Herman J. Crowley

Pentadienyl carboxamide derivatives as antagonists of platelet activating factor

A series of N-[4-(3-pyridinyl)butyl]-5,5-disubstituted-pentadienamides was prepared and evaluated for PAF-antagonist activity. Compounds were assayed in vitro in a PAF-binding assay employing washed, whole dog platelets as the receptor source and in vivo after intravenous or oral administration for their ability to prevent PAF-induced bronchoconstriction in guinea pigs. Criteria required for good oral activity in the latter model include an (E,-E)-5-phenyl-2,4-pentadienamide, a second phenyl or a four- or five-carbon alkyl moiety in the 5-position of the diene, and an (R)-[1-alkyl-4-(3-pyridinyl)butyl] substituent on the carboxamide nitrogen atom. The alkyl substituent on this side chain can be methyl, ethyl, or cyclopropyl. Two members of this series, [R-(E)]-5,5-bis(4-methoxy-phenyl)-N- [1-methyl-4-(3-pyridinyl)butyl]- 2,4-pentadienamide (31) and [R-(E,E)]-5-(4-methoxyphenyl)-N-[1-methyl-4- (3-pyridinyl)butyl]-2,4-decadienamide (58), were selected for further pharmacological evaluation. Both were found to be substantially longer acting after oral administration than the corresponding S enantiomers in the guinea pig bronchoconstriction assay. A second in vivo model used to evaluate PAF antagonists determines the ability of test compounds to decrease the area of skin wheals induced by an intradermal injection of PAF. In this model, using both rats and guinea pigs, compounds 31 and 58 were found to be as active as the reference PAF antagonist 3-[4-(2-chlorophenyl)-9-methyl-6H- 1-(4-morpholinyl)-1-propanone (45).

Biological activities of a chemically synthesized form of leukotriene E4

A chemically synthesized form of leukotriene E4 (LTE4) has been studied for its ability to induce contractions in isolated guinea pig ilea, to induce vascular permeability changes in rat skin when injected intradermally, and to induce bronchoconstriction in guinea pigs after intravenous injection. The synthetic compound induced a contraction in the guinea pig ileum which was slower in developing than that induced by histamine but faster in developing than that induced by a crude preparation of SRS-A isolated from guinea pig lung. The compound was 70-fold more active than histamine on the guinea pig ileum (EC50 of 5 x 10(-9) and 3.5 x 10(-7) M, respectively). FPL 55712, a known SRS-A antagonist, exhibited the same potency in blocking the contractions elicited by the synthetic material as it did in blocking contractions produced by guinea pig SRS-A generated biologically (IC50 of 3.5 x 10(-8) M). The synthetic LTE4 induced a dose dependent increase in vascular permeability in the rat skin which was antagonized by the intravenous injection of FPL 55712 (ID50 of 1.2 mg/kg). The synthetic material was also a potent bronchoconstrictor in the guinea pig when injected intravenously. The bronchoconstriction, too, was antagonized by FPL 55712 when injected intravenously (ID50 of 0.2 mg/kg). In both the rat and guinea pig, FPL 55712 exhibited a short duration of action in vivo. The in vivo model systems discussed in this study, utilizing the synthetic form of LTE4 should be useful in the future evaluation of other SRS-A antagonists.

Regional Cyclic Nucleotide Phosphodiesterase Activity in Cat Central Nervous System: Effects of Benzodiazepines

Summary Cyclic AMP and cGMP phosphodiesterase activity was found in the supernatant fraction of 15 freshly dissected regions of the cat central nervous system. Highest activity was found in the cerebral cortex; lesser activity was observed in other regions of the CNS. Diazepam and medazepam HCl were as active as the known cAMP-PD inhibitors papaverine and dipyridamole in cat cortex, rat brain, and mouse neuroblastoma cells. The diazepam metabolites N-demethyldiazepam, N-methyloxazepam, and oxazepam showed less inhibition of PD than the parent compound. No evidence was found for a regionally specific biochemical action of the benzodiazepines involving intracellular cAMP or cGMP. We thank Dr. A. Blume, Roche Institute of Molecular Biology, for the neuroblastoma cells. We also thank Gloria Wiggan for the cGMP assay, and Frank Zabransky for the cat brain samples.

In vitro studies on the mechanism of action of a new antiallergic, Ro 21-7634.

The effects of Ro 21-7634 and disodium cromoglycate (cromoglycate) on the in vitro release of mediators of anaphylaxis from rat peritoneal cells and guinea pig lung tissue were compared. Ro 21-7634 was 25 fold more potent than cromoglycate as an inhibitor of antigen-induced histamine release from passively sensitized (IgE) rat peritoneal cells. Ro 21-7634 was also the more potent inhibitor of both compound 48/80- and concanavalin A-induced histamine release from rat peritoneal cells. The two drugs shared the common properties of producing the same maximal level of inhibition in each of the above releasing systems and exhibiting a time and concentration dependent loss of inhibitory activity when added to the cells prior to the releasing agent. Neither drug inhibited ionophore A23187- or ionophore X537A-induced histamine release from these cells. Ro 21-7634 inhibited antigen-induced (IgG1) histamine and SRS-A release from actively sensitized guinea pig lung fragments, whereas cromoglycate did not. The results indicate that Ro 21-7634 and cromoglycate act through a common mechanism to inhibit allergic mediator release and that Ro 21-7634 is the more potent inhibitor.

