Biochemical and functional characterization of the p.A165T missense variant of mitochondrial amidoxime-reducing component 1.

Recent genome-wide association studies have identified a missense variant p.A165T in mitochondrial amidoxime-reducing component 1 (mARC1) that is strongly associated with protection from all-cause cirrhosis and improved prognosis in nonalcoholic steatohepatitis. The precise mechanism of this protective effect is unknown. Substitution of alanine 165 with threonine is predicted to affect mARC1 protein stability and to have deleterious effects on its function. To investigate the mechanism, we have generated a knock-in mutant mARC1 A165T and a catalytically dead mutant C273A (as a control) in human hepatoma HepG2 cells, enabling characterization of protein subcellular distribution, stability, and biochemical functions of the mARC1 mutant protein expressed from its endogenous locus. Compared to WT mARC1, we found that the A165T mutant exhibits significant mislocalization outside of its traditional location anchored in the mitochondrial outer membrane and reduces protein stability, resulting in lower basal levels. We evaluated the involvement of the ubiquitin proteasome system in mARC1 A165T degradation and observed increased ubiquitination and faster degradation of the A165T variant. In addition, we have shown that HepG2 cells carrying the MTARC1 p.A165T variant exhibit lower N-reductive activity on exogenously added amidoxime substrates in vitro. The data from these biochemical and functional assays suggest a mechanism by which the MTARC1 p.A165T variant abrogates enzyme function which may contribute to its protective effect in liver disease.

Pharmacokinetic Study of Islatravir and Etonogestrel Implants in Macaques.

The prevention of HIV and unintended pregnancies is a public health priority. Multi-purpose prevention technologies capable of long-acting HIV and pregnancy prevention are desirable for women. Here, we utilized a preclinical macaque model to evaluate the pharmacokinetics of biodegradable ε-polycaprolactone implants delivering the antiretroviral islatravir (ISL) and the contraceptive etonogestrel (ENG). Three implants were tested: ISL-62 mg, ISL-98 mg, and ENG-33 mg. Animals received one or two ISL-eluting implants, with doses of 42, 66, or 108 µg of ISL/day with or without an additional ENG-33 mg implant (31 µg/day). Drug release increased linearly with dose with median [range] plasma ISL levels of 1.3 [1.0-2.5], 1.9 [1.2-6.3] and 2.8 [2.3-11.6], respectively. The ISL-62 and 98 mg implants demonstrated stable drug release over three months with ISL-triphosphate (ISL-TP) concentr54ations in PBMCs above levels predicted to be efficacious for PrEP. Similarly, ENG implants demonstrated sustained drug release with median [range] plasma ENG levels of 495 [229-1110] pg/mL, which suppressed progesterone within two weeks and showed no evidence of altering ISL pharmacokinetics. Two of the six ISL-98 mg implants broke during the study and induced implant-site reactions, whereas no reactions were observed with intact implants. We show that ISL and ENG biodegradable implants are safe and yield sufficient drug levels to achieve prevention targets. The evaluation of optimized implants with increased mechanical robustness is underway for improved durability and vaginal efficacy in a SHIV challenge model.

Long-acting biodegradable implant for sustained delivery of antiretrovirals (ARVs) and hormones.

Women worldwide confront two major reproductive health challenges: the need for contraception and protection from sexually transmitted infections, including Human Immunodeficiency Virus (HIV). Multipurpose Prevention Technologies (MPTs) that simultaneously prevent unintended pregnancy and HIV could address these challenges with a single product. Here, we developed a long-acting (LA) subcutaneously administered and biodegradable implant system that provides sustained delivery of contraceptive and antiretroviral (ARV) with zero-order release kinetics. The MPT system involves two implants comprising an extruded tube of a biodegradable polymer, poly(ε-caprolactone) (PCL). Each implant is filled with a formulation of progestin [levonorgestrel (LNG) or etonogestrel (ENG)], or a formulation of a potent ARV [tenofovir alafenamide (TAF), or 4'-Ethynyl-2-fluoro-2'-deoxyadenosine (EFdA)]. We demonstrated sustained in-vitro release of LNG, ENG, and EFdA from the implant system for 13-17 months, while maintaining high stability of the drugs (>99%) within the implant reservoirs. We further elucidated the controlled release mechanism of the implant and leveraged several tunable parameters (e.g., type and quantity of the excipient, PCL properties, and implant wall thickness) to tailor the release kinetics and enhance the mechanical integrity of the MPT implant. The optimized MPT showed sustained in-vitro release of ENG and EFdA over 1 year while maintaining a high level of formulation stability and structural integrity. The MPT implant system was further evaluated in a preclinical study using a rodent model and demonstrated sustained release of EFdA (6 months) and ENG (12 months) with high stability of the drug formulation (>95%). This manuscript supports the continued advancement of LA delivery systems for MPTs.

