Reduction of canine myocardial infarct size by CI-959, an inhibitor of inflammatory cell activation.

CI-959, a cell-activation inhibitor that prevents the formation of oxygen-derived free radicals by inflammatory cells, was studied to determine its effects on myocardial infarct size and subsequent scar formation in dogs. The left circumflex coronary artery was occluded for 90 min, followed by 6 h of reperfusion. Drug infusion was started 15 min before reperfusion at a loading dose of 8 mg/kg i.v., followed immediately by 2 mg/kg i.v. infused over 80 min. The infarct size, assessed by TTC staining techniques, was significantly reduced in 12 dogs treated with CI-959 (23.3 +/- 3.6% of the area at risk) when compared to 11 vehicle-treated animals (35.5 +/- 4% of the area at risk, p less than 0.05). This reduction in infarct size was not attributed to changes in regional myocardial blood flow, as measured by radioactive microspheres, or to a reduction in myocardial oxygen demand, as estimated by changes in the rate-pressure product. The scar thickness, measured after a 6-week recovery period in 9 animals treated with CI-959, was not significantly reduced in comparison with 11 controls. In vitro, CI-959 effectively inhibited oxygen free radical formation by canine neutrophils. The results of this study show that CI-959 significantly reduces the myocardial infarct size without causing scar thinning, which might lead to ventricular aneurysm, and suggests the most likely mechanism for its beneficial action is the prevention of formation of toxic oxygen radicals.

Quinapril: overview of preclinical data.

Quinapril hydrochloride, a new, orally active, nonpeptide, nonsulfhydryl angiotensin-converting enzyme (ACE) inhibitor, has been studied extensively in a variety of in vitro and in vivo animal models. Quinapril inhibits the contractile and pressor effects of angiotensin I in rabbit aorta and in rats, respectively, and lowers blood pressure in both high- and normal-renin rodent and diuretic-treated dog models of hypertension. No tolerance to the antihypertensive effects of quinapril was noted in spontaneously hypertensive rats treated with quinapril for up to 14 consecutive days. As with other ACE inhibitors, quinapril had virtually no effect on the development of hypertension in the renin-independent one-kidney deoxycorticosterone (DOCA)-salt hypertensive rat. Antihypertensive activity best correlates with the inhibition of tissue (vascular) ACE, and thus the reduction in peripheral vascular resistance associated with plasma and tissue ACE most likely accounts for the therapeutic benefit of quinapril. Preliminary data from a trial of quinapril in cardiomyopathic hamsters show that the drug prevents the anticipated decline in left ventricular contractile function and retards the temporal progression of left ventricular failure. ACE inhibitors have been found to have a lipid-neutral profile, unlike some other classes of antihypertensives. Quinapril is rapidly absorbed and extensively distributed to all tissues except brain. It is rapidly hydrolyzed to quinaprilat, its pharmacologically active diacid form. Metabolism to other compounds is not extensive. Quinapril's preclinical toxicologic profile is similar to that of other ACE inhibitors. Long-term toxicology studies show that quinapril is not teratogenic, carcinogenic, or mutagenic.

Quinapril--a preclinical review of the pharmacology, pharmacokinetics, and toxicology.

Quinapril is an orally active, non-peptide, nonsulfhydryl angiotensin-converting enzyme (ACE) inhibitor that acts potently and specifically to interrupt the conversion of angiotensin I to angiotensin II in both plasma and tissue. Quinapril is enzymatically hydrolyzed to a pharmacologically active diacid form quinaprilat. Quinapril is efficacious in hypertensive models exhibiting both high (renal hypertensive rats, diuretic-treated dogs) and normal (spontaneously hypertensive rats) plasma renin activity. Quinapril does not prevent the development of hypertension when plasma renin activity (PRA) is markedly suppressed as in the deoxycorticosterone-saline treated rat. Hemodynamic studies in dogs indicate that quinapril decreases total peripheral and renal vascular resistance. Quinaprilat produces natriuresis and mild diuresis at doses that do not alter mean arterial blood pressure. Quinapril has the potential to affect plasma lipids beneficially or at least be "lipid neutral." Oral absorption of quinapril is rapid in rats, dogs, and monkeys. There is rapid and extensive distribution of radiolabel to most tissues except brain. Plasma radiolabel concentration-time profiles exhibit polyexponential decay with a prolonged terminal phase at low concentrations in all species. Metabolism to compounds other than quinaprilat is not extensive. Quinapril is excreted primarily as quinaprilat and to a lesser degree as quinapril. Quinapril is well tolerated in a variety of pharmacologic safety screens and its toxicity profile is similar to that of other ACE inhibitors. Quinapril does not adversely affect reproduction; it is not teratogenic, carcinogenic, or mutagenic.(ABSTRACT TRUNCATED AT 250 WORDS)

Pirmenol: preclinical pharmacology.

