Accumulating evidence suggests a prominent role of the arrestin-dependent signaling pathway in triggering most of the deleterious side effects observed using δ-OR targeting drugs. Numerous small molecules targeting the δ-OR receptors have been developed but their pharmacological properties, including their functional selectivity, have been poorly characterized. The absence of functionally selective opioid drugs, and the lack of knowledge of the pharmacological profile and signaling properties of the δ-OR receptor, limits its therapeutic exploitation. The development of functionally selective modulator toward the canonical G protein pathway could importantly increase the therapeutic potential of this receptor while decreasing its deleterious effects. An approach to fine-tune the functional selectivity of a GPCR is by using allosteric modulators. These allosteric modulators would reduce problems associated with drugs targeting the orthosteric site by not chronically activating the receptor. The overall goal of the proposed research is to study the molecular mechanism by which sodium-channel inhibitors allosterically regulates the delta opioid receptor (δ-OR) signaling and functional selectivity. Additionally, the signaling features of the δ-OR signal transduction triggered by biased receptor activation have been investigated. A combination of approaches, including functional studies, molecular modeling and mutagenesis, were used to study the general mechanism underlying the activation and tuning of the δ-OR signal transduction behavior. Thus, this work suggests the druggability of the allosteric sodium pocket by using sodium channel inhibitors. The current research represent discovery of two different allosteric profiles for the β-arrestin recruitment and one allosteric profile for the G-protein pathway at activated DOR and would serve as scaffold for further refinement of modulators with the desired pharmacological profile.

Alpha7 Neuronal nicotinic acetylcholine receptors (nAChRs) are involved in essential physiological functions and play a role in disorders such as Alzheimer’s disease. MD-354 (3-chlorophenylguanidine; 21), the first small–molecule negative allosteric modulator (NAM) at alpha7 nAChRs, served as a lead in developing structure–activity relationships for NAMs at a7 nAChRs. MD-354 (21) also binds at 5-HT3 receptors. Analogs of MD-354 with structural features detrimental to 5-HT3 receptor affinity were evaluated in patch-clamp recordings and an aniline N-methyl analog resulted in a more potent and selective NAM than MD-354. A new N-methyl series of compounds was synthesized in which the 3-position was replaced with different substituents considering their electronic, lipophilic, and steric nature. Comparative studies were initiated to investigate whether or not the MD-354 series and the N-methyl series bind in the same manner; 3D models of the extracellular domain of human alpha7 nAChRs were developed, allosteric sites identified, and docking studies conducted.

The α7 nicotinic acetylcholine receptor (nAChR) subtype is abundantly expressed in the central nervous system (CNS) and in the periphery. Positive allosteric modulators (PAMs) of the α7 increase the response to an agonist and are divided into two types depending on whether they also decrease desensitization of the receptor (type II) or not (type I). Therefore, this study aims to investigate whether the enhancement of endogenous α7 nAChR function will result in a beneficial effect in nociceptive, inflammatory and chronic neuropathic pain models. While NS1738 and PNU-120596 were not active to reduce acute thermal pain, measured by hot-plate and tail-flick tests, only PNU-120596 dose-dependently attenuated paw-licking behavior in the formalin test. Our results with selective (MEK) inhibitor U0126 argues for an important role of extracellular signal-regulated kinase (ERK1/2) pathways activation in PNU-120596’s antinociceptive effects in formalin-induced pain. The α7 antagonist MLA, via intrathecal and intraplantar administration, reversed PNU-120596’s effects, confirming PNU-120596’s action through central and peripheral α7 nAChRs. Tolerance to PNU-120596 was not developed after chronic treatment of the drug. Furthermore, mixtures of PNU-120596 and choline, an endogenous α7 nAChR agonist, synergistically reduced formalin-induced pain, while interactions of non-antinociceptive doses of PNU-120596 and PHA-543613, a selective α7 nAChR agonist, or nicotine resulted in antinociception. In contrast, PNU-120596 failed to enhance nicotine-induced convulsions, -hypomotility and –antinociception in acute pain models. Surprisingly, it enhanced nicotine-induced hypothermia via α7 nAChRs. In the carrageenan inflammatory test both NS1738 and PNU-120596 significantly reduced thermal hyperalgesia, while only PNU-120596 significantly reduced edema. Importantly, PNU-120596 reversed established thermal hyperalgesia and edema induced by carrageenan. In the chronic neuropathic pain (CCI) model, PNU-120596 had long-lasting (up to 6 hrs), dose-dependent anti-hyperalgesic and anti-allodynic effects after a single injection, while NS1738 was inactive. Subcutaneous and intrathecal administration of MLA reversed PNU-120596’s effects, suggesting the involvement of α7 nAChRs. Finally, PNU-120596 enhanced an ineffective dose of selective agonist PHA-543613 to produce anti-allodynic effects in the CCI model. Our results show a fundamental in vivo difference between type I and II α7 nAChR PAMs, and demonstrate type II’s potential for the treatment of chronic inflammatory pain.

