The acute and subchronic toxicity of BRB-I-28, a novel class Ib antiarrhythmic agent, in CD-1 mice.

The acute and subchronic toxic effects of BRB-I-28 (7-benzyl-3-thia-7-azabicyclo[3.3.1]nonane HCl), a novel class Ib antiarrhythmic agent, were investigated in male and female mice. The estimated oral LD(50) for BRB-I-28 was 128 mg/kg (male mice) and 131 mg/kg (female mice). In subchronic oral studies, four groups of mice (15/sex/group/dose) were fed daily with diets containing BRB-I-28 for 90 consecutive days. The equivalent daily doses were approximately 0, 16, 32, 76 (male) and 0, 18, 37, 89 mg/kg (female). All mice survived. Food consumption per day was decreased, but water consumption per day was increased (in a non-dose-dependent manner). However, both mean body weight and mean body weight gain were not significantly changed as were true for hematological and clinical chemistry profiles, except for serum Na(+) concentration (male) and serum K(+) concentration in male and female mice (high dose levels). Hepatocellular necrosis occurred in male and female mice (in a dose-dependent fashion). Renal cortical vacuoles and myocardial necrosis with low numbers of lymphocytic infiltrations were present in female mice (middle and high doses). Lesions in the liver, kidney and heart were mild with (very small) changes in serum biochemical values. These data suggest that BRB-I-28 has limited toxic potential, and coupled with low proarrhythmic and other desirable cardiovascular effects, makes BRB-I-28 worthy of further development.

Preliminary acute and subchronic toxicity studies of GLG-V-13, a novel class III antiarrhythmic agent, in mice.

The acute and subchronic toxic effects of GLG-V-13 (3-[4-(1H-imidazol-1-yl)benzoyl]-7-isopropyl-3,7-diazabicyclo[3.3.1]nona ne dihydroperchlorate, CAS 155029-33-7), a novel class III with some class Ib antiarrhythmic activity, were investigated in mice. The estimated LD50 for GLG-V-13 given orally were 419 mg/kg for male mice and 383 mg/kg for female mice, respectively. The acute toxic signs appeared to be of the central nervous system in origin. Four groups of mice (15 per sex, group and dose) were fed daily with diets containing GLG-V-13 for 90 consecutive days. The equivalent daily doses were 0, 22, 50 and 121 mg/kg/day and 0, 27, 60 and 136 mg/kg/day for male and female mice, respectively. All of the mice survived. Food consumption was decreased. However, mean body weight and body weight gain were not significantly changed. Gross pathological changes, especially in the lungs and liver, were found in the middle and high dose groups. Consistent increased mean corpuscular hemoglobin concentration and decreased mean corpuscular hemoglobin were observed in all dose groups. Hepatocellular necrosis was found in both male and female mice treated with the drug and was dose-dependent. Marked vacuolation of the X zone in the adrenal gland with mild to moderate deposition of ceroid pigments (brown degeneration) was observed in female mice. Lesions in the kidneys and adrenal glands may be a possible reason for changes in serum sodium and potassium ions concentrations leading to an increase in water intake. A significant reduction in cholesterol in the high dose group may be a favorable pharmacological effect of GLG-V-13. The data from the 90-day subchronic toxicity studies indicate that GLG-V-13 appears to have limited systemic toxicity potential.

Class III electrophysiologic actions of imidazole-substituted diheterabicyclononanes in canine myocardium.

