Differential effects of the CRF-R1 antagonist GSK876008 on fear-potentiated, light- and CRF-enhanced startle suggest preferential involvement in sustained vs phasic threat responses

The amplitude of the acoustic startle response is increased when elicited in the presence of brief cues that predict shock (fear-potentiated startle) and also when elicited during sustained exposure to bright light (light-enhanced startle). Although both effects are thought to reflect fear or anxiety, their neuroanatomical substrates differ. Although fear-potentiated startle is disrupted by reversible inactivation of the central nucleus of the amygdala (CeA) but not the closely related bed nucleus of the stria terminalis (BNST), light-enhanced startle is disrupted by BNST inactivation but not by CeA inactivation. Intraventricular infusions of corticotropin-releasing factor (CRF) also increase startle (CRF-enhanced startle) and this effect is mediated by CRF receptors within the BNST, with no involvement of the CeA. Together, these observations suggest that CeA- and BNST-dependent fear and anxiety may be differentially sensitive to CRF receptor blockade. We tested this by orally administering the novel, potent, and selective CRF-R1 antagonist GSK876008 to rats before CRF-enhanced, light-enhanced, or fear-potentiated startle testing. GSK876008 disrupted CRF-enhanced startle with a linear dose-response curve, and light-enhanced startle with a U-shaped dose-response curve, but did not disrupt fear-potentiated startle to a visual stimulus at any dose tested, and even augmented the response in some animals. GSK876008 also disrupted shock-related 'baseline' startle increases, which may have reflected context conditioning (shown elsewhere to also be BNST-dependent). Overall, these results suggest that short-duration CeA-dependent threat responses can be pharmacologically dissociated from longer duration BNST-dependent responses in terms of their sensitivity to CRF1 receptor antagonists.

The selective glycine antagonist gavestinel lacks phencyclidine-like behavioral effects

Gavestinel [GV150526A; ( E)-3[(phenylcarbamoil)ethenyl]-4,6-dichloroindole-2-carboxylic acid sodium salt] is a selective antagonist at the strychnine-insensitive glycine site of the -methyl-D-aspartate (NMDA) receptor. It was tested for its ability to substitute for phencyclidine (PCP) in rats and rhesus monkeys trained to discriminate PCP from saline, under a two-lever fixed-ratio (FR) food reinforcement schedule, and for its ability to maintain responding in rhesus monkeys trained to self-administer PCP under a FR reinforcement schedule. No PCP-lever responding was observed after gavestinel (1-56 mg/kg i.p.) administration to rats discriminating PCP (2.0 mg/kg i.p.) from saline. The highest dose of gavestinel (100 mg/kg i.p.) tested eliminated responding. Likewise, no PCP-lever responding was observed after gavestinel (1-30 mg/kg s.c.) administration to rhesus monkeys discriminating PCP (0.08 or 0.1 mg/kg i.m.) from saline; the highest dose of gavestinel (30 mg/kg s.c.) tested reduced response rates to approximately 50% of those observed after its vehicle ( -cyclodextrin in 0.9% saline). Gavestinel (0.1-1 mg/kg per i.v. infusion) was not self-administered by rhesus monkeys that reliably self-administered PCP (0.0056 or 0.01 mg/kg per i.v. infusion). Infusion rates at the highest dose were typically lower than those for vehicle or saline, suggesting behavioral activity. Together, these results suggest that at behaviorally active doses gavestinel is not PCP-like and is likely to have low abuse liability.

The continuing evolution of the drug discovery process in the pharmaceutical industry

Many early discoveries in the pharmaceutical industry were through serendipity. Later, targets were mainly identified in animals and systematically exploited through the identification of potent and selective molecules. A disease association was normally obtained through the clinical testing of candidate molecules in patients. The technological advances in the last few years offer the possibility of knowing more about the disease, and this is driving the industry towards a disease-based approach where understanding the disease becomes central to the process. This is now possible thanks to the recent explosion in molecular and cellular biology, together with the application of genetics and genomics. New screening technologies have also revolutionized the identification of chemical leads. Now, high throughput screening allows a wide chemical diversity to be applied in order to obtain tractable leads, which can then be optimized by the medicinal chemist. It is envisaged that these trends of continuously searching for process improvement will continue, being driven by the need to find medicines that add value in treating unmet medical need.

