Small molecule targeting NaV1.7 via inhibition of the CRMP2-Ubc9 interaction reduces and prevents pain chronification in a mouse model of oxaliplatin-induced neuropathic pain

SUMOylation and DeSUMOylation: Tug of War of Pain Signaling

SUMOylation is a post-translational modification that attaches a small ubiquitin-like modifier (SUMO) group to a target protein via SUMO ligases, while deSUMOylation refers to the removal of this SUMO group by sentrin-specific proteases (SENPs). Although the functions of these processes have been well described in the nucleus, the role of SUMOylation and deSUMOylation in regulating ion channels is emerging as a novel area of study. Despite this, their contributions to pain signaling remain less clear. Therefore, this review consolidates the current evidence on the link(s) between SUMOylation, deSUMOylation, and pain, with a specific focus on ion channels expressed in the sensory system. Additionally, we explore the role of SUMOylation in the expression and function of kinases, vesicle proteins, and transcription factors, which result in the modulation of certain ion channels contributing to pain. Altogether, this review aims to highlight the relationship between SUMOylation and deSUMOylation in the modulation of ion channels, ultimately exploring the potential therapeutic role of these processes in chronic pain.

Evaluation of an indirect NaV1.7 inhibitor as adjunctive analgesic in burn-related neuropathic pain in a cat

Burn-related neuropathic pain (BRNP) can arise following burn-induced nerve damage, affects approximately 6% of burned human patients and can result in chronic pain. Although widely studied in humans, data on BRNP or its treatment in animals is lacking. A 4-year-old domestic shorthair cat was presented with an infected, non-healing wound suspected to be a caustic burn. Initial treatments included surgical debridement, antimicrobials, and corticosteroids, but the cat developed persistent pruritus leading to self-inflicted trauma. Despite various interventions, including prednisone, chloramphenicol and cyclosporine, clinical signs persisted, leading to a referral for suspected BRNP. Additional support for neuropathic pain was provided through thermal sensitivity testing and applying a modified Neuropathic Pain Symptoms Inventory. Treatment with gabapentin, amantadine, and acupuncture yielded little improvement, prompting an increasing escalation in gabapentin dosage. The cat was then treated with gabapentin compounded with compound 194, a small molecule that is a potent and selective inhibitor of voltage-gated sodium channel 1.7 (NaV1.7). The cat exhibited significant pain relief and improvements in overall condition. After gabapentin was tapered, compound 194 effectively maintained pain control. The cat's clinical condition stabilized with no adverse effects. Hematology and serum biochemistry results remained within reference intervals throughout the treatment period. This case highlights the potential of NaV1.7 inhibitors in multimodal management of neuropathic pain in animals.

Small molecule targeting Na V 1.7 via inhibition of CRMP2-Ubc9 interaction reduces pain-related outcomes in a rodent osteoarthritic model

ABSTRACT

Osteoarthritis (OA) is a highly prevalent and disabling joint disease, characterized by pathological progressive joint deformation and clinical symptoms of pain. Disease-modifying treatments remain unavailable, and pain-mitigation is often suboptimal, but recent studies suggest beneficial effects by inhibition of the voltage-gated sodium channel Na V 1.7. We previously identified compound 194 as an indirect inhibitor of Na V 1.7 by preventing SUMOylation of the Na V 1.7-trafficking protein, collapsin response mediator protein 2. Compound 194 reduces the functional activity of Na V 1.7 channels and produces effective analgesia in a variety of acute and neuropathic pain models. However, its effectiveness has not yet been evaluated in models of OA. Here, we explore the effects of 194 on pain-related outcomes in the OA-like monoiodoacetate model using behavioral assessment, biochemistry, novel in vivo fiber photometry, and patch clamp electrophysiology. We found that the monoiodoacetate model induced (1) increased pain-like behaviors and calcium responses of glutamatergic neurons in the parabrachial nucleus after evoked cold and mechanical stimuli, (2) conditioned place aversion to mechanical stimulation, (3) functional weight bearing asymmetry, (4) increased sodium currents in dorsal root ganglia neurons, and (5) increased calcitonin gene-related peptide-release in the spinal cord. Crucially, administration of 194 improved all these pain-related outcomes. Collectively, these findings support indirect inhibition of Na V 1.7 as an effective treatment of OA-related pain through the inhibition of collapsin response mediator protein 2-SUMOylation via compound 194.

