Jane Gartlon

GSK189254, a Novel H3 Receptor Antagonist That Binds to Histamine H3 Receptors in Alzheimer's Disease Brain and Improves Cognitive Performance in Preclinical Models

6-[(3-Cyclobutyl-2,3,4,5-tetrahydro-1H-3-benzazepin-7-yl)oxy]-N-methyl-3-pyridinecarboxamide hydrochloride (GSK189254) is a novel histamine H3 receptor antagonist with high affinity for human (pKi = 9.59 –9.90) and rat (pKi = 8.51–9.17) H3 receptors. GSK189254 is >10,000-fold selective for human H3 receptors versus other targets tested, and it exhibited potent functional antagonism (pA2 = 9.06 versus agonist-induced changes in cAMP) and inverse agonism [pIC50 = 8.20 versus basal guanosine 5′-O-(3-[35S]thio)triphosphate binding] at the human recombinant H3 receptor. In vitro autoradiography demonstrated specific [3H]GSK189254 binding in rat and human brain areas, including cortex and hippocampus. In addition, dense H3 binding was detected in medial temporal cortex samples from severe cases of Alzheimers disease, suggesting for the first time that H3 receptors are preserved in late-stage disease. After oral administration, GSK189254 inhibited cortical ex vivo R-(–)-α-methyl[imidazole-2,5(n)-3H]histamine dihydrochloride ([3H]R-α-methylhistamine) binding (ED50 = 0.17 mg/kg) and increased c-Fos immunoreactivity in prefrontal and somatosensory cortex (3 mg/kg). Microdialysis studies demonstrated that GSK189254 (0.3–3 mg/kg p.o.) increased the release of acetylcholine, noradrenaline, and dopamine in the anterior cingulate cortex and acetylcholine in the dorsal hippocampus. Functional antagonism of central H3 receptors was demonstrated by blockade of R-α-methylhistamine-induced dipsogenia in rats (ID50 = 0.03 mg/kg p.o.). GSK189254 significantly improved performance of rats in diverse cognition paradigms, including passive avoidance (1 and 3 mg/kg p.o.), water maze (1 and 3 mg/kg p.o.), object recognition (0.3 and 1 mg/kg p.o.), and attentional set shift (1 mg/kg p.o.). These data suggest that GSK189254 may have therapeutic potential for the symptomatic treatment of dementia in Alzheimers disease and other cognitive disorders.

Long-term behavioural, molecular and morphological effects of neonatal NMDA receptor antagonism

Brief N‐methyl‐d‐aspartate (NMDA) receptor blockade in neonatal rats has been reported to increase neuronal apoptosis. We replicated this finding using MK‐801 (0.5 mg/kg) administered twice on postnatal day 7, and then studied the long‐term consequences. In adulthood, treated rats showed reduced volume and neuronal number within the hippocampus, and altered hippocampal NMDA receptor (NR1 subunit) expression. Synaptophysin mRNA was decreased in the thalamus (laterodorsal nucleus). Adult MK‐801‐treated females had prepulse inhibition deficits and increased locomotor activity. The data show that a transient and limited glutamatergic intervention during development can have chronic behavioural, structural and molecular effects. The effects are reminiscent of alterations reported in schizophrenia and, as such, are consistent with hypotheses advocating a role for NMDA receptor hypofunction, and aberrant apoptosis, in the neurodevelopmental pathogenesis of the disorder.

Attenuation of amphetamine-induced activity by the non-selective muscarinic receptor agonist, xanomeline, is absent in muscarinic M4 receptor knockout mice and attenuated in muscarinic M1 receptor knockout mice

The muscarinic acetylcholine receptor (mAChR) agonist, xanomeline, attenuates amphetamine-induced activity in WT mice. This effect is abolished in mice lacking the M(4) muscarinic acetylcholine receptor (M(4) mAChR KO) and partially attenuated in mice lacking M(1) muscarinic acetylcholine receptor (M(1) mAChR KO). Collectively, these data suggest that the efficacy exhibited by xanomeline in the mouse amphetamine-induced hyperactivity model, is mediated predominantly by M(4) muscarinic acetylcholine receptors, and that M(1) muscarinic acetylcholine receptors may play a more minor role. This supports the hypothesis that activation of M(4), and to a lesser extent M(1) muscarinic acetylcholine receptors, may represent a potential target for the treatment of psychosis seen in schizophrenia.

In vitro and in vivo characterization of the non-peptide NK3 receptor antagonist SB-223412 (talnetant): potential therapeutic utility in the treatment of schizophrenia.

