Preclinical predictors that the orthosteric mGlu2/3 receptor antagonist LY3020371 will not engender ketamine-associated neurotoxic, motor, cognitive, subjective, or abuse-liability-related effects.

The novel mGlu2/3 receptor antagonist, LY3020371, has been shown to produce antidepressant-like effects comparable to that of the clinically-effective antidepressant ketamine. In the present study, we investigated whether LY3020371 would be predicted to be free of the side-effects and safety pharmacology issues associated with ketamine. In contrast to ketamine, LY3020371 produced small increases in locomotion and did not impair motor performance on an inverted screen. Ketamine, but not LY3020371, increased dopamine efflux in the nucleus accumbens of rats. Ketamine also produced cognitively-impairing effects in rats in a T-maze and in a psychomotor vigilance task and altered theta synchrony between the hippocampus and mPFC, whereas LY3020371 had either no significant impact or lesser effects in these assays. In mice, ketamine, but not LY3020371, negatively affected spontaneous alternation in a Y-maze. Rats were trained to discriminate LY3020371 from vehicle where 30mg/kg produced 100% drug-appropriate responding and the ED50 for LY3020371 was 9.4mg/kg, i.p. In rats discriminating LY3020371, neither d-amphetamine nor phencyclidine fully substituted for LY3020371 (35-45%) and the mGlu2/3 receptor agonist LY354740 partially attenuated the discriminative stimulus effects of LY3020371. These are the first data to demonstrate the discriminative stimulus effects of an mGlu2/3 receptor antagonist. Some alterations were suggested to occur in the density of mGlu2/3 receptor binding sites in the drug discrimination rats relative to their age-matched non-drug-exposed controls. In preclinical toxicology studies of 14day dosing of doses up to 1000mg/kg, i.v. in rats and up to 500m/kg, i.v. in Cynomologous monkeys, LY3020371 produced uM plasma exposures without producing critical toxicological findings. It is concluded that LY3020371 does not recapitulate the motor, cognitive, subjective, neurochemical, electrophysiological, or toxicological findings reported with ketamine. Thus, LY3020371 possesses both the efficacy signatures of a rapidly-acting antidepressant and a safety profile enabling proof of concept studies in patients.

Comparative Effects of LY3020371, a Potent and Selective Metabotropic Glutamate (mGlu) 2/3 Receptor Antagonist, and Ketamine, a Noncompetitive N-Methyl-d-Aspartate Receptor Antagonist in Rodents: Evidence Supporting the Use of mGlu2/3 Antagonists, for the Treatment of Depression.

The ability of the N-methyl-d-aspartate receptor antagonist ketamine to alleviate symptoms in patients suffering from treatment-resistant depression (TRD) is well documented. In this paper, we directly compare in vivo biologic responses in rodents elicited by a recently discovered metabotropic glutamate (mGlu) 2/3 receptor antagonist 2-amino-3-[(3,4-difluorophenyl)sulfanylmethyl]-4-hydroxy-bicyclo[3.1.0]hexane-2,6-dicarboxylic acid (LY3020371) with those produced by ketamine. Both LY3020371 and ketamine increased the number of spontaneously active dopamine cells in the ventral tegmental area of anesthetized rats, increased O2 in the anterior cingulate cortex, promoted wakefulness, enhanced the efflux of biogenic amines in the prefrontal cortex, and produced antidepressant-related behavioral effects in rodent models. The ability of LY3020371 to produce antidepressant-like effects in the forced-swim assay in rats was associated with cerebrospinal fluid (CSF) drug levels that matched concentrations required for functional antagonist activity in native rat brain tissue preparations. Metabolomic pathway analyses from analytes recovered from rat CSF and hippocampus demonstrated that both LY3020371 and ketamine activated common pathways involving GRIA2 and ADORA1. A diester analog of LY3020371 [bis(((isopropoxycarbonyl)oxy)-methyl) (1S,2R,3S,4S,5R,6R)-2-amino-3-(((3,4-difluorophenyl)thio)methyl)-4-hydroxy-bicyclo[3.1.0]hexane-2,6-dicarboxylate (LY3027788)] was an effective oral prodrug; when given orally, it recapitulated effects of intravenous doses of LY3020371 in the forced-swim and wake-promotion assays, and augmented the antidepressant-like effects of fluoxetine or citalopram without altering plasma or brain levels of these compounds. The broad overlap of biologic responses produced by LY3020371 and ketamine supports the hypothesis that mGlu2/3 receptor blockade might be a novel therapeutic approach for the treatment of TRD patients. LY3020371 and LY3027788 represent molecules that are ready for clinical tests of this hypothesis.

