2-Fluoro-3-(4-nitro-phenyl)deschloroepibatidine Is a Novel Potent Competitive Antagonist of Human Neuronal α4β2 nAChRs

Abstract

A patch-clamp technique in a whole-cell configuration was used to examine the functional activity of recently developed 2-fluoro-3-(substituted phenyl)deschloroepibatidine analogs on two major subtypes of neuronal nicotinic acetylcholine receptors (nAChRs), ␣4␤2 and ␣3␤4, that predominate in the central and peripheral nervous systems, respectively. These epibatidine analogs have been shown previously to possess high binding affinity to ␣4␤2 but not to ␣7 nAChRs and to inhibit nicotine-induced analgesia in behavioral pain tests. The 2-fluoro-3-(4-nitro-phenyl)deschloroepibatidine (4-nitro-PFEB) exhibited the most pronounced antagonist activity among these analogs when tested electrophysiologically on ␣4␤2 nAChRs. It inhibited acetylcholine (ACh)-induced currents in a concentration-dependent manner with an IC 50 value of 0.1 M and produced complete inhibition at ϳ1 M concentration.4-Nitro-PFEB at 0.1 M concentration produced a 4-fold rightward shift in the ACh concentration-response curve without altering maximum ACh-induced response. This inhibitory effect of 4-nitro-PFEB was voltage-and use-independent and was partially reversible at its 1 M concentration. The rise and decay kinetics of ACh-induced currents was not altered in the presence of 4-nitro-PFEB. In contrast to ␣4␤2 nAChRs, this compound did not affect ␣3␤4 nAChR-mediated currents at Յ1 M (IC 50 ϳ63.9 M). Overall, these functional data agree with previous binding and behavioral findings and suggest collectively that 4-nitro-PFEB is the most effective and selective antagonist of ␣4␤2 versus ␣3␤4 and ␣7 nAChRs among the tested analogs, acting on ␣4␤2 nAChR through a competitive mechanism with a potency 17-fold higher than that of dihydro-␤-erythroidine.

Discriminative stimulus and hypothermic effects of some derivatives of the nAChR agonist epibatidine in mice

“…When tested in a nicotine discrimination assay in rats, RTI-7527-102 did not mimic the effects of nicotine (Tobey et al 2012). These effects in mice are consistent with in vitro data showing that RTI-7527-102 has low efficacy, as evidenced by electrophysiological responses at both human and rat α4β2 nAChR expressed in Xenopus oocytes (Abdrakhmanova et al 2006; Ondachi et al 2012). The efficacy of RTI-7527-36 and RTI-7527-76 at α4β2 nAChR in vitro has not been established.…”

Central Nicotinic Receptors: Structure, Function, Ligands, and Therapeutic Potential

“…[119] This trend of affinity/selectivity is confirmed by the work of other researchers [120] who have reported that compounds 58 show selectivity for the b2-containing receptors in binding studies; interestingly, the 4-CN derivative 58 b (X = H, Y = CN) possesses some agonistic properties on rat a3b4 nAChR (measurement of 86 …”

Modeling Differential Binding of α4β2 Nicotinic Acetylcholine Receptor with Agonists and Antagonists

“…The data in Table 1 indicate that the binding free energies calculated for the favorable binding of antagonists (1-20) with the closed-channel receptor and for the favorable binding of agonists (21)(22)(23)(24)(25)(26)(27) with the open-channel receptor are all close to the corresponding experimentally derived binding free energies. The good agreement between the computational and experimental data suggests that the determined binding structures and calculated binding free energies are reasonable.…”

“…As seen in Table 1, the ∆G bind value calculated for each of the antagonists (1-20) binding with the closed-channel R4 2 receptor is much lower than that calculated for its binding with the open-channel receptor. In contrast, the ∆G bind value calculated for each of the agonists (21)(22)(23)(24)(25)(26)(27) binding with the open-channel R4 2 receptor is much lower than that calculated for its binding with the closed-channel receptor. The calculated relative binding free energies are qualitatively consistent with the aforementioned notion concerning the modeled binding structures, i.e., all of the antagonists bind more favorably with the closed-channel receptor, whereas all of the agonists bind more favorably with the open-channel receptor.…”

“…Meanwhile, R4 2 nAChR antagonists have become Figure 1). [19][20][21][22][23] In order to design more potent and diverse antagonistic therapeutics, it is particularly important to understand how R4 2 nAChR can be functionally antagonized. Recent studies 3-5,24-31 on pharmacological and structural characteristics of nAChRs were performed on the extracellular ligand-binding domain (LBD) of nAChRs using the homologous acetylcholine binding protein (AChBP) as the prototype.…”