Preclinical and first-in-human evaluation of AL002, a novel TREM2 agonistic antibody for Alzheimer's disease

Abstract

Background: Variants of the gene triggering receptor expressed on myeloid cells-2 (TREM2) increase the risk of Alzheimer's disease (AD) and other neurodegenerative disorders. Signaling by TREM2, an innate immune receptor expressed by microglia, is thought to enhance phagocytosis of amyloid beta (Aβ) and other damaged proteins, promote microglial proliferation, migration, and survival, and regulate inflammatory signaling. Thus, TREM2 activation has potential to alter the progression of AD. AL002 is an investigational, engineered, humanized monoclonal immunoglobulin G1 (IgG1) antibody designed to target TREM2. In AD mouse models, an AL002 murine variant has been previously shown to induce microglial proliferation and reduce filamentous Aβ plaques and neurite dystrophy.

Methods: Preclinical studies assessed the safety, tolerability, pharmacokinetics, and pharmacodynamics of AL002 in cynomolgus monkeys. INVOKE-1 (NCT03635047) was a first-in-human phase 1, randomized, placebo-controlled, double-blind study assessing the safety, tolerability, PK, and PD of AL002 administered as single ascending doses (SAD) in healthy volunteers.

Results: In cynomolgus monkeys, weekly intravenous injections of AL002 for 4 weeks were well tolerated, dose-dependently decreased soluble TREM2 (sTREM2) in cerebrospinal fluid (CSF) and total TREM2 in hippocampus and frontal cortex, and increased biomarkers of TREM2 signaling in CSF and brain. In the phase 1 study of 64 healthy volunteers, a single intravenous infusion of AL002 demonstrated brain target engagement based on a dose-dependent reduction of sTREM2 in CSF and parallel increases in biomarkers of TREM2 signaling and microglia recruitment. Single-dose AL002 showed central nervous system penetrance and was well tolerated, with no treatment-related serious adverse events over 12 weeks.

Conclusions: These findings support the continued clinical development of AL002 for AD and other neurodegenerative diseases in which TREM2 activation may be beneficial. AL002 is currently being tested in a phase 2, randomized, double-blind, placebo-controlled study in early AD.

Trial registration: Clinicaltrials.gov, NCT03635047. Registered on August 15, 2018, https://www.

Clinicaltrials: gov/study/NCT03635047 .

Keywords: Alzheimer’s disease; Biomarkers; Microglia; Phase 1 clinical trial; TREM2.

Fig. 1

AL002 phase 1 study design. Cohorts A through C sequentially enrolled 3 HVs into 3 single-participant cohorts treated with AL002 0.003 mg/kg, 0.03 mg/kg, or 0.2 mg/kg. For Cohorts D through I, 8 HVs (6 active: 2 placebo) were sequentially enrolled and treated with single doses of AL002 or placebo, at the following dose levels: 0.6 mg/kg, 2 mg/kg, 6 mg/kg, 15 mg/kg, 30 mg/kg, and 60 mg/kg. In addition, 2 open-label single-dose cohorts were enrolled: Cohort K enrolled 6 participants treated at 45 mg/kg, and Cohort N enrolled 8 participants treated at 60 mg/kg with CSF sampled at later timepoints. CSF, cerebrospinal fluid; HV, healthy volunteer; PD, pharmacodynamic; PK, pharmacokinetic; RND, randomization

Fig. 2

Pharmacokinetics of repeat-dose AL002 in cynomolgus monkeys. (A) Mean + SD serum concentrations of AL002. For Days 1 to 22, n = 6 in 20 mg/kg and 80 mg/kg, n = 10 in 250 mg/kg. For Day 29, n = 4 in the 250 mg/kg group. (B) Mean ± SEM CSF concentration of AL002. LLOQ standard was 5.0 ng/mL. n = 6 in 20 mg/kg and 80 mg/kg, n = 10 in 250 mg/kg. Black arrows indicate time of dosing. CSF, cerebrospinal fluid; h, hours; LLOQ, lower limit of quantification; SD, standard deviation

