No abstract

One of the most recently identified serotonin (5-hydroxytryptamine (5-HT)) receptor subtypes is the 5-HT 6 receptor. Although in-depth localization studies reveal an exclusive distribution of 5-HT 6 mRNA in the central nervous system, the precise biological role of this receptor still remains unknown. In the present series of experiments, we report the pharmacological and neurochemical characterization of two novel and selective 5-HT 6 receptor agonists. WAY-181187 and WAY-208466 possess high affinity binding (2.2 and 4.8 nM, respectively) at the human 5-HT 6 receptor and profile as full receptor agonists (WAY-181187: EC 50 ¼ 6.6 nM, E max ¼ 93%; WAY-208466: EC 50 ¼ 7.3 nM; E max ¼ 100%). In the rat frontal cortex, acute administration of WAY-181187 (3-30 mg/kg, subcutaneous (s.c.)) significantly increased extracellular GABA concentrations without altering the levels of glutamate or norepinephrine. Additionally, WAY-181187 (30 mg/kg, s.c.) produced modest yet significant decreases in cortical dopamine and 5-HT levels. Subsequent studies showed that the neurochemical effects of WAY-181187 in the frontal cortex could be blocked by pretreatment with the 5-HT 6 antagonist, SB-271046 (10 mg/kg, s.c.), implicating 5-HT 6 receptor mechanisms in mediating these responses. Moreover, the effects of WAY-181187 on catecholamines were attenuated by an intracortical infusion of the GABA A receptor antagonist, bicuculline (10 mM), confirming a local relationship between 5-HT 6 receptors and GABAergic systems in the frontal cortex. In the dorsal hippocampus, striatum, and amygdala, WAY-181187 (10-30 mg/kg, s.c.) elicited robust elevations in extracellular levels of GABA without producing similar effects on concentrations of norepinephrine, serotonin, dopamine, or glutamate. In contrast to these brain regions, WAY-181187 had no effect on the extracellular levels of GABA in the nucleus accumbens or thalamus. Additional studies showed that WAY-208466 (10 mg/kg, s.c.) preferentially elevated cortical GABA levels following both acute and chronic (14 day) administration, indicating that neurochemical tolerance does not develop following repeated 5-HT 6 receptor stimulation. In hippocampal slice preparations (in vitro), 5-HT 6 receptor agonism attenuated stimulated glutamate levels elicited by sodium azide and high KCl treatment. Furthermore, in the rat schedule-induced polydipsia model of obsessive compulsive disorder (OCD), acute administration of WAY-181187 (56-178 mg/kg, po) decreased adjunctive drinking behavior in a dose-dependent manner. In summary, WAY-181187 and WAY-208466 are novel, selective, and potent 5-HT 6 receptor agonists displaying a unique neurochemical signature in vivo. Moreover, these data highlight a previously undescribed role for 5-HT 6 receptors to modulate basal GABA and stimulated glutamate transmission, as well as reveal a potential therapeutic role for this receptor in the treatment of some types of anxiety-related disorders (eg OCD).

The amyloid hypothesis states that a variety of neurotoxic ␤-amyloid (A␤) species contribute to the pathogenesis of Alzheimer's disease. Accordingly, a key determinant of disease onset and progression is the appropriate balance between A␤ production and clearance. Enzymes responsible for the degradation of A␤ are not well understood, and, thus far, it has not been possible to enhance A␤ catabolism by pharmacological manipulation. We provide evidence that A␤ catabolism is increased after inhibition of plasminogen activator inhibitor-1 (PAI-1) and may constitute a viable therapeutic approach for lowering brain A␤ levels. PAI-1 inhibits the activity of tissue plasminogen activator (tPA), an enzyme that cleaves plasminogen to generate plasmin, a protease that degrades A␤ oligomers and monomers. Because tPA, plasminogen and PAI-1 are expressed in the brain, we tested the hypothesis that inhibitors of PAI-1 will enhance the proteolytic clearance of brain A␤. Our data demonstrate that PAI-1 inhibitors augment the activity of tPA and plasmin in hippocampus, significantly lower plasma and brain A␤ levels, restore long-term potentiation deficits in hippocampal slices from transgenic A␤-producing mice, and reverse cognitive deficits in these mice.Alzheimer ͉ plasminogen activator inhibitor ͉ tissue plasminogen activator A lzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by the presence of intracellular neuronal tangles and extracellular parenchymal and vascular amyloid deposits containing ␤-amyloid peptide (A␤). A␤ is a 39-to 42-aa peptide derived from the proteolytic processing of the amyloid precursor protein (APP) (1). The ''amyloid hypothesis'' of AD postulates a central causal role for A␤ in AD pathogenesis and is supported by genetic and physiological evidence. All known early onset familial AD mutations result in enhanced levels of cytotoxic A␤ species, amyloid plaque deposition, and dementia. Furthermore, A␤ peptide is reported to be neurotoxic and synaptotoxic in vitro and in vivo, inhibiting long-term potentiation (LTP), a physiological correlate of memory (2). Based on these observations, a number of strategies to reduce brain A␤ levels are being pursued as therapeutic approaches to treat AD (3, 4).If the amyloid hypothesis of AD is correct and A␤ levels are pivotal to disease etiology, then the balance between A␤ production and catabolism is likely to be a key determinant of disease progression. It has been suggested that insufficient clearance of A␤ may account for elevated A␤ levels in the brain and the accumulation of pathogenic amyloid deposits in sporadic AD (5). A number of proteases have been implicated in the proteolytic clearance of A␤ from the CNS, including neprilysin, insulin-degrading enzyme, endothelin converting enzyme, and plasmin (3, 6-8). The relative contribution of these enzymes to A␤ catabolism remains unclear, but each protease may play a significant role in the degradation and clearance of A␤, resulting in a slowing of A␤ accumulation and aggregation and u...

The identification of small molecule aminohydantoins as potent and selective human beta-secretase inhibitors is reported. These analogues exhibit low nannomolar potency for BACE1, show comparable activity in a cell-based (ELISA) assay, and demonstrate >100x selectivity for the other structurally related aspartyl proteases BACE2, cathepsinD, renin, and pepsin. On the basis of the cocrystal structure of the HTS-hit 2 in the BACE1 active site and by use of a structure-based drug design approach, we methodically explored the comparatively large binding pocket of the BACE1 enzyme and identified key interactions between the ligand and the protein that contributed to the affinity. One of the more potent compounds, (S)-55, displayed an IC(50) value for BACE1 of 10 nM and exhibited comparable cellular activity (EC(50) = 20 nM) in the ELISA assay. Acute oral administration of (S)-55 at 100 mg/kg resulted in a 69% reduction of plasma A beta(40) at 8 h in a Tg2576 mouse (p < 0.001).

Certain classes of neuroactive steroids (NASs) are positive allosteric modulators (PAM) of synaptic and extrasynaptic GABA receptors. Herein, we report new SAR insights in a series of 5β-nor-19-pregnan-20-one analogues bearing substituted pyrazoles and triazoles at C-21, culminating in the discovery of 3α-hydroxy-3β-methyl-21-(4-cyano-1H-pyrazol-1'-yl)-19-nor-5β-pregnan-20-one (SAGE-217, 3), a potent GABA receptor modulator at both synaptic and extrasynaptic receptor subtypes, with excellent oral DMPK properties. Compound 3 has completed a phase 1 single ascending dose (SAD) and multiple ascending dose (MAD) clinical trial and is currently being studied in parallel phase 2 clinical trials for the treatment of postpartum depression (PPD), major depressive disorder (MDD), and essential tremor (ET).