Sumatriptan Causes Parallel Decrease in Plasma CGRP Concentration and Migraine Headache During Nitroglycerin-Induced Migraine Attack

Glycerol Trinitrate Acts Downstream of Calcitonin Gene-Related Peptide in Trigeminal Nociception-Evidence from Rodent Experiments with Anti-CGRP Antibody Fremanezumab

Calcitonin gene-related peptide (CGRP) and nitric oxide (NO) have been recognized as important mediators in migraine but their mechanisms of action and interaction have not been fully elucidated. Monoclonal anti-CGRP antibodies like fremanezumab are successful preventives of frequent migraine and can be used to study CGRP actions in preclinical experiments. Fremanezumab (30 mg/kg) or an isotype control monoclonal antibody was subcutaneously injected to Wistar rats of both sexes. One to several days later, glyceroltrinitrate (GTN, 5 mg/kg) mimicking nitric oxide (NO) was intraperitoneally injected, either once or for three consecutive days. The trigeminal ganglia were removed to determine the concentration of CGRP using an enzyme-linked immunosorbent assay (ELISA). In one series of experiments, the animals were trained to reach an attractive sugar solution, the access to which could be limited by mechanical or thermal barriers. Using a semi-automated registration system, the frequency of approaches to the source, the residence time at the source, and the consumed solution were registered. The results were compared with previous data of rats not treated with GTN. The CGRP concentration in the trigeminal ganglia was generally higher in male rats and tended to be increased in animals treated once with GTN, whereas the CGRP concentration decreased after repetitive GTN treatment. No significant difference in CGRP concentration was observed between animals having received fremanezumab or the control antibody. Animals treated with GTN generally spent less time at the source and consumed less sugar solution. Without barriers, there was no significant difference between animals having received fremanezumab or the control antibody. Under mechanical barrier conditions, all behavioral parameters tended to be reduced but animals that had received fremanezumab tended to be more active, partly compensating for the depressive effect of GTN. In conclusion, GTN treatment seems to increase the production of CGRP in the trigeminal ganglion independently of the antibodies applied, but repetitive GTN administration may deplete CGRP stores. GTN treatment generally tends to suppress the animals' activity and increase facial sensitivity, which is partly compensated by fremanezumab through reduced CGRP signaling. If CGRP and NO signaling share the same pathway in sensitizing trigeminal afferents, GTN and NO may act downstream of CGRP to increase facial sensitivity.

Annexin A1 exerts analgesic effect in a mouse model of medication overuse headache

Medication overuse headache (MOH) is a serious global condition. The interaction between headache attacks and medication overuse complicates the understanding of its pathophysiology. In this study, we developed a preclinical MOH model that incorporates these two key factors by overusing rizatriptan benzoate (RIZ, 4 mg/kg, i.g.) in a glyceryl trinitrate (GTN, 10 mg/kg, i.p.) induced chronic migraine mouse model. We observed that RIZ overuse aggravated GTN-induced cutaneous allodynia and caused a prolonged state of latent sensitization. We also detected a significant upregulation of Annexin-A1 (ANXA1), a protein mainly expressed in the microglia of the spinal trigeminal nucleus caudalis (SPVC), in GTN+RIZ mice. Intracerebroventricular injection of ANXA1-derived peptide Ac2-26 trifluoroacetic acid (TFA) (5 μg/mouse) inhibited bright light stress (BLS) induced acute allodynia via the formyl peptide receptor (FPR) in GTN+RIZ mice. These results suggest that ANXA1 may have an analgesic effect in triptan-associated MOH and could potentially serve as a therapeutic target.

Peripheral and central nervous system distribution of the CGRP neutralizing antibody [125I] galcanezumab in male rats

Objective

The objective of this investigation was to examine the distribution of galcanezumab and a control immunoglobulin 4 antibody containing the same constant regions as galcanezumab, into peripheral and central tissues.

Methods

Galcanezumab and a control immunoglobulin 4 antibody were radioiodinated with Iodine-125 to specific activities of 0.11 mCi/mg and 0.16 mCi/mg, respectively. At 24, 72, and 168 hours following subcutaneous injection of either antibody (4 mg/kg), cerebrospinal fluid and plasma were obtained followed by saline perfusion to remove residual blood and collection of selected tissues for determination of Iodine-125 content by gamma counting.

