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Highly selective, positive allosteric modulators (PAMs) of the M subtype of muscarinic acetylcholine receptor have emerged as an exciting new approach to potentially improve cognitive function in patients suffering from Alzheimer's disease and schizophrenia. Discovery programs have produced a structurally diverse range of M receptor PAMs with distinct pharmacological properties, including different extents of agonist activity and differences in signal bias. This includes biased M receptor PAMs that can potentiate coupling of the receptor to activation of phospholipase C (PLC) but not phospholipase D (PLD). However, little is known about the role of PLD in M receptor signaling in native systems, and it is not clear whether biased M PAMs display differences in modulating M-mediated responses in native tissue. Using PLD inhibitors and PLD knockout mice, we showed that PLD was necessary for the induction of M-dependent long-term depression (LTD) in the prefrontal cortex (PFC). Furthermore, biased M PAMs that did not couple to PLD not only failed to potentiate orthosteric agonist-induced LTD but also blocked M-dependent LTD in the PFC. In contrast, biased and nonbiased M PAMs acted similarly in potentiating M-dependent electrophysiological responses that were PLD independent. These findings demonstrate that PLD plays a critical role in the ability of M PAMs to modulate certain central nervous system (CNS) functions and that biased M PAMs function differently in brain regions implicated in cognition.
Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
BACKGROUND - We recently reported a quantitative relationship between the degree of functional perturbation reported in the literature for 356 variants in the cardiac sodium channel gene SCN5A and the penetrance of resulting arrhythmia phenotypes. In the course of that work, we identified multiple SCN5A variants, including R1193Q, that are common in populations but are reported in human embryonic kidney (HEK) cells to generate large late sodium current (I).
OBJECTIVE - The purpose of this study was to compare the functional properties of R1193Q with those of the well-studied type 3 long QT syndrome mutation ΔKPQ.
METHODS - We compared functional properties of SCN5A R1193Q with those of ΔKPQ in Chinese hamster ovary (CHO) cells at baseline and after exposure to intracellular phosphatidylinositol (3,4,5)-trisphosphate (PIP), which inhibits I generated by decreased Phosphoinositide 3-kinase (PI3K) activity. We also used CRISPR/Cas9 editing to generate R1193Q in human-induced pluripotent stem cells differentiated to cardiomyocytes (hiPSC-CMs).
RESULTS - Both R1193Q and ΔKPQ generated robust I in CHO cells. PIP abrogated the late current phenotype in R1193Q cells but had no effect on ΔKPQ. Homozygous R1193Q hiPSC-CMs displayed increased I and long action potentials with frequent triggered beats, which were reversed with the addition of PIP.
CONCLUSION - The consistency between the late current produced in HEK cells, CHO cells, and hiPSC-CMs suggests that the late current is a feature of the SCN5A R1193Q variant in human cardiomyocytes but that the mechanism by which the late current is produced is distinct and indirect, as compared with the more highly penetrant ΔKPQ. These data suggest that observing a late current in an in vitro setting does not necessarily translate to highly pathogenic type 3 long QT syndrome phenotype but depends on the underlying mechanism.
Copyright © 2019 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.
The antidepressant-sensitive serotonin (5-HT) transporter (SERT) dictates rapid, high-affinity clearance of the neurotransmitter in both the brain and periphery. In a study of families with multiple individuals diagnosed with autism spectrum disorder (ASD), we previously identified several, rare, missense coding variants that impart elevated 5-HT transport activity, relative to wild-type SERT, upon heterologous expression as well as in ASD subject lymphoblasts. The most common of these variants, SERT Ala56, located in the transporter's cytosolic N-terminus, has been found to confer in transgenic mice hyperserotonemia, an ASD-associated biochemical trait, an elevated brain 5-HT clearance rate, and ASD-aligned behavioral changes. Hyperfunction of SERT Ala56 has been ascribed to a change in 5-HT , though the physical basis of this change has yet to be elucidated. Through assessments of fluorescence resonance energy transfer (FRET) between cytosolic N- and C-termini, sensitivity to methanethiosulfonates, and capacity for N-terminal tryptic digestion, we obtain evidence for mutation-induced conformational changes that support an open-outward 5-HT binding conformation and . Aspects of these findings were also evident with another naturally occurring C-terminal SERT coding variant identified in our ASD study, Asn605. We conclude that biased conformations of surface resident transporters that can impact transporter function and regulation are an unappreciated consequence of heritable and disease-associated SERT coding variation.
