Comparison of cyclic and linear analogs of vasoactive intestinal peptide.

A series of i-->i + 4 side-chain to side-chain lactam analogs of vasoactive intestinal peptide has been prepared in order to study the effect of cyclization on biological activity. In vitro, on guinea pig tracheal smooth muscle and on human bronchial tissue, approximately half of the cyclic analogs showed increased potency and half were decreased over the linear analogs. Several cyclic compounds were between 10- and 20-fold more potent and one was 290-fold more potent than the linear species. In vivo, in guinea pigs, the cyclic compounds showed increased potency by up to 70-fold and significantly enhanced duration of action as compared to linear compounds.

Structure-activity studies on the vasoactive intestinal peptide pharmacophore. 1. Analogs of tyrosine.

From previous work, the primary functional groups, i.e. side chains, of the vasoactive intestinal peptide which are responsible for interaction with the VIP receptor have been identified. One of these sites, the side chain of tyrosine22 is essential for high receptor affinity. The present work aims to examine this site in greater detail. Several Boc-substituted-phenylalanine derivatives were prepared and incorporated into VIP analogs as replacement for tyrosine22. These analogs, of the form Ac-[Lys12,Nle17,X22,Val26,Thr28]-VIP, were assayed as smooth muscle relaxants and found to be full agonists of native VIP. Most of the analogs, however, proved to be less potent than the parent analog by up to 300-fold. A few analogs, all possessing electron-donating substituents, retained nearly full potency. Two compounds, 3-F,4-OH-Phe, 42 and 3-OCH3,4-OH-Phe, 43, were found to be 1.5- and 3.4-fold more potent than the parent compound, which equates to being 8.9- and 20-fold more potent than native VIP. Compound 43 was also found to be active as a bronchodilator in vivo in guinea pigs, with slightly over 2-fold enhanced potency and a significantly longer duration of action (> 20 min) when compared to the parent compound (5 min). The physical characteristics of the various substituents and their effect on biological activity are discussed with a brief analysis by QSAR techniques.

Essential fatty acids are antagonists of the leukotriene B4 receptor.

A series of essential fatty acids and fatty acid derivatives were evaluated for their ability to inhibit [3H] leukotriene B4 (LTB4) binding to pig neutrophil membranes. The fatty acids varied in chain length, extent of unsaturation, position of unsaturation, and isomerization. Generally, fatty acids with two or more unsaturated sites and chain lengths of 18-22 were potent inhibitors of [3H]LTB4 binding; both n-3 and n-6 fatty acids were inhibitory. The most potent compounds tested were homogammalinolenic acid and ricinelaidic acid which gave Ki values of 1 microM and 2 microM in the binding assay. Ricinelaidic acid was also tested for its ability to inhibit LTB4-mediated chemotaxis (IC50 = 10 microM) and LTB4-induced calcium fluxes (IC50 = 7 microM) in isolated human neutrophils. Ricinelaidic acid did not show agonist activity in these assays. In an in vivo model of LTB4-induced bronchoconstriction, ricinelaidic acid and homogammalinolenic acid gave 46% and 53% inhibition, respectively, at a 1 mg/kg i.v. dose. These results indicate that essential fatty acids are LTB4 receptor antagonists, which may account in part for their reported anti-inflammatory activities.

Ro 25-1553: a novel, long-acting vasoactive intestinal peptide agonist. Part I: In vitro and in vivo bronchodilator studies.

Ro 25-1553, a cyclic peptide analog of vasoactive intestinal peptide (VIP), was designed to overcome many of the deficiencies inherent in this natural neuropeptide. On isolated guinea pig tracheal smooth muscle, Ro 25-1553 produces concentration-dependent relaxation of contractile responses to a number of different spasmogens. Depending on the contractile stimulus, Ro 25-1553 is 24 to 89 times more potent than VIP as a relaxant of guinea pig trachea. The high potency of Ro 25-1553 extends to studies on isolated, histamine-contracted, human bronchial smooth muscle, where Ro 25-1553 exhibits a 390-fold enhancement over native VIP and is more potent than other bronchodilating drugs, such as the beta 2-adrenoceptor agonists isoproterenol and salbutamol. Ro 25-1553 was shown to displace the radioligand 125I-VIP from rat forebrain membranes with an IC50 value of 4.98 nM, thereby demonstrating that it acts at a VIP receptor. In addition, when tested in a battery of 40 other binding assays (e.g., muscarinic, histamine, LTs, Ca++, TxA2, endothelin, alpha and beta adrenergic, platelet-activating factor, neurokinins, etc.) at concentrations as high as 10 microM, Ro 25-1553 was found to be inactive; thus it appears to be specific for VIP receptors. The potent smooth muscle relaxant activity exhibited in vitro by Ro 25-1553 is also evident after in vivo intratracheal administration or aerosolization of the compound. Pulmonary responses evoked by histamine, leukotriene D4, platelet-activating factor and acetylcholine are inhibited dose-dependently by intratracheally instilled Ro 25-1553 with nearly identical potency (ED50 values ranging from 0.07 micrograms to 0.26 micrograms).(ABSTRACT TRUNCATED AT 250 WORDS)

Structure-activity studies of vasoactive intestinal peptide (VIP): cyclic disulfide analogs.

