Safety and efficacy of PNU-142633, a selective 5-HT1D agonist, in patients with acute migraine

The 5-HT1F receptor as the target of ditans in migraine - from bench to bedside

Migraine is a leading cause of disability in more than one billion people worldwide, yet it remains universally underappreciated, even by individuals with the condition. Among other shortcomings, current treatments (often repurposed agents) have limited efficacy and potential adverse effects, leading to low treatment adherence. After the introduction of agents that target the calcitonin gene-related peptide pathway, another new drug class, the ditans - a group of selective serotonin 5-HT_1F receptor agonists - has just reached the international market. Here, we review preclinical studies from the late 1990s and more recent clinical research that contributed to the development of the ditans and led to their approval for acute migraine treatment by the US Food and Drug Administration and the European Medicines Agency.

Serotonergic Modulation of Neurovascular Transmission: A Focus on Prejunctional 5-HT Receptors/Mechanisms

5-Hydroxytryptamine (5-HT), or serotonin, plays a crucial role as a neuromodulator and/or neurotransmitter of several nervous system functions. Its actions are complex, and depend on multiple factors, including the type of effector or receptor activated. Briefly, 5-HT can activate: (i) metabotropic (G-protein-coupled) receptors to promote inhibition (5-HT₁, 5-HT₅) or activation (5-HT₄, 5-HT₆, 5-HT₇) of adenylate cyclase, as well as activation (5-HT₂) of phospholipase C; and (ii) ionotropic receptor (5-HT₃), a ligand-gated Na⁺/K⁺ channel. Regarding blood pressure regulation (and beyond the intricacy of central 5-HT effects), this monoamine also exerts direct postjunctional (on vascular smooth muscle and endothelium) or indirect prejunctional (on autonomic and sensory perivascular nerves) effects. At the prejunctional level, 5-HT can facilitate or preclude the release of autonomic (e.g., noradrenaline and acetylcholine) or sensory (e.g., calcitonin gene-related peptide) neurotransmitters facilitating hypertensive or hypotensive effects. Hence, we cannot formulate a specific impact of 5-HT on blood pressure level, since an increase or decrease in neurotransmitter release would be favoured, depending on the type of prejunctional receptor involved. This review summarizes and discusses the current knowledge on the prejunctional mechanisms involved in blood pressure regulation by 5-HT and its impact on some vascular-related diseases.

The role of hippocampal 5-HT1D and 5-HT1F receptors on learning and memory in rats

Serotonin is a neurotransmitter, which is involved in memory via its receptors. The 5-HT_1D and 5-HT_1F receptors mainly exist in the hippocampus, which plays an important role in memory processing. However, few studies have assessed the effect of these serotonin receptors on memory. We evaluated the effect of a 5-HT_1D receptor agonist, PNU142633, 5-HT_1D receptor antagonist, BRL15572 hydrochloride, and 5-HT1F receptor agonist, LY344864, on the recognition and avoidance memory in the hippocampus area. Fifty adult male Wistar rats weighing 200-250 g were divided into the control, sham-operated, PNU, BRL, and LY groups (n=10 per group). Bilateral guide cannulas were implanted into the dentate gyrus area of the hippocampus. The drugs were administered at the dose of 1 μg/μl before the novel object recognition (NOR) and passive avoidance learning (PAL) tests. The results showed that in the NOR test, the administration of PNU and LY had no significant effect on recognition index; however, the recognition index was increased by BRL. In the PAL test, the administration of PNU had no significant effect on recognition index, but the administration of BRL and LY increased the time spent in the dark compartment of the apparatus and decreased the step-through latency into the dark compartment apparatus. It can be concluded that the inhibition of the hippocampal 5-HT_1D receptor improved cognition memory but impaired avoidance memory. Activation of the hippocampal 5-HT_1F receptor had no effect on cognitive memory but impaired avoidance memory.

Global Epidemiology, Clinical Features, Diagnosis and Current Therapeutic Novelties in Migraine Therapy and their Prevention: A Narrative Review

INTRODUCTION

The current article reviews the latest information on epidemiology, clinical features, diagnosis, recent advancements in clinical management, current therapeutic novelties, and the prevention of migraines. In a narrative review, all studies as per developed MeSH terms published until February 2023, excluding those irrelevant, were identified through a PubMed literature search.

METHODS

Overall, migraine affects more than a billion people annually and is one of the most common neurological illnesses. A wide range of comorbidities is associated with migraines, including stress and sleep disturbances. To lower the worldwide burden of migraine, comprehensive efforts are required to develop and enhance migraine treatment, which is supported by informed healthcare policy. Numerous migraine therapies have been successful, but not all patients benefit from them.