Pirmenol, a novel pyridinemethanol derivative, is active in a variety of experimental arrhythmic models of diverse etiology. Animal pharmacology studies showed that pirmenol is highly efficacious whether the arrhythmias were atrial or ventricular in origin; chemically, mechanically, or electrically induced; or of the automaticity or reentrant types. The conscious coronary artery-ligated (Harris) dog model best allowed simulation of a variety of clinical situations in which pirmenol could be used either alone or in combination. Pirmenol was highly effective by both the intravenous and oral routes, causing immediate suppression, prevention, or termination of cardiac arrhythmias. Preclinical studies in the dog showed an excellent correlation between the dose of pirmenol, plasma levels, and antiarrhythmic efficacy. Administration of pirmenol in the dog at intentionally accelerated infusion rates suggested a relatively wide margin of safety for pirmenol compared with other class I agents. In vitro electrophysiologic studies in dog Purkinje fibers revealed possibly unique differences of pirmenol from other antiarrhythmic agents. It depresses fast and slow response automaticity and its electrophysiologic effects were less variable than other class I drugs over a spectrum of potassium levels. To test the relevance of the in vitro electrophysiologic results, pirmenol's antiarrhythmic efficacy was assessed in several in vivo dog models in which serum potassium was either increased or decreased. Studies comparing pirmenol and disopyramide clearly showed a relative lack of serum potassium dependence for pirmenol, suggesting a potential clinical advantage over disopyramide and other antiarrhythmics in variable potassium settings. The clinical relevance of these observations will have to be established in patients with variable potassium levels. Overall, pirmenol compared favorably with other reference agents in efficacy and safety in extensive preclinical investigations.

Subclasses of cyclic AMP-specific phosphodiesterase in left ventricular muscle and their involvement in regulating myocardial contractility.

Ventricular muscle contains a low Km, cyclic AMP-specific form of phosphodiesterase (PDE III), which is believed to represent the site of action for several of new cardiotonic agents including imazodan (CI-914), amrinone, cilostamide, and enoximone. However, species differences in the inotropic response to these agents have raised questions about the relationship between PDE III inhibition and cardiotonic activity. The present study demonstrates that these differences can be accounted for by the presence of two subclasses of PDE III in ventricular muscle and variations in the intracellular localization of these two enzymes. For these experiments, PDE III was initially isolated from canine, guinea pig, and rat left ventricular muscle. The results demonstrate that canine left ventricular muscle contains two functional subclasses of PDE III: an imazodan-sensitive form, which is membrane bound, and an imazodan-insensitive form, which is soluble. Although only weakly inhibited by imazodan, this latter enzyme is potently inhibited by the selective PDE III inhibitors, Ro 20-1724 and rolipram. Guinea pig ventricular muscle also contains the imazodan-sensitive subclass of PDE III. Unlike canine left ventricle, however, thi enzyme is soluble in the guinea pig. No membrane-bound subclass of PDE III was observed in the guinea pig. Rat left ventricle possesses only the soluble form of PDE III, which apparently represents a mixture of the imazodan-sensitive and imazodan-insensitive subclasses of PDE III. Measurement of in vivo contractility in these three species showed that imazodan exerts a potent positive inotropic effect only in the dog, in which the imazodan-sensitive subclass of PDE III is membrane bound.(ABSTRACT TRUNCATED AT 250 WORDS)

Subclasses of cyclic AMP phosphodiesterase in cardiac muscle.

