New therapeutic target in primary headaches - blocking theCGRP receptor

Calcitonin gene-related peptide (CGRP) receptor antagonists: Heterocyclic modification of a novel azepinone lead

In our efforts to identify orally bioavailable CGRP receptor antagonists, we previously discovered a novel series of orally available azepinone derivatives that unfortunately also exhibited the unwanted property of potent time-dependent human CYP3A4 inhibition. Through heterocyclic replacement of the indazole ring, we discovered a series of heterocycle derivatives as high-affinity CGRP receptor antagonists. Some of them showed reasonable oral exposures, and the imidazolone derivatives that showed good oral exposure also exhibited substantially reduced time-dependent CYP3A4 inhibition. Several compounds showed strong in vivo efficacy in our marmoset facial blood flow assay with up to 87% inhibition of CGRP-induced activity. However, oral bioavailability generally remained low, emphasizing the challenges we and others encountered in discovering clinical development candidates for this difficult Class B GPCR target.

1,3-Diazepine: A privileged scaffold in medicinal chemistry

Privileged structures have been widely used as effective templates for drug discovery. While benzo-1,4-diazepine constitutes the first historical example of such a structure, the 1,3 analogue is just as rich in terms of applications in medicinal chemistry. The 1,3-diazepine moiety is present in numerous biological active compounds including natural products, and is used to design compounds displaying a large range of biological activities. It is present in the clinically used anticancer compound pentostatin, in several recent FDA approved β-lactamase inhibitors (e.g., avibactam) and also in coformycin, a natural product known as a ring-expanded purine analogue displaying antiviral and anticancer activities. Several other 1,3-diazepine containing compounds have entered into clinical trials. This heterocyclic structure has been and is still widely used in medicinal chemistry to design enzyme inhibitors, GPCR ligands, and so forth. This review endeavours to highlight the main use of the 1,3-diazepine scaffold and its derivatives, and their applications in medicinal chemistry, drug design, and therapy. We will focus more particularly on the development of enzyme inhibitors incorporating this scaffold, with a strong emphasis on the molecular interactions involved in the inhibition mechanism.

NOP-Related Mechanisms in Pain and Analgesia

Since the discovery of the NOP receptor and N/OFQ as the endogenous ligand, evidence has appeared demonstrating the involvement of this receptor system in pain. This was not surprising for members of the opioid receptor and peptide families, particularly since both the receptor and N/OFQ are highly expressed in brain regions involved in pain, spinal cord, and dorsal root ganglia. What has been surprising is the complicated picture that has emerged from 25 years of research. The original finding that N/OFQ decreased tail flick and hotplate latency, when administered i.c.v., led to the hypothesis that NOP receptor antagonists could have analgesic activity without abuse liability. However, as data accumulated, it became clear that not only the potency but the activity per se was different when N/OFQ or small molecule NOP agonists were administered in the brain versus the spinal cord and it also depended upon the pain assay used. When administered systemically, NOP receptor agonists are generally ineffective in attenuating heat pain but are antinociceptive in an acute inflammatory pain model. Most antagonists administered systemically have no antinociceptive activity of their own, even though selective peptide NOP antagonists have potent antinociceptive activity when administered i.c.v. Chronic pain models provide different results as well, as small molecule NOP receptor agonists have potent anti-allodynic and anti-hyperalgesic activity after systemic administration. A considerable number of electrophysiological and anatomical experiments, in particular with NOP-eGFP mice, have been conducted in an attempt to explain the complicated profile resulting from NOP receptor modulation, to examine receptor plasticity, and to elucidate mechanisms by which selective NOP agonists, bifunctional NOP/mu agonists, or NOP receptor antagonists modulate acute and chronic pain.

Synthesis and structure-activity relationship study of diaryl[d,f][1,3]diazepines as potential anti-cancer agents

We herein report the synthesis, biological activity and preliminary structure-activity relationships of a series of diaryl[1,3]diazepines. These compounds were able to inhibit the proliferation of many cancer cell lines, such as HeLa, MCF-7, SGC7901 and A549. When HeLa cells were treated with lead compounds 7j and 7k at 3 [Formula: see text] concentration, cell arrest was observed in the G2/M phase.

Ghrelin attenuated hyperalgesia induced by chronic nitroglycerin: CGRP and TRPV1 as targets for migraine management

Background

According to the neurovascular theory of migraine, activation of the trigeminovascular system contributes to the development of migraine. This study examined the effects of chronic intraperitoneal ghrelin (150 µg/kg) treatment on the development of chronic migraine induced by intermittent injection of nitroglycerin 10 mg/kg.

Methods

Baseline and post-drug (2 h following nitroglycerin injection) mechanical and thermal sensitivity were assessed by von Frey hair and tail immersion tests, respectively on days 1, 3, 5, 7, 9 and 11. Moreover, we investigated the effect of ghrelin treatment on nitroglycerin-induced aversive behavior by using a two-chamber conditioned place aversion paradigm. At the end of behavioral testing, on day 11, animals were sacrificed and plasma concentration of calcitonin gene-related peptide was measured using a rat-specific enzyme-linked immunosorbent assay kit. Also, real time polymerase chain reaction was used to quantify mRNA expression of calcitonin gene-related peptide and transient receptor potential vanilloid 1 in the trigeminal ganglion.

