Title: Research and development of donepezil hydrochloride, a new type of acetylcholinesterase inhibitor Sugimoto H, Ogura H, Arai Y, Limura Y, Yamanishi Y Ref: Japanese Journal of Pharmacology, 89:7, 2002 : PubMed
A wide range of evidence shows that cholinesterase (ChE) inhibitors can interfere with the progression of Alzheimer's disease (AD). The earliest known ChE inhibitors, namely, physostigmine and tacrine, showed modest improvement in the cognitive function of AD patients. However, clinical studies show that physostigmine has poor oral activity, brain penetration and pharmacokinetic parameters, while tacrine has hepatotoxic liability. Studies were then focused on finding a new type of acetylcholinesterase (AChE) inhibitor that would overcome the disadvantages of these two compounds. During the study, by chance we found a seed compound. We then conducted a structure-activity relationship study of this compound. After four years of exploratory research, we found donepezil hydrochloride (donepezil). Donepezil showed several positive characteristics including the following: 1) It has a novel structure compared to other conventional ChE inhibitors; 2) It shows strong anti-AChE activity and has long lasting efficacy; 3) The inhibitory characteristic of donepezil shows that it is highly selective for AChE as compared to butyrylcholinesterase (BuChE) and showed reversibility; 4) The results of clinical studies on donepezil show a very high significant difference on ADAS cog and CIBIC plus scores of AD patients. Donepezil is currently marketed in 56 countries all over the world.
Title: Central and peripheral activity of cholinesterase inhibitors as revealed by yawning and fasciculation in rats Ogura H, Kosasa T, Kuriya Y, Yamanishi Y Ref: European Journal of Pharmacology, 415:157, 2001 : PubMed
This study was designed to investigate the central and peripheral activity profile of cholinesterase inhibitors in rats. Intravenous injection of cholinesterase inhibitors caused fasciculation, a fine involuntary muscular movement. This peripheral cholinergic sign was tightly correlated with in vitro anti-acetylcholinesterase activity by cholinesterase inhibitors, suggesting that fasciculation is a valid index of peripheral cholinergic activation. Yawning, used as a marker of central cholinergic activation, was also monitored. E2030 (3-(2-(1-(1,3-dioxolan-2-ylmethyl)-4-piperidyl)ethyl)-2H-3,4-dihydro-1,3-benzoxazin-2,4-dione hydrochloride) elicited yawning at more than 4 mg/kg, while fasciculation was significantly intensified only at a dose of 16 mg/kg. Donepezil and tacrine induced both yawning and fasciculation at doses greater than 4 mg/kg, whereas physostigmine induced both behaviors at a dose of 8 mg/kg and above. Finally, ipidacrine elicited yawning at a dose of 16 mg/kg and fasciculation at doses greater than 8 mg/kg. Thus, all putative centrally acting cholinesterase inhibitors elicited yawning. TAK-147 (3-[1-(phenylmethyl)-4-piperidinyl]-1-(2,3,4,5-tetrahydro-1H-benzazepin-8-yl)-1-propanone fumarate) did not significantly elicit yawning at doses under 16 mg/kg, but elicited fasciculation at a dose of more than 4 mg/kg. Distigmine, a peripherally acting cholinesterase inhibitor, evoked fasciculations, but not yawning. When mild to moderate fasciculation was evoked, donepezil and E2030 elicited more than nine yawns over 30 min, while the other cholinesterase inhibitors elicited approximately five yawns at most during this period. These results indicated that E2030 and donepezil exhibited the most marked preferential central cholinergic activity, relative to peripheral activity, among cholinesterase inhibitors tested. Scopolamine, a centrally acting antimuscarinic drug, completely inhibited E2030-induced yawning, while peripherally acting methylscopolamine did not. Haloperidol, a dopamine receptor antagonist, partially blocked E2030-induced yawning, but did not block donepezil-induced yawning. These results suggest that central cholinergic and, in part, dopaminergic mechanisms are involved in E2030-induced yawning.
