Potential mechanisms of prospective antimigraine drugs: A focus on vascular (side) effects

Consensus of the Brazilian Headache Society (SBCe) for the Prophylactic Treatment of Episodic Migraine: part I

The Brazilian Headache Society (Sociedade Brasileira de Cefaleia, SBCe, in Portuguese) nominated a Committee of Authors with the aim of establishing a consensus with recommendations regarding prophylactic treatment for episodic migraine based on articles published in the worldwide literature, as well as personal experience. Migraine affects 1 billion people around the world and more than 30 million Brazilians. In addition, it is an underdiagnosed and undertreated disorder. It is well known within the medical community of neurologists, and especially among headache specialists, that there is a need to disseminate knowledge about prophylactic treatment for migraine. For this purpose, together with the need for drug updates and to expand knowledge of the disease itself (frequency, intensity, duration, impact and perhaps the progression of migraine), this Consensus was developed, following a full online methodology, by 12 groups who reviewed and wrote about the pharmacological categories of the drugs used and, at the end of the process, met to read and establish conclusions for this document. The drug classes studied were: anticonvulsants, tricyclic antidepressants, monoclonal anti-calcitonin gene-related peptide (anti-CGRP) antibodies, beta-blockers, antihypertensives, calcium channel inhibitors, other antidepressants (selective serotonin reuptake inhibitors, SSRIs, and dual-action antidepressants), other drugs, and polytherapy. Hormonal treatment and anti-inflammatories and triptans in minimum prophylaxis schemes (miniprophylaxis) will be covered in a specific chapter. The drug classes studied for part I of the Consensus were: anticonvulsants, tricyclic antidepressants, monoclonal anti-CGRP antibodies, and beta-blockers.

A critical review of the neurovascular nature of migraine and the main mechanisms of action of prophylactic antimigraine medications

INTRODUCTION

Migraine involves neurovascular, functional, and anatomical alterations. Migraineurs experience an intense unilateral and pulsatile headache frequently accompanied with vomiting, nausea, photophobia, etc. Although there is no ideal preventive medication, frequency in migraine days may be partially decreased by some prophylactics, including antihypertensives, antidepressants, antiepileptics, and CGRPergic inhibitors. However, the mechanisms of action involved in antimigraine prophylaxis remain elusive.

AREAS COVERED

This review recaps some of the main neurovascular phenomena related to migraine and currently available preventive medications. Moreover, it discusses the major mechanisms of action of the recommended prophylactic medications.

EXPERT OPINION

In the last three years, migraine prophylaxis has evolved from nonspecific to specific antimigraine treatments. Overall, nonspecific treatments  mainly involve neural actions, whereas specific pharmacotherapy (represented by CGRP receptor antagonists and CGRPergic monoclonal antibodies) is predominantly mediated by neurovascular mechanisms that may include, among others: (i) reduction in the cortical spreading depression (CSD)-associated events; (ii) inhibition of pain sensitization; (iii) blockade of neurogenic inflammation; and/or (iv) increase in cranial vascular tone. Accordingly, the novel antimigraine prophylaxis promises to be more effective, devoid of significant adverse effects (unlike nonspecific treatments), and more beneficial for the quality of life of migraineurs.

The locus of Action of CGRPergic Monoclonal Antibodies Against Migraine: Peripheral Over Central Mechanisms

Migraine is a complex neurovascular disorder characterized by attacks of moderate to severe unilateral headache, accompanied by photophobia among other neurological signs. Although an arsenal of antimigraine agents is currently available in the market, not all patients respond to them. As Calcitonin Gene-Related Peptide (CGRP) plays a key role in the pathophysiology of migraine, CGRP receptor antagonists (gepants) have been developed. Unfortunately, further pharmaceutical development (for olcegepant and telcagepant) was interrupted due to pharmacokinetic issues observed during the Randomized Clinical Trials (RCT). On this basis, the use of monoclonal antibodies (mAbs; immunoglobulins) against CGRP or its receptor has recently emerged as a novel pharmacotherapy to treat migraines. RCT showed that these mAbs are effective against migraines producing fewer adverse events. Presently, the U.S. Food and Drug Administration approved four mAbs, namely: (i) erenumab; (ii) fremanezumab; (iii) galcanezumab; and (iv) eptinezumab. In general, specific antimigraine compounds exert their action in the trigeminovascular system, but the locus of action (peripheral vs. central) of the mAbs remains elusive. Since these mAbs have a molecular weight of ∼150 kDa, some studies rule out the relevance of their central actions as they seem unlikely to cross the Blood-Brain Barrier (BBB). Considering the therapeutic relevance of this new class of antimigraine compounds, the present review has attempted to summarize and discuss the current evidence on the probable sites of action of these mAbs.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Characterization of binding, functional activity, and contractile responses of the selective 5-HT1F receptor agonist lasmiditan

BACKGROUND AND PURPOSE

Triptans are 5-HT1B/1D receptor agonists (that also display 5-HT1F receptor affinity) with antimigraine action, contraindicated in patients with coronary artery disease due to their vasoconstrictor properties. Conversely, lasmiditan was developed as an antimigraine 5-HT1F receptor agonist. To assess the selectivity and cardiovascular effects of lasmiditan, we investigated the binding, functional activity, and in vitro/in vivo vascular effects of lasmiditan and compared it to sumatriptan.

EXPERIMENTAL APPROACH

Binding and second messenger activity assays of lasmiditan and other serotoninergic agonists were performed for human 5-HT1A , 5-HT1B , 5-HT1D , 5-ht1E , 5-HT1F , 5-HT2A , 5-HT2B , and 5-HT7 receptors, and the results were correlated with their potency to constrict isolated human coronary arteries (HCAs). Furthermore, concentration-response curves to lasmiditan and sumatriptan were performed in proximal and distal HCA, internal mammary, and middle meningeal arteries. Finally, anaesthetized female beagle dogs received i.v. infusions of lasmiditan or sumatriptan in escalating cumulative doses, and carotid and coronary artery diameters were measured.