Neurokinin-3 (NK3) receptors are concentrated in forebrain and basal ganglia structures within the mammalian CNS. This distribution, together with the modulatory influence of NK3 receptors on monoaminergic neurotransmission, has led to the hypothesis that NK3 receptor antagonists may have therapeutic efficacy in the treatment of psychiatric disorders. Here we describe the in vitro and in vivo characterization of the highly selective NK3 receptor antagonist talnetant (SB-223412). Talnetant has high affinity for recombinant human NK3 receptors (pKi 8.7) and demonstrates selectivity over other neurokinin receptors (pKi NK2=6.6 and NK1<4). In native tissue-binding studies, talnetant displayed high affinity for the guinea pig NK3 receptor (pKi 8.5). Functionally, talnetant competitively antagonized neurokinin B (NKB)-induced responses at the human recombinant receptor in both calcium and phosphoinositol second messenger assay systems (pA2 of 8.1 and 7.7, respectively). In guinea pig brain slices, talnetant antagonized NKB-induced increases in neuronal firing in the medial habenula (pKB=7.9) and senktide-induced increases in neuronal firing in the substantia nigra pars compacta (pKB=7.7) with no diminution of maximal agonist efficacy, suggesting competitive antagonism at native NK3 receptors. Talnetant (3–30 mg/kg i.p.) significantly attenuated senktide-induced ‘wet dog shake’ behaviors in the guinea pig in a dose-dependent manner. Microdialysis studies demonstrated that acute administration of talnetant (30 mg/kg i.p.) produced significant increases in extracellular dopamine and norepinephrine in the medial prefrontal cortex and attenuated haloperidol-induced increases in nucleus accumbens dopamine levels in the freely moving guinea pigs. Taken together, these data demonstrate that talnetant is a selective, competitive, brain-penetrant NK3 receptor antagonist with the ability to modulate mesolimbic and mesocortical dopaminergic neurotransmission and hence support its potential therapeutic utility in the treatment of schizophrenia.

Developing New Drugs for Schizophrenia: From Animals to the Clinic

Publisher Summary Schizophrenia is typically a lifelong and often devastating, but relatively common (life-time risk of 1%), psychiatric disorder, which often begins in late adolescence or early adulthood. This chapter reviews the current drug treatments for schizophrenia, the outstanding unmet needs for patients, the current understanding of the neurobiology of schizophrenia, and strategies for drug discovery. It focuses particularly on the development of appropriate animal models and translational approaches to aid in the understanding of the neurobiology of schizophrenia and to investigate the potential efficacy of novel pharmacological approaches. It discusses the challenges in drug discovery from both a preclinical and clinical perspective and examines the exciting advances in the understanding of this disorder and the various Academic/Government/Industry initiatives that are likely to make a major impact upon drug discovery in this area. It also considers some approaches that exemplify novel strategies for drug discovery or clinical investigation that promise significant advances in this field. The collaborative spirit needs to continue to focus the attention upon approaches that may improve the treatment of this debilitating and multi-syndromal disease.

Effect of the selective dopamine D3 receptor antagonist SB-277011-A on regional c-Fos-like expression in rat forebrain

SB-277011-A is a dopamine D(3) receptor antagonist that exhibits over 100-fold selectivity over dopamine D(2) receptors and a broad spectrum of other receptor, ion channels, and enzymes. We employed c-Fos immunohistochemistry to characterise the functional neuroanatomical effects of acute administration of SB-277011-A and observed a time-dependent increase in the density of c-Fos-like positive nuclei in rat forebrain with maximal effects observed 2 h post-dose. The relative influence of the different brain regions on the overall effect of SB-277011-A was ranked by partial least squares discriminant analysis loadings plot which indicated that sites within the nucleus accumbens exerted the greatest influence on the separation of the vehicle and SB-277011-A treatment groups. At the 2 h time-point, c-Fos-like expression was shown to be significantly elevated (p<0.05) in the core and shell of the nucleus accumbens, at both rostral and caudal levels, and in the lateral septum. No significant changes were detected in the caudate nucleus (lateral or medial) or in the cingulate, infralimbic prefrontal, or somatosensory cortices. The capacity of SB-277011-A to trigger immediate early gene expression in these limbic regions of rat brain adds to a growing consensus of the potential utility of dopamine D(3) receptor antagonism in psychiatric disorders including schizophrenia and drug dependency.

The discovery of a series of N-substituted 3-(4-piperidinyl)-1,3-benzoxazolinones and oxindoles as highly brain penetrant, selective muscarinic M1 agonists.

