Photoswitchable ORG25543 Congener Enables Optical Control of Glycine Transporter 2.

Shannon N Mostyn,Parthasarathy Muthuraman,Christopher L Cioffi,Subhodeep Sarker,Arun Raja,Robert J Vandenberg,Tristan Rawling,Susan Shimmon

doi:10.1021/acschemneuro.9b00655

Abstract

Glycine neurotransmission in the dorsal horn of the spinal cord plays a key role in regulating nociceptive signaling, but in chronic pain states reduced glycine neurotransmission is associated with the development of allodynia and hypersensitivity to painful stimuli. This suggests that restoration of glycine neurotransmission may be therapeutic for the treatment of chronic pain. Glycine transporter 2 inhibitors have been demonstrated to enhance glycine neurotransmission and provide relief from allodynia in rodent models of chronic pain. In recent years, photoswitchable compounds have been developed to provide the possibility of controlling the activity of target proteins using light. In this study we have developed a photoswitchable noncompetitive inhibitor of glycine transporter 2 that has different affinities for the transporter at 365 nm compared to 470 nm light.

Highlights

Chronic neuropathic pain is a debilitating disease, which arises as a result of nerve damage and rewiring of circuits within the pain processing pathway.[1]
Glycine concentrations within inhibitory synapses are tightly controlled by the glycine transporter, GlyT2,5 and may be a promising target for therapeutics which would act to restore normal nociceptive control.[6−9] knockdown of GlyT2 via targeting siRNA to ∼30% expression produces analgesia in rat models of pain.[10]
It is apparent that both isomers can be accommodated in the binding site, which suggests there is conformational flexibility in this binding region which could inform the design of new inhibitors. We demonstrate that both conformations of 3 are noncompetitive inhibitors of GlyT2 and are readily reversible, an important consideration when developing GlyT2 targeting inhibitors to treat chronic pain

Summary

Introduction

Chronic neuropathic pain is a debilitating disease, which arises as a result of nerve damage and rewiring of circuits within the pain processing pathway.[1]. Glycine concentrations within inhibitory synapses are tightly controlled by the glycine transporter, GlyT2,5 and may be a promising target for therapeutics which would act to restore normal nociceptive control.[6−9] knockdown of GlyT2 via targeting siRNA to ∼30% expression produces analgesia in rat models of pain.[10] While partial knockdown of GlyT2 produces analgesia with no observable behavioral side effects, total gene knockout of GlyT2 in mice produces severe neuromotor symptoms, with death 2 weeks postnatal.[11] electrophysiological recordings from knockout GlyT2 mice show a reduction of postsynaptic glycinergic currents, which highlights the important role of GlyT2 for recycling of glycine into presynaptic vesicles. Mutation of the human gene encoding GlyT2 (SLC6A5) is the most common presynaptic cause of hyperekplexia, with mutations altering glycine and/or ion binding sites, as well as affecting localization and expression in the plasma cell membrane.[12−15]

Methods

Results

Conclusion