Hippocampal place cell dysfunction and the effects of muscarinic M1 receptor agonism in a rat model of Alzheimer's disease.

Alzheimer's disease (AD) is a neurodegenerative disease that disproportionately impacts memory and the hippocampus. However, it is unclear how AD pathology influences the activity of surviving neurons in the hippocampus to contribute to the memory symptoms in AD. One well-understood connection between spatial memory and neuronal activity in healthy brains is the activity of place cells, neurons in the hippocampus that fire preferentially in a specific location of a given environment (the place field of the place cell). In the present study, place cells were recorded from the hippocampus in a recently-developed rat model of AD (Tg-F344 AD) at an age (12-20 months) at which the AD rats showed marked spatial memory deficits. Place cells in the CA2 and CA3 pyramidal regions of the hippocampus in AD rats showed sharply reduced spatial fidelity relative to wild-type (WT) rats. In contrast, spiking activity of place cells recorded in region CA1 in AD rats showed good spatial fidelity that was similar to CA1 place cells in WT rats. Oral administration of the M1 muscarinic acetylcholine receptor agonist VU0364572 impacted place cell firing rates in CA1 and CA2/3 hippocampal regions, but did not improve the spatial fidelity of CA2/3 hippocampal place cells in AD rats. The results indicated that, to the extent the spatial memory impairment in AD rats was attributable to hippocampal dysfunction, the memory impairment was more attributable to dysfunction in hippocampal regions CA2 and CA3 rather than CA1.

Effects of selective activation of M1 and M4 muscarinic receptors on object recognition memory performance in rats.

Acetylcholine signaling through muscarinic receptors has been shown to benefit memory performance in some conditions, but pan-muscarinic activation also frequently leads to peripheral side effects. Drug therapies that selectively target M1 or M4 muscarinic receptors could potentially improve memory while minimizing side effects mediated by the other muscarinic receptor subtypes. The ability of three recently developed drugs that selectively activate M1 or M4 receptors to improve recognition memory was tested by giving Long-Evans rats subcutaneous injections of three different doses of the M1 agonist VU0364572, the M1 positive allosteric modulator BQCA or the M4 positive allosteric modulator VU0152100 before performing an object recognition memory task. VU0364572 at 0.1 mg/kg, BQCA at 1.0 mg/kg and VU0152100 at 3.0 and 30.0 mg/kg improved the memory performance of rats that performed poorly at baseline, yet the improvements in memory performance were the most statistically robust for VU0152100 at 3.0 mg/kg. The results suggested that selective M1 and M4 receptor activation each improved memory but that the likelihood of obtaining behavioral efficacy at a given dose might vary between subjects even in healthy groups depending on baseline performance. These results also highlighted the potential of drug therapies that selectively target M1 or M4 receptors to improve memory performance in individuals with impaired memory.

Novel allosteric agonists of M1 muscarinic acetylcholine receptors induce brain region-specific responses that correspond with behavioral effects in animal models.

M(1) muscarinic acetylcholine receptors (mAChRs) represent a viable target for treatment of multiple disorders of the central nervous system (CNS) including Alzheimer's disease and schizophrenia. The recent discovery of highly selective allosteric agonists of M(1) receptors has provided a major breakthrough in developing a viable approach for the discovery of novel therapeutic agents that target these receptors. Here we describe the characterization of two novel M(1) allosteric agonists, VU0357017 and VU0364572, that display profound differences in their efficacy in activating M(1) coupling to different signaling pathways including Ca(2+) and ß-arrestin responses. Interestingly, the ability of these agents to differentially activate coupling of M(1) to specific signaling pathways leads to selective actions on some but not all M(1)-mediated responses in brain circuits. These novel M(1) allosteric agonists induced robust electrophysiological effects in rat hippocampal slices, but showed lower efficacy in striatum and no measureable effects on M(1)-mediated responses in medial prefrontal cortical pyramidal cells in mice. Consistent with these actions, both M(1) agonists enhanced acquisition of hippocampal-dependent cognitive function but did not reverse amphetamine-induced hyperlocomotion in rats. Together, these data reveal that M(1) allosteric agonists can differentially regulate coupling of M(1) to different signaling pathways, and this can dramatically alter the actions of these compounds on specific brain circuits important for learning and memory and psychosis.

Continued optimization of the MLPCN probe ML071 into highly potent agonists of the hM1 muscarinic acetylcholine receptor.

This Letter describes the continued optimization of the MLPCN probe molecule ML071. After introducing numerous cyclic constraints and novel substitutions throughout the parent structure, we produced a number of more highly potent agonists of the M(1) mACh receptor. While many novel agonists demonstrated a promising ability to increase soluble APPα release, further characterization indicated they may be functioning as bitopic agonists. These results and the implications of a bitopic mode of action are presented.