Localization of opioid receptor antagonist [3H]-LY255582 binding sites in mouse brain: comparison with the distribution of mu, delta and kappa binding sites.

Agonist stimulation of opioid receptors increases feeding in rodents, while opioid antagonists inhibit food intake. The pan-opioid antagonist, LY255582, produces a sustained reduction in food intake and body weight in rodent models of obesity. However, the specific receptor subtype(s) responsible for this activity is unknown. To better characterize the pharmacology of LY255582, we examined the binding of a radiolabeled version of the molecule, [(3)H]-LY255582, in mouse brain using autoradiography. In mouse brain homogenates, the K(d) and B(max) for [(3)H]-LY255582 were 0.156 +/- 0.07 nM and 249 +/- 14 fmol/mg protein, respectively. [(3)H]-LY255582 bound to slide mounted sections of mouse brain with high affinity and low non-specific binding. High levels of binding were seen in areas consistent with the known localization of opioid receptors. These areas included the caudate putamen, nucleus accumbens, claustrum, medial habenula, dorsal endopiriform nucleus, basolateral nucleus of the amygdala, hypothalamus, thalamus and ventral tegmental area. We compared the binding distribution of [(3)H]-LY255582 to the opioid receptor antagonist radioligands [(3)H]-naloxone (mu), [(3)H]-naltrindole (delta) and [(3)H]-norBNI (kappa). The overall distribution of [(3)H]-LY255582 binding sites was similar to that of the other ligands. No specific [(3)H]-LY255582 binding was noted in sections of mu-, delta- and kappa-receptor combinatorial knockout mice. Therefore, it is likely that LY255582 produces its effects on feeding and body weight gain through a combination of mu-, delta- and kappa-receptor activity.

Muscarinic receptor agonists, like dopamine receptor antagonist antipsychotics, inhibit conditioned avoidance response in rats.

The purpose of our studies was to determine the effects of muscarinic receptor agonists on conditioned avoidance responding in the rat. Rats were trained to avoid or escape an electric shock delivered to the feet in a discrete trial procedure. The muscarinic receptor agonists pilocarpine and [2-ethyl-8-methyl-2,8-diazaspiro(4. 5)decane-1,3-dione] hydrochloride (RS86) and the cholinesterase inhibitor physostigmine all decreased the percentage of avoidance responses at doses that produced less than approximately 30% response failures. Similar results were obtained with the antipsychotic drugs haloperidol, trifluoperazine, chlorpromazine, and clozapine. However, the benzodiazepine anxiolytic diazepam did not decrease avoidance responding up to doses that produced ataxia. On the other hand, oxotremorine and arecoline decreased avoidance responding only by producing response failures, whereas aceclidine produced intermediate changes. The muscarinic receptor antagonists scopolamine, trihexyphenidyl, and benztropine were without effect when administered alone but antagonized the decreases in avoidance responding produced by pilocarpine and RS86. Scopolamine had little effect on the decreases in avoidance responding produced by haloperidol. The newer muscarinic receptor partial agonists or agonist/antagonists [R-(Z)-(+)-alpha-(methoxyimino)-1-azabicyclo[2.2. 2]octane-3-acetonitrile] hydrochloride, talsaclidine, milameline, and xanomeline also produced dose-related decreases in avoidance responding. Our results demonstrate that muscarinic receptor agonists can decrease avoidance responding in a manner similar to dopamine-receptor antipsychotic drugs, suggesting that muscarinic receptor agonists may provide an alternative approach to the treatment of psychosis.

Direct pharmacological comparison of the muscarinic receptors mediating relaxation and contraction in the rabbit thoracic aorta.

The purpose of the present studies was to directly compare the pharmacology of the muscarinic cholinergic receptors coupled to carbachol-induced relaxation and contraction of the intact and the endothelium-denuded rabbit thoracic aorta, respectively. The order of potencies of agonists for producing relaxation in the intact aorta was similar to that for producing contraction in the denuded aorta. In both preparations, the partial agonists pilocarpine, McN-A-343, and RS86 functioned as antagonists, indicating a lack of receptor reserve in both preparations. Further, the pA2 values for antagonists in both tissues were virtually identical and were consistent with the pharmacology of M3 receptors.

