Hypertension is the most common chronic disease worldwide. It is one of
the most important risk factors of cardiovascular and cerebrovascular
diseases, causing major complications of stroke, myocardial infarction,
heart failure and chronic kidney disease. Iptakalim
(2,3-dimethyl-N -(1-methylethyl)-2-butanamine), discovered by the
Institute of Pharmacology and Toxicology of the Academy of Military
Medical Sciences, is a selective KATP channel opener[1], which has undergone extensive pharmacological
and electrophysiological studies. Pre-clinical studies have shown that
it can reduce the endothelin levels in hypertensive state, inhibit the
vasoconstricting effect of endothelin, inhibiting the expression of
endothelin and endothelin converting enzymes, thereby exerting the blood
pressure-lowering effect[2].
Cardiotoxicity
has been one of the most common causes for withdrawing drugs from the
market. An undesirable property of some non-antiarrhythmic drugs is
their ability to delay cardiac repolarization, an effect that can be
measured by the prolonged QT interval on the electrocardiogram. A delay
in cardiac repolarization creates an electrophysiological environment
that favors the development of cardiac arrhythmia, most clearly torsade
de pointes (Tdp). A feature of Tdp is the pronounced prolongation of QT
interval in the supraventricular beat preceding the arrhythmia. Tdp can
degenerate into ventricular fibrillation, leading to sudden death.
The international Conference on Harmonization (ICH) issued a guidance in
May 2005 on the Clinical Evaluation
of QT/QTc Interval Prolongation and Proarrhythmic Potential for
Non-Antiarrhymic Drugs (the ICH E14 document[3]),
aiming to provide recommendations concerning the design, conduct,
analysis, and interpretation of clinical studies to assess the potential
of a drug to delay cardiac repolarization. Considering the drawbacks of
conducting thorough QT/QTc (TQT) study, Consortium for Innovation and
Quality in Pharmaceutical Development and the Cardiac Safety Research
Consortium (IQ-CSRC) recommended the design and conduct of clinical
study in healthy subjects using ER analysis to replace the TQT
studies[4]. Subsequent studies successfully
detected the QT effect of 5 drugs which are known to cause mild QT
prolongation, leading to the revision of the ICH E14 guideline and the
accompanying “Questions & Answers: The Clinical Evaluation of QT/QTc
Interval Prolongation and Proarrhythmic Potential for Non-Antiarrhythmic
Drugs”. Based on the growing experience in the ER analysis of TQT
studies and the results of the IQ-CSRC study, the ICH E14 document was
subsequently revised in December 2015 to describe the approach of using
ER analysis applied to data from small studies as an alternative of TQT
study. There are several studies using ER analysis in the estimation of
QT interval prolongation risks of drugs [5, 6].
Moreover, understandings of the safety and pharmacokinetic (PK) profiles
of new drugs are needed for clinical development; thus, we conducted a
phase I study to investigate the safety, PK profile, and the effect on
QT/QTc interval of ITKL in Chinese population.
Methods
Study and ethics
The objectives of the single-ascending dose (SAD) and multiple-ascending
dose (MAD) studies were to investigate safety, tolerability and PK of
ITKL following single and multiple dosing and to initially predict
whether ITKL had an effect on QT interval prolongation in healthy
Chinese subjects by establishing an ER model. Both studies were
double-blinded, randomized, and placebo-controlled. Part 1 followed a
single oral dose in 60 healthy adult subjects, and part 2 followed
multiple oral doses in 23 healthy adult subjects.
The study protocols were approved by the respective institutional review
board (IRB) or Independent Ethics Committee (IEC). The studies were
conducted in accordance with the Declaration of Helsinki (1989) and
local applicable laws and regulations. All subjects provided written
informed consent prior to their participation in the studies.