RESULTS

CGRP pathway-targeted therapy demonstrates the importance of translating mechanistic understanding into effective treatment. In this review, we discuss clinical features, diagnosis, and recently approved drugs, as well as a number of potential therapeutic targets, including pituitary adenylate cyclase-activating polypeptide (PACAP), adenosine, opioid receptors, potassium channels, transient receptor potential ion channels (TRP), and acid-sensing ion channels (ASIC).

CONCLUSION

In addition to providing more treatment options for improved clinical care, a better understanding of these mechanisms facilitates the discovery of novel therapeutic targets.

Lasmiditan and 5-Hydroxytryptamine in the rat trigeminal system; expression, release and interactions with 5-HT1 receptors

BACKGROUND

5-Hydroxytryptamine (5-HT) receptors 1B, 1D and 1F have key roles in migraine pharmacotherapy. Selective agonists targeting these receptors, such as triptans and ditans, are effective in aborting acute migraine attacks and inhibit the in vivo release of calcitonin gene-related peptide (CGRP) in human and animal models. The study aimed to examine the localization, genetic expression and functional aspects of 5- HT1B/1D/1F receptors in the trigeminal system in order to further understand the molecular sites of action of triptans (5-HT1B/1D) and ditans (5-HT1F).

METHODS

Utilizing immunohistochemistry, the localization of 5-HT and of 5-HT1B/1D/1F receptors was examined in rat trigeminal ganglion (TG) and combined with quantitative polymerase chain reaction to quantify the level of expression for 5-HT1B/1D/1F receptors in the TG. The functional role of these receptors was examined ex vivo with a capsaicin/potassium induced 5-HT and CGRP release.

RESULTS

5-HT immunoreactivity (ir) was observed in a minority of CGRP negative C-fibres, most neuron somas and faintly in A-fibres and Schwann cell neurolemma. 5-HT1B/1D receptors were expressed in the TG, while the 5-HT1F receptor displayed a weak ir. The 5-HT1D receptor co-localized with receptor activity-modifying protein 1 (RAMP1) in Aδ-fibres in the TG, while 5-HT1B-ir was weakly expressed and 5-HT1F-ir was not detected in these fibres. None of the 5-HT1 receptors co-localized with CGRP-ir in C-fibres. 5-HT1D receptor mRNA was the most prominently expressed, followed by the 5-HT1B receptor and lastly the 5-HT1F receptor. The 5-HT1B and 5-HT1D receptor antagonist, GR127935, could reverse the inhibitory effect of Lasmiditan (a selective 5-HT1F receptor agonist) on CGRP release in the soma-rich TG but not in soma-poor TG or dura mater. 5-HT release in the soma-rich TG, and 5-HT content in the baseline samples, negatively correlated with CGRP levels, showing for the first time a physiological role for 5-HT induced inhibition.

CONCLUSION

This study reveals the presence of a subgroup of C-fibres that store 5-HT. The data shows high expression of 5-HT1B/1D receptors and suggests that the 5-HT1F receptor is a relatively unlikely target in the rat TG. Furthermore, Lasmiditan works as a partial agonist on 5-HT1B/1D receptors in clinically relevant dose regiments.

Tegaserod for the Treatment of Irritable Bowel Syndrome

Background: Tegaserod (Zelnorm®) is a 5-hydroxytryptamine (serotonin) type 4 receptor agonist for the treatment of hypomotility disorders of the lower gastrointestinal tract associated with the irritable bowel syndrome with constipation (IBS-C).

Objective: The authors provide the reader with a better understanding on tegaserod mechanism of action, on its pharmacodynamics and pharmacokinetic properties, on safety and tolerability, with a summary of the key published clinical trials conducted in patients with irritable bowel syndrome (IBS). Its effects on colon inflammation have also been described.

Results: Tegaserod was withdrawn in 2007 due to increased risks of cardiovascular adverse effects. The manufacturer denied this, because pre-existing cardiovascular disease or risk factors were attributed to all affected patients. Thus, no causal relationship between tegaserod use and cardiovascular events was clearly shown. A matched case-control study of tegaserod-treated with untreated patients found no association between tegaserod and adverse cardiovascular outcomes. Despite its adverse effects, tegaserod resulted to be effective in treating chronic constipation in adult women aged < 65 years with IBS-C, while the safety and effectiveness of tegaserod in men with IBS-C have not been established.

