Development of M1 subtype selective muscarinic agonists for Alzheimer's disease: Translation of in vitro selectivity into in vivo efficacy

Clinical trials in Alzheimer's disease (AD) with first generation muscarinic agonists (e.g., arecoline, oxotremorine, pilocarpine) produced inconsistent results due to poor pharmacokinetic properties and a lack of separation between central and peripheral activities observed with these compounds. Second generation agonists have sought to optimize physicochemical properties, and in most cases, target specific subtypes of muscarinic receptor to overcome these limitations. Based upon receptor distribution in both central and peripheral nervous systems, agonists of the m1/M₁ subtype seem to possess the desired profile for AD treatment. For the discovery and characterization of these selective agents, the use of clonal cell lines expressing the five subtypes of muscarinic receptors (m1–m5) has become pivotal. However, their use is not without limitations. Results from functional assays (e.g., activation of second messengers) reliably measures subtype selectivity, whereas receptor binding underestimates selectivity. From a novel series of azabicyclic oximes, PD151832 has been chosen for further development and data obtained with this M₁ muscarinic agonist is used to exemplify central and peripheral animal models of cholinergic activity and the ability to translate in vitro subtype selectivity into in vivo efficacy. Drug Dev. Res. 40:133–143, 1997. © 1997 Wiley-Liss, Inc.     

Therapeutic strategies in Alzheimer's disease: M1 muscarinic agonists

The cholinergic hypofunction in Alzheimer's disease (AD) appears to be linked with two other major hallmarks of this disease, beta-amyloid and hyperphosphorylated tau protein. Formation of beta-amyloids might impair the coupling of M1 muscarinic acetylcholine receptors (mAChR) with G-proteins. This can lead to decreased signal transduction, a decrease of trophic and non-amyloidogenic amyloid precursor protein (APPs) and generation of more beta-amyloids, aggravating further the cholinergic deficiency. This review is an attempt to explore the M1 mAChR regulation of beta-amyloid metabolism, tau hyperphosphorylation and cognitive functions. The therapeutic potential of M1-selective muscarinic agonists including AF102B, AF150(S), AF267B (the AF series) is evaluated and compared, when possible, with several FDA-approved acetylcholinesterase inhibitors. These M1 agonists can elevate APPs, decrease tau protein phosphorylation/hyperphosphorylation in vitro and in vivo and restore cognitive impairments in several animal models for AD. Except for the M1 agonists, no other compounds were reported yet with combined effects; e.g., amelioration of cognition dysfunction and beneficial modulation of APPs/beta-amyloid together with tau hyperphosphorylation/phosphorylation. This property of M1 agonists to alter different aspects associated with AD pathogenesis could represent the most remarkable clinical value of such drugs.     

Tetrahydropyrimidine derivatives display functional selectivity for M1 muscarinic receptors in brain

Selective muscarinic agonists might be useful in the treatment of Alzheimer's disease. Previous studies identified several amidine derivatives as selective and efficacious m1 agonists, using muscarinic receptor subtypes expressed in cell lines. In the present studies, the functional selectivities, side effect profiles and memory-enhancing properties of these ligands were examined through a series of in vitro and in vivo experiments. CDD-0078, CDD-0097, and CDD-0102 behaved as partial agonists by stimulating PI turnover in rat cortical slices to roughly 100% above basal levels. Pirenzepine was more potent than either AF-DX 116 or p-F-hexahydrosiladifenidol (p-F-HHSiD) in blocking the PI responses of each ligand, suggesting that the responses were due to activation of M₁ receptors. The time course of pharmacological responses was examined following i.p. injections of muscarinic agonists. Low does (0.1 and 1.0 mg/kg) of CDD-0078, CDD-0097, and CDD-0102 did not elicit signs of cholinergic activity during the 2-hr testing period. The highest dose tested (10 mg/kg) produced a modest degree of salivation and lacrimation during the first 30-min period. Core body temperature remained unaffected. Central nervous system (CNS) penetration was evaluated through ex vivo binding studies. CDD-0097 inhibited 1.0 nM [³H]pirenzepine binding in a dose-dependent manner 30 min following i.p. injections. In behavioral studies, CDD-0097 (1.0 mg/kg) completely reversed the memory deficits induced by hemicholinium-3 or by IgG-192 saporin in two types of memory tasks. It did not impair the performance of control animals in either task. In summary, CDD-0097 displayed a limited side-effect profile and the ability to penetrate into the central nervous system and stimulate M₁ receptors. The amidine derivatives should be useful in further exploring the functional consequences of activating M₁ muscarinic receptors in the CNS. The beneficial effects of CDD-0097 on memory function warrant further examination of the compound as a selective M₁ agonist for the treatment of Alzheimer's disease. Drug Dev. Res. 40:171–184, 1997. © 1997 Wiley-Liss, Inc.     

