A series of fused tricyclic mGluR1 antagonists containing a pyridone ring were synthesized. In vitro, these antagonists were potent against both human and rat isozymes, as well as selective for inhibiting mGluR1 over mGluR5. When dosed orally, several examples were active in vivo in a rat SNL test.

The adenosine A(2A) receptor has been implicated in the underlying biology of various neurological and psychiatric disorders, including Parkinson's disease (PD) and depression. Preladenant and SCH 412348 [7-[2-[4-2,4-difluorophenyl]-1-piperazinyl]ethyl]-2-(2-furanyl)-7H-pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine] are potent competitive antagonists of the human A(2A) receptor (K(i) = 1.1 and 0.6 nM, respectively) and have >1000-fold selectivity over all other adenosine receptors, making these compounds the most selective A(2A) receptor antagonists reported to date. Both compounds attenuate hypolocomotion induced by the A(2A) receptor agonist CGS-21680 [2-[p-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamidoadenosine], suggesting that they inhibit A(2A) receptor activity in vivo. Their high degree of selectivity and robust in vivo activity make preladenant and SCH 412348 useful tools to investigate the role of the A(2A) receptor system in animal models of PD and depression. Oral administration of preladenant and SCH 412348 (0.1-1 mg/kg) to rats potentiated 3,4-dihydroxy-L-phenylalanine (L-Dopa)-induced contralateral rotations after 6-hydroxydopamine lesions in the medial forebrain bundle and potently attenuated the cataleptic effects of haloperidol. Preladenant (1 mg/kg) inhibited L-Dopa-induced behavioral sensitization after repeated daily administration, which suggests a reduced risk of the development of dyskinesias. Finally, preladenant and SCH 412348 exhibited antidepressant-like profiles in models of behavioral despair, namely the mouse tail suspension test and the mouse and rat forced swim test. These studies demonstrate that preladenant and SCH 412348 are potent and selective A(2A) receptor antagonists and provide further evidence of the potential therapeutic benefits of A(2A) receptor inhibition in PD (with reduced risk of dyskinesias) and depression (one of the primary nonmotor symptoms of PD).

Department of Neurobiology, Schering-Plough Research Institute, 2015 Galloping Hill Road, Kenilworth, NJ 07033, USA. (RAH, GBV, JEL, MEC-W, GAH, LEP, CF, YZ, EMP, JCH) Department of Neurobiology, Schering-Plough Research Institute, San Raffaele Science Park, Via Olgettina, 58, 20132, Milan, Italy. (RB, AF, SF, FI, EN, AR) Department of Chemical Research, Schering-Plough Research Institute, 2015 Galloping Hill Road, Kenilworth, NJ 07033, USA. (BRN, AWS) JPET Fast Forward. Published on March 30, 2009 as DOI:10.1124/jpet.108.149617

Antagonism of the adenosine A(2a) receptor offers great promise in the treatment of Parkinson's disease. In the course of exploring pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine A(2A) antagonists, which led to clinical candidate SCH 420814, we prepared 1,2,4-triazolo[1,5-c]pyrimidines with potent and selective (vs A(1)) A(2a) antagonist activity, including oral activity in the rat haloperidol-induced catalepsy model. Structure-activity relationships and plasma levels are described for this series.

Metabotropic glutamate receptor 1 (mGluR1) plays important roles in the neurotransmission and pathogenesis of several neurological disorders, including chronic pain. Antagonists of mGlur1 are suggested to be useful for the treatment of pain. Herein, we report the discovery of a novel series of tetracyclic mGluR1 antagonists, such as 23c and 23e, with oral efficacy of ED50 of 8 and 5.1 mg/kg, respectively, in rat spinal nerve ligation neuropathic pain model.