KEY RESULTS

Lasmiditan showed high selectivity for 5-HT1F receptors. Moreover, the functional potency of the analysed compounds to inhibit cAMP increase through 5-HT1B receptor activation positively correlated with their potency to contract HCA. In isolated human arteries, sumatriptan, but not lasmiditan, induced contractions. Likewise, in vivo, sumatriptan decreased coronary and carotid artery diameters at clinically relevant doses, while lasmiditan was devoid of vasoconstrictor activity at all doses tested.

CONCLUSIONS AND IMPLICATIONS

Lasmiditan is a selective 5-HT1F receptor agonist devoid of vasoconstrictor activity. This may represent a cardiovascular safety advantage when compared to the triptans.

Calcitonin Gene-Related Peptide (CGRP) Antagonists and Their Use in Migraines

Migraine is highly prevalent and associated with a large socio-economic burden in the United States. Current preventive medications have variable efficacy and their use is often limited by intolerable side effects. Calcitonin gene-related peptide (CGRP) has been identified as an integral part of migraine pathophysiology. There are currently seven CGRP antagonists under investigation, all of which are undergoing or have completed phase 3 clinical trials. Three of the investigated CGRP antagonists are approved for use within and outside of the United States. The trials have resulted in positive efficacy and safety data. The purpose of this review is to evaluate the seven CGRP antagonists and their future place in therapy.

The CGRP Pathway in Migraine as a Viable Target for Therapies

The neuropeptide calcitonin gene-related peptide is well established as a key player in the pathogenesis of migraine. Clinical studies show calcitonin gene-related peptide levels correlate with migraine attacks, and decreases in this neuropeptide can indicate antimigraine therapy effectiveness. Research has revealed a wide distribution of expression sites for calcitonin gene-related peptide in the central and peripheral nervous system. Of these, the calcitonin gene-related peptide receptor, which binds calcitonin gene-related peptide with high affinity, has attracted growing interest as a viable target for antimigraine therapies. An incentive to pursue such research is the continuing unmet medical need of patients. Triptans have offered some clinical benefit, but many patients do not respond and these drugs have important safety considerations. Initial calcitonin gene-related peptide-focused research led to development of the "gepant" small-molecule calcitonin gene-related peptide receptor blockers. Positive efficacy reports concerning the gepants have been tempered by safety findings which led to the discontinuation of some of these agents. Currently, there is considerable excitement regarding monoclonal antibodies against calcitonin gene-related peptide (eptinezumab, galcanezumab, fremanezumab) and the calcitonin gene-related peptide receptor (erenumab). To date, these monoclonal antibodies have shown promising efficacy in clinical trials, with no major safety concerns. If ongoing long-term studies show that their efficacy can be maintained, this may herald a new era for effective antimigraine therapies.

Network Meta-Analysis of Calcitonin Gene-Related Peptide Receptor Antagonists for the Acute Treatment of Migraine

Background: Research has indicated that calcitonin gene-related peptide (CGRP) receptor antagonists can be effective in the acute treatment of migraine. Six major drugs are included within this category: telcagepant, olcegepant, BI 44370, rimegepant (BMS-927711), MK3207, and ubrogepant. However, no previous studies have performed network meta-analyses to directly compare the effects of these drugs. In the present study, we assessed the therapeutic qualities of these six different drugs to inform further clinical research. Methods: We searched PubMed, Embase, Ovid MEDLINE, Web of Science, and the Cochrane Central Register for Controlled Trials for relevant randomized controlled trials (RCTs) published through to October 2018. Two reviewers performed a network meta-analysis of efficacy and toxicity on the basis of odds ratios (ORs). Results: Ten randomized controlled trials involving 8,174 patients were included in our analysis. Olcegepant (OR: 4.09; CI: 1.81, 9.25), ubrogepant (OR: 2.11; CI: 1.10, 4.05), and BI 44370 (OR: 3.36; CI: 2.24, 5.04) were more effective in ensuring pain relief 2 h after treatment than was placebo treatment. BI 44370 was associated with an increased risk of adverse events when compared with placebo treatment (OR: 1.57; CI: 1.32, 1.88). Surface under the cumulative ranking curve analysis revealed that olcegepant was most effective and ubrogepant was associated with the lowest risk of adverse events among the six treatment options. Conclusion: Olcegepant was more effective, and ubrogepant had lower toxicity than the remaining treatments. CGRP antagonists are promising for the acute treatment of migraine, especially among patients who are unable to take triptans.

Synthesis of a CGRP Receptor Antagonist via an Asymmetric Synthesis of 3-Fluoro-4-aminopiperidine

A practical and efficient enantioselective synthesis of the calcitonin gene-related peptide receptor antagonist 1 has been developed. The key structural component of the active pharmaceutical ingredient is a syn-1,2-amino-fluoropiperidine 4. Two approaches were developed to synthesize this important pharmacophore. Initially, Ru-catalyzed asymmetric hydrogenation of fluoride-substituted enamide 8 enabled the synthesis of sufficient quantities of compound 1 to support early preclinical studies. Subsequently, a novel, cost-effective route to this intermediate was developed utilizing a dynamic kinetic asymmetric transamination of ketone 9. This synthesis also features a robust Ullmann coupling to install a bis-aryl ether using a soluble Cu(I) catalyst. Finally, an enzymatic desymmetrization of meso-diester 7 was exploited for the construction of the γ-lactam moiety in 1.