Study design and treatment
Both studies were double-blind,
randomized, and placebo-controlled. Standard inclusion criteria for
studies in healthy subjects were used, including heart rate (HR) between
60 and 100 beats per minute (bpm), systolic blood pressure between 90
and 140 mmHg, diastolic blood pressure between 60 and 90 mmHg, blood
potassium between 3.5 and 5.5 mmol/L, and QTc interval< 430 milliseconds for men and < 450
milliseconds for women. In addition, in the SAD study, 60 healthy men
and women (30/30), aged between 18 and 44 years and with a body mass
index (BMI) between 19.2 and 25.2 kg/m2, were
enrolled. Subjects were randomized to single oral doses of 5,10,15 or 20
mg ITKL or placebo (active/placebo, 12/2 in 5 and 10 mg groups, 12/4 in
15 and 20 mg groups) following fasting for at least 10 hours. The
in-house period lasted for 4 days and 3 nights, starting on the day
before dosing. The administration of higher doses waited until the
administration of lower dose was finished and the safety and
tolerability assessment can support subsequent higher doses. In the MAD
study, 23 healthy men and women (12/11), aged between 21 and 44 years
and with a BMI between 19.4 and 25.9 kg/m2, were enrolled. Subjects were
randomized to multiple oral doses of 10 or 20 mg ITKL, following fasting
for at least 10 hours. The in-house period lasted for 12 days and 11
nights, starting on the day before dosing, and subjects were
administered on day 1 and days 3-9. Subjects dosed with placebo were
analyzed as a pooled group. Demographic data of the 83 subjects in the
SAD and MAD studies are summarized in Table 1. In all cohorts of the SAD
and MAD study, treatment was administered with 240 ml water under fasted
condition in the morning, and subjects were not allowed to drink during
the 2 hours before administration and 2 hours after administration. The
subjects had standard meals 4 hours after dosing.
PK data collection
In the SAD study, approximately 4ml blood samples were collected before
dosing (within 30 min), and at 0.5h, 1h, 1.5h, 2h, 3h, 4h, 6h, 8h, 12h,
24h, 36h after dosing. Indwelling catheters were used and 2ml of 0.9%
physiological saline was used to flush lines after sample collection.
Samples were centrifuged for 5 min at approximately 4°C and 2000g for 30
minutes after collection. The supernatant (plasma) was divided into two
parts. 1 ml of the plasma was used for drug monitoring, and the
remaining was kept as backup. Plasma samples were immediately frozen at
-20℃ or lower, and they were uniformly transferred to a refrigerator
below -70℃ for storage until PK analysis after the completion of one
period.
In the MAD study, approximately 4ml blood samples were collected before
dosing (within 30 min), and at 0.5h, 1h, 1.5h, 2h, 3h, 4h, 6h, 8h, 12h,
24h, 36h after dosing on day 1, and at predose (within 30 min), 2.5h
postdose on day 5~8, and at predose (within 30 min),
0.5h, 1h, 1.5h, 2h, 3h, 4h, 6h, 8h, 12h, 24h, 36h postdose on day 9.
Samples were processed as the same as in the SAD study.
An established and validated high-performance liquid chromatography
tandem mass spectrometry method was used to determine the ITKL
concentrations in plasma samples. The lower limit of quantification
(LLOQ) was 0.5 ng/ml. Calibration standard curve was linear over the
range of 0.5 ng/ml to 200 ng/ml, using a 1/x2 weighted
least-squares linear regression analysis ( r≥0.98). Concentrations below
the lower limit of quantification were labeled as below limit of
quantification (BLOQ). The inter-day assay accuracy (expressed as
percent relative error, %RE) determined from quality control (QC)
samples (at concentrations of 1 ng/ml, 10 ng/ml and 80 ng/ml) ranged
from 1.75% to 7.03%. Assay precision (expressed as the inter-day
percent relative standard error, %RSD) ranged from 4.67% to 10.65%.
ECG data collection
Twelve-lead ECGs were extracted at the prespecified times and analyzed
by timepoint and with ER modeling. If the scheduled time for an ECG
coincided with a blood collection, the ECG was performed at least 5
minutes prior to the blood collection. The rhythm, ventricular rate, PR
interval, QRS complex, QT interval, and QTcF (QT values after
Fridericia’s correction) interval were collected, and analyzed by
instrument and hand. The results of QTc were subject to the manual
measurement of two cardiographers.
In the SAD study, ECGs were obtained at -30 min, -20 min, -10 min before
dosing, and at 0.5h, 1h, 1.5h, 2h, 3h, 4h, 6h, 8h, 12h, 24h, 36h after
dosing, three times at each timepoint.