Synthesis and pharmacological characterization of chiral pyrrolidinylfuran derivatives: the discovery of new functionally selective muscarinic agonists

Building on the previously and successfully applied hypothesis that stereochemical complication in the proximity of the critical cationic head of a cholinergic agonist would result in subtype selective compounds, we synthesized a series of chiral derivatives of furmethide and 5-methylfurmethide, with the aim of obtaining compounds that are useful for treating diseases derived from cholinergic receptor dysfunctions and/or useful for further characterizing subtypes of cholinergic receptors. Unlike their parent compounds, the new molecules lack nicotinic activity, being pure muscarinic ligands. While binding studies on the five cloned human muscarinic receptors showed no subtype selectivity, functional assays revealed that some of the molecules of the series are potent M 2 selective partial agonists with interesting pharmacological profiles.     

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 Alzheimer's disease. Furthermore, behavioral symptoms associated with Alzheimer's 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. © 1997 Wiley-Liss, Inc.     

In vitro characterization of tripitramine, a polymethylene tetraamine displaying high selectivity and affinity for muscarinic M2 receptors.

1. The antimuscarinic effects of tripitramine were investigated in vitro in isolated driven left (force) and spontaneously beating right (force and rate) atria as well as in the ileum of guinea-pig and rat and in the trachea and lung strip of guinea-pig and compared with the effects of methoctramine. 2. Tripitramine was a potent competitive antagonist of muscarinic M2 receptors in right and left atria. The pA2 values ranged from 9.14 to 9.85. However, in the guinea-pig and rat left atria but not in guinea-pig right atria, tripitramine at lower concentrations (3-10 nM) produced a less than proportional displacement to the right of agonist-induced responses owing to the presence of a possible saturable removal process. 3. Tripitramine was about three orders of magnitude less potent in ileal and tracheal than in atrial preparations (pA2 values ranging from 6.34 to 6.81) which makes it more potent and more selective than methoctramine. 4. Another intriguing finding was the observation that the pA2 value of 7.91 observed for tripitramine in guinea-pig lung does not correlate with that found at both muscarinic M2 and M3 receptor subtypes, which clearly indicates that the contraction of guinea-pig lung strip is not mediated by these muscarinic receptor subtypes. 5. A combination of tripitramine with atropine resulted in addition of the dose-ratios for left atria as required for two antagonists interacting competitively with the same receptor site, whereas the same combination gave a supra-additive antagonism on guinea-pig ileum which suggests that tripitramine interacts with a second interdependent site. 6. Tripitramine was more specific than methoctramine since, in addition to muscarinic receptors, it inhibited only frog rectus abdominis muscular (pIC50 value of 6.14) and rat duodenum neuronal (pIC50 value of 4.87) nicotinic receptors among receptor systems investigated, namely alpha 1-, alpha 2-, and beta 1-adrenoceptors, H1- and H2-histamine receptors, and muscular and neuronal nicotinic receptors.     

Muscarinic M(1) agonists in the treatment of Alzheimer's disease

The treatment of Alzheimer's disease attempts to correct cholinergic deficiency in the brain. In addition to the established, but restricted, efficacy of acetylcholinesterase inhibitors, attempts are being made to develop agents which will stimulate muscarinic receptors directly. This approach is logical and was found efficacious in several animal models of the disease; however none of these agents succeeded in clinical studies. Several reasons might account for this failure, which are discussed, as well as the prospects for the future.     

