Functional and pharmacological characterization of the first specific agonist and antagonist for the V1b receptor in mammals.

By activating three distinct vasopressin receptor isoforms called V1a-R, V1b-R (V3-R) and V2-R, vasopressin (VP) mediates a wide number of biological effects in mammals and may be involved in several pathological states. Up to now only specific V1a and V2 receptor agonists and antagonists have been successfully designed. The role of the V1b-R still remains partially unknown, due to the lack of selective V1b-R ligands and orally-active molecules, which are crucial tools for investigating the central and peripheral functions or pathological disorders associated with this receptor. In this review, we report the biological and pharmacological properties of the first two specific V1b-R ligands: d[Cha4] AVP, a high affinity V1b-R agonist and SSR149415, a potent orally-active V1b-R antagonist with good selectivity with respect to other VP/OT receptor isoforms and able to control ACTH secretion in vitro and in vivo. Indeed, these molecules constitute invaluable tools for exploring the central and peripheral roles of VP mediated via V1b receptors. Interestingly, SSR149415 displays potent anxiolytic and antidepressant-like activities, indicating that this new class of drugs has a promising therapeutical potential in the treatment of stress-related disorders, anxiety and depression.

SSR181507, a dopamine D2 receptor antagonist and 5-HT1A receptor agonist. II: Behavioral profile predictive of an atypical antipsychotic activity.

SSR181507 ((3-exo)-8-benzoyl-N-(((2S)7-chloro-2,3-dihydro-1,4-benzodioxin-1-yl)methyl)-8-azabicyclo(3.2.1)octane-3-methanamine monohydrochloride) is a novel tropanemethanamine benzodioxane that displays antagonist activity at dopamine D(2) receptors and agonist activity at 5-HT(1A) receptors. SSR181507 antagonized apomorphine-induced climbing in mice and stereotypies in rats (ED(50) of 2 and 3.4 mg/kg i.p., respectively) and blocked D-amphetamine-induced hyperlocomotion in rats at lower doses (0.3-1 mg/kg i.p.). At 1-10 mg/kg, it was found to disrupt active avoidance in mice. SSR181507 did not induce catalepsy in rats (MED>60 mg/kg i.p.) and antagonized (3-10 mg/kg i.p.) haloperidol-induced catalepsy. SSR181507 was also active in two models sensitive to antidepressant/anxiolytic drugs: in a guinea-pig pup/mother separation test, it decreased (1-3 mg/kg i.p.) the time spent vocalizing during the separation episode, and in a lithium-induced taste aversion procedure in rats, it partially reversed (3 mg/kg i.p.) the decrease of intake of a saccharin solution. Furthermore, SSR181507 increased (3 mg/kg i.p.) the latency time to paradoxical sleep in rats, an effect commonly observed with antidepressants. Coadministration of the selective 5-HT(1A) blocker SL88.0338 produced catalepsy and antagonized the effects of SSR181507 in the depression/anxiety tests, confirming the view that activation of 5-HT(1A) receptors confers an atypical profile on SSR181507, and is responsible for its antidepressant/anxiolytic properties. Finally, SSR181507 (1-3 mg/kg) did not affect memory performance in a Morris water maze task in rats. The pharmacological profile of SSR181507 suggests that it should control the symptoms of schizophrenia, in the absence of extrapyramidal signs and cognitive deficits, with the additional benefit of antidepressant/anxiolytic activities.

The vasopressin V1b receptor as a therapeutic target in stress-related disorders.

The complexity of the stress response would appear to provide multiple opportunities for intervention, but treatment strategies are often centered on the improvement of symptoms rather than attempting to "treat" the stress response. However, recent efforts have begun to focus on the development of pharmacological agents that can attenuate the stress response itself, rather than the symptoms associated with stress. Although CRF, which is the main regulator of the stress system, is the focus of current interest, there is an accumulating body of evidence suggesting that the vasopressinergic system may play an equal role in the regulation of the stress response, and that V(1b) receptor antagonists may be of potential therapeutic benefit. The availability of SSR149415, the first selective antagonist for the V(1b) receptor has allowed us to evaluate this hypothesis. SSR149415 is able to attenuate some but not all stress-related behaviors in rodents. While the antidepressant-like activity of the compound was comparable to that of reference antidepressants, the overall profile displayed in anxiety tests was different from that of classical anxiolytics, such as benzodiazepines. The latter were active in a wide range of anxiety models, whereas the V(1b) receptor antagonist showed clear-cut effects only in particularly stressful situations. It is important to note that SSR149415 is devoid of central depressant effects, even at high doses, and does not affect cognitive processes, suggesting a large therapeutic window. Altogether, these findings suggest that V(1b) receptor antagonists might be useful as a treatment for major depression and stress disorders that result from traumatic events.