The need for new acutely acting antimigraine drugs: moving safely outside acute medication overuse

Background

The treatment of migraine is impeded by several difficulties, among which insufficient headache relief, side effects, and risk for developing medication overuse headache (MOH). Thus, new acutely acting antimigraine drugs are currently being developed, among which the small molecule CGRP receptor antagonists, gepants, and the 5-HT_1F receptor agonist lasmiditan. Whether treatment with these drugs carries the same risk for developing MOH is currently unknown.

Main body

Pathophysiological studies on MOH in animal models have suggested that decreased 5-hydroxytryptamine (5-HT, serotonin) levels, increased calcitonin-gene related peptide (CGRP) expression and changes in 5-HT receptor expression (lower 5-HT_1B/D and higher 5-HT_2A expression) may be involved in MOH. The decreased 5-HT may increase cortical spreading depression frequency and induce central sensitization in the cerebral cortex and caudal nucleus of the trigeminal tract. Additionally, low concentrations of 5-HT, a feature often observed in MOH patients, could increase CGRP expression. This provides a possible link between the pathways of 5-HT and CGRP, targets of lasmiditan and gepants, respectively. Since lasmiditan is a 5-HT_1F receptor agonist and gepants are CGRP receptor antagonists, they could have different risks for developing MOH because of the different (over) compensation mechanisms following prolonged agonist versus antagonist treatment.

Conclusion

The acute treatment of migraine will certainly improve with the advent of two novel classes of drugs, i.e., the 5-HT_1F receptor agonists (lasmiditan) and the small molecule CGRP receptor antagonists (gepants). Data on the effects of 5-HT_1F receptor agonism in relation to MOH, as well as the effects of chronic CGRP receptor blockade, are awaited with interest.

CGRP and migraine from a cardiovascular point of view: what do we expect from blocking CGRP?

Calcitonin gene-related peptide (CGRP) is a neuropeptide with a pivotal role in the pathophysiology of migraine. Blockade of CGRP is a new therapeutic target for patients with migraine. CGRP and its receptors are distributed not only in the central and peripheral nervous system but also in the cardiovascular system, both in blood vessels and in the heart. We reviewed the current evidence on the role of CGRP in the cardiovascular system in order to understand the possible short- and long-term effect of CGRP blockade with monoclonal antibodies in migraineurs.

In physiological conditions, CGRP has important vasodilating effects and is thought to protect organs from ischemia. Despite the aforementioned cardiovascular implication, preventive treatment with CGRP antibodies has shown no relevant cardiovascular side effects. Results from long-term trials and from real life are now needed.

Extracranial Trigger Site Surgery for Migraine: A Systematic Review With Meta-Analysis on Elimination of Headache Symptoms

Introduction: The headache phase of migraine could in selected cases potentially be treated by surgical decompression of one or more “trigger sites,” located at frontal, temporal, nasal, and occipital sites. This systematic review with subsequent meta-analysis aims at critically evaluating the currently available evidence for the surgical treatment of migraine headache and to determine the effect size of this treatment in a specific patient population.

Methods: This study was conducted following the PRISMA guidelines. An online database search was performed. Inclusion was based on studies published between 2000 and March 2018, containing a diagnosis of migraine in compliance with the classification of the International Headache Society. The treatment must consist of one or more surgical procedures involving the extracranial nerves and/or arteries with outcome data available at minimum 6 months.

Results: Eight hundred and forty-seven records were identified after duplicates were removed, 44 full text articles were assessed and 14 records were selected for inclusion. A total number of 627 patients were included in the analysis. A proportion of 0.38 of patients (random effects model, 95% CI [0.30–0.46]) experienced elimination of migraine headaches at 6–12 months follow-up. Using data from three randomized controlled trials, the calculated odds ratio for 90–100% elimination of migraine headaches is 21.46 (random effects model, 95% CI [5.64–81.58]) for patients receiving migraine surgery compared to sham or no surgery.

Conclusions: Migraine surgery leads to elimination of migraine headaches in 38% of the migraine patients included in this review. However, more elaborate randomized trials are needed with transparent reporting of patient selection, medication use, and surgical procedures and implementing detailed and longer follow-up times.

Peptide-Based Drug-Delivery Systems in Biotechnological Applications: Recent Advances and Perspectives

Peptides of natural and synthetic sources are compounds operating in a wide range of biological interactions. They play a key role in biotechnological applications as both therapeutic and diagnostic tools. They are easily synthesized thanks to solid-phase peptide devices where the amino acid sequence can be exactly selected at molecular levels, by tuning the basic units. Recently, peptides achieved resounding success in drug delivery and in nanomedicine smart applications. These applications are the most significant challenge of recent decades: they can selectively deliver drugs to only pathological tissues whilst saving the other districts of the body. This specific feature allows a reduction in the drug side effects and increases the drug efficacy. In this context, peptide-based aggregates present many advantages, including biocompatibility, high drug loading capacities, chemical diversity, specific targeting, and stimuli responsive drug delivery. A dual behavior is observed: on the one hand they can fulfill a structural and bioactive role. In this review, we focus on the design and the characterization of drug delivery systems using peptide-based carriers; moreover, we will also highlight the peptide ability to self-assemble and to actively address nanosystems toward specific targets.

Is selective 5-HT1F receptor agonism an entity apart from that of the triptans in antimigraine therapy?

