Analogs of Methyllycaconitine as Novel Noncompetitive Inhibitors of Nicotinic Receptors: Pharmacological Characterization, Computational Modeling, and Pharmacophore Development

Abstract

As a novel approach to drug discovery involving neuronal nicotinic acetylcholine receptors (nAChRs), our laboratory targeted nonagonist binding sites (i.e., noncompetitive binding sites, negative allosteric binding sites) located on nAChRs. Cultured bovine adrenal cells were used as neuronal models to investigate interactions of 67 analogs of methyllycaconitine (MLA) on native ␣3␤4* nAChRs. The availability of large numbers of structurally related molecules presents a unique opportunity for the development of pharmacophore models for noncompetitive binding sites. Our MLA analogs inhibited nicotinemediated functional activation of both native and recombinant ␣3␤4* nAChRs with a wide range of IC 50 values (0.9 -115 M). These analogs had little or no inhibitory effects on agonist binding to native or recombinant nAChRs, supporting noncompetitive inhibitory activity. Based on these data, two highly predictive 3D quantitative structure-activity relationship (comparative molecular field analysis and comparative molecular similarity index analysis) models were generated. These computational models were successfully validated and provided insights into the molecular interactions of MLA analogs with nAChRs. In addition, a pharmacophore model was constructed to analyze and visualize the binding requirements to the analog binding site. The pharmacophore model was subsequently applied to search structurally diverse molecular databases to prospectively identify novel inhibitors. The rapid identification of eight molecules from database mining and our successful demonstration of in vitro inhibitory activity support the utility of these computational models as novel tools for the efficient retrieval of inhibitors. These results demonstrate the effectiveness of computational modeling and pharmacophore development, which may lead to the identification of new therapeutic drugs that target novel sites on nAChRs.The physiological roles of neuronal nicotinic acetylcholine receptors (nAChRs) in synaptic release of acetylcholine and their involvement in the modulation of other important neurotransmitters such as norepinephrine, serotonin, GABA, glutamate, and dopamine make nAChRs prime targets for therapeutic interventions. In addition, nAChRs have been linked to pain, epilepsy, and many neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease, and psychiatric disorders, such as depression and schizophrenia. The development of new drugs to target these receptors has been slow for several reasons: 1) multiple subtypes of nAChRs are expressed in the central and peripheral nervous systems; 2) few drugs are available that selectively target nAChR subtypes; and 3) information on the physiological roles of specific nAChR subtypes is limited. A key approach to provide a better understanding of physiological processes and pathophysiological conditions involving

Effect of Novel Negative Allosteric Modulators of Neuronal Nicotinic Receptors on Cells Expressing Native and Recombinant Nicotinic Receptors: Implications for Drug Discovery

“…Table 2 established the feasibility of using this cell line. The relative potencies of nicotine, epibatidine, and one of our own antagonists, COB-2, were identical to values reported in the literature for native bovine adrenal nAChRs (McKay and TrentSanchez, 1990;McKay and Burkman, 1993;Wenger et al, 1997;McKay et al, 2007); native nAChRs showed slightly higher apparent affinities for the agonists. The inhibitory effects of the competitive antagonist tubocurarine and the noncompetitive antagonists mecamylamine and tetracaine were also compared (Table 2); no major differences were seen between native bovine and recombinant rat nAChRs.…”

“…Allosteric modulators exist for a variety of receptors (Wess, 2005). Allosteric modulation of nAChRs is considered to be one of the most promising approaches in ligand design for nAChR research and therapeutics (Cassels et al, 2005;Iorga et al, 2006), and the characterization and localization of these sites are beginning to be elucidated (Costa et al, 2003;Iorga et al, 2006;McKay et al, 2007).…”

Nicotinic acetylcholine receptors and the ascending dopamine pathways

“…A concerted hypothesis for the nicotinic control of burst firing [40] posits that nicotine rapidly and preferentially desensitises α4β2 nAChRs on GABAergic interneurons [41], relieving inhibition of midbrain dopamine neurons while maintaining a sustained activation of α7 nAChRs on dopaminergic cell bodies as well as glutamate terminals [30]. β2* nAChRs on dopamine cell bodies provide a coincident depolarisation that enhances excitability, and this is necessary for LTP and /or to drive changes in firing pattern.…”

Diastereoselective synthesis of a highly substituted cis-decahydroquinoline via a Knoevenagel condensation

“…27-30 All of the simple E ring analogues have been shown to be noncompetitive antagonists to the α3β4* nAChR, with no affinity to the agonist binding sites of either α7, α4β2, or α3β4* nAChRs. 31 We hoped that introducing a more rigid conformation to our previous E-ring analogues might provide a selective and competitive ligand to the α7 nAChR. A simple removal of the A, C, D and F rings of MLA provides a BE ring analog.…”