Conclusion: Tegaserod was resubmitted to the Food and Drug Administration in 2018 for use in a low-risk population. Moreover, tegaserod has also been shown to improve symptoms, enhance gastric accommodation and significantly attenuate visceral pain arising from the colon in functional dyspepsia patients. Treatment with tegaserod seems also to exert a protective effect in inflamed colons, reducing the severity of colitis in animal models.

Acute Treatment of Migraine: What has Changed in Pharmacotherapies?

Background

Migraine is the most prevalent neurological disorder and the leading cause of disability in individuals under 50 years of age. Two types of migraine therapies have been defined: acute therapy (abortive or symptomatic treatment), the purpose of which is to interrupt migraine attacks, and preventive treatment (prophylactic treatment), the purpose of which is to reduce the frequency and severity of migraine attacks.

Objective

This paper reviews research advances in new agents for acute therapy of migraine.

Material and Methods

This review provides an overview of emerging new drugs for acute treatment of migraine based on clinical evidence and summarizes the milestones of different stages of clinical development.

Results

Two new formulations of sumatriptan, DFN-11 (3 mg doses of subcutaneous sumatriptan) and DFN-02 (a nasal spray of sumatriptan 10 mg and a permeation-enhancing excipient), have been developed, and both of them showed a fast-onset action with efficacy for acute treatment of migraine with fewer adverse events. New drug discovery programs shifted the focus to the development of ditans, a group of antimigraine drugs targeting 5-HT_1F receptors. Only lasmiditan has progressed to phase III clinical trials and was finally approved by the Food and Drug Administration (FDA) for acute migraine treatment. The other target for acute therapy is CGRP receptor antagonists, namely, gepants. Ubrogepant and rimegepant demonstrated statistically significant efficacy, and both were recently approved by the FDA. These 5-HT_1F receptor agonists and CGRP receptor antagonists did not cause vasoconstriction, offering advantages over the current mainstay of specific acute migraine treatment.

Conclusions

Overall, these new agents have expanded the available acute therapies for migraine treatment and will likely change the strategy with which we treat patients with migraine in the future.

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.

Pharmacological treatment of migraine: CGRP and 5-HT beyond the triptans

Migraine is a highly disabling neurovascular disorder characterized by a severe headache (associated with nausea, photophobia and/or phonophobia), and trigeminovascular system activation involving the release of calcitonin-gene related peptide (CGRP). Novel anti-migraine drugs target CGRP signaling through either stimulation of 5-HT1F receptors on trigeminovascular nerves (resulting in inhibition of CGRP release) or direct blockade of CGRP or its receptor. Lasmiditan is a highly selective 5-HT1F receptor agonist and, unlike the triptans, is devoid of vasoconstrictive properties, allowing its use in patients with cardiovascular risk. Since lasmiditan can actively penetrate the blood-brain barrier, central therapeutic as well as side effects mediated by 5-HT1F receptor activation should be further investigated. Other novel anti-migraine drugs target CGRP signaling directly. This neuropeptide can be targeted by the monoclonal antibodies eptinezumab, fremanezumab and galcanezumab, or by CGRP-neutralizing L-aptamers called Spiegelmers. The CGRP receptor can be targeted by the monoclonal antibody erenumab, or by small-molecule antagonists called gepants. Currently, rimegepant and ubrogepant have been developed for acute migraine treatment, while atogepant is studied for migraine prophylaxis. Of these drugs targeting CGRP signaling directly, eptinezumab, erenumab, fremanezumab, galcanezumab, rimegepant and ubrogepant have been approved for clinical use, while atogepant is in the last stage before approval. Although all of these drugs seem highly promising for migraine treatment, their safety should be investigated in the long-term. Moreover, the exact mechanism(s) of action of these drugs need to be elucidated further, to increase both safety and efficacy and to increase the number of responders to the different treatments, so that all migraine patients can satisfactorily be treated.