Migraine is a neurovascular disorder that involves activation of the trigeminovascular system and cranial vasodilation mediated by release of calcitonin gene-related peptide (CGRP). The gold standard for acute migraine treatment are the triptans, 5-HT1B/1D/(1F) receptor agonists. Their actions are thought to be mediated through activation of: (i) 5-HT1B receptors in cranial blood vessels with subsequent cranial vasoconstriction; (ii) prejunctional 5-HT1D receptors on trigeminal fibers that inhibit trigeminal CGRP release; and (iii) 5-HT1B/1D/1F receptors in central nervous system involved in (anti)nociceptive modulation. Unfortunately, coronary arteries also express 5-HT1B receptors whose activation would produce coronary vasoconstriction; hence, triptans are contraindicated in patients with cardiovascular disease. In addition, since migraineurs have an increased cardiovascular risk, it is important to develop antimigraine drugs devoid of vascular (side) effects. Ditans, here defined as selective 5-HT1F receptor agonists, were developed on the basis that most of the triptans activate trigeminal 5-HT1F receptors, which may explain part of the triptans' antimigraine action. Amongst the ditans, lasmiditan: (i) fails to constrict human coronary arteries; and (ii) is effective for the acute treatment of migraine in preliminary Phase III clinical trials. Admittedly, the exact site of action is still unknown, but lasmiditan possess a high lipophilicity, which suggests a direct action on the central descending antinociceptive pathways. Furthermore, since 5-HT1F receptors are located on trigeminal fibers, they could modulate CGRP release. This review will be particularly focussed on the similarities and differences between the triptans and the ditans, their proposed sites of action, side effects and their cardiovascular risk profile.

CGRP – a target for acute therapy in migraine: Clinical data

Background

A better understanding of the mechanisms underlying the migraine attack has reinforced the concept that migraine is a complex brain disease, and has paved the way for the development of new migraine specific acute treatments. In recent years, targeting the calcitonin gene-related peptide and its receptors has been one of the most promising pharmacological strategies for both acute and preventive treatment of migraine.

Findings

Randomized double-blind placebo-controlled trials have demonstrated the superiority of small molecule calcitonin gene-related peptide receptor antagonists (gepants) over placebo in treating acute migraine attacks measured as the two-hour pain free endpoint. Gepants also improved migraine associated symptoms, such as nausea, photophobia and phonophobia. Two of the class have had their development stopped because of hepatotoxicity, which is emerging as being due to metabolites. Gepants have a good tolerability and can be safely used in patients with stable cardiovascular disease.

Conclusion

Exciting results have been obtained targeting the calcitonin gene-related peptide pathway to abort acute migraine attacks, thus reinforcing the relevance of mechanism-based treatments specific for migraine.

Side effects associated with current and prospective antimigraine pharmacotherapies

INTRODUCTION

Migraine is a neurovascular disorder. Current acute specific antimigraine pharmacotherapies target trigeminovascular 5-HT1B/1D, 5-HT1F and CGRP receptors but, unfortunately, they induce some cardiovascular and central side effects that lead to poor treatment adherence/compliance. Therefore, new antimigraine drugs are being explored. Areas covered: This review considers the adverse (or potential) side effects produced by current and prospective antimigraine drugs, including medication overuse headache (MOH) produced by ergots and triptans, the side effects observed in clinical trials for the new gepants and CGRP antibodies, and a section discussing the potential effects resulting from disruption of the cardiovascular CGRPergic neurotransmission. Expert opinion: The last decades have witnessed remarkable developments in antimigraine therapy, which includes acute (e.g. triptans) and prophylactic (e.g. β-adrenoceptor blockers) antimigraine drugs. Indeed, the triptans represent a considerable advance, but their side effects (including nausea, dizziness and coronary vasoconstriction) preclude some patients from using triptans. This has led to the development of the ditans (5-HT1F receptor agonists), the gepants (CGRP receptor antagonists) and the monoclonal antibodies against CGRP or its receptor. The latter drugs represent a new hope in the antimigraine armamentarium, but as CGRP plays a role in cardiovascular homeostasis, the potential for adverse cardiovascular side effects remains latent.

The role of α1- and α2-adrenoceptor subtypes in the vasopressor responses induced by dihydroergotamine in ritanserin-pretreated pithed rats

Background

Dihydroergotamine (DHE) is an acute antimigraine agent that displays affinity for dopamine D₂-like receptors, serotonin 5-HT_1/2 receptors and α₁/α₂-adrenoceptors. Since activation of vascular α₁/α₂-adrenoceptors results in systemic vasopressor responses, the purpose of this study was to investigate the specific role of α₁- and α₂-adrenoceptors mediating DHE-induced vasopressor responses using several antagonists for these receptors.

Methods

For this purpose, 135 male Wistar rats were pithed and divided into 35 control and 100 pretreated i.v. with ritanserin (100 μg/kg; to exclude the 5-HT₂ receptor-mediated systemic vasoconstriction). Then, the vasopressor responses to i.v. DHE (1–3100 μg/kg, given cumulatively) were determined after i.v. administration of some α₁/α₂-adrenoceptor antagonists.

Results

In control animals (without ritanserin pretreatment), the vasopressor responses to DHE were: (i) unaffected after prazosin (α₁; 30 μg/kg); (ii) slightly, but significantly, blocked after rauwolscine (α₂; 300 μg/kg); and (iii) markedly blocked after prazosin (30 μg/kg) plus rauwolscine (300 μg/kg). In contrast, after pretreatment with ritanserin, the vasopressor responses to DHE were: (i) attenuated after prazosin (α₁; 10 and 30 μg/kg) or rauwolscine (α₂; 100 and 300 μg/kg); (ii) markedly blocked after prazosin (30 μg/kg) plus rauwolscine (300 μg/kg); (iii) attenuated after 5-methylurapidil (α_1A; 30–100 μg/kg), L-765,314 (α_1B; 100 μg/kg), BMY 7378 (α_1D; 30–100 μg/kg), BRL44408 (α_2A; 100–300 μg/kg), imiloxan (α_2B; 1000–3000 μg/kg) or JP-1302 (α_2C; 1000 μg/kg); and (iv) unaffected after the corresponding vehicles (1 ml/kg).

