Discovery of pyrrolo[2,1-f][1,2,4]triazine-based inhibitors of adaptor protein 2-associated kinase 1 for the treatment of pain.

Adaptor protein 2-associated kinase 1 (AAK1) is a member of the Ark1/Prk1 family of serine/threonine kinases and plays a role in modulating receptor endocytosis. AAK1 was identified as a potential therapeutic target for the treatment of neuropathic pain when it was shown that AAK1 knock out (KO) mice had a normal response to the acute pain phase of the mouse formalin model, but a reduced response to the persistent pain phase. Herein we report our early work investigating a series of pyrrolo[2,1-f][1,2,4]triazines as part of our efforts to recapitulate this KO phenotype with a potent, small molecule inhibitor of AAK1. The synthesis, structure-activity relationships (SAR), and in vivo evaluation of these AAK1 inhibitors is described.

The discovery of VU0652957 (VU2957, Valiglurax): SAR and DMPK challenges en route to an mGlu4 PAM development candidate.

This letter describes the first account of the chemical optimization (SAR and DMPK profiling) of a new series of mGlu4 positive allosteric modulators (PAMs), leading to the identification of VU0652957 (VU2957, Valiglurax), a compound profiled as a preclinical development candidate. Here, we detail the challenges faced in allosteric modulator programs (e.g., steep SAR, as well as subtle structural changes affecting overall physiochemical/DMPK properties and CNS penetration).

Evidence for Classical Cholinergic Toxicity Associated with Selective Activation of M1 Muscarinic Receptors.

The muscarinic acetylcholine receptor subtype 1 (M1) receptors play an important role in cognition and memory, and are considered to be attractive targets for the development of novel medications to treat cognitive impairments seen in schizophrenia and Alzheimer's disease. Indeed, the M1 agonist xanomeline has been shown to produce beneficial cognitive effects in both Alzheimer's disease and schizophrenia patients. Unfortunately, the therapeutic utility of xanomeline was limited by cholinergic side effects (sweating, salivation, gastrointestinal distress), which are believed to result from nonselective activation of other muscarinic receptor subtypes such as M2 and M3. Therefore, drug discovery efforts targeting the M1 receptor have focused on the discovery of compounds with improved selectivity profiles. Recently, allosteric M1 receptor ligands have been described, which exhibit excellent selectivity for M1 over other muscarinic receptor subtypes. In the current study, the following three compounds with mixed agonist/positive allosteric modulator activities that are highly functionally selective for the M1 receptor were tested in rats, dogs, and cynomologous monkeys: (3-((1S,2S)-2-hydrocyclohexyl)-6-((6-(1-methyl-1H-pyrazol-4-yl)pyridin-3-yl)methyl)benzo[h]quinazolin-4(3H)-one; 1-((4-cyano-4-(pyridin-2-yl)piperidin-1-yl)methyl)-4-oxo-4H-quinolizine-3-carboxylic acid; and (R)-ethyl 3-(2-methylbenzamido)-[1,4'-bipiperidine]-1'-carboxylate). Despite their selectivity for the M1 receptor, all three compounds elicited cholinergic side effects such as salivation, diarrhea, and emesis. These effects could not be explained by activity at other muscarinic receptor subtypes, or by activity at other receptors tested. Together, these results suggest that activation of M1 receptors alone is sufficient to produce unwanted cholinergic side effects such as those seen with xanomeline. This has important implications for the development of M1 receptor-targeted therapeutics since it suggests that dose-limiting cholinergic side effects still reside in M1 receptor selective activators.

Inhibition of AAK1 Kinase as a Novel Therapeutic Approach to Treat Neuropathic Pain.

