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.

Meta-chlorophenylpiperazine induced changes in locomotor activity are mediated by 5-HT1 as well as 5-HT2C receptors in mice

1-(Meta-chloro)phenylpiperazine (m-CPP) is a 5-HT receptor agonist which has been purported to be relatively selective for the 5-HT2C receptor. In particular, the hypolocomotion produced by m-CPP has been suggested to be mediated by 5-HT2C receptors. m-CPP binds with high affinity to 5-HT1 as well as 5-HT2 receptors, thus effects of m-CPP on locomotor activity may be due to the physiologic summation of the actions of m-CPP at 5-HT1 as well as 5-HT2 receptors. The present study investigated the effects of m-CPP alone and in the presence of the 5-HT2 receptor antagonist 6-methyl-1-(-methyethyl)-ergoline-8beta-carboxylic acid 2-hydroxy-1-methylpropyl ester maleate (LY53857), the 5-HT1A receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]-ethyl]-N-(2pyridinyl)c yclohexanecarboxamide trihydrochloride (WAY 100,635), and the 5-HT(1B/1D) receptor antagonist 2'-methyl-4'-(5-methyl-[1,2,4]oxadiazol-3-yl)-biphenyl-4-corbox ylic acid [4-methoxy-3-(4-methyl-piperazin-1-yl)-phenyl]amide (GR 127935) on locomotor activity. Administration of m-CPP alone (0.3-10 mg/kg) produced a dose-related decrease in locomotor activity. The 5-HT(1B/1D) receptor antagonist GR 127935 (3.0 mg/kg) in combination with m-CPP produced a slight leftward shift of the dose-response curve of m-CPP. The 5-HT1A receptor antagonist WAY 100,635 (1.0 mg/kg) in combination with m-CPP did not alter the m-CPP dose-response curve. The non-selective 5-HT2 receptor antagonist LY53857 (1.0 mg/kg) in combination with m-CPP unmasked a hyperlocomotion produced by m-CPP. Furthermore, the hyperlocomotion produced by m-CPP in the presence of LY53857 (1.0 mg/kg) was blocked by both the 5-HT(1B/1D) receptor antagonist GR 127935 (3.0 mg/kg) and the 5-HT1A receptor antagonist WAY 100,635 (1.0 mg/kg). The present results demonstrate that the hyperlocomotion seen with the combination of m-CPP and LY53857 is mediated by 5-HT1 receptors. Taken together the data indicate that m-CPP affects locomotor activity by the physiologic summation of agonist activity at the 5-HT2C receptor as well as the 5-HT1 receptor family.

Conformationally constrained analogues of the muscarinic agonist 3-(4-(methylthio)-1,2,5-thiadiazol-3-yl)-1,2,5,6-tetrahydro-1-methylpyr idine. Synthesis, receptor affinity, and antinociceptive activity

Conformationally constrained analogues of the potent muscarinic agonist 3-(4-methylthio)-1,2,5-thiadiazol-3-yl)-1,2,5,6-tetrahydro-1-methy lpyridine (methylthio-TZTP, 17) were designed and synthesized with the aim of (a) improving the antinociceptive selectivity over salivation and tremor and (b) predicting the active conformation of 17 with respect to the dihedral angle C4-C3-C3'-N2'. Using MOPAC 6.0 tricyclic analogues (7, 15, 16) with C4-C3-C3'-N2' dihedral angles close to 180 degrees and a rotation hindered analogue (9) with a C4-C3-C3'-N2' dihedral angle close to 274 degrees were designed, as these conformations had previously been suggested as being the active conformations. The analogues were tested for central muscarinic receptor binding affinity, for their antinociceptive activity in the mouse grid shock test, and, in the same assay, for their ability to induce tremor and salivation. The data showed that the tricyclic analogues (7, 15, 16) were equipotent with 17 as analgesics, but with no improved side effect profiles. The rotation-hindered analogue 9 had neither muscarinic receptor binding affinity nor antinociceptive activity. These results suggest that the active conformation of 17 has a C3-C4-C3'-N2' dihedral angle close to 180 degrees.