The electrophysiologic effects of the imidazole-substituted diheterabicyclo[3.3.1]nonane compounds GLG-V-13 and KMC-IV-84 were evaluated in canine ventricular tissues using intracellular and extracellular recordings. The drugs produced a concentration-dependent prolongation of action potential duration at 90% of repolarization in Purkinje (338 +/- 26 to 611 +/- 43 msec, 10 mg/l GLG-V-13; 328 +/- 17 to 468 +/- 18 msec, 10 mg/l KMC-IV-84), in right ventricular subendocardium (260 +/- 18 to 335 +/- 18 msec, 10 mg/l GLG-V-13; 221 +/- 9 to 264 +/- 13 msec, 10 mg/l KMC-IV-84) and in left ventricular epicardium (195 +/- 13 to 256 +/- 18 msec, 10 mg/l GLG-V-13; 203 +/- 11 to 273 +/- 26 msec, 10 mg/l KMC-IV-84) without altering resting membrane potential, action potential amplitude, overshoot potential, Vmax, conduction velocity or Purkinje fiber automaticity. Prolongation of the effective refractory period was proportional to the change in action potential duration at 90% of repolarization. Prolongation of action potential duration at 90% of repolarization was maximal at paced cycle lengths exceeding 1000 msec and was minimal at a paced cycle length of 250 msec (Purkinje: 266 +/- 20 vs. 6 +/- 8 msec, GLG-V-13; 178 +/- 12 vs. 10 +/- 10 msec, KMC-IV-84. Right ventricular subendocardium: 70 +/- 12 vs. 10 +/- 2 msec, GLG-V-13; 60 +/- 8 vs. 19 +/- 6 msec. Left ventricular epicardium: 67 +/- 13 vs. 10 +/- 5 msec, GLG-V-13; 68 +/- 12 vs. 16 +/- 8 msec, KMC-IV-84). An increase in K+(o) to 12 mM reduced action potential prolongation by GLG-V-13 and KMC-IV-84 in left ventricular epicardium. The results demonstrate selective class III electrophysiologic properties for imidazole-substituted diheterabicyclo[3.3.1]nonane compounds.

Electrophysiological and inotropic characterization of a novel class III antiarrhythmic agent, GLG-V-13, in the mammalian heart.

GLG-V-13, a novel 3,7-diheterabicyclo(3.3.1)nonane, was examined both in vivo and in vitro to characterize its electrophysiological, hemodynamic, and inotropic properties. In anesthetized guinea pigs, GLG-V-13 [0.5-500 micrograms/kg intravenously (i.v.), n = 6] lengthened the epicardial monophasic action potential (MAP) duration, the atrioventricular (AV) conduction time and the RR interval in a dose-dependent manner. At the highest dose, these variables were increased by 30, 13, and 23%, respectively. No significant effects were noted on QRS duration or blood pressure (BP). In rabbit atrial and papillary muscle preparations, GLG-V-13 (0.32-3.2 mg/L) did not exert a negative inotropic action and in isolated rabbit cardiomyocytes the agent blocked the rapidly activating delayed rectifier K+ current (IKr, EC50 = 48 micrograms/L). In 10 intact anesthetized mongrel dogs, the left ventricular (LV) endocardial MAP was measured during atrial pacing before and after administration of GLG-V-13 (3 and 6 mg/kg i.v.). As compared with the drug-free state, the agent induced a significant prolongation of the MAP at all pacing frequencies (2.0-4.5 Hz). In 15 anesthetized dogs studied 1-4 days after two-stage ligation of the left anterior descending coronary artery (LAD), the antiarrhythmic/proarrhythmic potential of GLG-V-13 was compared with that of lidocaine. ECG, His bundle, LV (IZepi), and composite and normal zone composite electrograms were recorded. Programmed electrical stimulation (PES) and burst pacing (4.0-7.0 Hz) were delivered to the right ventricular outflow tract. In the drug-free state, sustained monomorphic ventricular tachycardia (SMVT) was inducible in 6 dogs (6 of 15). After lidocaine, SMVT was induced in 7 other dogs (13 of 15). GLG-V-13 prevented induction of SMVT in 5 of 6 dogs; a proarrhythmic action was noted in 1 dog only. GLG-V-13 slowed the heart rate (HR), increased the AH and the HV intervals, prolonged the paced (2.5 Hz) QT interval, and increased the ventricular effective refractory period (VERP). These effects were associated with 2:1 block of late potentials in the IZepi electrograms, a phenomenon also observed during rapid atrial pacing (2.5-3.5 Hz), suggestive of a marked prolongation of refractoriness in the ischemically damaged myocardium. In light of the recent Cardiac Arrhythmia Suppression Trial (CAST) study, the antiarrhythmic efficacy, together with the low proarrhythmic potential and lack of cardiodepressant properties of GLG-V-13, may merit further investigation of this novel class III antiarrhythmic agent.