Identification of Diarylurea Inhibitors of the Cardiac-Specific Kinase TNNI3K by Designing Selectivity Against VEGFR2, p38α, and B-Raf.

A series of diarylurea inhibitors of the cardiac-specific kinase TNNI3K were developed to elucidate the biological function of TNNI3K and evaluate TNNI3K as a therapeutic target for the treatment of cardiovascular diseases. Utilizing a structure-based design, enhancements in kinase selectivity were engineered into the series, capitalizing on the established X-ray crystal structures of TNNI3K, VEGFR2, p38α, and B-Raf. Our efforts culminated in the discovery of an in vivo tool compound 47 (GSK329), which exhibited desirable TNNI3K potency and rat pharmacokinetic properties as well as promising kinase selectivity against VEGFR2 (40-fold), p38α (80-fold), and B-Raf (>200-fold). Compound 47 demonstrated positive cardioprotective outcomes in a mouse model of ischemia/reperfusion cardiac injury, indicating that optimized exemplars from this series, such as 47, are favorable leads for discovering novel medicines for cardiac diseases.

High FGF23 Levels Failed to Predict Cardiac Hypertrophy in Animal Models of Hyperphosphatemia and Chronic Renal Failure.

Increased fibroblast growth factor 23 (FGF23) levels are an independent predictor for adverse cardiac events suggesting a role as a link that drives cardiomyopathic changes in cardiorenal syndrome. The search for the underlying mechanism driving this interaction has led to the hypothesis that FGF23 causes pathogenic changes in the heart. Increased serum FGF23 has been independently shown to cause increased cardiac morbidity, mortality, and hypertrophy by signalling through FGF receptor 4. This mechanistic concept was based on preclinical studies demonstrating inhibition of FGF23 signaling through FGF4, which led to suppression of left ventricular hypertrophy and fibrosis in a 2-week rat 5/6 nephrectomy study and a 12-week (2%) high-phosphate diet mouse model in which FGF23 levels were markedly elevated. In this report, renal dysfunction was observed in the 5/6 nephrectomy model, and FGF23 levels were significantly elevated, whereas no changes in left ventricular hypertrophy were observed at 2 or 4 weeks postnephrectomy. Mice placed on a high-phosphate diet that did not cause significant renal dysfunction resulted in significantly elevated FGF23 but no changes in left ventricular hypertrophy. The in vivo studies reported here, which were performed to recapitulate the observations of FGF23 as a driver of cardiac hypertrophy, did not lend support to the FGF23-driven cardiac remodelling hypothesis.

4,6-Diaminopyrimidines as Highly Preferred Troponin I-Interacting Kinase (TNNI3K) Inhibitors.

Structure-guided progression of a purine-derived series of TNNI3K inhibitors directed design efforts that produced a novel series of 4,6-diaminopyrimidine inhibitors, an emerging kinase binding motif. Herein, we report a detailed understanding of the intrinsic conformational preferences of the scaffold, which impart high specificity for TNNI3K. Further manipulation of the template based on the conformational analysis and additional structure-activity relationship studies provided enhancements in kinase selectivity and pharmacokinetics that furnished an advanced series of potent inhibitors. The optimized compounds (e.g., GSK854) are suitable leads for identifying new cardiac medicines and have been employed as in vivo tools in investigational studies aimed at defining the role of TNNI3K within heart failure.

Activation of the Amino Acid Response Pathway Blunts the Effects of Cardiac Stress.