The selective muscarinic agonist xanomeline improves both the cognitive deficits and behavioral symptoms of Alzheimer disease

The therapeutic effects of selective cholinergic replacement using oral xanomeline, an m1/m4 receptor agonist, were assessed in a multicenter study of 343 patients with Alzheimer disease (AD). Patients were randomized to parallel treatment arms (placebo, 25, 50, and 75 mg t.i.d. xanomeline) and followed through 6 months of double-blind therapy and 1 month of single-blind placebo washout. Completer analysis, using the cognitive subscale of the Alzheimer's Disease Assessment Scale (ADAS-Cog), revealed a significant treatment effect (75 mg t.i.d. vs. placebo; p = 0.045). Similar assessment of global status, using the Clinician's Interview-Based Impression of Change, was also significant (75 mg t.i.d. vs. placebo; p = 0.022). Treatment Emergent Signs and Symptoms analysis of the Alzheimer's Disease Symptomatology Scale, revealed highly significant (p < or = 0.002) dose-dependent reductions in vocal outbursts, suspiciousness, delusions, agitation, and hallucinations. On end-point analysis, the Nurses' Observational Scale for Geriatric Patients also showed a significant dose-response relationship (p = 0.018). The improvement in ADAS-Cog provides the first clinical evidence of involvement of the m1 muscarinic receptor in cognition. Furthermore, the favorable effects of xanomeline on disturbing behaviors suggest a novel approach for treatment of the noncognitive symptoms of AD. Although adverse effects (mainly gastrointestinal) associated with the oral formulation appear to limit its use, a large-scale study investigating the safety and efficacy of transdermal xanomeline is under way.

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.

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.

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.

Effects of xanomeline, a selective muscarinic receptor agonist, on cognitive function and behavioral symptoms in Alzheimer disease

OBJECTIVE

To evaluate the therapeutic effects of selective cholinergic replacement with xanomeline tartrate, an m1 and m4 selective muscarinic receptor (mAChR) agonist in patients with probable Alzheimer disease (AD).

DESIGN

A 6-month, randomized, double-blind, placebo-controlled, parallel-group trial followed by a 1-month, single-blind, placebo washout.

SETTING

Outpatients at 17 centers in the United States and Canada.

PARTICIPANTS

A total of 343 men and women at least 60 years of age with mild to moderate AD.

INTERVENTIONS

Patients received 75, 150, or 225 mg (low, medium, and high doses) of xanomeline per day or placebo for 6 months.

OUTCOME MEASURES

Scores on the cognitive subscale of the Alzheimer's Disease Assessment Scale (ADAS-Cog), the Clinician's Interview-Based Impression of Change (CIBIC+), the Alzheimer's Disease Symptomatology Scale (ADSS), and the Nurses' Observational Scale for Geriatric Patients (NOSGER).

RESULTS

A significant treatment effect existed for ADAS-Cog (high dose vs placebo; P < or = .05), and CIBIC+ (high dose vs placebo; P < or = .02). Treatment Emergent Signs and Symptoms analysis of the ADSS, which assesses behavioral symptoms in patients with AD, disclosed significant (P < or = .002) dose-dependent reductions in vocal outbursts, suspiciousness, delusions, agitation, and hallucinations. On end-point analysis, NOSGER, which assesses memory, instrumental activities of daily living, self-care, mood, social behavior, and disturbing behavior in the elderly, also showed a significant dose-response relationship (P < or = .02). In the high-dose arm, 52% of patients discontinued treatment because of adverse events; dose-dependent adverse events were predominantly gastrointestinal in nature. Syncope, defined as loss of consciousness and muscle tone, occurred in 12.6% of patients in the high-dose group.

