Analysis of Onset Mechanisms of a Sphingosine 1-Phosphate Receptor Modulator Fingolimod-Induced Atrioventricular Conduction Block and QT-Interval Prolongation.

Fingolimod, a sphingosine 1-phosphate (S1P) receptor subtype 1, 3, 4 and 5 modulator, has been used for the treatment of patients with relapsing forms of multiple sclerosis, but atrioventricular conduction block and/or QT-interval prolongation have been reported in some patients after the first dose. In this study, we directly compared the electropharmacological profiles of fingolimod with those of siponimod, a modulator of sphingosine 1-phosphate receptor subtype 1 and 5, using in vivo guinea-pig model and in vitro human ether-a-go-go-related gene (hERG) assay to better understand the onset mechanisms of the clinically observed adverse events. Fingolimod (0.01 and 0.1mg/kg) or siponimod (0.001 and 0.01mg/kg) was intravenously infused over 10min to the halothane-anaesthetized guinea pigs (n=4), whereas the effects of fingolimod (1µmol/L) and siponimod (1µmol/L) on hERG current were examined (n=3). The high doses of fingolimod and siponimod induced atrioventricular conduction block, whereas the low dose of siponimod prolonged PR interval, which was not observed by that of fingolimod. The high dose of fingolimod prolonged QT interval, which was not observed by either dose of siponimod. Meanwhile, fingolimod significantly inhibited hERG current, which was not observed by siponimod. These results suggest that S1P receptor subtype 1 in the heart could be one of the candidates for fingolimod- and siponimod-induced atrioventricular conduction block since S1P receptor subtype 5 is localized at the brain, and that direct IKr inhibition may play a key role in fingolimod-induced QT-interval prolongation.

Facile synthesis and utilization of bis(o-phosphinophenyl)zinc as isolable PZnP-pincer ligands enabled by boron-zinc double transmetallation.

Bis(o-phosphinophenyl)zinc derivatives were successfully synthesized by the reaction of o-phosphinophenylboronates with dimethylzinc via boron-zinc double transmetallation. The transmetallation was significantly accelerated by the presence of the ortho PR2 substituent to give diarylzinc selectively. These organozinc compounds act as isolable phenylene-tethered PZnP-pincer ligands, affording PZnP-palladium and ruthenium complexes with a σ-accepting Zn-metalloligand.

[Pharmacological profile and clinical findings of palbociclib (IBRANCE® capsule 25†mg/125†mg)].

Palbociclib is the world's first cyclin dependent kinase (CDK) 4 and 6 inhibitor. It's believed that palbociclib stops the cell cycle progression by inhibiting the activity of the complex consisting of CDK 4/6 and cyclin D, and suppresses tumor growth. In preclinical study using nonclinical model, it was confirmed that most of the cell lines sensitive to palbociclib are estrogen receptor (ER) positive. In addition, it was suggested that the expression of retinoblastoma protein (Rb) is needed for palbociclib to show its antitumor effect. By the preclinical studies using ER positive human breast cancer cell lines in combination administration of palbociclib and anti-estrogen drugs, it was confirmed that the antitumor effect was enhanced as compared with single agent administration of each drug. Based on these findings, the clinical studies in which hormone receptor positive/human epidermal growth factor receptor 2 negative (HR+/HER2-) advanced or metastatic breast cancer were conducted in combination with endocrine therapy. The PALOMA-2 study showed that progression-free survival (PFS) was longer with palbociclib plus letrozole than with placebo plus letrozole in the initial treatment of postmenopausal women with ER+/HER2- advanced breast cancer. In the PALOMA-3 study, the combination of palbociclib and fulvestrant was associated with significant improvements in PFS compared with fulvestrant plus placebo in patients with metastatic breast cancer. The rate of dose reduction or interruption of dosing by adverse events is higher in palbociclib group compared with placebo group in both studies while the rate of discontinuation of treatment was comparable.

Methodological validation of an existing telemetry system for QT evaluation in conscious guinea pigs.

INTRODUCTION: Guinea pigs are suitable for in vivo QT assessment of newly discovered drugs at the pre-clinical stage because of the ease with which these animals can be handled, the lower amount of compound required for testing, and the similarity of the ion channels between the guinea pig heart and the human. Our purpose was to provide detailed methodological information on an existing telemetry recording system for use in evaluating QT interval prolongation in guinea pigs. METHODS: Hartley guinea pigs weighing 400-700 g were used to investigate the appropriate configuration of electrodes to record defined T-waves and the influence of the surgical implantation of a transmitter on the QT interval, as well as to determine the appropriate formula for QT correction. In addition, the validity of using telemetry-monitored guinea pigs was tested by using compounds with (positive references) or without (vehicles) a QT-prolonging effect. RESULTS: A lead with the negative pole placed between the scapulas and the positive pole positioned close to the sternum was found to be the most appropriate to obtain well-defined T-waves. The period for recovery from transmitter implantation was estimated to be at least 1 week. The best-fit formula for our telemetry guinea pig model was a modified Bazett's formula. QTc was prolonged significantly in guinea pigs given positive references, and the QTc was unaffected when the animals were given vehicles. DISCUSSION: We believe that the information provided herein will be a quite helpful guide for researchers to evaluate the QT interval reliably and reproducibly in this telemetry guinea pig model.

Effect of autonomic nervous function on QT interval in dogs.

