Concentration-Dependent Modulation of Amyloid-␤ in Vivo and in Vitro Using the ␥-Secretase Inhibitor, LY-450139

ABSTRACT LY-450139 is a ␥-secretase inhibitor shown to have efficacy in multiple cellular and animal models. Paradoxically, robust elevations of plasma amyloid-␤ (A␤) have been reported in dogs and humans after administration of subefficacious doses. The present study sought to further evaluate A␤ responses to LY-450139 in the guinea pig, a nontransgenic model that has an A␤ sequence identical to that of human. Male guinea pigs were treated with LY-450139 (0.2-60 mg/kg), and brain, cerebrospinal fluid, and plasma A␤ levels were characterized at 1, 3, 6, 9, and 14 h postdose. Low doses significantly elevated plasma A␤ levels at early time points, with return to baseline within hours. Higher doses inhibited A␤ levels in all compartments at early time points, but elevated plasma A␤ 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 A␤ was significantly inhibited at 10 -30 mg/kg/day, but significantly elevated at 1 mg/kg/day. To further understand the mechanism of A␤ elevation by LY-450139, H4 cells overexpressing the Swedish mutant of amyloid-precursor protein and a mouse embryonic stem cell-derived neuronal cell line were studied. In both cellular models, elevated levels of secreted A␤ were observed at subefficacious concentrations, whereas dose-responsive inhibition was observed at higher concentrations. These results suggest that LY-450139 modulates the ␥-secretase complex, eliciting A␤ lowering at high concentrations but A␤ elevation at low concentrations. The pathological accumulation of amyloid-␤ peptide into dense core plaques in the brains of Alzheimer's disease patients is the ultimate target of multiple disease-modifying drug discovery efforts. One strategy that has entered the clinic is the use of a ␥-secretase inhibitor to reduce central A␤ production. Preclinically, multiple ␥-secretase inhibitors have demonstrated central and peripheral A␤-lowering activity in transgenic mouse lines overexpressing human mutant amyloid precursor protein The ability of plasma and CSF A␤ to track pharmacological changes in brain A␤ provides a useful method for tracking the efficacy of ␥-secretase inhibitors in the clinic. Because each compartment may have varying degrees of drug exposure and different clearance rates for both drug and A␤, it is important to understand the dynamics of A␤ in each compartment. Dose-response and time course studies with ␥-secretase inhibitors in transgenic mice have revealed difArticle, publication date, and citation information can be found at http://jpet.aspetjournals.org. doi:10.1124/jpet.106.110700. ABBREVIATIONS

A Computational Approach to Enzyme Design: Predicting ω‑Aminotransferase Catalytic Activity Using Docking and MM-GBSA Scoring

Enzyme design is an important area of ongoing research with a broad range of applications in protein therapeutics, biocatalysis, bioengineering, and other biomedical areas; however, significant challenges exist in the design of enzymes to catalyze specific reactions of interest. Here, we develop a computational protocol using an approach that combines molecular dynamics, docking, and MM-GBSA scoring to predict the catalytic activity of enzyme variants. Our primary focuses are to understand the molecular basis of substrate recognition and binding in an <i>S</i>-stereoselective ω-aminotransferase (ω-AT), which naturally catalyzes the transamination of pyruvate into alanine, and to predict mutations that enhance the catalytic efficiency of the enzyme. The conversion of (<i>R</i>)-ethyl 5-methyl-3-oxooctanoate to (3<i>S</i>,5<i>R</i>)-ethyl 3-amino-5-methyloctanoate in the context of several ω-AT mutants was evaluated using the computational protocol developed in this work. We correctly identify the mutations that yield the greatest improvements in enzyme activity (20–60-fold improvement over wild type) and confirm that the computationally predicted structure of a highly active mutant reproduces key structural aspects of the variant, including side chain conformational changes, as determined by X-ray crystallography. Overall, the protocol developed here yields encouraging results and suggests that computational approaches can aid in the redesign of enzymes with improved catalytic efficiency

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 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