To identify novel targets for neuropathic pain, 3097 mouse knockout lines were tested in acute and persistent pain behavior assays. One of the lines from this screen, which contained a null allele of the adapter protein-2 associated kinase 1 (AAK1) gene, had a normal response in acute pain assays (hot plate, phase I formalin), but a markedly reduced response to persistent pain in phase II formalin. AAK1 knockout mice also failed to develop tactile allodynia following the Chung procedure of spinal nerve ligation (SNL). Based on these findings, potent, small-molecule inhibitors of AAK1 were identified. Studies in mice showed that one such inhibitor, LP-935509, caused a reduced pain response in phase II formalin and reversed fully established pain behavior following the SNL procedure. Further studies showed that the inhibitor also reduced evoked pain responses in the rat chronic constriction injury (CCI) model and the rat streptozotocin model of diabetic peripheral neuropathy. Using a nonbrain-penetrant AAK1 inhibitor and local administration of an AAK1 inhibitor, the relevant pool of AAK1 for antineuropathic action was found to be in the spinal cord. Consistent with these results, AAK1 inhibitors dose-dependently reduced the increased spontaneous neural activity in the spinal cord caused by CCI and blocked the development of windup induced by repeated electrical stimulation of the paw. The mechanism of AAK1 antinociception was further investigated with inhibitors of α2 adrenergic and opioid receptors. These studies showed that α2 adrenergic receptor inhibitors, but not opioid receptor inhibitors, not only prevented AAK1 inhibitor antineuropathic action in behavioral assays, but also blocked the AAK1 inhibitor-induced reduction in spinal neural activity in the rat CCI model. Hence, AAK1 inhibitors are a novel therapeutic approach to neuropathic pain with activity in animal models that is mechanistically linked (behaviorally and electrophysiologically) to α2 adrenergic signaling, a pathway known to be antinociceptive in humans.

Oxazolidinone-based allosteric modulators of mGluR5: Defining molecular switches to create a pharmacological tool box.

Herein we describe the structure activity relationships uncovered in the pursuit of an mGluR5 positive allosteric modulator (PAM) for the treatment of schizophrenia. It was discovered that certain modifications of an oxazolidinone-based chemotype afforded predictable changes in the pharmacological profile to give analogs with a wide range of functional activities. The discovery of potent silent allosteric modulators (SAMs) allowed interrogation of the mechanism-based liabilities associated with mGluR5 activation and drove our medicinal chemistry effort toward the discovery of low efficacy (fold shift) PAMs devoid of agonist activity. This work resulted in the identification of dipyridyl 22 (BMS-952048), a compound with a favorable free fraction, efficacy in a rodent-based cognition model, and low potential for convulsions in mouse.

Difluorocyclobutylacetylenes as positive allosteric modulators of mGluR5 with reduced bioactivation potential.

Schizophrenia is a serious illness that affects millions of patients and has been associated with N-methyl-d-aspartate receptor (NMDAR) hypofunction. It has been demonstrated that activation of metabotropic glutamate receptor 5 (mGluR5) enhances NMDA receptor function, suggesting the potential utility of mGluR5 positive allosteric modulators (PAMs) in the treatment of schizophrenia. Herein we describe the optimization of an mGluR5 PAM by replacement of a phenyl with aliphatic heterocycles and carbocycles as a strategy to reduce bioactivation in a biaryl acetylene chemotype. Replacement with a difluorocyclobutane followed by further optimization culminated in the identification of compound 32, a low fold shift PAM with reduced bioactivation potential. Compound 32 demonstrated favorable brain uptake and robust efficacy in mouse novel object recognition (NOR) at low doses.

Structure activity relationship studies on chemically non-reactive glycine sulfonamide inhibitors of diacylglycerol lipase.

N-Benzylic-substituted glycine sulfonamides that reversibly inhibit diacylglycerol (DAG) lipases are reported. Detailed herein are the structure activity relationships, profiling characteristics and physico-chemical properties for the first reported series of DAG lipase (DAGL) inhibitors that function without covalent attachment to the enzyme. Highly potent examples are presented that represent valuable tool compounds for studying DAGL inhibition and constitute important leads for future medicinal chemistry efforts.

Discovery of D1 Dopamine Receptor Positive Allosteric Modulators: Characterization of Pharmacology and Identification of Residues that Regulate Species Selectivity.

