A series of 2-sulfonamidopyridine C-region derivatives of 2-(3-fluoro-4-methylsulfonamidophenyl)propanamide were investigated as hTRPV1 ligands. Systematic modification on the 2-sulfonamido group provided highly potent TRPV1 antagonists. The N-benzyl phenylsulfonamide derivatives 12 and 23 in particular showed higher affinities than that of lead compound 1. Compound 12 exhibited strong analgesic activity in the formalin pain model. Docking analysis of its chiral S-form 12S in our hTRPV1 homology model indicated that its high affinity might arise from additional hydrophobic interactions not present in lead compound 1S.

Nicotinic acetylcholine receptors (nAChRs) play a crucial role in a number of clinically relevant mental and neurological pathways, as well as autonomic and immune functions. The development of subtype-selective ligands for nAChRs therefore is potentially useful for targeted therapeutic management of conditions where nAChRs are involved. We tested if selectivity for a particular nAChR subtype can be achieved through small structural modifications of a lead compound containing the nicotinic pharmacophore by changing the distance between the electronegative elements. For this purpose, analogs of A-84543 were designed, synthesized and characterized as potentially new nAChR subtype-selective ligands. Compounds were tested for their binding properties in rat cerebral cortical tissue homogenates, and subtype-selectivity was determined using stably transfected HEK cells expressing different nAChR subtypes. All compounds synthesized were found to competitively displace [3H]-epibatidine ([3H]EB) from the nAChR binding site. Of all the analogues, H-11MNH showed highest affinity for nAChRs compared to a ~ 5 to10-fold lower affinity of A-84543. All other compounds had affinities > 10,000 nM. Both A-84543 and H-11MNH have highest affinity for α2β2 and α4β2 nAChRs and show moderate affinity for β4- and α7-containing receptors. H-11MNH was found to be a full agonist with high potency at α3β4, while A-84543 is a partial agonist with low potency. Based on their unique pharmacological binding properties we suggest that A-84543 and its desmethylpyrrolidine analog can be useful as pharmacological ligands for studying nAChRs if selective pharmacological and/or genetic tools are used to mask the function of other receptors subtypes.

Nicotine has been shown to regulate the dopamine transporter (DAT) in a tissue dependent manner and to affect increase both the function of DAT as well as its surface expression (Middleton et al., 2004; Zhu et al., 2009). Here we have looked for a correlation in DAT distribution with sites rich in nAChRS. The binding of DAT was determined using [125I]RTI‐121 and was compared to that of [125I]EB and [125I]α‐BTX in rat brain using receptor autoradiography. Our preliminary results showed a high level of correlation between DAT to non‐α7 nAChRs primarily in mesolimbic and mesocortical areas, but not so in nigrostriatal areas. In the mesocortical and mesolimbic pathways, there were relatively high levels of non‐α7 nAChRs in habenula, nucleus accumbens, prefrontal cortex and cingulated cortex, but only low levels in the olfactory tubercle, hippocampus or in the VTA. There was little or no correlation between DAT and α7 nAChRs. Only modest levels of α7 nAChRs were found in the hippocampus, mammilary bodies, superior colliculus, lateral hypothalamus and entorhinal cortex, and non where found in substantia nigra, VTA, lateral caudate, or olfactory tubercle, areas rich in DAT. Since new studies have found that increase dopamine release is involved with changes in the level of clearance of DA it is important that we further characterize the nAChRs subtype involved in this regulation. The fact that α7‐containing receptors do not correlate to the distribution of DAT will help narrow future studies to the high affinity receptors.This research was supported by NIH R24 MH067627‐01A to MDG Project 2.

The development of subtype‐selective ligands for nAChRs holds high potential for better, more targeted therapeutic management of conditions where nicotinic acetylcholine receptors are implicated, including brain and peripheral neuropathies. Here it is proposed that subtype selectivity for a particular nAChR may be achieved by small structural modifications of a ligand, including a change in the distance between the electronegative elements of the compound containing the nicotinic pharmacophore. In order to test this hypothesis, analogs of A‐84543 (compound 1) were designed and synthesized as potentially new nAChR subtype‐selective ligands. A‐84543 and four analogues (compounds 2‐5) were characterized in rat brain tissues. All synthesized analogs of A‐84543 were partially characterized and their binding affinities and subtype‐selectivity and function were determined using stably transfected cell lines expressing different nAChR subtypes. Of all the analogs, only compound 1 and 2 were shown to have higher selectivity for β2‐containing, compared to β4‐containing nAChRs, with a selectivity ratio between α3β4 and α4β2 of 1,350 and 530 fold, respectively. Finally, A‐84543 was shown to be a partial agonist at α3β4 nAChRs (EC50 = 160 ± 40 nM, Emax of 45%), while compound 2 was a full agonist and had higher potency (EC50 = 24 ± 1 nM, Emax of 100%), compared to 100 µM nicotine. Based on its higher efficacy and good selectivity ratio, compound 2 can be useful as a pharmacological tool for β2‐containing as well as α3β4*‐containing nAChRs receptors if selective pharmacological tools are used to protect or mask the other receptors. From our results we conclude that compound 2, has good potential as a lead compound to produce more selective ligands. Grant Funding Source: This research was supported in part by NIH grant R24MH06762701 and 5U54NS039407 to MDG.