Canine and guinea-pig left ventricular muscle contains multiple molecular forms of phosphodiesterase (PDE) which vary according to substrate specificity, stimulation by calmodulin and response to various selective and nonselective phosphodiesterase inhibitors. Both species possess a cyclic AMP-specific form of phosphodiesterase (PDE III). In the dog, both soluble and particulate forms of PDE III are present. The particulate form of PDE III is potently inhibited by cyclic GMP and the selective PDE III inhibitors imazodan (CI-914) and cilostamide, but is only weakly inhibited by the selective PDE III inhibitors Ro 20-1724 and rolipram. In contrast, the soluble form of PDE III in canine left ventricle is only weakly inhibited by cyclic GMP, imazodan and cilostamide, but is potently inhibited by Ro 20-1724 and rolipram. Guinea-pig left ventricle contains only one subclass of PDE III, which is potently inhibited by cyclic GMP, imazodan and cilostamide, but not by Ro 20-1724 or rolipram. However, whereas the imazodan-sensitive subclass of PDE III is a particulate enzyme in the canine left ventricle, in the guinea-pig this subclass of PDE III is a soluble enzyme. Both soluble and particulate PDE III's are (i) insensitive to calmodulin; (ii) possess comparable Km and Vmax values for hydrolysis of cyclic AMP; (iii) are equally inhibited by the nonselective PDE inhibitor theophylline, and (iv) are eluted from DEAE-cellulose anion-exchange resin by comparable concentrations of sodium acetate. The demonstration of distinct subclasses of the cyclic AMP-specific phosphodiesterase (PDE III) in canine left ventricular muscle associated with different domains of the cell suggests compartmentation of cyclic AMP. In addition, the observation that the imazodan-sensitive form of PDE III is a particulate enzyme in canine left ventricle and a soluble enzyme in guinea-pig left ventricle may explain the species differences which exist regarding the positive inotropic response to imazodan in these two species.

Preclinical pharmacology of pirmenol.

Pirmenol, a novel pyridinemethanol derivative, is active in a variety of experimental arrhythmic models of diverse etiology and has a favorable therapeutic index compared with other class I agents. Animal pharmacology studies showed that pirmenol is highly efficacious whether the arrhythmias were atrial or ventricular in origin, chemically, mechanically or electrically induced or of the automaticity or reentrant types. The conscious coronary artery-ligated (Harris) dog model best allowed simulation of a variety of clinical situations in which pirmenol could be used either alone or in combination. Pirmenol was highly effective by both the intravenous and oral routes, causing immediate suppression, prevention or termination of cardiac arrhythmias. Preclinical studies in the dog showed an excellent correlation between the dose of pirmenol, plasma levels and antiarrhythmic efficacy. Administration of pirmenol in the dog at intentionally accelerated infusion rates suggested a relatively wide margin of safety for pirmenol compared with other class I agents. Analysis of the pharmacokinetic data led to the modeling of a rapid infusion-slow infusion bolus for sustained intravenous administration, thereby optimizing therapeutic utility. In vitro electrophysiologic studies in dog Purkinje fibers revealed possibly unique differences of pirmenol from other antiarrhythmic agents. It depresses fast and slow response automaticity and its electrophysiologic effects were less variable than other class I drugs over a spectrum of potassium levels. To test the relevance of the in vitro electrophysiologic results, pirmenol's antiarrhythmic efficacy was assessed in several in vivo dog models in which serum potassium was either increased or decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacology of bevantolol hydrochloride.