Novel 3,7-diheterabicyclo[3.3.1]nonanes that possess predominant class III antiarrhythmic activity in 1-4 day post infarction dog models: X-ray diffraction analysis of 3-[4-(1H-imidazol-1-yl)benzoyl]-7-isopropyl-3,7-diazabicyclo[3.3.1]nona ne dihydroperchlorate.

Several 3,7-diheterabicyclo[3.3.1]nonanes (DHBCNs) were prepared and screened in the Harris dog model for their ability to abolish pace-induced and sustained ventricular tachycardia (SVT) or prevent induction of ventricular tachycardia. In addition, an electrophysiological examination was made in the infarcted hearts of each animal to determine if more than one class activity was present. The examples exhibited predominately class III antiarrhythmic activity via a prolongation of the ventricular effective refractory period (VERP) in the models, although there may well be an underlying class Ib action present as exemplified by the ability of several of the agents to slow conduction in the myocardial infarcted dog hearts. 3-[4-(1H-Imidazol-1-yl)benzoyl]-7-isopropyl-3,7-diazabicyclo[3.3.1]nonan e dihydroperchlorate displayed powerful class III activity in the model systems while several other DHBCNs exhibited various degrees of class III action. An X-ray diffraction analysis revealed that this compound has a 3,7-diazabicyclo[3.3.1]nonane bicyclic unit in a chair-chair conformation.

Pharmacokinetics and plasma protein binding of the new potent class III antiarrhythmic agent 3-[4-(1H-imidazol-1-yl)benzoyl]-7-isopropyl-3, 7-diazabicyclo[3.3.1]nonane dihydroperchlorate.

GLG-V-13 (3-[4-(1H-imidazol-1-yl)benzoyl]-7-isopropyl-3,7-diazabicyclo [3.3.1] nonane dihydroperchlorate, CAS 155029-33-7) has been shown to be a potent class III antiarrhythmic agent. The oral and intravenous pharmacokinetics and plasma protein binding of GLG-V-13 in dogs and in rabbits have now been investigated. Plasma GLG-V-13 concentration-time profiles, following an i.v. bolus dose of 6 mg/kg, were fitted to a 2-compartment model. The volume of distribution at steady state (Vd(ss)), the total systemic (ClB), and the elimination half-life (t1/2 beta) were 4.441 l/kg, 1.113 l/h/kg, and 2.485 h in dogs and 3.723 l/kg, 1.548 l/h/kg, and 1.401 h in rabbits. Following i.v. dosing, approximately 9.38% of the parent compound was excreted in dogs urine (0-72 h). Changes in plasma GLG-V-13 concentrations, after oral administration of GLG-V-13 (6 mg/kg), were best described by the 1-compartment pharmacokinetic model. The tmax and Cmax were 1.69 h, 0.54 mg/l in dogs and 1.44 h, 0.35 mg/l in rabbits. On oral administration, GLG-V-13 was moderately eliminated (t1/2kel' 1.867 h-1 in dogs and 3.961 h-1 in rabbits, respectively). Oral bioavailability was estimated to be 53.2% +/- 11.3% in dogs and 66.7% +/- 7.7% in rabbits. About 8.74% of the oral dose (6 mg/kg) was excreted via the dog urine (0-72 h). In vitro binding of GLG-V-13 to dog plasma protein was 29.4 +/- 9.90% (from 0.5 to 4 mg/l). Ex vivo binding of GLG-V-13 to dog plasma protein was 10.4 +/- 7.20%.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism and metabolite pharmacokinetics of BRB-I-28, a class Ib antiarrhythmic agent.