Results

Our results indicated that nitroglycerin activated the trigeminovascular system, which was reflected by mechanical and thermal hypersensitivity and elevation of mRNA expression of calcitonin gene-related peptide and transient receptor potential vanilloid-1, as migraine markers, and plasma calcitonin gene-related peptide levels. Moreover, chronic nitroglycerin injection induced conditioned place aversion and body weight loss. Nevertheless, ghrelin modulated nitroglycerin-triggered changes in transient receptor potential vanilloid-1 and calcitonin gene-related peptide expression, and mitigated nitroglycerin-induced hyperalgesia.

Conclusion

These results provide the first convincing evidence that ghrelin has a modulating effect on central sensitization induced by chronic intermittent nitroglycerin, and its antinociceptive effect may be related to a reduction of these factors in the trigeminal ganglion.

The effect of melatonin on gene expression of calcitonin gene-related peptide and some proinflammatory mediators in patients with pure menstrual migraine

The neuropeptide calcitonin gene-related peptide (CGRP), a potent vasoactive and a marker of trigeminal inflammation, has been considered as an important mediator in various types of migraine such as pure menstrual migraine. Earlier studies have shown that CGRP can modulate the synthesis and release of other inflammatory factor including nitric oxide (NO) and interleukin-1beta (IL-1β) from trigeminal ganglion glial cells. Exogenous melatonin protects the tissues from inflammatory damages. The goal of this study was to determine the anti-inflammatory effects of melatonin on the CGRP expression, inducible nitric oxide synthase (iNOS) activity, NO, and IL-1β release in cultured peripheral blood mononuclear cells (PBMCs) from pure menstrual migraine patients and healthy subjects. This study was performed on 12 pure menstrual migraine patients and 12 age-and sex-matched healthy subjects. PBMCs were isolated and treated with melatonin for 12 h at pharmacological dose. Gene expression was evaluated by real-time PCR. CGRP and IL-1β proteins in culture supernatant were determined by ELISA method. iNOS activity in PBMCs was determined by colorimetric assays. Total nitrite as an indicator of NO concentrations in the culture supernatants was measured using Griess method. We found that melatonin treatment significantly decreases mRNA expression of CGRP release, NO production, and iNOS activity in the patient groups. Taken together, it appears that melatonin reduces inflammation through decreasing CGRP level and iNOS activity in the patients with migraine; however, further studies are needed in this regard.

Asymmetric Synthesis of the Major Metabolite of a Calcitonin Gene-Related Peptide Receptor Antagonist and Mechanism of Epoxide Hydrogenolysis

An asymmetric synthesis of the major metabolite of the calcitonin gene-related peptide recepotor antagonist BMS-846372 is presented. The variously substituted cyclohepta[b]pyridine ring system represents an underexplored ring system and showed some unexpected chemistry. Reactivities of epoxide and ketone functional groups on the cycloheptane ring were extensively controlled by a remote bulky TIPS group. The rate difference of the hydrogenolysis between two diastereomeric epoxide intermediates shed some light on the mechanism of epoxide hydrogenolysis, and further, deuterium labeling studies revealed more mechanistic details on this well-known chemical transformation for the first time.

Inhibitory effect of chronic oral treatment with fluoxetine on capsaicin-induced external carotid vasodilatation in anaesthetised dogs

Background

During migraine, capsaicin-sensitive trigeminal sensory nerves release calcitonin gene-related peptide (CGRP), resulting in cranial vasodilatation and central nociception. Moreover, 5-HT is involved in the pathophysiology of migraine and depression. Interestingly, some limited lines of evidence suggest that fluoxetine may be effective in migraine prophylaxis, but the underlying mechanisms are uncertain. Hence, this study investigated the canine external carotid vasodilator responses to capsaicin, α-CGRP and acetylcholine before and after acute and chronic oral treatment with fluoxetine.

Methods

Forty-eight vagosympathectomised male mongrel dogs were prepared to measure blood pressure, heart rate and external carotid blood flow. The thyroid artery was cannulated for infusions of agonists. In 16 of these dogs, a spinal cannula was inserted (C1–C3) for infusions of 5-HT.

Results

The external carotid vasodilator responses to capsaicin, α-CGRP and acetylcholine remained unaffected after intracarotid or i.v. fluoxetine. In contrast, the vasodilator responses to capsaicin, but not those to α-CGRP or acetylcholine, were inhibited after chronic oral treatment with fluoxetine (300 µg/kg; for 90 days) or intrathecal 5-HT.

Conclusions

Chronic oral fluoxetine inhibited capsaicin-induced external carotid vasodilatation, and this inhibition could partly explain its potential prophylactic antimigraine action.

Discovery of potent, cyclic calcitonin gene-related peptide receptor antagonists

Calcitonin gene-related peptide (CGRP), a potent dilator of cerebral and dural vasculature, is known to be elevated in plasma and cerebral spinal fluid during migraine attacks. Selective blockade of the CGRP receptor offers the promise of controlling migraine headache more effectively and without the side-effects associated with the use of triptans. Our efforts to develop a novel, peptide-based CGRP antagonist focused on the C-terminal portion of the peptide which is known to bind the receptor but lack agonist properties. Extensive SAR studies of the C-terminal CGRP (27-37) region identified a novel cyclic structure: Bz-Val-Tyr-cyclo[Cys-Thr-Asp-Val-Gly-Pro-Phe-Cys]-Phe-NH(2) (23) with a kb value of 0.126 nM against the cloned human CGRP receptor. Additional SAR studies directed at enhancement of potency and improvement of physicochemical properties yielded a series of analogs with kb values in the 0.05-0.10 nM range.

