The synergic modeling for the binding of fluoroquinolone antibiotics to the hERG potassium channel.

The fluoroquinolone antibiotic binding site in the hERG potassium channel was examined for the residues involved and their position in the tetrameric channel. The blocking effect of the two fluoroquinolones levofloxacin and sparfloxacin to tandem dimers of the hERG mutants were evaluated electrophysiologically. The results indicated that two Tyr652s in the neighboring subunits and one or two Phe656s in the diagonal subunits contributed to the blockade in the case of both compounds, and Ser624 was also involved. The docking studies suggested that the protonated carboxyl group in the compounds strongly interacts with Phe656 as a π acceptor.

Synthesis, structure-activity relationship, and pharmacological studies of novel melanin-concentrating hormone receptor 1 antagonists 3-aminomethylquinolines: reducing human ether-a-go-go-related gene (hERG) associated liabilities.

Recently, we discovered 3-aminomethylquinoline derivative 1, a selective, highly potent, centrally acting, and orally bioavailable human MCH receptor 1 (hMCHR1) antagonist, that inhibited food intake in F344 rats with diet-induced obesity (DIO). Subsequent investigation of 1 was discontinued because 1 showed potent hERG K(+) channel inhibition in a patch-clamp study. To decrease hERG K(+) channel inhibition, experiments with ligand-based drug designs based on 1 and a docking study were conducted. Replacement of the terminal p-fluorophenyl group with a cyclopropylmethoxy group, methyl group introduction on the benzylic carbon at the 3-position of the quinoline core, and employment of a [2-(acetylamino)ethyl]amino group as the amine portion eliminated hERG K(+) channel inhibitory activity in a patch-clamp study, leading to the discovery of N-{3-[(1R)-1-{[2-(acetylamino)ethyl]amino}ethyl]-8-methylquinolin-7-yl}-4-(cyclopropylmethoxy)benzamide (R)-10h. The compound (R)-10h showed potent inhibitory activity against hMCHR1 and dose-dependently suppressed food intake in a 2-day study on DIO-F344 rats. Furthermore, practical chiral synthesis of (R)-10h was performed to determine the molecule's absolute configuration.

Docking model of drug binding to the human ether-à-go-go potassium channel guided by tandem dimer mutant patch-clamp data: a synergic approach.

To characterize drug binding to the human ether-a-go-go related gene (hERG) channel, a synergic approach interplaying patch-clamp experiments and a docking study was developed. Mutations were introduced into concatenated dimers of the hERG channel that were assembled into a heterotetramer with mutated diagonal subunits. The binding affinities of three drugs (cisapride, terfenadine, and N-[4-[[1-[2-(6-methyl-2-pyridinyl)ethyl]-4-piperidinyl]carbonyl]phenyl]methanesulfonamide dihydrochloride (E-4031, 1)) to a set of mutant channels were examined electrophysiologically to assess the involved residues, their number, and relative positions. Cisapride and 1 interacted with Tyr652 residues on adjacent subunits, while terfenadine interacted with Tyr652 residues on diagonal, but not on adjacent, subunits. Phe656 was involved in the binding of all three drugs, and Ser624 was found to be only involved in cisapride and 1. The docking models demonstrated that pi-pi and CH-pi interactions rather than cation-pi interaction play a key role in drug binding to the hERG channel.

Topological mapping of the asymmetric drug binding to the human ether-à-go-go-related gene product (HERG) potassium channel by use of tandem dimers.

The human ether-à-go-go related gene product (HERG) channel is essential for electrical activity of heart cells, and block of this channel by many drugs leads to lethal arrhythmias. Tyr(652) and Phe(656) of the sixth transmembrane helix are candidates for the drug binding site. In the tetrameric HERG channel, a drug with asymmetric structure should interact unevenly with multiple residues from different subunits. To elucidate the topology of the drug-binding site, we constructed tandem dimers of HERG channels and the aromatic Tyr(652) and Phe(656) residues were replaced by alanine singly or doubly. Eight types of HERG channels, including homotetrameric mutants, having different numbers and arrangements of aromatic residues at the blocking site, were studied. Effects of cisapride on channels expressed in Xenopus laevis oocytes were examined electrophysiologically. The inhibition constants (K(i)) were increased significantly as the diagonal Tyr(652) were deleted, whereas those for the diagonal Phe(656)-deleted mutant were not changed. These results suggest that Tyr(652) residues from adjacent subunits contributed to the binding. Two types of double mutants of tandem dimers showed significantly distinct affinities, suggesting that the coexistence of Tyr(652) and Phe(656) on a subunit in diagonal position is crucial to having a high affinity. Thermodynamic double-mutant cycle analyses revealed interactions between Tyr(652) and Phe(656) upon binding. The kinetics and voltage-dependence of blocking suggested transitions of the binding site from low to high affinity. These approaches using a set of mutant HERG channels gave a dynamic picture of the spatial arrangements of residues that contribute to the drug-channel interaction.