Bevantolol is a cardioselective, beta-adrenoreceptor antagonist, devoid of intrinsic beta sympathomimetic activity and with weak membrane-stabilizing and local anesthetic properties. The 3,4-dimethoxyphenylethylamino moiety, substituted on the side chain amine function, confers cardioselectivity, which has been confirmed by a number of experiments. In vitro, bevantolol demonstrated greater antagonism of atrial than tracheal responses to isoproterenol. In vivo, bevantolol preferentially inhibited isoproterenol-induced tachycardias in conscious and anesthetized dogs, compared with the nonselective agent propranolol. Conversely, its effect on blood pressure after isoproterenol was minimal compared with propranolol, reflecting its muted effect on beta 2 peripheral receptors. A functional difference between bevantolol and propranolol was demonstrated in histamine-challenged guinea pigs. Bevantolol had little effect on the antiasthmatic effect of isoproterenol, whereas propranolol blocked it totally. Bevantolol's lack of intrinsic sympathomimetic activity was demonstrated in normal and reserpinized dogs, where it was devoid of intrinsic sympathomimetic activity at doses up to 10 mg/kg. Similarly, intravenous doses of 10 mg/kg had to be administered before direct myocardial depression occurred in the reserpinized animals. Metabolite 3, which is excreted in trace amounts in human urine, demonstrates intrinsic sympathomimetic activity when administered in pharmacologic doses to dogs; however, any clinical relevance remains to be established. Several laboratories have demonstrated that bevantolol interacts at alpha-adrenergic sites. These data require further investigation. The dose-related antihypertensive effect of bevantolol has been demonstrated in spontaneously hypertensive and 2 kidney, 1 clip renal hypertensive rats. Animal experiments also suggest that bevantolol may be useful in angina: It caused a favorable redistribution of blood flow in dogs in which the left circumflex artery had been stenosed.(ABSTRACT TRUNCATED AT 250 WORDS)

Bevantolol hydrochloride--preclinical pharmacologic profile.

Bevantolol hydrochloride, a beta adrenoceptor antagonist, can be categorized using conventional schemes as being cardioselective, devoid of intrinsic sympathomimetic activity and having weak membrane-stabilizing and local anesthetic properties. The cardioselectivity of bevantolol was conferred by the incorporation of a 3,4-dimethoxyphenyl moiety into the terminal amino portion of the molecule. This portion of the molecule also appears to account for bevantolol's in vitro binding affinity at alpha-adrenoceptor sites; the in vivo significance of which remains unclear. In the various cardiovascular disease-state models, bevantolol's profile differed from that of propranolol, i.e., there was no initial pressor response in spontaneously hypertensive or renal hypertensive rats. In a myocardial ischemia model, bevantolol, unlike propranolol, increased contractile function in the ischemic myocardium. A ring hydroxylated urinary metabolite, which occurred only in trace amounts in human urine, had an interesting profile when studied in animals at pharmacologic doses. It ranked high in cardioselectivity (like bevantolol), but unlike bevantolol showed significant intrinsic beta sympathomimetic activity. The clinical significance of this metabolite, if any, remains to be established. Collectively the preclinical profile of bevantolol showed it to have an interesting profile for a beta adrenoceptor antagonist in a variety of pharmacologic test systems.

Multiple molecular forms of phosphodiesterase and the regulation of cardiac muscle contractility.

Two approaches were taken to examine the role which the different forms of phosphodiesterase present in cardiac muscle play in regulating contractility. In an initial study, the effect of selective inhibitors of i) the calmodulin-stimulated phosphodiesterase (M & B 22, 948), ii) the cyclic GMP-stimulated phosphodiesterase (dipyridamole), and iii) the low Km, cyclic AMP-specific phosphodiesterase (imazodan) on the contractility of isolated guinea pig left atria was examined. Of the three selective phosphodiesterase inhibitors, only imazodan increased atrial contractility. In a subsequent study, the effect of imazodan on in vivo contractility was evaluated. Imazodan was found to potently increase contractility in the dog and the Rhesus monkey, while exerting only modest-to-minimal effects of contractility in the guinea pig and the hamster. Imazodan produced no positive inotropic effect in the rat. These species differences can apparently be attributed to i) the presence of subclasses of the low Km, cyclic AMP-specific phosphodiesterase (PDE III) in cardiac muscle, one of which is potently inhibited by the selective PDE III inhibitors imazodan, cyclic GMP and cilostamide, and the other which is selectively inhibited by rolipram and Ro 20-1724, and ii) variations in the intracellular localization of imazodan-sensitive subclass of PDE III. Thus, the maximum inotropic response to imazodan was observed only in those species in which the imazodan-sensitive subclass of PDE III was present and was membrane-bound, e.g., Rhesus monkey and dog. In the dog, the imazodan-insensitive subclass PDE III does not appear to play an important role in regulating cardiac contractility. These observations provide further support for the hypothesis that the inotropic response to imazodan, amrinone and related cardiotonics is due to their inhibitory effects on the cyclic AMP-specific form of phosphodiesterase, and also provides new insight into the relationship between cyclic AMP, phosphodiesterase and myocardial contractility.