Discordance between preclinical and clinical testing of NaV1.7-selective inhibitors for pain

ABSTRACT

The voltage-gated sodium channel NaV1.7 plays an important role in pain processing according to genetic data. Those data made NaV1.7 a popular drug target, especially since its relatively selective expression in nociceptors promised pain relief without the adverse effects associated with broader sodium channel blockade. Despite encouraging preclinical data in rodents, NaV1.7-selective inhibitors have not yet proven effective in clinical trials. Discrepancies between preclinical and clinical results should raise alarms. We reviewed preclinical and clinical reports on the analgesic efficacy of NaV1.7-selective inhibitors and found critical differences in several factors. Putting aside species differences, most preclinical studies tested young male rodents with limited genetic variability, inconsistent with the clinical population. Inflammatory pain was the most common preclinical chronic pain model whereas nearly all clinical trials focused on neuropathic pain despite some evidence suggesting NaV1.7 channels are not essential for neuropathic pain. Preclinical studies almost exclusively measured evoked pain whereas most clinical trials assessed average pain intensity without distinguishing between evoked and spontaneous pain. Nearly all preclinical studies gave a single dose of drug unlike the repeat dosing used clinically, thus precluding preclinical data from demonstrating whether tolerance or other slow processes occur. In summary, preclinical testing of NaV1.7-selective inhibitors aligned poorly with clinical testing. Beyond issues that have already garnered widespread attention in the pain literature, our results highlight the treatment regimen and choice of pain model as areas for improvement.

Exploring protein-protein interactions for the development of new analgesics

The development of new analgesics has been challenging. Candidate drugs often have limited clinical utility due to side effects that arise because many drug targets are involved in signaling pathways other than pain transduction. Here, we explored the potential of targeting protein-protein interactions (PPIs) that mediate pain signaling as an approach to developing drugs to treat chronic pain. We reviewed the approaches used to identify small molecules and peptide modulators of PPIs and their ability to decrease pain-like behaviors in rodent animal models. We analyzed data from rodent and human sensory nerve tissues to build associated signaling networks and assessed both validated and potential interactions and the structures of the interacting domains that could inform the design of synthetic peptides and small molecules. This resource identifies PPIs that could be explored for the development of new analgesics, particularly between scaffolding proteins and receptors for various growth factors and neurotransmitters, as well as ion channels and other enzymes. Targeting the adaptor function of CBL by blocking interactions between its proline-rich carboxyl-terminal domain and its SH3-domain-containing protein partners, such as GRB2, could disrupt endosomal signaling induced by pain-associated growth factors. This approach would leave intact its E3-ligase functions, which are mediated by other domains and are critical for other cellular functions. This potential of PPI modulators to be more selective may mitigate side effects and improve the clinical management of pain.

Peptide and Peptidomimetic Inhibitors Targeting the Interaction of Collapsin Response Mediator Protein 2 with the N-Type Calcium Channel for Pain Relief