In the MAD study, ECGs were obtained at -30 min, -20 min, -10 min before
dosing, and at 0.5h, 1h, 1.5h, 2h, 3h, 4h, 6h, 8h, 12h, 24h, 36h after
dosing on day 1, and at predose (within 10 min), 2.5h postdose on day
5~8, and at -30 min, -20 min, -10 min before dosing, and
at 0.5h, 1h, 1.5h, 2h, 3h, 4h, 6h, 8h, 12h, 24h, 36h after dosing on day
9.
In order to reduce the dependence of QT on HR, we used Fridericia’s
correction for all analyses.
\begin{equation}
QTcF=QT/RR0.33,\ (RR=60/HR)\nonumber \\
\end{equation}Exposure (concentration)-response (QT/QTc) Model
This study used nonlinear mixed effect method to establish ITKL drug
plasma concentration and Δ QTcF model. According to the recommendations
of scientific white paper[7], if the five
hypothesis (see left column of table 3) are met, the preset linear model
can be used for analysis.
QTcF and Δ QTcF calculation method is as follows:
\begin{equation}
QT\text{cF}=\frac{Q\text{T\ intervel}}{\text{RR}^{0.33}}\nonumber \\
\end{equation}Formula (1)
\begin{equation}
{QTcF}_{\text{ijk}}=\text{QTcF}_{\text{ijk}}-\overset{\overline{}}{\text{QTcF}_{i,j,k=0}}\nonumber \\
\end{equation}Formula (2)
\(\text{QTcF}_{\text{ijk}}\) is the measurement point k of the ith
subject in group j, \(\overline{\text{QTcF}_{i,j,k=0}}\) is the
baseline QTcF value of the ith subject, that is, the mean value of QTcF
for the three times before
administration.
Basic model selection
This study used nonlinear mixed effect method to establish drug plasma
concentration (independent variables) and ΔQTcF model. ΔQTcF represents
the QTcF value minus the average QTcF, which is used as a dependent
variable. The preset model of relations among drug plasma concentration
and ΔQTcF was the first choice. When model hypothesis 3 (no delay
hypothesis) or hypothesis 4 (linear relation hypothesis) is rejected, a
custom model is used for analysis. The custom model is as follows:
\begin{equation}
{QTcF}_{\text{ijk}}=\left(\theta_{0}+\eta_{0,i}\right)+\theta_{1}\text{TR}T_{j}+\left(\theta_{2}+\eta_{2,i}\right)C_{\text{ijk}}+\theta_{3}\text{TIM}E_{j}+\theta_{4}(\text{QTcF}_{i,j,k=0}-\overset{\overline{}}{\text{QTc}F_{0}}\nonumber \\
\end{equation}Formula (3)
The ΔQTcF ijk and Cijk are the
measurements of ΔQTcF and drug plasma concentration, respectively, at
time-point k of the ith subject in the first j group. θ0is the typical intercept value of the group without treatment (placebo
effect); θ1 is the fixed effect of group
TRTj (j=0, placebo; J =1, ITKL); θ2 is
the typical value of the slope group estimated by the model;
θ3 is the fixed effect of correction time factor;
θ4 is the fixed effect of correction baseline; QTcFi,j=0 is the baseline QTcF;\(\overline{\text{QTcF}_{0}}\ \)is the mean of QTcF at time 0 (baseline)
for all subjects. η0, i and η2, i are a
respectively random effects between
individual
θ1 and θ2.
Model selection of random effects
Random model is also known as a statistical model, which describes the
inter-individual random effect (variation) and intra-individual random
effect (variation). According to formula (3), the addition of
inter-individual random effect is adopted:
Formula (4)
PTV is the typical values of a parameter group,
Pi is the individual parameter value, and
ηi is the random effect between individuals, in line
with normal distribution with a mean of 0 and a variance of
ω2.
The additive model is used for intra-individual random effect
(residual):
\(Y_{obs,ij}=Y_{pred,ij}+\varepsilon_{\text{ij}}\) Formula (5)
Yobs,ij and Ypred,ij are the observed
and predicted values of the effect, respectively.