Development of a highly selective, orally bioavailable and CNS penetrant M1 agonist derived from the MLPCN probe ML071.

Herein we report the discovery and SAR of a novel series of M(1) agonists based on the MLPCN probe, ML071. From this, VU0364572 emerged as a potent, orally bioavailable and CNS penetrant M(1) agonist with high selectivity, clean ancillary pharmacology and enantiospecific activity.

The antipsychotic potential of muscarinic allosteric modulation.

The cholinergic hypothesis of schizophrenia emerged over 50 years ago based on clinical observations with both anticholinergics and pan-muscarinic agonists. Not until the 1990s did the cholinergic hypothesis of schizophrenia receive renewed enthusiasm based on clinical data with xanomeline, a muscarinic acetylcholine receptor M(1)/M(4)-preferring orthosteric agonist. In a clinical trial with Alzheimer's patients, xanomeline not only improved cognitive performance, but also reduced psychotic behaviors. This encouraging data spurred a second clinical trial in schizophrenic patients, wherein xanomeline significantly improved the positive, negative and cognitive symptom clusters. However, the question remained: Was the antipsychotic efficacy due to activation of M(1), M(4) or both M(1)/M(4)? Classical orthosteric ligands lacked the muscarinic receptor subtype selectivity required to address this key question. More recently, functional assays have allowed for the discovery of ligands that bind at allosteric sites, binding sites distinct from the orthosteric (acetylcholine) site, which are structurally less conserved and thereby afford high levels of receptor subtype selectivity. Recently, allosteric ligands, with unprecedented selectivity for either M(1) or M(4), have been discovered and have demonstrated comparable efficacy to xanomeline in preclinical antipsychotic and cognition models. These data suggest that selective allosteric activation of either M(1) or M(4) has antipsychotic potential through distinct, yet complimentary mechanisms.

Higher integration scores are associated with facial emotion perception differences in dissociative identity disorder.

BACKGROUND: Recovery from dissociative identity disorder (DID) is associated with the process of integration, which includes an increasing sense of self-cohesion and ownership over one's own emotions. Emotion perception is a construction based on interplay between stored knowledge (past experience), and incoming sensory inputs, suggesting changes in emotion perception might occur at different levels of integration - but this remains unexplored. Therefore, we examined the association between integration, psychiatric symptoms, and facial emotion perception. We hypothesized higher integration would be associated with fewer psychiatric symptoms, and differences in the perception of emotions. METHODS: Participants were 82 respondents to a cross-sectional web-based study. All participants met self-report cutoff scores for posttraumatic stress disorder (PTSD) and DID using the PTSD Checklist for DSM-5 and Multiscale Dissociation Inventory, respectively. Participants completed a psychometrically-matched test of facial emotion perception for anger, fear, and happiness called the Belmont Emotion Sensitivity Test. Participants also completed the Beck Depression Inventory II, Childhood Trauma Questionnaire, and Integration Measure, a validated measure of self-cohesion. RESULTS: Higher integration scores were associated with lower depression, PTSD, and autobiographical memory disturbance scores. Repeated-measures ANCOVA confirmed integration significantly interacted with emotion category on the facial emotion perception task. Specifically, higher integration scores were associated with greater accuracy to fearful and angry faces. CONCLUSIONS: While acknowledging the limitations of a cross-sectional design, our results suggest that the process of integration is associated with fewer psychiatric symptoms, and more accurate facial emotion perception. This supports treatment guidelines regarding integration as a therapeutic goal for DID.

Allosteric modulation of kinases and GPCRs: design principles and structural diversity.

Allosteric binding sites, as opposed to traditional orthosteric binding sites, offer unparalleled opportunities for drug discovery by providing high levels of selectivity, mimicking physiological conditions, affording fewer side effects because of desensitization/downregulation, and engendering ligands with chemotypes divergent from orthosteric ligands. For kinases, allosteric mechanisms described to date include alteration of protein kinase conformation blocking productive ATP binding which appear 'ATP competitive' or blocking kinase activation by conformational changes that are 'ATP non-competitive'. For GPCRs, allosteric mechanisms impart multiple modes of target modulation (positive allosteric modulation (PAM), negative allosteric modulation (NAM), neutral cooperativity, partial antagonism (PA), allosteric agonism and allosteric antagonism). Here, we review recent developments in the design principles and structural diversity of allosteric ligands for kinases and GPCRs.

MAOS ls for the general synthesis and lead optimization of 3,6-disubstituted-[1,2,4]triazolo[4,3-b]pyridazines.

General, high-yielding MAOS protocols for the expedient synthesis of functionalized 3,6-disubstituted-[1,2,4]triazolo[4,3-b]pyridazines are described amenable to an iterative analog library synthesis strategy for the lead optimization of an M1 antagonist screening hit. Optimized compounds proved to be highly selective M1 antagonists.