The effects of drugs on the QT interval should be evaluated precisely in the early stages of drug development because QT prolongation can trigger the so-called torsades de pointes, a life-threatening polymorphic ventricular tachycardia. It has been reported that the QT interval is affected by autonomic nervous tone besides the heart rate. In this study, we investigated the direct effect of autonomic nervous tone on the QT interval using the parameters of heart rate variability in dogs, when the RR interval was constant (400 or 700 msec). Our results showed that the QT interval at the high HF (high vagal tone) or low LF/HF ratio (low sympathetic tone) was longer than that at the low HF (low vagal tone) or high LF/HF ratio (high sympathetic tone), when the RR intervals were constant, and that the effect of vagal tone on the QT interval might be somewhat stronger than that of the sympathetic tone. The present observations would support the idea that sympathetic as well as parasympathetic tone regulates QT interval and that QT interval may be controlled physiologically by myocardial autonomic nerves via and not via a sinus node. Therefore, a more precise correction formula of QT interval could be established using autonomic parameters other than RR interval (heart rate), while the QT interval is widely known to be dependent on the RR interval or heart rate.

Practical application of guinea pig telemetry system for QT evaluation.

The purpose of this study was to evaluate a telemetry system for examining QT evaluation in the conscious free-moving guinea pig using 10 reference compounds whose effects on human QT interval are well established: 8 positive references (bepridil, terfenadine, cisapride, haloperidol, pimozide, quinidine, E-4031 and thioridazine), and 2 negative references (propranolol and nifedipine). Pharmacokinetic experiments were also performed for the 8 positive references. Telemetry transmitters were implanted subcutaneously in male Hartley guinea pigs, and the RR and QT intervals were measured. All 8 positive references prolonged QTc (QTc = k x QT/RR(1/2)) 10% or more during the 60 min observation period. When the values of the QTc changes were plotted against the serum concentrations, the resulting curves exhibited an anticlockwise hysteresis loop for all 8 references. In guinea pigs treated with haloperidol, changes of the T-wave shape from positive to flat were observed. The 2 negative references did not prolong the QTc. These findings suggest that the present telemetry guinea pig model is useful for QT evaluation in the early stages of drug development, because of the small body size of guinea pigs and their action potential configuration, which is similar to that of humans.

Aging-related changes of QT and RR intervals in conscious guinea pigs.

INTRODUCTION: Although guinea pigs are suitable for in vivo QT assessment of newly discovered drugs at the pre-clinical stage because of the similarity of the ion channels between the guinea pig heart and the human, there is limited data available regarding the characteristics of QT interval in conscious guinea pigs. Aging is one of several factors which have been shown to affect the QT interval in humans and animals. In the present study, we examined the influence of age on QT and RR intervals in conscious guinea pigs. METHODS: Electrocardiograms were recorded from female Hartley guinea pigs at the age of 6 weeks (young; n=6) and 23 months (old; n=4) via a telemetry system. The QT and RR intervals were measured during daytime and nighttime, and following intravenous bolus injection of E-4031 (0.1 mg/kg) or terfenadine (4 mg/kg). Comparisons were made to determine group differences in: (1) the normal values of the QT and RR intervals, (2) the best-fit QT-correction formula, (3) the circadian rhythm of QT and RR intervals, and (4) drug effects on repolarization. RESULTS: The normal values of QT and RR intervals in the old group were significantly longer than those in the young group. The best-fit formula for correcting QT interval was a modified Bazett's formula for both young and old groups. The old group did not show the nocturnal variation of either QT or RR interval. Terfenadine caused significantly greater QTc prolongation in the old group compared to the young. DISCUSSION: Aging affects resting QT and RR intervals in conscious female guinea pigs, a factor which should be considered when examining the effects of compounds on cardiac repolarization. Also, the present study suggests a possibility that age can affect QTc prolongation induced by some IKr blockers.

Changes in hematology, biochemical values, and restraint ECG of rhesus monkeys (Macaca mulatta) following 6-month laboratory acclimation.

The aim of this study was to determine if 6-month acclimation would enable accurate evaluation of hematological, biochemical data, and ECG recorded under restraint for conscious rhesus monkeys of both sexes. Periodic evaluation of these parameters was made during the 6-month period of acclimation. The platelet count, alkaline phosphatase, glucose, and sodium levels significantly decreased, whereas creatinine increased, compared with pre-acclimation values. The heart rate was significantly reduced compared with pre-acclimation values. QT-RR relation followed the square root regression function, which means modification of Bazett's QTc formula can be applied even if the ECG is recorded under restraint. In conclusion, 6-month acclimation was effective for stabilizing the blood data and for allowing accurate evaluation of the ECG even under restraint. Current results show that an acclimation period at least 3 months may be necessary prior to using rhesus monkeys for chronic studies.

Accurate evaluation of QT interval in conscious rhesus monkeys (Macaca mulatta) by use of Holter ECG.

The aim of this study was to determine the best method to evaluate the QT interval with respect to the heart rate in rhesus monkeys. Rhesus monkeys (Macaca mulatta) are widely used in cardiovascular research, but the characteristics of QT-RR formulas as regards rhesus monkeys has not been sufficiently related. We analyzed the physiological QT-RR relation for practical evaluation of the QT interval in conscious rhesus monkeys by use of 24-h Holter ECG monitoring. As the QT interval varies with dependency on the RR interval, 14 QT regression functions were evaluated by use of about 50 pairs of QT-RR points per animal in 5 male rhesus monkeys. The accuracy of fit with the measured data was assessed according to the minimum Akaike information criterion. Among one-parameter linear regression functions, QT = a x (RR)(1/2), where "a" is the regression coefficient, gave the best fit, which was almost comparable to that of all multi-parameter regression functions. Our results also suggest that the QTc formula derived from the square root regression function is the most practical for evaluation of QT intervals in rhesus monkeys. In conclusion, concerning the heart rate of rhesus monkeys, we propose the modification of Bazett's formula (QTc = QT x (500)(1/2)/(RR)(1/2), where the dimension of RR and QT interval is milliseconds). We believe the information herein is quite useful for cardiovascular studies on rhesus monkeys.