Impairment of TNF-alpha production and action by imidazo[1,2- alpha] quinoxalines, a derivative family which displays potential anti-inflammatory properties.

In a previous study, we analysed the synthesis and properties of a series of imidazo[1,2-alpha]quinoxalines designed in our laboratory as possible imiquimod analogues. We found that these imidazo[1,2-alpha]quinoxalines were in fact potent inhibitors of phosphodiesterase 4 enzymes (PDE4). PDE4 inhibition normally results in an increase in intracellular cAMP which, in PBMC, induces the suppression of TNF-alpha mRNA transcription and thus cytokine synthesis. Such an effect is antagonistic to that of imiquimod. Furthermore, some TNF-alpha-induced activity, such as cell apoptosis which is dependent on the intracellular cAMP levels might also be affected. Therefore, by counteracting the properties of TNF-alpha and/or its production, the imidazo[1,2-alpha]quinoxalines could be considered as potential anti-inflammatory drugs. The present study was performed to confirm or refute this hypothesis. For this, we characterized the effects of imidazo[1,2-alpha]quinoxalines both on TNF-alpha activity and synthesis in regard to their ability to act as inhibitors of PDE4 (IPDE4). We found that the imidazo[1,2-alpha]quinoxalines dose-dependently prevented the TNF-alpha-triggered death of L929 cells, with the 8-series (-NHCH3 in R4) being the most potent. Moreover, when the effect of the 8-series on TNF-alpha production was investigated using gamma9delta2 T cells, it was observed that these compounds impaired the TCR:CD3-triggered TNF-alpha production. Structure-activity analysis revealed that these properties of the drugs did not coincide with their IPDE4 properties. This prompted further exploration into other signalling mechanisms possibly involved in TNF-alpha action and production, notably the p38 MAPK and the PI3K pathway. We demonstrate here that the imidazo[1,2-alpha]quinoxalines targeted these pathways in a different way: they activated the p38 MAPK pathway whilst inhibiting the PI3K pathway. Such effects on cell signalling could account for the imidazo[1,2-alpha]quinoxalines effects on 1) action and 2) production of TNF-alpha, which define these drugs as potential anti-inflammatory agents.

Antimalarial activity of molecules interfering with Plasmodium falciparum phospholipid metabolism. Structure-activity relationship analysis.

A series of 80 compounds, primary, secondary, and tertiary amines and quaternary ammonium and bisammonium salts, most of them synthesized as potential choline or ethanolamine analogs, were tested against the in vitro growth of Plasmodium falciparum, the human malaria parasite. They were active over the 10(-3)-10(-8) M concentration range. A structure-activity relationship study was carried out using autocorrelation vectors as structural descriptors, and multidimensional analysis. Principal component analysis, ascending hierarchical classification, and stepwise discriminant analysis showed that both the size and shape of the molecule were essential for antimalarial potency, making the lipophilicity and electronegativity distribution in the molecular space essential. Using the autocorrelogram describing the molecular shape and the electronegativity distribution on the molecular graph, 98% of the molecules were correctly classified either as poorly active or active with only three explanatory variables. The most active compounds were quaternary ammoniums salts whose nitrogen atom had only one long lipophilic chain of 11 or 12 methylene groups (E5, E6, E10, E13, E20, E21, E22, E23, F4, F8), or the bisammoniums whose polar heads were linked by linear alkyl chains of 10 to 12 carbon atoms (G4, G23). The hydroxyethyl group of choline was not very beneficial, whereas the charge and substitutions of nitrogen (aimed at increasing lipophilicity) were essential for optimal interactions. A crude topographic model of the ligand (choline) binding site was thus drawn up.

Cardiovascular effects of SCA40, a novel potassium channel opener, in rats.