Orally bioavailable imidazoazepanes as calcitonin gene-related peptide (CGRP) receptor antagonists: discovery of MK-2918

In our ongoing efforts to develop CGRP receptor antagonists for the treatment of migraine, we aimed to improve upon telecagepant by targeting a compound with a lower projected clinical dose. Imidazoazepanes were identified as potent caprolactam replacements and SAR of the imidazole yielded the tertiary methyl ether as an optimal substituent for potency and hERG selectivity. Combination with the azabenzoxazinone spiropiperidine ultimately led to preclinical candidate 30 (MK-2918).

Migraine is a neuronal disease

Migraine is a common, paroxysmal, highly disabling primary headache disorder with a genetic background. The primary cause and the origin of migraine attacks are enigmatic. Numerous clinical and experimental results suggest that activation of the trigeminal system (TS) is crucial in its pathogenesis, but the primary cause of this activation is not fully understood. Since activation of the peripheral and central arms of the TS might be related to cortical spreading depression and to the activity of distinct brainstem nuclei (e.g. the periaqueductal grey), we conclude that migraine can be explained as an altered function of the neuronal elements of the TS, the brainstem, and the cortex, the centre of this process comprising activation of the TS. In light of our findings and the literature data, therefore, we can assume that migraine is mainly a neuronal disease.

Randomized, controlled trial of telcagepant over four migraine attacks

METHODS

This study evaluated the calcitonin gene-related peptide (CGRP) receptor antagonist telcagepant (tablet formulation) for treatment of a migraine attack and across four attacks. Adults with migraine were randomized, double-blind, to telcagepant 140 mg, telcagepant 280 mg, or control treatment sequences to treat four moderate-to-severe migraine attacks. Control patients received placebo for three attacks and telcagepant 140 mg for one attack. Efficacy for the first attack (Attack 1) and consistency of efficacy over multiple attacks were assessed. For an individual patient, consistent efficacy was defined as ≥ 3 successes, and lack of consistent efficacy was defined as ≥ 2 failures, in treatment response. A total of 1677 patients treated ≥ 1 attack and 1263 treated all four attacks.

RESULTS

Based on Attack 1 data, telcagepant 140 mg and 280 mg were significantly (p < .001) more effective than placebo for 2-hour pain freedom, 2-hour pain relief, 2-hour absence of migraine-associated symptoms (phonophobia, photophobia, nausea), and 2-24 hours sustained pain freedom. The percentage of patients with 2-hour pain freedom consistency and 2-hour pain relief consistency was significantly (p < .001) higher for both telcagepant treatment sequences versus control. Adverse events within 48 hours for telcagepant with an incidence ≥ 2% and twice that of placebo were somnolence (placebo = 2.3%, 140 mg = 5.9%, 280 mg = 5.7%) and vomiting (placebo = 1.4%, 140 mg = 1.0%, 280 mg = 2.9%).

CONCLUSION

Telcagepant 140 mg and 280 mg were effective for treatment of a migraine attack and were more consistently effective than control for intermittent treatment of up to four migraine attacks. Telcagepant was generally well tolerated. (Clinicaltrials.gov; NCT00483704).

Calcitonin gene-related peptide receptor antagonists for the treatment of migraine: a patent review

BACKGROUND

Migraine is a debilitating headache disorder which affects approximately 12% of the general population and is the cause of significant loss of productivity (i.e., lost time from work or school) for those afflicted. The current standard of care, the 5-HT(1B/1D) agonists known as triptans, is contraindicated in patients with cardiovascular disease due to their inherent vasoconstrictive activity; thus, there is a need to develop an alternative therapy for the treatment of the disorder.

OBJECTIVE

This article reviews patent publications related to the use of small molecule calcitonin gene-related peptide (CGRP) receptor antagonists for the treatment of migraine that have appeared in the literature within the past decade. The commentary is supplemented by information presented in journal articles and focuses on the activity of several major pharmaceutical companies in the field.

CONCLUSION

Two small molecule CGRP receptor antagonists, olcegepant and telcagepant, have been shown to be clinically efficacious in the treatment of migraine, and thus provide validation of this novel therapeutic mechanism.

Acute treatment of migraine

Acute treatment of migraine has benefited first from major advances in pharmacological science followed in short order, sometimes preceded, by an improved understanding of pathogenesis, especially of headache. This chapter reviews the mechanisms of migraine that provide an understanding of the pharmacology and therapeutic targets for acute migraine medications. General clinical approaches to acute therapy are reviewed, and indices of acceptable acute therapeutic outcomes are discussed. Currently the serotonin (5-HT) 1B/1D agonist group of drugs, triptans, forms the mainstay of acute therapeutic regimens. Other approaches to acute treatment such as simple analgesics, non-steroidal anti-inflammatory drugs (NSAIDs), ergots, and combination medications are reviewed. Finally, the newest acute treatments that are currently exploratory or under clinical investigation are discussed.

Efficacy and tolerability of MK-0974 (telcagepant), a new oral antagonist of calcitonin gene-related peptide receptor, compared with zolmitriptan for acute migraine: a randomised, placebo-controlled, parallel-treatment trial

BACKGROUND

Calcitonin gene-related peptide (CGRP) probably has a role in migraine pathophysiology, and antagonism of its receptors might provide treatment without the vasoconstrictor effects of triptans. We aimed to assess the clinical profile of MK-0974 (telcagepant), an orally bioavailable antagonist of CGRP receptor.