BACKGROUND: The amino acid response (AAR) is an evolutionarily conserved protective mechanism activated by amino acid deficiency through a key kinase, general control nonderepressible 2. In addition to mobilizing amino acids, the AAR broadly affects gene and protein expression in a variety of pathways and elicits antifibrotic, autophagic, and anti-inflammatory activities. However, little is known regarding its role in cardiac stress. Our aim was to investigate the effects of halofuginone, a prolyl-tRNA synthetase inhibitor, on the AAR pathway in cardiac fibroblasts, cardiomyocytes, and in mouse models of cardiac stress and failure. METHODS AND RESULTS: Consistent with its ability to inhibit prolyl-tRNA synthetase, halofuginone elicited a general control nonderepressible 2-dependent activation of the AAR pathway in cardiac fibroblasts as evidenced by activation of known AAR target genes, broad regulation of the transcriptome and proteome, and reversal by l-proline supplementation. Halofuginone was examined in 3 mouse models of cardiac stress: angiotensin II/phenylephrine, transverse aortic constriction, and acute ischemia reperfusion injury. It activated the AAR pathway in the heart, improved survival, pulmonary congestion, left ventricle remodeling/fibrosis, and left ventricular function, and rescued ischemic myocardium. In human cardiac fibroblasts, halofuginone profoundly reduced collagen deposition in a general control nonderepressible 2-dependent manner and suppressed the extracellular matrix proteome. In human induced pluripotent stem cell-derived cardiomyocytes, halofuginone blocked gene expression associated with endothelin-1-mediated activation of pathologic hypertrophy and restored autophagy in a general control nonderepressible 2/eIF2α-dependent manner. CONCLUSIONS: Halofuginone activated the AAR pathway in the heart and attenuated the structural and functional effects of cardiac stress.

Substituent Effects on Drug-Receptor H-bond Interactions: Correlations Useful for the Design of Kinase Inhibitors.

Investigation of troponin I-interacting kinase (TNNI3K) as a potential target for the treatment of heart failure has produced a series of substituted N-methyl-3-(pyrimidin-4-ylamino)benzenesulfonamide inhibitors that display excellent potency and selectivity against a broad spectrum of protein kinases. Crystal structures of prototypical members bound to the ATP-binding site of TNNI3K reveal two anchoring hydrogen bond contacts: (1) from the hinge region amide N-H to the pyrimidine nitrogen and (2) from the sulfonamide N-H to the gatekeeper threonine. Evaluation of various para-substituted benzenesulfonamides defined a substituent effect on binding affinity resulting from modulation of the sulfonamide H-bond donor strength. An opposite electronic effect emerged for the hinge NH-pyrimidine H-bond interaction, which is further illuminated in the correlation of calculated H-bond acceptor strength and TNNI3K affinity for a variety of hinge binding heterocycles. These fundamental correlations on drug-receptor H-bond interactions may be generally useful tools for the optimization of potency and selectivity in the design of kinase inhibitors.

GSK114: A selective inhibitor for elucidating the biological role of TNNI3K.

A series of selective TNNI3K inhibitors were developed by modifying the hinge-binding heterocycle of a previously reported dual TNNI3K/B-Raf inhibitor. The resulting quinazoline-containing compounds exhibit a large preference (up to 250-fold) for binding to TNNI3K versus B-Raf, are useful probes for elucidating the biological pathways associated with TNNI3K, and are leads for discovering novel cardiac medicines. GSK114 emerged as a leading inhibitor, displaying significant bias (40-fold) for TNNI3K over B-Raf, exceptional broad spectrum kinase selectivity, and adequate oral exposure to enable its use in cellular and in vivo studies.

Identification of Purines and 7-Deazapurines as Potent and Selective Type I Inhibitors of Troponin I-Interacting Kinase (TNNI3K).

A series of cardiac troponin I-interacting kinase (TNNI3K) inhibitors arising from 3-((9H-purin-6-yl)amino)-N-methyl-benzenesulfonamide (1) is disclosed along with fundamental structure-function relationships that delineate the role of each element of 1 for TNNI3K recognition. An X-ray structure of 1 bound to TNNI3K confirmed its Type I binding mode and is used to rationalize the structure-activity relationship and employed to design potent, selective, and orally bioavailable TNNI3K inhibitors. Identification of the 7-deazapurine heterocycle as a superior template (vs purine) and its elaboration by introduction of C4-benzenesulfonamide and C7- and C8-7-deazapurine substituents produced compounds with substantial improvements in potency (>1000-fold), general kinase selectivity (10-fold improvement), and pharmacokinetic properties (>10-fold increase in poDNAUC). Optimal members of the series have properties suitable for use in in vitro and in vivo experiments aimed at elucidating the role of TNNI3K in cardiac biology and serve as leads for developing novel heart failure medicines.

