Riluzole series. Synthesis and in vivo "antiglutamate" activity of 6-substituted-2-benzothiazolamines and 3-substituted-2-imino-benzothiazolines.

Two series of analogues of riluzole, a blocker of excitatory amino acid mediated neurotransmission, have been synthesized: monosubstituted 2-benzothiazolamines and 3-substituted derivatives. Of all the compounds prepared in the first series, only 2-benzothiazolamines bearing alkyl, polyfluoroalkyl, or polyfluoroalkoxy substituents in the 6-position showed potent anticonvulsant activity against administration of glutamic acid in rats. The most active compounds displaying in vivo "antiglutamate" activity were the 6-OCF(3) (riluzole), 6-OCF(2)CF(3), 6-CF(3), and 6-CF(2)CF(3) substituted derivatives with ED(50) values between 2.5 and 3.2 mg/kg i.p. Among the second series of variously substituted benzothiazolines, compounds as active as riluzole or up to 3 times more potent were identified in two series: benzothiazolines bearing a beta-dialkylaminoethyl moiety and compounds with an alkylthioalkyl chain and their corresponding sulfoxides and sulfones. The most potent derivatives were 2-imino-3-(2-methylthio)- and 2-imino-3-(2-methylsulfinyl)-ethyl-6-trifluoromethoxybenzothiazolines (61 and 64, ED(50) = 1.0 and 1.1 mg/kg i.p., respectively). In addition, intraperitoneal administration of some of the best benzothiazolines protected mice from mortality produced by hypobaric hypoxia.

New indole derivatives as potent and selective serotonin uptake inhibitors.

A series of new indole derivatives (2-28) has been prepared in the search for novel 5-HT uptake inhibitors. These compounds were obtained by the condensation of N-(chloroalkyl) naphthalenesultam derivatives with the appropriate amine in presence of a base, at reflux of DMF or THF. The yields were moderate (12-56%), except for the piperazine derivative 20 (85%). The affinity of the compounds for uptake site and 5-HT2, alpha 1, and D2 receptors was measured. Some compounds were studied in vivo by their potentiating effect of 5-HTP-induced symptomatology. The most potent and selective (uptake, 5-HT2 versus alpha 1, D2 sites) compounds contain a 3-[(4-piperidinyl)methyl]indole moiety. 5-Fluoro-3-[(4-piperidinyl)methyl]indole itself (compound 1) displayed a high affinity for the uptake site but was devoided of in vivo activity. N-Methylation of this compound abolished the affinity. In contrast N-substitution by a two-carbon chain linked to a naphthalenesultam or related heterocycle led to compounds exhibiting high affinity for the uptake site. One of them, 1-[2-[4-((5-fluoro-1H-indol-3-yl)methyl-1- piperidinyl]ethyl]-5,6-dihydro-1H,4H-1,2,5-thiadiazolo[4,3,2- ij]quinoline 2,2-dioxide (compound 24), was found as active as fluoxetine in vivo.

Pharmacological characterization of RP 62203, a novel 5-hydroxytryptamine 5-HT2 receptor antagonist.

1. RP 62203 (2-[3-(4-(4-fluorophenyl)-piperazinyl)propyl]naphto[1,8- ca]isothiazole-1,1-dioxide) is a novel naphtosultam derivative which shows very high affinity for 5-HT2 receptors in the rat cerebral cortex (Ki = 50.0 pM). 2. RP 62203 is relatively selective for this sub-type of 5-hydroxytryptamine (5-HT) receptor, having lower affinity for the 5-HT1A receptor and very low affinity for the 5-HT, receptor. RP 62203 displayed low to moderate affinity for alpha 1-adrenoceptors, dopamine D2 receptors and histamine H1 receptors. 3. In vivo binding experiments demonstrated that oral administration of low doses of RP 62203 led to a long-lasting (greater than 6 h) occupation of cortical 5-HT2 receptors (ID50 = 0.39 mgkg-1). 4. In cortical slices from the neonatal rat, RP 62203 potently inhibited inositol phosphate formation evoked by 5-HT, with an IC50 of 7.76 nM. 5. The activity of neurones in the raphé and their responses to microiontophoretically applied 5-HT were studied with extracellular recording electrodes in the anaesthetized rat. RP 62203 potently and dose-dependently blocked excitations evoked by 5-HT when administered at doses of 0.5-4.0 mg kg-1, i.p. In contrast, neither 5-HT-evoked depressions nor glutamate-evoked excitations of raphé neuronal firing were blocked by RP 62203 at doses as high as 8.0 mg kg-1, i.p. 6. Head twitches induced by 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) could be abolished by low doses of RP 62203 in mice (ED50 = 0.44 mg kg-1, p.o.) and in rats (ED50 = 1.54 p.o.). Similar results were obtained with mescaline and 5-hydroxytryptophan (5-HTP). 7. The potency of RP 62203 was compared with that of three other 5-HT2 receptor antagonists, ritanserin, ICI 169,369 and ICI 170,809. In all models, RP 62203 showed similar activity to ritanserin, whilst either ICI 169,369 or ICI 170,809 was several fold less active. 8. It is concluded that RP 62203 is a potent and selective antagonist at 5-HT2 receptors in the rodent central nervous system.

