Type 2 diabetes has become a pervasive public health problem. The etiology of the disease has not been fully defined but appears to involve abnormalities in peripheral and central nervous system pathways, as well as prominent inflammatory components. Because nicotinic acetylcholine receptors (nAChRs) are known to interact with anti-inflammatory pathways and have been implicated in control of appetite and body weight, as well as lipid and energy metabolism, we examined their role in modulating biological parameters associated with the disease. In a model of type 2 diabetes, the homozygous leptin-resistant db/db obese mouse, we measured the effects of a novel ␣7 nAChR-selective agonist [5-methyl-N-[2-(pyridin-3-ylmethyl)-1-azabicyclo[2.2.2]oct-3-yl]thiophene-2-carboxamide (TC-7020)] on body mass, glucose and lipid metabolism, and proinflammatory cytokines. Oral administration of TC-7020 reduced weight gain and food intake, reduced elevated glucose and glycated hemoglobin levels, and lowered elevated plasma levels of triglycerides and the proinflammatory cytokine tumor necrosis factor-␣. These changes were reversed by the ␣7-selective antagonist methyllycaconitine, confirming the involvement of ␣7 nAChRs. Prevention of weight gain, decreased food intake, and normalization of glucose levels were also blocked by the Janus kinase 2 (JAK2) inhibitor ␣-cyano-(3,4-dihydroxy)-N-benzylcinnamide (AG-490), suggesting that these effects involve linkage of ␣7 nAChRs to the JAK2-signal transducer and activator of transcription 3 signaling pathway. The results show that ␣7 nAChRs play a central role in regulating biological parameters associated with diabetes and support the potential of targeting these receptors as a new therapeutic strategy for treatment.In 2000 it was reported that at least 171 million people worldwide (2.8% of the population) suffered from diabetes, and it has been estimated that the incidence will almost double by the year 2030 (Wild et al., 2004). The Centers for Disease Control and Prevention has designated the disease an epidemic. Specific pathogenic entities contributing to diabetic risk, such as central adiposity, ectopic fat accumulation, hyperlipidemia, and inflammation, have been well characterized. In general, diabetes is believed to be secondary to an insulin-resistant state, which is associated with excess adiposity (Sykiotis and Papavassiliou, 2001). Insulin resistance in skeletal muscle, liver, and adipose tissue impedes glucose uptake and results in the release of free fatty acids and the characteristically associated dyslipidemia. Elevations in postprandial blood glucose levels and ultimately in fasting glucose levels result in compensatory hyperinsulinemia, a condition that is initially accompanied by islet ␤-cell hypertrophy and eventual failure (Sykiotis and Papavassiliou, 2001).A key factor that underlies the development of diabetes is a characteristic systemic inflammation, marked by increases in the venous blood concentrations of C-reactive protein, interleukin 6 (IL-6), and tum...

Neuronal nicotinic acetylcholine receptors (nAChRs) are ligand gated ion channels of broad distribution and structural heterogeneity. Their functional diversity demonstrated involvement in a variety of neuronal processes (e.g., sensory gating and cognitive function) and generated great interest in them as targets for therapeutic intervention in a number of neuropathological conditions and diseases. In order to control distinct nicotinic functions pharmacologically, it is important to design ligands that selectively interact with distinct receptor subtypes in such a way as to maximize the therapeutic effect and minimize the adverse effects. The alpha7 nAChR, a CNS subtype, has been the most intensively studied nAChR in recent years. Selective alpha7 nAChR agonists have been developed as potential candidates for the treatment of schizophrenia, cognitive disorders (including Alzheimer's disease), and inflammation. Despite early concerns that the rapid desensitization property of the alpha7 nAChR would limit their therapeutic potential, several have already been advanced to clinical trials (e.g., PH-399733, Pfizer; MEM 3454, Memory Pharmaceuticals/Roche). Further development of allosteric modulators and pharmaceutically relevant antagonists might expand the therapeutic potential of compounds that target alpha7 nAChRs. In this review we briefly describe the structure and function of the alpha7 nAChR and its in vitro and in vivo pharmacology, discuss the clinical relevance of these efforts, and review the current progress in alpha7 ligand development.

The pharmacokinetic and safety profiles of clinical drug candidates are greatly influenced by their requisite physicochemical properties. In particular, it has been shown that 2D molecular descriptors such as fraction of Sp3 carbon atoms (Fsp3) and number of stereo centers correlate with clinical success. Using the proteomic off-target hit rate of nicotinic ligands, we found that shape-based 3D descriptors such as the radius of gyration and shadow indices discriminate off-target promiscuity better than do Fsp3 and the number of stereo centers. We have deduced the relevant descriptor values required for a ligand to be nonpromiscuous. Investigating the MDL Drug Data Report (MDDR) database as compounds move from the preclinical stage toward the market, we have found that these shape-based 3D descriptors predict clinical success of compounds at preclinical and phase1 stages vs compounds withdrawn from the market better than do Fsp3 and LogD. Further, these computed 3D molecular descriptors correlate well with experimentally observed solubility, which is among well-known physicochemical properties that drive clinical success. We also found that about 84% of launched drugs satisfy either Shadow index or Fsp3 criteria, whereas withdrawn and discontinued compounds fail to meet the same criteria. Our studies suggest that spherical compounds (rather than their elongated counterparts) with a minimal number of aromatic rings may exhibit a high propensity to advance from clinical trials to market.

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(2S,3R)-N-[2-(Pyridin-3-ylmethyl)-1-azabicyclo[2.2.2]oct-3-yl]benzo[b]furan-2-carboxamide (7a, TC-5619), a novel selective agonist of the α7 neuronal nicotinic acetylcholine receptor, has been identified as a promising drug candidate for the treatment of cognitive impairment associated with neurological disorders. 7a demonstrated more than a thousand-fold separation between the affinities for the α7 and α4β2 receptor subtypes and had no detectable effects on muscle or ganglionic nicotinic receptor subtypes, indicating a marked selectivity for the central nervous system over the peripheral nervous system. Results obtained from homology modeling and docking explain the observed selectivity. 7a had positive effects across cognitive, positive, and negative symptoms of schizophrenia in animal models and was additive or synergistic with the antipsychotic clozapine. Compound 7a, as an augmentation therapy to the standard treatment with antipsychotics, demonstrated encouraging results on measures of negative symptoms and cognitive dysfunction in schizophrenia and was well tolerated in a phase II clinical proof of concept trial in patients with schizophrenia.

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Diversification of essential nicotinic cholinergic pharmacophoric elements, i.e., cationic center and hydrogen bond acceptor, resulted in the discovery of novel potent α4β2 nAChR selective agonists comprising a series of N-acyldiazabicycles. Core characteristics of the series are an exocyclic carbonyl moiety as a hydrogen bond acceptor and endocyclic secondary amino group. These features are positioned at optimal distance and with optimal relative spatial orientation to provide near optimal interactions with the receptor. A novel potent and highly selective α4β2 nAChR agonist 3-(5-chloro-2-furoyl)-3,7-diazabicyclo[3.3.0]octane (56, TC-6683, AZD1446) with favorable pharmaceutical properties and in vivo efficacy in animal models has been identified as a potential treatment for cognitive deficits associated with psychiatric or neurological conditions and is currently being progressed to phase 2 clinical trials as a treatment for Alzheimer's disease.

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