaques were randomized into three groups of 12 individuals each to balance the body weight distribution. For GNE-7915 testing, the remaining four animals from each treatment group of the MLi-2 study (n = 12) and two naïve animals from the original cohort were allowed to recover for an additional 28 to 29 weeks. These animals (n = 14) were re-randomized into two groups considering their previous treatment allocation to evenly distribute them into vehicle (n = 6) and GNE-7915 (n = 8) treatment groups. Histology for both MLi-2– and GNE-7915–treated animals was conducted by Lovelace Respiratory Research Institute, Merck & Co., and Genentech, in a similar manner to the histology studies conducted by Covance. No data generated from the animals were excluded.

Repeat-dose toxicological assessment

The in-life phase, necropsy, biospecimen collection, anatomic pathology evaluation, and PK assessment were conducted at Covance Laboratories Inc. All necropsies were conducted at 4 hours after the last dose, the expected maximal plasma concentration (Cmax) of the compounds tested. Studies were conducted in 28 Asian cynomolgus macaques (Macaca fascicularis) aged 3 to 4 years and weighing 2 to 5 kg at the start of the study (Covance Research Products Inc.). The schedule of dosing, monitoring, necropsies, and tissue collections are detailed in table S4.

Doses and dosing regimen

The dose and dosing schedules were based on PK-PD studies and associated modeling of each compound conducted by the participating companies Merck & Co., Genentech, and Pfizer. The in vivo potency of each molecule was determined by assessment of pSer935 reduction in the brains of male C57Bl/6 mice (weighing 20 to 25 g, 8 to 10 weeks old) and data were expressed relative to unbound drug IC50. The IC50 values were then used to calculate exposure multiples in macaques according to the formula: predicted macaque unbound plasma AUC over 24 hours divided by the unbound drug concentrations equal to the IC50 for pS935-LRRK2 reduction in mouse brain over 24 hours. The low doses of MLi-2 and PFE-360 were predicted to produce plasma exposure multiples of at least 1×, similar to that of GNE-7915, and the high doses were targeted to reach exposure multiples of 8 to 10× (Table 1).

Biospecimen collection

Following sample collection for histopathology, additional biospecimens were collected, as detailed in table S1, weighed, snap-frozen in liquid nitrogen, placed on dry ice, and stored at −60° to −80°C until processing for various analyses.

Blood was collected from the femoral artery in separate aliquots. EDTA tubes were used to harvest plasma for analysis of toxicokinetics and the lipid biomarker di-22:6-BMP. PBMCs were obtained from whole blood by density gradient separation using Ficoll-Paque PLUS (Sigma-Aldrich) for studies of target inhibition.

Cerebrospinal fluid (CSF) was collected from the cisterna magna at necropsy at about 4 hours after final dosing to analyze compound concentrations. Urinary aliquots were collected at baseline and about 4 hours after dosing on day 15 and day 28 (recovery phase) for analysis of di-22:6-BMP concentrations.

At necropsy, brain, lungs, and kidneys were collected unilaterally for compound exposures, target inhibition assessment, and analysis of 22:6-BMP.

Compound concentrations in plasma, CSF, and brain tissue

Plasma, CSF, and tissue concentrations of compounds were determined by liquid chromatography–tandem mass spectrometry analyses (LC-MS/MS). The plasma and brain protein binding of test compounds were determined by equilibrium dialysis. All data were expressed relative to unbound compound.

Plasma, urine, lung, kidney, and brain tissues from animals treated with all LRRK2 kinase inhibitors were analyzed for di-22:6-BMP concentrations by LC-MS/MS at Nextcea Inc. (Woburn, MA) using extraction and analysis methods described in (30, 31).

Histopathology

Unilateral lung tissues (right median and diaphragmatic lobes) were collected at necropsy and immersion-fixed in 10% neutral-buffered formalin for at least 2 days, but no more than 3 days of fixation before being transferred to 70% ethyl alcohol. Tissues were then processed to paraffin block and sectioned at 4 to 6 μm for routine H&E staining and examination by light microscopy. Additional samples of lung were also collected in Karnovsky’s fixative and processed for evaluation by transmission electron microscopy as described previously (13).