des-Formylflustrabromine (dFBr), isolated from the marine organism Flustra foliacea, is the first selective, positive allosteric modulator (PAM) of α4β2 nicotinic acetylcholine receptors that potentiates the action of the neurotransmitter acetylcholine (ACh). Most agonists for this receptor population are not selective and can activate other nACh receptors. A selective PAM, which activates α4β2 nACh receptors only in the presence of ACh, might find application in the treatment of of various neurological diseases such as Alzheimer’s disease or autism. dFBr was examined and found to produce a biphasic dose-response curve over a wide concentration range (i.e., potentiation at low concentration, but inhibition of the ACh-induced response at high concentrations). Our goal was to examine various structural features of dFBr required for potentiation; a secondary goal was to examine the same for inhibition. To understand the structural requirements of dFBr, a systematic ‘deconstruction reconstruction and elaboration’ approach (see p. 48) was employed to determine the contribution of various structural components of dFBr to its activity at α4β2 nACh receptors. Novel compounds were synthesized and characterized. Human α4β2 nACh receptors were expressed in Xenopus oocytes and the actions of dFBr and its analogs were measured using a two-electrode voltage clamp technique. Dose-response curves were obtained for the compounds in the absence and presence of 100 μM ACh. Structural features of dFBr optimal and/or required for PAM action at 42 nACh receptors were identified. A novel reconstructed analog with all the essential features for PAM action was synthesized and submitted for biological testing. Elaborated analogs of dFBr further helped in identification of various structural features important for PAM action and the inhibition of action of ACh. The ‘deconstruction reconstruction and elaboration’ approach (see p.48) identified important structural features of dFBr that modify its actions as a PAM or an antagonist (NAM? or channel blocker?) at α4β2 nACh receptors. This information should be useful for the subsequent design of novel analogs to evaluate their potential for the treatment of neurological disorders associated with ACh.

Neuronal nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that are necessary in memory and cognition. They are pentameric and consist of α and β subunits. They are most commonly heteromeric but, can sometimes be homomeric. nAChRs are activated by many ligands including nicotine (exogenous) and acetylcholine (endogenous).nAChRs are located on hippocampal interneurons. The interneurons, although sparse, control the synchronous firing of the pyramidal cells. However, the hippocampal interneuron structure and function is quite diverse and not fully characterized. Therefore, we sought to quantify nAChR subunit mRNA levels using real-time PCR of CA1 hippocampal interneurons.Surprisingly we found that the α3 and β2 mRNA subunits were the highest expressed and highest co-expressed subunits. Additionally, the α4 mRNA subunit was the lowest expressed of the subunits detected. The α4 subunit is one of the most pharmacologically targeted nAChR subunits and is found throughout the rest of the brain at much higher levels than the α3 mRNA subunit. Upon PCR analysis two subpopulations of the α3 and β2 subunits emerged: those that contained 3X more α3 than β2 and those that contained 3X more β2 than α3. Therefore, we hypothesized that two likely α3β2 nAChR stoichiometries are present in hippocampal interneurons. We differentiated their kinetic properties using electrophysiology.Additionally, like the α4 subunit, the α7 subunit is highly targeted in cognitive therapeutics. Since, the α7 subunit is the most characterized nAChR subunit, there are current efforts to develop allosteric modulators of the α7 subunit. The α7 subunit is found at moderate levels within hippocampal interneurons and remains a valid target. Current treatment options for Alzheimer's disease, and other dementias are limited and only mildly effective. Therefore, we sought to characterize the effect of 3-furan-2-yl-N-p-tolyl-acrylamide (PAM-2) on α7.Furthermore, there are no current methods to distinguish the α7 from the α7β2 nAChRs during whole cell electrophysiological recordings. Therefore, we also characterized the PAM-2 effect on α7β2 nAChRs. Our results highlight at least 2 ways PAM-2 can be used to differentiate α7 from the α7β2 during whole-cell recordings.