Results

The peak plasma levels of Iodine-125 galcanezumab and Iodine-125 control immunoglobulin 4 were observed at 72 hours and remained high at 168 hours post-dose. The rank order of tissue levels was dura mater = spleen > trigeminal ganglia ≫hypothalamus = spinal cord = prefrontal cortex = cerebellum. Iodine-125 galcanezumab levels in peripheral tissue (dura mater, spleen, and trigeminal ganglia) averaged 5% to 11% of plasma, whereas all of the central nervous system (CNS) tissue levels and the cerebrospinal fluid levels were < 0.4% of plasma. Distribution of the antibodies into the dura mater and the trigeminal ganglia was similar to that observed in the spleen and significantly greater than exposure in the brain or spinal cord.

Conclusions

The central levels of galcanezumab were relatively low, which would favor the dura mater and trigeminal ganglia as sites of action for its observed clinical efficacy. However, a central site of action cannot be excluded.

Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of the CGRP Binding Monoclonal Antibody LY2951742 (Galcanezumab) in Healthy Volunteers

Background: Calcitonin gene-related peptide (CGRP) is pivotal in the pathophysiology of migraine headaches and represents a promising target for migraine treatment. The humanized monoclonal antibody galcanezumab (LY2951742) binds to CGRP and may be effective in migraine prophylaxis.

Objectives: The primary objective was to evaluate the safety and tolerability of single and multiple doses of galcanezumab in humans. Secondary objectives included assessing the pharmacokinetics and evaluating target engagement.

Methods: A double-blind, randomized, placebo-controlled study (NCT 01337596) with single escalating and multiple subcutaneous (SC) doses of galcanezumab was performed in healthy male volunteers. Single doses of 1, 5, 25, 75, 200, and 600 mg of galcanezumab (n = 7/dose) or placebo (n = 2/dose) were injected SC in six consecutive cohorts of nine subjects each. One cohort of nine subjects received multiple (4) 150 mg doses of galcanezumab or placebo every other week. Target engagement was evaluated by measuring inhibition of capsaicin-induced increase in dermal blood flow (DBF).

Findings: Sixty-three subjects were randomized and included in the safety analyses. Galcanezumab was well tolerated in single doses (1–600 mg SC) and consecutive doses (150 mg SC). There was no dose-dependent difference in type or frequency of treatment-emergent adverse events, and no clinically meaningful difference when compared with placebo. Pharmacokinetics were linear. Galcanezumab induced a robust, dose-dependent, and durable inhibition of capsaicin-induced increase in DBF, supporting the continued clinical development of galcanezumab for prophylaxis in migraine patients.

Efficacy of (S)-Lacosamide in preclinical models of cephalic pain

Migraine is one of the world's most common neurological disorders. Current acute migraine treatments have suboptimal efficacy, and new therapeutic options are needed. Approaches targeting calcitonin gene related peptide (CGRP) signaling are clinically effective, but small molecule antagonists have not been advanced because of toxicity. In this study, we explored the axonal growth/specification collapsin response mediator protein 2 (CRMP2) as a novel “druggable” target for inhibiting CGRP release and for potential relevance for treatment of migraine pain. Collapsin response mediator protein 2 has been demonstrated to regulate N-type voltage-gated Ca²⁺ channel activity and Ca²⁺-dependent CGRP release in sensory neurons. The coexpression of CRMP2 with N-type voltage-gated Ca²⁺ channel and CGRP in trigeminal ganglia (TGs) sensory neurons suggested the possibility of a novel approach to regulate CGRP release in the trigeminal system. Screening protocols surprisingly revealed that (S)-lacosamide ((S)-LCM), an inactive analog of the clinically approved small molecule antiepileptic drug (R)-lacosamide (Vimpat), inhibited CRMP2 phosphorylation by cyclin-dependent kinase 5 in rat TG slices and decreased depolarization-evoked Ca²⁺ influx in TG cells in culture. (S)-LCM significantly blocked capsaicin-evoked CGRP release from dural nerve terminals in the rat in ex vivo cranial cup preparation. Additionally, cephalic and extracephalic cutaneous allodynia induced in rats by activation of dural nociceptors with a cocktail of inflammatory mediators, was inhibited by oral administration of (S)-LCM. The confirmation of CRMP2 as an upstream mediator of CGRP release, together with the brain penetrance of this molecule suggests (S)-LCM as a potential therapy for acute migraine.