Inhibition of field stimulation-induced contractions of rabbit vas deferens by muscarinic receptor agonists: selectivity of McN-A-343 for M1 receptors

Inhibition of the field stimulation-induced twitch responses of the rabbit vas deferens by the muscarinic receptor agonist, McN-A-343, has been attributed to presynaptic muscarinic receptors of the M1 subtype located on noradrenergic nerve terminals. Stimulation of these receptors causes inhibition of transmitter release and inhibition of the contractile response. However, the selectivity of McN-A-343 for M1 receptors has been questioned and this throws doubt on whether the prejunctional receptors of the rabbit vas deferens are of the M1 subtype. In this study we have undertaken a comprehensive re-evaluation of the inhibition of prostatic and epididymal portions of the rabbit isolated field-stimulated vas deferens by several agonists, including McN-A-343, and quantified the antagonism by M1-selective antagonists, pirenzepine and telenzepine. Prostatic and epididymal portions of vasa deferentia from New Zealand White rabbits were immersed in a low Ca2+ Krebs solution at 32+/-0.5 degrees C gassed with 5% CO2 in oxygen. Yohimbine (1.0mM) was present throughout to block prejunctional alpha2-adrenoceptors. Field stimulation was applied by repeated application of single pulses (30 V, 0.05 Hz, 0.5 ms) and isometric contractions recorded. Carbachol and oxotremorine initially potentiated the epididymal contractions but at higher concentrations there was inhibition. In the prostatic portion, oxotremorine only inhibited. McN-A-343 produced inhibitory responses only in both epididymal and prostatic portions. Pirenzepine shifted the concentration-response curves forthe inhibitory responses to oxotremorine to the right. However, the potentiation of the twitches also became more apparent with the lower concentrations of oxotremorine. Schild plots for the antagonism by pirenzepine yielded pA2 values of 7.96+/-0.004 and 7.7+/-0.02 for the epididymal and prostatic portions, respectively. The concentration-response curves for the inhibition of twitches by McN-A-343 were displaced to the right in a parallel manner by pirenzepine in both prostatic and epididymal portions with no potentiation of the twitches. The Schild plot for this antagonism generated pA2 values of 7.68+/-0.01 and 8.07+/-0.01, respectively. Telenzepine caused parallel shifts of the McN-A-343 concentration-response curves to the right in prostatic portions, the pA2 value being 8.70+/-0.13. Telenzepine (10(-7) M) abolished the inhibitory effect of carbachol to reveal only concentration-dependent potentiation of the contractions. The Schild plot for antagonism of this contractile effect yielded a pA2 value (7.07+/-0.09) that was significantly less by almost two orders of magnitude (1.70) than the value for the antagonism by telenzepine of the McN-A-343-induced inhibitory response. The pA2 values of pirenzepine and telenzepine against the inhibitory responses of the rabbit vas deferens are consistent with the involvement of M1 receptors. This leads to the conclusion that McN-A-343 causes inhibition through this receptor type. The doubts concerning the selectivity of McN-A-343 for M1 receptors are therefore unfounded. The fact that McN-A-343 does not display a selective binding profile suggests that its selectivity does not arise from affinity differences but probably resides in its intrinsic efficacy.     

Design, synthesis, and biological characterization of bivalent 1-methyl-1,2,5,6-tetrahydropyridyl-1,2,5-thiadiazole derivatives as selective muscarinic agonists.

Selective muscarinic agonists could be useful in the treatment of neurological disorders such as Alzheimer's disease, schizophrenia, and chronic pain. Many muscarinic agonists have been developed, yet most exhibit at best limited functional selectivity for a given receptor subtype perhaps because of the high degree of sequence homology within the putative binding site, which appears to be buried within the transmembrane domains. Bivalent compounds containing essentially two agonist pharmacophores within the same molecule were synthesized and tested for receptor binding affinity and muscarinic agonist activity. A series of bis-1,2,5-thiadiazole derivatives of 1,2,5,6-tetrahydropyridine linked by an alkyloxy moiety exhibited very high affinity (K(i) < 1 nM) and strong agonist activity. The degree of activity depended on the length of the linking alkyl group, which could be replaced by a poly(ethylene glycol) moiety, resulting in improved water solubility, binding affinity, and agonist potency.     

Parainfluenza virus type 1 reduces the affinity of agonists for muscarinic receptors in guinea-pig lung and heart

Membrane preparations of guinea-pig lung (containing multiple muscarinic receptor subtypes) and heart (containing M2 receptors only) were incubated with either neuraminidase, parainfluenza virus (which contains neuraminidase), or virus plus 2,3-dehydro-2-deoxy-N-acetylneuraminic acid, a neuraminidase inhibitor. None of these treatments affected [3H]quinuclidinyl benzilate [( 3H]QNB) binding. In the lung and heart, carbachol displaced 0.2 nM [3H]QNB from two sites. After treatment with either neuraminidase or virus the high affinity site was shifted to the right, and carbachol displaced QNB from one site with low affinity in the lung. In contrast, neuraminidase or virus decreased the affinity of carbachol for both sites in the heart. The neuraminidase inhibitor completely blocked virus-induced changes in carbachol affinity in both tissues. These results suggest that parainfluenza virus decreases the affinity of agonists for some of the muscarinic receptors in the lung, and for all of the muscarinic receptors in the heart due to its neuraminidase activity, which results in removal of sialic acid. The decreased agonist affinity in the lung may be responsible for the increased vagally induced bronchoconstriction seen in viral respiratory infections.     