Effects of cholecystokinin peptides and GV 150013, a selective cholecystokininB receptor antagonist, on electrically evoked endogenous GABA release from rat cortical slices

The effects of cholecystokinin (CCK) agonists and antagonists on spontaneous and electrically evoked endogenous GABA release from rat cerebral cortex slices were evaluated. Neither the nonselective and CCK(B)-selective receptor agonists CCK-8S (3-1,000 nM) and CCK-4 (3-1,000 nM), respectively, nor the selective CCK(B) and CCK(A) receptor antagonists GV 150013 (3-30 nM) and L-364,718 (10-100 nM), respectively, significantly affected spontaneous GABA release. CCK-8S (1-1,000 nM) and CCK-4 (1-1,000 nM) increased the electrically (5 and 10 Hz)-evoked GABA release. On the contrary, GV 150013 (10 and 30 nM) significantly decreased the electrically evoked GABA release only when the slices were stimulated at the higher 10 Hz frequency. The CCK-8S- and CCK-4-induced increases in electrically evoked GABA release were counteracted by GV 150013, but not by L-364,718. Furthermore, GV 150013 at 3 nM shifted to the right the CCK-4 concentration-response curve, whereas at the higher 10 nM concentration it dramatically flattened the curve. Finally, in cortical slices obtained from rats chronically treated with GV 150013, the concentration-response curve of CCK-4 was shifted to the left and the peak effect of the peptide was significantly higher than that observed in naive animals. These results suggest that CCK increases electrically evoked, but not spontaneous, endogenous GABA release from rat cortical slices, possibly by activating local CCK(B) receptors. In addition, chronic treatment with the novel CCK(B) receptor antagonist GV 150013 leads to an enhanced responsiveness of cortical slices to CCK-4 application.

GV 150526A, 7-Cl-kynurenic acid and HA 966 antagonize the glycine enhancement of N-methyl-D-aspartate-induced [3H]noradrenaline and [3H]dopamine release

The effect of selective antagonists (7-Cl-kynurenic acid, 3-amino-1-hydroxypyrrolid-2-one (HA 966) and GV 150526A) at strychnine-insensitive glycine sites was studied by measuring how much glycine potentiated the [3H]dopamine and [3H]noradrenaline release induced by 100 microM N-methyl-D-aspartate (NMDA) from superfused striatal and hippocampal synaptosomes, respectively, in a Mg2+-free buffer. Glycine, which per se had no effect on [3H]catecholamine release, concentration-dependently potentiated the effect of NMDA, with similar potency in the two brain regions (EC50 0.25 and 0.27 microM for [3H]dopamine and [3H]noradrenaline release, respectively). 7-Cl-Kynurenic acid reduced the effect of NMDA alone and antagonized the effect of 1 microM glycine, with Ki values of 1.1 and 0.6 microM for [3H]dopamine and [3H]noradrenaline release, respectively. HA 966 did not inhibit the effect of NMDA alone, but reduced the effect of glycine with Ki = 11.5 and 66 microM for [3H]dopamine and [3H]noradrenaline release. GV 150526A inhibited the effect of NMDA alone and potently antagonized the effect of glycine, with Ki = 12.4 and 17.3 nM for [3H]dopamine and [3H]noradrenaline release. Our results are consistent with the possibility that HA 966 is a partial agonist, while 7-Cl-kynurenic acid and GV 150526A are competitive antagonists at the strychnine-insensitive glycine sites. In addition HA 966 shows regional differences in its interaction with the strychnine-insensitive glycine receptor, being about six times more potent on striatal than on hippocampal synaptosomes, suggesting a possible heterogeneity of glycine sites recognized by HA 966 or different intrinsic activity in the two brain regions. The nanomolar potency of GV 150526A in reducing NMDA receptor function by competitively acting at the strychnine-insensitive glycine sites suggests that GV 150526A could be effective in vivo to reduce NMDA receptor over-stimulation, like in brain ischemia.