Histopathological assessment was conducted in a qualitative manner. This is standard practice used in the evaluation of tissues for evidence of toxicity associated with the administration of test articles. This is widely accepted by regulatory authorities and is an efficient method for the identification of test article–related pathology similar to that described in this manuscript. Although quantitative methods are available and can sometimes provide useful supplementary information, the value of this type of data depends on the nature of the pathologic finding as well as the degree to which these data are needed to support the overall goals of the study. Quantitative assessment of this particular lung finding has been conducted previously (13), although in that instance, the goal was to thoroughly characterize a newly identified lung lesion that had just been identified as potentially being LRRK2 related. Since then, our experience in characterizing this lung effect has demonstrated it to be remarkably consistent in terms of its severity relative to control animals regardless of dose level or study duration. Given this limited range of severity, we did not feel that the addition of a quantitative assessment would offer sufficient value beyond that already provided by standard qualitative assessment, particularly since the principal purpose of the histopathologic evaluation in our study was to confirm the presence or absence of the lung effect. Furthermore, although the analyses were not conducted blind to the treatment conditions, the independent peer review conducted by five toxicology groups (Covance, Lovelace Respiratory Research Institute, Merck, Pfizer, and Genentech) was blinded and all independently came to the same conclusions.

Target inhibition assessed by Western blotting

pSer935-LRRK2 and total LRRK2. PBMC pellets and all other tissues were homogenized in Lysis Buffer from Meso-Scale Discovery supplemented with protease (Roche cOmplete Mini) and phosphatase inhibitor tablets (Roche PhosStop). Lysates were centrifuged at 13.2 × 1000 rpm for 20 min at 4°C. Supernatants were collected and protein content per sample was determined by bicinchoninic acid (BCA) colorimetric assay, using BSA as a standard (Life Technologies). One hundred micrograms of protein was reduced [10% NuPAGE (polyacrylamide gel electrophoresis) reducing agent and 5 μl of LDS sample buffer] and denatured at 70°C for 10 min and then resolved on 3 to 8% tris-acetate gels (Life Technologies) and transferred to polyvinylidene difluoride membranes (Life Technologies). Membranes were blocked in 5% dry milk in tris-buffered saline (TBS) plus Tween 20 (Sigma) for 1 hour at 4°C and probed with rabbit anti–LRRK2–pSer935-LRRK2 (Abcam; 1 μg/ml) overnight at 4°C. Membranes were then incubated with donkey anti-rabbit conjugated to horseradish peroxidase (HRP; Life Technologies; 1 μg/ml) combined with the IRDye 680CW (LI-COR, 926-68076) for 30 min at 4°C. LRRK2-pSer935-HRP signals were subsequently developed by luminol-enhanced chemiluminescence (SuperSignal Substrate) and then visualized and analyzed on a LI-COR Odyssey system. For total LRRK2 detection, membranes were subsequently stripped (Life Technologies, Restore PLUS, 46430), re-blocked as above, and probed with rabbit anti-LRRK2 antibody [Abcam, MJFF2 clone 41-2, AB133474; 1:500 (v/v)] combined with mouse anti-GAPDH (Millipore, MAB374) overnight at 4°C. Membranes were then incubated with donkey anti-rabbit conjugated to HRP (Life Technologies, A16035; 1 μg/ml) combined with the IRDye 800CW goat anti-mouse antibody (LI-COR) for 30 min at 4°C. HRP was then developed, visualized, and analyzed as above. For quantification, pSer935-LRRK2 signals were normalized to total LRRK2. GAPDH levels were used for further normalization of protein loading for all samples to enable total LRRK2 quantification.

pThr73-Rab 10. Lung tissue (500 mg) was homogenized in 500 μl of cold lysis buffer [50 mM tris-HCl, pH 7.5, 1% (v/v) Triton X-100, 50 mM NaF, 5 mM MgCl2, 10 mM β-glycerophosphate, 5 mM sodium pyrophosphate, 270 mM sucrose,1 mM sodium orthovanadate, mycrocystin-LR (0.1 μg/ml), and complete EDTA-free protease inhibitor cocktail]. Lysates were centrifuged at 13.2 × 1000 rpm for 20 min at 4°C. Supernatants were collected, and protein concentrations were determined by Bradford assay using BSA as standard.

