Botulinum Neurotoxin Light Chains Expressed by Defective Herpes Simplex Virus Type-1 Vectors Cleave SNARE Proteins and Inhibit CGRP Release in Rat Sensory Neurons

Embracing the Versatility of Botulinum Neurotoxins in Conventional and New Therapeutic Applications

Botulinum neurotoxins (BoNTs) have been used for almost half a century in the treatment of excessive muscle contractility. BoNTs are routinely used to treat movement disorders such as cervical dystonia, spastic conditions, blepharospasm, and hyperhidrosis, as well as for cosmetic purposes. In addition to the conventional indications, the use of BoNTs to reduce pain has gained increased recognition, giving rise to an increasing number of indications in disorders associated with chronic pain. Furthermore, BoNT-derived formulations are benefiting a much wider range of patients suffering from overactive bladder, erectile dysfunction, arthropathy, neuropathic pain, and cancer. BoNTs are categorised into seven toxinotypes, two of which are in clinical use, and each toxinotype is divided into multiple subtypes. With the development of bioinformatic tools, new BoNT-like toxins have been identified in non-Clostridial organisms. In addition to the expanding indications of existing formulations, the rich variety of toxinotypes or subtypes in the wild-type BoNTs associated with new BoNT-like toxins expand the BoNT superfamily, forming the basis on which to develop new BoNT-based therapeutics as well as research tools. An overview of the diversity of the BoNT family along with their conventional therapeutic uses is presented in this review followed by the engineering and formulation opportunities opening avenues in therapy.

Cellular and molecular mechanisms involved in the analgesic effects of botulinum neurotoxin: A literature review

Botulinum neurotoxins (BoNTs), derived from Clostridium botulinum, have been employed to treat a range of central and peripheral neurological disease. Some studies indicate that BoNT may be beneficial for pain conditions as well. It has been hypothesized that BoNTs may exert their analgesic effects by preventing the release of pain-related neurotransmitters and neuroinflammatory agents from sensory nerve endings, suppressing glial activation, and inhibiting the transmission of pain-related receptors to the neuronal cell membrane. In addition, there is evidence to suggest that the central analgesic effects of BoNTs are mediated through their retrograde axonal transport. The purpose of this review is to summarize the experimental evidence of the analgesic functions of BoNTs and discuss the cellular and molecular mechanisms by which they can act on pain conditions. Most of the studies reviewed in this article were conducted using BoNT/A. The PubMed database was searched from 1995 to December 2022 to identify relevant literature.

Type I collagen concentration affects neurite outgrowth of adult rat DRG explants by altering mechanical properties of hydrogels

Type I collagen is a predominant fibrous protein that makes up the extracellular matrix. Collagen enhances cell attachment and is commonly used in three-dimensional culture systems, to mimic the native extracellular environment, for primary sensory neurons such as dorsal root ganglia (DRG). However, the effects of collagen concentration on adult rat DRG neurite growth have not been assessed in a physiologically relevant, three-dimensional culture. This study focuses on the effects of type I collagen used in a methacrylated hyaluronic acid (MAHA)-laminin-collagen gel (triple gel) on primary adult rat DRG explants in vitro. DRGs were cultured in triple gels, and the neurite lengths and number of support cells were quantified. Increased collagen concentration significantly reduced neurite length but did not affect support cell counts. Mechanical properties, fiber diameter, diffusivity, and mesh size of the triple gels with varying collagen concentration were characterized to further understand the effects of type I collagen on hydrogel property that may affect adult rat DRG explants. Gel stiffness significantly increased as collagen concentration increased and is correlated to DRG neurite length. Collagen concentration also significantly impacted fiber diameter but there was no correlation with DRG neurite length. Increasing collagen concentration had no significant effect on mesh size and diffusivity of the hydrogel. These data suggest that increasing type I collagen minimizes adult rat DRG explant growth in vitro while raising gel stiffness. This knowledge can help develop more robust 3D culture platforms to study sensory neuron growth and design biomaterials for nerve regeneration applications.