The reverse translation of a quantitative neuropsychiatric framework into preclinical studies: Focus on social interaction and behavior.

Following the Research Domain Criteria (RDoC) concept, major brain circuits are conserved in evolution and malfunctioning of a brain circuit will lead to specific behavioral symptoms. Reverse translation of patient-based findings from Alzheimer's disease (AD), schizophrenia (SZ) and major depression (MD) patients to preclinical models accordingly can be a starting point for developing a deeper understanding of the functional circuit biology and contribute to the validation of new hypotheses for therapeutic intervention in patients. In the context of the EU funded PRISM project, a preclinical test battery of tasks has been selected and aligned with the clinical test battery. It allows for assessment of social functioning, sensory processing, attention and working memory and is designed for validation of biological substrates from human molecular landscaping of social withdrawal. This review will broadly summarize the available literature on tasks for studying social behavior in rodents and outline the development of a preclinical test battery for the PRISM project by reverse translation.

Positive allosteric modulators of the metabotropic glutamate receptor subtype 4 (mGluR4): Part I. Discovery of pyrazolo[3,4-d]pyrimidines as novel mGluR4 positive allosteric modulators.

This letter describes the synthesis and SAR, developed through an iterative analogue library approach, of an mGluR4 positive allosteric modulator lead based on a pyrazolo[3,4-d]pyrimidine scaffold. Despite tremendous therapeutic potential, Compound 7, VU0080421, and related congeners represent only a handful of mGluR4 positive allosteric modulators ever described.

Disease-Modifying Effects of M1 Muscarinic Acetylcholine Receptor Activation in an Alzheimer's Disease Mouse Model.

Alzheimer's disease (AD) is the leading cause of dementia worldwide, and currently no disease-modifying therapy is available to slow or prevent AD, underscoring the urgent need for neuroprotective therapies. Selective M1 muscarinic acetylcholine receptor (mAChR) activation is an attractive mechanism for AD therapy since M1 mediates key effects on memory, cognition, and behavior and has potential for disease-modifying effects on Aß formation and tau phosphorylation. To validate M1 as a neuroprotective treatment target for AD, the M1-selective agonist, VU0364572, was chronically dosed to 5XFAD mice from a young age preceding Aß pathology (2 months) to an age where these mice are known to display memory impairments (6 months). Chronic M1 activation prevented mice from becoming memory-impaired, as measured by Morris water maze (MWM) testing at 6 months of age. Additionally, M1 activation significantly reduced levels of soluble and insoluble Aß40,42 in the cortex and hippocampus of these animals, as measured by ELISA and immunohistochemistry. Moreover, soluble hippocampal Aß42 levels were strongly correlated with MWM memory impairments and M1 activation with VU0364572 abolished this correlation. Finally, VU0364572 significantly decreased oligomeric (oAß) levels in the cortex, suggesting one mechanism whereby VU0364572 may be exerting its neuroprotective effects is by reducing the available oAß pool in the brain. These findings suggest that chronic M1 activation has neuroprotective potential for preventing memory impairments and reducing neuropathology in AD. M1 activation therefore represents a promising avenue for preventative treatment, as well as a promising opportunity to combine symptomatic and disease-modifying effects for early AD treatment.

Effects of Selective M1 Muscarinic Receptor Activation on Hippocampal Spatial Representations and Neuronal Oscillations.

The muscarinic M1 acetylcholine receptor is a key target for drugs aimed at treating cognitive dysfunction, including the memory impairment in Alzheimer's disease. The overall question of the current study was to ask how systemic administration of the bitopic M1 agonist VU0364572, the M1 positive allosteric modulator BQCA, and the acetylcholinesterase inhibitor donepezil (current standard of care for Alzheimer's disease), would impact spatial memory-related hippocampal function in rats. Hippocampal pyramidal neuron spiking and local field potentials were recorded from regions CA1 and CA3 as rats freely foraged in a recording enclosure. To assess the relative stability versus flexibility of the rats' spatial representations, the walls of the recording enclosure were reshaped in 15-m intervals. As compared to the control condition, systemic administration of VU0364572 increased spatial correlations of CA1 and CA3 pyramidal neuron spiking across all enclosure shape comparisons, whereas BQCA and donepezil appeared to decrease these spatial correlations. Further, both VU0364572 and BQCA increased intrahippocampal synchrony as measured by CA3-CA1 field-field coherence in frequency ranges that tended to align with the prominence of those oscillations for the behavioral state (i.e., theta during locomotion and slow gamma during stationary moments). The results indicated that VU0364572 and BQCA influenced hippocampal function differently but in ways that might both be beneficial for treating memory dysfunction.