The role that broadly neutralizing antibodies (bNAbs) play in natural clearance of human hepatitis C virus (HCV) infection and the underlying mechanisms remain unknown. Here, we investigate the mechanism by which bNAbs, isolated from two humans who spontaneously cleared HCV infection, contribute to HCV control. Using viral gene sequences amplified from longitudinal plasma of the two subjects, we found that these bNAbs, which target the front layer of the HCV envelope protein E2, neutralized most autologous HCV strains. Acquisition of resistance to bNAbs by some autologous strains was accompanied by progressive loss of E2 protein function, and temporally associated with HCV clearance. These data demonstrate that bNAbs can mediate clearance of human HCV infection by neutralizing infecting strains and driving escaped viruses to an unfit state. These immunopathologic events distinguish HCV from HIV-1 and suggest that development of an HCV vaccine may be achievable.
Copyright © 2018 Elsevier Inc. All rights reserved.
Ebolaviruses cause severe disease in humans, and identification of monoclonal antibodies (mAbs) that are effective against multiple ebolaviruses are important for therapeutics development. Here we describe a distinct class of broadly neutralizing human mAbs with protective capacity against three ebolaviruses infectious for humans: Ebola (EBOV), Sudan (SUDV), and Bundibugyo (BDBV) viruses. We isolated mAbs from human survivors of ebolavirus disease and identified a potent mAb, EBOV-520, which bound to an epitope in the glycoprotein (GP) base region. EBOV-520 efficiently neutralized EBOV, BDBV, and SUDV and also showed protective capacity in relevant animal models of these infections. EBOV-520 mediated protection principally by direct virus neutralization and exhibited multifunctional properties. This study identified a potent naturally occurring mAb and defined key features of the human antibody response that may contribute to broad protection. This multifunctional mAb and related clones are promising candidates for development as broadly protective pan-ebolavirus therapeutic molecules.
Copyright © 2018 The Author(s). Published by Elsevier Inc. All rights reserved.
This letter describes the chemical optimization of a new series of M positive allosteric modulators (PAMs) based on a novel benzomorpholine core, developed via iterative parallel synthesis, and culminating in the highly utilized rodent in vivo tool compound, VU0486846 (7), devoid of adverse effect liability. This is the first report of the optimization campaign (SAR and DMPK profiling) that led to the discovery of VU0486846 and details all of the challenges faced in allosteric modulator programs (both steep and flat SAR, as well as subtle structural changes affecting CNS penetration and overall physiochemical and DMPK properties).
Copyright © 2018 Elsevier Ltd. All rights reserved.
During reduced energy intake, skeletal muscle maintains homeostasis by rapidly suppressing insulin-stimulated glucose utilization. Loss of this adaptation is observed with deficiency of the fatty acid transporter CD36. A similar loss is also characteristic of the insulin-resistant state where CD36 is dysfunctional. To elucidate what links CD36 to muscle glucose utilization, we examined whether CD36 signaling might influence insulin action. First, we show that CD36 deletion specific to skeletal muscle reduces expression of insulin signaling and glucose metabolism genes. It decreases muscle ceramides but impairs glucose disposal during a meal. Second, depletion of CD36 suppresses insulin signaling in primary-derived human myotubes, and the mechanism is shown to involve functional CD36 interaction with the insulin receptor (IR). CD36 promotes tyrosine phosphorylation of IR by the Fyn kinase and enhances IR recruitment of P85 and downstream signaling. Third, pretreatment for 15 min with saturated fatty acids suppresses CD36-Fyn enhancement of IR phosphorylation, whereas unsaturated fatty acids are neutral or stimulatory. These findings define mechanisms important for muscle glucose metabolism and optimal insulin responsiveness. Potential human relevance is suggested by genome-wide analysis and RNA sequencing data that associate genetically determined low muscle CD36 expression to incidence of type 2 diabetes.