Tissue lysates were denatured in Laemmli’s SDS-PAGE sample buffer [250 mM tris-HCl (pH 6.8), 8% SDS (w/v), 40% glycerol (v/v), 0.02% bromophenol blue (v/v), and 4% 2-mercaptoethanol] at 70°C for 10 min and spun at 13.2 × 1000 rpm for 1 min at room temperature. Forty-five micrograms of lysates was loaded onto phostag gels (50 μM phostag, Supersep Phos-tag 15%, and 17-well, Wako catalog no. 196-16701) with WIDE-VIEW Prestained Protein Size Marker III, run at 70 V (40 min) for stacking and at 140 V (3 hours) in running buffer (25 mM tris, 192 mM glycine, and 0.1% SDS, Wako catalog no. 184-01291). After washing, proteins were wet-transferred to nitrocellulose membranes. Membranes were blocked with 5% dry and skim milk dissolved in TBS containing 0.1% Tween. Membranes were probed with the primary, anti-Rab10 antibody [Cell Signaling, diluted 1:1000 with Solution One from SignalBoost Immunoreaction Enhancer Kit (EMD Millipore) containing 5% milk]. Secondary antibody incubation was with anti-rabbit HRP-labeled immunoglobulin G diluted 1:4000 in solution 2 for 1 hour. GAPDH level was determined using mouse monoclonal antibody (ab8245) and Li-Cor fluorescent second antibody. Images were developed for 3 min using SuperSignal West Dura Extended Duration substrate and captured by Odyssey Imager. The band intensity was measured and analyzed with image studio software. The total Rab10 level was defined by adding top pT73-Rab10 band and bottom Rab10 band intensity measurement. Percentage of phospho-Rab10 was calculated by (phospho Rab/total Rab) × 100.

Frozen nonhuman primate lung tissues (right cranial region, 150 to 250 mg) were placed in prechilled 1.5-ml Eppendorf tube, with one tungsten carbide beads (3 mm, Qiagen) and lysis buffer (5× of the tissue weight, e.g., 1000 μl of lysis buffer for 200 mg of tissue). The lysis buffer was composed of 50 mM tris-HCl (pH 7.4), 10 mM β-glycerophosphate, 10 mM sodium pyrophosphate, 0.1 μM mycrocystin-LR, 150 mM NaCl, 5 mM MgCl2, 1 mM EDTA, 1 mM dithiothreitol, 1% (v/v) Trion X-100, 10% glycerol, 100 nM guanosine 5′-O-(3′-thiotriphosphate), and cOmplete EDTA-free Protease Inhibitor Cocktail (Roche). The tissues were then homogenized for 6 min at 4°C on TissueLyser II (Qiagen) at a frequency of 30/s, 3 min per time. Lysates were centrifuged at 14,000 rpm for 30 min at 4°C. Supernatants were collected, and protein concentrations were measured using Pierce BCA Protein Assay (ThermoFisher). Protein concentrations were normalized for equal protein loading and mixed with NuPAGE LDS sample buffer (4×, ThermoFisher) and NuPAGE sample reducing agent (10×, ThermoFisher). Samples were incubated at 10 min at 70°C to denature proteins. Fifty micrograms of tissue lysates were loaded onto NuPAGE 4 to 12% Bis-Tris Midi Protein Gels (ThermoFisher) and transferred to nitrocellulose membranes for 7 min using Trans-Blot Turbo TransferSystem (Bio-Rad). Membranes were blocked with Odyssey Blocking Buffer (TBS, LI-COR), incubated with primary antibody overnight at 4°C, and then incubated with secondary antibodies (1:20,000, LI-COR) for 1 hour at room temperature. The primary antibodies used were rabbit anti–pT73-Rab10 (1 μg/ml, polyclonal antibody, MJF-20, E8263, provided by D. R. Alessi), mouse anti-Rab10 (1 μg/ml; Abcam, ab104859), and mouse anti–β-actin (1:5000, Sigma, A2228). LI-COR Odyssey system was used for Western blot detection and quantitation. Western blot images were quantified using Image Studio software (LI-COR). The pT73-Rab10 or total Rab10 signal was normalized using the β-actin signal for each sample to control for loading. Data were plotted using GraphPad Prism 7.

