No abstract

Converging lines of evidence implicate the beta-amyloid peptide (Ab) as causative in Alzheimer's disease. We describe a novel class of compounds that reduce Ab production by functionally inhibiting g-secretase, the activity responsible for the carboxy-terminal cleavage required for Ab production. These molecules are active in both 293 HEK cells and neuronal cultures, and exert their effect upon Ab production without affecting protein secretion, most notably in the secreted forms of the amyloid precursor protein (APP). Oral administration of one of these compounds, N-[N-(3,5-di¯uoro-phenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester, to mice transgenic for human APP V717F reduces brain levels of Ab in a dose-dependent manner within 3 h. These studies represent the ®rst demonstration of a reduction of brain Ab in vivo. Development of such novel functional g-secretase inhibitors will enable a clinical examination of the Ab hypothesis that Ab peptide drives the neuropathology observed in Alzheimer's disease.

BACE1 is a key protease controlling the formation of amyloid ␤, a peptide hypothesized to play a significant role in the pathogenesis of Alzheimer's disease (AD). Therefore, the development of potent and selective inhibitors of BACE1 has been a focus of many drug discovery efforts in academiaandindustry.Herein,wereportthenonclinicalandearlyclinicaldevelopmentofLY2886721,aBACE1activesiteinhibitorthatreached phase 2 clinical trials in AD. LY2886721 has high selectivity against key off-target proteases, which efficiently translates in vitro activity into robust in vivo amyloid ␤ lowering in nonclinical animal models. Similar potent and persistent amyloid ␤ lowering was observed in plasma and lumbar CSF when single and multiple doses of LY2886721 were administered to healthy human subjects. Collectively, these data add support for BACE1 inhibition as an effective means of amyloid lowering and as an attractive target for potential disease modification therapy in AD.

Amylin, a 37-amino-acid amyloidogenic peptide, bears biophysical similarities to the amyloid-beta peptide (A beta) deposited in Alzheimer's disease. Using embryonic rat hippocampal cultures we tested whether amylin induces neurotoxicity similar to that previously observed with A beta(1-40). Treatment with human amylin(1-37) resulted in prominent toxicity as assessed by phase-contrast microscopy and quantification of lactate dehydrogenase in the medium. Amylin-induced neurotoxicity was morphologically similar to that induced by A beta(1-40). In contrast, the nonamyloidogenic rat amylin showed negligible neurotoxicity despite having 95% sequence similarity to human amylin. Only full-length human amylin was toxic; various amylin peptide fragments including amino acid residues 20-29 were nontoxic at similar concentrations. These studies suggest that unrelated amyloidogenic peptides like human amylin and A beta can adopt a similar neurotoxic conformation in vitro. Similar conformation-dependent neurotoxicity may drive the prominent neurite degeneration around compacted but not diffuse deposits of A beta in Alzheimer's disease.

Clusterin is a secreted glycoprotein that is markedly induced in many disease states and after tissue injury. In the CNS, clusterin expression is elevated in neuropathological conditions such as Alzheimer's disease (AD), where it is found associated with amyloid-/3 (A/I) plaques. Clusterin also coprecipitates with A/I from CSF, suggesting a physiological interaction with A/I. Given this interaction with A/I, the goal of this study was to determine whether clusterin could modulate A/I neurotoxicity. A mammalian recombinant source of human clusterin was obtained by stable transfection of hamster kidney fibroblasts with pADHC-9, a full-length human cDNA clone for clusterin. Recombinant clusterin obtained from this cell line, as well as a commercial source of native clusterin purified from serum, afforded dosedependent neuroprotection against A/I(1-40) when tested in primary rat mixed hipppocampal cultures. Clusterin afforded substoichiometric neuroprotection against several lots of A/3(1 -40) but not against H 202 or kainic acid excitotoxicity. These results suggest that the elevated expression of clusterin found in AD brain may have effects on subsequent amyloid-/3 plaque pathology.