The present studies represent the first published report of a dopamine D1 positive allosteric modulator (PAM). D1 receptors have been proposed as a therapeutic target for the treatment of cognitive deficits associated with schizophrenia. However, the clinical utility of orthosteric agonist compounds is limited by cardiovascular side effects, poor pharmacokinetics, lack of D1 selectivity, and an inverted dose response. A number of these challenges may be overcome by utilization of a selective D1 PAM. The current studies describe two chemically distinct D1 PAMs: Compound A [1-((rel-1S,3R,6R)-6-(benzo[d][1,3]dioxol-5-yl)bicyclo[4.1.0]heptan-3-yl)-4-(2-bromo-5-chlorobenzyl)piperazine] and Compound B [rel-(9R,10R,12S)-N-(2,6-dichloro-3-methylphenyl)-12-methyl-9,10-dihydro-9,10-ethanoanthracene-12-carboxamide]. Compound A shows pure PAM activity, with an EC50 of 230 nM and agonist activity at the D2 receptor in D2-expressing human embryonic kidney cells. Compound B shows superior potency (EC50 of 43 nM) and selectivity for D1 versus D2 dopamine receptors. Unlike Compound A, Compound B is selective for human and nonhuman primate D1 receptors, but lacks activity at the rodent (rat and mouse) D1 receptors. Using molecular biology techniques, a single amino acid was identified at position 130, which mediates the species selectivity of Compound B. These data represent the first described D1-selective PAMs and define critical amino acids that regulate species selectivity.

The discovery of potent agonists for GPR88, an orphan GPCR, for the potential treatment of CNS disorders.

Modulating GPR88 activity is suggested to have therapeutic utility in the treatment of CNS disorders, such as schizophrenia. This Letter will describe the discovery and SAR development of a class of potent GPR88 agonists.

Design, synthesis, and evaluation of phenylglycinols and phenyl amines as agonists of GPR88.

Small molecule modulators of GPR88 activity (agonists, antagonists, or modulators) are of interest as potential agents for the treatment of a variety of psychiatric disorders including schizophrenia. A series of phenylglycinol and phenylamine analogs have been prepared and evaluated for their GPR88 agonist activity and pharmacokinetic (PK) properties.

In vitro Characterization of a small molecule inhibitor of the alanine serine cysteine transporter -1 (SLC7A10).

NMDA receptor hypofunction is hypothesized to contribute to cognitive deficits associated with schizophrenia. Since direct activation of NMDA receptors is associated with serious adverse effects, modulation of the NMDA co-agonists, glycine or D-serine, represents a viable alternative therapeutic approach. Indeed, clinical trials with glycine and D-serine have shown positive results, although concerns over toxicity related to the high-doses required for efficacy remain. Synaptic concentrations of D-serine and glycine are regulated by the amino acid transporter alanine serine cysteine transporter-1 (asc-1). Inhibition of asc-1 would increase synaptic D-serine and possibly glycine, eliminating the need for high-dose systemic D-serine or glycine treatment. In this manuscript, we characterize Compound 1 (BMS-466442), the first known small molecule inhibitor of asc-1. Compound 1 selectively inhibited asc-1 mediated D-serine uptake with nanomolar potency in multiple cellular systems. Moreover, Compound 1 inhibited asc-1 but was not a competitive substrate for this transporter. Compound 1 is the first reported selective inhibitor of the asc-1 transporter and may provide a new path for the development of asc-1 inhibitors for the treatment of schizophrenia.

Discovery of a cyclopentylamine as an orally active dual NK1 receptor antagonist-serotonin reuptake transporter inhibitor.

Cyclopentylamine 4 was identified as a potent dual NK1R antagonist-SERT inhibitor. This compound demonstrated significant oral activity in the gerbil forced swimming test, suggesting that dual NK1R antagonists-SERT inhibitors may be useful in treating depression disorders.

Structure activity relationship studies of 3-arylsulfonyl-pyrido[1,2-a]pyrimidin-4-imines as potent 5-HT6 antagonists.

Comprehensive structure activity relationship (SAR) studies were conducted on a focused screening hit, 2-(methylthio)-3-(phenylsulfonyl)-4H-pyrido[1,2-a]pyrimidin-4-imine (1, IC50: 4.0 nM), as 5-HT6 selective antagonists. Activity was improved some 2-4 fold when small, electron-donating groups were added to the central core as observed in 19, 20 and 26. Molecular docking of key compounds in a homology model of the human 5-HT6 receptor was used to rationalize our structure-activity relationship (SAR) findings. In pharmacokinetic experiments, compound 1 displayed good brain uptake in rats following intra-peritoneal administration, but limited oral bioavailability.