Targeting the 5-HT1B/1D and 5-HT1F receptors for acute migraine treatment

Migraine is a common and highly disabling headache disorder associated with a substantial socioeconomic burden. Migraine treatments can be categorized as preventive treatment, aimed at reducing the frequency and severity of migraine attacks, and acute therapy, intended to abort attacks. Traditionally, acute treatment can be classified as specific (ergot derivatives and triptans) or nonspecific (analgesics and nonsteroidal anti-inflammatory drugs). Triptans, a class of 5-HT1B/1D receptor agonists with some affinity for the 5-HT1F receptor subtype, have been proven to be efficacious for acute treatment of moderate to severe migraine and have been deemed the gold standard. The availability of triptans in non-oral formulations, such as subcutaneous (SC) and intranasal forms, can be beneficial for patients who suffer from prominent nausea or vomiting, have a suboptimal response to oral agents, and/or seek a more rapid onset of treatment effects. However, triptans are contraindicated in patients with preexisting cardiovascular and/or cerebrovascular diseases due to their 5-HT1B-mediated vasoconstrictive action. For this reason, studies have focused on the development of ditans, a group of antimigraine drugs targeting 5-HT1D and 5-HT1F receptors. Unfortunately, 5-HT1D receptor agonists have been shown to be ineffective in the acute treatment of migraine. Several ditans targeting the 5-HT1F receptor have been developed and have shown no vasoconstrictive effect in preclinical studies, but only two of them, lasmiditan and LY334370, have been tested in clinical trials for migraine, and only lasmiditan has reached to Phase III clinical trials. These Phase III trials have demonstrated the efficacy and safety of lasmiditan, a selective 5-HT1F receptor agonist, in acute migraine treatment. Lasmiditan might offer an alternative migraine therapy without cardiovascular risks. This review will summarize the development of agents targeting the 5-HT1B/1D and 5-HT1F receptors and the clinical evidence supporting the use of these agents for acute migraine treatment.

Therapeutic novelties in migraine: new drugs, new hope?

Background

In the past decade, migraine research has identified novel drug targets. In this review, we discuss recent data on emerging anti-migraine therapies.

Main body

The development of ditans, gepants and anti-calcitonin gene-related peptide monoclonal antibodies for the treatment of migraine is one of the greatest advances in the migraine field. Lasmiditan, rimegepant and ubrogepant will extend our therapeutic armamentarium for managing acute migraine attacks when triptans are not effective or contraindicated due to cardiovascular disorders. The monoclonal antibodies are migraine specific prophylactic drugs with high responder rates and favorable adverse event profiles. Furthermore, they offer convenient treatment regimens of 4- or 12-week intervals.

Conclusion

Collectively, novel migraine therapies represent a major progress in migraine treatment and will undoubtedly transform headache medicine.

Shared Fate of Meningeal Mast Cells and Sensory Neurons in Migraine

Migraine is a primary headache disorder which has complex neurogenic pathophysiological mechanisms still requiring full elucidation. The sensory nerves and meningeal mast cell couplings in the migraine target tissue are very effective interfaces between the central nervous system and the immune system. These couplings fall into three categories: intimacy, cross-talk and a shared fate. Acting as the immediate call-center of the neuroimmune system, mast cells play fundamental roles in migraine pathophysiology. Considerable evidence shows that neuroinflammation in the meninges is the key element resulting in the sensitization of trigeminal nociceptors. The successive events such as neuropeptide release, vasodilation, plasma protein extravasation, and mast cell degranulation that form the basic characteristics of the inflammation are believed to occur in this persistent pain state. In this regard, mast cells and sensory neurons represent both the target and source of the neuropeptides that play autocrine, paracrine, and neuro-endocrine roles during this inflammatory process. This review intends to contribute to a better understanding of the meningeal mast cell and sensory neuron bi-directional interactions from molecular, cellular, functional points of view. Considering the fact that mast cells play a sine qua non role in expanding the opportunities for targeted new migraine therapies, it is of crucial importance to explore these multi-faceted interactions.

Effect of a 5-HT1D receptor agonist on the reinstatement phase of the conditioned place preference test and hippocampal long-term potentiation in methamphetamine-treated rats

Methamphetamine (METH)-seeking relapse is associated with memory and synaptic plasticity changes. Serotonin is a key neuromodulator in this process. While there is a known distribution of 5-HT_1D receptors in reward and memory areas, such as the hippocampus, its physiological function is currently unknown. Here, we evaluated effect of a 5-HT_1D receptor agonist, PNU142633, on the reinstatement of METH-seeking behavior and long-term potentiation. Rats were implanted with a cannula into lateral ventricle, then treated with saline or METH (5 mg/kg) during the acquisition phase of the conditioned place preference (CPP) test. On day 13 of the extinction phase, METH groups were divided into four groups: METH (0: saline, 1, or 2.5 (priming METH) mg/kg; i.p.) + vehicle (5 µl/rat) or a priming dose of METH (2.5 mg/kg; i.p.) + PNU (2 µg/5 µl; i.c.v.) and their preference scores were calculated on reinstatement day (day 14). Immediately following this, electrophysiology was performed to assay the field excitatory postsynaptic potential (fEPSP) slope and population spike (PS) amplitude between groups. The results showed that CPP induction by METH gradually declined to extinction on days 12 and 13. A priming METH treatment significantly increased preference for the METH-paired chamber when compared with other groups, but pre-treatment with PNU significantly attenuated this effect. PS amplitude and fEPSP slopes in vehicle + priming METH rats were greater when compared with other groups. Furthermore, PNU attenuated the priming METH-induced increase in PS amplitude. These findings suggest that PNU can decrease synaptic transmission and prevent METH reinstatement in rats.

