Concentration-dependent modulation of Aβ in vivo and in vitro using the γ-secretase inhibitor, LY-450139 Running Title: γ-secretase inhibitor modulates Aβ production Corresponding Author

Abstract

Abstract LY-450139 is a γ-secretase inhibitor shown to have efficacy in multiple cellular and animal models. Paradoxically, robust elevations of plasma Aβ have been reported in dogs and humans following administration of sub-efficacious doses. The present study sought to further evaluate Aβ responses to LY-450139 in the guinea pig, a non-transgenic model that has an Aβ sequence identical to that of human. Male guinea pigs were treated with LY-450139 (0.2-60 mg/kg), and brain, CSF, and plasma Aβ levels were characterized at 1, 3, 6, 9, and 14h post-dose. Low doses significantly elevated plasma Aβ levels at early time points, with return to baseline within hours. Higher doses inhibited Aβ levels in all compartments at early time points, but elevated plasma Aβ levels at later time points. To determine whether this phenomenon occurs under steadystate drug exposure, guinea pigs were implanted with subcutaneous minipumps delivering LY-450139 (0.3-30 mg/kg/day) for 5 days. Plasma Aβ was significantly inhibited at 10-30 mg/kg/day, but significantly elevated at 1 mg/kg/day. To further understand the mechanism of Aβ elevation by LY-450139, H4 cells over-expressing APP Sw and a mouse embryonic stem cell-derived neuronal cell line were studied. In both cellular models, elevated levels of secreted Aβ was observed at sub-efficacious concentrations, while dose-responsive inhibition was observed at higher concentrations. These results suggest that LY-450139 modulates the γ-secretase complex, eliciting Aβ lowering at high concentrations, but Aβ elevation at low concentrations. JPET # 110700 (4