Yuan Ping Pang

Evaluation of short-tether bis-THA AChE inhibitors. A further test of the dual binding site hypothesis.

To provide a further test of the dual binding site hypothesis proposed for acetylcholinesterase (AChE) inhibitor heptylene-linked bis-(9-amino-1,2,3,4-tetrahydroacridine) A7A, short-tether (ethylene hexylene) homologs A2A-A6A were prepared. En route to these compounds, convenient and scaleable syntheses of useful pharmaceutical intermediate 9-chloro-1.2,3,4-tetrahydroacridine 3 and A7A were developed. AChE and butyrylcholinesterase (BChE) inhibition assays of A2A-A10A confirm that a seven methylene tether (A7A) optimizes AChE inhibition potency and AChE/BChE selectivity. Finally, these studies indicate that simultaneous binding of alkylene-linked 9-amino-1,2,3,4-tetrahydroacridine dimers to the catalytic and peripheral sites of AChE is possible with a tether length as short as 5 methylenes.

Bis(7)-tacrine attenuates β amyloid-induced neuronal apoptosis by regulating L-type calcium channels

β Amyloid protein (Aβ) and acetylcholinesterase (AChE) have been shown to be closely implicated in the pathogenesis of Alzheimers disease. In the current study, we investigated the effects of bis(7)‐tacrine, a novel dimeric AChE inhibitor, on Aβ‐induced neurotoxicity in primary cortical neurons. Bis(7)‐tacrine, but not other AChE inhibitors, elicited a marked reduction of both fibrillar and soluble oligomeric forms of Aβ‐induced apoptosis as evidenced by chromatin condensation and DNA specific fragmentation. Both nicotinic and muscarinic receptor antagonists failed to block the effects of bis(7)‐tacrine. Instead, nimodipine, a blocker of L‐type voltage‐dependent Ca2+ channels (VDCCs), attenuated Aβ neurotoxicity, whereas N‐, P/Q‐ or R‐type VDCCs blockers and ionotropic glutamate receptor antagonists did not. Fluorescence Ca2+ imaging assay revealed that, similar to nimodipine, bis(7)‐tacrine reversed Aβ‐triggered intracellular Ca2+ increase, which was mainly contributed by the extracellular Ca2+ instead of endoplasmic reticulum and mitochondria Ca2+. Concurrently, using whole cell patch‐clamping technique, it was found that bis(7)‐tacrine significantly reduced the augmentation of high voltage‐activated inward calcium currents induced by Aβ. These results suggest that bis(7)‐tacrine attenuates Aβ‐induced neuronal apoptosis by regulating L‐type VDCCs, offers a novel modality as to how the agent exerts neuroprotective effects.

In vitro binding and CNS effects of novel neurotensin agonists that cross the blood-brain barrier

Animal studies with neurotensin (NT) directly injected into brain suggest that it has pharmacological properties similar to those of antipsychotic drugs. Here, we present radioligand binding data for some novel hexapeptide analogs of NT(8-13) at the molecularly cloned rat and human neurotensin receptors (NTR-1), along with behavioral and physiological effects of several of these peptides after intraperitoneal (i.p.) administration in rats. One unique analog, NT66L, which had high affinity (0.85 nM) for the molecularly cloned rat neurotensin receptor (NTR-1), caused a drop in body temperature and antinociception at doses as low as 0.1 mg/kg after i.p. injection. At 30 min post-injection, the ED50 for NT66L-induced hypothermia (rectal temperature) and antinociception (hot plate test) was 0.5 and 0.07 mg/kg, respectively. At a dose of 1 mg/kg i.p., NT66L caused 100% of the maximum possible effect for antinociception for up to 2 h after administration. At this dose body temperature lowering was greater than -2.5 degrees C from 20 to 120 min after i.p. administration. These results in animals suggest that NT66L has agonist properties at NTR-1 in vivo after extracranial administration and provide support for its further study in behavioral tests predictive of neuroleptic activity.

Bis(7)-tacrine, a promising anti-Alzheimer's agent, reduces hydrogen peroxide-induced injury in rat pheochromocytoma cells: comparison with tacrine.