Multimodal Migraine Management and the Pursuit of Migraine Freedom: A Narrative Review

Migraine is a neurologic disease with a complex pathophysiology that can be controlled with current treatment options but not cured. Therefore, treatment expectations are highly variable. The concept of migraine freedom was recently introduced and can mean different things, with some, for example, expecting complete freedom from headache and associated symptoms and others accepting the occasional migraine attack if it does not impact functioning. Therefore, migraine management should be optimized so that patients can have the best opportunity to achieve their optimal treatment goals. With migraine freedom as a goal and, given the complex pathophysiology of migraine and the high incidence of comorbidities among individuals with migraine, treatment with a single modality may be insufficient, as it may not achieve migraine freedom in those with more frequent or disabling attacks. In this clinical perspective article, we have identified four key, partially overlapping principles of multimodal migraine treatment: (1) manage common comorbidities; (2) control modifiable risk factors for progression by addressing medication and caffeine overuse; (3) diagnose and treat secondary causes of headache, if present; and (4) individualize acute and preventive treatments to minimize pain, functional disability, and allodynia. There are many barriers to pursuing migraine freedom, and strategies to overcome them should be optimized. Migraine freedom should be an aspirational goal both at the individual attack level and for the disease overall. We believe that a comprehensive and multimodal approach that addresses all barriers people with migraine face could move patients closer to migraine freedom.

Effects of Botulinum Toxin Type A on the Nociceptive and Lemniscal Somatosensory Systems in Chronic Migraine: An Electrophysiological Study

(1) Background: OnabotulinumtoxinA (BoNT-A) is a commonly used prophylactic treatment for chronic migraine (CM). Although randomized placebo studies have shown its clinical efficacy, the mechanisms by which it exerts its therapeutic effect are still incompletely understood and debated. (2) Methods: We studied in 15 CM patients the cephalic and extracephalic nociceptive and lemniscal sensory systems using electrophysiological techniques before and 1 and 3 months after one session of pericranial BoNT-A injections according to the PREEMPT protocol. We recorded the nociceptive blink reflex (nBR), the trigemino-cervical reflex (nTCR), the pain-related cortical evoked potential (PREP), and the upper limb somatosensory evoked potential (SSEP). (3) Results: Three months after a single session of prophylactic therapy with BoNT-A in CM patients, we found (a) an increase in the homolateral and contralateral nBR AUC, (b) an enhancement of the contralateral nBR AUC habituation slope and the nTCR habituation slope, (c) a decrease in PREP N-P 1st and 2nd amplitude block, and (d) no effect on SSEPs. (4) Conclusions: Our study provides electrophysiological evidence for the ability of a single session of BoNT-A injections to exert a neuromodulatory effect at the level of trigeminal system through a reduction in input from meningeal and other trigeminovascular nociceptors. Moreover, by reducing activity in cortical pain processing areas, BoNT-A restores normal functioning of the descending pain modulation systems.

Development and Assessment of Herpes Simplex Virus Type 1 (HSV-1) Amplicon Vectors with Sensory Neuron-Selective Promoters

Background: Neurogenic detrusor overactivity (NDO) is a severe pathological condition characterized by involuntary detrusor contractions leading to urine leakage. This condition is frequent after spinal cord injury (SCI). Gene therapy for NDO requires the development of vectors that express therapeutic transgenes driven by sensory neuron-specific promoters. The aim of this study was to develop and assess tools for the characterization of sensory neuron-specific promoters in dorsal root ganglia (DRG) neurons after transduction with herpes simplex virus type 1 (HSV-1)-based amplicon defective vectors. Methods: The HSV-1 vector genome encoded two independent transcription cassettes: one expressed firefly luciferase (FLuc) driven by different promoters’ candidates (rTRPV1, rASIC3, rCGRP, or hCGRP), and the other expressed a reporter gene driven by an invariable promoter. The strength and selectivity of promoters was assessed in organotypic cultures of explanted adult DRG, or sympathetic and parasympathetic ganglia from control and SCI rats. Results: The rCGRP promoter induced selective expression in the DRG of normal rats. The rTRPV-1 promoter, which did not display selective activity in control rats, induced selective expression in DRG explanted from SCI rats. Conclusions: This study provides a methodology to assess sensory neuron-specific promoters, opening new perspectives for future gene therapy for NDO.