Naphthosultam derivatives: a new class of potent and selective 5-HT2 antagonists.

A series of 2-(aminoalkyl)naphth[1,8-cd]isothiazole 1,1-dioxides was synthesized and examined in various receptor binding tests. Most compounds demonstrated high affinity for the 5-HT2 receptor with moderate to high selectivity. A member of this series, compound 24 (RP 62203), displays high 5-HT2 receptor affinity (Ki = 0.26 nM), which is respectively more than 100 and 1000 times higher than its affinity for alpha 1 (Ki = 38 nM) and D2 (Ki greater than 1000 nM) receptors. This compound is a potent orally effective and long lasting 5-HT2 antagonist in the mescaline-induced head-twitches test in mice and rats.

Binding sites for a peripheral type benzodiazepine antagonist ([3H]PK 11195) in human iris.

Peripheral-type benzodiazepine binding sites have been characterized on sections of 8 normal human iris/ciliary-body preparations. Saturability was determined at 25 degrees C with [3H] PK 11195 (1 nM) a specific ligand of peripheral type sites. The studies revealed a single class of binding sites for PK 11195 with a nanomolar range affinity (KD = 1.45 nM) and a maximal capacity (Bmax) of 35.5 fmol/mg protein. The displacement potency order of the benzodiazepines tested suggest that these sites belong to the peripheral type: PK 11211 (IC50 = 12 nM) greater than Ro 5-4864 (IC50 = 770 nM) greater than clonazepam (IC50 = 20,000 nM). The present data demonstrate that high affinity binding sites for peripheral type benzodiazepines are present in human iris/ciliary-body. This tissue is therefore a suitable tool for evaluation of the putative functional role of these binding sites.

Quantitative autoradiographic determination of binding sites for a peripheral benzodiazepine ligand ([3H]PK 11195) in human iris.

Specific binding sites of peripheral-type benzodiazepines were investigated in human iris/ciliary body (8 eyes). Examination of color-coded prints and densitometric quantification of autoradiograms were performed on slides (20 micron) labelled with [3H]PK 11195 (1 nM) at 25 degrees C. Nonspecific binding was determined with PK 11211 (5 microM) or Ro 5-4864 (5 microM). Binding sites were present on all the slides, with equivalent density in the 3 regions of the preparation (ciliary body, iris, and pupil margin). The numbers of binding sites in ciliary body, iris, and pupil margin, respectively, were: 42.7 +/- 0.2, 30.1 +/- 0.5, and 37.4 +/- 0.4 femtomol/mg protein. Labelling on the pupil margin seemed to coincide with the iris sphincter muscle. The presence of peripheral benzodiazepine binding sites in iris muscular tissue, and particularly in the pupil margin, suggests that the iris preparation may be a valuable tool to detect putative physiological effects of peripheral benzodiazepines on muscular motility.

Circadian rhythm in the membrane of circulating human blood cells: microviscosity and number of benzodiazepine binding sites. A search for regulation by plasma ions, nucleosides, proteins or hormones.