Pharmacological analysis of carboxyphenylglycines at metabotropic glutamate receptors

Three carboxyphenylglycine derivatives were examined for their activity on glutamate metabotropic receptors negatively linked to adenylate cyclase. Chinese hamster ovary cells stably expressing mGlu2 and mGlu4 were utilised for this study. A receptor binding analysis was also performed for the main classes of glutamate ionotropic receptors and for the glycine binding site on the NMDA-receptor complex. In mGlu2 expressing cells (S)4-carboxy-3-hydroxyphenylglycine and (S)4-carboxy-phenylglycine antagonized forskolin-stimulated cAMP levels, with EC50 of 21 and 970 microM, respectively, acting as agonists at this receptor subtype, whereas (RS) alpha-methyl-4-carboxyphenylglycine antagonized glutamate response in these cells. None of these compounds showed any agonistic or antagonistic activity on mGlu4 expressing cells. No affinity for the ionotropic receptors (NMDA, AMPA and kainate) and for the glycine site of the NMDA-receptor complex was found using the receptor binding approach, except for (RS)4-carboxy-3-hydroxyphenylglycine which showed a pKi of 5.68 in ((+/-)2-carboxypiperazin-4-yl)propyl-1-phosphonic acid binding for NMDA receptor, although this can be ascribed to the (R) form of the racemic mixture.

In-vivo binding of (+)-[3H]PN 200-110 to peripheral tissues and brain of spontaneously hypertensive rats: effect of lacidipine

The time-course of dihydropyridine receptor occupancy by lacidipine and its relationship with pharmacological activity has been studied in spontaneously hypertensive rat (SHR), as measured by the inhibition of specific (+)-[3H]PN 200-110 binding in-vivo. After oral administration of doses active in reducing blood pressure, lacidipine did not show tissue target differences in respect to binding sites labelled by (+)-[3H]PN 200-110 in cerebral cortex, heart, ileum, bladder and thoracic aorta. The relative occupancy of receptors in heart 60 min after oral administration of 1 mg kg-1 lacidipine was 75%. After 12 h, when lacidipine was still effective in reducing blood pressure in SHR, a low (15%) but detectable proportion of receptors was still occupied by the drug. The percentage decrease of blood pressure was linear with the percentage of receptor occupancy obtained by different doses of lacidipine; that is, there was a close correspondence between ED25 for decrease in blood pressure (0.33 mg kg-1) and ED25 for inhibition of (+)-[3H]PN 200-110 specific binding in the heart (0.36 mg kg-1). The long-lasting effect of lacidipine on blood pressure might be explained by its selective interaction with dihydropyridine binding sites labelled in-vivo by (+)-[3H]PN 200-110.

Analysis of the CCKB receptor antagonism of virginiamycin in guinea-pig ileum longitudinal myenteric plexus

1. Virginiamycin, a macrolide reported to bind selectively to CCKB/gastrin receptors has been studied in a functional test, namely cholecystokinin-induced contraction of guinea-pig ileum myenteric plexus (LMMP). 2. Virginiamycin (1-10 microM) antagonized the selective CCKB agonist cholecystokinin tetrapeptide (CCK-4). The antagonism appeared not to be competitive as the highest concentration (10 microM) caused a reduction of its maximal effect. An apparent pA2 of 6.64 +/- 0.06 (s.e.) could be estimated if this depression was ignored. The selective CCKB antagonist, L-365,260 (0.01-0.3 microM) antagonized competitively the CCK-4 induced contraction and a pKB of 8.60 +/- 0.16 (s.e.) was estimated. 3. The combined dose-ratio analysis for virginiamycin, tested at 3 and 10 microM in association with 0.03 and 0.1 microM L-365,260, respectively, resulted in observed log dose-ratios of 1.39 and 1.53. That was consistent with both antagonists acting on the same receptor in LMMP. 4. These data, represent the first evidence of the antagonism of virginiamycin in a functional assay and they support the hypothesis of homogeneity between CCKB receptors in the CNS and in peripheral tissues.

Analysis of the interaction between lacidipine and BAY K 8644 in two isolated rabbit arteries

The calcium antagonist activity of the long-acting 1,4-dihydropyridine (DHP) lacidipine has been analyzed in rabbit ear artery (REA) and rabbit basilar artery (RBA). Its potency has been estimated from its interaction with BAY K 8644 using a three state gating model of the voltage-operated calcium channel. As a contractile agent, BAY K 8644 exhibited a bell-shaped concentration-response curve in both arteries. For fitting purposes, a second binding interaction between BAY K 8644 and the channel has been used to describe the descending part of the curve. The K(app)s for lacidipine and three other DHPs (nifedipine, nitrendipine and amlodipine) have been compared to pA2 values obtained from displacement of calcium concentration-response curves. In both REA and RBA the K(app)s for the four DHPs were not significantly different compared to their pA2s. The pK(app) values for lacidipine were estimated as 9.80 for REA and 10.20 for RBA.