Ion channels serve pleiotropic functions. Often found in complexes, their activities and functions are sculpted by auxiliary proteins. We discovered that collapsin response mediator protein 2 (CRMP2) is a binding partner and regulator of the N-type voltage-gated calcium channel (CaV2.2), a genetically validated contributor to chronic pain. Herein, we trace the discovery of a new peptidomimetic modulator of this interaction, starting from the identification and development of CBD3, a CRMP2-derived CaV binding domain peptide. CBD3 uncouples CRMP2-CaV2.2 binding to decrease CaV2.2 surface localization and calcium currents. These changes occur at presynaptic sites of nociceptive neurons and indeed, CBD3 ameliorates chronic pain in preclinical models. In pursuit of a CBD3 peptidomimetic, we exploited a unique approach to identify a dipeptide with low conformational flexibility and high solvent accessibility that anchors binding to CaV2.2. From a pharmacophore screen, we obtained CBD3063, a small-molecule that recapitulated CBD3's activity, reversing nociceptive behaviors in rodents of both sexes without sensory, affective, or cognitive effects. By disrupting the CRMP2-CaV2.2 interaction, CBD3063 exerts these effects indirectly through modulating CaV2.2 trafficking, supporting CRMP2 as an auxiliary subunit of CaV2.2. The parent peptide CBD3 was also found by us and others to have neuroprotective properties at postsynaptic sites, through N-methyl-d-aspartate receptor and plasmalemmal Na+/Ca2+ exchanger 3, potentially acting as an auxiliary subunit for these pathways as well. Our new compound is poised to address several open questions regarding CRMP2's role in regulating the CaV2.2 pathways to treat pain with the potential added benefit of neuroprotection.

Sodium channels Nav1.7, Nav1.8 and pain; two distinct mechanisms for Nav1.7 null analgesia

Genetic deletion and pharmacological inhibition are distinct approaches to unravelling pain mechanisms, identifying targets and developing new analgesics. Both approaches have been applied to the voltage-gated sodium channels Nav1.7 and Nav1.8. Genetic deletion of Nav1.8 in mice leads to a loss of pain and antagonists are effective analgesics. The situation with Nav1.7 is more complex. Complete embryonic loss of Nav1.7 in humans or in mouse sensory neurons leads to anosmia as well as profound analgesia as a result of diminished neurotransmitter release. This is mediated by enhanced endogenous opioid signaling in humans and mice. In contrast, anosmia is opioid-independent. Sensory neuron excitability and autonomic function appear to be normal. Adult deletion of Nav1.7 in sensory neurons also leads to analgesia, but through diminished sensory and autonomic neuron excitability. There is no opioid component of analgesia or anosmia as shown by a lack of effect of naloxone. Pharmacological inhibition of Nav1.7 in mice and humans leads both to analgesia and dramatic side-effects on the autonomic nervous system with no therapeutic window. These data demonstrate that specific Nav1.7 channel blockers will fail as analgesic drugs. The viability of embryonic null mutants suggests that there are compensatory changes to replace the lost Nav1.7 channel. Here we show that sensory neuron sodium channels Nav1.1, Nav1.2 and β4 subunits detected by Mass Spectrometry are upregulated in Nav1.7 embryonic null neurons and, together with other proteome changes, potentially compensate for the loss of Nav1.7. Interestingly, many of the upregulated proteins are known to interact with Nav1.7.

Ion Channel and Transporter Involvement in Chemotherapy-Induced Peripheral Neurotoxicity

The peripheral nervous system can encounter alterations due to exposure to some of the most commonly used anticancer drugs (platinum drugs, taxanes, vinca alkaloids, proteasome inhibitors, thalidomide), the so-called chemotherapy-induced peripheral neurotoxicity (CIPN). CIPN can be long-lasting or even permanent, and it is detrimental for the quality of life of cancer survivors, being associated with persistent disturbances such as sensory loss and neuropathic pain at limb extremities due to a mostly sensory axonal polyneuropathy/neuronopathy. In the state of the art, there is no efficacious preventive/curative treatment for this condition. Among the reasons for this unmet clinical and scientific need, there is an uncomplete knowledge of the pathogenetic mechanisms. Ion channels and transporters are pivotal elements in both the central and peripheral nervous system, and there is a growing body of literature suggesting that they might play a role in CIPN development. In this review, we first describe the biophysical properties of these targets and then report existing data for the involvement of ion channels and transporters in CIPN, thus paving the way for new approaches/druggable targets to cure and/or prevent CIPN.