Lung function studies

A nonhuman primate study to evaluate pulmonary function was conducted at the Lovelace Respiratory Research Institute. The overall study design is shown in fig. S1, with all necropsies conducted at the same time points as for the histopathological/toxicological analysis, that is, 4 hours after the final dose. Full toxicokinetics analysis was not performed in this study to not disturb functional endpoints.

Animals, drug treatment, and testing regimens

Female cynomolgus macaques (Chinese origin, Charles River; age range, 2.5 to 7.2 years at the start of the study; body weight range, 3.5 to 4.5 kg) were randomized into three groups of 12 individuals each to balance the body weight distribution. Group A: Vehicle [0.5% (w/v) methylcellulose], group B: MLi-2 (15 mg/kg, PO, QD), and group C: MLi-2 (50 mg/kg, PO, QD). These groups were staggered with respect to treatments and assessments. Two animals were maintained throughout the study without any treatment and used later for GNE-7915 assessment (see below).

MLi-2 assessment. The test article or vehicle was administered by oral gavage once daily, in the morning, for 15 consecutive days. After day 15 pulmonary functional tests (PFTs; see below) and biospecimen collection, a subset of nonhuman primates (four from each cohort) were euthanized and submitted for necropsy and sample collection (detailed below). Another subset of four nonhuman primates went through the recovery phase (13 days) followed by euthanasia, necropsy, and biospecimen collection.

GNE-7915 assessment. The remaining four animals from each treatment group of the MLi-2 study (total N = 12) and two naïve animals from the original cohort were allowed to recover for an additional 28 to 29 weeks. These NHPs were re-randomized into two groups, considering their previous treatment allocation to evenly distribute them into vehicle (n = 6) and GNE-7915 (n = 8) treatment groups. Vehicle and GNE-7915 (30 mg/kg) were administered twice daily, about 8 hours apart, by oral gavage for 15 consecutive days. Immediately after last PFT measurements and BAL/blood collections, all animals were euthanized and submitted for necropsy and sample collection to determine any effects of treatment.

Biospecimen collection. Blood was collected by venipuncture for toxicokinetics and PBMC isolation. Blood (<2 ml) was collected into tubes containing EDTA. For MLi-2, blood was collected before dosing and 0.5, 1, 4, and 8 hours after dose on days 1, 8, 15, and 28 before PFT assessments and BAL. For GNE-7915, blood samples for TK analysis were collected before dosing and 0.5, 1, 4, and 8 hours after dose on days 1 and 8 of treatment. Additional blood samples were taken on day 15 before PFT and processed for PBMC isolation and clinical chemistry.

Anesthesia and pulmonary function tests. Pulmonary function tests were administered at baseline (day 0) and on days 7, 15, and 28 (for MLi-2 only). Animals were administered ketamine (5 to 10 mg/kg, intramuscularly) followed by isoflurane (5% for induction, 1.5 to 3% for maintenance). DLCO, Cqs, forced maneuver ventilation capacities to include FVC, FEV, forced expiratory flows, and bronchoalveolar lavage of two lung segments were conducted. Animals were anesthetized and intubated with an endotracheal tube of appropriate size for the animal. The animal was placed in a heated whole-body volume displacement plethysmograph.

DLCO, Cqs, and forced expiratory flow-volume curves, including FEV were measured during induced inhalations, exhalations during transient apnea, and then inflating and deflating the lung using either a syringe or an automated system of valves and pressure reservoirs calibrated for this purpose.

