Identification of 3-sulfonylindazole derivatives as potent and selective 5-HT(6) antagonists.

As part of our efforts to develop agents for cognitive enhancement, we have been focused on the 5-HT(6) receptor in order to identify potent and selective ligands for this purpose. Herein we report the identification of a novel series of 3-sulfonylindazole derivatives with acyclic amino side chains as potent and selective 5-HT(6) antagonists. The synthesis and detailed SAR of this class of compounds are reported.

Identification of a series of benzoxazoles as potent 5-HT6 ligands.

As part of our continuing efforts to identify therapeutics for CNS diseases such as schizophrenia and Alzheimer's disease (AD), we have been focused on the 5-HT(6) receptor in order to identify potent and selective ligands as a potential treatment for cognitive dysfunction. Herein we report the identification of a novel series of benzoxazole derivatives as potent 5-HT(6) ligands. The synthesis and detailed SAR of this class of compounds are reported. The compounds have been shown to be full antagonists in a cyclic AMP functional assay.

Identification of a novel series of 3-piperidinyl-5-sulfonylindazoles as potent 5-HT6 ligands.

Cognitive dysfunction is a characteristic of various forms of dementia such as Alzheimer's disease (AD) and a core feature of schizophrenia. As part of our continuing efforts to develop agents for cognitive enhancement, we have been focused on the 5-HT(6) receptor-one of the emerging therapeutic targets in this area. Herein, we report the identification of a novel series of 3-piperidinyl-5-sulfonylindazole derivatives as potent 5-HT(6) antagonists. The synthesis and SAR of this class of compounds are reported.

1-Sulfonylindazoles as potent and selective 5-HT6 ligands.

As part of our continuing efforts to identify therapeutics for CNS diseases, such as schizophrenia and Alzheimer's disease (AD), we have been focused on the 5-HT(6) receptor in an attempt to identify ligands as a potential treatment for cognitive dysfunction. Herein we report the identification of a novel series of 1-sulfonylindazole derivatives as potent and selective 5-HT(6) antagonists. The synthesis and SAR of this class of compounds are reported. Several potent compounds in both binding and cyclase functional assays also display good selectivity, microsomal stability, solubility, and brain penetration as well as low cytochrome P450 inhibition. One compound exemplified in this series showed 24% oral bioavailability and in vivo efficacy in a NOR cognition model at 10mg/kg following an oral administration in rats.

A regiospecific synthesis of a series of 1-sulfonyl azepinoindoles as potent 5-HT6 ligands.

A regiospecific synthesis of a series of 1-sulfonyl azepinoindoles as potent 5-HT6 ligands is reported.

Distinct functional profiles of aripiprazole and olanzapine at RNA edited human 5-HT2C receptor isoforms.

In this study we have functionally characterized aripiprazole (OPC-14597; 7-(4-[4-(2,3-dichlorophenyl)-1-piperazinyl]butyloxy-3,4-dihydro-2-(1H)-quinolinone), the prototype of a new generation antipsychotic drug termed dopamine-serotonin-system stabilizer, in cells expressing 5-hydroxytryptamine2 (5-HT2) receptor subtypes in comparison with olanzapine. In Chinese hamster ovary (CHO) cells stably expressing 5-HT2 receptors, aripiprazole displayed a dual agonist/antagonist profile for 5-HT2C receptor (VNI isoform) mediated calcium signaling (EC50 1070 nM, IC50 281 nM). It exhibited no appreciable 5-HT2A or 5-HT2B agonism, whereas it antagonized 5-HT-stimulated calcium increase at either 5-HT2A or 5-HT2B receptor expressed in CHO cells (IC50s of 369 and 0.46 nM, respectively). In comparison, olanzapine was devoid of agonism but was an antagonist at all three subtypes, with a potency rank order of 5-HT2A (IC50, 2.5 nM)>5-HT2B (47 nM)>5-HT2C (69 nM). In human embryonic kidney (HEK) cells transiently expressing 5-HT2C receptor isoforms, aripiprazole exhibited full agonism at the unedited INI, but partial agonism at the partially edited VNI and fully edited VSV isoforms (EC50s of 571, 1086 and 2099 nM, respectively). A partial antagonism was also observed for aripiprazole at the two edited isoforms (IC50s of 1138 and 1000 nM, respectively). In contrast, while lacking agonist activity at the VNI and VSV, olanzapine showed inverse agonism at the INI isoform (IC50 594 nM), reaching a maximal attenuation of 20%. In addition, olanzapine was a full antagonist at all three isoforms, with a rank order of potency of VNI (IC50, 79 nM)>VSV (101 nM)>INI (3856 nM). The modest 5-HT2A antagonism and 5-HT2C partial agonism, along with reported D2 and 5-HT1A partial agonism, may allow aripiprazole to stabilize the disturbed dopamine-serotonin interplay in schizophrenia with a moderate yet adequate pharmacological intervention. 5-HT2C agonism may also underlie the minimal weight gain seen with aripiprazole.