Title: Inhibitory effect of orally administered donepezil hydrochloride (E2020), a novel treatment for Alzheimer's disease, on cholinesterase activity in rats Kosasa T, Kuriya Y, Matsui K, Yamanishi Y Ref: European Journal of Pharmacology, 389:173, 2000 : PubMed
Donepezil hydrochloride ((+/-)-2-[(1-benzylpiperidin-4-yl)methyl]-5, 6-dimethoxy-indan-1-one monohydrochloride: E2020: donepezil) is a potent and selective acetylcholinesterase inhibitor developed for the treatment of Alzheimer's disease. The present experiments were designed to compare the inhibitory effects of orally administered donepezil and other cholinesterase inhibitors, tacrine (9-amino-1,2, 3,4-tetrahydroacridine hydrochloride), (S)-N-ethyl-3-[(1-dimethyl-amino)ethyl]-N-methyl-phenylcarbamate hydrogentartrate (ENA-713, rivastigmine) and 3-[1-(phenylmethyl)-4-piperidinyl]-1-(2,3,4, 5-tetrahydro-1H-1-benzazepin-8-yl)-1-propanone fumarate (TAK-147), on the cholinesterase activity in the brain and plasma of rats. Moreover, in order to validate the cholinesterase inhibition data, we measured the brain and plasma concentrations of these drugs. Oral administration of donepezil, tacrine, ENA-713 or TAK-147, caused a dose-dependent inhibition of brain and plasma cholinesterase activities. The ID(50) values of these compounds for brain cholinesterase activity were 6.3, 40.5, 7.2 and 26.8 micromol/kg, respectively. On the other hand, the ID(50)170, 9.7 and 51.2 micromol/kg, respectively. Thus, the ratios of the ID(50)4.2, 1.3 and 1.9, respectively. Brain and plasma concentrations of donepezil, tacrine and TAK-147 increased dose-dependently. The ratios of the concentrations (brain/plasma) of these compounds were 6.1-8.4 for donepezil, 14.5-54.6 for tacrine and 7.0-20.6 for TAK-147. The values of 50% inhibitory concentration of these drugs in the brain were 0.42, 3.5 and 1.1 nmol/g, respectively. In contrast, the brain and plasma concentrations of ENA-713 at all doses, except the two highest doses, were below the quantification limit. These results suggest that orally administered donepezil satisfactorily penetrates into the brain and inhibits cholinesterase there, and that donepezil is a potent and selective inhibitor of brain cholinesterase in comparison with plasma cholinesterase in vivo.
Title: Comparison of inhibitory activities of donepezil and other cholinesterase inhibitors on acetylcholinesterase and butyrylcholinesterase in vitro Ogura H, Kosasa T, Kuriya Y, Yamanishi Y Ref: Methods Find Exp Clin Pharmacol, 22:609, 2000 : PubMed
This study was designed to compare the in vitro inhibitory effects on acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) of donepezil and some other cholinesterase (ChE) inhibitors which have been developed for the treatment of Alzheimer's disease. The carbamate derivatives physostigmine and rivastigmine needed preincubation to exhibit appropriate anti-ChE activity. The maximum ChE inhibition by physostigmine developed within 30-60 min, while the inhibitory effect of rivastigmine on AChE and BuChE activities reached its peak after 48 and 6 h, respectively. The order of inhibitory potency (IC50) towards AChE activity under optimal assay conditions for each ChE inhibitor was: physostigmine (0.67 nM) > rivastigmine (4.3 nM) > donepezil (6.7 nM) > TAK-147 (12 nM) > tacrine (77 nM) > ipidacrine (270 nM). The benzylpiperidine derivatives donepezil and TAK-147 showed high selectivity for AChE over BuChE. The carbamate derivatives showed moderate selectivity, while the 4-aminopyridine derivatives tacrine and ipidacrine showed no selectivity. The inhibitory potency of these ChE inhibitors towards AChE activity may illustrate their potential in vivo activity.