Calculation method of Δ Δ QTcF based on the model
ΔΔQTcF, which is equal to the QTcF value minus the placebo and the
average QTcF, is used for the baseline and the placebo effect
correction. When the Δ QTcF group typical values under the specific drug
plasma concentrations is obtained by the model, the difference between Δ
QTcF group typical values and the Δ QTcF group typical values in placebo
group was calculated:
\begin{equation}
Mean\ QTc\left(C\right)=Mean\left({QTc}_{\text{ijk}}j=1,\ C_{\text{ijk}}=C\right)-Mean\left({QTc}_{\text{ijk}}|j=0,\ C_{\text{ijk}}=0\right)\nonumber \\
\end{equation}Formula (6)
C is the drug concentration (the geometric mean of each dose group
Cmax).
When the preset model is used, combining formula (3) and formula (6),
the calculation formula of typical value of ΔΔ QTCF group at a specific
concentration, along with two-sided 90% CI can be obtained:
\begin{equation}
Estimated\ Mean\ \ QTc\left(C\right)=\theta_{1,Est}+\theta_{2,Est}*C\ \ \ \nonumber \\
\end{equation}Formula (7)
\begin{equation}
Estimated\ SE=\sqrt{\text{var}\left(\theta_{1,Est}\right)+C^{2}*var\left(\theta_{2,Est}\right)+2C*\left[\text{cov}\left(\theta_{1,Est}\theta_{2,Est}\right)\right]}\nonumber \\
\end{equation}Formula (8)
\begin{equation}
90\%\ CI=Estmated\ Mean\ QTc\left(C\right)\pm t\times Estmated\ SE\nonumber \\
\end{equation}Formula (9)
θ1,Est and θ2,Est are the intercept and
slope estimated by the model, respectively; var(θ1,Est)
and var(θ2,Est) are the inter-individual variances
estimated by the model; t is the boundary value at the corresponding
significance level. In this study, the two-sided 90% CI was calculated
and the t value was 1.645.
When using a custom model, Δ Δ QTcF group typical values under certain
concentration are the value after the deduction of the baseline and time
effect of the model. The two-sided 90% prediction interval (PI)
calculation method used nonparametric Bootstrap resampling the parameter
to calculate Δ Δ QTcF, 5th, 95thpoints digits was used as the Bootstrap 90% CI.
When the preset model were used, the 90% CI of Δ Δ QTcF calculated by
Bootstrap method were also used as auxiliary.
Model evaluation method
Goodness of Fit (GOF) was used to evaluate the skew or deviation
(prediction errors) of the final model. Bootstrap method was used to
verify the accuracy of the model. That is, 1000 new data sets are
obtained by sampling the original data 1000 times, and the model
parameters of each data set are calculated. The nonparametric
statistical method is used to estimate the parameter points (median) and
their 95% PI, that is, 2.5 and 97.5 quantiles of 1000 results.
Results
Study population
All of the 60 (30 female and 30 male) and 23 (11 female and 12 male)
healthy volunteers in each study group completed the treatment phases.
The average age of each study group ranged from 28.8 to 33.5 years. Mean
age and BMI were similar in male and female participants. A summary of
the demographic characteristics of the subjects is presented in Table 1.
Safety and PK analysis following ascending single and
multiple oral doses
In the SAD study, the mean plasma concentrations of ITKL of the 48
healthy subjects after oral single dosage of 5mg, 10mg, 15mg and 20mg
are presented in Figure 1a. The mean ITKL plasma concentration-time
profiles over the 36-hour sampling time are presented. The PK profiles
for all doses of ITKL under the fasted condition were characterized by a
rapid absorption phase. The median Tmax ranged from
0.75h to 1.50h. The median terminal elimination half-life
(t1/2z) was similar at each dose level, ranging from
6.66h to 8.03h. Analysis of AEs in the study showed there were 13 cases
(21.7%) and 14 times of AE occurrence in all groups. There were 3 cases
(25.0%) 3 times in 5mg group, 1 case (8.3%) 1 time in 10mg group, 4
cases (33.3%) 5 times in 15mg group, 3 cases (25.0%) 4 times in 20mg
group, and 2 cases (16.7%) 2 times in the placebo group. The incidence
of AEs was not dose-dependent. All groups showed level Ⅰ AEs.
In the MAD study, the mean plasma concentrations of ITKL of 23 healthy
adults after oral multiple dosage of 10mg and 20mg are presented in
Figure 1b. The median Tmax ranged from 1.25h to 1.50h.