Potential role of muscarinic receptors in schizophrenia.

The role of muscarinic receptors in schizophrenia was investigated using the muscarinic agonist PTAC. PTAC was highly selective for muscarinic receptors, was a partial agonist at muscarinic M2/M4 receptors and an antagonist at M1, M3 and M5 receptors. PTAC was highly active in animal models predictive of antipsychotic behavior including inhibition of conditioned avoidance responding in rats and blockade of apomorphine-induced climbing behavior in mice. d-Amphetamine-induced Fos expression in rat nucleus accumbens was inhibited by PTAC, thus directly demonstrating the ability of PTAC to modulate DA activity. In electrophysiological studies in rats, PTAC acutely inhibited the firing of A10 DA cells and after chronic administration decreased the number of spontaneously firing DA cells in the A10 brain area. However, PTAC did not appreciably alter the firing of A9 DA cells. Thus, PTAC appears to have novel antipsychotic-like activity and these data suggest that muscarinic compounds such as PTAC may represent a new class of antipsychotic agents.

Unexpected antipsychotic-like activity with the muscarinic receptor ligand (5R,6R)6-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[3.2.1]octane .

(5R,6R)6-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[3 .2.1]octane (PTAC) is a potent muscarinic receptor ligand with high affinity for central muscarinic receptors and no or substantially less affinity for a large number of other receptors or binding sites including dopamine receptors. The ligand exhibits partial agonist effects at muscarinic M2 and M4 receptors and antagonist effects at muscarinic M1, M3 and M5 receptors. PTAC inhibited conditioned avoidance responding, dopamine receptor agonist-induced behavior and D-amphetamine-induced FOS protein M5 expression in the nucleus accumbens without inducing catalepsy, tremor or salivation at pharmacologically relevant doses. The effect of PTAC on conditioned avoidance responding and dopamine receptor agonist-induced behavior was antagonized by the acetylcholine receptor antagonist scopolamine. The compound selectively inhibited dopamine cell firing (acute administration) as well as the number of spontaneously active dopamine cells (chronic administration) in the limbic ventral tegmental area (A10) relative to the non-limbic substantia nigra, pars compacta (A9). The results demonstrate that PTAC exhibits functional dopamine receptor antagonism despite its lack of affinity for the dopamine receptors and indicate that muscarinic receptor partial agonists may be an important new approach in the medical treatment of schizophrenia.

Xanomeline compared to other muscarinic agents on stimulation of phosphoinositide hydrolysis in vivo and other cholinomimetic effects.

Activation of muscarinic m1 receptors which are coupled to the phosphoinositide (PI) second messenger transduction system is the initial objective of cholinergic replacement therapy in Alzheimer's disease. Thus, we evaluated the ability of the selective muscarinic receptor agonist (SMRA) xanomeline to stimulate in vivo phosphoinositide (PI) hydrolysis and compared it to a number of direct acting muscarinic agonists, two cholinesterase inhibitors and a putative m1 agonist/muscarinic m2 antagonist. Using a radiometric technique, it was determined that administration of xanomeline robustly stimulated in vivo PI hydrolysis and the effect was blocked by muscarinic antagonists, demonstrating mediation by muscarinic receptors. The non-selective muscarinic agonists pilocarpine, oxotremorine, RS-86, S-aceclidine, but not the less active isomer R-aceclidine, also effectively stimulated PI hydrolysis in mice. Amongst the putative m1 agonists, thiopilocarpine, hexylthio-TZTP as well as xanomeline effectively stimulated PI hydrolysis, but milameline, WAL 2014, SKB 202026 and PD 142505 did not significantly alter PI hydrolysis. Furthermore, WAL 2014 and SKB 202026 inhibited agonist-induced PI stimulation, suggesting that they act as antagonists at PI-coupled receptors in vivo. The cholinesterase inhibitors, tacrine and physostigmine, and the mixed muscarinic m1 agonist/m2 antagonist LU25-109 did not activate in vivo PI hydrolysis. Xanomeline, hexylthio-TZTP and thiopilocarpine were relatively free of cholinergic side effects, whereas milameline, WAL 2014 and SKB 202026 produced non-selective effects. Therefore, these data demonstrate that xanomeline selectively activates in vivo PI hydrolysis, consistent with activation of biochemical processes involved in memory and cognition and xanomeline's beneficial clinical effects on cognition in Alzheimers patients.