METHODS

In a randomised, parallel-treatment, placebo-controlled, double-blind, trial at 81 sites in the Europe and the USA, adults with migraine diagnosed by International Headache Society criteria treated moderate or severe attacks with either oral telcagepant 150 mg or 300 mg, zolmitriptan 5 mg, or placebo. The five co-primary endpoints were pain freedom, pain relief, or absence of photophobia, phonophobia, or nausea at 2 h after treatment. Analysis was by the full analysis set and multiplicity was controlled for with a step-down closed-testing procedure. This trial is registered with ClinicalTrials.gov, number NCT00442936.

FINDINGS

1380 patients were randomly assigned to receive telcagepant 150 mg (n=333) or 300 mg (354), zolmitriptan (345), or placebo (348). Telcagepant 300 mg was more effective than placebo for pain freedom (95 [27%] of 353 patients vs 33 [10%] of 343 [p<0.0001]), pain relief (194 [55%] of 353 vs 95 [28%] of 343 [p<0.0001]), and absences of phonophobia (204 [58%] of 353 vs 126 [37%] of 342 [p<0.0001]), photophobia (180 [51%] of 353 vs 99 [29%] of 342 [p<0.0001]), and nausea (229 [65%] of 352 vs 189 [55%] of 342 [p=0.0061]). Efficacy of telcagepant 300 mg and zolmitriptan 5 mg were much the same, and both were more effective than telcagepant 150 mg. Adverse events were recorded for 31% taking telcagepant 150 mg, 37% taking telcagepant 300 mg, 51% taking zolmitriptan 5 mg, and 32% taking placebo.

INTERPRETATION

Telcagepant 300 mg is effective as an acute treatment for migraine with efficacy comparable to that of zolmitriptan 5 mg, but with fewer associated adverse effects.

FUNDING

Merck Research Laboratories.

Synthesis of the (3R,6S)-3-amino-6-(2,3-difluorophenyl)azepan-2-one of telcagepant (MK-0974), a calcitonin gene-related peptide receptor antagonist for the treatment of migraine headache

Two novel routes have been developed to the (3 R,6 S)-3-amino-6-(2,3-difluorophenyl)-1-(2,2,2-trifluoroethyl)azepan-2-one 2 of the CGRP receptor antagonist clinical candidate telcagepant (MK-0974, 1). The first employs a ring-closing metathesis of the styrene 7 as the key reaction, while the second makes use of a highly diastereoselective Hayashi-Miyaura Rh-catalyzed arylboronic acid addition to nitroalkene 16. The latter route has been implemented to produce multigram quantities of telcagepant for extensive preclinical evaluation.

Potent, orally bioavailable calcitonin gene-related peptide receptor antagonists for the treatment of migraine: discovery of N-[(3R,6S)-6-(2,3-difluorophenyl)-2-oxo-1- (2,2,2-trifluoroethyl)azepan-3-yl]-4- (2-oxo-2,3-dihydro-1H-imidazo[4,5-b]pyridin- 1-yl)piperidine-1-carboxamide (MK-0974)

Calcitonin gene-related peptide (CGRP) has been implicated in the pathogenesis of migraine. Herein we describe optimization of CGRP receptor antagonists based on an earlier lead structure containing a (3R)-amino-(6S)-phenylcaprolactam core. Replacement of the phenylimidazolinone with an azabenzimidazolone gave stable derivatives with lowered serum shifts. Extensive SAR studies of the C-6 aryl moiety revealed the potency-enhancing effect of the 2,3-difluorophenyl group, and trifluoroethylation of the N-1 amide position resulted in improved oral bioavailabilities, ultimately leading to clinical candidate 38 (MK-0974).

New and future migraine therapy

Modern neuroscience advanced our understanding of putative migraine mechanisms, which led to improved therapeutics. Indeed, mechanism-based acute migraine therapy gained steam in the early 1990s after the introduction of the triptans (5-HT1B,D agonists). Post-triptans, novel targets such as calcitonin gene-related peptide (CGRP) antagonists, inhibitors of excitatory glutamatergic receptors, and nitric oxide synthase (NOS) inhibitors are leading the pack in this exploding field of discovery research. In contrast, novel therapeutic targets for migraine prevention are lacking despite a hugely unmet need. To date, migraine prophylactic drugs are advanced based on expanded indications for already approved pharmaceuticals (e.g., topiramate, valproate, propranolol, and timolol). An improved understanding of the predisposition to an attack, genomic discoveries, valid and reliable biomarkers and surrogates, and predictive preclinical models likely will unravel the neuronal substrates for central hyperexcitability and nociceptive dysmodulation, hopefully leading us to better mechanism-based targets for prevention, and ultimately yielding drugs with optimal therapeutic ratios or indices.

Benzodiazepine calcitonin gene-related peptide (CGRP) receptor antagonists: optimization of the 4-substituted piperidine

In our continuing effort to identify CGRP receptor antagonists for the acute treatment of migraine, we have undertaken a study to evaluate alternative 4-substituted piperidines to the lead dihydroquinazolinone 1. In this regard, we have identified the piperidinyl-azabenzimidazolone and phenylimidazolinone structures which, when incorporated into the benzodiazepine core, afford potent CGRP receptor antagonists (e.g., 18 and 29). These studies produced a potent analog (18) which overcomes the instability issues associated with the lead structure 1. A general pharmacophore for the 4-substituted piperidine component of these CGRP receptor antagonists is also presented.