Inhibition of the cardiomyocyte-specific kinase TNNI3K limits oxidative stress, injury, and adverse remodeling in the ischemic heart.

Percutaneous coronary intervention is first-line therapy for acute coronary syndromes (ACS) but can promote cardiomyocyte death and cardiac dysfunction via reperfusion injury, a phenomenon driven in large part by oxidative stress. Therapies to limit this progression have proven elusive, with no major classes of new agents since the development of anti-platelets/anti-thrombotics. We report that cardiac troponin I-interacting kinase (TNNI3K), a cardiomyocyte-specific kinase, promotes ischemia/reperfusion injury, oxidative stress, and myocyte death. TNNI3K-mediated injury occurs through increased mitochondrial superoxide production and impaired mitochondrial function and is largely dependent on p38 mitogen-activated protein kinase (MAPK) activation. We developed a series of small-molecule TNNI3K inhibitors that reduce mitochondrial-derived superoxide generation, p38 activation, and infarct size when delivered at reperfusion to mimic clinical intervention. TNNI3K inhibition also preserves cardiac function and limits chronic adverse remodeling. Our findings demonstrate that TNNI3K modulates reperfusion injury in the ischemic heart and is a tractable therapeutic target for ACS. Pharmacologic TNNI3K inhibition would be cardiac-selective, preventing potential adverse effects of systemic kinase inhibition.

Novel nicotinic acetylcholine receptor agonists containing carbonyl moiety as a hydrogen bond acceptor.

A novel series of α4ß2 nAChR agonists lacking common pyridine or its bioisosteric heterocycle have been disclosed. Essential pharmacophoric elements of the series are exocyclic carbonyl moiety as a hydrogen bond acceptor and secondary amino group within diaza- or azabicyclic scaffold. Computer modeling studies suggested that molecular shape of the ligand also contributes to promotion of agonism. Proof of concept for improving working memory performance in a novel object recognition task has been demonstrated on a representative of the series, 3-propionyl-3,7-diazabicyclo[3.3.0]octane (34).

NADPH oxidase-dependent and -independent mechanisms of reported inhibitors of reactive oxygen generation.

NADPH oxidase isoform-2 (NOX2) generates reactive oxygen species (ROS) that contribute to neurodegenerative and cardiovascular pathologies. However, validation of NOX2 as a pharmacotherapeutic target has been hampered by a lack of mechanistically-defined inhibitors. Using cellular and biochemical assays, we explored previously reported inhibitors of ROS production (perhexiline, suramin, VAS2870 and two Shionogi patent compounds) as direct NOX2 inhibitors. All but suramin, which presumably lacks cell penetrance, inhibit cellular ROS production. However, only perhexiline and suramin inhibit biochemical NOX2 activity. Indeed, our data suggest that NOX2 inhibition by perhexiline may contribute significantly to its demonstrated cardioprotective effects. Inhibition of protein kinase CßII explains the cellular activity of the Shionogi compounds, whereas VAS2870 inhibits by an as-yet unidentified mechanism unrelated to direct NOX2 function or subunit assembly. These data delineate the mechanisms of action of these compounds and highlight their strengths and limitations for use in future target validation studies.

Discovery of 3-(5-chloro-2-furoyl)-3,7-diazabicyclo[3.3.0]octane (TC-6683, AZD1446), a novel highly selective α4ß2 nicotinic acetylcholine receptor agonist for the treatment of cognitive disorders.

Diversification of essential nicotinic cholinergic pharmacophoric elements, i.e., cationic center and hydrogen bond acceptor, resulted in the discovery of novel potent α4ß2 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 α4ß2 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.

Effects of AZD3480, a neuronal nicotinic acetylcholine receptor agonist, and donepezil on dizocilpine-induced attentional impairment in rats.

