Classification of γ-secretase modulators and their effect on pharmacological profiles of amyloid β peptides

MALDI-TOF profiling enables rapid P2-513 Introduction γ-Secretase modulators (GSMs) decrease the cleavage of amyloid precursor protein (APP) at the site that generates 42-amino acid amyloid β protein (Aβ42) while sparing the normal cleavage of Notch. However, the mechanism by which GSMs modulate γ-secretase is not clear and may not proceed through a single mechanism, as evidenced by the differential effects GSMs can have on other A peptides. The objective of this study was to determine the pharmacologic profiles of literature GSMs and novel Satori SPI compounds by examining the effect on various A peptides using two different MS-based detection methods. We have examined the cleavage profile of APP in the presence of various GSMs by immunoprecipitation/MALDI-TOF and quantified key Aβ peptides by LC/MS/MS. While all GSMs reduce A1-42 production, structurally distinct classes of GSMs affected Aβ1-38 and Aβ1-39 in opposite directions, i.e., Aβ38-increasing GSMs decreased Aβ39 production while characterization of multiple A peptides 4331.15 4132.93 2463.30 4330.75 2463.15 3153.02 3263.71 4132.64 3712.45 2316.29 3868.85 2897.94 2645.34 4515.39 3457.22 A1-20 A11-38 A11-39 A11-37 A11-40 A1-28 A1-33 A1-34 A1-38 A1-39 A1-37 A1-40 A1-42 Vehicle Aβ38-decreasing GSMs increased Aβ39 production. These two classes of GSMs did not dramatically change the levels of total Aβ (Aβ1-x) at the concentrations that reduced Aβ1-42, presumably because increases in the production of shorter peptides compensate for the loss of longer peptides like Aβ1-42. Quantification of individual peptides (Aβ37, 38, 39, 40 and 42) by LC/MS/MS revealed significant perturbations in the concentrations of the shorter Aβ species. GSMs may slightly shift γ-secretase along the -helical domain of APP transmembrane domain without changing total γ-secretase activity by shifting the cleavage from longer to shorter peptides. Method 4330.55