Donitriptan, but not sumatriptan, inhibits capsaicin-induced canine external carotid vasodilatation via 5-HT1B rather than 5-HT1D receptors

BACKGROUND AND PURPOSE

It has been suggested that during a migraine attack capsaicin-sensitive trigeminal sensory nerves release calcitonin gene-related peptide (CGRP), resulting in cranial vasodilatation and central nociception; hence, trigeminal inhibition may prevent this vasodilatation and abort migraine headache. This study investigated the effects of the agonists sumatriptan (5-HT(1B/1D) water-soluble), donitriptan (5-HT(1B/1D) lipid-soluble), PNU-142633 (5-HT(1D) water-soluble) and PNU-109291 (5-HT(1D) lipid-soluble) on vasodilator responses to capsaicin, alpha-CGRP and acetylcholine in dog external carotid artery.

EXPERIMENTAL APPROACH

59 vagosympathectomized dogs were anaesthetized with sodium pentobarbitone. Blood pressure and heart rate were recorded with a pressure transducer, connected to a cannula inserted into a femoral artery. A precalibrated flow probe was placed around the common carotid artery, with ligation of the internal carotid and occipital branches, and connected to an ultrasonic flowmeter. The thyroid artery was cannulated for infusion of agonists.

KEY RESULTS

Intracarotid infusions of capsaicin, alpha-CGRP and acetylcholine dose-dependently increased blood flow through the carotid artery. These responses remained unaffected after intravenous (i.v.) infusions of sumatriptan, PNU-142633, PNU-109291 or physiological saline; in contrast, donitriptan significantly attenuated the vasodilator responses to capsaicin, but not those to alpha-CGRP or acetylcholine. Only sumatriptan and donitriptan dose-dependently decreased the carotid blood flow. Interestingly, i.v. administration of the antagonist, SB224289 (5-HT(1B)), but not of BRL15572 (5-HT(1D)), abolished the inhibition by donitriptan.

CONCLUSIONS AND IMPLICATIONS

Our results suggest that the inhibition produced by donitriptan of capsaicin-induced external carotid vasodilatation is mainly mediated by 5-HT(1B), rather than 5-HT(1D), receptors, probably by a central mechanism.

Non-peptide calcitonin gene-related peptide receptor antagonists from a benzodiazepinone lead

High-throughput screening of the Merck sample collection identified benzodiazepinone tetralin-spirohydantoin 1 as a CGRP receptor antagonist with micromolar activity. Comparing the structure of 1 with those of earlier peptide-based antagonists such as BIBN 4096 BS, a key hydrogen bond donor-acceptor pharmacophore was hypothesized. Subsequent structure activity studies supported this hypothesis and led to benzodiazepinone piperidinyldihydroquinazolinone 7, CGRP receptor K(i)=44nM and IC(50)=38nM. Compound 7 was orally bioavailabile in rats and is a lead in the development of orally bioavailable CGRP antagonists for the treatment of migraine.

New Treatments for Neuropathic Pain

Existing treatments for neuropathic pain deliver inadequate pain relief, unacceptable side effects, or both. The unmet medical need for more effective treatment is driving a large volume of research to discover new drugs. Most existing treatments are drugs introduced to treat other pain conditions or other medical conditions, such as antidepressants and anticonvulsants, which were found empirically to be effective for neuropathic pain. Only recently have drug discovery efforts have become mechanistically driven, addressing targets identified by a molecular neurobiological approach to the pathophysiology of neuropathic states.

Lack of effect of the adenosine A1 receptor agonist, GR79236, on capsaicin-induced CGRP release in anaesthetized pigs

Migraine is a common neurological disorder that is associated with an increase in plasma calcitonin gene-related peptide (CGRP) levels. CGRP, a potent vasodilator released from the activated trigeminal sensory nerves, dilates intracranial blood vessels and transmits vascular nociception. Hence, inhibition of trigeminal CGRP release may prevent neurotransmission and, thereby, ameliorate migraine headache. Therefore, the present study in anaesthetized pigs investigates the effects of a selective adenosine A(1) receptor agonist, GR79236 (3, 10 and 30 microg/kg, i.v.) on capsaicin-induced carotid haemodynamic changes and on plasma CGRP release. Intracarotid (i.c.) infusion of capsaicin (10 microg/kg/min, i.c.) increased the total carotid blood flow and conductance as well as carotid pulsations, but decreased the difference between arterial and jugular venous oxygen saturations. These responses to capsaicin were dose-dependently attenuated by GR79236. However, the increases in the plasma CGRP concentrations by capsaicin remained essentially unmodified after GR79236 treatment. The above results suggest that GR79236 may have an antimigraine potential due to its postjunctional effects (carotid vasoconstriction) rather than to prejunctional inhibition of trigeminal CGRP release.

Ovarian steroids regulate neuropeptides in the trigeminal ganglion

Women are more than three times as likely as men to experience migraine headaches and temporomandibular joint pain, and painful episodes are often linked to the menstrual cycle. To understand how hormone levels may influence head and face pain, we assessed expression of pain-associated neuropeptides and estrogen receptor alpha (ERalpha) during the natural estrous cycle in mice. Gene expression was analyzed in the trigeminal ganglia of cycling female mice at proestrus, estrus and diestrus using RT-PCR. Peptide/protein expression in trigeminal neurons was analyzed using immunohistochemistry. ERalpha mRNA was present at all stages and highest at estrus. ERalpha protein was present in the cytoplasm of medium-sized and small trigeminal neurons. ERalpha immunoreactive neurons were most common at diestrus. CGRP and ANP mRNAs did not change across the estrous cycle, while expression of galanin and NPY mRNAs were strongly linked to the estrous cycle. Galanin mRNA levels peaked at proestrus, when expression was 8.7-fold higher than the diestrus levels. Galanin immunoreactivity also peaked at proestrus. At proestrus, 7.5% of trigeminal neurons contained galanin, while at estrus, 6.2% of trigeminal neurons contained galanin, and at diestrus, 4.9% of trigeminal neurons contained galanin. NPY mRNA peaked at estrus, when levels were 4.7-fold higher than at diestrus. Our findings suggest that estrogen receptors in trigeminal neurons modulate nociceptive responses through effects on galanin and NPY. Variations in neuropeptide content in trigeminal neurons across the natural estrous cycle may contribute to increases in painful episodes at particular phases of the menstrual cycle.