Evaluation of Recombinant Botulinum Neurotoxin Type A1 Efficacy in Peripheral Inflammatory Pain in Mice

Well-established efficacy of botulinum neurotoxin type A (BoNT/A) in aesthetic dermatology and neuromuscular hyperactivity disorders relies on canonical interruption of acetylcholine neurotransmission at the neuromuscular junction at the site of the injection. The mechanisms and the site of activity of BoNT/A in pain, on the other hand, remain elusive. Here, we explored analgesic activity of recombinant BoNT/A1 (rBoNT/A1; IPN10260) in a mouse model of inflammatory pain to investigate the potential role of peripheral sensory afferents in this activity. After confirming analgesic efficacy of rBoNT/A1 on CFA-induced mechanical hypersensitivity in C57Bl6J mice, we used GCaMP6s to perform in vivo calcium imaging in the ipsilateral dorsal root ganglion (DRG) neurons in rBoNT/A1 vs. vehicle-treated mice at baseline and following administration of a range of mechanical and thermal stimuli. Additionally, immunohisochemical studies were performed to detect cleaved SNAP25 in the skin, DRGs and the spinal cord. Injection of CFA resulted in reduced mechanical sensitivity threshold and increased calcium fluctuations in the DRG neurons. While rBoNT/A1 reduced mechanical hypersensitivity, calcium fluctuations in the DRG of rBoNT/A1- and vehicle-treated animals were similar. Cleaved SNAP25 was largely absent in the skin and the DRG but present in the lumbar spinal cord of rBoNT/A1-treated animals. Taken together, rBoNT/A1 ameliorates mechanical hypersensitivity related to inflammation, while the signal transmission from the peripheral sensory afferents to the DRG remained unchanged. This strengthens the possibility that spinal, rather than peripheral, mechanisms play a role in the mediation of analgesic efficacy of BoNT/A in inflammatory pain.

Real-World Evidence for the Safety and Efficacy of CGRP Monoclonal Antibody Therapy Added to OnabotulinumtoxinA Treatment for Migraine Prevention in Adult Patients With Chronic Migraine

Background: OnabotulinumtoxinA and calcitonin gene-related peptide (CGRP) monoclonal antibodies (mAbs) target different migraine pathways, therefore, combination treatment may provide additional effectiveness for the preventive treatment of chronic migraine (CM) than either treatment alone. The objective of this study was to collect real-world data to improve the understanding of the safety, tolerability, and effectiveness of adding a CGRP mAb to onabotulinumtoxinA treatment for the preventive treatment of CM. Methods: This was a retrospective, longitudinal study conducted using data extracted from a single clinical site's electronic medical records (EMR) of adult patients (≥18 years) with CM treated with ≥2 consecutive cycles of onabotulinumtoxinA before ≥1 month of continuous onabotulinumtoxinA and CGRP mAb (erenumab, fremanezumab, or galcanezumab) combination treatment. Safety was evaluated by the rate of adverse events (AE) and serious adverse events (SAE). The proportion of patients who discontinued either onabotulinumtoxinA, a CGRP mAb, or combination treatment, and the reason for discontinuation, if available, was collected. The effectiveness of combination preventive treatment was assessed by the reduction in monthly headache days (MHD). Outcome data were extracted from EMR at the first CGRP mAb prescription (index) and up to four assessments at ~3, 6, 9, and 12 months post-index. The final analyses were based on measures consistently reported in the EMR. Results: EMR were collected for 192 patients, of which 148 met eligibility criteria and were included for analysis. Erenumab was prescribed to 56.7% of patients, fremanezumab to 42.6%, and galcanezumab to 0.7%. Mean (standard deviation [SD]) MHD were 20.4 (6.6) prior to onabotulinumtoxinA treatment and 14.0 (6.9) prior to the addition of a CGRP mAb (baseline). After real-world addition of a CGRP mAb, there were significant reductions in MHD at the first assessment (~3 months) (mean -2.6 days/month, 95% CI -3.7, -1.4) and at all subsequent visits. After ~12 months of continuous combination treatment, MHD were reduced by 4.6 days/month (95% CI -6.7, -2.5) and 34.9% of patients achieved ≥50% MHD reduction from index. AEs were reported by 18 patients (12.2%), with the most common being constipation (n = 8, 5.4% [onabotulinumtoxinA plus erenumab only]) and injection site reactions (n = 5, 3.4%). No SAEs were reported. Overall, 90 patients (60.8%) discontinued one or both treatments. The most common reason for discontinuing either treatment was lack of insurance coverage (40%); few (~14%) patients discontinued a CGRP mAb and none discontinued onabotulinumtoxinA due to safety/tolerability. Conclusion: In this real-world study, onabotulinumtoxinA was effective at reducing MHD and the addition of a CGRP mAb was safe, well-tolerated and associated with incremental and clinically meaningful reductions in MHD for those who stayed on the combination treatment. No new safety signals were identified. Of those who discontinued, the majority reported lack of insurance coverage as a reason. Prospective real-world and controlled trials are needed to further evaluate the safety and potential benefits of this combination treatment paradigm for people with CM.

