ORCID Profile
0000-0003-0688-6060
Current Organisation
Monash University
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Publisher: Wiley
Date: 03-08-2015
DOI: 10.1111/JNC.13245
Abstract: Pinnatoxins are members of the cyclic imine group of marine phycotoxins that are highly toxic in in vivo rodent bioassays, causing rapid death due to respiratory depression. Recent studies have shown that pinnatoxins E, F and G, found in New Zealand and Australian shellfish, act as antagonists at muscle-type nicotinic acetylcholine receptors (nAChRs) at the neuromuscular junction. In the present study, binding affinities and modes of these pinnatoxin isomers at neuronal and muscle nAChRs were assessed using radioligand binding, electrophysiological and molecular modelling techniques. Radioligand-binding studies revealed that all three pinnatoxins bound with high affinity to muscle-type nAChRs, as well as to the α7 and α4β2 neuronal receptors, with an order of affinity of muscle type > α7 > α4β2. The rank order of potency at all receptors was pinnatoxin F > G > E. Pinnatoxins F and G also antagonized ACh-evoked responses in α7 and α4β2 neuronal receptors expressed in Xenopus oocytes. Molecular modelling revealed that pinnatoxins E, F and G make multiple hydrogen bond interactions with the binding site of muscle-type and α7 receptors, with few interactions at the α4β2 binding site, reflecting the binding affinity and functional data. This study shows for the first time that pinnatoxins E, F and G bind to, and functionally antagonize neuronal nAChRs, with interactions potentially playing a role in pinnatoxin toxicity.
Publisher: Elsevier BV
Date: 09-2014
DOI: 10.1016/J.TOXICON.2014.05.013
Abstract: Fluorescent molecules are regularly utilised to study ligand-receptor interactions. Many ligands for nicotinic receptors have been conjugated with fluorophores to study receptor kinetics, recycling and ligand binding characteristics. These include small agonist molecules, as well as large peptidic antagonists. However, no small molecule antagonists have been investigated using this method. Pinnatoxin F is a newly discovered non-peptidic muscle type nicotinic receptor antagonist produced by the marine dinoflagellate species Vulcanodinium rugosum. This molecule has the potential for conjugation to a fluorophore, allowing subsequent visualisation of interactions with nicotinic receptors. Pinnatoxin F was modified by addition of diaminopolyether spacers, to which a fluorophore (VivoTag(®) 645) was conjugated. The fluorescent pinnatoxin was then applied to muscle sections from thy1-YFP-H transgenic mice, which express YFP in motor nerves, to allow direct visualization of fluorescent binding at the neuromuscular junction. The addition of both the diaminopolyether spacer and the VivoTag(®) 645 reduced the potency of pinnatoxin F, as evidenced by a reduction in in vitro neuromuscular blocking activity and in vivo toxicity. Despite this reduced potency, the fluorescent molecule selectively labelled endplate regions in thy1-YFP mouse muscle sections and this labelling was inhibited by pre-exposure of muscle sections to native pinnatoxin F or the nicotinic antagonist α-bungarotoxin. This study proves nicotinic receptor binding activity of pinnatoxin F and is the first ex le of a fluorophore-conjugated small-molecule antagonist for nicotinic receptors. These results indicate the potential for other small-molecule nicotinic receptor antagonists to be fluorescently labelled and used as probes for specific nicotinic receptor subtypes.
Publisher: Wiley
Date: 26-08-2019
DOI: 10.1111/JNC.14844
Abstract: Allosteric modulators of metabotropic glutamate receptor 5 (mGlu
Publisher: American Society for Pharmacology & Experimental Therapeutics (ASPET)
Date: 18-02-2021
Publisher: Wiley
Date: 07-05-2019
DOI: 10.1111/BCPT.13239
Abstract: Allosteric modulators bind sites distinct from orthosteric ligands, allowing for improved spatiotemporal control of receptors and greater subtype selectivity. However, we recently showed that allosteric ligands previously classified as selective for select Class C G protein-coupled receptors (GPCRs) had unappreciated activity at other off-target receptors, in some cases higher affinity, within the class. Here, we extended our investigation of off-target activity of "selective" allosteric ligands for the sweet taste receptor. Using metabotropic glutamate receptor 5 (mGlu
Publisher: American Society for Pharmacology & Experimental Therapeutics (ASPET)
Date: 07-03-2018
Abstract: Numerous positive and negative allosteric modulators (PAMs and NAMs) of class C G protein-coupled receptors (GPCRs) have been developed as valuable preclinical pharmacologic tools and therapeutic agents. Although many class C GPCR allosteric modulators have undergone subtype selectivity screening, most assay paradigms have failed to perform rigorous pharmacologic assessment. Using mGlu
Publisher: Elsevier BV
Date: 07-2020
Publisher: Elsevier BV
Date: 12-2013
DOI: 10.1016/J.TOXICON.2013.10.009
Abstract: Pinnatoxins are produced by dinoflagellates and belong to the cyclic imine family of toxins. They are fast-acting and highly toxic when administered in vivo in rodent bioassays, causing death by respiratory depression within minutes. Studies have revealed that some cyclic imine toxins cause their toxicity by antagonizing both muscle type and heteromeric and homomeric neuronal nicotinic acetylcholine receptors (nAChRs). Pinnatoxins E, F and G all display potent toxicity in in vivo bioassays, with symptoms of toxicity similar to other cyclic imine toxins. However, very little work has been done on the mechanism of action of these pinnatoxin isomers. Thus the aim of the current study was to investigate the rank order of potency and mechanism of action of pinnatoxins E, F and G. The effects of pinnatoxin E, F and G on in vitro rat hemidiaphragm preparations were investigated using twitch tension and electrophysiological techniques to determine the effects of these toxins on cholinergic transmission at the neuromuscular junction. Pinnatoxins E, F and G all produced concentration-dependent reductions in the nerve evoked twitch response of the rat hemidiaphragm, with IC50 values ranging from 11 to 53 nM and a rank order of potency of F > G > E. Only complete washout of pinnatoxin E was evident, with pinnatoxins F and G displaying slow and incomplete washout profiles. Pinnatoxins F and G also reduced the litudes of spontaneous miniature endplate potentials and evoked endplate potentials at the neuromuscular junction, without affecting miniature endplate potential frequency or the resting membrane potential of the muscle fibres. These results show that pinnatoxins E, F and G are all potent neuromuscular blocking agents and cause toxicity by acting as antagonists at muscle type nicotinic acetylcholine receptors.