Reproducibility of forearm vasodilator response to intra-arterial infusion of calcitonin gene-related peptide assessed by venous occlusion plethysmography

AIMS

To assess the reproducibility of the forearm blood flow (FBF) response to intra-arterial infusion of calcitonin-gene related peptide (CGRP), measured by venous occlusion plethysmography. In addition, to compare different ways of expressing the FBF response and perform sample size calculations.

METHODS

On two separate visits, CGRP (10 ng min(-1) dl(-1) forearm) was infused for 45 min into the brachial artery of six healthy subjects. Reproducibility was assessed by calculating mean difference, repeatability coefficient, within-subject coefficient of variation (WCV) and intraclass correlation coefficient.

RESULTS

CGRP increased FBF from 2.8 +/- 0.4 and 3.2 +/- 0.7 (at baseline) to 15.4 +/- 1.4 and 15.2 +/- 1.5 ml min(-1) dl(-1) forearm (at 45 min) on visits 1 and 2, respectively (P < 0.0001 for both visits). Mean difference in FBF at 45 min between both visits was 0.3 ml min(-1) dl(-1) forearm (repeatability coefficient: 4.1 ml min(-1) dl(-1) forearm). This FBF response appeared to be more reproducible when expressed as absolute FBF in the infused arm (WCV 11%) compared with absolute FBF-ratio between both arms (WCV 37%), percentage change from baseline in FBF in the infused arm (WCV 29%) and percentage change from baseline in FBF-ratio (WCV 40%). When expressed as absolute FBF, a sample size of five (95% confidence interval: 2-12) subjects gives 90% power at a type I error probability of 0.05 to detect a 25% shift in FBF response.

CONCLUSIONS

Intra-arterial infusion of CGRP results in a forearm vasodilator response which is reproducible between days. This response is most reproducible when expressed as absolute FBF. The presented methodology provides a suitable pharmacodynamic model to assess the in vivo activity of CGRP-receptor antagonists in a small number of subjects.

XI Congress of the International Headache Society

The XI Congress of the International Headache Society (IHC) provided useful feedback for a wide range of disciplines for all scientists involved in basic and applied research concerning headaches. The major topics of the Congress included comorbidity, paediatric headache, phenotypic markers, genetics, migraine therapy, trigeminal neuralgia and paroxysmal facial pain with autonomic signs. The most recent advances were presented and discussed and all efforts were made to transfer these new understandings of pathogenesis, clinical features and treatments, to clinical practice, in an attempt to gain a better understanding of patient problems and requests. The Presidential Symposium, which anticipated the scientific sessions, provided the most updated knowledge regarding neuroimaging, neurophysiological and potential clinical implications of the activation of brainstem structures as well as the dependency of cortical events on this activation during migraine attacks. The results of the strenuous work carried out from autumn 1999 to 2003 of an International Committee of headache experts, presided by J. Olesen, reached its peak with the presentation of the new International Headache Classification ICHD-II. There are many relevant changes in the new classification, even though the basic structure and the most important criteria, such as those for migraine without aura and tension-type headache, have been maintained. Several new entities have been added including chronic migraine for patients having migraine >or= 15 days/month. New rules separate primary and secondary headaches and a new chapter now presents headaches attributed to psychiatric disorders. Headaches due to disturbance of homeostasis has been brought together in a new chapter and the diagnostic criteria for secondary headaches are now more systematically constructed. All these changes will hopefully promote research, especially for the novel entities reported in the appendix, which have not been sufficiently validated or for which sufficient evidence still has not been published.

Localization of calcitonin gene-related peptide in cardiomyocytes: comparison of neonatal and dedifferentiating cells to adult myocytes

The purpose of this study was to localize sites of calcitonin gene-related peptide binding in neonatal, freshly isolated and dedifferentiated adult cardiac myocytes in order to help us elucidate the mechanisms of action of this neuropeptides. Previous work has shown that treatment with calcitonin gene-related peptide results in dramatic changes in calcium transients, so we carried out multi-channel acquisitions of fluorescently labeled images to reveal where calcitonin gene-related protein and the L-type calcium channel were localized. Calcitonin gene-related protein was sparse and randomly distributed in rod-like adult cardiomyocytes, found in abundance in areas of the cell where striations were apparent and not where adhesion proteins predominated in dedifferentiating adult myocytes, and in a large perinuclear concentration, with some spreading into the cytoplasm in neonatal cells. Subsequent modeling demonstrated that calcitonin gene-related peptide and the L-type calcium channel protein were closely associated in each of the three myocyte types, suggesting that while the peptide has dramatic and different effects on intracellular calcium levels of the various cardiomyocytes, the action is probably via diverse mechanisms as a result of effects on different channels or pump proteins due to alterations in intracellular calcium concentrations.

