Pharmacological characterization of a series of novel n-alkyl nicotinium analogues as neuronal nicotinic receptor subtype-selective antagonists.

다국어 초록 (Multilingual Abstract)

Molecular techniques have dramatically increased our knowledge of the diversity of nicotinic acetylcholine (nACh) receptors during the past decade. Multiple nACh receptor subtypes have been identified using cell expression systems. However, the identity of the specific subtypes in neural pathways, and their roles in the pharmacological response to nicotine remain to be elucidated. The lack of selective pharmacological tools to probe specific receptor subtypes has impeded the comprehensive understanding of the pharmacology of native nACh receptors. The focus of the current work was the development of novel subtype-selective nACh receptor antagonists. The hypothesis to be tested was that n-alkylation of the pyridine nitrogen of nicotine (S(−)NIC) converts it from an agonist to an antagonist, and furthermore, that altering the chain length of the <italic>N</italic>-n-alkyl substituent would optimize potency and selectivity.
Functional and equilibrium binding assays were utilized to determine novel <italic>N</italic>-alkyl analogue interaction with respective nACh receptor subtypes. Inhibition of S(−)NIC evoked [<super>3</super>H]dopamine release from superfused rat striatal slices (an assay for an α3β2* subtype), inhibition of radioligand binding to brain homogenates and sections, and inhibition of S(−)NIC-evoked <super>86</super>Rb<super>+</super> efflux were the assays utilized to assess the structure-activity relationship (SAR) between analogues of <italic>N</italic>-alkyl chain lengths of from C₁ to C₁₂. Results of the SAR analysis identified <italic>N</italic>-octyl nicotinium iodide (C₈, NONI) and <italic>N</italic>-decyl nicotinium iodide (C₁₀, NDNI) as lead antagonists. NONI potently and completely inhibited S(−)NIC-evoked [<super>3</super>H]dopamine release, but was ineffective as an inhibitor of S(−)-[<super>3</super>H]NIC binding and the high-affinity component of S(−)NIC-evoked <super>86</super>Rb<super> +</super> efflux (binding and functional assays for an α4β2* subtype). In contrast, NDNI exhibited high affinity for the α4β2* subtype as determined in the binding and <super>86</super>Rb<super>+</super> efflux assays, but was ineffective as an inhibitor of an α3β2* subtype defined by the S(−)NIC-evoked [<super>3</super>H]dopamine release assay. Autoradiographic analysis revealed that neither NONI nor NDNI interact with receptors containing β4 or α7 subunits. Taken together, the results of these studies suggest that NONI interacts selectively with an α3β2* subtype, and NDNI interacts selectively with an α4β2* subtype. This research provides the basis for further SAR analyses to optimize development of pharmacophores affording selective interaction with nACh receptor subtypes.