title: Crizotinib Inhibits Hyperpolarization-activated Cyclic Nucleotide-Gated Channel 4 Activity.
abstract: BACKGROUND
  Sinus bradycardia is frequently observed in patients treated with crizotinib, a receptor tyrosine kinase inhibitor used for the treatment of anaplastic lymphoma kinase (ALK)-rearranged non-small cell lung cancer (NSCLC). We investigated whether crizotinib could influence heart rate (HR) through direct cardiac effects.
  
  
  METHODS
  The direct effect of crizotinib on HR was studied using ECG analysis of Langendorff-perfused mouse hearts. The whole-cell patch clamp technique was used to measure the effects of crizotinib on the hyperpolarization-activated funny current, If, in mouse sinoatrial node cells (SANCs) and hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4) activity in HEK-293 cells stably expressing human HCN4.
  
  
  RESULTS
  Crizotinib resulted in a dose-dependent reduction in HR in isolated intact mouse hearts with a half maximal inhibitory concentration (IC50) of 1.7 ± 0.4 μmol/L. Because ECG analysis revealed that crizotinib (0-5 μmol/L) resulted in significant reductions in HR in isolated mouse hearts without changes in PR, QRS, or QT intervals, we performed whole-cell patch clamp recordings of SANCs which showed that crizotinib inhibited Ifwhich regulates cardiac pacemaker activity. Crizotinib resulted in diminished current density of HCN4, the major molecular determinant of If, with an IC50 of 1.4 ± 0.3 μmol/L. Crizotinib also slowed HCN4 activation and shifted the activation curve to the left towards more hyperpolarized potentials.
  
  
  CONCLUSIONS
  Our results suggest that crizotinib's effects on HCN4 channels play a significant role in mediating its observed effects on HR.
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, NC USA 27710.
authors.forename: Zhushan
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, NC USA 27710.
authors.forename: Tai-Qin
authors.initials: TQ
authors.lastname: Huang
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, NC USA 27710.
authors.forename: Igor
authors.initials: I
authors.lastname: Nepliouev
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, NC USA 27710.
authors.forename: Hengtao
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, NC USA 27710.
authors.forename: Adam S
authors.initials: AS
authors.lastname: Barnett
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, NC USA 27710.
authors.forename: Paul B
authors.initials: PB
authors.lastname: Rosenberg
authors.affiliation: Department of Medicine, University of California Irvine School of Medicine, Orange, CA 92868.
authors.forename: Sai-Hong I
authors.initials: SI
authors.lastname: Ou
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, NC USA 27710.
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Stiber
keywords: HCN4; bradycardia; crizotinib; non-small cell lung cancer; sinoatrial node