Conclusion

These results suggest that the DHE-induced vasopressor responses in ritanserin-pretreated pithed rats are mediated by α₁- (probably α_1A, α_1B and α_1D) and α₂- (probably α_2A, α_2B and α_2C) adrenoceptors. These findings could shed light on the pharmacological profile of the vascular side effects (i.e. systemic vasoconstriction) produced by DHE and may lead to the development of more selective antimigraine drugs devoid vascular side effects.

Triptans and CGRP blockade - impact on the cranial vasculature

The trigeminovascular system plays a key role in the pathophysiology of migraine. The activation of the trigeminovascular system causes release of various neurotransmitters and neuropeptides, including serotonin and calcitonin gene-related peptide (CGRP), which modulate pain transmission and vascular tone. Thirty years after discovery of agonists for serotonin 5-HT1B and 5-HT1D receptors (triptans) and less than fifteen after the proof of concept of the gepant class of CGRP receptor antagonists, we are still a long way from understanding their precise site and mode of action in migraine. The effect on cranial vasculature is relevant, because all specific anti-migraine drugs and migraine pharmacological triggers may act in perivascular space. This review reports the effects of triptans and CGRP blocking molecules on cranial vasculature in humans, focusing on their specific relevance to migraine treatment.

A human trigeminovascular biomarker for antimigraine drugs: A randomised, double-blind, placebo-controlled, crossover trial with sumatriptan

Objective

The objective of this report is to establish a biomarker for the CGRP-interfering effect of antimigraine drugs.

Methods

We quantified the effect of sumatriptan on the trigeminal nerve-mediated rise in forehead dermal blood flow (DBF), induced by capsaicin application (0.6 mg/ml) and electrical stimulation (0.2–1.0 mA), in a randomised, double-blind, placebo-controlled, crossover study in healthy male ( n = 11, age ± SD: 29 ± 8 years) and female ( n = 11, 32 ± 7 years) individuals.

Results

DBF responses to capsaicin were attenuated by sumatriptan (ΔDBF, mean ± SEM: 82 ± 18 AU, p = 0.0002), but not by placebo (ΔDBF: 21 ± 12 AU, p = 0.1026).

Conclusion

We demonstrated that sumatriptan inhibits increases in DBF, induced by the release of, most likely, CGRP. Thus, our model may be used as a biomarker to establish the trigeminovascular effects of (potential) antimigraine drugs, such as CGRP receptor antagonists or antibodies directed against CGRP or its receptor.

Intranasal Eutectic Powder of Zolmitriptan with Enhanced Bioavailability in the Rat Brain

Intranasal administration can potentially deliver drugs to the brain because of the proximity of the delivery site to the olfactory lobe. We prepared triturates of micronized or crystalline zolmitriptan with a GRAS substance, nicotinamide, to form a eutectic. We characterized the formulation using differential scanning calorimetry, powder X-ray diffraction, and FTIR spectroscopy to confirm its eutectic nature and generated a phase diagram. The eutectic formulation was aerosolized using an in-house insufflator into the nares of rats. Groups of rats received zolmitriptan intravenously or intranasally, or intranasal eutectic formulation. Zolmitriptan was estimated in the olfactory lobe, cerebral cortex, cerebellum, and blood plasma at different time-points by LC-MS. Pharmacokinetics in these tissues indicated the superiority of the intranasal eutectic formulation for brain targeting when compared with results of IV solution and intranasal pure zolmitriptan powder. Enhancement of nose-to-brain transport is likely to have resulted from more rapid dissolution of the eutectic as compared to pure drug.

Characterizing the PK/PD relationship for inhibition of capsaicin-induced dermal vasodilatation by MK-3207, an oral calcitonin gene related peptide receptor antagonist

AIMS

Calcitonin gene related peptide (CGRP) receptor antagonists are effective acute migraine treatments. A capsaicin-induced dermal vasodilatation (CIDV) model has been developed to provide target-engagement information in healthy volunteers. In the model, CGRP release is provoked after dermal capsaicin application, by activating transient receptor potential vanilloid-type-1 (TRPV1) receptors at peripheral sensory nerves. Laser Doppler imaging is used to quantify CIDV and subsequent inhibition by CGRP receptor antagonists. We sought to evaluate a CGRP receptor antagonist, MK-3207, in the biomarker model and to assess the predictability of the CIDV response to migraine clinical efficacy.

METHODS

An integrated population pharmacokinetic/pharmacodynamic (PK/PD) model was developed to describe the exposure-response relationship for CIDV inhibition by CGRP and TRPV1 receptor antagonists. MK-3207 dose-response predictions were made based on estimated potency from the PK/PD model and mean plasma concentrations observed at the doses investigated.

RESULTS

The results suggested that a 20 mg dose of MK-3207 (EC50 of 1.59 nm) would be required to attain the peripheral CIDV response at a target level that was shown previously to correlate with 2 h clinical efficacy based on phase 3 telcagepant clinical data, and that a plateau of the dose-response would be reached around 40-100 mg. These predictions provided a quantitative rationale for dose selection in a phase 2 clinical trial of MK-3207 and helped with interpretation of the efficacy results from the trial.

CONCLUSIONS

The integrated CIDV PK/PD model provides a useful platform for characterization of PK/PD relationships and predictions of dose-response relationships to aid in future development of CGRP and TRPV1 receptor antagonists.