SL651498, a GABAA receptor agonist with subtype-selective efficacy, as a potential treatment for generalized anxiety disorder and muscle spasms.

SL651498 (6-fluoro-9-methyl-2-phenyl-4-(pyrrolidin-1-yl-carbonyl)-2,9-dihydro-1H-pyrido[3,4-b]indol-1-one) was identified as a drug development candidate from a research program designed to discover subtype-selective GABA(A) receptor agonists for the treatment of generalized anxiety disorder and muscle spasms. The drug displays high affinity for rat native GABA(A) receptors containing alpha(1) (K(i) = 6.8 nM) and alpha(2) (K(i) = 12.3 nM) subunits, and weaker affinity for alpha5-containing GABA(A) receptors (K(i) = 117 nM). Studies on recombinant rat GABA(A) receptors confirm these findings and indicate intermediate affinity for the alpha(3)beta(2)gamma(2) subtype. SL651498 behaves as a full agonist at recombinant rat GABA(A) receptors containing alpha(2) and alpha(3) subunits, and as a partial agonist at recombinant GABA(A) receptors expressing alpha(1) and alpha(5) subunits. SL651498 produced anxiolytic-like and skeletal muscle relaxant effects qualitatively similar to those of benzodiazepines (BZs) [minimal effective dose (MED): 1 to 10 mg/kg, i.p. and 3 to 10 mg/kg, p.o.]. However, unlike these latter drugs, SL651498 induced muscle weakness, ataxia or sedation at doses much higher than those having anxiolytic-like activity (MED: 30 to 100 mg/kg, i.p. or p.o.). Moreover, in contrast to BZs, SL651498 did not produce tolerance to its anticonvulsant activity or physical dependence. It was much less active than BZs in potentiating the depressant effects of ethanol or impairing cognitive processes in rodents. The differential profile of SL651498 as compared to BZs may be related to its selective efficacy at the alpha(2)- and alpha(3)-containing GABA(A) receptors. This suggests that selectively targeting GABA(A) receptor subtypes can lead to drugs with increased clinical specificity. SL651498 represents a promising alternative to agents currently used for the treatment of anxiety disorders and muscle spasms without the major side effects seen with classical BZs.

SSR240600 [(R)-2-(1-[2-[4-[2-[3,5-bis(trifluoromethyl)phenyl]acetyl]-2-(3,4-dichlorophenyl)-2-morpholinyl]ethyl]-4-piperidinyl)-2-methylpropanamide], a centrally active nonpeptide antagonist of the tachykinin neurokinin 1 receptor: II. Neurochemical and behavioral characterization.

SSR240600 [(R)-2-(1-[2-[4-[2-[3,5-bis(trifluoromethyl)phenyl]acetyl]-2-(3,4-dichlorophenyl)-2-morpholinyl]ethyl]-4-piperidinyl)-2-methylpropanamide], a new nonpeptide tachykinin neurokinin 1 (NK1) receptor antagonist, was evaluated against the neurochemical, electrophysiological, and behavioral effects provoked by direct activation of brain tachykinin NK1 receptors or by stress in guinea pigs. SSR240600 (0.1-10 mg/kg i.p. or p.o.) antagonized the excitatory effect of i.c.v. infusion of [Sar(9),Met(O2)(11)]substance P (SP) on the release of acetylcholine in the striatum of anesthetized and awake guinea pigs. This antagonistic action was still observed after repeated administration of SSR240600 (5 days, 10 mg/kg p.o., once a day). SSR240600 (10 mg/kg i.p.) inhibited the phosphorylation of the cAMP response element-binding protein in various brain regions induced by i.c.v. administration of [Sar9,Met(O2)(11)]SP. In slice preparations, neuronal firing of the locus coeruleus (LC) neurons elicited by the application of [Sar9,Met(O2)(11)]SP was suppressed by SSR240600 at 100 nM. Norepinephrine release in the prefrontal cortex, elicited either by an intra-LC application of [Sar9,Met(O2)(11)]SP or by an i.c.v administration of corticotropin-releasing factor, was reduced by SSR240600 (0.3-1 mg/kg and 1-10 mg/kg i.p., respectively). SSR240600 (1-10 mg/kg i.p.) inhibited vocalizations induced in adult guinea pigs by an i.c.v. administration of the NK1 receptor agonist, GR73632 [D-Ala-[L-Pro9,Me-Leu8]substance P(7-11)]. Furthermore, SSR240600 (1-10 mg/kg i.p.) inhibited distress vocalizations produced in guinea pig pups by maternal separation. SSR240600 also reduced maternal separation-induced increase in the number of neurons displaying NK1 receptor internalization in the amygdala. Finally, SSR240600 counteracted the increase in body temperature induced by isolation stress. In conclusion, SSR240600 is able to antagonize various NK1 receptor-mediated as well as stress-mediated effects in the guinea pig.

