Celia A. Whitesitt

Angiotensin ii antagonists

Acute blockade of the renin-angiotensin system with the parenterally active angiotensin II antagonist saralasin has been shown to effectively lower blood pressure in a large fraction of patients with essential hypertension and to improve hemodynamics in some patients with congestive heart failure. It is now possible to antagonize chronically angiotensin II at its receptor using the non-peptide angiotensin II inhibitor losartan (DuP 753, MK 954). When administered by mouth, this compound induces a dose-dependent inhibition of the pressor response to exogenous angiotensin II. This effect is closely related to circulating levels of the active metabolite E3174. Preliminary studies performed in hypertensive patients suggest that losartan has a blood pressure lowering action equivalent to that of an ACE inhibitor. Whether this compound will compare favorably with ACE inhibitors requires however further investigation.

Xanomeline: A selective muscarinic agonist for the treatment of Alzheimer's disease

Xanomeline is a novel muscarinic receptor agonist relatively devoid of parasympathomimetic side effects. Xanomeline had high affinity for muscarinic receptors and much lower affinity for a variety of other neuronal receptors in radioligand binding assays. Functional studies in cell lines transfected with the muscarinic receptor subtypes demonstrated that xanomeline had higher potency and efficacy for m1 and m4 receptors than m2, m3, and m5 receptor subtypes. Similarly, in isolated tissue studies, xanomeline had higher potency and efficacy for M1 receptors in rabbit vas deferens than at M2 receptors in guinea pig atria or M3 receptors in guinea pig bladder. Secretion of soluble amyloid precursor protein from m1 cell lines was potently stimulated by xanomeline. In vivo, xanomeline robustly stimulated phosphoinositide hydrolysis in brain, consistent with m1 agonism. Xanomeline produced modest increases in brain acetylcholine levels and did not produce bradycardia, suggesting little, if any, m2 agonist activity in vivo. Additionally, xanomeline did not induce nonselective cholinergic agonist side effects such as tremor, hypothermia and salivation. In animal behavior studies, xanomeline reduced locomotion and blocked memory deficits that were induced by a muscarinic antagonist in a passive avoidance paradigm. Xanomeline was found to be safe and reasonably well tolerated in safety studies in humans. In a placebo controlled double blind clinical trial of 6 months duration, xanomeline halted cognitive decline in patients with Alzheimers disease. Furthermore, behavioral symptoms associated with Alzheimers disease such as hallucinations, delusions and vocal outbursts were significantly decreased by xanomeline treatment. Additional clinical trials are under way to assess the novel therapeutic effects of xanomeline. Drug Dev. Res. 40:158–170, 1997.

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.

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 Alzheimers 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 xanomelines beneficial clinical effects on cognition in Alzheimers patients.

Synthesis and structure-activity relationships of benzophenones as inhibitors of cathepsin D

Abstract Non peptide inhibitors of cathepsin D, an aspartyl protease that has been implicated in many disease states including Alzheimers disease, were prepared and evaluated. The most potent inhibitor of cathepsin D in this series was found to be (Z)-5-[[4-(4-benzoyl-3-hydroxy-2-propylphenoxy) methylphenyl]methylene]-2-thioxo-4-thiazolidinone ( 3f , IC 50 = 210 nM).

Muscarinic receptor agonists decrease cocaine self-administration rates in drug-naive mice.

(5R,6R)-6-(3-Propylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[ 3.2.1]octane (PTAC) is a selective muscarinic receptor ligand. The compound exhibits high affinity for central muscarinic receptors with partial agonist mode of action at muscarinic M(2) and M(4) and antagonist mode of action at muscarinic M(1), M(3) and M(5) receptor subtypes. The compound was earlier reported to exhibit functional dopamine receptor antagonism in rodents despite its lack of affinity for dopamine receptors. In the present study, we report that PTAC, as well as the muscarinic receptor agonists pilocarpine and oxotremorine, dose-dependently decreased rates of intravenous self-administration (fixed ratio 1) of the indirect dopamine receptor agonist cocaine in drug naive mice. Similar decreases in cocaine self-administration rates were obtained with the dopamine receptor antagonists olanzapine, clozapine, risperidone, fluphenazine and haloperidol. These findings suggest that compounds with partial muscarinic receptor agonist mode of action may be used in the medical treatment of cocaine abuse.

The muscarinic receptor agonist BuTAC, a novel potential antipsychotic, does not impair learning and memory in mouse passive avoidance

(5R,6R)-6-(3-butylthio-1,2,5-thiadiazol-4-yl)-1-azabicyclo[3.2.1]octane) (BuTAC) is a novel, selective muscarinic receptor ligand with partial agonist mode of action at muscarinic M2 and M4 and antagonist mode of action at M1, M3 and M5 receptor subtypes in cloned cell lines. BuTAC exhibits functional dopamine receptor antagonism despite its lack of affinity for dopamine receptors, and parasympathomimetic effects in mice are produced only at doses well beyond the doses exhibiting the antipsychotic-like effects. In the present study we investigated the effects of BuTAC and the antipsychotic compounds clozapine, sertindole and olanzapine using one trial passive avoidance with mice as a model of learning and memory. Pharmacologically relevant doses of BuTAC and reference antipsychotics were identified, based on inhibition of apomorphine-induced climbing in mice as an assay measuring antidopaminergic potency. When ratios between the minimum effective dose (MED) for impairment of retention in passive avoidance and the MED for inhibition of apomorphine-induced climbing were calculated, BuTAC displayed a high ratio of >10, compared with clozapine (0.3), sertindole (3) and olanzapine (3). These data suggest that BuTAC is a potential novel antipsychotic which may have favourable effects on aspects of learning and memory.

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.

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.

Chiral recognition of the angiotensin II (AT1) receptor by a highly potent phenoxyproline octanoamide

Abstract The synthesis and in vitro biological evaluation of a novel series of diastereomeric phenoxyproline octanoamides ( 3–h ) as angiotensin II (AT 1 ) receptor antagonists are reported.