BACKGROUND AND RATIONALE: Nicotinic acetylcholine systems play major roles in cognitive function. Nicotine and a variety of nicotinic agonists improve attention, and nicotinic antagonist exposure impairs it. This study was conducted to investigate the effect of a novel nicotinic receptor agonist at α4ß2 nicotinic receptors (AZD3480) on attention and reversal of pharmacologically induced attentional impairment produced by the NMDA glutamate antagonist dizocilpine (MK-801). METHODS: Adult female Sprague-Dawley rats were trained to perform an operant visual signal detection task to a stable baseline of accuracy. The rats were then injected subcutaneously following a repeated measures, counter-balanced design with saline, AZD3480 (0.01, 0.1, and 1 mg/kg), dizocilpine (0.05 mg/kg), or their combinations 30 min before the test. The effect of donepezil on the same pharmacologically induced attentional impairment was also tested. A separate group of rats was injected with donepezil (0.01, 0.1, and 1 mg/kg), dizocilpine (0.05 mg/kg), or their combinations, and their attention were assessed. Saline was the vehicle control. RESULTS: Dizocilpine caused a significant (p < 0.0005) impairment in percent correct performance. This attentional impairment was significantly (p < 0.0005) reversed by 0.01 and 0.1 mg/kg of AZD3480. AZD3480 by itself did not alter the already high baseline control performance. Donepezil (0.01-1.0 mg/kg) also significantly (p < 0.005) attenuated the dizocilpine-induced attentional impairment. CONCLUSIONS: AZD3480, similar to donepezil, showed significant efficacy for counteracting the attentional impairment caused by the NMDA glutamate antagonist dizocilpine. Low doses of AZD3480 may provide therapeutic benefit for reversing attentional impairment in patients suffering from cognitive impairment due to glutamatergic dysregulation and likely other attentional disorders.

Development of a high-throughput cell-based assay for superoxide production in HL-60 cells.

Superoxide affects many normal and pathogenic cellular processes, and the detection of superoxide produced by cells is therefore of interest for potential therapeutic applications. To develop a high-throughput cell-based assay for the detection of extracellular superoxide production that could be run in a 384-well or 1536-well format, 2 luminescent reagents, Lucigenin and Diogenes, and one fluorescent reagent, Oxyburst Green BSA, were tested. HL-60 cells, which had been differentiated to a neutrophil-like phenotype with DMSO and frozen in large batches, were used in assays. All 3 superoxide detection reagents performed well statistically in terms of IC(50) reproducibility and met a desired Z' value requirement of >0.4. When tested against a 1408-compound test set at 5 or 10 microM compound concentration, a higher hit rate was obtained with the 2 luminescent reagents compared with that obtained with the fluorescent Oxyburst Green BSA reagent. The Oxyburst Green BSA assay was ultimately chosen for compound profiling and high-throughput screening activities. This 1536 superoxide detection assay using cryopreserved differentiated HL-60 cells represents a shifting paradigm toward the utilization of more therapeutically relevant cells in early drug development activities.

TC-5214 (S-(+)-mecamylamine): a neuronal nicotinic receptor modulator with antidepressant activity.

Both clinical and preclinical data support a potential therapeutic benefit of modulating the activity of CNS neuronal nicotinic receptors (NNRs) to treat depression and anxiety disorders. Based on the notion that the depressive states involve hypercholinergic tone, we have examined the potential palliative role of NNR antagonism in these disorders, using TC-5214 (S-(+) enantiomer of mecamylamine), a noncompetitive NNR antagonist. TC-5214 demonstrated positive effects in a number of animal models of depression and anxiety. TC-5214 was active in the forced swim test in rats (minimum effective dose (MED)=3 mg/kg i.p.), a classical depression model. It was also active in the behavioral despair test in mice (0.1-3.0 mg/kg i.p.), another model of depression. In the social interaction paradigm in rats, a model of generalized anxiety disorder (GAD), TC-5214 was active at a dose of 0.05 mg/kg s.c. In the light/dark chamber paradigm in rats, a model of GAD and phobia, TC-5214 was also active at a dose of 0.05 mg/kg s.c. Although TC-5214 shows modest selectivity among NNR subtypes, the antidepressant and anxiolytic effects seen in these studies are likely attributable to antagonist effects at the alpha4beta2 NNRs. This is supported by the observation of similar effects with alpha4beta2-selective partial agonists such as cytisine and with alpha4beta2-selective antagonists such as TC-2216. TC-5214 was well tolerated in acute and chronic toxicity studies in mice, rats, and dogs, showed no mutagenicity and displayed safety pharmacology, pharmacokinetic and metabolic profiles appropriate for therapeutic development. Overall, the results support a novel nicotinic cholinergic antagonist mechanism for antidepressant and anxiolytic effects and highlight the potential of NNR antagonists such as TC-5214 as therapeutics for the treatment of anxiety and depression.