1. Experiments have been performed to investigate the cardiovascular actions in the rat of SCA40, a novel potassium channel opener which is a potent relaxant of guinea-pig airway smooth muscle in vivo and in vitro. 2. SCA40 (0.01-30 microM) caused a complete and concentration-dependent relaxation of rat isolated thoracic aorta contracted with 20 mM KCl but failed to inhibit completely the spasmogenic effects of 80 mM KCl. 3. The ATP-sensitive K(+)-channel blocker, glibenclamide (3 microM), failed to antagonize the relaxant action of SCA40 on 20 mM KCl-contracted rat isolated thoracic aorta. 4. SCA40 (0.001-100 microM) had dual effects on rat isolated atria. At low concentrations, SCA40 produced a concentration-dependent decrease in the rate and force of contractions. At higher concentrations (greater than 1 microM) SCA40 induced concentration-dependent increases of atrial rate and force. 5. In vivo, in normotensive Wistar rats, SCA40 elicited a dose-dependent (1-100 micrograms kg-1) decrease in mean arterial pressure which was accompanied by a moderate dose-dependent increase in heart rate. SCA40 (100 micrograms kg-1) had a slightly greater hypotensive effect than cromakalim (100 micrograms kg-1) but the duration of the hypotension was longer with cromakalim than with SCA40. 6. The hypotensive effect of SCA40 was not reduced by propranolol, atropine, NG-nitro-L-arginine methyl ester (L-NAME) or glibenclamide. 7. It is concluded that the mechanism by with SCA40 relaxes vascular smooth muscle in vitro and in vivo involves activation of K(+)-channels distinct from glibenclamide-sensitive ATP-sensitive K(+)-channels.

[Echocardiography in the diagnosis of mitral valve insufficiency due to valve mutilations or chordal ruptures. 41 cases with anatomical findings]. / Apport de l'échocardiographie dans les insuffisances mitrales par mutilations valvulaires ou ruptures de cordages. A propos de 41 cas avec corrélations anatomiques.

This study analyses the echocardiographic findings in 41 cases of severe mitral regurgitation due to chordal rupture (33 cases), elongation of chordae (4 cases) or valve trauma (4 cases). The operative findings are given. It was possible to make the diagnosis of chordal rupture in 60% of cases by recording one or more of the following signs:--For the anterior cusp: amplitude of motion equal to or greater than 38 mm; co-existence of chaotic diastolic fluttering and multiple systolic echoes; recording of several diastolic wave forms of the anterior cusp, out of phase and crossing each other;--For the posterior cusp: paradoxical movement of the cusp in systole and diastole; presence of an echo in the left atrium in systole. The group studied was compared with a group of 40 normal subjects and 48 cases of other types of mitral regurgitation which were severe and received surgery. The various signs had good specificity. The sensitivity of the different signs varied from 33 to 50% of cases. It was greater when the number of chordal ruptures was greater. Whichever cusp was affected, it was sometimes the site of high frequency and large amplitude systolic vibrations, which were found in a quarter of the patients. The specificity of this sign is discussed. The diagnosis of rupture of chordae is possible in a large proportion of cases and the causes of error are analysed.

[SCA 40 and derivatives: new bronchodilators in an imidazo(1,2-a)pyrazine series]. / SCA40 et dérivés: nouveaux bronchodilatateurs en série imidazo[1,2-a]pyrazinique.

Asthma is a complex disease characterised by bronchoconstriction and airways inflammation. Recent advances in medicinal chemistry will surely lead to a better reappraisal of therapeutic strategies. 8-(Methylamino)imidazo(1,2-a)pyrazines with substitution either on position 2 or 3 powerful relaxing agents in vitro as well as in vivo in animals. 6-Bromo-8-(methylamino)imidazo[1,2-a]pyrazine- 2-carbonitrile, SCA40, is a new and potent bronchodilator. Chemical synthesis of such a series of derivatives involves a condensation reaction with formation of the imidazole ring and/or diverse electrophilic substitutions. Chemical reactivity of the heterocycle can be modulated by introduction on position 8 of electrodonating groups that highly favor electrophilic substitution on position 3. Interestingly, lithiation studies on the heterocycle exhibit regioselectivity, leading either to an halogen exchange when position 3 is occupied by a bromine atom or an ortho-directed metalation in accord with the presence of an halogen on position 6.

Variable mapping of structure-activity relationships: application to 17-spirolactone derivatives with mineralocorticoid activity.

Fifty-four steroid homologs, belonging to the series of 17-spirolactones, were modelled by molecular and quantum mechanics. We studied the affinity of these compounds for the cytosolic mineralocorticoid receptor by way of various parameters describing each structure and its molecular properties. After the failure of a classic preliminary QSAR study, demonstrating the nonlinear relationships between affinity and structural descriptors, we constructed a model allowing us to predict the affinity of new compounds. Our method is based on simple graphic tools coupled to a cluster significance analysis. A complementary study of the activity relating the prediction of the antagonist/agonist character of 37 high-affinity compounds was also carried out using the same methodology. The principal electronic and structural characteristics leading to a selective activity were revealed.