Title: [Pharmacological properties of donepezil hydrochloride (Aricept), a drug for Alzheimer's disease] Ogura H, Kosasa T, Araki S, Yamanishi Y Ref: Nihon Yakurigaku Zasshi, 115:45, 2000 : PubMed
One of the most consistent changes associated with Alzheimer's disease (AD) is a deficit in central cholinergic neurotransmission. Donepezil hydrochloride (DPZ), a novel class of cholinesterase (ChE) inhibitors, inhibits degradation of acetylcholine (ACh) and activates central cholinergic system. In in vitro studies, DPZ more selectively inhibited acetylcholinesterase (IC50: 6.7 nM) than butyrylcholinesterase (IC50: 7400 nM), while tacrine inhibited both acetylcholinesterase (IC50: 77 nM) and butyrylcholinesterase (IC50: 69 nM). After oral dosing, DPZ (ID50: 2.6 mg/kg) inhibited brain ChE dose-dependently without any remarkable effect on ChE in the heart and small intestine, whereas tacrine (ID50: 9.5 mg/kg) inhibited ChE equally in the brain and peripheral tissues. Brain microdialysis revealed that DPZ (2.5 mg/kg) enhanced extracellular ACh concentrations in the cerebral cortex and hippocampus in rats. In behavioral studies, DPZ counteracted both the deficit in passive avoidance induced by lesioning of the nucleus basalis magnocellularis (0.125-1.0 mg/kg) and the impairment in acquisition of a hidden-platform water maze task after lesioning of the medial septum in rats (0.5 mg/kg). DPZ also inhibited the scopolamine-induced impairment of radial maze performance (0.5 mg/kg). Placebo-controlled clinical studies of 12- and 24-week treatments of DPZ (5 mg, 10 mg/day) clearly showed an improvement in cognitive scores of probable AD patients.
Title: Donepezil, a centrally acting acetylcholinesterase inhibitor, alleviates learning deficits in hypocholinergic models in rats Ogura H, Kosasa T, Kuriya Y, Yamanishi Y Ref: Methods Find Exp Clin Pharmacol, 22:89, 2000 : PubMed
Donepezil is a member of a new class of centrally acting cholinesterase inhibitors which preferentially inhibit acetylcholinesterase rather than butyrylcholinesterase. The effects of donepezil on learning impairments were investigated in some hypocholinergic models in rats. In nucleus basalis magnocellularis (NBM)-lesioned rats, donepezil alleviated deficits in passive avoidance response at a dose of 0.125 mg/kg and higher, while tacrine had only a tendency toward improved performance. Donepezil at 0.5 mg/kg effectively counteracted acquisition impairments in the water maze task induced by lesions of the medial septum; tacrine had no significant effects on impairments in this task. Scopolamine caused an increase of errors in the 8-arm radial maze. Donepezil significantly decreased scopolamine-induced errors in the radial maze at 0.5 mg/kg, whereas tacrine decreased errors at 2 mg/kg. These results suggest that donepezil can clearly minimize learning impairments induced by treatments that cause central cholinergic deficiencies in rats. These findings support the clinical efficacy of donepezil in Alzheimer's disease.
A wide range of evidence shows that acetylcholinesterase (AChE) inhibitors can interfere with the progression of Alzheimer's disease (AD). The successful development of these compounds was based on a well-accepted theory that the decline in cognitive and mental functions associated with AD is related to the loss of cortical cholinergic neurotransmission. The earliest known AChE inhibitors, namely, physostigmine and tacrine, showed modest improvement in the cognitive function of Alzheimer's patients. However, clinical studies show that physostigmine has poor oral activity, brain penetration and pharmacokinetic parameters while tacrine has hepatotoxic liability. Studies were then focused on finding a new type of acetylcholinesterase inhibitor that would overcome the disadvantages of these two compounds. Donepezil hydrochloride inaugurates a new class of AChE inhibitors with longer and more selective action with manageable adverse effects. Currently, there are about 19 new Alzheimer's drugs in various phases of clinical development.