Analogs of vasoactive intestinal peptide with cysteine residues incorporated at selected sites within the sequence were prepared by solid phase methods, oxidized to the corresponding cyclic disulfides and purified to homogeneity by preparative HPLC. The cyclic compounds were assayed as smooth muscle relaxants on isolated guinea pig trachea, as bronchodilators in vivo in guinea pigs, and for binding to VIP receptors in guinea pig lung membranes. Of the analogs prepared at the N-terminus, one compound, Ac-[D-Cys6,D-Cys11,Lys12,Nle17,Val26,Th r28]-VIP, was found to be a full agonist with slightly more than one tenth the potency of native VIP. Most other cyclic analogs in the N-terminal region were found to be inactive. A second analog, Ac-[Lys12,Cys17,Val26,Cys28]-VIP, was also found to be a full agonist with potency about one third that of native VIP. Furthermore, this compound was active as a bronchodilator in vivo in guinea pig, but with somewhat diminished potency as compared to native VIP. Strikingly, this cyclic compound was found to have significantly longer duration of action (> 40 min) when compared to an analogous acyclic compound (5 min). The conformational restrictions imposed by formation of the cyclic ring structures may have stabilized the molecule to degradation, thus enhancing the effective duration of action. Analysis of this series of cyclic analogs has also yielded information about the requirements for the receptor-active conformation of VIP.

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.

beta 1-selective adrenoceptor antagonists. 1. Synthesis and beta-adrenergic blocking activity of a series of binary (aryloxy)propanolamines.

A series of binary (aryloxy)propanolamines has been prepared and examined in vitro and in vivo for beta-adrenoreceptor blocking activity. These symmetrical compounds consist of two (S)-(phenyloxy)propanolamine pharmacophores coupled through alkylenedioxy or poly(oxyethylenedioxy) linking units of varying lengths. Examples of such binary compounds linked through the 2,2', 3,3', and 4,4' positions in the aromatic rings of the pharmacophores have been prepared. In vitro and in vivo test data indicate that the 2,2' compounds tend to be selective beta 2-adrenergic blocking agents, the 4,4' binaries tend to be selective beta 1-blocking agents, and those compounds with 3,3' linkages exhibit intermediate selectivities. One of the 4,4'-linked binary compounds, 4s, exhibited potent, cardioselective beta-blockade in vivo, which was of short duration and was accompanied by a prolonged tachycardia.

An in vivo model for measuring antigen-induced SRS-A-mediated bronchoconstriction and plasma SRS-A levels in the guinea-pig.

1 Pharmacological modulation of antigen-induced anaphylaxis in actively sensitized guinea-pigs with intravenously administered indomethacin (10 mg/kg), pyrilamine (2.0 mg/kg) and propranolol (0.1 mg/kg) resulted in a delayed onset, slowly developing bronchoconstriction indicative of a slow-reacting substance of anaphylaxis (SRS-A) response. 2 Measurements of pulmonary mechanics on the drug-pretreated animals challenged with ovalbumin demonstrated a more prominent effect on dynamic compliance than resistance. This is consistent with the more potent effects of SRS-A on peripheral rather than central airways. 3 The slowly developing bronchoconstriction obtained after treatment with indomethacin, pyrilamine and propranolol was inhibited by the standard SRS-A antagonist, FPL 55712 and the SRS-A synthesis inhibitors, phenidone, BW 755C and nordihydroguaiaretic acid. 4 Plasma SRS-A levels were determined in guinea-pigs following antigen challenge. The appearance of SRS-A in the plasma preceded the onset of bronchoconstriction and SRS-A levels remained elevated throughout its development. Coincident with the inhibition of bronchoconstriction by the SRS-A synthesis inhibitor, phenidone, was a dose-dependent reduction in plasma SRS-A. The intravenous ED50 in each case was 4 mg/kg. 5 This model of antigen-induced SRS-A-mediated bronchoconstriction should prove useful for the in vivo evaluation and development of therapeutics which regulate the synthesis of SRS-A.

Metal ion and guanine nucleotide regulation of the inhibition of lung adenylate cyclase by adenosine analogs.

Adenosine inhibits guinea-pig lung adenylate cyclase (ATP pyrophosphatelyase (cyclizing), EC 4.6.1.1) through a 'P' type regulatory site. The inhibition is of a non-competitive type. Divalent cations which activate the enzyme (Mg2+ and Mn2+) and also those which inhibit (Ca2+) increase the inhibitory potency of 'P' site analogs at this site. Guanine nucleotides also increase the inhibitory potency at this regulatory site but this does not appear to be directly related to the ability of the guanine nucleotides to activate the enzyme. Other regulators of lung adenylate cyclase, epinephrine and isoproterenol, do not affect the adenosine inhibitory process when examined at physiological concentrations. These studies demonstrate that two types of ligand which regulate the catalytic activity of the lung adenylate cyclase (metal ions and guanine nucleotides) also have a role in regulating the inhibition of the enzyme by adenosine.

3-Phenyl-5-[2,2,2-trifluoro-1-hydroxy-1-(trifluoromethyl)ethyl]indole-2-carbonitrile, a potent inhibitor of prostaglandin synthetase and of platelet aggregation.

A number of indoles containing the 2,2,2-trifluoro-1-hydroxy-1-(trifluoromethyl)ethyl side chain have been prepared by standard methods. Alternate, novel syntheses of indole-2-carboxamides and indole-2-carbonitriles have been developed. The title compound, 7e, was found to be a potent inhibitor of bovine prostaglandin synthetase in vitro and to lower serum prostaglandin levels after oral or intraperitoneal administration to rats. Consistent with prostaglandin synthetase inhibition, 7e prevented arachidonic acid induced diarrhea in mice and also collagen, ADP, or epinephrine induced platelet aggregation in human platelet-rich plasma. In contrast to many prostaglandin synthetase and platelet-aggregation inhibitors, 7e had neither ulcerogenicity nor systemic antiinflammatory activity in rats.