Intranasal CRMP2-Ubc9 inhibitor regulates Na V 1.7 to alleviate trigeminal neuropathic pain

ABSTRACT

Dysregulation of voltage-gated sodium Na V 1.7 channels in sensory neurons contributes to chronic pain conditions, including trigeminal neuropathic pain. We previously reported that chronic pain results in part from increased SUMOylation of collapsin response mediator protein 2 (CRMP2), leading to an increased CRMP2/Na V 1.7 interaction and increased functional activity of Na V 1.7. Targeting this feed-forward regulation, we developed compound 194 , which inhibits CRMP2 SUMOylation mediated by the SUMO-conjugating enzyme Ubc9. We further demonstrated that 194 effectively reduces the functional activity of Na V 1.7 channels in dorsal root ganglia neurons and alleviated inflammatory and neuropathic pain. Here, we used a comprehensive array of approaches, encompassing biochemical, pharmacological, genetic, electrophysiological, and behavioral analyses, to assess the functional implications of Na V 1.7 regulation by CRMP2 in trigeminal ganglia (TG) neurons. We confirmed the expression of Scn9a , Dpysl2 , and UBE2I within TG neurons. Furthermore, we found an interaction between CRMP2 and Na V 1.7, with CRMP2 being SUMOylated in these sensory ganglia. Disrupting CRMP2 SUMOylation with compound 194 uncoupled the CRMP2/Na V 1.7 interaction, impeded Na V 1.7 diffusion on the plasma membrane, and subsequently diminished Na V 1.7 activity. Compound 194 also led to a reduction in TG neuron excitability. Finally, when intranasally administered to rats with chronic constriction injury of the infraorbital nerve, 194 significantly decreased nociceptive behaviors. Collectively, our findings underscore the critical role of CRMP2 in regulating Na V 1.7 within TG neurons, emphasizing the importance of this indirect modulation in trigeminal neuropathic pain.

Thermal escape box: A cost-benefit evaluation paradigm for investigating thermosensation and thermal pain

Thermosensation, the ability to detect and estimate temperature, is an evolutionarily conserved process that is essential for survival. Thermosensing is impaired in various pain syndromes, resulting in thermal allodynia, the perception of an innocuous temperature as painful, or thermal hyperalgesia, an exacerbated perception of a painful thermal stimulus. Several behavioral assays exist to study thermosensation and thermal pain in rodents, however, most rely on reflexive withdrawal responses or the subjective quantification of spontaneous nocifensive behaviors. Here, we created a new apparatus, the thermal escape box, which can be attached to temperature-controlled plates and used to assess temperature-dependent effort-based decision-making. The apparatus consists of a light chamber with an opening that fits around temperature-controlled plates, and a small entryway into a dark chamber. A mouse must choose to stay in a brightly lit aversive area or traverse the plates to escape to the enclosed dark chamber. We quantified escape latencies of adult C57Bl/6 mice at different plate temperatures from video recordings and found they were significantly longer at 5 °C, 18 °C, and 52 °C, compared to 30 °C, a mouse's preferred ambient temperature. Differences in escape latencies were abolished in male Trpm8-/- mice and in male Trpv1-/- animals. Finally, we show that chronic constriction injury procedures or oxaliplatin treatement significantly increased escape latencies at cold temperatures compared to controls, the later of which was prevented by the analgesic meloxicam. This demonstrates the utility of this assay in detecting cold pain. Collectively, our study has identified a new and effective tool that uses cost-benefit valuations to study thermosensation and thermal pain.

Rare variants with large effects provide functional insights into the pathology of migraine subtypes, with and without aura

Migraine is a complex neurovascular disease with a range of severity and symptoms, yet mostly studied as one phenotype in genome-wide association studies (GWAS). Here we combine large GWAS datasets from six European populations to study the main migraine subtypes, migraine with aura (MA) and migraine without aura (MO). We identified four new MA-associated variants (in PRRT2, PALMD, ABO and LRRK2) and classified 13 MO-associated variants. Rare variants with large effects highlight three genes. A rare frameshift variant in brain-expressed PRRT2 confers large risk of MA and epilepsy, but not MO. A burden test of rare loss-of-function variants in SCN11A, encoding a neuron-expressed sodium channel with a key role in pain sensation, shows strong protection against migraine. Finally, a rare variant with cis-regulatory effects on KCNK5 confers large protection against migraine and brain aneurysms. Our findings offer new insights with therapeutic potential into the complex biology of migraine and its subtypes.