No description available.

Schizophrenia is a chronic psychotic illness affecting ~21 million people globally. Currently available antipsychotic agents act through a dopamine D2 receptor mechanism, and produce extrapyramidal or metabolic side effects. Hence, there is a need for novel targets and agents. The mGlu2/5-HT2A receptor heteromer has been implicated in the action of antipsychotic agents, and represents a novel and attractive therapeutic target for the treatment of schizophrenia. A long-term goal of this project is to synthesize bivalent ligands where a 5-HT2A receptor antagonist is tethered to an mGlu2 PAM via a linker. The goals of the investigation were to study the SAR of risperidone (an atypical antipsychotic agent) at 5-HT2A receptors using a “deconstruction-reconstruction-elaboration” approach to determine the minimal structural features of risperidone that contribute to its 5-HT2A receptor affinity and antagonism, and to determine where on the “minimized risperidone” structure an mGlu2 PAM can be introduced. Additional goals included studying the binding modes of various mGlu2 PAMs and identifying where on an mGlu2 PAM a risperidone “partial” structure could be introduced. Biological studies of deconstructed/elaborated analogs of risperidone suggest that the entire structure of risperidone is not necessary for 5-HT2A receptor affinity and antagonism, and that a fluoro group contributes to 5-HT2A binding. 6-Fluoro-3-(4-piperidinyl)-1,2-benz[d]isoxazole that has only half the structural features of risperidone retains 5-HT2A receptor affinity and antagonist activity, and represents the “minimized risperidone” structure with the piperidine nitrogen atom representing a potential linker site for eventual construction of bivalent ligands. Molecular modeling studies at 5-HT2A receptors suggest that risperidone and its analogs have more than one binding mode. Modeling studies to evaluate binding modes of various PAMs at mGlu2 receptors, coupled with known SAR information, were used to identify a PAM (JNJ-40411813), and the pyridone nitrogen atom of JNJ-40411813 as a potential linker site. Additionally, potential synthetic routes for JNJ-40411813 were explored that might be of value in the synthesis of bivalent ligands. Based on the structural features of 6-fluoro-3-(4-piperidinyl)-1,2-benz[d]isoxazole, a new pharmacophore for 5-HT2A receptor antagonists, consisting of one aromatic region, a basic protonated amine and hydrogen bond acceptors, has been proposed.

No description available.

α7 Neuronal nicotinic acetylcholine receptors are one of two major classes of receptors responsible for cholinergic neurotransmission in the central nervous system. The existence of α7 neuronal nAChRs in different regions of the nervous system suggests their involvement in certain essential physiological functions as well as in disorders such as Alzheimer’s disease (AD), drug dependence, and depression. This project was aimed toward the discovery and development of small–molecule arylguanidines that modulate α7 nAChR function with improved subtype-selectivity through an allosteric approach. Identifying the required structural features of these small molecules allowed optimization of their negative allosteric modulator (NAM) actions at α7 neuronal nAChRs. MD-354 (3-chlorophenylguanidine) was the first small–molecule NAM at α7 nAChRs; however, it also binds at 5-HT3 receptors. The N-methyl analog of MD-354 appeared to be more selective toward α7 nAChRs than 5-HT3 receptors. Comparative studies using two series of novel compounds based on MD-354 and its N-methyl analog explored the aryl 3-position and investigated whether or not the MD-354 series and the N-methyl series bind in the same manner. Biological potencies of the MD-354 series and the N-methyl series of compounds, obtained from electrophysiological assays with Xenopus laevis oocytes expressing human α7 nAChRs in two-electrode voltage-clamp assays, showed that N-(3-iodophenyl)-N- methylguanidine (28) is the most potent analog at α7 nAChRs. Our comparative study and Hansch analyses indicated different binding modes of the two series. In addition, we investigated: i) the length/size of the aliphatic side chain at the anilinic nitrogen, ii) the effect of alkylating the guanidine nitrogen atoms, and iii) the necessity of the presence of these nitrogen atoms for the inhibitory effects of arylguanidines at α7 nAChRs. In efforts to explain the varied functional activity of these arylguanidines, homology models of the extracellular domain and the transmembrane domain of human α7 nAChRs were developed, allosteric sites identified, and docking studies and hydropathic analysis conducted. The 3D quantitative structure-activity relationships for our compounds were also analyzed using CoMFA. A pharmacophore for arylguanidines as α7 nAChR NAMs was identified. Together, these data should be useful for the subsequent design of novel arylguanidine analogs for their potential treatment of neurological disorders.