Circadian rhythms in both the number of peripheral type binding sites for benzodiazepines in platelet membranes and the microviscosity of the erythrocyte membrane were demonstrated in 7 healthy men. Neither variable appeared to be linked to each other, or regulated by the plasma concentrations of total or free cortisol, testosterone, potassium, magnesium, calcium, cAMP, cGMP or proteins or by the erythrocytic concentration of magnesium or potassium or by the plasma cAMP:cGMP ratio or by the ratio of intra-erythrocyte:plasma concentrations of potassium or magnesium. A highly significant negative correlation was found between the microviscosity of the erythrocyte membrane and the activity of the membrane-bound enzyme, methyltransferase I. Such a correlation was validated both on raw data and on 24 hr-means (r = 0.84; P less than 0.01). A circadian rhythm in the activity of this enzyme was also demonstrated. Moreover, a highly significant correlation was also found between plasma transcortin concentration (TRC) and microviscosity (r = 0.50, P less than 0.01), and between TRC and methyltransferase I activity (r = 0.61, P less than 0.01). Such findings may constitute clues towards the understanding of the regulation of the circadian rhythm in the fluidity of the red blood cell membrane in man and guide future steps with regard to the role of this rhythm upon the availability of drug binding sites at the cell surface.

Labelling of peripheral-type benzodiazepine binding sites in human brain with [3H]PK 11195: anatomical and subcellular distribution.

The peripheral-type benzodiazepine binding site, erstwhile characterized in the rodent and feline brain, has now been characterized in post-mortem human brain using [3H]PK 11195. The kinetics and pharmacological properties of the binding of this ligand are similar to peripheral-type benzodiazepine binding sites elsewhere. The potency of RO5-4864 for this site in human brain is close to that seen in ruminant and carnivore tissues but considerably lower than in rodent tissues. The regional distribution of these binding sites would suggest a neuronal rather than a glial localization. [3H]PK 11195 bound in a similar fashion to slide-mounted sections of human brain, thus allowing quantitative studies of the regional distribution of peripheral-type benzodiazepine binding sites to be made. The binding sites were distributed heterogeneously, but were restricted to the grey matter. Highest densities of binding sites were found in forebrain structures. The localization was not limited to any functional system, nor did it resemble any previously described transmitter system. The similarities between peripheral-type benzodiazepine binding sites in human and in feline brain in terms of their pharmacological characteristics and their regional and subcellular distribution suggest that the cat, rather than the rat, may be the better model for studying a possible role for this site in human cerebral function.

Partial purification and pharmacology of peripheral-type benzodiazepine receptors.

This report describes the results obtained with a new photoaffinity ligand for the "peripheral-type" benzodiazepine binding site (PBS), using a digitonin solubilized preparation from rat heart or adrenals. The specific binding activity of the solubilized adrenal preparation is higher than 50 pmol/mg protein, with binding properties and pharmacological specificity identical to the membrane bound PBS. The apparent molecular weight of the solubilized PBS, determined by gel filtration is 215 KDa. The photoaffinity ligand (PK 14105) is a nitrophenyl derivative of PK 11195, which attaches covalently and specifically to all the PBS when cardiac membranes are irradiated with this compound under ultraviolet light. After photolabelling with [3H]PK 14105 and solubilization in SDS of heart or adrenal membranes, gel electrophoresis indicates the existence of a single protein band whose molecular weight (18 KDa) is unaltered by incubation with sulphydryl-reducing or protein cross-linking agents. This molecule seems to be a low molecular weight, acidic protein. Diethylpyrocarbonate decreases partially (60%) the binding of [3H]PK 11195 without affecting [3H] RO5-4864 binding, which implies a vital histidine residue in the binding domain of [3H]-PK 11195. Treatment with phospholipase A2 or mellitin, a stimulant of endogenous PLA2, led to a selective loss of [3H] RO5-4864 binding with no change in the binding of [3H]PK 11195. Such differences between a benzodiazepine ligand and an isoquinoline ligand suggest that these compounds may induce, on binding, different conformational changes in the PBS, which is compatible with the hypothesis that RO5-4864 and PK 11195 may be an agonist and an antagonist respectively at the PBS.

Photoaffinity labeling of peripheral-type benzodiazepine-binding sites.