Identification and targeting of a unique NaV1.7 domain driving chronic pain

Small molecules directly targeting the voltage-gated sodium channel (VGSC) NaV1.7 have not been clinically successful. We reported that preventing the addition of a small ubiquitin-like modifier onto the NaV1.7-interacting cytosolic collapsin response mediator protein 2 (CRMP2) blocked NaV1.7 function and was antinociceptive in rodent models of neuropathic pain. Here, we discovered a CRMP2 regulatory sequence (CRS) unique to NaV1.7 that is essential for this regulatory coupling. CRMP2 preferentially bound to the NaV1.7 CRS over other NaV isoforms. Substitution of the NaV1.7 CRS with the homologous domains from the other eight VGSC isoforms decreased NaV1.7 currents. A cell-penetrant decoy peptide corresponding to the NaV1.7-CRS reduced NaV1.7 currents and trafficking, decreased presynaptic NaV1.7 expression, reduced spinal CGRP release, and reversed nerve injury-induced mechanical allodynia. Importantly, the NaV1.7-CRS peptide did not produce motor impairment, nor did it alter physiological pain sensation, which is essential for survival. As a proof-of-concept for a NaV1.7 -targeted gene therapy, we packaged a plasmid encoding the NaV1.7-CRS in an AAV virus. Treatment with this virus reduced NaV1.7 function in both rodent and rhesus macaque sensory neurons. This gene therapy reversed and prevented mechanical allodynia in a model of nerve injury and reversed mechanical and cold allodynia in a model of chemotherapy-induced peripheral neuropathy. These findings support the conclusion that the CRS domain is a targetable region for the treatment of chronic neuropathic pain.

Intranasal CRMP2-Ubc9 Inhibitor Regulates Na V 1.7 to Alleviate Trigeminal Neuropathic Pain

Dysregulation of voltage-gated sodium Na V 1.7 channels in sensory neurons contributes to chronic pain conditions, including trigeminal neuropathic pain. We previously reported that chronic pain results in part from increased SUMOylation of collapsin response mediator protein 2 (CRMP2), leading to an increased CRMP2/Na V 1.7 interaction and increased functional activity of Na V 1.7. Targeting this feed-forward regulation, we developed compound 194 , which inhibits CRMP2 SUMOylation mediated by the SUMO-conjugating enzyme Ubc9. We further demonstrated that 194 effectively reduces the functional activity of Na V 1.7 channels in dorsal root ganglia neurons and alleviated inflammatory and neuropathic pain. Here, we employed a comprehensive array of investigative approaches, encompassing biochemical, pharmacological, genetic, electrophysiological, and behavioral analyses, to assess the functional implications of Na V 1.7 regulation by CRMP2 in trigeminal ganglia (TG) neurons. We confirmed the expression of Scn9a , Dpysl2 , and UBE2I within TG neurons. Furthermore, we found an interaction between CRMP2 and Na V 1.7, with CRMP2 being SUMOylated in these sensory ganglia. Disrupting CRMP2 SUMOylation with compound 194 uncoupled the CRMP2/Na V 1.7 interaction, impeded Na V 1.7 diffusion on the plasma membrane, and subsequently diminished Na V 1.7 activity. Compound 194 also led to a reduction in TG neuron excitability. Finally, when intranasally administered to rats with chronic constriction injury of the infraorbital nerve (CCI-ION), 194 significantly decreased nociceptive behaviors. Collectively, our findings underscore the critical role of CRMP2 in regulating Na V 1.7 within TG neurons, emphasizing the importance of this indirect modulation in trigeminal neuropathic pain.