1,2,5-Thiadiazole analogues of aceclidine as potent m1 muscarinic agonists.

The acetyl group of the muscarinic agonist aceclidine 4 was replaced by various 1,2,5-thiadiazoles to provide a new series of potent m1 muscarinic agonists 17 and 18. Optimal m1 muscarinic agonist potency was achieved when the 1,2,5-thiadiazole substituent was either a butyloxy, 17d, or butylthio, 18d, group. Although 1,2,5-oxadiazole 37 and pyrazine 39 are iso-pi-electronic with 1,2,5-thiadiazole 17d, both analogues were substantially less active than 17d. Compounds with high muscarinic affinity and/or m1 muscarinic agonist efficacy were also obtained when the 3-oxyquinuclidine moiety of 17d or 18c was replaced by ethanolamines, hydroxypyrrolidines, hydroxyazetidine, hydroxyisotropanes, or hydroxyazanorbornanes. The structure-activity data support the participation of the oxygen or sulfur atom in the substituent on the 1,2,5-thiadiazole in the activation of the m1 receptor. Several of these new 1,2,5-thiadiazoles have m1 agonist efficacy, potency, and selectivity comparable to those of xanomeline 2 in the muscarinic tests investigated.

M1 receptor agonist activity is not a requirement for muscarinic antinociception.

The analgesic effects of a series of muscarinic agonists were investigated by use of the mouse acetic acid writhing, grid-shock, hot-plate and tail-flick tests. The compounds tested were oxotremorine, pilocarpine, arecoline, aceclidine, RS86 and four 3-3(substituted-1,2,5-thiadiazol-4-yl)-1,2,5,6-tetrahy-dro-1 -methyl pyridines (substituted TZTP), these being propoxy-TZTP, 3-Cl-propylthio-TZTP, xanomeline (hexyloxy-TZTP) and hexylthio-TZTP. These agonists were also assayed for their ability to displace [3H]oxotremorine-M and [3H]pirenz-epine binding and for their functional selectivity at pharmaco-logic M1, M2 and M3 receptors. These compounds all produced dose-dependent antinociceptive effects in all of the mouse analgesia tests. The effects of oxotremorine in the writhing test were fully antagonized by the muscarinic antagonist scopolamine (0.1 mg/kg), but only partially antagonized by methsco-polamine (10 mg/kg) and unaffected by the opioid antagonist naltrexone. 3-Cl-propylthio-TZTP and propoxy-TZTP had virtually no effect at the M1 receptor subtype as measured by the human m1 clone expressed in baby hamster kidney cells or the rabbit vas deferens assay. These compounds, however, were more potent in the analgesia tests than the selective M1 agonists xanomeline and hexylthio-TZTP. These data suggest that muscarinic analgesia is mediated by central muscarinic receptors. However, activity at the M1 receptor subtype is not a requirement for antinociceptive activity.

Butylthio[2.2.2] (NNC 11-1053/LY297802): an orally active muscarinic agonist analgesic.

Butylthio[2.2.2] ((+)-(S)-3-(4-(Butylthio)-1,2,5-thiadiazol-3-yl)-1-azabicyclo[2.2. 2] octane) is an agonist/antagonist at muscarinic receptors. The analgesic potential of butylthio[2.2.2] was assessed in the mouse by use of the grid-shock, tail-flick, hotplate and writhing tests. The ED50 values ranged from 0.19 to 1.47 mg/kg and 1.51 to 12.23 mg/kg 30 min after s.c. and p.o. administration, respectively, yielding p.o./s.c. ratios ranging from 7 to 27. The ED50 values for salivation and tremor were > 30 and 12.31 mg/kg s.c., and > 60 and > 60 mg/kg p.o., yielding therapeutic windows > 130 and 54, and, > 40 and > 40, after s.c. and p.o. administration, respectively. Motor impairment or lethality were only seen at doses 116 and 254 times higher than the antinociceptive doses. Butylthio[2.2.2] was equieffective to, and 3- to 24-fold more potent than morphine. The duration of action was similar to that of morphine. The dose-response curve was shifted dose dependently to the right by the muscarinic antagonist scopolamine but not by the opioid antagonist naltrexone. The antinociceptive effect of butylthio[2.2.2] was reversed by the centrally acting muscarinic antagonist scopolamine but not by the peripherally acting muscarinic antagonist methscopolamine. After 6.5 days repeated dosing in mice, morphine produced marked tolerance, whereas butylthio[2.2.2] produced minimal, if any, tolerance. In the rat grid-shock test, ED50 values of 0.26 mg/kg s.c. and 25.28 mg/kg p.o. were obtained. These data show that butylthio[2.2.2] is a potent and efficacious antinociceptive with a very favorable therapeutic window after s.c. and p.o. administration in mice, and with good efficacy in rats.