Emerging drugs in migraine treatment

Ergot alkaloids have been the mainstay of acute migraine therapy for most of the 20th century. They have been supplanted by sumatriptan-like drugs ('triptans'), which, while keeping some of the ergotś mechanisms of action, show improved safety profiles due to their increased receptor selectivity. However, triptans are still far from being perfect drugs: they can constrict human coronary arteries at therapeutic doses and, therefore, are contra-indicated in the presence of cardiovascular disease. Another problem with these agents is recurrence of moderate-to-severe pain within 24 h of initial headache relief. While mechanism-driven drug design has led to the development of various novel, albeit still imperfect, acute antimigraine medications, only a few new prophylactic agents have been made available to migraine clinicians. The efficacy of most, if not all of them has been discovered serendipitously. This is probably due to the fact that, while the pathophysiology of a migraine attack is now reasonably understood, the mechanisms leading to an attack are still mostly unknown. This update analyses the profile of some antimigraine drugs in clinical trials, their mode of action and their potential advantages or drawbacks over already available agents.

Effects of sumatriptan on capsaicin-induced carotid haemodynamic changes and CGRP release in anaesthetized pigs

It is suggested that during a migraine attack capsaicin-sensitive trigeminal sensory nerves release calcitonin gene related peptide (CGRP), resulting in cranial vasodilatation and central nociception. Hence, inhibition of trigeminal CGRP release may prevent the above vasodilatation and, accordingly, abort migraine headache. Therefore, this study investigated the effects of sumatriptan (100 and 300 microg/kg, i.v.) on capsaicin-induced carotid haemodynamic changes and on CGRP release. Intracarotid (i.c.) infusions of capsaicin (10 microg/kg/min, i.c.) increased total carotid, arteriovenous anastomotic and capillary conductances as well as carotid pulsations, but decreased the difference between arterial and jugular venous oxygen saturations. Except for some attenuation of arteriovenous anastomotic changes, the capsaicin-induced responses were not affected by sumatriptan. Moreover, i.c. infusions of capsaicin (0.3, 1, 3 and 10 microg/kg/min, i.c.) dose-dependently increased the jugular venous plasma concentrations of CGRP, which also remained unaffected by sumatriptan. The above results support the contention that the therapeutic action of sumatriptan is mainly due to cranial vasoconstriction rather than trigeminal (CGRP release) inhibition.

Noncompetitive antagonism of BIBN4096BS on CGRP-induced responses in human subcutaneous arteries

We investigated the antagonistic effect of 1-piperidinecarboxamide, N-[2-[[5amino-l-[[4-(4-pyridinyl)-l-piperazinyl]carbonyl]pentyl]amino]-1-[(3,5-dibromo-4-hydroxyphenyl)methyl]-2-oxoethyl]-4-(1,4-dihydro-2-oxo-3(2H)-quinazolinyl) (BIBN4096BS) on the calcitonin gene-related peptide (CGRP)-induced responses by using isometric myograph and FURA-2 technique in human subcutaneous arteries removed in association with abdominal surgery. BIBN4096BS, at the concentration of 1 pm, had no significant effect on the CGRP-induced relaxation in these vessels. At the concentration of 10 pM, BIBN4096BS had a competitive antagonistic-like behaviour characterized by parallel rightward shift in the log CGRP concentration-tension curve with no depression of the E(max). At the higher concentrations (0.1 and 1 nM), BIBN4096BS had a concentration-dependent noncompetitive antagonistic effect on the CGRP-induced responses. The efficacy and potency of CGRP was significantly greater in the smaller (lumen diameter approximately 200 microM) human subcutaneous arteries compared to the larger ones. The apparent agonist equilibrium dissociation constant, K(A), for CGRP(1) receptors in the human subcutaneous arteries was approximately 1 nM. Analysis of the relationship between receptor occupancy and response to CGRP indicates that the receptor reserve is relatively small. Using reverse transcriptase-polymerase chain reaction (RT-PCR), the presence of mRNA sequences encoding the calcitonin receptor-like receptor, receptor activity modifying protein (RAMP1, RAMP2, RAMP3) and receptor component protein were demonstrated in human subcutaneous arteries, indicating the presence of CGRP(1)-like receptor and the necessary component for the receptor activation. In conclusion, the inhibitory action of BIBN4096BS at the low concentration (10 pM) on the CGRP-tension curve (but not intracellular calcium concentration ([Ca(2+)](i)) resembles what is seen with a reversible competitive antagonist. However, at the higher concentrations (0.1 and 1 nM), BIBN4096BS acts as a selective noncompetitive inhibitor at CGRP(1) receptors in human subcutaneous arteries.

Regulation of the cell-specific calcitonin/calcitonin gene-related peptide enhancer by USF and the Foxa2 forkhead protein

An 18-bp enhancer controls cell-specific expression of the calcitonin/calcitonin gene-related peptide gene. The enhancer is bound by a heterodimer of the bHLH-Zip protein USF-1 and -2 and a cell-specific factor from thyroid C cell lines. In this report we have identified the cell-specific factor as the forkhead protein Foxa2 (previously HNF-3beta). Binding of Foxa2 to the 18-bp enhancer was demonstrated using electrophoretic mobility shift assays. The cell-specific DNA-protein complex was selectively competed by a series of Foxa2 DNA binding sites, and the addition of Foxa2 antiserum supershifted the complex. Likewise, a complex similar to that seen with extracts from thyroid C cell lines was generated using an extract from heterologous cells expressing recombinant Foxa2. Interestingly, overexpression of Foxa2 activated the 18-bp enhancer in heterologous cells but only in the presence of the adjacent helix-loop-helix motif. Likewise, coexpression of USF proteins with Foxa2 yielded greater activation than by Foxa2 alone. Unexpectedly, Foxa2 overexpression repressed activity in the CA77 thyroid C cell line, suggesting that Foxa2 may interact with additional cofactors. The stimulatory role of Foxa2 at the calcitonin/calcitonin gene-related peptide gene enhancer was confirmed by short interfering RNA-mediated knockdown of Foxa2. As seen with Foxa2 overexpression, the effect of Foxa2 knockdown also required the adjacent helix-loop-helix motif. These results provide the first evidence for combinatorial control of gene expression by bHLH-Zip and forkhead proteins.