Chemical modification of the M(1) agonist VU0364572 reveals molecular switches in pharmacology and a bitopic binding mode.

We previously reported the discovery of VU0364572 and VU0357017 as M(1)-selective agonists that appear to activate M(1) through actions at an allosteric site. Previous studies have revealed that chemical scaffolds for many allosteric modulators contain molecular switches that allow discovery of allosteric antagonists and allosteric agonists or positive allosteric modulators (PAMs) based on a single chemical scaffold. Based on this, we initiated a series of studies to develop selective M(1) allosteric antagonists based on the VU0364572 scaffold. Interestingly, two lead antagonists identified in this series, VU0409774 and VU0409775, inhibited ACh-induced Ca(2+) responses at rat M(1-5) receptor subtypes, suggesting they are nonselective muscarinic antagonists. VU0409774 and VU0409775 also completely displaced binding of the nonselective radioligand [(3)H]-NMS at M(1) and M(3) mAChRs with affinities similar to their functional IC(50) values. Finally, Schild analysis revealed that these compounds inhibit M(1) responses through a fully competitive interaction at the orthosteric binding site. This surprising finding prompted further studies to determine whether agonist activity of VU0364572 and VU0357017 may also engage in previously unappreciated actions at the orthosteric site on M(1). Surprisingly, both VU0364572 and VU0357017 completely displaced [(3)H]-NMS binding to the orthosteric site of M(1)-M(5) receptors at high concentrations. Furthermore, evaluation of agonist activity in systems with varying levels of receptor reserve and Furchgott analysis using a cell line expressing M(1) under control of an inducible promotor was consistent with an action of these compounds as weak orthosteric partial agonists of M(1). However, consistent with previous studies suggesting actions at a site that is distinct from the orthosteric binding site, VU0364572 or VU0357017 slowed the rate of [(3)H]-NMS dissociation from CHO-rM(1) membranes. Together, these results suggest that VU0364572 and VU0357017 act as bitopic ligands and that novel antagonists in this series act as competitive orthosteric site antagonists.

The evolution of histamine H3 antagonists/inverse agonists.

This article describes our efforts along with recent advances in the development, biological evaluation and clinical proof of concept of small molecule histamine H3 antagonists/inverse agonists. The H3 receptor is a presynaptic autoreceptor within the Class A GPCR family, but also functions as a heteroreceptor modulating levels of neurotransmitters such as dopamine, acetylcholine, norepinephrine, serotonin, GABA and glutamate. Thus, H3R has garnered a great deal of interest from the pharmaceutical industry for the possible treatment of obesity, epilepsy, sleep/wake, schizophrenia, Alzheimer's disease, neuropathic pain and ADHD. Within the two main classes of H3 ligands, both imidazole and non-imidazole derived, have shown sufficient potency and specificity which culminated with efficacy in preclinical models for various CNS disorders. Importantly, conserved elements have been identified within the small molecule H3 ligand scaffolds that resulted in a highly predictive pharmacophore model. Understanding of the pharmacophore model has allowed several groups to dial H3R activity into scaffolds designed for other CNS targets, and engender directed polypharmacology. Moreover, Abbott, GSK, Pfizer and several others have reported positive Phase I and/or Phase II data with structurally diverse H3R antagonists/inverse agonists.

Discovery and characterization of novel subtype-selective allosteric agonists for the investigation of M(1) receptor function in the central nervous system.

Cholinergic transmission in the forebrain is mediated primarily by five subtypes of muscarinic acetylcholine receptors (mAChRs), termed M(1)-M(5). Of the mAChR subtypes, M(1) is among the most heavily expressed in regions that are critical for learning and memory, and has been viewed as the most critical mAChR subtype for memory and attention mechanisms. Unfortunately, it has been difficult to develop selective activators of M(1) and other individual mAChR subtypes, which has prevented detailed studies of the functional roles of selective activation of M(1). Using a functional HTS screen and subsequent diversity-oriented synthesis approach we have discovered a novel series of highly selective M(1) allosteric agonists. These compounds activate M(1) with EC(50) values in the 150 nM to 500 nM range and have unprecedented, clean ancillary pharmacology (no substantial activity at 10µM across a large panel of targets). Targeted mutagenesis revealed a potentially novel allosteric binding site in the third extracellular loop of the M(1) receptor for these allosteric agonists. Optimized compounds, such as VU0357017, provide excellent brain exposure after systemic dosing and have robust in vivo efficacy in reversing scopolamine-induced deficits in a rodent model of contextual fear conditioning. This series of selective M(1) allosteric agonists provides critical research tools to allow dissection of M(1)-mediated effects in the CNS and potential leads for novel treatments for Alzheimer's disease and schizophrenia.