Anxiolytic- and antidepressant-like effects of the non-peptide vasopressin V1b receptor antagonist, SSR149415, suggest an innovative approach for the treatment of stress-related disorders.

The limbic localization of the arginine vasopressin V(1b) receptor has prompted speculation as to a potential role of this receptor in the control of emotional processes. To investigate this possibility, we have studied the behavioral effects of SSR149415, the first selective and orally active non-peptide antagonist of vasopressin V(1b) receptors, in a variety of classical (punished drinking, elevated plus-maze, and light/dark tests) and atypical (fear/anxiety defense test battery and social defeat-induced anxiety) rodent models of anxiety, and in two models of depression [forced swimming and chronic mild stress (CMS)]. When tested in classical tests of anxiety, SSR149415 produced anxiolytic-like activity at doses that ranged from 1 to 30 mg/kg (i.p. or p.o.), but the magnitude of these effects was overall less than that of the benzodiazepine anxiolytic diazepam, which was used as a positive control. In contrast, SSR149415 produced clear-cut anxiolytic-like activity in models involving traumatic stress exposure, such as the social defeat paradigm and the defense test battery (1-30 mg/kg, p.o.). In the forced swimming test, SSR149415 (10-30 mg/kg, p.o.) produced antidepressant-like effects in both normal and hypophysectomized rats. Moreover, in the CMS model in mice, repeated administration of SSR149415 (10 and 30 mg/kg, i.p.) for 39 days improved the degradation of the physical state, anxiety, despair, and the loss of coping behavior produced by stress. These findings point to a role for vasopressin in the modulation of emotional processes via the V(1b) receptor, and suggest that its blockade may represent a novel avenue for the treatment of affective disorders.

4-(2-Chloro-4-methoxy-5-methylphenyl)-N-[(1S)-2-cyclopropyl-1-(3-fluoro-4-methylphenyl)ethyl]5-methyl-N-(2-propynyl)-1,3-thiazol-2-amine hydrochloride (SSR125543A): a potent and selective corticotrophin-releasing factor(1) receptor antagonist. I. Biochemical and pharmacological characterization.

4-(2-Chloro-4-methoxy-5-methylphenyl)-N-[(1S)-2-cyclopropyl-1- (3-fluoro-4-methylphenyl)ethyl]5-methyl-N-(2-propynyl)-1,3-thiazol-2-amine hydrochloride (SSR125543A), a new 2-aminothiazole derivative, shows nanomolar affinity for human cloned or native corticotrophin-releasing factor (CRF)(1) receptors (pK(i) values of 8.73 and 9.08, respectively), and a 1000-fold selectivity for CRF(1) versus CRF(2 alpha) receptor and CRF binding protein. SSR125543A antagonizes CRF-induced stimulation of cAMP synthesis in human retinoblastoma Y 79 cells (IC(50) = 3.0 +/- 0.4 nM) and adrenocorticotropin hormone (ACTH) secretion in mouse pituitary tumor AtT-20 cells. SSR125543A is devoid of agonist activity in these models. Its brain penetration was demonstrated in rats by using an ex vivo [(125)I-Tyr(0)] ovine CRF binding assay. SSR125543A displaced radioligand binding to the CRF(1) receptor in the brain with an ID(50) of 6.5 mg/kg p.o. (duration of action >24 h). SSR125543A also inhibited the increase in plasma ACTH levels elicited in rats by i.v. CRF (4 microg/kg) injection (ID(50) = 1, 5, or 5 mg/kg i.v., i.p., and p.o., respectively); this effect lasted for more than 6 h when the drug was given orally at a dose of 30 mg/kg. SSR125543A (10 mg/kg p.o.) reduced by 73% the increase in plasma ACTH levels elicited by a 15-min restraint stress in rats. Moreover, SSR125543A (20 mg/kg i.p.) also antagonized the increase of hippocampal acetylcholine release induced by i.c.v. injection of 1 microg of CRF in rats. Finally, SSR125543A reduced forepaw treading induced by i.c.v. injection of 1 microg of CRF in gerbils (ID(50) = approximately 10 mg/kg p.o.). Altogether, these data indicate that SSR125543A is a potent, selective, and orally active CRF(1) receptor antagonist.

