Jeffrey E. Campbell

Functional characterization of the novel neuronal nicotinic acetylcholine receptor ligand GTS-21 in vitro and in vivo

(2.4)-Dimethoxybenzylidene anabaseine dihydrochloride (GTS-21), a compound that interacts with rat neuronal nicotinic acetylcholine receptors (nAChRs), was evaluated using human recombinant nAChRs in vitro and various pharmacokinetic and behavioral models in rodents, dogs and monkeys. GTS-21 bound to human alpha 4 beta 2 nAChR (K1-20 nM) 100-fold more potently than to human alpha 7 nAChR, and was 18- and 2-fold less potent than (-)-nicotine at human alpha 4 beta 2 and alpha 7 nAChR, respectively. Functionally. GTS-21 stimulated [5H]dopamine release from rat striatal slices with an EC50 of 10 +/- 2 microM (250-fold less potent and 70% as efficacious as (-)-nicotine), an effect blocked by the nAChR antagonist dihydro-beta-erythroidine. However, GTS-21 did not stimulate human alpha 4 beta 2 nor human ganglionic nAChRs significantly. In vivo, GTS-21 had no adverse effect on dog blood pressure (< or = 2.5 micromol/kg i.v. bolus infusion), in marked contrast with (-)-nicotine, GTS-21 (-62 micromol/kg.s.e.) also did not cross-discriminate significantly with (-)-nicotine in rats and did not reduce temperature or locomotion in mice. Neither was it active in the elevated plus maze anxiety model (0.19-6.2 micromol/kg.IP) in normal mice. However, GTS-21 did improve learning performance of monkeys in the delayed matching-to-sample task (32-130 nmol/kg.i.m.).

A-85380 [3-(2(S)-azetidinylmethoxy) pyridine]: In Vitro pharmacological properties of a novel, high affinity α4β2 nicotinic acetylcholine receptor ligand

Abstract The in vitro pharmacological properties of a novel cholinergic channel ligand, A-85380 [3-(2( S )-azetidinylmethoxy) pyridine], were examined using tissue preparations that express different putative nAChR subtypes. In radioligand binding studies, A-85380 is shown to be a potent and selective ligand for the human α4β2 nAChR subtype ( K i = 0.05 ± 0.01 nM) relative to the human α7 ( K i = 148 ± 13 nM) and the muscle α1β1dg subtype expressed in Torpedo electroplax ( K i = 314 ± 12 nM). The R -enantiomer of A-85380, A-159470, displays little enantioselectivity towards the α4β2 and α1β1δγ subtypes but does display 12-fold enantioselectivity towards the α7 subtype ( K i = 1275 ± 199 nM). (+)- and (−)-Epibatidine display similar potencies at the human human α4β2 ( K i = 0.04 ± 0.02 nM and 0.07 ± 0.02 nM, respectively), human α7 ( K i = 16 ± 2 nM and 22 ± 3 nM, respectively) and muscle α1β1δg ( K i = 2.5 ± 0.9 nM and 5.7 ± 1.0 nM, respectively) nAChRs. Functionally, A-85380 is a potent activator of cation efflux through the human α4β2 (EC 50 = 0.7 ± 0.1 μ M) and ganglionic (EC 50 = 0.8 ± 0.09 μ M) subtypes, effects that are attenuated by pretreatment with mecamylamine (10 μM). Further, A-85380 can activate (EC 50 = 8.9 ± 1.9 μ M) currents through channels formed by injection of the human α7 subunit into Xenopus oocytes, effects that are attenuated by pretreatment with the α7 nAChR antagonist, methyllycaconitine (10 nM). In all cases, A-85380 is more potent than (−)-nicotine but less potent than (±)-epibatidine. In neurotransmitter release studies, A-85380 stimulates the release of dopamine with an EC 50 value of 0.003 ± 0.001 μ M which is equipotent to (±)-epibatidine, and 20-fold more potent that (−)-nicotine (EC 50 = 0.04 ± 0.009 μ M). Thus, A-85380 displays a profile of robust activation of a number of nAChR subtypes with substantially less affinity for [ 125 I]α-BgT sites than [ 3 H](-)-cytisine sites, suggesting that it may serve as a more selective pharmacologic probe for the αx4β2 subtype relative to the α7 and α1β1δg nAChRs than (±)-epibatidine.

Structure-activity studies related to ABT-594, a potent nonopioid analgesic agent: Effect of pyridine and azetidine ring substitutions on nicotinic acetylcholine receptor binding affinity and analgesic activity in mice

Analogs of A-98593 (1) and its enantiomer ABT-594 (2) with diverse substituents on the pyridine ring were prepared and tested for affinity to nicotinic acetylcholine receptor binding sites in rat brain and for analgesic activity in the mouse hot plate assay. Numerous types of modifications were consistent with high affinity for [3H]cytisine binding sites. By contrast, only selected modifications resulted in retention of analgesic potency in the same range as 1 and 2. Analogs of 2 with one or two methyl substituents at the 3-position of the azetidine ring also were prepared and found to be substantially less active in both assays.