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.

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.

5-HT Receptor Nomenclature: Naming Names, Does It Matter? A Tribute to Maurice Rapport

The naming of 5-HT receptors has been challenging, especially in the early days when the concept of multiple receptors for a single neurotransmitter was considered to be unrealistic at best. Yet pharmacological (rank orders of potency in functional or biochemical settings) and transductional evidence (second messengers, electrophysiology) clearly indicated the existence of receptor families and subfamilies. The genetic revolution, with the cloning and study of recombinantly expressed receptors, and eventually the cloning of the human and other genomes have made such reservations obsolete. Further, the advances in structural biology, with the possibility to study ligand receptor complexes as crystals and/or using solution NMR have largely confirmed the complexity of the 5-HT receptor system: species differences, existence of multiple receptor active and inactive states, splice variants, editing variants, complexes with multiple interacting proteins and transduction bias. This is a short personal history on how advances in biochemistry, molecular biology, biophysics, imaging and medicinal chemistry, some lateral thinking, and a decent amount of collaborative spirit within the 5-HT receptor nomenclature committee and the 5-HT community at large have helped to better define the pharmacology of the 5-HT receptor family.

Low 5-HT1B receptor binding in the migraine brain: A PET study

Background The pathophysiology of migraine may involve dysfunction of serotonergic signaling. In particular, the 5-HT_1B receptor is considered a key player due to the efficacy of 5-HT_1B receptor agonists for treatment of migraine attacks. Aim To examine the cerebral 5-HT_1B receptor binding in interictal migraine patients without aura compared to controls. Methods Eighteen migraine patients, who had been migraine free for >48 hours, and 16 controls were scanned after injection of the 5-HT_1B receptor specific radioligand [¹¹C]AZ10419369 for quantification of cerebral 5-HT_1B receptor binding. Patients who reported migraine <48 hours after the PET examination were excluded from the final analysis. We defined seven brain regions involved in pain modulation as regions of interest and applied a latent variable model (LVM) to assess the group effect on binding across these regions. Results Our data support a model wherein group status predicts the latent variable ( p = 0.038), with migraine patients having lower 5-HT_1B receptor binding across regions compared to controls. Further, in a whole-brain voxel-based analysis, time since last migraine attack correlated positively with 5-HT_1B receptor binding in the dorsal raphe and in the midbrain. Conclusion We report here for the first time that migraine patients have low 5-HT_1B receptor binding in pain modulating regions, reflecting decreased receptor density. This is either a primary constitutive trait of the migraine brain or secondary to repeated exposure to migraine attacks. We also provide indirect support for the dorsal raphe 5-HT_1B receptors being temporarily downregulated during the migraine attack, presumably in response to higher cerebral serotonin levels in the ictal phase.

Marked sexual dimorphism in 5-HT1 receptors mediating pronociceptive effects of sumatriptan

Amongst the side effects of triptans, a substantial percentage of patients experience injection site pain and tenderness, the underlying mechanism of which is unknown. We found that the dose range from 10fg to 1000ng (intradermal) of sumatriptan induced a complex dose-dependent mechanical hyperalgesia in male rats, with distinct peaks, at 1pg and 10ng, but no hyperalgesia at 1ng. In contrast, in females, there was 1 broad peak. The highest dose (1000ng) did not produce hyperalgesia in either sex. We evaluated the receptors mediating sumatriptan hyperalgesia (1pg, 1 and 10ng). In males, the injection of an antagonist for the serotonin (5-HT) receptor subtype 1B (5-HT_1B), but not 5-HT_1D, markedly inhibited sumatriptan (1pg)-induced hyperalgesia, at 10ng a 5-HT_1D receptor antagonist completely eliminated hyperalgesia. In contrast, in females, the 5-HT_1D, but not 5-HT_1B, receptor antagonist completely blocked sumatriptan (1pg and 10ng) hyperalgesia and both 5-HT_1B and 5-HT_1D receptor antagonists attenuated hyperalgesia (1ng) in females, which is GPR30 estrogen receptor dependent. While selective 5-HT_1D or 5-HT_1B, agonists produce robust hyperalgesia in female and male rats, respectively, when co-injected the hyperalgesia induced in both sexes was attenuated. Mechanical hyperalgesia induced by sumatriptan (1pg and 10ng) is dependent on the G-protein α_i subunit and protein kinase A (PKA), in IB4-positive and negative nociceptors. Understanding the mechanisms responsible for the complex dose dependence for triptan hyperalgesia may provide useful information for the design of anti-migraine drugs with improved therapeutic profiles.

