The β-secretase BACE1 (β-site amyloid precursor (APP) cleaving enzyme 1) is a major drug target for Alzheimer's disease (AD), as it catalyzes the first step in amyloid β (Aβ) generation, but has addit Show more
The β-secretase BACE1 (β-site amyloid precursor (APP) cleaving enzyme 1) is a major drug target for Alzheimer's disease (AD), as it catalyzes the first step in amyloid β (Aβ) generation, but has additional substrates and functions, in particular in the brain. Several advanced clinical trials with BACE1 inhibitors were stopped because of an adverse event, a mild cognitive worsening. The underlying mechanism is not yet known but may result from co-inhibition of the BACE1-homolog BACE2. While a cerebrospinal fluid (CSF) biomarker for measuring BACE2 activity is not yet established, VCAM-1 has been suggested as such a biomarker, but has not yet been tested upon prolonged dosing in vivo. Using CSF pharmacoproteomics and a subchronic dosing paradigm in non-human primates, we demonstrate that compound 89, a BACE inhibitor not yet tested in humans, and the clinically tested drug elenbecestat inhibit BACE1 in vivo, with little or no effect on BACE2, as seen with a reduction of substrates of BACE1, but not of the BACE2 substrate VCAM-1. As a control, verubecestat, which inhibits both BACE2 and BACE1, reduced CSF abundance of BACE1 substrates as well as of VCAM-1. This study demonstrates the suitability of VCAM-1 as a pharmacodynamic biomarker for measuring BACE2 target engagement in CSF. Show less
The β-secretase β-site APP cleaving enzyme (BACE1) is a central drug target for Alzheimer's disease. Clinically tested, BACE1-directed inhibitors also block the homologous protease BACE2. Yet little i Show more
The β-secretase β-site APP cleaving enzyme (BACE1) is a central drug target for Alzheimer's disease. Clinically tested, BACE1-directed inhibitors also block the homologous protease BACE2. Yet little is known about physiological BACE2 substrates and functions in vivo. Here, we identify BACE2 as the protease shedding the lymphangiogenic vascular endothelial growth factor receptor 3 (VEGFR3). Inactivation of BACE2, but not BACE1, inhibited shedding of VEGFR3 from primary human lymphatic endothelial cells (LECs) and reduced release of the shed, soluble VEGFR3 (sVEGFR3) ectodomain into the blood of mice, nonhuman primates, and humans. Functionally, BACE2 inactivation increased full-length VEGFR3 and enhanced VEGFR3 signaling in LECs and also in vivo in zebrafish, where enhanced migration of LECs was observed. Thus, this study identifies BACE2 as a modulator of lymphangiogenic VEGFR3 signaling and demonstrates the utility of sVEGFR3 as a pharmacodynamic plasma marker for BACE2 activity in vivo, a prerequisite for developing BACE1-selective inhibitors for safer prevention of Alzheimer's disease. Show less