No abstract

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...

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common genetic cause of familial and sporadic Parkinson's disease (PD). That the most prevalent mutation, G2019S, leads to increased kinase activity has led to a concerted effort to identify LRRK2 kinase inhibitors as a potential disease-modifying therapy for PD. An internal medicinal chemistry effort identified several potent and highly selective compounds with favorable drug-like properties. Here, we characterize the pharmacological properties of cis-2,6-dimethyl-4-(6-(5-(1-methylcyclopropoxy)-1H-indazol-3-yl)pyrimidin-4-yl)morpholine (MLi-2), a structurally novel, highly potent, and selective LRRK2 kinase inhibitor with central nervous system activity. MLi-2 exhibits exceptional potency in a purified LRRK2 kinase assay in vitro (IC 50 5 0.76 nM), a cellular assay monitoring dephosphorylation of LRRK2 pSer935 LRRK2 (IC 50 5 1.4 nM), and a radioligand competition binding assay (IC 50 5 3.4 nM). MLi-2 has greater than 295-fold selectivity for over 300 kinases in addition to a diverse panel of receptors and ion channels. Acute oral and subchronic dosing in MLi-2 mice resulted in dosedependent central and peripheral target inhibition over a 24-hour period as measured by dephosphorylation of pSer935 LRRK2. Treatment of MitoPark mice with MLi-2 was well tolerated over a 15-week period at brain and plasma exposures .100Â the in vivo plasma IC 50 for LRRK2 kinase inhibition as measured by pSer935 dephosphorylation. Morphologic changes in the lung, consistent with enlarged type II pneumocytes, were observed in MLi-2-treated MitoPark mice. These data demonstrate the suitability of MLi-2 as a compound to explore LRRK2 biology in cellular and animal models.

Abstract.A retrospective histologic study of 12 canine and eight feline epithelial odontogenic tumors and cysts was conducted from oral masses (n = 3,9 17) obtained between 1980 and 1990. No sex or breed predilection was identified. Ameloblastoma was observed in two dogs (case Nos. 1, 2) 6 and 8 months of age. Calcifying epithelial odontogenic tumors were seen in a dog (case No. 3) and in two cats (case Nos. 4, 5) between 8 and 16 years of age. Ameloblastic fibroma (or fibroameloblastoma) was observed in cats (case Nos. 6-10) only. Inductive fibroameloblastoma was observed in four cats (case Nos. 6-9) up to 1 year of age, whereas ameloblastic fibroma was seen in a 14-year-old cat (case No. 10). A single ameloblastic odontoma was identified in a 20-month-old dog (case No. 11). Two complex odontomas occurred in a 6-month-old (case No. 12) and a 4-yearold (case No. 13) dog. Odontogenic cysts were identified in five dogs (case Nos. 14-1 8) aged 4.5 months to 16 years and in a 1 -year-old cat (case No. 19) and have not been previously reported in these species. These cysts were lined by a stratified epithelium reminiscent of the appearance of ameloblastic epithelium. An odontogenic keratocyst with prominent central parakeratotic keratinization was identified in one 9-year-old female dog (case No. 20). Almost all epithelial odontogenic tumors were circumscribed, benign tumors that warranted a good prognosis for survival, although local recurrence may have followed (or may follow) incomplete excision. Calcifying epithelial odontogenic tumors may be locally invasive. Of six odontogenic cysts (case Nos. 14-1 9), two (case Nos. 15, 18) gave rise to basi-squamous carcinomas. The classification and behavior of epithelial odontogenic tumors and cysts in human beings, dogs, and cats are discussed.