Understanding migraine: Potential role of neurogenic inflammation

Neurogenic inflammation, a well-defined pathophysiologial process is characterized by the release of potent vasoactive neuropeptides, predominantly calcitonin gene-related peptide (CGRP), substance P (SP), and neurokinin A from activated peripheral nociceptive sensory nerve terminals (usually C and A delta-fibers). These peptides lead to a cascade of inflammatory tissue responses including arteriolar vasodilation, plasma protein extravasation, and degranulation of mast cells in their peripheral target tissue. Neurogenic inflammatory processes have long been implicated as a possible mechanism involved in the pathophysiology of various human diseases of the nervous system, respiratory system, gastrointestinal tract, urogenital tract, and skin. The recent development of several innovative experimental migraine models has provided evidence suggestive of the involvement of neuropeptides (SP, neurokinin A, and CGRP) in migraine headache. Antidromic stimulation of nociceptive fibers of the trigeminal nerve resulted in a neurogenic inflammatory response with marked increase in plasma protein extravasation from dural blood vessels by the release of various sensory neuropeptides. Several clinically effective abortive antimigraine medications, such as ergots and triptans, have been shown to attenuate the release of neuropeptide and neurogenic plasma protein extravasation. These findings provide support for the validity of using animal models to investigate mechanisms of neurogenic inflammation in migraine. These also further strengthen the notion of migraine being a neuroinflammatory disease. In the clinical context, there is a paucity of knowledge and awareness among physicians regarding the role of neurogenic inflammation in migraine. Improved understanding of the molecular biology, pharmacology, and pathophysiology of neurogenic inflammation may provide the practitioner the context-specific feedback to identify the novel and most effective therapeutic approach to treatment. With this objective, the present review summarizes the evidence supporting the involvement of neurogenic inflammation and neuropeptides in the pathophysiology and pharmacology of migraine headache as well as its potential significance in better tailoring therapeutic interventions in migraine or other neurological disorders. In addition, we have briefly highlighted the pathophysiological role of neurogenic inflammation in various other neurological disorders.

Lasmiditan for acute migraine treatment

Lasmiditan is a new neurally acting antimigraine drug that acts as a highly selective serotonin1F receptor agonist. Its chemical structure is distinctly different from that of triptans. Its dose-dependent clinical efficacy was proven in two clinical Phase II trials using intravenous and oral formulations. Oral lasmiditan showed significant headache relief after 2 h at doses of 50, 100, 200 and 400 mg. Adverse events of lasmiditan were dose-dependent and mainly associated with the CNS. They predominantly included dizziness, paresthesia and fatigue, and were mostly mild-to-moderate in intensity. Preclinical studies showed that, unlike triptans, lasmiditan lacks any vasoconstrictive activity, which makes it a promising drug for patients with contraindications to triptans owing to cardio- or cerebro-vascular diseases, or an elevated vascular risk profile.

Facile synthesis of 4,5,6a,7-tetrahydrodibenzo[de,g]chromene heterocycles and their transformation to phenanthrene alkaloids

Oxa-Pictet-Spengler cyclization and microwave-assisted C-H arylation have been implemented as key steps in the synthesis of new isochroman heterocycles containing a 4,5,6a,7-tetrahydrodibenzo[de,g]chromene motif. These isochromans may be easily transformed to phenanthrene alkaloids via acidic cleavage of the isochroman ring and standard synthetic manipulations thereafter. The route described is attractive in that it provides access to two biologically interesting scaffolds in simple and high yielding synthetic steps.