Fig. 3

Pharmacodynamic effects of repeat-dose AL002 in cynomolgus monkeys. (A) CSF sTREM2 from the non-GLP DRF study (n = 4 per dose group). From the 4-week GLP study (n = 6 per dose group), (B) total TREM2 levels in the frontal cortex and (C) hippocampus. (D) Volcano plot of SomaScan data for CSF protein for 250 mg/kg group vs. vehicle 48 h after the Day 1 dose. (E) SPP1 mRNA expression in frontal cortex, normalized to control values, from the 4-week GLP study. (F) CSF SPP1 protein levels at predose baseline and Day 1 (i.e., 48 h after dose). (G) Longitudinal CSF SPP1 protein levels from the non-GLP interval study (n = 5 for the vehicle and 250 mg/kg dose group; n = 4–5 for the 80 mg/kg dose group). From the 4-week GLP study, (H) CSF1R mRNA expression in frontal cortex, normalized to control values, (I) CSF1R protein levels in frontal cortex, and (J) IL1RN protein levels in CSF at predose baseline, 48 h after Day 1 dose, and 48 h after Day 29 dose. Black arrows indicate time of dosing. Data are means ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001. a.u., arbitrary units; CSF, cerebrospinal fluid; CSF1R, soluble colony-stimulating factor 1 receptor; DRF, dose range finding; GLP, good laboratory practices; h, hours; LLOQ, lower limit of quantification; sCSF1R, soluble CSF1R; SEM, standard error of the mean; sTREM2, soluble TREM2; TREM2, triggering receptor expressed on myeloid cells-2

Fig. 4

Pharmacokinetics of single ascending dose AL002 in healthy volunteers. (A) Mean ± SD serum concentrations of AL002 (semi-logarithmic). LLOQ was 0.0200 µg/mL. (B) Mean ± SD CSF concentration of AL002 (semi-logarithmic). LLOQ was 5.0 ng/mL. n = 6 for the 6 mg/kg, 15 mg/kg, and 30 mg/kg dose groups; n = 5 for the 45 mg/kg group; n = 5–6 for 60 mg/kg group. Data for the 60 mg/kg dose at Day 57 are not shown, as n = 1. CSF, cerebrospinal fluid; LLOQ, lower limit of quantification; SD, standard deviation

Fig. 5

Pharmacodynamics of single ascending dose AL002 in CSF of healthy volunteers. (A-B) sTREM2, (C) SPP1 protein, (D) sCSF1R, and (E) IL1RN protein were measured in CSF samples collected at the indicated time points. Data are presented as unadjusted mean ± SD percent change from baseline. (A), (C), (D), and (E) n = 6 in placebo, 6 mg/kg, 15 mg/kg, 30 mg/kg cohorts; n = 5 in 45 mg/kg cohort; n = 5–6 in 60 mg/kg cohorts I and N. (B) In 60 mg/kg cohort N, n = 2 at Day 13, n = 5 at Day 30 and 43, n = 3 at Day 57. Nudging was used to differentiate overlapping datasets. CSF, cerebrospinal fluid; CSF1R, colony-stimulating factor 1 receptor; LLOQ, lower limit of quantification; NHP, nonhuman primate; sCSF1R, soluble CSF1R; SEM, standard error of the mean; sTREM2, soluble TREM2; TREM2, triggering receptor expressed on myeloid cells-2

Fig. 6

Pharmacodynamics of single ascending dose AL002 in plasma of healthy volunteers. (A) IL1RN protein and (B) sTREM2 were measured in plasma samples collected at the indicated time points. Data are presented as unadjusted mean ± SEM percent change from baseline. (A), (B), n = 11 in placebo, n = 3 in 0.003-0.2 mg/kg, n = 6 in each of 0.6 mg/kg, 2 mg/kg, 6 mg/kg, 15 mg/kg, 30 mg/kg, 45 mg/kg; n = 11–14 in 60 mg/kg cohorts I and N. EOI, end of injection; h, hours; SEM, standard error of the mean; sTREM2, soluble TREM2; TREM2, triggering receptor expressed on myeloid cells-2

Fig. 7

Proposed mechanism of action of AL002. (A) TREM2 is constitutively shed into sTREM2. (B) AL002 binding promotes TREM2 clustering and activation via DAP12 and SYK phosphorylation, thus leading to SPP1 and IL1RN protein production. (C) AL002-mediated TREM2/DAP12 phosphorylation induces activation-mediated internalization of TREM2, thus leading to TREM2 degradation. This mechanism is typical of ITAM-containing receptors, thus preventing prolonged and massive stimulation of the receptor. ITAM, immunoreceptor tyrosine-based activation motif; sTREM2, soluble TREM2; TREM2, triggering receptor expressed on myeloid cells-2