Neuraxial drug delivery in pain management: An overview of past, present, and future

Activation of neuraxial nociceptive linkages leads to a high level of encoding of the message that is transmitted to the brain and that can initiate a pain state with its attendant emotive covariates. As we review here, the encoding of this message is subject to a profound regulation by pharmacological targeting of dorsal root ganglion and dorsal horn systems. Though first shown with the robust and selective modulation by spinal opiates, subsequent work has revealed the pharmacological and biological complexity of these neuraxial systems and points to several regulatory targets. Novel therapeutic delivery platforms, such as viral transfection, antisense and targeted neurotoxins, point to disease-modifying approaches that can selectively address the acute and chronic pain phenotype. Further developments are called for in delivery devices to enhance local distribution and to minimize concentration gradients, as frequently occurs with the poorly mixed intrathecal space. The field has advanced remarkably since the mid-1970s, but these advances must always address the issues of safety and tolerability of neuraxial therapy.

Cell specific regulation of NaV1.7 activity and trafficking in rat nodose ganglia neurons

The voltage-gated sodium NaV1.7 channel sets the threshold for electrogenesis. Mutations in the gene encoding human NaV1.7 (SCN9A) cause painful neuropathies or pain insensitivity. In dorsal root ganglion (DRG) neurons, activity and trafficking of NaV1.7 are regulated by the auxiliary collapsin response mediator protein 2 (CRMP2). Specifically, preventing addition of a small ubiquitin-like modifier (SUMO), by the E2 SUMO-conjugating enzyme Ubc9, at lysine-374 (K374) of CRMP2 reduces NaV1.7 channel trafficking and activity. We previously identified a small molecule, designated 194, that prevented CRMP2 SUMOylation by Ubc9 to reduce NaV1.7 surface expression and currents, leading to a reduction in spinal nociceptive transmission, and culminating in normalization of mechanical allodynia in models of neuropathic pain. In this study, we investigated whether NaV1.7 control via CRMP2-SUMOylation is conserved in nodose ganglion (NG) neurons. This study was motivated by our desire to develop 194 as a safe, non-opioid substitute for persistent pain, which led us to wonder how 194 would impact NaV1.7 in NG neurons, which are responsible for driving the cough reflex. We found functioning NaV1.7 channels in NG neurons; however, they were resistant to downregulation via either CRMP2 knockdown or pharmacological inhibition of CRMP2 SUMOylation by 194. CRMP2 SUMOylation and interaction with NaV1.7 was consered in NG neurons but the endocytic machinery was deficient in the endocytic adaptor protein Numb. Overexpression of Numb rescued CRMP2-dependent regulation on NaV1.7, rendering NG neurons sensitive to 194. Altogether, these data point at the existence of cell-specific mechanisms regulating NaV1.7 trafficking.

Computational design of peptides to target NaV1.7 channel with high potency and selectivity for the treatment of pain

The voltage-gated sodium Na_V1.7 channel plays a key role as a mediator of action potential propagation in C-fiber nociceptors and is an established molecular target for pain therapy. ProTx-II is a potent and moderately selective peptide toxin from tarantula venom that inhibits human Na_V1.7 activation. Here we used available structural and experimental data to guide Rosetta design of potent and selective ProTx-II-based peptide inhibitors of human Na_V1.7 channels. Functional testing of designed peptides using electrophysiology identified the PTx2-3127 and PTx2-3258 peptides with IC₅₀s of 7 nM and 4 nM for hNa_V1.7 and more than 1000-fold selectivity over human Na_V1.1, Na_V1.3, Na_V1.4, Na_V1.5, Na_V1.8, and Na_V1.9 channels. PTx2-3127 inhibits Na_V1.7 currents in mouse and human sensory neurons and shows efficacy in rat models of chronic and thermal pain when administered intrathecally. Rationally designed peptide inhibitors of human Na_V1.7 channels have transformative potential to define a new class of biologics to treat pain.