P3–421: Identification of Structural Determinants on PS–1 and PS–2 That Affect Inhibitor Potency

Production and deposition of Aβ peptide in amyloid plaques contributes the hallmark pathology of Alzheimer's disease in brains of affected patients. Two presenilin homologues, referred to as PS1 and PS2, comprise the catalytic core of gamma secretase, a critical enzyme in Aβ production. Gamma secretase also mediates intramembrane cleavage of Notch and other substrates. Inhibition of Notch signaling by non–selective gamma secretase inhibitors is an important issue for the clinical development of this class of therapeutics. The observation that PS1 KO mice exhibit perinatal lethality, whereas PS2 KO mice are viable suggests that PS2 selective inhibitors may spare Notch signaling while lowering Aβ. To identify PS selective inhibitors, and to map the underlying structural basis, We employed murine cell lines lacking PS1 and PS2. We performed transient transfections on these cells with Swedish APP plus either PS1, or PS2, or a chimerical presenilin molecule derived from portions of PS1 and PS2. We observed that sulfonamides, as represented by BMS 299897, were significantly more potent inhibitors of Aβ production from PS1–gamma secretase than PS2–gamma secretase for Aβ production. In contrast, other classes of gamma inhibitors we tested were largely equipotent for PS1– or PS2–gamma secretase. Using the combination of chimerical constructs and point mutants, we identified specific amino acid residues that can account for differences in inhibition potency of PS1 vs. PS2 gamma secretase by BMS299897, as well as related compounds.