Prophylactic effects of asiaticoside-based standardized extract of Centella asiatica (L.) Urban leaves on experimental migraine: Involvement of 5HT1A/1B receptors

The present study aimed at evaluation of prophylactic efficacy and possible mechanisms of asiaticoside (AS) based standardized extract of Centella asiatica (L.) Urban leaves (INDCA) in animal models of migraine. The effects of oral and intranasal (i.n.) pretreatment of INDCA (acute and 7-days subacute) were evaluated against nitroglycerine (NTG, 10 mg·kg(-1), i.p.) and bradykinin (BK, 10 μg, intra-arterial) induced hyperalgesia in rats. Tail flick latencies (from 0 to 240 min) post-NTG treatment and the number of vocalizations post-BK treatment were recorded as a measure of hyperalgesia. Separate groups of rats for negative (Normal) and positive (sumatriptan, 42 mg·kg(-1), s.c.) controls were included. The interaction of INDCA with selective 5-HT1A, 5-HT1B, and 5-HT1D receptor antagonists (NAN-190, Isamoltane hemifumarate, and BRL-15572 respectively) against NTG-induced hyperalgesia was also evaluated. Acute and sub-acute pre-treatment of INDCA [10 and 30 mg·kg(-1) (oral) and 100 μg/rat (i.n.) showed significant anti-nociception activity, and reversal of the NTG-induced hyperalgesia and brain 5-HT concentration decline. Oral pre-treatment with INDCA (30 mg·kg(-1), 7 d) showed significant reduction in the number of vocalization. The anti-nociceptive effects of INDCA were blocked by 5-HT1A and 5-HT1B but not 5-HT1D receptor antagonists. In conclusion, INDCA demonstrated promising anti-nociceptive effects in animal models of migraine, probably through 5-HT1A/1B medicated action.

Stimulatory effect of pituitary adenylate cyclase-activating polypeptide 6-38, M65 and vasoactive intestinal polypeptide 6-28 on trigeminal sensory neurons

Pituitary adenylate cyclase-activating polypeptide (PACAP) acts on G protein-coupled receptors: the specific PAC1 and VPAC1/VPAC2 receptors. PACAP6-38 was described as a potent PAC1/VPAC2 antagonist in several models, but recent studies reported its agonistic behaviors proposing novel receptorial mechanisms. Since PACAP in migraine is an important research tool, we investigated the effect of PACAP and its peptide fragments on trigeminal primary sensory neurons. Effect of the peptides was studied with ratiometric Ca-imaging technique using the fluorescent indicator fura-2 AM on primary cultures of rat and mouse trigeminal ganglia (TRGs) neurons. Specificity testing was performed on PAC1, VPAC1 and VPAC2 receptor-expressing cell lines with both fluorescent and radioactive Ca-uptake methods. Slowly increasing intracellular free calcium concentration [Ca(2+)]i was detected after PACAP1-38, PACAP1-27, vasoactive intestinal polypeptide (VIP) and the selective PAC1 receptor agonist maxadilan administration on TRG neurons, but interestingly, PACAP6-38, VIP6-28 and the PAC1 receptor antagonist M65 also caused similar activation. The VPAC2 receptor agonist BAY 55-9837 induced similar activation, while the VPAC1 receptor agonist Ala(11,22,28)VIP had no significant effect on [Ca(2+)]i. It was proven that the Ca(2+)-influx originated from intracellular stores using radioactive calcium-45 uptake experiment and Ca-free solution. On the specific receptor-expressing cell lines the antagonists inhibited the stimulating actions of the respective agonists, but had no effects by themselves. PACAP6-38, M65 and VIP6-28, which were described as antagonists in numerous studies in several model systems, act as agonists on TRG primary sensory neurons. Currently unknown receptors or splice variants linked to distinct signal transduction pathways might explain these differences.

Development of anti-migraine therapeutics using the capsaicin-induced dermal blood flow model

The efficacy of calcitonin gene-related peptide (receptor) (CGRP-(R)) blocking therapeutics in the treatment of acute migraine headache provided proof-of-concept for the involvement of CGRP in the pathophysiology of this disorder. One of the major hurdles for the development of any class of drugs, including CGRP blocking therapeutics, is the early clinical development process during which toxic and inefficacious compounds need to be eliminated as early as possible in order to focus on the most promising molecules. At this stage, human models providing proof of target engagement, combined with safety and tolerability studies, are extremely valuable in focusing on those therapeutics that have the highest engagement from the lowest exposure. They guide the go/no-go decision making, establish confidence in the candidate molecule by de-risking toxicity and safety issues and thereby speed up the early clinical development. In this review the focus is on the so called 'capsaicin model' as a typical example of a target engagement biomarker used as a human model for the development of CGRP blocking therapeutics. By applying capsaicin onto the skin, TRPV1 channels are activated and a CGRP-mediated increase in dermal blood flow can be quantified with laser Doppler perfusion imaging. Effective CGRP blocking therapeutics in turn, display blockade of this response. The translation of this biomarker model from animals to humans is discussed as well as the limitations of the assay in predicting the efficacy of anti-migraine drugs.

PET tracers for serotonin receptors and their applications

Serotonin receptors (5-HTRs) are implicated in the pathophysiology of a variety of neuropsychiatric and neurodegenerative disorders and are also targets for drug therapy. In the CNS, most of these receptors are expressed in high abundance in specific brain regions reflecting their role in brain functions. Quantifying binding to 5-HTRs in vivo may permit assessment of physiologic and pathologic conditions, and monitoring disease progression, evaluating treatment response, and for investigating new treatment modalities. Positron emission tomography (PET) molecular imaging has the sensitivity to quantify binding of 5-HTRs in CNS disorders and to measure drug occupancy as part of a process of new drug development. Although research on PET imaging of 5-HTRs have been performed more than two decades, the successful radiotracers so far developed for human studies are limited to 5-HT₁AR, 5-HT₁BR, 5-HT₂AR, 5-HT₄R and 5-HT₆R. Herein we review the development and application of radioligands for PET imaging of 5-HTRs in living brain.