© 2018 by the American Diabetes Association.
Selective activation of the M subtype of muscarinic acetylcholine receptor, via positive allosteric modulation (PAM), is an exciting strategy to improve cognition in schizophrenia and Alzheimer's disease patients. However, highly potent M ago-PAMs, such as MK-7622, PF-06764427, and PF-06827443, can engender excessive activation of M, leading to agonist actions in the prefrontal cortex (PFC) that impair cognitive function, induce behavioral convulsions, and result in other classic cholinergic adverse events (AEs). Here, we report a fundamentally new and highly selective M PAM, VU0486846. VU0486846 possesses only weak agonist activity in M-expressing cell lines with high receptor reserve and is devoid of agonist actions in the PFC, unlike previously reported ago-PAMs MK-7622, PF-06764427, and PF-06827443. Moreover, VU0486846 shows no interaction with antagonist binding at the orthosteric acetylcholine (ACh) site (e.g., neither bitopic nor displaying negative cooperativity with [H]-NMS binding at the orthosteric site), no seizure liability at high brain exposures, and no cholinergic AEs. However, as opposed to ago-PAMs, VU0486846 produces robust efficacy in the novel object recognition model of cognitive function. Importantly, we show for the first time that an M PAM can reverse the cognitive deficits induced by atypical antipsychotics, such as risperidone. These findings further strengthen the argument that compounds with modest in vitro M PAM activity (EC > 100 nM) and pure-PAM activity in native tissues display robust procognitive efficacy without AEs mediated by excessive activation of M. Overall, the combination of compound assessment with recombinant in vitro assays (mindful of receptor reserve), native tissue systems (PFC), and phenotypic screens (behavioral convulsions) is essential to fully understand and evaluate lead compounds and enhance success in clinical development.
Positive allosteric modulators (PAMs) of the M subtype of muscarinic acetylcholine receptor have attracted intense interest as an exciting new approach for improving the cognitive deficits in schizophrenia and Alzheimer's disease. Recent evidence suggests that the presence of intrinsic agonist activity of some M PAMs may reduce efficacy and contribute to adverse effect liability. However, the M PAM PF-06827443 was reported to have only weak agonist activity at human M receptors but produced M-dependent adverse effects. We now report that PF-06827443 is an allosteric agonist in cell lines expressing rat, dog, and human M and use of inducible cell lines shows that agonist activity of PF-06827443 is dependent on receptor reserve. Furthermore, PF-06827443 is an agonist in native tissue preparations and induces behavioral convulsions in mice similar to other ago-PAMs. These findings suggest that PF-06827443 is a robust ago-PAM, independent of species, in cell lines and native systems.
Highly selective positive allosteric modulators (PAMs) of the M subtype of muscarinic acetylcholine receptor have emerged as an exciting new approach for improving cognitive function in patients suffering from Alzheimer's disease and schizophrenia. However, excessive activation of M is known to induce seizure activity and have actions in the prefrontal cortex (PFC) that could impair cognitive function. We now report a series of pharmacological, electrophysiological, and behavioral studies in which we find that recently reported M PAMs, PF-06764427 and MK-7622, have robust agonist activity in cell lines and agonist effects in the mouse PFC, and have the potential to overactivate the M receptor and disrupt PFC function. In contrast, structurally distinct M PAMs (VU0453595 and VU0550164) are devoid of agonist activity in cell lines and maintain activity dependence of M activation in the PFC. Consistent with the previously reported effect of PF-06764427, the ago-PAM MK-7622 induces severe behavioral convulsions in mice. In contrast, VU0453595 does not induce behavioral convulsions at doses well above those required for maximal efficacy in enhancing cognitive function. Furthermore, in contrast to the robust efficacy of VU0453595, the ago-PAM MK-7622 failed to improve novel object recognition, a rodent assay of cognitive function. These findings suggest that in vivo cognition-enhancing efficacy of M PAMs can be observed with PAMs lacking intrinsic agonist activity and that intrinsic agonist activity of M PAMs may contribute to adverse effects and reduced efficacy in improving cognitive function.