Diffusing capacity of the lung for carbon monoxide. The single-breath method was used to measure DLCO. The inflation volume required to reach +20-cm H2O transpulmonary pressure (Ptp) was determined before each measurement. A syringe was flushed and filled with that volume of test gas (mixture of CO and Ne in air). The lung was insufflated with the test gas, and a period of “breath hold” at end inspiration (6 s) occurred followed by withdrawal of 75% of the insufflated volume. A portion of the gas remaining in the airway was withdrawn into a small gas-tight syringe, and its composition was analyzed using gas chromatography. The inhaled and exhaled gas concentrations, inflation volume, and inflation time were recorded and used to calculate DLCO, which is the pressure-adjusted uptake rate of CO across the alveolar-capillary membrane.

Quasi-static lung compliance (Cqs10). The Cqs maneuver was performed by insufflating the lungs slowly to total lung capacity, which was defined as the lung volume at a Ptp of +30 cm H2O, and then deflating the lung slowly until flow stopped. Cqs was calculated as the slope of the pressure-volume curve between 0- and +10-cm H2O Ptp and termed Cqs10.

FVC, FEV, and forced expiratory flow rates. The forced expiratory maneuver was induced during apnea by inflating the lung to total lung capacity and then rapidly deflating by opening a large bore valve to a negative pressure reservoir while recording flow, volume, and Ptp. The lung volume obtained from the forced expiratory maneuver from +30 cm H2O to the point at which expiratory flow ceases is the FVC. The lung volume obtained at a given time interval, e.g., 0.1 s, from the start of expiration is the FEV for that time interval. FEV at the point of maximal flow is also included. The expiratory flow rates at 75 and 25% of FVC were averaged to derive MMEF. Further, the flow rates at various steps of lung volume are also presented, i.e., 75, 50, 25, and 10%. The flows are also normalized to lung volume by dividing by FVC from a given maneuver.

Bronchoalveolar lavage. Following pulmonary function assessment, a bronchoscope (BF-XP40, Olympus America Inc., Melville, NY) was maneuvered through the endotracheal tube and wedged in about a fourth- to sixth-generation airway in the left diaphragmatic lung lobe. Three aliquots of 5-ml sterile United States Pharmacopeia (USP)–grade saline were instilled and aspirated in succession followed by further aspiration with an empty syringe to recover as much as possible. The process was then repeated for the contralateral lung. Each sample was stored on ice until processing. Ten microliters of BAL fluid was aliquoted into an Eppendorf tube. Phospholipids were extracted with the addition of 900 μl of our extraction solvent: dichloromethane:isopropanol:methanol (25:10:65, v/v/v), containing 200 nM 1,2-dilauroyl-sn-glycero-3-phosphocholine internal standard. Phospholipid extracts were then analyzed by ultraperformance LC (UPLC)–MS/MS using a Waters Acquity UPLC coupled to a Sciex QTRAP 5500 mass spectrometer. Lipid classes were separated by reversed-phase chromatography on a Waters Acquity UPLC BEH300 C4 column, 1.7 μm, 2.1 mm by 50 mm. Phospholipid species were then analyzed on the mass spectrometer using positive ion electrospray ionization in the multiple-reaction monitoring mode. LC chromatogram peak integration was performed with Sciex MultiQuant software. All data reduction was performed with in-house software.

Necropsy and pathology. Animals were euthanatized and submitted for necropsy after the 15-day treatment period (MLi-2 and GNE-7915) and the 13-day recovery period (MLi-2 only). Standard necropsies were performed in addition to collection of blood, urine, and CSF. About half of the lung, kidney, and brain were collected and stored in fixative as described in part 1 for histopathology and the other half was flash-frozen and stored at −70° to −90°C for compound levels and biomarker analyses.

Statistical analysis. Because of the small number of animals in the toxicological study, all toxicokinetic and histopathology data analyses were limited to the calculation of means and SDs without hypothesis testing via statistical methods such as regression or group comparisons. The effect of the LRRK2 inhibitors on the amounts of pSer935-LRRK2 and pRab10 in the brain and peripheral tissues was analyzed by a one-way ANOVA followed by Dunnett’s multiple comparison test. For di-22:6-BMP amounts in urine, plasma, brain, lung, and kidney, unpaired t tests were conducted to compare LRRK2 inhibitor–dosed groups with the vehicle control group at the end of the dosing period.