Chemical mediators of migraine: preclinical and clinical observations

Migraine is a neurovascular disorder, and although the pathophysiology of migraine has not been fully delineated, much has been learned in the past 50 years. This knowledge has been accompanied by significant advancements in the way migraine is viewed as a disease process and in the development therapeutic options. In this review, we will focus on 4 mediators (nitric oxide, histamine, serotonin, and calcitonin gene-related peptide) which have significantly advanced our understanding of migraine as a disease entity. For each mediator we begin by reviewing the preclinical data linking it to migraine pathophysiology, first focusing on the vascular mechanisms, then the neuronal mechanisms. The preclinical data are then followed by a review of the clinical data which support each mediator's role in migraine and highlights the pharmacological agents which target these mediators for migraine therapy.

Argyreia nervosa (Burm. f.): receptor profiling of lysergic acid amide and other potential psychedelic LSD-like compounds by computational and binding assay approaches

ETHNOPHARMACOLOGICAL RELEVANCE

The convolvulacea Argyreia nervosa (Burm. f.) is well known as an important medical plant in the traditional Ayurvedic system of medicine and it is used in numerous diseases (e.g. nervousness, bronchitis, tuberculosis, arthritis, and diabetes). Additionally, in the Indian state of Assam and in other regions Argyreia nervosa is part of the traditional tribal medicine (e.g. the Santali people, the Lodhas, and others). In the western hemisphere, Argyreia nervosa has been brought in attention as so called "legal high". In this context, the seeds are used as source of the psychoactive ergotalkaloid lysergic acid amide (LSA), which is considered as the main active ingredient.

AIM OF THE STUDY

As the chemical structure of LSA is very similar to that of lysergic acid diethylamide (LSD), the seeds of Argyreia nervosa (Burm. f.) are often considered as natural substitute of LSD. In the present study, LSA and LSD have been compared concerning their potential pharmacological profiles based on the receptor binding affinities since our recent human study with four volunteers on p.o. application of Argyreia nervosa seeds has led to some ambiguous effects.

MATERIAL AND METHODS

In an initial step computer-aided in silico prediction models on receptor binding were employed to screen for serotonin, norepinephrine, dopamine, muscarine, and histamine receptor subtypes as potential targets for LSA. In addition, this screening was extended to accompany ergotalkaloids of Argyreia nervosa (Burm. f.). In a verification step, selected LSA screening results were confirmed by in vitro binding assays with some extensions to LSD.

RESULTS

In the in silico model LSA exhibited the highest affinity with a pKi of about 8.0 at α1A, and α1B. Clear affinity with pKi>7 was predicted for 5-HT1A, 5-HT1B, 5-HT1D, 5-HT6, 5-HT7, and D2. From these receptors the 5-HT1D subtype exhibited the highest pKi with 7.98 in the prediction model. From the other ergotalkaloids, agroclavine and festuclavine also seemed to be highly affine to the 5-HT1D-receptor with pKi>8. In general, the ergotalkaloids of Argyreia nervosa seem to prefer serotonin and dopamine receptors (pKi>7). However, with exception of ergometrine/ergometrinine only for 5-HT3A, and histamine H2 and H4 no affinities were predicted. Compared to LSD, LSA exhibited lower binding affinities in the in vitro binding assays for all tested receptor subtypes. However, with a pKi of 7.99, 7.56, and 7.21 a clear affinity for 5-HT1A, 5-HT2, and α2 could be demonstrated. For DA receptor subtypes and the α1-receptor the pKi ranged from 6.05 to 6.85.

CONCLUSION

Since the psychedelic activity of LSA in the recent human study was weak and although LSA from Argyreia nervosa is often considered as natural exchange for LSD, LSA should not be regarded as LSD-like psychedelic drug. However, vegetative side effects and psychotropic effects may be triggered by serotonin or dopamine receptor subtypes.

Activation of 5-hydroxytryptamine1B/1D/1F receptors as a mechanism of action of antimigraine drugs

INTRODUCTION

The introduction of the triptans (5-hydroxytryptamine (5-HT)1B/1D receptor agonists) was a great improvement in the acute treatment of migraine. However, shortcomings of the triptans have prompted research on novel serotonergic targets for the treatment of migraine.

AREAS COVERED

In this review the different types of antimigraine drugs acting at 5-HT receptors, their discovery and development are discussed. The first specific antimigraine drugs were the ergot alkaloids, consisting of ergotamine, dihydroergotamine and methysergide, which are agonists at 5-HT receptors, but can also bind α-adrenoceptors and dopamine receptors. In the 1990s, the triptans became available on the market. They are 5-HT1B/1D receptor agonists, showing fewer side effects due to their receptor specificity. In the last years, compounds that bind specifically to 5-HT1D, 5-HT1F and 5-HT7 receptors have been explored for their antimigraine potential. Furthermore, the serotonergic system seems to act in tight connection with the glutamatergic as well as the CGRP-ergic systems, which may open novel therapeutic avenues.