The metabolism of BRB-I-28 (7-benzyl-3-thia-7-azabicyclo[3.3.1]nonane), a novel class Ib antiarrhythmic agent, was characterized in vivo in dogs and rats and in vitro with rat liver microsomal preparations containing a NADPH-generating system. In dogs, rats and the in vitro hepatic microsomal oxidation system, BRB-I-28 was extensively metabolized to form 7-benzyl-3-thia-7-azabicyclo [3.3.1]nonane-3-oxide (I), a major metabolite. The metabolite I was produced via S-oxidation, presumably by the hepatic P-450 system. Formation of minor metabolite, 7-benzyl-3-thia-7-azabicyclo[3.3.1]nonane (II) via the oxidation of the benzylic site was also identified in rats. Following intravenous and oral administration of BRB-I-28 to dogs, the plasma concentration of major metabolite I could be test described by a 1-compartmental model. The plasma AUC of metabolite I was 20% (i.v.) and 179.4% (oral) of that of the parent BRB-I-28, respectively, suggesting that BRB-I-28 was metabolized significantly by the first pass effect following oral administration. Extensive metabolism of BRB-I-28 to form metabolites I and II, which have demonstrated much lower antiarrhythmic activities, further supports previously observed pharmacodynamic and pharmacokinetic findings.

Effects of novel antiarrhythmic agents, BRB-I-28 and its derivatives, on the heart mitochondrial respiratory chain and sarcoplasmic reticulum Ca(2+)-ATPase.

The effects of BRB-I-28 and its derivatives (GLG-V-13, SAZ-VII-22 and SAZ-VII-23), a novel group of antiarrhythmic agents, were investigated on the rat heart mitochondrial respiratory chain. The results indicate that BRB-I-28 and its derivatives have concentration-dependent inhibitory effects on NADH oxidase and NADH-CoQ reductase (complex I), but they have no significant effects on succinate oxidase, succinate dehydrogenase (complex II), CoQ-cytochrome c reductase (complex III), cytochrome c oxidase (complex IV), and NADH-K3Fe(CN)6 reductase. The site of inhibition of BRB-I-28 and its derivatives on the respiratory chain was localized between flavoprotein n (FPn) and CoQ, which is similar to the effect of rotenone and several other antiarrhythmic drugs such as amiodarone, propranolol, etc. BRB-I-28 and its derivatives also have significant inhibitory effects on mitochondrial ATPase activity as reported for other antiarrhythmic drugs such as amiodarone, propranolol, quinidine, and lidocaine. However, BRB-I-28 and its derivatives have no direct effects on sarcoplasmic reticulum Ca(2+)-ATPase activity. The inhibitory effects of BRB-I-28 and its derivatives on mitochondrial oxidative phosphorylation may result in the depletion of ATP. This effect, in combination with their effects on Na+,K(+)-ATPase, could possibly produce an increase in Ca2+ concentration in cytosol. This may be another mechanism by which these DHBCN derivatives produce an increase in systemic arterial blood pressure and contractile force of isolated cardiac muscle. On the other hand, inhibition on mitochondrial respiration may account for some of the potential toxic effects of these diheterabicyclo[3.3.1]nonane derivatives.

The comparative antiarrhythmic and proarrhythmic activity of a 3,7-diheterobicyclo[3.3.1]nonane, BRB-I-28, and lidocaine in the 1-4-day-old infarcted dog heart.

We compared the electrophysiological effects and quantified the antiarrhythmic/proarrhythmic potential of the 3,7-diheterobicyclo[3.3.1]nonane-derivative, BRB-I-28 and lidocaine in 15 consecutive postinfarction dogs. Electrophysiologic studies were performed in anesthetized animals, 1-4 days (mean +/- SE = 2.47 +/- 0.36) after the two-stage ligation of the left anterior descending coronary artery. Inducibility of sustained monomorphic ventricular tachycardia (SMVT) was compared in the pre-drug state, and after i.v. lidocaine (3 and 6 mg/kg) and BRB-I-28 (3 and 6 mg/kg) administration. During the control state, SMVT was inducible in 6/15 dogs (40%). After the administration of lidocaine, the rate of the inducible SMVT slowed (353 +/- 91 to 272 +/- 96 beat/min; p < 0.01), but due to the proarrhythmic action of the drug, SMVT became inducible in 13/15 dogs (87%). Sustained reentry was induced after 3 mg/kg lidocaine in 3 dogs and after 6 mg/kg in 4. The mean aortic blood pressure in these SMVTs was 36 +/- 8 mm Hg. After administration of BRB-I-28 (6 mg/kg) SMVT was not inducible in 2/6 and in 4 the SMVT rate was slowed (380 +/- 104 to 208 +/- 105 beat/min; p < 0.005) before termination in 3. In 2 dogs SMVT was induced after BRB-I-28 was given whereas they were non-inducible in the control state (proarrhythmic effect: 13%). Furthermore the hemodynamic state during the SMVTs was more stable after BRB-I-28 (mean aortic blood pressure = 65 +/- 7 mm Hg; post-BRB-I-28 vs post-lidocaine, p < 0.001). During sinus rhythm, lidocaine caused a transient lowering of the MBP (105 +/- 17 to 84 +/- 18 mm Hg; p < 0.001), whereas, BRB-I-28, induced a consistent but short-lasting pressor response (98 +/- 18 to 120 +/- 29 mm Hg; p < 0.001) after its bolus injection. The low proarrhythmic activity and the lack of a cardiodepressant action makes this new chemical class of antiarrhythmics worthy of further development.