Title: Effect of donepezil hydrochloride (E2020) on basal concentration of extracellular acetylcholine in the hippocampus of rats Kosasa T, Kuriya Y, Matsui K, Yamanishi Y Ref: European Journal of Pharmacology, 380:101, 1999 : PubMed
The effects of oral administration of the centrally acting acetylcholinesterase (AChE) inhibitors, donepezil hydrochloride (donepezil: E2020: (+/-)-2-[(1-benzylpiperidin-4-yl)methyl]-5,6-dimethoxy-indan-1-one monohydrochloride), tacrine (9-amino-1,2,3,4-tetrahydroacridine hydrochloride) and ENA-713 (rivastigmine: (S)-N-ethyl-3-[(1-dimethyl-amino)ethyl]-N-methyl-phenylcarbamate hydrogentartrate), which have been developed for the treatment of Alzheimer's disease, on the extracellular acetylcholine concentration in the hippocampus of rats were evaluated by using a microdialysis technique without adding cholinesterase inhibitor to the perfusion solution. We also compared the inhibition of brain AChE and the brain concentrations of these drugs. Donepezil at 2.5 mg/kg and tacrine at 5 mg/kg showed significant effects for more than 6 h. At these doses, the maximum increases were observed at about 1.5 h after administration of donepezil, and at about 2 h with tacrine, and were 499% and 422% of the pre-level, respectively. ENA-713 produced significant effects at doses of 0.625, 1.25 and 2.5 mg/kg, which lasted for about 1, 2 and 4 h, respectively. The maximum increases produced by these doses at about 0.5 h after administration were 190, 346 and 458% of the pre-level, respectively. The time courses of brain AChE inhibition with donepezil at 2.5 mg/kg, tacrine at 10 mg/kg and ENA-713 at 2.5 mg/kg were mirror images of the extracellular acetylcholine-increasing action at the same doses. The time courses of the brain concentrations of drugs after oral administration of donepezil at 2.5 mg/kg and tacrine at 10 mg/kg were consistent with those of brain AChE inhibition at the same doses, and there was a linear relation between these parameters. Brain concentration of ENA-713 at 2.5 mg/kg was below the limit of quantification at all time points measured. These results suggest that oral administration of donepezil, tacrine and ENA-713 increases acetylcholine concentration in the synaptic cleft of the hippocampus mostly through AChE inhibition, and that donepezil has a more potent activity than tacrine and a longer-lasting effect than ENA-713 on the central cholinergic system.
Title: Inhibitory effects of donepezil hydrochloride (E2020) on cholinesterase activity in brain and peripheral tissues of young and aged rats Kosasa T, Kuriya Y, Matsui K, Yamanishi Y Ref: European Journal of Pharmacology, 386:7, 1999 : PubMed
Donepezil hydrochloride (donepezil: E2020: (+/-)-2-[(1-benzylpiperidin-4-yl)methyl]-5,6-dimethoxy-indan-1-one monohydrochloride)) is a centrally acting acetylcholinesterase inhibitor developed for the treatment of Alzheimer's disease. In the present study, its inhibitory effect on the activity of cholinesterase ex vivo was evaluated in the brain, plasma, erythrocytes, heart, small intestine, liver and pectoral muscle of young adult as well as aged rats, in comparison with that of tacrine (9-amino-1,2,3,4-tetrahydroacridine hydrochloride). In aged animals, cholinesterase activity in heart, small intestine and pectoral muscle was lower, whereas that in plasma and liver was higher than in young rats. Both groups showed the highest levels in the brain. Donepezil, at doses of 1.25, 2.5 and 5 mg/kg, p.o., inhibited brain, plasma, erythrocyte, liver and pectoral muscle cholinesterase activity in young rats in a dose-dependent manner but had less effect on cholinesterase activity in heart and small intestine. In aged animals, inhibition of cholinesterase activity in the brain, erythrocytes and pectoral muscle by donepezil was more potent than that in young animals. Tacrine, at doses of 5, 10 and 20 mg/kg, p.o., dose-dependently inhibited cholinesterase activity in all tissues of both young and aged animals, but most potently in heart, small intestine and liver. The inhibition of cholinesterase activity by tacrine in the brain, plasma, erythrocytes, heart and liver was more potent in aged rats than in tissues of young rats. Brain and plasma concentrations of unchanged donepezil and tacrine were measured in the same animals as used for the cholinesterase inhibition study. Brain and plasma concentrations of donepezil and tacrine were higher in aged than in young animals. It is concluded that the inhibitory effects of donepezil and tacrine on cholinesterase activity are greater in aged than in young rats, owing to differences in the tissue concentrations of these compounds between young and aged animals. It is also suggested that the effect of donepezil on cholinesterase activity is more tissue-selective than that of tacrine.