Pharmacology of butylthio[2.2.2] (LY297802/NNC11-1053): a novel analgesic with mixed muscarinic receptor agonist and antagonist activity.

Butylthio[2.2.2], ((+)-(S)-3-(4-butylthio-1,2,5-thiadiazol-3-yl)-1-azabicyclo[2.2.2] octane; LY297802/NNC11-1053) is a muscarinic receptor ligand which is equiefficacious to morphine in producing antinociception. In vitro, butylthio[2.2.2] had high affinity for muscarinic receptors in brain homogenates, but had substantially less or no affinity for several other neurotransmiter receptors and uptake sites. In isolated tissues, butylthio[2.2.2] was an agonist with high affinity for M1 receptors in the rabbit vas deferens (IC50 = 0.33 nM), but it was an antagonist at M2 receptors in guinea pig atria (pA2 = 6.9) and at M3 receptors in guinea pig urinary bladder (pA2 = 7.4) and a weak partial agonist in guinea pig ileum, which contains a heterogeneous population of muscarinic receptors. In vivo, butylthio[2.2.2] was without effect on acetylcholine, dopamine and serotonin levels in rat brain. Moreover, butylthio[2.2.2] did not decrease charcoal meal transit in mice, nor did it significantly alter heart rate in rats. Further, butylthio[2.2.2] did not produce parasympathomimetic effects such as salivation or tremor in mice, but it antagonized salivation and tremor produced by the nonselective muscarinic agonist oxotremorine. The present data demonstrate that butylthio[2.2.2] is a novel muscarinic receptor mixed agonist/antagonist and its pharmacological profile suggests that it may have clinical utility in the management of pain as an alternative to opioids.

Muscarinic analgesics with potent and selective effects on the gastrointestinal tract: potential application for the treatment of irritable bowel syndrome.

Irritable bowel syndrome (IBS) is a pathopysiolocal condition characterized by abnormal bowel habits that are frequently accompanied by abdominal pain. Current therapy based on reducing high-amplitude GI contractions with nonselective muscarinic antagonists is limited in efficacy due to typical muscarinic side effects and provides no pain relief. We have previously found potent antinociceptive agents acting through muscarinic receptors. In the present work, new 1,2,5-thiadiazole-based structures with muscarinic activity have been evaluated both for activity as analgesics in the mouse withing assay and for activity in normalizing spontaneous cluster contractions in ferret jejunum as a model of IBS in humans. (5R,6R)-exo-6-[4-[(4,4,4-Trifluorobutyl)thio]-1,2,5-thiadiazol+ ++-3-yl] -1-azabicyclo[3.2.1]octane (35, LY316108/NNC11-2192) was found to offer an exceptional profile combining analgesic potency in mouse writhing (ED50 = 0.1 mg/kg) along with potency for normalization of GI motility (ED50 = 0.17 mg/kg). This combination of GI and analgesic potency suggests 35 as an excellent candidate for evaluation as a potential treatment of IBS.

In vivo pharmacology of butylthio[2.2.2] (LY297802 / NNC11-1053), an orally acting antinociceptive muscarinic agonist.

Butylthio[2.2.2] (LY297802 / NNC11-1053) is a mixed muscarinic cholinergic receptor agonist/antagonist that produces antinociception in mice and rats. As such, butylthio[2.2.2] may have therapeutic utility in the treatment of pain. Butylthio[2.2.2] was fully efficacious in the mouse grid shock, writhing, tail-flick and hot plate tests with ED50 values ranging from 1.5 to 12.2 mg/kg after oral administration. In contrast, the ED50 values for morphine ranged from 7.3 to 72 mg/kg after oral administration. Scopolamine was a competitive antagonist of the antinociceptive effects of butylthio[2.2.2]. Butylthio[2.2.2] did not produce either salivation or tremor at therapeutic doses; rather, there was a 50- to >100-fold separation between therapeutic doses and doses which produced side-effects. Butylthio[2.2.2] had high affinity for muscarinic receptors, but little if any affinity for other neurotransmitter receptors or uptake sites. In isolated tissues, butylthio[2.2.2] was an agonist with high affinity at M1 receptors in rabbit vas deferens, an antagonist at M2 receptors in guinea pig atria as well as an antagonist at M3 receptors in guinea pig urinary bladder. Although it has been suggested that M1 receptors mediate the antinociceptive effects of muscarinic agonists, M1 efficacy is not a requirement for antinociception, and, in vivo, the antinociceptive effects of muscarinic agonists are blocked by the intrathecal administration of pertussis toxin, indicating the involvement of m2 or m4 receptors. Since butylthio[2.2.2] is an M2 antagonist, antinociception is therefore most likely mediated by m4 receptors. Butylthio[2.2.2] is currently undergoing clinical development as a novel analgesic.

