P2‐341: A robotic screen of a small‐molecule chemical library for inhibitors of Aβ oligomer formation

C-terminus of A 40, was administered to 5-month-old plaque-bearing APPxPS1 mice (Swedish mutation of APP, E9 mutation of PS1). Brain, CSF, and plasma were harvested 5 days following a single intraperitoneal injection of vehicle or 0.1-10 mg/kg PF-4360365 to determine the effect on A levels. Results: A 1-X, 1-40, and 1-42 were not significantly reduced in cortex. In hippocampus, all three A fragments were significantly reduced to varying degrees, although no dose-response relationship was observed. A 1-X levels in CSF were significantly elevated at the 10 mg/kg dose; no other significant changes were detected. Assaying samples revealed up to 10,000% increase in plasma A 1-X but only up to 35% change in A 1-40 due to interference of the therapeutic antibody with A 1-40 detection. Samples were extracted with guanidine and antibodies were removed using solid-phase extraction (SPE). Following this clean-up step, A 1-40 levels correlated with A 1-X levels. A 1-42 levels in plasma appeared to be reduced by up to 50% before SPE and increased by up to 300% following SPE. However, using synthetic A standards in solution or spiked into plasma, it was discovered that excess A 1-40 concentrations can increase the apparent A 1-42 signal with the polyclonal antibodies being used to measure A 42. When a proprietary monoclonal A 42selective monoclonal antibody was used to capture A 42, no change in plasma A 42 levels were observed after PF-4360365 treatment. Therapeutic antibody concentrations in plasma significantly correlated to A 1-X and A 1-40 in plasma, but not to any A fragment in CSF or brain. No inter-compartmental correlation was observed for A levels in vehicle or antibody-treated mice. Conclusions: A single injection of PF-4360365 showed selective mobilization of A in the CNS, accompanied by robust elevation of A 40 in novel A assays following denaturation and chromatographic separation of the antigen-antibody complex.