La maladie de Parkinson (MP) est une maladie neurodégénérative chronique qui apparait en moyenne à partir 55 ans. Sa cause reste inconnue mais son apparition et son développement sont corrélés avec la perte progressive des neurones dopaminergique de la substance noire qui innervent les ganglions de la base (GB). Jusqu'à ce jour le traitement le plus efficace est basé sur la compensation du déficit en dopamine (DA) par l'administration de son précurseur, la L-DOPA, qui est métabolisé en DA. Ce traitement améliore les symptômes moteurs de la maladie et donc la qualité de vie des patients. Néanmoins, après une certaine période des effets secondaires invalidants apparaissent, en particulier des fluctuations motrices et des mouvements anormaux involontaires appelés dyskinésies. De plus, ce traitement n'apporte pas de réponse à la progression de la dégénérescence et donc de la maladie. C'est pour ces raisons que la communauté scientifique est à la recherche d'une thérapie pharmacologique alternative à la L-DOPA, ou du moins visant à minimiser ses effets indésirables. Dans ce contexte, les récepteurs métabotropiques du glutamate, en particulier mGluR4, semblent constituer une cible privilégiée. En effet, mGluR4 est situé à des synapses des GB supposées hyperactives dans la MP, et son activation par des moyens pharmacologiques pourrait donc rétablir une activité normale grâce à son action inhibitrice sur la libération de neurotransmetteur. Nos résultats démontrent le bien-fondé de cette hypothèse sur le plan fonctionnel, en utilisant un nouvel agoniste allostérique spécifique de mGluR4, Lu AF21934. / Parkinson's disease (PD) is a progressive neurodegenerative disorder that appears around 55 years of age. The causes of PD remain unknown but its appearance and progression are correlated with the progressive loss of dopaminergic neurons of substantia nigra pars compacta innervating the basal ganglia (BG). Up to date, the most efficient treatment is based on restoring a normal level of dopamine (DA) in the brain by the administration of L-DOPA, a DA precursor that is metabolized to DA. However, at long term, L-DOPA treatment induces some side-effects, in particular the highly disabling L-DOPA-induced dyskinesia (LID). For this reason, the scientific community is searching for a pharmacological treatment alternative to L-DOPA and/or minimizing LID. In this context, metabotropic glutamate receptors, in particular mGluR4, are targets of interest. mGlu4 are localized at presynaptic terminals within BG circuitry that become hyperactive in PD. For this reason, mGluR4 has been considered a key strategic target for non-dopaminergic pharmacological treatments aimed at modulating these synapses, due to its ability to reduce neurotransmitter release. Herein we provide physiological and functional support to this hypothesis using Lu AF21934, a novel selective and brain-penetrant mGluR4 positive allosteric modulator (PAM). By in vitro electrophysiological recordings we demonstrate that Lu AF21934 inhibits corticostriatal synaptic transmission. In rats rendered parkinsonian, Lu AF21934 combined with sub-threshold doses of L-DOPA acted synergistically in alleviating akinesia in a dose-dependent manner and, notably, also reduced the incidence of LID.