The t1/2z was similar at each dose level, ranging from
7.01h to 7.91h. Among the AEs, 1 case in the 20mg group were lost to
follow-up, and subject No. 607 in 10mg group was judged as level Ⅱ AEs
due to constipation and was treated with Enema Glycerin. Subject No. 711
was judged as level Ⅱ AEs and treated with oral ammonium chloride
Glycyrrhiza solution due to cough. The rest were level Ⅰ AEs, but they
were not related to the study drug. Except for one case which were lost
to follow-up, the rest were all in remission and no SAEs and AEs leading
to withdrawal from the study occurred.
ΔΔQTcF and Cmax data of SAD and MAD
Descriptive statistics Cmax andΔΔQTcF by timepoint are
presented in Table 2.
- ER analysis
- Model analysis
The drug plasma concentration data and QTc data of 83 patients with
single and continuous administration were combined for model
construction. A C-QTc model was established with the plasma
concentration as the independent variable and Δ QTcF as the dependent
variable. When a research hypothesis is established, the preset linear
model is preferred to describe the relationship between plasma
concentration and Δ QTcF (Table3): Hypothesis 1: since the ΔΔ HR of
subjects after administration is within ± 10 bpm as shown in Figure 2a,
it is judged that the drug has no effect on the HR of subjects;
Hypothesis 2: there was no significant correlation between QTcF and HR,
as shown in Figure 2b; Hypothesis 3: the Tmax of drug
plasma concentration and Δ QTcF in 10mg, 15mg and 20mg groups were all
less than 1 hour, as shown in Figure 2d. The Tmax of Δ
QTcF in both 5mg and placebo groups was 6 hours, but the
Tmax of drug plasma concentration of 5mg group was 1
hour.
The facts that the drug plasma concentrations of the 5mg group did not
change much between 1h to 6h and the Tmax of Δ QTcF of
the 5mg group and placebo group were the same suggested that the delay
between plasma concentration of 5mg and Δ QTcF may be caused by non-drug
factors. Therefore, there is no delay in judging the change of blood
concentration and Δ QTcF; Hypothesis 4: there is linear relationship
between plasma concentration and Δ QTcF, as shown in Figure 2c;
Hypothesis 5: the drug plasma concentrations of the single and multiple
administration groups showed high consistence, because the same protocol
and plasma analysis procedures were applied. Therefore, single and
multiple administration studies can be combined for analysis.
Based on these data review, it is concluded that this study meets the
five research hypotheses in Table 3, and can be analyzed using a preset
linear model (Formula 3).
Model evaluation
The predicted mean ΔΔQTcF at the observed geometric mean
Cmax of the low dose of 5 mg group and the high dose of
20 mg group were calculated (Table 4). The two-sided 90% CIs of the
estimate were calculated using a bias-corrected nonparametric Bootstrap
1,000 resampling and subject is the unit of resampling. Table 5 lists
the final model parameters. The success rate of fitting minimization was
97.6%. The median and 95% PI of Bootstrap basically is coincide with
the parameter estimation and 95% CI, and the model shows high accuracy.
The GOF diagram of the final model is shown in Figure 2e. The regression
trend line almost coincides with the standard line, and the conditional
weight residual (CWRES) values are distributed between ±4 and uniformly
distributed on both sides of the coordinate axis.
Endpoint analysis
ΔQTcF variation over time is shown in Figure 3a. The specific changes of
ΔΔQTcF over time after merging single and multiple dosing data are shown
in Figure
3b.
It is concluded that ITKL would have no effect on QTc intervals, if the
upper bound of the two-sided 90% CI for predicted ΔΔQTcF at the
geometric mean Cmax of the high dose (20mg) group was no
more than 10 ms according to preset modeling. The drug ITKL would have
an effect on QTc intervals, if the upper bound of the two-side 90% CI
for predicted ΔΔQTcF at the geometric mean Cmax of the
low dose (5mg) grou was more than 10 ms according to preset modeling.
The ΔΔQTcF at the Cmax geometric mean of each dose group
and its two-sided 90% CI are calculated using the model formula. The
results are shown in Table 2, Figure 3c and 3d. The upper limit of 90%
CI of ΔΔQTcF in each dose group was less than 10 ms, indicating negative
QT interval prolongation.
