Anxiolytic- and antidepressant-like profiles of the galanin-3 receptor (Gal3) antagonists SNAP 37889 and SNAP 398299.

The neuropeptide galanin mediates its effects through the receptor subtypes Gal(1), Gal(2), and Gal(3) and has been implicated in anxiety- and depression-related behaviors. Nevertheless, the receptor subtypes relevant to these behaviors are not known because of the lack of available galanin-selective ligands. In this article, we use behavioral, neurochemical, and electrophysiological approaches to investigate the anxiolytic- and antidepressant-like effects of two potent small-molecule, Gal(3)-selective antagonists, SNAP 37889 and the more soluble analog SNAP 398299. Acute administration of SNAP 37889 or SNAP 398299 enhanced rat social interaction. Furthermore, acute SNAP 37889 was also shown to reduce guinea pig vocalizations after maternal separation, to attenuate stress-induced hyperthermia in mice, to increase punished drinking in rats, and to decrease immobility and increase swimming time during forced swim tests with rats. Moreover, SNAP 37889 increased the social interaction time after 14 days of treatment and maintained its antidepressant effects during forced swim tests with rats after 21 days of treatment. In microdialysis studies, SNAP 37889 partially antagonized the galanin-evoked reduction in hippocampal serotonin (5-hydroxytryptamine, 5-HT), as did the 5-HT(1A) receptor antagonist WAY100635. Their combination produced a complete reversal of the effect of galanin. SNAP 398299 partially reversed the galanin-evoked inhibition of dorsal raphe cell firing and galanin-evoked hyperpolarizing currents. These results indicate that Gal(3)-selective antagonists produce anxiolytic- and antidepressant-like effects, possibly by attenuating the inhibitory influence of galanin on 5-HT transmission at the level of the dorsal raphe nucleus.

Use of Caenorhabditis elegans G{alpha}q chimeras to detect G-protein-coupled receptor signals.

G-protein-coupled receptors (GPCRs) activate heterotrimeric G-proteins (G(i)-, G(s)-, G(q)-, or G(12)-like) to generate specific intracellular responses, depending on the receptor/G-protein coupling. The aim was to enable a majority of GPCRs to generate a predetermined output by signaling through a single G-protein-supported pathway. The authors focused on calcium responses as the output, then engineered Galpha(q) to promote promiscuous receptor interactions. Starting with a human Galpha(q) containing 5 Galpha(z) residues in the C-terminal receptor recognition domain (hGalpha(q/z5)), they evaluated agonist-stimulated calcium responses for 33 diverse GPCRs (G(i)-, G(s)-, and G(q)-coupled) and found 20 of 33 responders. In parallel, they tested Caenorhabditis elegans Galpha(q) containing 5 or 9 C-terminal Galpha(z) residues (cGalpha(q/z5), cGalpha(q/z9)). Signal detection was enhanced with cGalpha(q/z5) and cGalpha(q/z9) (yielding 25/33 and 26/33 responders, respectively). In a separate study of Galpha(s)-coupled receptors, the authors compared hGalpha(q/s5) versus hGalpha(q/s9), cGalpha(q/s9), andcGalphaq/s21 and observed optimal function with cGalpha(q/s9). Cotransfection of an engineered Galpha(q) "cocktail" (cGalpha(q/z5) plus cGalpha(q/s9)) provided a powerful and efficient screening platform. When the chimeras included N-terminal myristoylation sites (to promote membrane localization), calcium responses were sustained or improved, depending on the receptor. This approach toward a "universal functional assay" is particularly useful for orphan GPCRs whose signaling pathways are unknown.

Substituted furo[3,2-b]pyridines: novel bioisosteres of 5-HT 1F receptor agonists.

Synthesis and evaluation of a series of 2,3,5- and 3,5-substituted furo[3,2-b]pyridines were undertaken in order to investigate their utility as bioisosteres of 5-HT(1F) receptor agonist indole analogues, 1-3. The replacement proved to be effective, providing compounds with similar 5-HT(1F) receptor affinity and improved selectivity when compared with the indole analogues. Through these studies we identified 4-fluoro-N-[3-(1-methyl-piperidin-4-yl)-furo[3,2-b]pyridin-5-yl]-benzamide (5), a potent and selective 5-HT(1F) receptor agonist with the potential to treat acute migraine.

Novel potent 5-HT(1F) receptor agonists: structure-activity studies of a series of substituted N-[3-(1-methyl-4-piperidinyl)-1H-pyrrolo[3,2-b]pyridin-5-yl]amides.

Compound 1a (LY334370), a selective 5-HT(1F) receptor agonist (SSOFRA), inhibited dural inflammation in the neurogenic plasma protein extravasation model of migraine and demonstrated clinical efficacy for the acute treatment of migraine. Although 1a was greater than 100-fold selective over both the 5-HT(1B) and 5-HT(1D) receptors, it exhibited appreciable 5-HT(1A) receptor affinity. Described here is the synthesis and evaluation of a series of pyrrolo[2,3-c]pyridine and pyrrolo[3,2-b]pyridine (2a and 3a) as well as pyrrolo[3,2-d]pyrimidine (4a) analogues of 1a, compounds prepared in an effort to identify SSOFRAs with improved selectivity over other 5-HT(1) receptor subtypes. The pyrrolo[3,2-b]pyridine analogue 3a showed high 5-HT(1F) receptor affinity but offered no improvement in selectivity compared to 1a. However, the C-5 acetamide derivative, 3b, was greater than 100-fold selective over the 5-HT(1A), 5-HT(1B), and 5-HT(1D) receptors. SAR studies of this series determined that alkylamides in particular exhibited high selectivity for the 5-HT(1F) receptor. Replacement at C-5 with other substituents decreased affinity or selectivity. These SAR studies identified SSOFRAs that demonstrated oral activity in the neurogenic plasma protein extravasation model, a model indicative of antimigraine activity.

Trace amine receptors as targets for novel therapeutics: legend, myth and fact.

Trace amines are attracting attention as neurotransmitters because they are believed to play a role in human disorders such as schizophrenia, depression, attention deficit disorder and Parkinson's disease. Research to date is promising and confirms the need for continuing work to forge the way for new drug discovery.

Antidepressant, anxiolytic and anorectic effects of a melanin-concentrating hormone-1 receptor antagonist.

Melanin concentrating hormone (MCH) is an orexigenic hypothalamic neuropeptide, which plays an important role in the complex regulation of energy balance and body weight. Here we show that SNAP-7941, a selective, high-affinity MCH1 receptor (MCH1-R) antagonist, inhibited food intake stimulated by central administration of MCH, reduced consumption of palatable food, and, after chronic administration to rats with diet-induced obesity, resulted in a marked, sustained decrease in body weight. In addition, after mapping the binding sites for [(3)H]SNAP-7941 in rat brain, we evaluated its effects in a series of behavioral models. SNAP-7941 produced effects similar to clinically used antidepressants and anxiolytics in three animal models of depression/anxiety: the rat forced-swim test, rat social interaction and guinea pig maternal-separation vocalization tests. Given these observations, an MCH1-R antagonist may be useful not only in the management of obesity but also as a treatment for depression and/or anxiety.