Glutamate receptor antagonists in the management of migraine

Migraine is a neurovascular disorder that is associated with severe headache and neurologic symptoms. The pathogenesis of migraine is believed to involve trigeminovascular system activation with the primary dysfunction located in brainstem. Glutamate, the major excitatory neurotransmitter in the central nervous system, and its receptors have since long been suggested in migraine pathophysiology. Different preclinical studies have confirmed their potential role in migraine. Moreover, several glutamate receptor modulators have been studied in clinical studies, some with promising results. In this review, we will give an overview of what is known about the role of glutamate in the pathogenesis of migraine, which will be followed by an overview of available efficacy, safety and tolerability data for glutamate receptor inhibitors in clinical development for the treatment of migraine.

Headache, cerebral aneurysms, and the use of triptans and ergot derivatives

BACKGROUND

Uncertainty exists regarding the correlation between unruptured cerebral aneurysms and their role in headache etiology. It is also unclear whether surgical endovascular treatment may improve or worsen the headache, and if there are predictable factors for headache outcome such as pre-existing headache features, aneurysm characteristics, or other medical history. There is debate regarding safe treatment of migraine in patients with aneurysms, both before and after endovascular treatments. Particularly, there is hesitancy to use the triptans and ergot derivatives such as dihydroergotamine because of their vasoconstrictive effects and concern for adverse events related to the aneurysm such as aneurysmal instability and rupture.

OBJECTIVE

To review the literature regarding the anatomy, pathophysiology, and association between headache, untreated vs surgically treated aneurysms, and the use of triptans and ergot derivatives for migraine treatment in this setting.

CONCLUSION

Associations between some headaches and aneurysms may exist. Some chronic headaches may respond to surgical aneurysm repair while others may worsen. These associations are undefined by current literature because of variable results, study methods, and limited data. Prospective studies are needed which incorporate pre- and post-procedure headache character and diagnosis, aneurysm characteristics, type of aneurysm repair, associated risk factors for worsening post-procedure headache, and ultimately combining all of these data to better predict headache outcome following surgical aneurysm treatment. Lastly, the caution and avoidance of triptan and ergot derivative use for migraine in the setting of aneurysm is not supported by the current evidence, and much of this concern may be excessive and unwarranted, although more evidence confirming safety is needed.

Receptor binding peptides for target-selective delivery of nanoparticles encapsulated drugs

Active targeting by means of drug encapsulated nanoparticles decorated with targeting bioactive moieties represents the next frontier in drug delivery; it reduces drug side effects and increases the therapeutic index. Peptides, based on their chemical and biological properties, could have a prevalent role to direct drug encapsulated nanoparticles, such as liposomes, micelles, or hard nanoparticles, toward the tumor tissues. A considerable number of molecular targets for peptides are either exclusively expressed or overexpressed on both cancer vasculature and cancer cells. They can be classified into three wide categories: integrins; growth factor receptors (GFRs); and G-protein coupled receptors (GPCRs). Therapeutic agents based on nanovectors decorated with peptides targeting membrane receptors belonging to the GPCR family overexpressed by cancer cells are reviewed in this article. The most studied targeting membrane receptors are considered: somatostatin receptors; cholecystokinin receptors; receptors associated with the Bombesin like peptides family; luteinizing hormone-releasing hormone receptors; and neurotensin receptors. Nanovectors of different sizes and shapes (micelles, liposomes, or hard nanoparticles) loaded with doxorubicin or other cytotoxic drugs and externally functionalized with natural or synthetic peptides are able to target the overexpressed receptors and are described based on their formulation and in vitro and in vivo behaviors.

Effect of telcagepant on spontaneous ischemia in cardiovascular patients in a randomized study

OBJECTIVE

The primary purpose of the study was to explore the safety and tolerability of telcagepant in patients with stable coronary artery disease.

BACKGROUND

Triptans are effective acute anti-migraine drugs whose vasoconstrictive effects limit their use in patients at risk for adverse cardiovascular events. Telcagepant, a calcitonin gene-related peptide receptor antagonist, is being developed for the acute treatment of migraine. Antagonism of calcitonin gene-related peptide, which does not appear to cause vasoconstriction, may allow for treatment of migraine in patients with coronary artery disease.

METHODS

In this randomized, double-blind, placebo-controlled, crossover study, patients with documented stable coronary artery disease were assigned to 1 of 2 treatment sequences: telcagepant then placebo, or placebo then telcagepant. In each treatment period, patients received 2 doses of telcagepant 300-mg or placebo 2 hours apart. They remained in the research center for 24 hours after receiving the first dose of each period, during which time continuous 12-lead ambulatory electrocardiographic (Holter) monitoring was performed.

RESULTS

Twenty-eight patients were enrolled; all patients completed the study and were included in all analyses. Telcagepant was generally well tolerated. No laboratory or serious adverse experiences were reported, and no patient discontinued due to an adverse experience. There were no consistent treatment-related changes in laboratory, vital signs or electrocardiogram safety parameters. Three patients (2 after receiving placebo and 1 after receiving telcagepant) experienced ST segment depression during the study; none of these patients reported chest pain.

CONCLUSIONS

Two doses of 300-mg telcagepant, administered 2 hours apart, did not appear to exacerbate spontaneous ischemia and were generally well tolerated in a small cohort of patients with stable coronary artery disease. Results of this study support further evaluation of telcagepant in patients with stable coronary artery disease.

Bombesin peptide antagonist for target-selective delivery of liposomal doxorubicin on cancer cells

PURPOSE

This study addresses novel peptide modified liposomal doxorubicin to specifically target tissues overexpressing bombesin (BN) receptors.