Title: Effect of donepezil hydrochloride (E2020) on extracellular acetylcholine concentration in the cerebral cortex of rats Kosasa T, Kuriya Y, Yamanishi Y Ref: Japanese Journal of Pharmacology, 81:216, 1999 : PubMed
Donepezil hydrochloride (donepezil), a potent and selective acetylcholinesterase inhibitor, has been developed for the treatment of Alzheimer's disease. We studied the effect of oral administration of this drug on the extracellular acetylcholine (ACh) concentration in the cerebral cortex of rats using microdialysis. We also observed fasciculation, a peripheral cholinergic sign induced by activation of neuromuscular transmission, after oral administration of the drug as an index of peripheral cholinergic activation. Other cholinesterase inhibitors, tacrine, ENA-713 and TAK-147, were used as reference drugs. Donepezil significantly and dose-dependently increased the extracellular ACh concentration in the rat cerebral cortex within the dose range of 2.5-10 mg/kg. Tacrine, ENA-713 and TAK-147 also elevated the extracellular concentration of ACh. The minimum effective doses of donepezil, tacrine, ENA-713 and TAK-147 were (< or = 2.5, 10, 10 and < or = 10 mg/kg, respectively. Donepezil produced fasciculation at doses of 2.5 mg/kg and above, with a dose-dependent increase in incidence and intensity. The reference compounds also induced fasciculation in a dose-dependent manner. The threshold doses of tacrine, ENA-713 and TAK-147 for fasciculation were 5, 2.5 and 2.5 mg/kg, respectively. The values of the ratio of the minimum effective dose for the ACh-increasing action to that for the fasciculation-producing action were: donepezil, < or = 1; tacrine, 2; ENA-713, 4; TAK-147, < or = 4. These results indicate that orally administered donepezil has a potent and selective activity on the central cholinergic system.
The most consistent change of neurotransmitter in the brain of Alzheimer's patients is the dramatic decrease of cholinergic innervation due to the loss of neurons in the basal forebrain. The most widely studied acetylcholinesterase inhibitors (AChEIs) have been physostigmine and tacrine. Physostigmine has very short duration, and tacrine has liability to hepatotoxicity. These are the defects of the inhibitors. Our objective was to find a new type of AChEIs that would overcome the disadvantages of physostigmine and tacrine. Through a random screening, we incidentally found an N-benzylpiperazine derivative which showed positive cholinergic behavior in rats. We replaced the N-benzylpiperazine moiety with N-benzylpiperidine moiety and found a dramatic increase in anti-AChE activity. Even after the replacement of an amide group with a ketone group the activity was held. Furthermore, the cyclic-amide derivative showed enhanced inhibitory activity. On the basis of these results, an indanone derivative was designed. Among these indanone derivatives, donepazil hydrochloride (E2020), brand name ARICEPT was found to be the most balanced compound. The clinical studies of donepezil hydrochloride demonstrated statistically significant effects on ADAS-cog (Alzheimer's Disease Assessment Scale cognitive sub.) and CIBIC Plus (Clinician's Interview-Based Impression of Change plus).
