Structural Determinants of HERG Channel Block by Clofilium and Ibutilide

Abstract

Block of human ether-a-go-go related gene (HERG) Kϩ channels by a variety of medications has been linked to acquired long QT syndrome, a disorder of cardiac repolarization that predisposes to lethal arrhythmias. The drug-binding site is composed of residues that face into the central cavity of the channel. Two aromatic residues located on the S6 domain (Tyr652 and Phe656) are particularly important structural determinants of drug block. The role of pore helix residues (Thr623, Ser624, Val625) is less clear. In this study, we compared the pharmacological properties of two structurally related compounds, ibutilide and clofilium. Both compounds are charged amines with a single phenyl ring. Clofilium, a chlorobenzene derivative, is a potent blocker of HERG channels, but has a remarkably slower time course for recovery from block than ibutilide, a methanesulfonanilide. The difference in the rate of recovery from block can be explained simply by variation in drug trapping. There is little recovery from clofilium block with D540K HERG channels that permit untrapping at hyperpolarized potentials. Alanine-scanning mutagenesis of the S6 domain and a portion of the pore helix revealed that the binding site residues were the same for both compounds. However, S624A, located at the base of the pore helix, was the only HERG mutation that enabled rapid recovery from clofilium block. In summary, the pore helix residues are important components of the HERG drug binding site, and may be particularly important for drugs with polar substituents, such as a halogen (e.g., clofilium) or a methanesulfonamide (e.g., ibutilide).

Structure-Guided Topographic Mapping and Mutagenesis to Elucidate Binding Sites for the Human Ether-a-Go-Go-Related Gene 1 Potassium Channel (KCNH2) Activator NS1643

“…Previous studies in Sanguinetti's laboratory (Sanguinetti and Xu, 1999;Mitcheson et al, 2000b;Tristani-Firouzi et al, 2002;Perry et al, 2004) have provided compelling evidence that the inward conductance elicited by hyperpolarizing pulses in the D540K mutant is related to an inward movement of the voltage-sensing S4 segment. D540K is located in the S4S5 linker near the cytosolic terminus of Fig.…”

“…The previously reported hERG1 D540K mutation generates a time-dependent inward conductance during the application of hyperpolarizing pulses (Sanguinetti and Xu, 1999;Mitcheson et al, 2000b;Tristani-Firouzi et al, 2002;Perry et al, 2004). Therefore, this mutation was chosen for additional experimental studies.…”

The protease inhibitor atazanavir blocks hERG K+ channels expressed in HEK293 cells and obstructs hERG protein transport to cell membrane

“…The structural requirements for the drug-binding site in hERG K + channels have been previously studied in detail [19,22]. The Y652 and F656 residues are located in the S6 domain and within the inner helices of the hERG channel.…”

Drug-Induced Arrhythmia

“…Molecularly targeted modification of drugs will become increasingly feasible to retain the desirable properties of therapeutic agents while avoiding undesirable cardiac electrophysiological properties such as QTc prolongation. A greater understanding of the interaction of drugs with relevant structures such as the HERG channel 20 will greatly facilitate this process.…”