title: Drug binding to aromatic residues in the HERG channel pore cavity as possible explanation for acquired Long QT syndrome by antiparkinsonian drug budipine.
abstract: Budipine is a non-dopaminergic antiparkinsonian drug causing acquired forms of Long QT syndrome (aLQTS). As a consequence, the manufacturer has restricted the use of budipine in patients who exhibit additional risk factors for the development of "Torsades-de-Pointes" tachycardias (TdP). The molecular basis of this serious side effect has not been elucidated yet. Human ether-a-go-go related gene (HERG) channel block being the main cause of drug induced QT prolongation, we investigated the effect of budipine on the rapid component of the delayed-rectifier potassium current (I(K(r))) in guinea pig cardiomyocytes and on HERG potassium channels heterologously expressed in Xenopus oocytes. In guinea pig cardiomyocytes, budipine (10 microM) inhibited I(K(r)) by 86% but was without any effect on calcium currents. In Xenopus oocytes, HERG potassium channels were blocked by budipine with an IC(50) of 10.2 microM. Onset of block was fast and block was only slowly and incompletely reversible upon washout. Budipine blocked HERG channels in the open and inactivated state, but not in the closed states. The half-maximal activation voltage was slightly shifted towards more negative potentials. Steady-state inactivation of HERG was also influenced by budipine. Budipine block was neither voltage- nor frequency-dependent. In HERG channel mutants Y652A and F656A, drug affinity was reduced dramatically. Therefore, these two aromatic residues in the channel pore are likely to form a main part of the binding site for budipine. In summary, this is the first study that provides a molecular basis for the budipine-associated aLQTS observed in clinical practice. Furthermore, these findings underline the importance of the aromatic residues Y652 and F656 in the binding of lipophilic drugs to HERG channels.
authors.affiliation: 3rd Department of Internal Medicine (Cardiology), University of Heidelberg Medical School, Bergheimerstrasse 58, 69115, Heidelberg, Germany.
authors.forename: Eberhard P
authors.initials: EP
authors.lastname: Scholz
authors.forename: Edgar
authors.initials: E
authors.lastname: Zitron
authors.forename: Claudia
authors.initials: C
authors.lastname: Kiesecker
authors.forename: Sonja
authors.initials: S
authors.lastname: Lueck
authors.forename: Sven
authors.initials: S
authors.lastname: Kathöfer
authors.forename: Dierk
authors.initials: D
authors.lastname: Thomas
authors.forename: Slawomir
authors.initials: S
authors.lastname: Weretka
authors.forename: Simon
authors.initials: S
authors.lastname: Peth
authors.forename: Volker A W
authors.initials: VA
authors.lastname: Kreye
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Schoels
authors.forename: Hugo A
authors.initials: HA
authors.lastname: Katus
authors.forename: Johann
authors.initials: J
authors.lastname: Kiehn
authors.forename: Christoph A
authors.initials: CA
authors.lastname: Karle
mesh_terms: D000818:Animals; D000978:Antiparkinson Agents / Q000009:adverse effects*; D001665:Binding Sites; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D027682:Cation Transport Proteins; D051638:Ether-A-Go-Go Potassium Channels; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008133:Long QT Syndrome / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D009865:Oocytes / Q000187:drug effects; D018408:Patch-Clamp Techniques; D010880:Piperidines / Q000009:adverse effects*; D015221:Potassium Channels / Q000378:metabolism* / Q000502:physiology; D024642:Potassium Channels, Voltage-Gated; D013997:Time Factors; D014982:Xenopus laevis
chemical_list: D000978:Antiparkinson Agents; D015220:Calcium Channels; D027682:Cation Transport Proteins; D051638:Ether-A-Go-Go Potassium Channels; C092509:KCNH6 protein, human; D010880:Piperidines; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; C026710:budipine