High-performance liquid chromatographic determination of BRB-I-28, a novel antiarrhythmic agent, in dog plasma and urine.

A sensitive reversed-phase high-performance liquid chromatographic (HPLC) technique with ultraviolet detection has been developed to determine the concentration of BRB-I-28 (I), a novel antiarrhythmic agent, in dog plasma and urine. The mobile phase was acetonitrile-methanol-37.5 mM phosphate buffer, pH 6.8-triethylamine (50:50:75:0.1, v/v). The compound was extracted from dog plasma and urine with chloroform after alkalinization with sodium hydroxide. The extraction recovery was 83% from plasma and 84% from urine. Good linearity (r > 0.996) was observed throughout the ranges 0.1-12.0 micrograms/ml (plasma) and 0.1-8.0 micrograms/ml (urine). Intra- and inter-assay variabilities were less than 4%. The lower limit of quantitation was 0.08 microgram/ml in either plasma or urine. HPLC analysis of plasma and urine samples from a dog treated with I has demonstrated that the method was accurate and reproducible.

Effects of BRB-I-28, a novel antiarrhythmic agent, and its derivatives on cardiac Na+,K(+)-ATPase, Mg(2+)-ATPase activities and contractile force.

The effects of BRB-I-28, SAZ-VII-22 and SAZ-VII-23, a novel class of antiarrhythmic agents and other 3,7-diheterobicyclo[3.3.1]nonane (DHBCN) derivatives on guinea pig myocardial Na+,K(+)-ATPase and Mg(2+)-activated ATPase activities were investigated in comparison with those of tedisamil, lidocaine and ouabain. BRB-I-28, SAZ-VII-22, SAZ-VII-23, tedisamil and their derivatives produced concentration-dependent inhibition on both Na+,K(+)-ATPase and Mg(2+)-activated ATPase. Ouabain had no effect on the Mg(2+)-activated ATPase activity and GLG-IV-44 had no significant inhibition on Na+,K(+)-ATPase. Molar refractivity, retention time in reverse-phase HPLC, and partition coefficients were determined and the influence of these three parameters on the inhibitory effects of DHBCN on ATPase was examined. It seems that inhibitory effects of DHBCN derivatives on Na+,K(+)-ATPase and Mg(2+)-activated ATPase increase with an increase in lipophilicity, while hydrophilic groups of the drugs may not be important for interaction between drugs and ATPases. The effects of BRB-I-28 on contractile force development in rabbit atrial and papillary muscles were studied. At paced rates of 0.5 and 1.0 Hz in atrial muscle, BRB-I-28 produced an apparent positive inotropic effect in isolated rabbit atrial muscle, which is consistent with its inhibitory effects on Na+,K(+)-ATPase and Mg(2+)-ATPase activities. Inhibitory effects on myocardial Na+,K(+)-ATPase and Mg(2+)-activated ATPase activities may be the basis of some electrophysiological effects of antiarrhythmic properties of BRB-I-28, SAZ-VII-22, SAZ-VII-23, and tedisamil.