Assessment of a model for the opposing effects of N-ethylmaleimide on the affinity of muscarinic agonists for M2 receptors.

1. Homogenates of guinea pig right atrium (M2 receptors) were treated with N-ethylmaleimide, after which the ability of carbachol to inhibit binding of [3H]quinuclidinyl benzilate was studied. 2. At 37 degrees C, 10(-4) M and 10(-3) M, but not 10(-5) M, N-ethylmaleimide increased the affinity of carbachol for the receptor. At 2 degrees C, 10(-5) M and 10(-4) M, but not 10(-3) M, N-ethylmaleimide decreased carbachol affinity. At 2 degrees C, after the homogenate had been incubated at 37 degrees C without N-ethylmaleimide, 10(-5) M N-ethylmaleimide decreased carbachol affinity, as at 2 degrees C without preincubation, but 10(-3) M N-ethylmaleimide increased carbachol affinity, as at 37 degrees C. 10(-4) M N-ethylmaleimide was without effect. 3. The results are discussed with respect to a previously proposed model in which N-ethylmaleimide interacts with two sites, causing an increase or decrease in agonist affinity respectively.     

L-689,660, a novel cholinomimetic with functional selectivity for M1 and M3 muscarinic receptors.

1. L-689,660, 1-azabicyclo[2.2.2]octane, 3-(6-chloropyrazinyl)maleate, a novel cholinomimetic, demonstrated high affinity binding (pKD (apparent) 7.42) at rat cerebral cortex muscarinic receptors. L-689,660 had a low ratio (34) of pKD (apparent) values for the displacement of binding of the antagonist ([3H]-N-methylscopolamine ([3H]-NMS) compared with the displacement of the agonist [3H]-oxotremorine-M ([3H]-Oxo-M), in rat cerebral cortex. Low NMS/Oxo-M ratios have been shown previously to be a characteristic of compounds that are low efficacy partial agonists with respect to stimulation of phosphatidyl inositol turnover in the cerebral cortex. 2. L-689,660 showed no muscarinic receptor subtype selectivity in radioligand binding assays but showed functional selectivity in pharmacological assays. At M1 muscarinic receptors in the rat superior cervical ganglion, L-689,660 was a potent (pEC50 7.3 +/- 0.2) full agonist in comparison with (+/-)-muscarine. At M3 receptors in the guinea-pig ileum myenteric plexus-longitudinal muscle or in trachea, L-689,660 was again a potent agonist (pEC50 7.5 +/- 0.2 and 7.7 +/- 0.3 respectively) but had a lower maximum response than carbachol. In contrast L-689,660 was an antagonist at M2 receptors in guinea-pig atria (pA2 7.2 (95% confidence limits 7, 7.4)) and at muscarinic autoreceptors in rat hippocampal slices. 3. The putative M1-selective muscarinic agonist, AF102B (cis-2-methylspiro-(1,3-oxathiolane 5,3')-quinuclidine hydrochloride) was found to have a profile similar to L-689,660 but had up to 100 times less affinity in binding and functional assays.(ABSTRACT TRUNCATED AT 250 WORDS)     

Synthesis and biological characterization of 1-methyl-1,2,5,6-tetrahydropyridyl-1,2,5-thiadiazole derivatives as muscarinic agonists for the treatment of neurological disorders

Muscarinic agonists might be useful in the treatment of neurological disorders, including Alzheimer's disease, schizophrenia, chronic pain, and drug abuse. Previous studies identified a series of bis-1,2,5-thiadiazole derivatives of 1,2,5,6-tetrahydropyridine with high activity and selectivity for muscarinic receptors. To develop compounds with improved central nervous system penetration, several new derivatives were synthesized and characterized for muscarinic receptor binding and activity. One ligand (11) exhibited agonist activity at M(1), M(2), and M(4) receptors, a selectivity profile suggesting potential utility in the treatment of schizophrenia.     

