Dustin J. Mergott

The Potent BACE1 Inhibitor LY2886721 Elicits Robust Central Aβ Pharmacodynamic Responses in Mice, Dogs, and Humans

BACE1 is a key protease controlling the formation of amyloid β, a peptide hypothesized to play a significant role in the pathogenesis of Alzheimers disease (AD). Therefore, the development of potent and selective inhibitors of BACE1 has been a focus of many drug discovery efforts in academia and industry. Herein, we report the nonclinical and early clinical development of LY2886721, a BACE1 active site inhibitor that reached phase 2 clinical trials in AD. LY2886721 has high selectivity against key off-target proteases, which efficiently translates in vitro activity into robust in vivo amyloid β lowering in nonclinical animal models. Similar potent and persistent amyloid β lowering was observed in plasma and lumbar CSF when single and multiple doses of LY2886721 were administered to healthy human subjects. Collectively, these data add support for BACE1 inhibition as an effective means of amyloid lowering and as an attractive target for potential disease modification therapy in AD.

COMBINATION THERAPY WITH A PLAQUE-SPECIFIC ABETA ANTIBODY AND A BACE INHIBITOR RESULTS IN DRAMATIC PLAQUE REDUCTION IN A DOSE-DEPENDENT MANNER IN AGED PDAPP TRANSGENIC MICE

lowed. Results:High antibody responses were found in both species. In the rabbit, 277.16 118.4 mg/ml plasmaweremeasured after 5 immunizations with no significant differences between the dose groups. Antibody levels declined slightly to 246.66 109.5 mg/ml after a resting period of two months. Low levels of IFNg and IL-17 secreting splenocytes were found in the ELISPOTassays from rabbit splenocytes. Rhesusmonkeys reachedmean antibody levels of 114.2 6 41.67 mg/ml plasma after five immunizations. The isotype profile was high on IgG4 antibodies, indicative of a Th2 immune response. After three immunizations, no IL-17 or IFNg producing cells were found in ELISPOT assays from PBMCs. Conclusions: DNA Ab42 immunization leads to high antibody titers in large mammals, and is likely to produce high antibody levels and a safe (Th2 biased) immune response in humans as well. supported by NIA/NIH P30AG12300-21, Zale Foundation, Rudman Foundation, AWARE, Presbyterian Village North, Freiberger, and Denker Family Funds

MEASUREMENT OF ENDOGENOUS MOUSE TAU IN CEREBROSPINAL FLUID FROM AGED PDAPP MICE FOLLOWING TREATMENT WITH AB-LOWERING COMPOUNDS

Background:Dementia is usually attributable to one or a combination of neuropathologic abnormalities, including Alzheimer amyloid plaques and neurofibrillary tangles. Most demented individuals have at least two types of dementia-related abnormality. Older decedents without abnormalities may be viewed as showing resistance to the relevant pathogenic processes. Others with brain or cognitive reserves may maintain normal cognitive performance even when 1 or 2 types of histopathologic abnormality have developed. We hypothesize essential resilience as a third defense against established neuropathology. Methods: Analyses involved 572 autopsied HAAS participants (Japanese-American men) dying at age 80 or older whose baseline Cognitive Assessment and Screening Instrument (CASI) score had been normal (>1⁄474). End-of-life severe impairment was based on a final CASI score <60. Four overlapping reserve elements were each dichotomized as 0 or 1: (i) negligible brain atrophy, (ii) higher education, (iii) higher occupational complexity, (iv) higher adult life cognitive test scores. A neuropathologic burden index (Neurology, March 2016) was the sum of four histopathologic abnormalities, each scored 0.4 (moderate) or 1.0 (severe) for Alzheimer lesions, microinfarcts, Lewy bodies, and hippocampal sclerosis. Results:Among 159 participants with a neuropathologic burden index of zero, 145 (91%) maintained normal cognition. Among 387 with burden indices 0.4 1.8 (most with two moderate or severe lesion types), the proportions developing severe impairment fell from 49%, to 35%, to 29%, to 25%, to 13% respectively in decedents with zero, 1, 2, 3, or all 4 reserve elements. Of 26 decedents with neuropathologic burden indices >1⁄42, 22 (85%) developed severe cognitive impairment. We continue to search for factors determining essential resilience. Conclusions: In this autopsied cohort, brain and/or cognitive reserves provided a powerful attenuation of cognitive impairment attributable to a panel of neuropathological abnormalities. A hypothesized additional contribution by essential resilience remains to be demonstrated.