[Effects of toxins, apamine, charybdotoxin and iberiotoxin on the relaxation of the smooth muscular fiber induced by imidazo(1,2-a)pyrazine derivative]. / Effets de toxines, apamine, charybdotoxine et ibériotoxine sur la relaxation de la fibre musculaire lisse induite par un dérivé de l'imidazo[1,2-a]pyrazine.

Experiments have been performed in order to analyse the mechanism whereby SCA40, a new imidazo[1,2-a]pyrazine derivative relaxes airway smooth muscle. We investigated the effect of different toxins, known to be K(+)-channel blockers on guinea-pig smooth muscle relaxant activity of SCA40. The small conductance Ca(2+)-activated K(+)-channel blocker apamin (100 nM) did not antagonize the relaxant activity of SCA40 in 1 microM carbachol-contracted isolated guinea pig trachea. The large conductance Ca(2+)-activated K(+)-channel blocker, iberiotoxin (30, 60 and 180 nM) antagonized the relaxant activity of SCA40 in an apparently competitive manner. The concentration-relaxation curves to SCA40 were shifted to the right with no significant alteration in the maximum response. The relaxant activity of SCA40 in 1 microM carbachol-contracted isolated trachea was antagonized by both charybdotoxin (60 nM) and iberiotoxin (60 nM), but the antagonism induced by iberiotoxin appears to be more potent than that induced by charybdotoxin. It is concluded that the potent relaxant activity of SCA40 on guinea-pig airway smooth muscle in vitro involves a charybdotoxin and iberiotoxin sensitive K(+)-channel.

Antimalarial activity of 77 phospholipid polar head analogs: close correlation between inhibition of phospholipid metabolism and in vitro Plasmodium falciparum growth.

Seventy-seven potential analogs of phospholipid polar heads, choline and ethanolamine, were evaluated in vitro as inhibitors of Plasmodium falciparum growth. Their IC50 ranged from 10(-3) to 10(-7) mol/L. Ten compounds showed similar antimalarial activity when tested against three different parasite strains (2 chloroquine-sensitive strains and 1 chloroquine-resistant strain). Compounds showing marked antimalarial activity were assayed for their effects on phospholipid metabolism. The most active compounds (IC50 of 1 to 0.03 micromol/L) were inhibitors of de novo phosphatidylcholine (PC) biosynthesis from choline. For a series of 50 compounds, there was a close correlation between impairment of phospholipid biosynthesis and inhibition of in vitro malaria parasite growth. High choline concentrations caused a marked specific shift in the curves for PC biosynthesis inhibition. Concentrations inhibiting 50% PC metabolism from choline were in close agreement with the Ki of these compounds for the choline transporter in Plasmodium knowlesi-infected erythrocytes. By contrast, measurement of the effects of 12 of these compounds on rapidly dividing lymphoblastoid cells showed a total absence of correlation between parasite growth inhibition and human lymphoblastoid cell growth inhibition. Specific antimalarial effects of choline or ethanolamine analogs are thus likely mediated by their alteration of phospholipid metabolism. This indicates that de novo PC biosynthesis from choline is a very realistic target for new malaria chemotherapy, even against pharmacoresistant strains.

New imidazo(1,2-a)pyrazine derivatives with bronchodilatory and cyclic nucleotide phosphodiesterase inhibitory activities.

New imidazo[1,2-a]pyrazine derivatives have been synthesized either by direct cyclization from pyrazines or by electrophilic substitutions. The presence of electron donating groups on position 8 greatly enhances the reactivity of the heterocycle towards such reactions on position 3 of the heterocycle. The activities of these derivatives in trachealis muscle relaxation and in inhibiting cyclic nucleotide phosphodiesterase (PDE) isoenzyme types III and IV have been assessed. All compounds demonstrated significantly higher relaxant potency than theophylline. All the derivatives were moderately potent in inhibiting the type IV isoenzyme of PDE but only those with a cyano group on position 2 were potent in inhibiting the type III isoenzyme.