CONCLUSIONS

The observed improvements in ADAS-Cog and CIBIC+ following treatment with xanomeline provide the first evidence, from a large-scale, placebo-controlled clinical trial, that a direct-acting muscarinic receptor agonist can improve cognitive function in patients with AD. Furthermore, the dramatic and favorable effects on disturbing behaviors in AD suggest a novel approach for treatment of noncognitive symptoms.

Intrathecal pertussis toxin produces hyperalgesia and allodynia in mice

Pertussis toxin (PTX), which causes the ADP-ribosylation and thereby inactivation of Gi-proteins, has been employed in analgesia testing to elucidate receptors that are coupled to inhibitory G-proteins, such as the mu-opioid receptor. Consistent with previous findings, the antinociceptive effects of morphine (1-10 microg) as measured by tail-flick latency using a 55 degrees C water bath, were blocked by a single intrathecal injection of 0.5 microg PTX 6 days prior to intrathecal morphine administration. In addition, mice treated intrathecally with 0.5 microg of PTX had significantly shorter baseline tail-flick latencies compared with vehicle treated mice using a 55 degrees C water bath when tested 6 days after PTX or vehicle administration. Morphine-induced antinociception was blocked in a dose-dependent manner by PTX with complete blockade of morphine following a 0.3-microg dose of PTX. Further, mice administered 0.1 microg or 0.3 microg PTX intrathecally had significantly shorter tail-flick latencies compared with vehicle injected mice using a 40, 45 or 50 degrees C water bath when tested 7 days after intrathecal injection. Shorter tail-flick latencies were observed at 45 degrees C as early as 48 h after intrathecal administration of 0.03, 0.1 or 0.3 microg PTX and these shorter tail-flick latencies were observed up to 90 days after intrathecal PTX administration. The intrathecal administration of PTX caused hyperalgesia and allodynia that appears similar to the symptoms reported by patients suffering from neuropathic pain, and suggests that deficiencies in inhibitory systems, as compared with increases in excitatory systems, may play a role in the pathophysiology of at least some central or neuropathic pain states.

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.

Blockade of phencyclidine-induced hyperlocomotion by olanzapine, clozapine and serotonin receptor subtype selective antagonists in mice

In humans, phencyclidine (PCP) is known to produce a syndrome of behavioral effects which have many characteristics in common with schizophrenia. Therefore, antagonism of PCP effects might be evidence for antipsychotic efficacy of a compound. In the present studies, the effects of the D2-like antagonist haloperidol, the mixed D2-like/5-HT2 antagonists olanzapine and clozapine, and a series of 5-HT receptor subtype selective antagonists on the hyperlocomotion produced by PCP were evaluated in mice. PCP (0.3-10 mg/kg) produced a dose-related increase in locomotor activity, with a peak effect at 3.0 mg/kg. The D2-like antagonist haloperidol produced a dose-related decrease in locomotor activity when administered alone, and blocked the hyperactivity effects of PCP over the same dose-range (minimal effective dose, MED = 0.3 mg/kg for both effects). In contrast, olanzapine and clozapine reversed the hyperlocomotion effects of PCP at doses (MED = 0.03 and 0.3 mg/kg, respectively) approximately 30- and 10-fold, respectively, below those that decreased activity when administered alone (MED = 1.0 and 3.0 mg/kg, respectively). The selective 5-HT2 antagonist LY53857 (0.3-3.0 mg/kg) administered alone had no effect on locomotor activity but reversed (MED = 0.1 mg/kg) the effects of PCP. Similarly, the selective 5-HT2A/2C antagonist ritanserin (0.001-1.0 mg/kg) alone had no effect on locomotor activity, but reversed (MED = 0.01 mg/kg) the effects of PCP. The selective 5-HT2A antagonists ketanserin (MED = 3.0 mg/kg) and MDL 100,907 (MED = 0.3 mg/kg) produced dose-related decreases in locomotor activity and ketanserin (MED = 0.1 mg/kg) and MDL 100,907 (MED = 0.003 mg/kg) reversed the effects of PCP. The selective 5-HT3 antagonist zatosetron (0.01-10 mg/kg) and the selective 5-HT1A antagonist WAY 100,635 (0.001-3 mg/kg) were without effects on spontaneous locomotor activity. Zatosetron reversed the effects of 3.0 mg/kg PCP at the nonselective dose of 10 mg/kg whereas WAY 100,635 (0.001-1 mg/kg) did not affect PCP-induced hyperlocomotion. The present results indicate that PCP increases locomotor activity, at least in part, due to actions at 5-HT2A, but not 5-HT3 or 5-HT1A, receptors. Further, the present findings support the hypothesis that antagonism at 5-HT2A receptors contributes to the in vivo actions of atypical antipsychotics such as olanzapine and clozapine.