A CORRELATIONAL ANALYSIS OF EXPOSURE AND PHARMACODYNAMIC EFFECTS OF THE BACE1 INHIBITOR LY3202626 IN PDAPP MICE FOLLOWING ACUTE ORAL DOSING

Background: LY3202626 is a potent, freely CNS-penetrant small molecule BACE1 inhibitor in development for the treatment of Alzheimer’s disease (AD). Herein, we demonstrate strong pharmacokinetic / pharmacodynamic (PK/PD) relationships in PDAPP mice between central LY3202626 exposure and central (hippocampal and cortical brain tissue) BACE1 inhibition as determined by quantifying markers of amyloid precursor protein (APP) metabolism. Methods: In a dose response study, young female PDAPP mice (n1⁄46/group) were orally administered 0, 0.3, 1.0, or 3.0 mg LY3202626/kg and were sacrificed at 3 hr post-dose. In a separate time course study, young female PDAPP mice were sacrificed at 3, 6, 9, or 12 hours following a 3 mg LY3202626/kg oral dose. In all studies, LY3202626 concentrations were determined in plasma and brain samples by LC/MS/MS and concentrations of sAPPbeta, C99 and Abeta 1-X were determined in hippocampus and cortex using ELISA methodology. Results: Oral administration of LY3202626 to PDAPPmice produced dose-dependent reductions in brain Abeta, C99, and sAPPbeta with LY3202626 brain concentrations negatively-correlated with all three PD endpoints (r values > 0.56). Changes in each BACE1 biomarker were similar in the cortical and hippocampal brain regions (all r values > 0.90). In a timecourse study following a dose of 3 mg/kg LY3202626, free brain exposure over the 3-12 hour time-course study correlated well with hippocampal Abeta 1-X changes (r 1⁄4 0.60), indicating that the robust PK/PD relationship was maintained over time. All correlations were significant, with p-values <0.0001. Observed free (unbound) concentrations in brain and plasma across these studies suggest LY3202626 is highly brain penetrant in PDAPP mice. Conclusions:LY3202626 is a potent inhibitor of BACE1. Administration of LY3202626 results in significant changes in central biomarkers of BACE1 activity, and the magnitude of these changes correlate well with observed.

A COMPARISON OF IN VIVO POTENCY IN TWO BACE INHIBITORS AS DETERMINED IN HUMANS AND DOGS

P1-365 A COMPARISON OF IN VIVO POTENCY IN TWO BACE INHIBITORS AS DETERMINED IN HUMANS AND DOGS Brian A. Willis, Patrick C. May, Scott A. Monk, Stephen L. Lowe, Stuart Friedrich, Dustin J. Mergott, Leonard Boggs, Hakop Gevorkyan, Stan Jhee, Robert A. Dean, Masako Nakano, Celedon R. Gonzales, Eli Lilly and Co., Indianapolis, Indiana, United States; Eli Lilly and Company, Indianapolis, Indiana, United States; Lilly NUS Center of Clinical Pharmacology, Singapore, Singapore; Eli Lilly and Company, Indianapolis, Indiana, United States; Eli Lilly and Co., Indianapolis, Indiana, United States; Parexel International, Glendale, California, United States; Eli Lilly Japan K.K., Kobe, Japan. Contact e-mail: p.c. may@lilly.com