For lung function tests, data are presented as mean and SEM for continuous variables. Pulmonary function and bronchoalveolar lavage fluid data were analyzed using the two-way ANOVA. Bonferroni post hoc tests were conducted by comparing treated groups to the vehicle-treated group per study day and comparing each post-treatment value to corresponding pretreatment values for a given group. A P value of ≤0.05 indicates statistical significance. Analyses were completed using GraphPad Prism (GraphPad Software Inc., San Diego, CA, USA).

SUPPLEMENTARY MATERIALS

stm.sciencemag.org/cgi/content/full/12/540/eaav0820/DC1

Fig. S1. Overview of the workflow for the LRRK2 Safety Initiative.

Fig. S2. Rab10 protein phosphorylation in lung (Phos-tag gels).

Fig. S3. Design of lung function tests.

Table S1. Macroscopic and microscopic analysis of macaque brain, lung, and kidney.

Table S2. Unbound and total plasma/tissue concentrations of LRRK2 inhibitors after 15 days of treatment.

Table S3. Microscopic lung observations after lung function tests.

Table S4. Schedule for dosing, monitoring, necropsy, and tissue collection.

Data file S1. Western blotting of pS935-LRRK2 and total LRRK2 in macaque lung, PBMCs, and brain.

Data file S2. Data for correlating the unbound drug concentration in macaque plasma with the IC50 for pSer935-LRRK2 inhibition in mouse brain.

Data file S3. Concentration of di-22:6-BMP in the urine of macaques.

Data file S4. Lung function tests in macaques treated with MLi-2.

Data file S5. Phosphatidylcholine in bronchoalveolar lavage from MLi-2–treated animals.

Data file S6. Western blotting of pThr73 Rab10 in lung of GNE-7915–treated macaques.

REFERENCES AND NOTES

Acknowledgments: We thank E. Murphy and S. Meola for help with manuscript preparation and F. Diez for technical assistance with the protein phosphorylation (Phos-tag) gels. We would like to dedicate this publication in loving memory of C.M. Funding: This work was funded by The Michael J. Fox Foundation for Parkinson’s Research through grants to Covance Laboratories Inc. (#10144 and 10144.01) and The Lovelace Respiratory Research Institute (#10233), which conducted the histopathological/toxicological studies and lung function tests, respectively. Author contributions: W.A.M., S.P., A.K.S., and C.T. at Covance Laboratories Inc. conducted the histopathological and toxicological studies for Fig. 1. C.M., C.H., and R.N.F. conducted the review of the histopathology and toxicology studies for Merck, Pfizer, and Genentech, respectively. M.J.F., D.K.B., M.E.K., S.H., Z.Y., H.Y., W.H., A.S., S.B., and E.N. performed Western blotting in Fig. 2. X.L., H.M., M.L.M., and S.S. analyzed data for Fig. 3. R.N.F. analyzed data for Fig. 4. T.B., C.R., and K.R. at The Lovelace Respiratory Research Institute conducted the lung function tests for Fig. 5. M.J.F. and W.H. analyzed data for Fig. 6. A.G.H. and X.W. conducted and analyzed experiments for Fig. 7. P.G., J.M.E., and A.A.E. provided all chemistry support. M.A.S.B., K.M., B.K.F., and T.B.S. wrote the manuscript and designed all studies. Competing interests: R.N.F. and X.L. are paid employees of Genentech. M.E.K., M.J.F., D.K.B., M.L.M., H.M., Z.Y., and H.Y. are all paid employees of Merck & Co. Inc. A.A.E., A.G.H., and X.W. are all paid employees of Denali Therapeutics. C.H. is a paid employee of Pfizer. K.M. is a senior advisor to the Michael J. Fox Foundation for Parkinson’s Research, and in the last 36 months, she has consulted for the following pharmaceutical companies and private investors: Lysosomal Therapeutics, Origami Therapeutics, Sinopia Biosciences, and Vomisa (Angel investor). Data and materials availability: All data associated with this study are present in the paper or the Supplementary Materials. The LRRK2 inhibitors GNE-7915, MLi-2, and PFE-360 are all commercially available.
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