RATIONALE:Modulation of metabotropic glutamate receptor (mGluR) subtypes represents a novel approach for the treatment of neurological and psychiatric disorders.OBJECTIVES:This study was conducted to investigate the role of the mGluR5 and mGluR1 subtypes in the modulation of pain and anxiety.METHODS:The mGluR5 antagonists, 2-methyl-6-(phenylethynyl)pyridine (MPEP) and 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP), and the mGluR1 antagonist, (4-methoxy-phenyl)-(6-methoxy-quinazolin-4-yl)-amine HCl (LY456236), were tested in models of pain [mouse formalin test, rat spinal nerve ligation (SNL)] and anxiety [Vogel conflict, conditioned lick suppression (CLS)], and their efficacious effects were compared to any associated side effects.RESULTS:The systemic administration of MPEP, MTEP, and LY456236 reduced hyperalgesia induced by formalin and mechanical allodynia following SNL. However, only LY456236 completely reversed the allodynia. In the anxiety models, MPEP (3--30 mg/kg), MTEP (3--10 mg/kg), and LY456236 (10--30 mg/kg) produced anxiolytic-like effects similar to the benzodiazepine, chlordiazepoxide (CDP, 6 mg/kg). However, only MPEP and MTEP were able to produce a level of anxiolysis comparable to CDP. In a series of tests examining potential side effects, MPEP and MTEP reduced body temperature and locomotor activity and impaired operant responding for food and rotarod performance at doses of 3--30 and 1--30 mg/kg, respectively. LY456236 reduced operant responding at 30 mg/kg.CONCLUSION:Both mGluR5 and mGluR1 antagonists are effective in models of pain and anxiety. However, an mGluR1 antagonist was more efficacious than the two mGluR5 antagonists in the pain models, which, conversely, appeared more efficacious in the anxiety models. These findings support the potential utility of mGluR5 and mGluR1 antagonists for both the treatment of chronic pain and as novel anxiolytics.

The A2A receptor has recently attracted considerable interest as a potential target for Parkinson's disease (PD) therapy based on the motor-enhancing and neuroprotective effects of A2A antagonists in animal models of PD. The unique neuronal localization of the adenosine A2A receptor in the basal ganglia and its extensive interactions with dopaminergic and glutamatergic systems led the authors to investigate a potential role of the A2A receptor in the development of behavioral sensitization in response to repeated dopaminergic stimulation. Because dopamine-induced behavioral sensitization shares several neurochemical and behavioral features with dyskinesia, characterizing this novel aspect of A2A receptor function may enhance understanding and management of dyskinesia in PD. Recent studies from several laboratories suggest that the A2A receptor may be an important mediator of maladaptive changes in response to long-term dopamine stimulation. The authors summarize their investigation of the role of A2A receptors in two paradigms of behavioral sensitization elicited by daily treatment with either L-dopa in hemiparkinsonian mice or amphetamine in naive mice. The results demonstrate that the A2A receptor is required for the development of behavioral sensitization in response to repeated L-dopa treatment in hemiparkinsonian mice and repeated amphetamine administration in normal mice. Together with pharmacologic studies, these results raise the possibility that the maladaptive dyskinetic responses to long-term L-dopa management of PD may be attenuated by A2A receptor blockade. Potential presynaptic, postsynaptic (cellular), and trans-synaptic (network) mechanisms are discussed.

The potential neuroprotective effects of the novel nitro-derivate of aspirin (NCX4016) on permanent focal cerebral ischemia in spontaneously hypertensive rats (SHRs) was investigated. Reference compounds were acetylsalicilic acid (ASA) and FK506 (tacrolimus). Ten minutes after surgery, SHRs were randomly divided into four groups of ten, pharmacologically treated and sacrificed 24 h after treatment. Brains were removed and processed to measure infarct volume, 70 kDa heat shock protein (hsp70), glial fibrillary acidic protein (GFAP) and vimentin (Vim) immunoreactivity (IR), and apoptosis using terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-digoxigenin nick end-labeling (TUNEL) assay. NCX-4016 significantly reduced total infarct volume compared to ASA (−20%, P<0.05), FK506 (−18%, P<0.05) and vehicle treatment (−20%, P<0.05). Experimental groups did not differ in hsp70-IR and GFAP-IR. Conversely, hyperplastic astrocytes, measured by Vim-IR, were significantly lower in NCX-4016 than in the vehicle group (−36%, P<0.01). TUNEL assay indicated a significantly lower degree of apoptosis in NCX-4016 group than vehicle in both the homolateral (−27%, P<0.01) and contralateral hemisphere (−29%, P<0.05). These findings indicate that NO release associated with aspirin confers neuroprotective effects against ischemic injury.

The time course of 72-kDa heat-shock protein (hsp72) induction was evaluated by immunoblotting in cerebral cortex, striatum, hippocampus, cerebellum, liver, and kidney of rats subjected to 60-min focal cerebral ischemia following proximal unilateral occlusion of the right middle cerebral artery (MCA). Neurological examinations indicated that maximum deficits in reflex and sensorimotor functions occurred 24-48 h after reperfusion (40% lower than baseline), while significant recovery occurred at 72 h (33% higher than 48 h). hsp72 was present in all tissues at 6 h. The regions perfused by the occluded MCA showed a higher induction than the corresponding contralateral ones. hsp72 reached its maximum level in ipsilateral cerebral cortex and striatum at 24 h, whereas in the contralateral cortex and cerebellum the protein reached its maximum expression at 48 h, that is 24 h before functional recovery. This delay suggests a role of the protein in plastic events sustaining neurological recovery.