Characterization of the 5-HT6 receptor coupled to Ca2+ signaling using an enabling chimeric G-protein.

We examined the feasibility of coupling the 5-HT(6) receptor to a Ca(2+) signaling read-out using a chimeric G-protein, comprising of G(alphaq) with the C-terminal five amino acids from G(alphas), to facilitate assays on the fluorometric imaging plate reader (FLIPR). Using a transient transfection assay in human embryonic kidney (HEK) cells, Ca(2+) signaling in response to serotonin (5-HT) was facilitated by co-transfection of the 5-HT(6) receptor with the G(alphaq)/G(alphas) chimera, but not with the 5-HT(6) receptor alone or with a similar chimera incorporating the C-terminal five amino acids of G(alphai3). A series of agonist concentration-response curves were constructed using the 5-HT(6)-G(alphaq)/G(alphas) signaling assay generating the following rank order of agonist potency; 5-methoxytryptamine (EC(50), 9 nM)=5-HT (12 nM)=2-methyl 5-HT (13 nM)>tryptamine (86 nM)=5-carboxamidotryptamine (5-CT) (119 nM)>>lisuride (>1 microM). In comparison, essentially identical EC(50) values were observed for the stimulation of cAMP accumulation with the same compounds; 5-methoxytryptamine (EC(50), 6 nM)=5-HT (6 nM)=2-methyl 5-HT (15 nM)>tryptamine (91 nM)=5-CT (153 nM)>lisuride (>350 nM). Clozapine and SB 271046 both produced a concentration-dependent antagonism of the 5-HT-stimulated Ca(2+) response with IC(50) values of 45 and 11 nM, respectively. In contrast, aripiprazole, a recently launched atypical anti-psychotic with a novel mechanism of action described as a dopamine/serotonin stabilizer, was essentially devoid of 5-HT(6) receptor antagonist activity. Our results demonstrate that a FLIPR-based Ca(2+) signaling assay is a feasible approach to the functional characterization of 5-HT(6) receptor ligands. Moreover, the equivalent coupling efficiency, as indexed by agonist potency, observed using this system compared with the native coupling assay to cAMP suggests that the C-terminal five amino acids of G(alphas) are the major determinant for the receptor/G-protein interaction of the 5-HT(6) receptor subtype.

Development of an improved IP(1) assay for the characterization of 5-HT(2C) receptor ligands.

The 5-hydroxytryptamine 2C (5-HT(2C)) receptor is a member of the serotonin 5-HT(2) subfamily of G-protein-coupled receptors signaling predominantly via the phospholipase C (PLC) pathway. Stimulation of phosphoinositide (PI) hydrolysis upon 5-HT(2C) receptor activation is traditionally assessed by measuring inositol monophosphate (IP(1)) using time-consuming and labor-intensive anion exchange radioactive assays. In this study, we have developed and optimized a cellular IP(1) assay using homogeneous time-resolved fluorescence (HTRF), a fluorescence resonance energy transfer (FRET)-based technology (Cisbio; Gif sur Yvette, France). The measurement is simple to carry out without the cumbersome steps associated with radioactive assays and may therefore be used as an alternative tool to evaluate PI hydrolysis activated by 5-HT(2C) agonists. In Chinese hamster ovary (CHO) cells stably expressing 5-HT(2C) receptors, characterization of 5-HT(2C) agonists with the HTRF platform revealed a rank order of potency (EC(50), nM) comparable to that from intracellular calcium mobilization studies measured by the fluorometric imaging plate reader (FLIPR). A similar rank order of potency was seen with conventional radioactive PI assay with the exception of 5-HT. Lastly, the new assay data correlated better with agonist-induced calcium responses in FLIPR (R(2) = 0.78) than with values determined by radioactive IP(1) method (R(2) = 0.64). Our study shows that the HTRF FRET-based assay detects IP(1) with good sensitivity and may be streamlined for high-throughput (HTS) applications.

5-Piperazinyl-3-sulfonylindazoles as potent and selective 5-hydroxytryptamine-6 antagonists.

As part of our efforts to develop agents for CNS diseases, we have been focused on the 5-HT(6) receptor in order to identify potent and selective ligands for cognitive enhancement. Herein we report the identification of a novel series of 5-piperazinyl-3-sulfonylindazoles as potent and selective 5-HT(6) antagonists. The synthesis, SAR, and pharmacokinetic and pharmacological activities of some of the compounds including 3-(naphthalen-1-ylsulfonyl)-5-(piperazin-1-yl)-1H-indazole (WAY-255315 or SAM-315) will be described.