Synthesis and biological activity of modified peptide inhibitors of angiotensin-converting enzyme.

A series of non-sulfhydryl modified dipeptides related to CI-906, CI-907, and enalapril was prepared in which various isosteric moieties (O, S, SO, SO2) have been substituted for the amino group and in which the proline residue has been replaced with various hydrophobic amino acids. The compounds were evaluated in vitro for inhibition of angiotensin-converting enzyme and in vivo for antihypertensive activity. Compound 7c, the most potent member of this series, had an in vitro IC50 of 1.4 X 10(-8) M and showed modest oral antihypertensive activity at 30 mg/kg in conscious, two kidney, one clip Goldblatt hypertensive rats. Structure-activity relationships are discussed.

Antihypertensive profile of the angiotensin-converting enzyme inhibitors CI-906 and CI-907.

CI-906 and CI-907, new orally active nonsulfhydryl angiotensin-converting enzyme inhibitors, were examined for antihypertensive effects in unanesthetized hypertensive rats and dogs. In two-kidney, one-clip Goldblatt hypertensive rats, single oral daily doses (0.03-30 mg/kg) produced dose-dependent decreases in blood pressure; a single 3 mg/kg oral dose lowered blood pressure to normotensive levels. In spontaneously hypertensive rats, 30 mg/(kg X day) orally administered for 5 consecutive days achieved the same blood pressure decrease as that obtained on the first day in the renal hypertensive rats. In diuretic-pretreated renal hypertensive dogs, a 10 mg/kg oral dose decreased blood pressure by 25%. No adverse side effects were observed with CI-906 and CI-907 in any of the conscious animals. These studies indicate that CI-906 and CI-907 are potent, orally active antihypertensive agents without any apparent limiting side effects.

CI-906 and CI-907: new orally active nonsulfhydryl angiotensin-converting enzyme inhibitors.

CI-906, [3S-[2[R*(R*)]], 3R*]-2-[2-[[1-(ethoxycarbonyl)-3-phenylpropyl]-amino]-1-oxopropyl] 1,2,3,4-tetrahydro-3-isoquinolinecarboxylic acid, monohydrochloride, and CI-907, [2S-[1[R*(R*)]], 2 alpha, 3a beta, 7a 7a beta]-1-[2-[[1-(ethoxycarbonyl)-3-phenylpropyl]amino] 1-oxopropyl]octahydro-1H-indole-2-carboxylic acid, monohydrochloride, are two new nonsulfhydryl-type angiotensin-converting enzyme (ACE) inhibitors. Monoester (prodrug) and diacid forms produced concentration-related ACE inhibition in guinea pig serum (IC50 for CI-906 = 8.3 X 10(-9) M, diacid = 2.8 X 10(-9) M; CI-907 = 1.0 X 10(-7) M, diacid = 2.6 X 10(-9) M). In isolated rabbit aortic rings and in in vivo rat and dog autonomic studies, both compounds were highly specific in suppressing the contractile or pressor responses to angiotensin I. In two-kidney, one-clip Goldblatt (renin-dependent) hypertensive rats there was a good correlation between the inhibition of vascular converting enzyme and blood pressure lowering and a poor correlation between blood pressure lowering and plasma and brain converting enzyme inhibition. Cardiovascular, pulmonary, and central nervous system performance evaluations showed no side effects or gross toxicity. The preclinical profile shows CI-906 and CI-907 to be specific, potent, orally active ACE inhibitors. They are expected to have therapeutic utility in hypertension and in any other condition where converting enzyme inhibition would be useful.

Antihypertensive effects of CI-907 (indolapril): a novel nonsulfhydryl angiotensin converting enzyme inhibitor.