Real-World Evidence for Control of Chronic Migraine Patients Receiving CGRP Monoclonal Antibody Therapy Added to OnabotulinumtoxinA: A Retrospective Chart Review

INTRODUCTION

Combination use of onabotulinumtoxinA and calcitonin gene-related peptide (CGRP) monoclonal antibodies (mAbs) has the potential to be more effective than either therapy alone for migraine prevention.

METHODS

This retrospective, longitudinal chart review included adults with chronic migraine treated at one clinical site with ≥ 2 consecutive cycles of onabotulinumtoxinA and ≥ 1 month of subsequent combination treatment with CGRP mAbs. Charts at time of mAb prescription (baseline) and up to four visits ~ 3, 6, 9, and 12 months post-baseline were reviewed for safety, tolerability, and outcome measures (monthly headache days [MHDs], headache intensity, and migraine-related disability [MIDAS]).

RESULTS

Of 300 charts reviewed, 257 patients met eligibility criteria (mean age: 50 years; 82% women). Average headache frequency was 21.5 MHDs before initiation of onabotulinumtoxinA and 12.1 MHDs before adding CGRP mAb therapy. Prescribed mAbs were erenumab (78%), fremanezumab (6%), and galcanezumab (16%). Over the entire study, patients discontinued CGRP mAb more frequently than onabotulinumtoxinA (23 vs. 3%). Adverse events occurred in 28% of patients, most commonly constipation (9%). Compared with onabotulinumtoxinA alone (baseline), MHDs decreased significantly at all visits (mean decrease: 3.5-4.0 MHDs over ~ 6-12 months of combination treatment); 45.1% of patients had clinically meaningful improvement in migraine-related disability (≥ 5-point reduction in MIDAS score) after ~ 6 months.

CONCLUSIONS

In this real-world study, combination treatment with onabotulinumtoxinA and CGRP mAbs was well tolerated, with no new safety signals identified, and was associated with additional clinically meaningful benefits. More real-world and controlled trials should be considered to further assess safety and potential benefits of combination treatment. Video abstract: Real-world data suggests that CGRP inhibitors improve onabotulinumtoxinA efficacy for chronic migraine (MP4 20,067 kb).

Selective Expression of a SNARE-Cleaving Protease in Peripheral Sensory Neurons Attenuates Pain-Related Gene Transcription and Neuropeptide Release

Chronic pain is a leading health and socioeconomic problem and an unmet need exists for long-lasting analgesics. SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) are required for neuropeptide release and noxious signal transducer surface trafficking, thus, selective expression of the SNARE-cleaving light-chain protease of botulinum neurotoxin A (LCA) in peripheral sensory neurons could alleviate chronic pain. However, a safety concern to this approach is the lack of a sensory neuronal promoter to prevent the expression of LCA in the central nervous system. Towards this, we exploit the unique characteristics of Pirt (phosphoinositide-interacting regulator of TRP), which is expressed in peripheral nociceptive neurons. For the first time, we identified a Pirt promoter element and cloned it into a lentiviral vector driving transgene expression selectively in peripheral sensory neurons. Pirt promoter driven-LCA expression yielded rapid and concentration-dependent cleavage of SNAP-25 in cultured sensory neurons. Moreover, the transcripts of pain-related genes (TAC1, tachykinin precursor 1; CALCB, calcitonin gene-related peptide 2; HTR3A, 5-hydroxytryptamine receptor 3A; NPY2R, neuropeptide Y receptor Y2; GPR52, G protein-coupled receptor 52; SCN9A, sodium voltage-gated channel alpha subunit 9; TRPV1 and TRPA1, transient receptor potential cation channel subfamily V member 1 and subfamily A member 1) in pro-inflammatory cytokines stimulated sensory neurons were downregulated by viral mediated expression of LCA. Furthermore, viral expression of LCA yielded long-lasting inhibition of pain mediator release. Thus, we show that the engineered Pirt-LCA virus may provide a novel means for long lasting pain relief.