Discussion
Single
dose PK and general safety profiles of ITKL have been studied in a
previous phase I clinical trials[8]. Unlike
previous studies, we included more healthy subjects (60) and added a
15mg dose group in this single dose study. Moreover, a multiple dose
study with 23 subjects was also performed. ITKL showed linear PK
characteristics in the dose range of 5mg ~ 20mg in
Chinese healthy subjects. ITKL was eliminated from the body mainly
through urine excretion. There was no significant difference between
male and female in single dose exposures of 5mg and 10mg, and there was
a slight difference between men and women in single dose exposures of
15mg and 20mg. Multiple dosing study indicated continuous oral
administration of ITKL tablets 10mg or 20mg basically had no
accumulation effect. The incidence of AEs in both groups was high, but
they were mild transient reactions, such as conjunctival congestion,
decreased blood pressure, dizziness and so on, which may be related to
the therapeutic mechanism of vasodilation by ITKL. There were no SAEs
and AEs that led to withdrawal. Continuous oral administration of ITKL
10mg or 20mg was safe and well tolerated.
The effect of drugs on QT interval is often directly related to the drug
plasma concentration.
ER analysis has enabled definitive evaluation of a drug’s potential
cardiotoxicity in standard clinical pharmacology studies, such as the
first-in-human study, in which many small groups of subjects are given
single-ascending or multiple doses of the new chemical entity. Its
application in the evaluation of cardiac safety of specific drugs is
constantly affirmed[9], and it is more efficient
compared with conducting a stand-alone TQT study, as defined in the
previous ICH E14[10]. An assessment of the effects
of Asenapine on QTc interval in patients with schizophrenia revealed a
discrepancy between the results obtained by the intersection-union test:
the intersection-union test can produce biased estimates resulting in a
high false-positive rate in individual TQT studies. In such cases,
simulation with an ER model can aid the reconciliation of the results
from intersection-union test and this may be used to support the use of
ER results as a basis for labeling[11]. On the
other hand,recent studies have shown that the rate of false-negative
results of ER model was acceptably low in placebo-controlled studies,
especially for drugs with no or small QT effect, high plasma
concentrations, and well-controlled variability of QT
data[10].
According to the white paper[7] recommendations,
this study meets all the applicability conditions of C-QT test exemption
from traditional TQT research as described in the C-QT white paper which
were showed as following: 1) According to the pre-clinical data of phase
III, the clinical recommended dose of ITKL is 10mg. The dose of 20mg in
this trial group is twice of the clinical related exposure, which can
ensure a low false-negative rate; 2) The QTc of ECG in this experiment
was measured manually and interpreted by the technician of ECG room in a
blind way. Before the interpretation, detailed SOP and corresponding
training were carried out. The whole process was controlled by two
person interpretation, and the interpretation result was reliable; 3) 83
healthy subjects were enrolled in the study, 60 cases of SAD were
enrolled in the study, and they were divided into 4 dose groups
(including 12 placebo) in the range of 5mg ~ 20mg, each
group was half male and half female; 23 cases of MAD were enrolled in
the study, including 12 cases in the 10mg group (half male and half
female), 11 cases in the 20mg group (6 male and 5 female), the sample
size met the requirements; 4) For model analysis, the planned blood
sample and ECG collection time shall prevail, When the difference
between the actual time and the planned time is within ±5min, the
difference is within the range allowed by the time window, and the
planned time is used to calculate. In this study, no data beyond the
time window is found, which meets this condition; 5) After
administration, Δ Δ HR was within ± 10 bpm, which met this condition. So
traditional TQT research can be exempted to assess the impact of drugs
on QT
interval.