Discovery of disubstituted piperidines and homopiperidines as potent dual NK1 receptor antagonists-serotonin reuptake transporter inhibitors for the treatment of depression.

This report describes the synthesis, structure-activity relationships and activity of piperidine, homopiperidine, and azocane derivatives combining NK1 receptor (NK1R) antagonism and serotonin reuptake transporter (SERT) inhibition. Our studies culminated in the discovery of piperidine 2 and homopiperidine 8 as potent dual NK1R antagonists-SERT inhibitors. Compound 2 demonstrated significant activity in the gerbil forced swimming test, suggesting that dual NK1R antagonists-SERT inhibitors may be useful in treating depression disorders.

Postsynaptic diacylglycerol lipase mediates retrograde endocannabinoid suppression of inhibition in mouse prefrontal cortex.

Depolarization-induced suppression of inhibition (DSI) is a prevailing form of endocannabinoid signalling. However, several discrepancies have arisen regarding the roles played by the two major brain endocannabinoids, 2-arachidonoylglycerol (2-AG) and anandamide, in mediating DSI. Here we studied endocannabinoid signalling in the prefrontal cortex (PFC), where several components of the endocannabinoid system have been identified, but endocannabinoid signalling remains largely unexplored. In voltage clamp recordings from mouse PFC pyramidal neurons, depolarizing steps significantly suppressed IPSCs induced by application of the cholinergic agonist carbachol. DSI in PFC neurons was abolished by extra- or intracellular application of tetrahydrolipstatin (THL), an inhibitor of the 2-AG synthesis enzyme diacylglycerol lipase (DAGL). Moreover, DSI was enhanced by inhibiting 2-AG degradation, but was unaffected by inhibiting anandamide degradation. THL, however, may affect other enzymes of lipid metabolism and does not selectively target the α (DAGLα) or ß (DAGLß) isoforms of DAGL. Therefore, we studied DSI in the PFC of DAGLα(-/-) and DAGLß(-/-) mice generated via insertional mutagenesis by gene-trapping with retroviral vectors. Gene trapping strongly reduced DAGLα or DAGLß mRNA levels in a locus-specific manner. In DAGLα(-/-) mice cortical levels of 2-AG were significantly decreased and DSI was completely abolished, whereas DAGLß deficiency did not alter cortical 2-AG levels or DSI. Importantly, cortical levels of anandamide were not significantly affected in DAGLα(-/-) or DAGLß(-/-) mice. The chronic decrease of 2-AG levels in DAGLα(-/-) mice did not globally alter inhibitory transmission or the response of cannabinoid-sensitive synapses to cannabinoid receptor stimulation, although it altered some intrinsic membrane properties. Finally, we found that repetitive action potential firing of PFC pyramidal neurons suppressed synaptic inhibition in a DAGLα-dependent manner. These results show that DSI is a prominent form of endocannabinoid signalling in PFC circuits. Moreover, the close agreement between our pharmacological and genetic studies indicates that 2-AG synthesized by postsynaptic DAGLα mediates DSI in PFC neurons.

Molecular characterization and identification of surrogate substrates for diacylglycerol lipase α.

Diacylglycerol lipase α is the key enzyme in the formation of the most prevalent endocannabinoid, 2-arachidonoylglycerol in the brain. In this study we identified the catalytic triad of diacylglycerol lipase α, consisting of serine 472, aspartate 524 and histidine 650. A truncated version of diacylglycerol lipase α, spanning residues 1-687 retains complete catalytic activity suggesting that the C-terminal domain is not required for catalysis. We also report the discovery and the characterization of fluorogenic and chromogenic substrates for diacylglycerol lipase α. Assays performed with these substrates demonstrate equipotent inhibition of diacylglycerol lipase α by tetrahydrolipastatin and RHC-20867 as compared to reactions performed with the native diacylglycerol substrate. Thus, confirming the utility of assays using these substrates for identification and kinetic characterization of inhibitors from pharmaceutical collections.