Synthesis and structure-activity relationships of pyridine-modified analogs of 3-[2-((S)-pyrrolidinyl)methoxy]pyridine, A-84543, a potent nicotinic acetylcholine receptor agonist

Analogs of 3-[2-((S)-pyrrolidinyl)methoxy]pyridine, (A-84543, 1) with 2-, 4-, 5-, and 6-substituents on the pyridine ring were synthesized. These analogs exhibited Ki values ranging from 0.15 to > 9,000 nM when tested in vitro for neuronal nicotinic acetylcholine receptor binding activity. Assessment of functional activity at subtypes of neuronal nicotinic acetylcholine receptors indicates that pyridine substitution can have a profound effect on efficacy at these subtypes, and several subtype-selective agonists and antagonists have been identified.

2-(Aryloxymethyl) azacyclic analogues as novel nicotinic acetylcholine receptor (nAChR) ligands

Abstract A series of 2-(aryloxymethyl) azetidine and pyrrolidine nAChR ligands in which the 3-pyridyl moiety of a previously described series 1 was replaced by a substituted phenyl group was explored. Aromatic substitution afforded analogues with K i values ranging from 3 to >10,000 nM. Generally, substitution at the ortho - and para -position was unfavorable, whereas electron-withdrawing groups at the meta -position improved the K i values.

Phenyl pyrrolidine analogues as potent nicotinic acetylcholine receptor (nAChR) ligands

Abstract The synthesis and SAR of a series of 2-phenyl pyrrolidines as neuronal nAChR ligands are described. Substitution on the aryl ring had a dramatic effect on receptor binding affinity, with Ki values ranging from 46 nM to >10,000 nM. Analogues 8, 9, and 14 were the most potent ligands evaluated, having Ki values of 68 nM, 75 nM, and 46 nM; respectively.

Structure-activity studies on a novel series of cholinergic channel activators based on a heteroaryl ether framework.

Analogs of compound 1 with a variety of azacycles and heteroaryl groups were synthesized. These analogs exhibited Ki values ranging from 0.15 to > 10,000 nM when tested in vitro for cholinergic channel receptor binding activity (displacement of [3H](-) cytisine from whole rat brain synaptic membranes).

Synthesis of 5- and 6-(6-Chloro-3-pyridyl)-2-azabicyclo[2.2.0]hexanes. Epibatidine Analogs

Abstract Synthetic routes to vicinal -6-(6-Cl-3-pyridyl)- and distal -5-(6-Cl-3-pyridyl)-2-azabicyclo-[2.2.0]hexane analogs of the potent nicotinic receptor agonist epibatidine are described. Both exo -regioisomers are available from a readily available 2-azabicyclo[2.2.0]hex-5-ene by way of stereoselective reductive Heck addition of the 6-Cl-3-pyridyl moiety. Stereochemical inversion of the 6- and 5-aryl groups provides entry to the endo isomers.

Synthesis of 3- and 5-endo-(6-Chloro-3-pyridoxy)-methyl-2-azabicyclo[2.2.0]hexane and 3-endo-(6-Chloro-3-pyridoxy)-methyl-2-azabicyclo[2.2.0]hex-5-ene. ABT-594 Analogs

Abstract Stereoselective photochemical ring closure of a 2-hydroxymethyl-1,2-dihydropyridine has been utilized for the syntheses of 3- endo -(6-Cl-3-pyridoxy)-methyl-2-azabicyclo[2.2.0]hex-5-ene and hexane analogs of the nicotinic acetylcholine receptor agonist ABT-594. The photochemical ring closure of a 4-hydroxymethyl-1,2-dihydropyridine has been utilized in the preparation of 5- endo -(6-chloro-3-pyridoxy)-methyl-2-azabicyclo[2.2.0]hexane.

ABT‐089 [3‐(2(S)‐pyrrolidinylmethoxy)‐2‐methyl‐pyridine]: An orally effective cholinergic channel modulator with potential once‐a‐day dosing and cardiovascular safety

ABT‐089 [3‐(2(S)‐pyrrolidinylmethoxy)‐2‐methylpyridine] is a cholinergic channel modulator (ChCM) that selectively affects the function of neuronal nicotine acetylcholine receptor (nAChR) subtypes, enhances cognitive performance and has neuroprotective activity. Previous reports indicate that, unlike the other nicotinic receptor ligands, ABT‐418 and (‐)‐ nicotine, ABT‐089 exhibits a more complex profile, having agonist, partial agonist, and inhibitory activities depending on the putative nAChR subtype with which it interacts. This study provides safety and pharmacokinetic information that clearly differentiate ABT‐089 from both (‐)‐nicotine and ABT‐418. ABT‐089 has a reduced activation of ganglionic nAChRs, resulting in a reduced propensity to elicit side effects at high doses. Studies using guinea pig ileum indicate that ABT‐089, in contrast to (‐)‐ nicotine and the muscarinic agonist,methacholine, has no detectable effects on smooth muscle contractility, suggesting low potential for interference with gastrointestinal mobility. ABT‐089 is orally available (33–76% in rat, dog, and monkey) and preliminary formulation data indicates that once‐a‐day formulation is feasible. In contrast, ABT‐418 and (‐)‐nicotine have poor oral bioavailability in dog and monkey (<5%) and moderate bioavailability in rat (27 and 19%, respectively). Prolonged administration of ABT‐089 does not result in cardiovascular liability in dogs. ABT‐089 may be a safe and effective ChCM for the potential once‐a‐day oral treatment of the cognitive impairments and neurodegenerative processes associated with disorders such as Alzheimers disease. Drug Dev. Res. 41:31–43, 1997.