Engineering Botulinum Neurotoxins for Enhanced Therapeutic Applications and Vaccine Development

Botulinum neurotoxins (BoNTs) show increasing therapeutic applications ranging from treatment of locally paralyzed muscles to cosmetic benefits. At first, in the 1970s, BoNT was used for the treatment of strabismus, however, nowadays, BoNT has multiple medical applications including the treatment of muscle hyperactivity such as strabismus, dystonia, movement disorders, hemifacial spasm, essential tremor, tics, cervical dystonia, cerebral palsy, as well as secretory disorders (hyperhidrosis, sialorrhea) and pain syndromes such as chronic migraine. This review summarizes current knowledge related to engineering of botulinum toxins, with particular emphasis on their potential therapeutic applications for pain management and for retargeting to non-neuronal tissues. Advances in molecular biology have resulted in generating modified BoNTs with the potential to act in a variety of disorders, however, in addition to the modifications of well characterized toxinotypes, the diversity of the wild type BoNT toxinotypes or subtypes, provides the basis for innovative BoNT-based therapeutics and research tools. This expanding BoNT superfamily forms the foundation for new toxins candidates in a wider range of therapeutic options.

Mechanism of Action of OnabotulinumtoxinA in Chronic Migraine: A Narrative Review

Objective

To review the literature on the mechanism of action of onabotulinumtoxinA in chronic migraine.

Background

OnabotulinumtoxinA is a chronic migraine preventive treatment that significantly reduces headache frequency. The traditional mechanism described for onabotulinumtoxinA – reducing muscle contractions – is insufficient to explain its efficacy in migraine, which is primarily a sensory neurological disease.

Methods

A narrative literature review on the mechanism of action of onabotulinumtoxinA in chronic migraine.

Results

Following injection into tissues, onabotulinumtoxinA inhibits soluble N‐ethylmaleimide‐sensitive fusion attachment protein receptor (SNARE)‐mediated vesicle trafficking by cleaving one of its essential proteins, soluble N‐ethylmaleimide‐sensitive fusion attachment protein (SNAP‐25), which occurs in both motor and sensory nerves. OnabotulinumtoxinA inhibits regulated exocytosis of motor and sensory neurochemicals and proteins, as well as membrane insertion of peripheral receptors that convey pain from the periphery to the brain, because both processes are SNARE dependent. OnabotulinumtoxinA can decrease exocytosis of pro‐inflammatory and excitatory neurotransmitters and neuropeptides such as substance P, calcitonin gene‐related peptide, and glutamate from primary afferent fibers that transmit nociceptive pain and participate in the development of peripheral and central sensitization. OnabotulinumtoxinA also decreases the insertion of pain‐sensitive ion channels such as transient receptor potential cation channel subfamily V member 1 (TRPV1) into the membranes of nociceptive neurons; this is likely enhanced in the sensitized neuron. For chronic migraine prevention, onabotulinumtoxinA is injected into 31‐39 sites in 7 muscles of the head and neck. Sensory nerve endings of neurons whose cell bodies are located in trigeminal and cervical ganglia are distributed throughout the injected muscles, and are overactive in people with migraine. Through inhibition of these sensory nerve endings, onabotulinumtoxinA reduces the number of pain signals that reach the brain and consequently prevents activation and sensitization of central neurons postulated to be involved in migraine chronification.

Conclusion

OnabotulinumtoxinA likely acts via sensory mechanisms to treat chronic migraine.