The use of a novel photoaffinity label for the peripheral-type benzodiazepine-binding site is described. This compound, PK 14105, has high affinity (4 nM) and selectivity for cardiac benzodiazepine-binding sites. Under ultraviolet light, PK 14105 couples covalently to an 18,000-Da membrane protein which apparently corresponds to the (or a part of the) cardiac benzodiazepine-binding site. Since covalent attachment of PK 14105 totally precludes the binding of other ligands to this binding site, it is suggested that, during ultraviolet irradiation, this compound inserts covalently into the binding domain of the peripheral-type benzodiazepine-binding site.

Stereoselective inhibition of the binding of [3H]PK 11195 to peripheral-type benzodiazepine binding sites by a quinolinepropanamide derivative.

The specific binding of [3H]PK 11195 to the peripheral-type benzodiazepine binding site is inhibited by the l-enantiomer of N,N-diethyl-alpha-methyl-2-phenyl-4-quinolinepropanamide ((-)Q1) but not by its d-enantiomer ((+)Q1). (-)Q1 inhibited [3H]PK 11195 binding to several rat tissues with an IC50 of less than 10 nM whereas (+)Q1 was at least 500 times less potent. This stereoselectivity was observed in all the tissues tested (brain, heart, kidney and adrenals). The same stereoselectivity was found for the displacement of the binding of [3H]PK 11195 in vivo, where (-)Q1 had an ID50 between 4-15 mg/kg and (+)Q1 was completely inactive at all doses tested (i.e. up to 40 mg/kg). Neither isomer had appreciable affinity for central-type benzodiazepine binding sites ([3H]diazepam) nor for voltage-sensitive calcium channels ([3H]PN 200210 and [3H]verapamil).

4-Amino-6-chloro-2-piperazinopyrimidines with selective affinity for alpha 2-adrenoceptors.

A series of 4-amino-6-chloro-2-piperazinopyrimidines were synthesized and evaluated for their ability to interact with alpha 1- and alpha 2-adrenoceptors in vitro in binding assays using [3H]WB-4101, [3H]clonidine, and [3H]idazoxan as radioligands. Some compounds were also tested as inhibitors of [3H]spiroperidol binding. Several members of this series showed high and selective affinity for alpha 2-adrenoceptors. The nature of the 4-amino substituent seems to be the most critical factor in determining the potency at these receptors.

Modulation of voltage-operated, but not receptor-operated, calcium channels in the rabbit aorta by PK 11195, an antagonist of peripheral-type benzodiazepine receptors.

We compared the effects of PK 11195, an antagonist of peripheral benzodiazepine receptors, on contractions of rabbit aorta by activation of either voltage-operated calcium channels (VOC) using BAY K 8644 (a calcium "agonist") and KCl or receptor-operated channels (ROC) using phenylephrine and B-HT 920, (alpha 1- and alpha 2-adrenoceptor agonist, respectively). In partially depolarized muscle strips, BAY K 8644 induced contractions that were noncompetitively inhibited by PK 11195 (pD'2 = 5.6 +/- 0.15). The effect of this calcium agonist was also antagonized by nitrendipine (competitively) and by yohimbine (noncompetitively), while prazosin was inactive. Contractions induced by KCl were inhibited by nitrendipine and, weakly, by PK 11195. Contractions induced by phenylephrine and B-HT 920 were inhibited competitively by prazosin and yohimbine and noncompetitively by nitrendipine, while PK 11195 was ineffective. It is concluded that PK 11195 behaves as an antagonist of VOC activated by BAY K 8644 and to a lesser extent by KCl depolarization but not of ROC coupled to alpha 1- and alpha 2-receptors.

PK 11195, an antagonist of peripheral type benzodiazepine receptors, modulates Bay K8644 sensitive but not beta- or H2-receptor sensitive voltage operated calcium channels in the guinea pig heart.