CI-907 is a new orally active nonsulfhydryl angiotensin converting enzyme (ACE) inhibitor. Monoester (prodrug) and diacid forms produced concentration related ACE inhibition in guinea-pig serum (IC50 for monoester, 1.7 X 10(-7) M and for diacid, 2.6 X 10(-9) M). In isolated rabbit aortic rings and in rat and dog autonomic studies, CI-907 is highly specific in suppressing the contractile or pressor responses to angiotensin I. In two-kidney, one-clip Goldblatt hypertensive rats, single daily doses (0.03-30 mg/kg p.o.) produced dose-dependent decreases in blood pressure; 3 mg/kg lowered blood pressure to normotensive levels. In the spontaneously hypertensive rat, subacute administration of CI-907 (30 mg/kg/day for 5 days) produced the same decrease in blood pressure as that obtained in the renal hypertensive rat. In diuretic-pretreated renal hypertensive dogs, 10 mg/kg normalized blood pressure. For equivalent drops in blood pressure, heart rate increases were less in CI-907 than in enalapril-treated renal hypertensive dogs. No side effects were observed with CI-907 in any of the conscious animals. The antihypertensive response to CI-907 (0.03-1.0 mg/kg p.o.) was found to correlate with inhibition of vascular tissue ACE, but not plasma or brain ACE in two-kidney, one-clip renal hypertensive rats. These studies indicate that CI-907 is a potent antihypertensive agent with a heart rate profile different from enalapril.

The methylenedioxyindenes, a novel class of "intracellular calcium antagonists": effects on contractility and on processes involved in regulating intracellular calcium homeostasis.

The 2-substituted methylenedioxyindenes are a novel class of "calcium antagonists" which have been characterized as acting intracellularly. In the present study, the effect of 2-propyl-methylenedioxyindene (p-MDI) on the contractility of isolated rabbit papillary muscles and aortic rings as well as on several metabolic processes believed to be important in regulating calcium movement within the cell was examined. p-MDI was found to exert a dose-dependent negative inotropic effect in the range of 1.0 X 10(-5) to 1.0 X 10(-3) M (1.0 X 10(-3) M p-MDI produced a total cessation of contractility). At a concentration of 1.0 X 10(-4) M p-MDI, this depressant effect could be partially reversed by increasing the level of calcium in the tissue bath. p-MDI also relaxed aortic rings previously contracted with 50 mM KCl or 10 microM norepinephrine, although the concentration of p-MDI required to relax norepinephrine-contracted rings was 3 times greater than that required to relax KCl-contracted rings. Such selectivity was also observed when the effects of verapamil on norepinephrine- and KCl-contracted rings were examined, but was not observed with papaverine. To determine whether the effects of p-MDI on cardiac and vascular smooth muscle were due to direct interference with any of the metabolic processes which regulate intracellular calcium homeostasis, the effects of p-MDI on isolated cardiac sarcoplasmic reticulum and mitochondria and on the intracellular calcium-binding protein calmodulin were examined. At concentrations which depressed cardiac contractility, p-MDI had no effect on 1) calcium transport, uptake or ethyleneglycol bis(beta-aminoethyl ether)N,N,N',N'-tetraacetic acid-induced calcium release by sarcoplasmic reticulum, 2) calcium uptake by mitochondria or 3) calmodulin. p-MDI did, however, exert a biphasic effect of glutamate-supported mitochondrial respiration; stimulating oxygen consumption at concentrations of 1.0 X 10(-5) and 1.0 X 10(-4) M and inhibiting respiration at 1.0 X 10(-3) M. It is therefore concluded that p-MDI has no apparent direct effect on intracellular calcium movement per se and that the calcium antagonist effect of p-MDI may be due in part to calcium channel blockage. Inhibition of mitochondrial respiration may also contribute to the negative inotropic effect of high concentrations of p-MDI.

Antihypertensive activity of 6-arylpyrido[2,3-d]pyrimidin-7-amine derivatives. 2. 7-Acyl amide analogues.

The effect of acylation with a variety of acids on the antihypertensive activity of 6-(2,6-dichlorophenyl)pyrido[2,3-d]pyrimidine-7-amine (1) is reported, and structure-activity relationships are discussed. Although several of the compounds show good oral antihypertensive activity in the conscious, spontaneously hypertensive rat (SHR), their activity profile appears to differ from 1 in that the onset of action is shortened at comparable blood pressure lowering doses, and the magnitude of effect is considerably greater at higher doses. A variety of urea, thiourea, guanidine, and amidine analogues also were prepared. Although many of these derivatives showed some antihypertensive effects when dosed orally to SHR, this activity was weaker and of shorter duration than that obtained with 1. Aqueous solubilities and hydrolytic stabilities for four of the more active compounds were measured and suggest that these do not function as prodrugs of 1.