Publisher: American Society for Pharmacology & Experimental Therapeutics (ASPET)
Date: 15-03-2023
Publisher: Elsevier BV
Date: 05-2019
Publisher: Elsevier
Date: 2021
Publisher: Elsevier BV
Date: 02-2017
DOI: 10.1016/J.COPH.2016.10.007
Abstract: The metabotropic glutamate (mGlu) receptor family is a potential therapeutic target for multiple central nervous system (CNS) disorders. However, aspects of mGlu receptor signaling and their role in neural pathways remain to be fully elucidated. Novel subtype selective allosteric modulators have revealed new roles for mGlu receptors in brain health and disease, as well as expanding on previously underappreciated aspects of mGlu signaling such as biased agonism and modulation. Recent advances have improved our understanding of mGlu receptor function. Harnessing these new insights to inform drug discovery programs has the potential to lead to the design and discovery of mGlu allosteric modulators that specifically drive glutamatergic activity toward therapeutically beneficial effects and avoid on-target adverse effect liability.
Publisher: Elsevier BV
Date: 07-2020
Publisher: Springer Science and Business Media LLC
Date: 16-11-2022
Publisher: Cold Spring Harbor Laboratory
Date: 05-07-2023
DOI: 10.1101/2023.07.05.545810
Abstract: Metabotropic glutamate receptor 1 (mGlu 1 ) is a promising therapeutic target for neurodegenerative CNS disorders including spinocerebellar ataxias (SCAs). Clinical reports have identified naturally-occurring mGlu 1 mutations in rare SCA subtypes and clinical symptoms of mGlu 1 mutations have been described. However, how mutations alter mGlu 1 function remains unknown. We explored SCA-associated mutation effects on mGlu 1 cell surface expression and canonical signal transduction. Orthosteric agonists and positive allosteric modulators (PAMs) and negative allosteric modulators (NAMs) were assessed at two functional endpoints (iCa 2+ mobilisation and IP 1 accumulation). mGlu 1 mutants exhibited differential impacts on receptor expression, with a truncating C-terminus mutation significantly reducing mGlu 1 expression. Mutations differentially influenced orthosteric ligand affinity, efficacy, and functional cooperativity between allosteric and orthosteric ligands. Loss-of-function mutations L454F and N885del reduced orthosteric affinity and efficacy, respectively. Gain-of-function Y792C mutant mGlu 1 displayed enhanced constitutive activity in IP 1 assays, which manifested as reduced orthosteric agonist activity. mGlu 1 PAMs restored glutamate potency in iCa 2+ mobilisation for loss-of-function mutations, and mGlu 1 NAMs displayed enhanced inverse agonist activity at Y792C relative to wild-type mGlu 1 . Collectively, these data highlight distinct mechanisms by which mGlu 1 mutations affect receptor function and show allosteric modulators may present a means to restore aberrant mGlu 1 function in rare SCA subtypes.
Publisher: American Chemical Society (ACS)
Date: 12-05-2020
Publisher: Elsevier BV
Date: 12-2011
DOI: 10.1016/J.TOXICON.2011.09.006
Abstract: Members of the cyclic imine group of toxins, gymnodimine and spirolides, have been found to be potent antagonists of both muscle type and neuronal nicotinic acetylcholine receptors. These toxins exhibit fast acting toxicity in vivo, causing death within minutes by respiratory depression. This toxicity is shared by the novel cyclic imine pinnatoxins E and F, produced by marine dinoflagellates and recently isolated from New Zealand shellfish. However, there is currently very little data available regarding the mechanism of action for any of the pinnatoxins, and no data at all on the novel pinnatoxins E and F. The aim of the current study was to investigate potential antagonism of nicotinic acetylcholine receptors by pinnatoxins E and F using two in vitro tissue preparations. Compound muscle action potentials elicited by stimulation of the phrenic nerve were recorded from the hemidiaphragm in order to test effects on muscle type heteromeric nicotinic receptors, while effects on α7 homomeric neuronal nicotinic receptors were investigated by recording gamma oscillations in response to tetanic stimulation of the CA1 region of the hippoc us. Both a crude extract containing a mixture of pinnatoxins E and F, as well as pure pinnatoxin F, had no effect on gamma oscillation spectral density or spike count at any concentrations. Conversely, at these same concentrations, both crude and pure pinnatoxin caused an almost complete abolition of nerve-evoked hemidiaphragm action potential responses, without any effect on electrically-evoked (direct) responses. This neuromuscular block could not be reversed by neostigmine. These results show that pinnatoxins E and F block neuromuscular transmission and suggest that observed in vivo muscle paralysis by pinnatoxin is due to selective antagonism of muscle type nicotinic acetylcholine receptors.
No related grants have been discovered for Shane Dennis Hellyer.