In a partially depolarized guinea pig papillary muscle preparation, BAY K8644 stimulated voltage-operated calcium channels, promoting slow action potentials; this effect was dose-dependent over a concentration range of 3 X 10(-7) M to 3 X 10(-6) M. Isoproterenol and histamine also induced slow action potentials by stimulating beta or H2 receptors, respectively. PK 11195, the antagonist of peripheral type benzodiazepine receptors, inhibited the effect of BAY K8644, but not those of histamine or isoproterenol. Moreover, PK 11195 "dose-dependently" antagonized the ability of RO5-4864 to inhibit the slow action potentials elicited by barium chloride. Thus, in the heart, PK 11195, an antagonist of peripheral type benzodiazepine receptors, can modulate voltage-operated calcium channels when they are activated directly, but not when they are activated by stimulation of neurotransmitter receptors.

Dihydropyridine and peripheral type benzodiazepine binding sites: subcellular distribution and molecular size determination.

Electrophysiological and pharmacological studies have shown that peripheral-type benzodiazepine receptors modulate voltage-sensitive calcium channels in the heart. We have compared these binding sites with binding sites for [3H]dihydropyridines, which are believed to label such channels. Although no direct or allosteric interaction could be demonstrated between the two sites, their subcellular distribution--sarcolemma and ryanodine-sensitive sarcoplasmic reticulum--was parallel. Size determination of the two sites suggests that the receptors for these two classes of compounds are separate molecules packaged in the same membrane compartment.

[Biochemical characterization and study by quantitative autoradiography of the binding sites of indalpine, a 5-HT uptake inhibitor, in cat brain]. / Caractérisation biochimique et étude par autoradiographie quantitative des sites de fixation de l'indalpine, un inhibiteur de la recapture de 5-HT, dans le cerveau de chat.

The [3H]indalpine binding sites have been characterized in slide-mounted cat brain sections. This inhibitor of 5-HT reuptake binds with a very high affinity to sites which have the pharmacological properties of the serotonin carrier. These sites can, however, be differentiated from the [3H]imipramine binding sites by their Na+ dependency and competitive inhibition by serotonin. Quantitative autoradiographic studies demonstrate that indalpine binding sites are localized in structures rich in serotonergic neurons. The widespread distribution of indalpine binding sites in limbic and associative areas is consisted with its well characterized antidepressant activity in human.

2-Amino-6-trifluoromethoxy benzothiazole, a possible antagonist of excitatory amino acid neurotransmission--II. Biochemical properties.

Two models have been chosen to study the effect of 2-amino-6-trifluoromethoxy benzothiazole (PK 26124) on excitatory amino acid neurotransmission: the pool of cyclic guanosine monophosphate (cGMP) in the cerebellum and the release of acetylcholine in the striatum and olfactory tubercles. The release of acetylcholine induced by N-methyl-DL-aspartate in the striatum and olfactory tubercles was antagonized by PK 26124 which was less potent on the release of acetylcholine induced electrically. The increase in levels of cGMP in the cerebellum induced by excitatory amino acids such as glutamate and quisqualate was antagonized by PK 26124, but the drug was inactive against N-methyl-DL-aspartate, L-aspartate, kainate and cysteine sulphinate. In vivo it antagonized the increases of cGMP in the cerebellum elicited by all these excitatory compounds. All these results are compatible with a possible antagonism by PK 26124 of the excitatory amino acid neurotransmission and may explain its anticonvulsant properties.

Quantitative autoradiography of [3H]indalpine binding sites in the rat brain: I. Pharmacological characterization.

The binding of [3H]indalpine (4-[2-(3-indolyl)]ethyl piperidine) to slide-mounted sections of rat brain has been characterized. This 5-hydroxytryptamine (5-HT) uptake blocker binds to sections with high affinity (KD approximately 1 nM). The binding is saturable, and can be displaced by the addition of clomipramine (1 microM). Other drugs inhibiting the uptake of 5-HT also have the capacity to inhibit the binding of [3H]indalpine. A significant correlation (r = 0.86) was found between the capacity of these compounds to inhibit the uptake of 5-HT and their potencies as inhibitors of [3H]indalpine binding. Binding was Na+ - and Cl- -dependent and was inhibited competitively by 5-HT. Furthermore, electrolytic lesions of the dorsal raphe or medial forebrain bundle, which cause a degeneration of 5-HT cell bodies and fibers, respectively, resulted in a 30-40% reduction in the binding of [3H]indalpine. [3H]Indalpine binds to the 5-HT uptake recognition sites in a different manner from imipramine-like compounds.