Prevention of stress- or nitric oxide donor-induced medication overuse headache by a calcitonin gene-related peptide antibody in rodents

Objective The objective of this study was the determination of the role of calcitonin gene-related peptide (CGRP) in the induction of medication overuse headache (MOH)-related migraine in an injury-free preclinical model. Methods Rats were primed by a 7-day period of exposure to acute migraine therapies including sumatriptan and morphine. After an additional 14-day drug-free period, rats were exposed to putative migraine triggers including bright light stress (BLS) or nitric oxide (NO) donor in the presence or absence of TEV48125, a fully humanized CGRP antibody. Cutaneous allodynia (CA) was used as an outcome measure and CGRP blood and cerebrospinal fluid (CSF) levels were measured. Results BLS and NO donor challenge evoked delayed, long-lasting CA selectively in rats that were previously treated with sumatriptan or morphine. BLS produced a significant increase in CGRP in the plasma, but not CSF, in animals that were previously exposed to sumatriptan compared to saline controls. TEV48125 did not modify baseline tactile thresholds or produce behavioral side effects, but significantly inhibited both BLS- and NO donor-induced CA in animals that were previously primed with sumatriptan or morphine; an isotype control protein that does not bind CGRP had no effect. Interpretation These data suggest that acute migraine medications may promote MOH in susceptible individuals through CGRP-dependent mechanisms and that anti-CGRP antibodies may be a useful clinical strategy for the treatment of MOH.

Targeting TRP channels for novel migraine therapeutics

Migraine is increasingly understood to be a disorder of the brain. In susceptible individuals, a variety of “triggers” may influence altered central excitability, resulting in the activation and sensitization of trigeminal nociceptive afferents surrounding blood vessels (i.e., the trigeminovascular system), leading to migraine pain. Transient receptor potential (TRP) channels are expressed in a subset of dural afferents, including those containing calcitonin gene related peptide (CGRP). Activation of TRP channels promotes excitation of nociceptive afferent fibers and potentially lead to pain. In addition to pain, allodynia to mechanical and cold stimuli can result from sensitization of both peripheral afferents and of central pain pathways. TRP channels respond to a variety of endogenous conditions including chemical mediators and low pH. These channels can be activated by exogenous stimuli including a wide range of chemical and environmental irritants, some of which have been demonstrated to trigger migraine in humans. Activation of TRP channels can elicit CGRP release, and blocking the effects of CGRP through receptor antagonism or antibody strategies has been demonstrated to be effective in the treatment of migraine. Identification of approaches that can prevent activation of TRP channels provides an additional novel strategy for discovery of migraine therapeutics.

Triptan-induced latent sensitization: a possible basis for medication overuse headache

OBJECTIVE

Identification of the neural mechanisms underlying medication overuse headache resulting from triptans.

METHODS

Triptans were administered systemically to rats by repeated intermittent injections or by continuous infusion over 6 days. Periorbital and hind paw sensory thresholds were measured to detect cutaneous allodynia. Immunofluorescent histochemistry was employed to detect changes in peptidic neurotransmitter expression in identified dural afferents. Enzyme-linked immunoabsorbent assay was used to measure calcitonin gene-related peptide (CGRP) levels in blood.

RESULTS

Sustained or repeated administration of triptans to rats elicited time-dependent and reversible cutaneous tactile allodynia that was maintained throughout and transiently after drug delivery. Triptan administration increased labeling for CGRP in identified trigeminal dural afferents that persisted long after discontinuation of triptan exposure. Two weeks after triptan exposure, when sensory thresholds returned to baseline levels, rats showed enhanced cutaneous allodynia and increased CGRP in the blood following challenge with a nitric oxide donor. Triptan treatment thus induces a state of latent sensitization characterized by persistent pronociceptive neural adaptations in dural afferents and enhanced responses to an established trigger of migraine headache in humans.

INTERPRETATION

Triptans represent the treatment of choice for moderate and severe migraine headaches. However, triptan overuse can lead to an increased frequency of migraine headache. Overuse of these medications could induce neural adaptations that result in a state of latent sensitization, which might increase sensitivity to migraine triggers. The latent sensitization could provide a mechanistic basis for the transformation of migraine to medication overuse headache.