Title: Synthesis and structure-activity relationships of acetylcholinesterase inhibitors: 1-benzyl-4-[(5,6-dimethoxy-1-oxoindan-2- yl)methyl]piperidine hydrochloride and related compounds Sugimoto H, Iimura Y, Yamanishi Y, Yamatsu K Ref: Journal of Medicinal Chemistry, 38:4821, 1995 : PubMed
Following the discovery of a new series of anti-acetylcholinesterase (anti-AChE) inhibitors such as 1-benzyl-4-[2-(N-benzoylamino)ethyl]piperidine (1), we reported that its rigid analogue, 1-benzyl-4-(2-isoindolin-2-ylethyl)piperidine (5), had more potent activity. We have extended the structure-activity relationship (SAR) study for the rigid analogue and found that the 2-isoindoline moiety in compound 5 can be replaced with a indanone moiety (8) without a major loss in potency. Among the indanone derivatives, 1-benzyl-4-[(5,6-dimethoxy-1-oxoindan-2-yl)methyl]piperidine (13e) (E2020) (IC50 = 5.7 nM) was found to be one of the most potent anti-AChE inhibitors. Compound 13e showed a selective affinity 1250 times greater for AChE than for butyrylcholinesterase. In vivo studies demonstrated that 13e has a longer duration of action than physostigmine at a dose of 5 mg/kg (po) and produced a marked and significant increase in acetylcholine content in rat cerebral cortex. We report the synthesis, SAR, and a proposed hypothetical binding site of 13e (E2020).
Following the discovery of a new series of 1-benzyl-4-[2-(N-benzoyl-N-methylamino)ethyl]piperidine (2) derivatives with a potent anti-acetylcholinesterase (anti-AChE) activity, we extended the structure-activity relationships (SAR) to rigid analogues (4) and 1-benzyl-4-[2-(N-benzoyl-N-phenylamino)ethyl]piperidine derivatives (3). Introduction of a phenyl group on the nitrogen atom of the amide moieties resulted in enhanced activity. The rigid analogue containing isoindolone (9) was found to exhibit potent anti-AChE activity comparable to that of 2. Furthermore, replacement of the isoindolone with other heterobicyclic ring systems was examined. Among the compounds prepared in these series, 1-benzyl-4-[2-[4-(benzoylamino)phthalimido]ethyl]piperidine hydrochloride (19) (IC50 = 1.2 nM) is one of the most potent inhibitors of AChE. Compound 19 showed a definite selectivity to AChE over the BCHE (about 34700-fold) and, at dosages of 10-50 mg/kg, exerted a dose-dependent inhibitory effect on AChE in rat brain.
A series of 1-benzyl-4-[2-(N-benzoylamino)ethyl]piperidine derivatives was synthesized and evaluated for anti-acetylcholinesterase (anti-AChE) activity. Substituting the benzamide with a bulky moiety in the para position led to a substantial increase in activity. Introduction of an akyl or phenyl group at the nitrogen atom of benzamide dramatically enhanced the activity. The basic quality of the nitrogen atom of piperidine appears to play an important role in the increased activity, since the N-benzoylpiperidine derivative was almost inactive. We found that 1-benzyl-4-[2-(N-[4'-(benzylsulfonyl) benzoyl]-N-methylamino]ethyl]piperidine hydrochloride (21) (IC50 = 0.56 nM) is one of the most potent inhibitors of acetylcholinesterase. Compound 21 showed an affinity 18,000 times greater for AChE than for BuChE. At a dose of 3 mg/kg, 21 produced a marked and significant increase in acetylcholine (ACh) content in the cerebral vortex and hippocampus of rats. Compound 21 was chosen for advanced development as an antidementia agent.