Thus, this study was conducted to demonstrate whether ITKL can affect QT
intervals using ER analysis to assess the relationship between drug
concentration and QTc. The results showed that the highest dose (20mg)
of ITKL did not cause QT prolongation with a predicted ΔΔQTcF effect of
1.67 milliseconds under geometric Cmax, meeting the
criteria for negative QT assessment. Using the results from ER analysis,
the drug effect on ΔΔQTcF associated with this concentration was
expected to be relatively small. But there are some issues we should
consider before we make conclusion showed in Table 2: first, there was
hysteresis between concentration and ΔQTcF in group 5 mg; secondly, we
are worried about the QC of ECG reading. About the first point, although
the difference value of Tmax of plasma concentration and ΔQTcF was 5h,
As we discussed above, we thought it was caused by non-pharmaceutical
factors considering both of Tmax of ΔQTcF in group 5 mg and placebo were
6h; about the second point, ECG was read by two electro cardiographers,
all ECG of one subject should be read in a blind method by one electro
cardiographer, and the other one re-checks. To evaluate the consistency,
two electro caidiographers was required to read 50 pieces of ECG before
reading ECG of subjects. In summary, as we discussed with sponsor, we
reached a consensus that the issues as mentioned above would not affect
the result of the trial, so our conclusion is relatively reliable, that
is, there was no substantial effect on QTcF prolongation observed
following ITKL treatment through the dose range of 5mg, 10mg, 15mg and
20mg.
ITKL is a more potent activator of the SUR2B/Kir6.1 subtype of KATP
channels, this selectivity is not seen in other K-channel openers such
as diazoxide or pinacidil[2]. KATP channels are
ubiquitously expressed on the plasma membrane of cells in multiple
organs, including the heart, pancreas and
brain[12]. The molecular structure of KATP
channels is thought to be a heteromultimeric (tetrameric) assembly of
these complexes: Kir6.2 with SUR1 (SUR1/Kir6.2, pancreatic type), Kir6.2
with SUR2A (SUR2A/ Kir6.2, cardiac type), and Kir6.1 with SUR2B
(SUR2B/Kir6.1, Vascular smooth muscle type) [i.e., (SUR/Kir6.x)
4][13]. Diverse classes of KATP channels exist
in different tissues and cell types. For example, sarcolemmal KATP
channels in conduction system, smooth muscle and endothelium have the
same pore-forming subunit (Kir6.1) and regulatory subunit
(SUR2B)[14]. Iptakalim is a KATP channel opener
with a unique chemical structure that differs from other KATP openers.
Among the 3 different subtypes of KATP channels, Iptakalim exhibits
significant selectivity for SUR2B/Kir6.1 channels (being absent in the
atrium and ventricles), mild effects on SUR2A/Kir6.2 channels (existing
in the atrium and ventricle), and fails to open SUR1/Kir6.2 channels
(existing in the atrium). Therefore, Iptakalim has relatively little
effect on atrium and ventricle. in vitro experiments showed that
Iptakalim could selectively regulate gene expression in important
organs, heart, brain and liver of rats, and repeated administration of
ITKL did not lead to pharmacological changes of the heart, and no
pathological changes were found in myocardial tissue and its
ultrastructure[15]. The clinical trial with
hypertension patients also showed that ITKL had significant
antihypertensive effect, but no significant effect on QT interval
dispersion[16], which is consistent with our
findings.
However, in another experimental system, it was showed that Iptakalim
had an effect on the isolated heart of spontaneously hypertensive rats:
1μmol/L showed simple HR acceleration, 10μmol/L showed positive
frequency and negative inotropic effect, 100μmol/L showed simple
negative inotropic effect[17], this experimental
effect in vitro may be related to the wild direct effect on SUR2A/Kir6.2
in high concentration Iptakalim environment. The effect on the heart of
patients with hypertension under the normal concentration of Iptakalim
administration remains to be researched. And orther preclinical
experiments showed that ITKL exhibits selective effects on cardiac
function and hemodynamics in rats, but this effect is not obvious under
normal blood pressure[18]. It is not clear whether
this selectivity would be reflected in the AEs of QT interval
prolongation until now. Therefore, we can only conclude that the
therapeutic dose of ITKL has little effect on the cardiac QT interval of
healthy adults, and its cardiotoxicity in patients with hypertension
needs to be further explored.
Conclusion
In healthy people, ITKL appears safe when administered orally via single
dose and multiple dose, and continuous oral administration of ITKL
tablets 10mg or 20mg exhibited no accumulation effect. We used ER
analysis to assess potential QT prolongation by ITKL. The upper bounds
of the 90% CI of the model-predicted ΔΔQTcF effect at
Cmax in all dose groups were below 10 ms, suggesting
that ITKL did not prolong QT interval.
Declarations