Inhibition of ␥-secretase, one of the enzymes responsible for the cleavage of the amyloid precursor protein (APP) to produce the pathogenic ␤-amyloid (A␤) peptides, is an attractive approach to the treatment of Alzheimer disease. In addition to APP, however, several other ␥-secretase substrates have been identified (e.g. Notch), and altered processing of these substrates by ␥-secretase inhibitors could lead to unintended biological consequences. To study the in vivo consequences of ␥-secretase inhibition, the ␥-secretase inhibitor LY-411,575 was administered to C57BL/6 and TgCRND8 APP transgenic mice for 15 days. Although most tissues were unaffected, doses of LY-411,575 that inhibited A␤ production had marked effects on lymphocyte development and on the intestine. LY-411,575 decreased overall thymic cellularity and impaired intrathymic differentiation at the CD4 ؊ CD8 ؊ CD44 ؉ CD25 ؉ precursor stage. No effects on peripheral T cell populations were noted following LY-411,575 treatment, but evidence for the altered maturation of peripheral B cells was observed. In the intestine, LY-411,575 treatment increased goblet cell number and drastically altered tissue morphology. These effects of LY-411,575 were not seen in mice that were administered LY-D, a diastereoisomer of LY-411,575, which is a very weak ␥-secretase inhibitor. These studies show that inhibition of ␥-secretase has the expected benefit of reducing A␤ in a murine model of Alzheimer disease but has potentially undesirable biological effects as well, most likely because of the inhibition of Notch processing. Alzheimer disease (AD)1 is the third most common cause of death and the leading cause of dementia in the United States (1). Although the exact cause of AD is still unknown, the etiology of the disease is almost certainly linked to several neuropathological hallmarks observed in the brains of AD victims, particularly extracellular neuritic amyloid plaques and intracellular neurofibrillary tangles (2-4). Although both of these neuropathological lesions probably contribute to progressive neuronal cell death in AD, the proximal lesion appears to be the amyloid plaques and their principal component, the A␤ peptides. A large body of evidence strongly suggests that overproduction, aggregation, and/or plaque deposition of the A␤ peptides, particularly A␤42, are central to the pathogenesis of AD (reviewed in Ref. 5). In fact, two recent studies of patients immunized against the A␤42 peptide have provided the first preliminary clinical evidence that A␤ does indeed contribute to the cognitive decline in AD patients (6, 7).The A␤ peptides are produced by the sequential proteolytic cleavage of the amyloid precursor protein (APP) by ␤-and ␥-secretase. ␥-Secretase is a complex composed of at least four proteins, namely presenilins (presenilin 1 or -2), nicastrin, PEN-2, and APH-1 (8). Presenilin 1 and -2 have been proposed to be the novel aspartyl proteases responsible for the catalytic activity of ␥-secretase (9, 10). Because of the essential role of ␥-secretase i...

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We previously reported the discovery of 4-[(Z)-(4-bromophenyl)(ethoxyimino)methyl]-1'-[(2,4-dimethyl-3-pyridinyl)carbonyl]-4'-methyl-1,4'-bipiperidine N-oxide 1 (SCH 351125) as an orally bioavailable human CCR5 antagonist for the treatment of HIV-1 infection. Herein, we describe in detail the discovery of 1 from our initial lead compound as well as the synthesis and SAR studies directed toward optimization of substitution at the phenyl, oxime, and right-hand side amide groups in the oximino-piperidino-piperidine series. Substitutions (4-Br, 4-CF(3), 4-OCF(3), 4-SO(2)Me, and 4-Cl) at the phenyl group are well-tolerated, and small alkyl substitutions (Me, Et, (n)()Pr, (i)()Pr, and cyclopropyl methyl) at the oxime moiety are preferred for CCR5 antagonism. The 2,6-dimethylnicotinamide N-oxide moiety is the optimal choice for the right-hand side. Several compounds in this series, including compound 1, exhibited excellent antiviral activity in vitro. Compound 1, which has a favorable pharmacokinetic profile in rodents and primates, excellent oral bioavailability, and potent antiviral activity against a wide range of primary HIV-1 isolates, is a potentially promising new candidate for treatment of HIV-1 infection.

Accumulation of the β-amyloid (Aβ) peptides is one of the major pathologic hallmarks in the brains of Alzheimer's disease (AD) patients. Aβ is generated by sequential proteolytic cleavage of the amyloid precursor protein (APP) catalyzed by β- and γ-secretases. Inhibition of Aβ production by γ-secretase inhibitors (GSIs) is thus being pursued as a target for treatment of AD. In addition to processing APP, γ-secretase also catalyzes proteolytic cleavage of other transmembrane substrates, with the best characterized one being the cell surface receptor Notch. GSIs reduce Aβ production in animals and humans but also cause significant side effects because of the inhibition of Notch processing. The development of GSIs that reduce Aβ production and have less Notch-mediated side effect liability is therefore an important goal. γ-Secretase is a large membrane protein complex with four components, two of which have multiple isoforms: presenilin (PS1 or PS2), aph-1 (aph-1a or aph-1b), nicastrin, and pen-2. Here we describe the reconstitution of four γ-secretase complexes in Sf9 cells containing PS1--aph-1a, PS1--aph-1b, PS2--aph-1a, and PS2--aph-1b complexes. While PS1--aph-1a, PS1--aph-1b, and PS2--aph-1a complexes displayed robust γ-secretase activity, the reconstituted PS2--aph-1b complex was devoid of detectable γ-secretase activity. γ-Secretase complexes containing PS1 produced a higher proportion of the toxic species Aβ42 than γ-secretase complexes containing PS2. Using the reconstitution system, we identified MRK-560 and SCH 1500022 as highly selective inhibitors of PS1 γ-secretase activity. These findings may provide important insights into developing a new generation of γ-secretase inhibitors with improved side effect profiles.

Cyclic hydroxyamidines were designed and validated as isosteric replacements of the amide functionality. Compounds with these structural motifs were found to be metabolically stable and to possess highly desirable pharmacokinetic profiles. These designs were applied in the identification of γ-secretase modulators leading to highly efficacious agents for reduction of central nervous system Aβ(42) in various animal models.