4-(2-Chloro-4-methoxy-5-methylphenyl)-N-[(1S)-2-cyclopropyl-1-(3-fluoro-4-methylphenyl)ethyl]5-methyl-N-(2-propynyl)-1, 3-thiazol-2-amine hydrochloride (SSR125543A), a potent and selective corticotrophin-releasing factor(1) receptor antagonist. II. Characterization in rodent models of stress-related disorders.

The present study investigated the effects of the novel corticotrophin-releasing factor (CRF)(1) receptor antagonist 4-(2-chloro-4-methoxy-5-methylphenyl)-N-[(1S)-2-cyclopropyl-1-(3-fluoro-4-methylphenyl)ethyl]5-methyl-N-(2-propynyl)-1,3-thiazol-2-amine hydrochloride (SSR125543A) in a variety of rodent models of anxiety, including conflict procedures (punished drinking and four-plate), exploration models (elevated plus-maze and light/dark), a fear/anxiety defense test battery, and several procedures based on stress-induced changes in physiological (isolation-induced hyperthermia and tail pinch-induced cortical norepinephrine release) or behavioral (social defeat-induced anxiety, maternal separation-induced vocalization) parameters. Moreover, the effects of SSR125543A were investigated in acute (forced swimming) and chronic (chronic mild stress; CMS) models of depression. SSR125543A and the CRF(1) receptor antagonist antalarmin displayed limited efficacy in exploration-based anxiety models. In contrast, both compounds produced clear-cut anxiolytic-like activity in models involving inescapable stress, including the conflict procedures, the social defeat-induced anxiety paradigm and the defense test battery (3-30 mg/kg i.p. or p.o.). These effects paralleled those of the anxiolytic diazepam. In addition, SSR125543A and antalarmin antagonized stress-induced hyperthermia, distress vocalization, and cortical norepinephrine release. In the forced swimming test, 30 mg/kg p.o. SSR125543A and 3 to 30 mg/kg p.o. antalarmin produced clear antidepressant-like effects. These latter results were strengthened by the findings from the CMS, which showed that repeated administration of 10 mg/kg i.p. SSR125543A for 30 days improved the degradation of the physical state, the reduction of body weight gain, and anxiety produced by stress. Together, these data indicate that SSR125543A shows good activity in acute and chronic tests of unavoidable stress exposure, suggesting that it may have a potential in the treatment of depression and some forms of anxiety disorders.

Characterization of (2S,4R)-1-[5-chloro-1-[(2,4-dimethoxyphenyl)sulfonyl]-3-(2-methoxy-phenyl)-2-oxo-2,3-dihydro-1H-indol-3-yl]-4-hydroxy-N,N-dimethyl-2-pyrrolidine carboxamide (SSR149415), a selective and orally active vasopressin V1b receptor antagonist.

(2S,4R)-1-[5-Chloro-1-[(2,4-dimethoxyphenyl)sulfonyl]-3-(2-methoxy-phenyl)-2-oxo-2,3-dihydro-1H-indol-3-yl]-4-hydroxy-N,N-dimethyl-2-pyrrolidine carboxamide (SSR149415), the first selective, nonpeptide vasopressin V1b receptor antagonist yet described, has been characterized in vitro and in vivo. SSR149415 showed competitive nanomolar affinity for animal and human V1b receptors and exhibited much lower affinity for rat and human V1a, V2, and oxytocin receptors. Moreover, this compound did not interact with a large number of other receptors, enzymes, or ion channels. In vitro, SSR149415 behaved as a full antagonist and potently inhibited arginine vasopressin (AVP)-induced Ca2+ increase in Chinese hamster ovary cells expressing rat or human V1b receptors. The in vivo activity of SSR149415 has been studied in several models of elevated corticotropin secretion in conscious rats. SSR149415 inhibited exogenous AVP-induced increase in plasma corticotropin, from 3 mg/kg i.p. and 10 mg/kg p.o. upwards. Similarly, this compound antagonized AVP-potentiated corticotropin release provoked by exogenous corticoliberin at 3 mg/kg p.o. The effect lasted for more than 4 h at 10 mg/kg p.o. showing a long-lasting oral effect. SSR149415 (10 mg/kg p.o.) also blocked corticotropin secretion induced by endogenous AVP increase subsequent to body water loss. Moreover, 10 mg/kg i.p SSR149415 inhibited plasma corticotropin elevation after restraint-stress in rats by 50%. In the four-plate test, a mouse model of anxiety, SSR149415 (3 mg/kg p.o. upwards) displayed anxiolytic-like activity after acute and 7-day repeated administrations. Thus, SSR149415 is a potent, selective, and orally active V1b receptor antagonist. It represents a unique tool for exploring the functional role of V1b receptors and deserves to be clinically investigated in the field of stress and anxiety.