Characterization of small intestinal submucosa regenerated canine detrusor: assessment of reinnervation, in vitro compliance and contractility

PURPOSE

We characterized small intestinal submucosa regenerated canine bladder.

MATERIALS AND METHODS

We subjected 15-month small intestinal submucosa regenerated canine bladder strips to in vitro muscle bath compliance, contractility testing and immunohistochemical staining.

RESULTS

Compliance studies demonstrated no significant difference between small intestinal submucosa regenerated and control bladders, which were 30-fold more compliant than native small intestinal submucosal graft material. Contractility studies demonstrated contractile responses and innervation similar to those of normal canine bladder. Afferent nerves were demonstrated through immunohistochemical techniques.

CONCLUSIONS

These characteristics further support the regenerative capacity of small intestinal submucosa and its potential use as a bladder augmentation material.

PET study of the M1-agonists [11C]xanomeline and [11C]butylthio-TZTP in monkey and man

Xanomeline, a substituted TZTP, is a new M1 selective muscarinic agonist in clinical trials for Alzheimer's disease. The brain uptake of [11C]xanomeline and the analog [11C]butylthio-TZTP was examined by positron emission tomography (PET). Radioactivity accumulated most markedly in the neocortex and the striatum. Pharmacological characterization in vitro and in cynomolgus monkeys in vivo by PET indicated specific [11C]butylthio-TZTP binding to muscarinic receptors and to sigma-1 recognition sites. More than 5% of the radioactivity was in the human brain 5 min after i.v. injection of [11C]xamomeline or [11C]butylthio-TZTP. This high brain uptake may be clinically advantageous in the sense that substituted TZTP may induce central muscarinic agonist effects at a dose level for which there is a low risk of peripheral side-effects.

Muscarinic agonist inhibition of rat striatal adenylate cyclase is enhanced by dopamine stimulation

Rat striatal adenylate cyclase stimulated with combinations of 100 microM dopamine plus 40-100 nM forskolin was inhibited to a significantly greater extent by the muscarinic agonist carbachol than was forskolin-stimulated activity in the absence of dopamine. In the presence of Ro 201724 as phosphodiesterase inhibitor, a 100 microM concentration of the adenosine agonist 2-chloroadenosine stimulated adenylate cyclase activity 6.6 -fold over basal activity. In contrast to dopamine-stimulated activity, carbachol did not significantly inhibit adenylate cyclase activity elevated by the adenosine agonist, indicating specificity of the muscarinic response for dopamine stimulation. The effects of muscarinic antagonists on striatal versus heart adenylate cyclase indicated that the striatal response was mediated primarily through M4 receptors. The present results suggest that muscarinic M4 and dopamine D1 receptors are co-localized and functionally coupled in rat striatum.

Detrusor regeneration in the rat using porcine small intestinal submucosal grafts: functional innervation and receptor expression

PURPOSE

To evaluate functional characteristics of regenerated bladder induced by small intestinal submucosa (SIS).

MATERIALS AND METHODS

Strips from bladder regenerated from SIS and normal rat bladder were evaluated by in vitro muscle bath contractility studies.