Synthesis and structural determination of stereoisomers of muscarinic ligands of the (3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicycloalkane type.

Methods for the synthesis of each of the four stereoisomers of 6-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[3.2.1]oc tane (10, 11, 12, and 13) and 3-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[2.2.1]he ptane (18, 19, 20, and 21), and the two stereoisomers of 3-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[2.2.2]oc tane (27 and 28) were developed. The relative configuration of the compounds was determined on the basis of previously described 1H NOE experiments, and the absolute configuration of 6-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[3.2.1]oc tanes (10, 11, 12, and 13) and 3-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[2.2.2]oc tane (27 and 28) was determined by single crystal X-ray crystallography. Optical purity was determined by capillary electrophoresis (CE) using chiral selectors as trimethyl-beta-cyclodextrin and heparin dissolved in the running buffer. All the 3-(3-propylthio-1,2,5-thiadiazol-4-yl)-1-azabicycles had low nanomolar affinity for muscarinic receptors as determined by displacement of radiolabelled oxotremorine-M (3H-Oxo-M) and pirenzepine (3H-Pz) from cortical rat brain homogenates. The binding assay discriminated between diastereomers, but only a minor degree of enantioselectivity was observed in the binding assays.

Functionally selective M1 muscarinic agonists. 3. Side chains and azacycles contributing to functional muscarinic selectivity among pyrazinylazacycles.

In an attempt to improve upon the M1 agonist activity of the selective M1 agonist xanomeline and related compounds, the M1 muscarinic efficacies and potencies of 3- and 6-substituted pyrazinylazacycles were varied by changing both the 3- and 6-substituents as well as the azacycle. Significant improvements in efficacy and potency over the previously prepared [3-(hexyloxy)pyrazinyl]tetrahydropyridine 19 were obtained with the [3-(hexyloxy)pyrazinyl]-quinuclidine 5i. The M1 activity of 5i showed some enantioselectivity with (S)-5i being ca. 4-fold more potent than (R)-5i. Like 19 and xanomeline, 5i was a functionally selective M1 agonist that showed greater functional selectivity than widely studied pyrazinylquinuclidine 5n (L-689,660). The improved functional selectivity of 5i over 5n could be attributed to the additional binding interactions between the hexyloxy side chain of 5i and the M1 receptor that are not available to 5n. Although 5i may show M1 functional selectivity comparable to xanomeliine, 5i is a less efficacious and potent M1 agonist than xanomeline.

Novel alkoxy-oxazolyl-tetrahydropyridine muscarinic cholinergic receptor antagonists.

The purpose of the present studies was to compare a novel series of alkoxy-oxazolyl-tetrahydropyridines (A-OXTPs) as muscarinic receptor antagonists. The affinity of these compounds for muscarinic receptors was determined by inhibition of [3H]pirenzepine to M1 receptors in hippocampus, [3H]QNB to M2 receptors in brainstem, and [3H]oxotremorine-M to high affinity muscarinic agonist binding sites in cortex. All of the compounds had higher affinity for [3H]pirenzepine than for [3H]QNB or [3H]oxotremorine-M labeled receptors, consistent with an interpretation that they are relatively selective M1 receptor antagonists, although none were as selective as pirenzepine. In addition, dose-response curves were determined for antagonism of oxotremorine-induced salivation (mediated by M3 receptors) and tremor (mediated by non-M1 receptors) in mice. In general, the A-OXTPs were equipotent and equieffective in antagonizing both salivation and tremor, although there were modest differences for some compounds. Dose-response curves also were determined on behavior maintained under a spatial-alternation schedule of food presentation in rats as a measure of effects on working memory. The A-OXTPs produced dose-related decreases in percent correct responding at doses three- to ten-fold lower than those which decreased rates of responding. However, only one compound, MB-OXTP, produced effects on percent correct responding consistent with a selective effect on memory as opposed to non-memory variables. The present results provide evidence that these alkoxy-oxazolyl-tetrahydropyridines are a novel series of modestly M1-selective muscarinic receptor antagonists, and that one member of the series, MB-OXTP, appears to be more selective in its effects on memory than previously studies muscarinic antagonists.