Evidence for two cholecystokinin receptors mediating the contraction of the guinea pig isolated ileum longitudinal muscle myenteric plexus

In guinea pig isolated ileum longitudinal muscle myenteric plexus, cholecystokinin octapeptide (CCK-8S) produced a rapid (phasic) contraction followed by a slower tonic phase. The tetrapeptide derivative CCK-4 and pentagastrin elicited only the phasic response up to 10(-6) M, whereas the tonic phase was also apparent at higher concentrations. The rank order of potency for the effect of agonists on the tonic and phasic responses were CCK-8S much greater than gastrin greater than CCK-8US congruent to pentagastrin greater than CCK-4 and CCK-8S greater than gastrin congruent to pentagastrin greater than CCK-4 greater than CCK-8US, respectively. Phasic responses of CCK-8S and CCK-4 were sensitive to atropine, whereas the tonic response could be completely abolished with the neurokinin-1 antagonist GR82334. The CCK-A receptor antagonist L-364,718 up to 10(-7) M had little effect on the phasic contracture of CCK-4. The CCK-B/gastrin receptor antagonist L-365,260 had no effect on the CCK-8S phasic response up to 10(-7) M, but antagonized the phasic response induced by low concentrations of CCK-4 in a competitive manner with an estimated pKB of 8.51. This value is close to that of 8.53 found in a guinea pig cortical binding assay. Both the second phase of the CCK-4 phasic concentration response curve (CRC) and the tonic contraction were insensitive to L-365,260.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological analysis of 5-hydroxytryptamine effects on electrically stimulated human isolated urinary bladder

1. 5-Hydroxytryptamine (5-HT) is able to potentiate the contractions induced by electrical field stimulation of pieces of human isolated urinary bladder. On the basis of available selective 5-HT agonists and antagonists, we have further investigated the receptors involved and their site of action. 2. 5-HT produced a concentration-dependent increase of the contractile response to electrical field stimulation from 0.1 nM to 1 microM. At higher concentrations (up to 100 microM) the effect decreased. These activities were mimicked by a variety of 5-HT agonists, for which the following rank order of potency was found: 5-HT greater than alpha-methyl 5-HT greater than 5-methoxytryptamine greater than 5-carboxamidotryptamine greater than 2-methyl 5-HT much greater than GR 43175. In addition the gastro-prokinetics agents metoclopramide, cisapride and the 5-HT3 antagonist ICS 205-930 behaved as 5-HT agonists, their EC50 values being 2.3, 0.3, and 0.5 (microM) respectively. 3. The 5-HT potentiating effect was resistant to antagonism by ondansetron (1 microM) and cyanopindolol (1 microM), selective 5-HT3 and 5-HT1A/1B antagonists respectively. The 5-HT2 antagonists ketanserin (1 microM), spiperone (1 microM) and methysergide (1 microM) also showed a weak inhibitory activity. Methiothepin (0.1-1 microM) antagonized only the inhibitory effect of 5-HT. Metoclopramide (0.1-1 microM), cisapride (0.01-0.1 microM) and ICS 205-930 (0.3-3 microM) all produced a rightward displacement of the 5-HT response curve with concomitant reduction of the maximum response. The pA2 values calculated were 7.4, 8.5 and 7.0 respectively. The antagonism of metoclopramide was receptor specific and was not apparently related to interactions with dopaminergic activity since domperidone showed no antagonism of 5-HT, and metoclopramide, itself, did not antagonize the potentiating effect of prostaglandin F2a.4. The receptor involved in the potentiating effect of 5-HT may be located prejunctionally because 5-HT did not potentiate responses to acetylcholine (ACh) or electrical field stimulation with the parameters of direct muscle excitation. Also, since the 5-HT potentiating effect was blocked by atropine, it may be attributed to a release of ACh.5. This study suggests that in the human urinary bladder 5-HT causes two opposite effects on the contractile response to electrical field stimulation. A potentiating effect at low concentrations due to an interaction with an atypical receptor, different from the classical 5-HT1, 5-HT2 or 5-HT3 subtypes and an inhibitory effect at greater concentrations probably due to an interaction with 5-HT1-like receptors. The possibility that this atypical receptor possesses some characteristics of those found in other isolated preparations like guinea-pig ileum, rat oesophagus and mouse embryo colliculi neurones is discussed.