RESULTS

The present results indicate that SIS-regenerated bladder 1) demonstrates contractile activity; 2) expresses muscarinic, purinergic and beta adrenergic receptors; and 3) exhibits functional cholinergic and purinergic innervation that is similar to the normal rat urinary bladder muscle.

CONCLUSIONS

These functional characteristics of SIS-regenerated tissue demonstrated in the present study further support use of SIS material as a bladder augmentation material.

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.

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.

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.

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.

Neurochemical effects of the M1 muscarinic agonist xanomeline (LY246708/NNC11-0232)

Xanomeline [3(3-hexyloxy-1,2,5-thiadiazol-4-yl)-1,2,5,6-tetrahydro-1-me thylpyridine)] was evaluated in vivo in rat brain for effects on neurotransmitter turnover and inhibition of ex vivo binding of muscarinic radioligands. Xanomeline produced dose-related increases in the metabolite of dopamine, dihydroxyphenylacetic acid (DOPAC), in striatum. The increases in striatal DOPAC levels produced by xanomeline were antagonized by the relatively selective M1 antagonist trihexyphenidyl, suggesting that xanomeline interacts with M1 heteroreceptors on dopamine nerve terminals. Xanomeline produced small increases in striatal acetylcholine levels and did not antagonize the large increases in acetylcholine produced by the nonselective muscarinic agonist oxotremorine, indicating that xanomeline did not block M2 autoreceptors. Xanomeline inhibited ex vivo binding of muscarinic radioligands to homogenates of brain and the inhibition of ex vivo binding occurred in the same dose range as increases in DOPAC levels. Xanomeline did not appreciably induce salivation or antagonize oxotremorine-induced salivation indicating that xanomeline does not interact with M3 receptors. The effects of xanomeline on ex vivo binding and DOPAC levels lasted for about 3 hr and were evident after oral administration. An analog of xanomeline with similar in vivo effects did not inhibit acetylcholinesterase or choline acetyltransferase and inhibited choline uptake only at concentrations much higher than those required to inhibit binding. These data indicate xanomeline is selective agonist for M1 over M2 and M3 receptors in vivo in rat. It is not known whether xanomeline interacts with m4 or m5 receptors in vivo.

Comparative behavioral and neurochemical activities of cholinergic antagonists in rats

The comparative behavioral and neurochemical activities of the muscarinic cholinergic antagonists scopolamine, trihexyphenidyl and pirenzepine, and the nicotinic cholinergic antagonist mecamylamine were evaluated in rats. The three muscarinic antagonists, but not the nicotinic antagonist, impaired memory performance in a spatial alternation task. The minimal effective doses required to disrupt behavior were 0.03, 1.0 and 10 mg/kg for scopolamine, trihexyphenidyl and pirenzepine, respectively. Scopolamine and trihexyphenidyl inhibited ex vivo binding of [3H] pirenzepine to M1 receptors in cerebral cortex, indicating ready penetration into the brain. In contrast, pirenzepine penetrated into the brain at relatively high doses, suggesting poor penetration into the brain. Scopolamine and trihexyphenidyl, but not pirenzepine, inhibited [3H]quinuclidinyl benzilate binding to brain stem M2 receptors ex vivo after subcutaneous administration. In addition, scopolamine and trihexyphenidyl, but not pirenzepine, decreased acetylcholine (ACh) levels in striatum and hippocampus, presumably by increasing ACh release by blocking ACh feedback inhibition at M2 receptors. Scopolamine and trihexyphenidyl also produced modest decreases in levels of the dopamine metabolite 3,4-dihydroxyphenylacetic acid in striatum, most likely due to blockade of M1 heteroreceptors on dopamine nerve terminals. The present results are consistent with the interpretation that muscarinic antagonists impair memory performance in rats, at least in part, by blocking M1 muscarinic receptors. The present results do not support a role for blockade of M2 receptors. Further research is needed to determine the extent to which blockade of other (M3, M4, M5) muscarinic receptor subtypes contributes to the memory-impairing effects of muscarinic cholinergic antagonists.