The muscarinic M1 agonist xanomeline increases soluble amyloid precursor protein release from Chinese hamster ovary-m1 cells.

The functionally selective M1 agonist xanomeline, which is currently undergoing clinical trials as a therapy for Alzheimer's disease, was compared to the muscarinic agonist carbachol for effects on secretion of soluble amyloid precursor protein (APPs) from Chinese hamster ovary cells transfected with the human m1 receptor (CHO-m1). Release of APPs from CHO-m1 cells was increased maximally (4-10 fold) by 100 microM carbachol (EC50 = 11 microM) and by 100 nM xanomeline (EC50 = 10 nM). Stimulation of APPs secretion by xanomeline and carbachol was blocked by preincubation with 1 microM atropine. Carbachol did not stimulate APPs secretion from non-transfected CHO cells. Pilocarpine at 1 mM also increased APPs release. The efficacy of carbachol, xanomeline and pilocarpine for stimulating APPs secretion did not differ significantly. Activation of protein kinase C (PKC) in m1 transfected cell lines by 1 microM phorbol dibutyrate (PDBu) increased APPs release, and this was inhibited 97% by the PKC inhibitor bisindolemalemide. The PKC inhibitor decreased xanomeline and carbachol-stimulated APPs secretion by only 25-30%. These results demonstrate that xanomeline increased APPs release by activation of m1 muscarinic receptors and support the possibility that cholinergic replacement therapy for Alzheimer's Disease may reduce amyloid deposition.

Muscarinic agonists as analgesics. Antinociceptive activity versus M1 activity: SAR of alkylthio-TZTP's and related 1,2,5-thiadiazole analogs.

Alkylthio-TZTPs (3-(3-alkylthio-1,2,5-thiadiazol-4-yl)-1,2,5,6-tetrahydro-1-met hylpyridines) and corresponding azabicyclic analogs were tested for m1 efficacy in cloned human m1 receptors and for antinociceptive activity in the mouse grid shock assay. The m1 (%PI) SAR were distinctly different from the analgesia and the salivation SAR, suggesting that analgesia is mediated by neither m1 nor M3 muscarinic receptors.

Xanomeline: a novel muscarinic receptor agonist with functional selectivity for M1 receptors.

Xanomeline [3(3-hexyloxy-1,2,5-thiadiazol-4-yl)-1,2,5,6-tetrahydro-1- methylpyridine] has been evaluated as a muscarinic receptor agonist. In vitro, xanomeline had high affinity for muscarinic receptors in brain homogenates, but had substantially less or no affinity for a number of other neurotransmitter receptors and uptake sites. In cells stably expressing genetic m1 receptors, xanomeline increased phospholipid hydrolysis in CHO, BHK and A9 L cells to 100, 72 and 55% of the nonselective agonist carbachol. In isolated tissues, xanomeline had high affinity for M1 receptors in the rabbit vas deferens (IC50 = 0.006 nM), low affinity for M2 receptors in guinea pig atria (EC50 = 3 microM), was a weak partial agonist in guinea pig ileum and was neither an agonist nor antagonist in guinea pig bladder. In vivo, xanomeline increased striatal levels of dopamine metabolites, presumably by acting at M1 heteroreceptors on dopamine neurons to increase dopamine release. In contrast, xanomeline had only a relatively small effect on acetylcholine levels in brain, indicating that it is devoid of actions at muscarinic autoreceptors. In the gastrointestinal tract, xanomeline inhibited small intestinal and colonic motility, but increased small intestinal transmural potential difference. In contrast to the nonselective muscarinic agonist oxotremorine, xanomeline did not produce salivation, tremor nor hypothermia; it did, however, increase heart rate. The present data are consistent with the interpretation that xanomeline is a novel muscarinic receptor agonist with functional selectivity for M1 muscarinic receptors both in vitro and in vivo.