The present study investigates the effects of bis(7)-tacrine, a novel dimeric acetylcholinesterase inhibitor, on hydrogen peroxide(H(2)O(2))-induced cell injury with comparison to the corresponding monomer, tacrine. Exposure of rat pheochromocytoma line PC12 cells to H(2)O(2) induced significant cell damage. This reagent also caused redox desequilibrium as indicated by a decrease in activities of intracellular antioxidant enzymes such as glutathione peroxidase as well as catalase and an accumulation of malondialdehyde, a product of lipid peroxidation. Pretreatment of cells with bis(7)-tacrine or tacrine attenuated H(2)O(2)-induced cell toxicity, and bis(7)-tacrine demonstrated higher potency than tacrine in improving redox desequilibrium. These results suggest that bis(7)-tacrine and tacrine significantly protect against H(2)O(2) insult, which might be beneficial for their potential usage in the prevention and treatment of Alzheimers disease.

Effects of bis(7)-tacrine, a novel anti-Alzheimer's agent, on rat brain AChE

The anticholinesterase effects of bis(7)-tacrine were compared with tacrine in vitro and in vivo. Based on IC50 ratios, the dimeric analog bis(7)-tacrine was, in a reversible manner, up to 150-fold more potent and 250-fold more selective than tacrine for acetylcholinesterase (AChE) over butyrylcholinesterase (BChE). Following a single oral administration, both bis(7)-tacrine and tacrine produced dose-dependent inhibitions of AChE in rat brain, but bis(7)-tacrine exhibited higher efficacy and AChE/BChE selectivity than tacrine. The anti-AChE efficacy of bis(7)-tacrine was quite similar following an oral or i.p. administration, but tacrine showed much lower efficacy when administered orally than when given i.p. These findings suggest bis(7)-tacrine, a highly potent and selective inhibitor of AChE, can probably be used as an improved drug in the palliative treatment of AD.

Potent, easily synthesized huperzine A-tacrine hybrid acetylcholinesterase inhibitors

Hybrid acetylcholinesterase inhibitors composed of a key fragment of huperzine A and an intact tacrine unit were prepared. The syntheses are quite direct, proceeding in a maximum of 4 linear steps from commercially available starting materials. The optimum hybrid inhibitor (+/-)-9g is 13-fold more potent than (-)-huperzine A, and 25-fold more potent than tacrine.

Novel Anti-Alzheimer's Dimer Bis(7)-Cognitin : cellular and molecular mechanisms of neuroprotection through multiple targets

SummaryAlzheimer’s disease (AD) is a progressive and degenerative brain disorder that has emerged as one of the major public health problems in adults. Unfortunately, its molecular pathology and therapeutic strategies remain elusive. Because there are multiple factors closely indicated in the pathogenesis of AD, multiple drug therapy will be required to address the varied pathological aspects of this disease. Existing pharmacological approaches with one-molecule-one-target are limited in their ability to modify the pathology of AD. Novel therapeutics strategies comprise multifunctional compounds specifically designed to target concurrently on different sites at multifactorial etiopathogenesis of AD, thereby providing greater therapeutic efficacy. Over the past decade, our group has developed several series of dimeric acetylcholinesterase (AChE) inhibitors derived from tacrine and huperzine A, a unique anti-Alzheimer’s drug originally discovered from a traditional Chinese medicinal plant. Bis(7)-Cognitin, one of our novel dimers, through inhibition of AChE, N-methyl-D-aspartate receptor, nitric oxide synthase, and amyloid precursor protein/β-amyloid cascade concurrently, possesses remarkable neuroprotective activities. More importantly, the synergism between these targets might serve as one of the most effective therapeutic strategies to arrest/modify pathological process of AD in addition to improving the cognitive functions for AD.