A series of N-substituted 3-(4-piperidinyl)-1,3-benzoxazolinones and oxindoles are reported which were found to be potent and selective muscarinic M1 agonists. By control of the physicochemical characteristics of the series, particularly the lipophilicity, compounds with good metabolic stability and excellent brain penetration were identified. An exemplar of the series was shown to be pro-cognitive in the novel object recognition rat model of temporal induced memory deficit.

Pharmacological characterization of N‐[(2S)‐5‐(6‐fluoro‐3‐pyridinyl)‐2, 3‐dihydro‐1H‐inden‐2‐yl]‐2‐propanesulfonamide: a novel, clinical AMPA receptor positive allosteric modulator

AMPA receptor positive allosteric modulators represent a potential therapeutic strategy to improve cognition in people with schizophrenia. These studies collectively constitute the preclinical pharmacology data package used to build confidence in the pharmacology of this molecule and enable a clinical trial application.

Behavioural and cerebral metabolism assessment of TASTPM transgenic mice using a ‘touchscreen’-based cognitive task

However, APP transgenic mice over express APP and even though FADmutations ensures high production of As species the by-products sAPP and intracellular domain of APP (AICD) are also generated, both of which have physiological functions. This leads to uncertainties as to whether the various observed phenotypes are caused by increased As or by the overproduction of sAPP, AICD or APP. To address these issues, we generated a novel type of AD mouse model by applying a gene knock-in strategy.Methods:We constructed a targeting vector of the mouse APP gene that included the humanized As sequence harboring the Swedish mutation (KM670/671NL) and the Iberian mutation (I716F). The knock-in micewere investigated by biochemical, pathological and behavioral studies.Results: The mutations in the generated mice (APP-NL/F-KI), gave rise to increased As 42 and decreased As 40 levels even in heterozygous mice (wt/NL-F) and already at the age of 2 month, so that As 42/A b 40 ratios were >15 fold increased in the brain compared to wild type mice. In addition, A b 42/A b 40 ratios of the homozygous (NL-F/NL-F) were>50 fold increased vs. wild type. So far, depositions of As 1-42, in partially thioflavin-S positive plaques, were visible from 6 month age of NL-F/NL-F mice. 5 months old homozygous mice also showed behavioral abnormality. In 12month old NL-F/NL-Fmice brain, accumulation of N3pE-As species and Asx43 species could be detected. In addition, tau phosphorylation was also accelerated in 12 month old NL-F/ NL-F mice. Conclusions: We are currently assessing this mouse model at older ages with respect to different paradigms. Such mice, after crossbreeding with other type of mouse models for AD, would be powerful mouse models in AD research.

Levels of ionotropic glutamate and muscarinic receptors in three animal models of schizophrenia

There are well validated rodent paradigms of schizophrenia which are based on environmental manipulation (e.g. altered rearing conditions) or drug challenges. These manipulations induce behavioural changes in rodents that are thought to involve neuronal circuitry similar to the ones that are affected by the pathophysiology of the disorder. This study has investigated whether three such rodent paradigms (isolation rearing, neonatal PCP treatment or sub-chronic PCP treatment) are associated with changes in muscarinic receptors (CHRMs) or ionotropic glutamate receptors, some of which have been reported to be altered in the CNS of subjects with schizophrenia. ( 3 H)pirenzepine (CHRM1), ( 3 H)4DAMP (CHRM1/CHRM3), ( 3 H)MK801 (NMDA receptors) and ( 3 H)kainate (kainate receptors; KAR) binding were measured using in situ radioligand binding and autoradiography. Isolation rearing caused widespread decreases in ( 3 H)4DAMP (p = 0.01) and ( 3 H)kainate binding (p = 0.03). Neonatal PCP caused widespread increases in ( 3 H)4DAMP binding (p <0.0001), whereas sub-chronic PCP treatment caused widespread decreases in the binding of that radioligand (p < 0.002) and widespread increases in (3H)MK801 binding (p < 0.0001). There were no changes in ( 3 H)pirenzepine binding to CHRM1 receptors in any paradigm or no significant within region changes in the binding of any radioligand. In conclusion, in the absence of any changes in CHRM1 receptors, our ( 3 H)4DAMP and the binding of (3H)MK801 data would suggest that different rodent paradigms cause variable changes in levels of CHRM3 and KAR in the rat CNS. Our data raises the possibility that such changes may, in part, modulate the behavioural differences that have been observed after isolation rearing, neonatal PCP treatment or sub-chronic PCP treatment.