Selectivity of oxomemazine for the M1 muscarinic receptors

The binding characteristics of pirenzepine and oxomemazine to muscarinic receptor were studied to evaluate the selectivity of oxomemazine for the muscarinic receptor subtypes in rat cerebral microsomes. Equilibrium dissociation constant (KD) of (-)-[3H]quinuclidinyl benzilate([3H]QNB) determined from saturation isotherms was 64 pM. Analysis of the pirenzepine inhibition curve of [3H]QNB binding to cerebral microsome indicated the presence of two receptor subtypes with high (Ki = 16 nM, M1 receptor) and low (Ki = 400 nM, M3 receptor) affinity for pirenzepine. Oxomemazine also identified two receptor subtypes with about 20-fold difference in the affinity for high (Ki = 84 nM, OH receptor) and low (Ki = 1.65 microM, OL receptor) affinity sites. The percentage populations of M1 and M3 receptors to the total receptors were 61:39, and those of OH and OL receptors 39:61, respectively. Both pirenzepine and oxomemazine increased the KD value for [3H]QNB without affecting the binding site concentrations and Hill coefficient for the [3H]QNB binding. Oxomemazine had a 10-fold higher affinity at M1 receptors than at M3 receptors, and pirenzepine a 8-fold higher affinity at OH receptors than at OL receptors. Analysis of the shallow competition binding curves of oxomemazine for M1 receptors and pirenzepine for OL receptors yielded that 69% of M1 receptors were of OH receptors and the remaining 31% of OL receptors, and that 29% of OL receptors were of M1 receptors and 71% of M3 receptors. However, M3 for oxomemazine and OH for pirenzepine were composed of a uniform population. These results suggest that oxomemazine could be classified as a selective drug for M1 receptors and also demonstrate that rat cerebral microsomes contain three different subtypes of M1, M3 and the other site which is different from M1, M2 and M3 receptors.     

Estimation of relative microscopic affinity constants of agonists for the active state of the receptor in functional studies on M2 and M3 muscarinic receptors

In prior work, we have shown that it is possible to estimate the product of observed affinity and intrinsic efficacy of an agonist expressed relative to that of a standard agonist simply through the analysis of their respective concentration-response curves. In this report, we show analytically and through mathematical modeling that this product, termed intrinsic relative activity (RA(i)), is equivalent to the ratio of microscopic affinity constants of the agonists for the active state of the receptor. We also compared the RA(i) estimates of selected muscarinic agonists with a relative estimate of the product of observed affinity and intrinsic efficacy determined independently through the method of partial receptor inactivation. There was good agreement between these two estimates when agonist-mediated inhibition of forskolin-stimulated cAMP accumulation was measured in Chinese hamster ovary cells stably expressing the human M(2) muscarinic receptor. Likewise, there was good agreement between the two estimates when agonist activity was measured on the ileum from M(2) muscarinic receptor knockout mice, a convenient assay for M(3) receptor activity. The RA(i) estimates of agonists in the mouse ileum were similar to those estimated at the human M(3) receptor with the exception of 4-(m-chlorophenyl-carbamoyloxy)-2-butynyltrimethylammonium (McN-A-343), which is known to be an M(1)- and M(4)-selective muscarinic agonist. Additional experiments showed that the response to McN-A-343 in the mouse ileum included a non-M(3) muscarinic receptor component. Our results show that the RA(i) estimate is a useful receptor-dependent measure of agonist activity and ligand-directed signaling.     

Cholinergic agonists and the treatment of Alzheimer's disease

Over the past decade, considerable effort was focused on the development of muscarinic and nicotinic agonists for the treatment of Alzheimer's disease. The rationale for developing muscarinic agonists was based on the role of acetylcholine in learning and memory function and the consistent neurochemical finding that cholinergic neurons degenerated in Alzheimer's patients. Thus far, the clinical utility of muscarinic agonists remains unproven, yet recent studies suggest that muscarinic agonists might be useful in treating not only memory deficits, but also psychiatric disturbances and some of the underlying causes of Alzheimer's disease, such as the deposition of Abeta. In addition, nicotinic receptors may play a role in cognitive function and help regulate the toxicity of amyloid precursor protein. Ultimately, cholinergic agonists may prove useful in the treatment of Alzheimer's disease.     