Bis(7)-tacrine, a novel acetylcholinesterase inhibitor, reverses AF64A-induced deficits in navigational memory in rats

The novel dimer bis(7)-tacrine (1,7-N-Heptylene-bis-9,9-amino-1,2,3, 4-tetrahydroacridine), which exhibits higher potency, selectivity and oral activity on acetylcholinesterase inhibition in vivo than tacrine, was evaluated for its ability to reverse AF64A-induced spatial memory impairment in rats using the Morris water maze. The intracerebroventricular injection of AF64A (3 nmol/side) resulted in a substantial increase in the escape latency to find the platform (F(1,7)=30.2, P<0.01). The observed impairment of spatial memory was paralleled by a 47% decrease in choline acetyltransferase activity in the hippocampus. Oral administration of bis(7)-tacrine (0.22-0.89 micromol/kg) dose-dependently reversed the AF64A-induced latency delay to the level of the saline control group (F(4,28)=7.45, P<0. 05). The present study provides additional evidence of bis(7)-tacrine as an ideal candidate for the palliative treatment of Alzheimers disease.

Synergistic neuroprotection by bis(7)-tacrine via concurrent blockade of N-methyl-D-aspartate receptors and neuronal nitric-oxide synthase

The excessive activation of the N-methyl-d-aspartate receptor (NMDAR)/nitric oxide (NO) pathway has been proposed to be involved in the neuropathology of various neurodegenerative disorders. In this study, NO was found to mediate glutamate-induced excitotoxicity in primary cultured neurons. Compared with the NO synthase (NOS) inhibitor, NG-monomethyl-l-arginine (l-NMMA), and the NMDAR antagonist memantine, bis(7)-tacrine was found to be more potent in reducing NO-mediated excitotoxicity and the release of NO caused by glutamate. Moreover, like l-NMMA but not like 5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801) and memantine, bis(7)-tacrine showed greater neuroprotection and inhibition on NO release when neurons were pretreated for a prolonged time between 0 and 24 h and remained quite potent even when neurons were post-treated 1 h after the glutamate challenge. Bis(7)-tacrine was additionally found to be as moderately potent as memantine in competing with [3H]MK-801, inhibiting NMDA-evoked currents and reducing glutamate-triggered calcium influx, which eventually reduced neuronal NOS activity. More importantly, at neuroprotective concentrations, bis(7)-tacrine substantially reversed the overactivation of neuronal NOS caused by glutamate without interfering with the basal activity of NOS. Furthermore, in vitro pattern analysis demonstrated that bis(7)-tacrine competitively inhibited both purified neuronal and inducible NOS with IC50 values at 2.9 and 9.3 μM but not endothelial NOS. This result was further supported by molecular docking simulations that showed hydrophobic interactions between bis(7)-tacrine and three NOS isozymes. Taken together, these results strongly suggest that the substantial neuroprotection against glutamate by bis(7)-tacrine might be mediated synergistically through the moderate blockade of NMDAR and selective inhibition of neuronal NOS.

East meets west in the search for alzheimer's therapeutics - novel dimeric inhibitors from tacrine and huperzine A

Alzheimers disease (AD) is linked to cholinergic deficiency and the overactivation of glutamate receptors. The acetylcholinesterase (AChE) inhibition treatment approach has produced the most encouraging results in clinical practice, and memantine, a moderate antagonist of N-methyl-D-aspartate (NMDA) receptors, has been approved for treating AD. However, AChE inhibitors have limited success as they only improve memory in mild dementia but cannot stop the process of neurodegeneration; while memantine possesses neuroprotective effects only with a little ability in memory enhancement. There has been a major rush among neuroscience research institutions and pharmaceutical firms worldwide to search for safer and more effective therapeutic agents for AD. The novel dimers, derived from tacrine and the fragment of huperzine A (HA), have been demonstrated to be potent and selective reversible inhibitors of AChE. Bis(7)-tacrine, bis(12)-hupyridone (E12E) and HA(10)-tacrine, are representatives of three series of novel dimers. According to the preclinical studies, these compounds have been shown to have low toxicity and high efficacy for improving cognitive deficits in several animal models. More interestingly, bis(7)-tacrine, similar to memantine, prevents glutamate-induced neurotoxicity by moderately blocking glutamate receptor NMDA subtype. Furthermore, bis(7)-tacrine, as well as E12E, possesses multiple neuroprotective effects in vitro and in vivo. Taking together, these dimeric AChE inhibitors, especially bis(7)-tacrine, E12E and HA(10)-tacrine, may provide beneficial effects in AD and other neurodegenerative diseases.