METHODS

DOTA-(AEEA)₂-peptides containing the [7-14]bombesin and the new BN-AA1 sequence have been synthesized to compare their binding properties and in serum stabilities. The amphiphilic peptide derivative (MonY-BN-AA1) containing BN-AA1, a hydrophobic moiety, polyethylenglycole (PEG), and diethylenetriaminepentaacetate (DTPA), has been synthesized. Liposomes have been obtained by mixing of MonY-BN-AA1 with 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC).

RESULTS

Both ¹¹¹In labeled peptide derivatives present nanomolar Kd to PC-3 cells. ¹⁷⁷Lu labeled peptide DOTA-(AEEA)₂-BN-AA1 is very stable (half-life 414.1 h), while DOTA-(AEEA)₂-BN, shows a half-life of 15.5 h. In vivo studies on the therapeutic efficacy of DSPC/MonY-BN-AA1/Dox in comparison to DSPC/MonY-BN/Dox, were performed in PC-3 xenograft bearing mice. Both formulations showed similar tumor growth inhibition (TGI) compared to control animals treated with non-targeted DSPC/Dox liposomes or saline solution. For DSPC/MonY-BN-AA1/Dox the maximum effect was observed 19 days after treatment.

CONCLUSIONS

DSPC/MonY-BN-AA1/Dox nanovectors confirm the ability to selectively target and provide therapeutic efficacy in mice. The lack of receptor activation and possible acute biological side effects provided by using the AA1 antagonist bombesin sequence should provide safe working conditions for further development of this class of drug delivery vehicles.

Randomized, controlled study of telcagepant in patients with migraine and coronary artery disease

OBJECTIVE

To evaluate the efficacy of telcagepant in patients with migraine and coronary artery disease.

BACKGROUND

Calcitonin gene-related peptide receptor antagonists, such as telcagepant, may be useful for acute migraine treatment in patients with cardiovascular disease, a population for whom triptans are contraindicated.

METHODS

Randomized, double-blind, two-period (6 weeks per period) crossover study in patients with stable coronary artery disease and migraine. Patients were randomized 1:1 to either: (1) Period 1: telcagepant (280-mg tablet/300-mg capsule), Period 2: acetaminophen (1000-mg); or (2) Period 1: placebo for attack 1 then acetaminophen for subsequent attacks, Period 2: telcagepant. Patients could treat up to 12 migraine attacks per period to assess the tolerability of telcagepant. The primary efficacy analysis evaluated telcagepant vs placebo on 2-hour pain freedom during the first attack of Period 1.

RESULTS

One hundred and sixty-five of the planned 400 patients were enrolled, and 114 took at least one dose of treatment. Telcagepant was not statistically different from placebo for 2-hour pain freedom (25.0% vs 18.9%, odds ratio = 1.62 [95% confidence interval: 0.62, 4.25]). The median number of attacks treated per period was 3. No cardiovascular thrombotic adverse events occurred within 14 days of dosing.

CONCLUSION

The study was underpowered due to enrollment difficulties and did not demonstrate a significant efficacy difference between telcagepant and placebo for the treatment of a migraine attack in patients with stable coronary artery disease. Telcagepant was generally well tolerated for acute intermittent migraine treatment in these patients.

Calcitonin gene-related peptide in migraine: intersection of peripheral inflammation and central modulation

Over the past two decades, a convergence of basic and clinical evidence has established the neuropeptide calcitonin-gene-related peptide (CGRP) as a key player in migraine. Although CGRP is a recognised neuromodulator of nociception, its mechanism of action in migraine remains elusive. In this review, we present evidence that led us to propose that CGRP is well poised to enhance neurotransmission in migraine by both peripheral and central mechanisms. In the periphery, it is thought that local release of CGRP from the nerve endings of meningeal nociceptors following their initial activation by cortical spreading depression is critical for the induction of vasodilation, plasma protein extravasation, neurogenic inflammation and the consequential sensitisation of meningeal nociceptors. Mechanistically, we propose that CGRP release can give rise to a positive-feedback loop involved in localised increased synthesis and release of CGRP from neurons and a CGRP-like peptide called procalcitonin from trigeminal ganglion glia. Within the brain, the wide distribution of CGRP and CGRP receptors provides numerous possible targets for CGRP to act as a neuromodulator.

Pharmacological and expression profile of the prostaglandin I(2) receptor in the rat craniovascular system

Activation of the trigeminal nerve terminals around cerebral and meningeal arteries is thought to be an important patho-mechanism in migraine. Vasodilatation of the cranial arteries may also play a role in increasing nociception. Prostaglandin I(2) (PGI(2)) is capable of inducing a headache in healthy volunteers, a response that is likely to be mediated by the prostaglandin I(2) receptor (IP). This study investigates the functional and molecular characteristics of the IP receptor in the rat craniovascular system. In the closed cranial window model, iloprost, an IP receptor agonist, dilated the rat middle meningeal artery (MMA) (E(max)=170%±16%; pED(50)=6.5±0.2) but not the rat cerebral artery (CA) in vivo. The specific antagonist of the IP receptor, CAY10441, significantly blocked the iloprost-induced response dose-dependently, with the highest dose attenuating iloprost (1μgkg(-1)) induced dilatations by 70% (p<0.05). CAY10441 did not have any effect on the prostaglandin E(2)-induced vasodilatory response, thus suggesting no interaction with EP(2) and EP(4) receptors. IP receptor mRNA transcripts and protein were present in meningeal as well as in cerebral rat vasculature, and localized the IP receptor protein to the smooth vasculature of the cranial arteries (MMA, MCA and basilar artery). Together, these results demonstrate that the IP receptor mediates the dilatory effect of PGI(2) in the cranial vasculature in rats. Antagonism of this receptor might be of therapeutic relevance in acute migraine treatment.