Analogs of arachidonic acid methylated at C-7 and C-10 as inhibitors of leukotriene biosynthesis

The syntheses and biological activity of (all Z)-7,7-dimethyl-5,8,11,14- eicosatetraenoic acid, (all Z)-7,7,-dimethyl-5,8,11-eicosatrienoic acid, (Z,Z)-7,7-dimethyl-5,8-eicosadienoic acid, (all Z)-10,10-dimethyl-5,8,11,14-eicosatetraenoic acid, (all Z)-10,10-dimethyl-5,8,11-eicosatrienoic acid, and rac.-(Z,Z)-15-hydroxy-7,7-dimethyl-5,8-eicosadienoic acid are described. These arachidonic acid analogs are all inhibitors of ionophore-induced SRS-A biosynthesis in rat peritoneal cells. Their mode of action may involve inhibition of phospholipase A2 rather than delta 5-lipoxygenase. These compounds failed to exhibit significant activity in an in vivo model designed to detect inhibitors of antigen-induced, leukotriene-mediated bronchoconstriction in sensitized guinea pigs.

Inhibition of platelet aggregation by papaverine-like drugs: Evidence for a novel mechanism of action

Abstract Trimethoquinol [6,7-dihydroxy-1-(3′,4′,5′-trimethoxybenzyl)-1,2,3,4-tetrahydroisoquinoline] (TMQ) was chosen as a model compound for studying inhibition of platelet aggregation in vitro , because of its β-adrenoceptor agonist properties and structural resemblance to the anti-aggregatory agent, papaverine. TMQ inhibited collagen-induced aggregation of human platelet-rich plasma (I 50 , 2 μM), the second wave of aggregation induced by 2.5 μM ADP (I 50 , 0.9 μM), and the second wave of aggregation induced by 45 μM epinephrine (I 50 , 2.5 μM). Collagen-induced aggregation of human washed platelets was inhibited by TMQ (I 50 , 1 μM). TMQ was a better inhibitor than aspirin and papaverine and had an inhibitory activity similar to indomethacin in all of the systems studied. TMQ retained inhibitory activity in the presence of both β-adrenoceptor antagonist: propranolol (50 μM), and α-adrenoceptor antagonist: phentolamine (2.5 μM). Platelet adenylate cyclase was not activated and neither cAMP nor cGMP-phosphodiesterase activities were inhibited by TMQ, PGF 2α , biosynthesis by aggregating platelets during the coagulation of blood obtained from rats pretreated with aspirin (10 mg/kg, p.o. ) or indomethacin (1 mg/kg, p.o. ) was inhibited. However, similar pretreatment with TMQ (100 mg.kg, p.o. ) and papaverine hydrochloride (100 mg/kg, p.o. ) had no effect. TMQ acted synergistically with the aggregation inhibitors: papaverine, aspirin, and PGE 1 . The in vitro inhibitory action of papaverine, aspirin, and TMQ was enhanced by increasing calcium concentration. These data indicate that the platelet anti-aggregation activity of TMQ, in contrast to its myocardial stimulating and bronchodilating mechanism, is independent of adrenergic activation. Cyclic AMP accumulation or prostaglandin biosynthesis also seem not to be involved in TMQ action. Therefore, it appears that TMQ may have a novel anti-aggregatory mechanism of action.

The effect of Ro 21-7634 on the antigen-induced production of bronchoconstrictive arachidonic acid metabolites in the guinea pig lung

Ro 21-7634 has previously been shown to inhibit histamine and SRS-A release from actively-sensitized guinea pig lung fragments upon antigen challenge. In the studies described herein, it was observed that Ro 21-7634 does not decrease SRS-A release but instead acts to inhibit the synthesis of this mediator. This was confirmed by studying SRS-A synthesisin vitro in rat peritoneal cells after challenge with ionophore A23187. In the peritoneal cell system, Ro 21-7634 exhibited an IC50 of 500 μM, in comparison with 5,8,11,14-eicosatetraynoic acid, phenidone and BW755C (IC50s of 2, 100, and 100 μM, respectively). When studied at 10−4 and 10−3M in perfused guinea pig lung, Ro 21-7634 inhibited antigen-induced thromboxane A2 production by 68 and 96%, respectively. In this system, antigen is believed to induce thromboxane A2 production through the release of histamine and SRS-A from lung tissue. These mediators then interact at receptor sites in the lung parenchyma to induce thromboxane A2 synthesis. Ro 21-7634 could thus be inhibiting thromboxane A2 production by preventing the release of histamine and synthesis of SRS-A in the perfused lung system. Such a mechanism is suggested by the fact that although Ro 21-7634 was effective in inhibiting antigen-induced thromboxane production, it was ineffective in inhibiting thromboxane A2 production induced in the guinea pig lung system by the direct perfusion of histamine or SRS-A through the lung.