Cloning, purification, crystallization and preliminary X-ray analysis of the catalytic domain of human receptor-like protein tyrosine phosphatase γ in three different crystal forms.

Protein tyrosine phosphatase γ is a membrane-bound receptor and is designated RPTPγ. RPTPγ and two mutants, RPTPγ(V948I, S970T) and RPTPγ(C858S, S970T), were recombinantly expressed and purified for X-ray crystallographic studies. The purified enzymes were crystallized using the hanging-drop vapor-diffusion method. Crystallographic data were obtained from several different crystal forms in the absence and the presence of inhibitor. In this paper, a description is given of how three different crystal forms were obtained that were used with various ligands. An orthorhombic crystal form and a trigonal crystal form were obtained both with and without ligand, and a monoclinic crystal form was only obtained in the presence of a particularly elaborated inhibitor.

Viable mouse gene ablations that robustly alter brain Aß levels are rare.

BACKGROUND: Accumulation of amyloid-ß (Aß) peptide in the brain is thought to play a key pathological role in Alzheimer's disease. Many pharmacological targets have therefore been proposed based upon the biochemistry of Aß, but not all are equally tractable for drug discovery. RESULTS: To search for novel targets that affect brain Aß without causing toxicity, we screened mouse brain samples from 1930 novel gene knock-out (KO) strains, representing 1926 genes, using Aß ELISA assays. Although robust Aß lowering was readily apparent in brains from a BACE1 KO strain, none of the novel strains exhibited robust decreases in brain Aß, including a GPR3 KO strain, which had previously been proposed as an Aß target. However, significantly increased Aß was observed in brain samples from two KO strains, corresponding to genes encoding the glycosylphosphatidylinositol mannosyl transferase PIGZ and quinolinate phosphoribosyltransferase (QPRT). CONCLUSIONS: Thus, gene ablations that are permissive for mouse survival and that also have a robust effect on Aß levels in the brain are rare.

Effects of BMS-902483, an α7 nicotinic acetylcholine receptor partial agonist, on cognition and sensory gating in relation to receptor occupancy in rodents.

The α7 nicotinic acetylcholine receptor is thought to play an important role in human cognition. Here we describe the in vivo effects of BMS-902483, a selective potent α7 nicotinic acetylcholine receptor partial agonist, in relationship to α7 nicotinic acetylcholine receptor occupancy. BMS-902483 has low nanomolar affinity for rat and human α7 nicotinic acetylcholine receptors and elicits currents in cells expressing human or rat α7 nicotinic acetylcholine receptors that are about 60% of the maximal acetylcholine response. BMS-902483 improved 24h novel object recognition memory in mice with a minimal effective dose (MED) of 0.1mg/kg and reversed MK-801-induced deficits in a rat attentional set-shifting model of executive function with an MED of 3mg/kg. Enhancement of novel object recognition was blocked by the silent α7 nicotinic acetylcholine receptor agonist, NS6740, demonstrating that activity of BMS-902483 was mediated by α7 nicotinic acetylcholine receptors. BMS-902483 also reversed ketamine-induced deficits in auditory gating in rats, and enhanced ex vivo hippocampal long-term potentiation examined 24h after dosing in mice. Results from an ex vivo brain homogenate binding assay showed that α7 receptor occupancy ranged from 64% (novel object recognition) to ~90% (set shift and gating) at the MED for behavioral and sensory processing effects of BMS-902483.

BMS-933043, a Selective α7 nAChR Partial Agonist for the Treatment of Cognitive Deficits Associated with Schizophrenia.

The therapeutic treatment of negative symptoms and cognitive dysfunction associated with schizophrenia is a significant unmet medical need. Preclinical literature indicates that α7 neuronal nicotinic acetylcholine (nACh) receptor agonists may provide an effective approach to treating cognitive dysfunction in schizophrenia. We report herein the discovery and evaluation of 1c (BMS-933043), a novel and potent α7 nACh receptor partial agonist with high selectivity against other nicotinic acetylcholine receptor subtypes (>100-fold) and the 5-HT3A receptor (>300-fold). In vivo activity was demonstrated in a preclinical model of cognitive impairment, mouse novel object recognition. BMS-933043 has completed Phase I clinical trials.