Muscarinic agonists for the treatment of Alzheimer's disease: progress and perspectives

Much interest has focused on the development of selective muscarinic agonists for the treatment of Alzheimer's disease (AD). Cholinergic replacement therapy is thought to be beneficial in alleviating some of the cognitive dysfunctions in this disorder. The cholinergic neuronal tracts are involved in memory and learning processes, and the extent of the degeneration of the cortical projections correlates with the severity of the dementia. An M1 selective muscarinic agonist may be effective in treating at least some of the cognitive symptoms in AD. Highly selective M1 agonists, producing cellular excitation, should be beneficial in AD, regardless of the extent of degeneration of presynaptic cholinergic projections to the frontal cortex or hippocampus. Functional abnormalities in AD may also occur along various signal transduction pathways mediated, in part, at least, by muscarinic receptors. In general, activities associated with mAChR subtypes and m1 receptors, in particular, indicate that M1 agonists may also be useful for this aspect of AD. Mismetabolism of amyloid precursor proteins (APPs) may induce AD. Recent studies indicate that the formation of the b-amyloid peptide (Abeta) and amyloid plaques is linked to the loss of cholinergic function in AD. New data on the activation of m1 mAChRs in conjunction with recent findings that the induction of such receptors stimulates neurotrophic-like activities, decreases tau phosphorylation and inhibits apoptosis indicate that restoring the cholinergic tone in AD may be useful both in improving memory function and in altering the onset and progression of AD dementia. This article focuses on the recent, promising developments in this field and assesses the value of muscarinic agonists currently under development for the treatment of AD.     

Development of CDD‐0102 as a selective M1 agonist for the treatment of Alzheimer's disease

Selective muscarinic agonists might be useful in the treatment of Alzheimer's disease. To help characterize the activity and functional selectivity of two M₁ muscarinic agonists, secretion of amyloid precursor protein, brain penetration, side effect profiles, cognition‐enhancing properties, oral bioavailability, and acute toxicity were evaluated. CDD‐0102 stimulated the secretion of APP from CHO‐K1 cells expressing M₁ receptors and penetrated into the brain following i.p. administration in rodents. CDD‐0102 produced relatively few cholinergic side effects (e.g., diarrhea, salivation) following i.p. administration in mice. The effects of muscarinic agonists on memory function were examined following bilateral injections of 192 IgG‐saporin into the diagonal band of rats to lesion basal forebrain cholinergic pathways. 192 IgG‐saporin produced decreases in cortical and hippocampal choline acetyltransferase activity and impaired performance of a paired‐run, delayed‐alternation task in a T‐maze relative to vehicle‐injected controls. Toxin‐treated rats performed significantly better following i.p. injections (1 mg/kg) of either xanomeline or CDD‐0102 as compared with saline. Prominent cholinergic side effects (e.g., diarrhea) were apparent only following xanomeline treatments. In separate studies, oral administration of CDD‐0102 (10 mg/kg) reversed the memory deficits induced by 192 IgG‐saporin in the T‐maze task. Rats achieved 54 ± 4.2% correct choices with saline, but 94 ± 1.2% following CDD‐0102 injection. In acute toxicity studies in mice, the LD₅₀ of CDD‐0102 was greater than 1,000 mg/kg orally; 190 mg/kg i.p. The LD₅₀ of xanomeline was 100 mg/kg p.o. and 75 mg/kg i.p. In summary, both xanomeline and CDD‐0102 displayed beneficial effects on memory function, while CDD‐0102 also exhibited a low side effect profile and low toxicity. CDD‐0102 warrants further evaluation as a therapeutic agent for the treatment of Alzheimer's disease. Drug Dev. Res. 57:200–213, 2002. © 2003 Wiley‐Liss, Inc.     

Clinical immunologic approaches for the treatment of Alzheimer's disease

Recent clinical trials of active vaccination against beta-amyloid (Abeta) have succeeded in clearing Abeta plaques; however, further understanding of immunization with regards to inflammation and other hallmarks of Alzheimer's disease pathology is required. Antibodies generated with this first-generation vaccine may not have had the desired therapeutic properties or targeted the 'correct' mechanism, but they have opened the way for new clinical approaches, which are now under consideration. Passive administration of monoclonal antibodies directed to various regions of Abeta peptide and/or administration of immunoconjugates of only small fragments of the N-terminal region may lead to the development of an improved second generation of Abeta vaccines. Amyloid immunotherapy offers genuine opportunities for disease treatment; however, such an approach towards treating and preventing Alzheimer's disease patients requires careful antigen and antibody selection to maximize efficacy and minimize adverse events.