(E)-metanicotine hemigalactarate (TC-2403-12) inhibits IL-8 production in cells of the inflamed mucosa.

BACKGROUND: Nicotine is of therapeutic value in ulcerative colitis, but its administration is connected with adverse events. Nicotine derivatives are currently being tested to maintain the therapeutic effects and minimize adverse events. TC-2403-12 is a (E)-metanicotine hemigalactarate. The aim of this study was to determine the effectiveness of TC-2403-12 in the inhibition of TNF- and lipopolysaccharide (LPS)-induced cell activation. METHODS: Colonic epithelial cells (CEC), monocytes (MM6), granulocytes, and the intestinal epithelial cell line HT-29 were stimulated with TNF and LPS and treated with TC-2403-12. IL-8 secretion in the cell supernatants and NF-kappaB activation were determined by ELISA. Apoptosis was quantified by flow cytometry. RESULTS: In MM6 cells, IL-8 secretion was significantly decreased to 30% of control after TC-2403-12 treatment, with best results after pretreatment for 24 h. This decrease in cell activation was not due to apoptosis and was not mediated by inhibition of NF-kappaB activation. IL-8 production in neutrophils and primary CEC also tended to be decreased after TC-2403-12 treatment. TC-2403-12 had no influence on IL-8 secretion of HT-29 cells. CONCLUSION: TC-2403-12 effectively inhibited TNF- and LPS-induced IL-8 production in different cell types. No toxic effects occurred at the concentrations used. Preincubation of cells with TC-2403-12 showed the best effects.

Therapeutic potential of novel selective drugs targeting nicotinic acetylcholine receptors.

The potential therapeutic benefit of nicotinic ligands in a variety of neurodegenerative pathologies involving the CNS has energized research efforts to develop nicotinic acetylcholine receptor (nAChR) subtype-selective ligands (Bencherif and Schmitt, 2005). In particular, there has been a concerted effort to develop nicotinic compounds with selectivity for CNS nAChRs as potential pharmaceutical tools in the management of these disorders. Clinical and experimental data demonstrate a central role for alpha7 and alpha4beta2 nAChRs in cognitive function, sensory processing, mood, and neuroprotection (Bencherif and Schmitt, 2005; Buccafusco et al., 2005). The development of safe alpha7-selective ligands has been hampered by their lack of discrimination with hERG channels and 5-HT3 receptors. We have developed a number of compounds that display nanomolar affinity to the alpha7 and/or the alpha4beta2 receptor. Investigation of alpha7 functional activity showed a full range of activities from antagonists to full agonists without any significant activity at the human 5-HT3 receptor, P450 isozymes, hERG channels, or in the AMES test. Our findings demonstrate that potent and highly selective nAChR ligands can be designed.

Ispronicline: a novel alpha4beta2 nicotinic acetylcholine receptor-selective agonist with cognition-enhancing and neuroprotective properties.

To date, the primary treatments for Alzheimer's disease with proven efficacy have been acetylcholinesterase inhibitors that prevent the hydrolysis of acetylcholine (ACh) in the synaptic cleft, thereby prolonging its activity. Although these agents have some benefit in alleviating cognitive impairment, they have limited clinical utility because of insufficient efficacy and marginal tolerability. Within the last decade, there has been much experimental support for the use of therapeutics that directly target nicotinic ACh receptors (nAChRs) to improve cognitive function and slow neurodegenerative disease progression. These findings have spurred considerable research efforts to develop ligands selective for nAChRs, such as ABT-418 (Arneric et al., 1995), SIB-1553 (Bontempi et al., 2001), TC-2403 (Lippiello et al., 1996), and TC-2559 (Bencherif et al., 2000). There is abundant evidence that nAChR modulators have the potential to alleviate cognitive impairment in demented states. In addition to improving cognitive function, a large body of research implicates a role for nAChRs in neuroprotection, suggesting potential for disease modification. An impact of nAChR agonists on disease progression would provide an advantage over currently available treatments for memory loss. The profile of previous nAChR-targeted clinical candidates has not been adequate to warrant further development owing to poor oral bioavailability, side effects, and/or lack of efficacy. Thus, a challenge in nAChR drug design and development has been the reduction of undesirable effects that result from activity at specific nAChRs in the CNS and PNS, including cardiovascular toxicity, emesis, seizures, and hypothermia.