Calcitonin gene-related peptide (CGRP) antagonists: blockers of neuronal transmission in migraine

The neuropeptide calcitonin gene-related peptide (CGRP) is a potent vasodilator that is contained in and released from sensory nerves. CGRP has been implicated in migraine, and the nonpeptide CGRP antagonist BIBN4096BS has been shown to be effective in clinical trials in migraine. To date, it has been largely assumed that the CGRP antagonist is effective due to its ability to block vasodilator activity. Goadsby and co-workers present data that now suggest that CGRP antagonists may also block neuronal transmission in migraine.

Vascular Actions of Calcitonin Gene-Related Peptide and Adrenomedullin

This review summarizes the receptor-mediated vascular activities of calcitonin gene-related peptide (CGRP) and the structurally related peptide adrenomedullin (AM). CGRP is a 37-amino acid neuropeptide, primarily released from sensory nerves, whilst AM is produced by stimulated vascular cells, and amylin is secreted from the pancreas. They share vasodilator activity, albeit to varying extents depending on species and tissue. In particular, CGRP has potent activity in the cerebral circulation, which is possibly relevant to the pathology of migraine, whilst vascular sources of AM contribute to dysfunction in cardiovascular disease. Both peptides exhibit potent activity in microvascular beds. All three peptides can act on a family of CGRP receptors that consist of calcitonin receptor-like receptor (CL) linked to one of three receptor activity-modifying proteins (RAMPs) that are essential for functional activity. The association of CL with RAMP1 produces a CGRP receptor, with RAMP2 an AM receptor and with RAMP3 a CGRP/AM receptor. Evidence for the selective activity of the first nonpeptide CGRP antagonist BIBN4096BS for the CGRP receptor is presented. The cardiovascular activity of these peptides in a range of species and in human clinical conditions is detailed, and potential therapeutic applications based on use of antagonists and gene targeting of agonists are discussed.

Stress-induced suppression of the gonadotropin-releasing hormone pulse generator in the female rat: a novel neural action for calcitonin gene-related peptide

In addition to its role as a potent vasodilator, calcitonin gene-related peptide (CGRP) is centrally involved in a variety of stress responses, including activation of the hypothalamo-pituitary-adrenocortical axis. It is well known that stress suppresses the activity of the hypothalamic GnRH pulse generator, the central regulator of LH and FSH pulses, resulting in reproductive dysfunction. The aim of this study was to test the hypothesis that CGRP has a critical role in mediating stress-induced suppression of pulsatile LH secretion in the rat. Ovariectomized rats were implanted with intracerebroventricular and iv cannulae. Central administration of CGRP (75 pmol-1.2 nmol) into the lateral cerebral ventricle resulted in a profound, dose-dependent suppression of LH pulses, which was reversed by a CGRP receptor antagonist (CGRP(8-37),1 nmol). Although the site of action of CGRP remains to be established, the induction of c-Fos expression in the preoptic area and hypothalamic paraventricular nucleus might suggest an involvement of these brain regions. Intravenous administration of CGRP did not affect LH pulses. Coadministration (intracerebroventricular) of CGRP (400 pmol) with a CRH antagonist (alpha-helical CRF(9-41), 26 nmol) partly blocked the CGRP-induced suppression of LH pulses. Furthermore, CGRP(8-37) (1 nmol) completely blocked hypoglycemic stress-induced suppression of LH pulses. These results suggest that the suppression of pulsatile LH secretion by central administration of CGRP may be mediated in part by CRH, and that CGRP may play a pivotal role in the normal physiological response of stress-induced suppression of the hypothalamic GnRH pulse generator, and hence the reproductive system.

Short bioactive Spiegelmers to migraine-associated calcitonin gene-related peptide rapidly identified by a novel approach: tailored-SELEX

We developed an integrated method to identify aptamers with only 10 fixed nucleotides through ligation and removal of primer binding sites within the systematic evolution of ligands by exponential enrichment (SELEX) process. This Tailored-SELEX approach was validated by identifying a Spiegelmer ('mirror-image aptamer') that inhibits the action of the migraine-associated target calcitonin gene-related peptide 1 (alpha-CGRP) with an IC50 of 3 nM at 37 degrees C in cell culture. Aptamers are oligonucleotide ligands that can be generated to bind to targets with high affinity and specificity. Stabilized aptamers and Spiegelmers have shown activity in vivo and may be used as therapeutics. Aptamers are isolated by in vitro selection from combinatorial nucleic acid libraries that are composed of a central randomized region and additional fixed primer binding sites with approximately 30-40 nt. The identified sequences are usually not short enough for efficient chemical Spiegelmer synthesis, post-SELEX stabilization of aptamers and economical production. If the terminal primer binding sites are part of the target recognizing domain, truncation of aptamers has proven difficult and laborious. Tailored-SELEX results in short sequences that can be tested more rapidly in biological systems. Currently, our identified CGRP binding Spiegelmer serves as a lead compound for in vivo studies.