EXPERT OPINION

Although the triptans are very effective in treating migraine attacks, their shortcomings have stimulated the search for novel drugs. Currently, the focus is on 5-HT1F receptor agonists, which seem devoid of vascular side effects. Moreover, novel compounds that affect multiple transmitter and/or neuropeptide systems that are involved in migraine could be of therapeutic relevance.

Autoradiographic Mapping of 5-HT(1B/1D) Binding Sites in the Rhesus Monkey Brain Using [carbonyl-C]zolmitriptan

Zolmitriptan is a serotonin 5-HT(1B/1D) receptor agonist that is an effective and well-tolerated drug for migraine treatment. In a human positron emission tomography study, [(11)C]zolmitriptan crossed the blood-brain barrier but no clear pattern of regional uptake was discernable. The objective of this study was to map the binding of [(11)C]zolmitriptan in Rhesus monkey brain using whole hemisphere in vitro autoradiography with [(11)C]zolmitriptan as a radioligand. In saturation studies, [(11)C]zolmitriptan showed specific (90%) binding to a population of high-affinity binding sites (Kd 0.95-5.06 nM). There was regional distribution of binding sites with the highest density in the ventral pallidum, followed by the external globus pallidus, substantia nigra, visual cortex, and nucleus accumbens. In competitive binding studies with 5-HT(1) receptor antagonists, [(11)C]zolmitriptan binding was blocked by selective 5-HT(1B) and 5-HT(1D) ligands in all target areas. There was no appreciable change in binding with the addition of a 5-HT(1A) receptor antagonist.

The relevance of preclinical research models for the development of antimigraine drugs: focus on 5-HT(1B/1D) and CGRP receptors

Migraine is a complex neurovascular syndrome, causing a unilateral pulsating headache with accompanying symptoms. The past four decades have contributed immensely to our present understanding of migraine pathophysiology and have led to the introduction of specific antimigraine therapies, much to the relief of migraineurs. Pathophysiological factors culminating into migraine headaches have not yet been completely deciphered and, thus, pose an additional challenge for preclinical research in the absence of any direct experimental marker. Migraine provocation experiments in humans use a head-score to evaluate migraine, as articulated by the volunteer, which cannot be applied to laboratory animals. Therefore, basic research focuses on different symptoms and putative mechanisms, one at a time or in combination, to validate the hypotheses. Studies in several species, utilizing different preclinical approaches, have significantly contributed to the two antimigraine principles in therapeutics, namely: 5-HT(1B/1D) receptor agonists (known as triptans) and CGRP receptor antagonists (known as gepants). This review will analyze the preclinical experimental models currently known for the development of these therapeutic principles, which are mainly based on the vascular and/or neurogenic theories of migraine pathogenesis. These include models based on the involvement of cranial vasodilatation and/or the trigeminovascular system in migraine. Clearly, the preclinical strategies should involve both approaches, while incorporating the newer ideas/techniques in order to get better insights into migraine pathophysiology.

Current and emerging treatment options for migraine and other primary headache disorders

Primary headache disorders are highly prevalent worldwide. The impact of primary headaches to the individual is significant and reflects physical suffering and decreased social and occupational functioning. The economic burden to society is enormous and represents direct healthcare costs and the indirect costs associated with decreased workplace productivity and work absences. The last decade has witnessed tremendous advances both in our understanding of the biology of headache and in our therapeutic armamentarium. This review outlines how these developments may be rationally implemented by highlighting individual treatment options and general treatment strategies. The state-of-the-art methods for the abortive and prophylactic treatment of tension-type headache, migraine and cluster headache are reviewed.

5-HT(1F) Receptor agonists: a new treatment option for migraine attacks?

Migraine is a debilitating disorder of the CNS. Although therapeutic options for migraine attacks have tremendously advanced with the development of triptans more than a decade ago, several conditions (such as vascular disease) restrict their use. Moreover, some patients do not respond to triptans and other currently available medications. Therefore, treatment alternatives are needed. Study data show that 5-HT(1F) receptor agonists successfully abort migraine attacks. These data also suggest a favorable vascular side-effect profile of these substances, which could be beneficial for migraine treatment in subjects with cardiac or vascular disease. We discuss the current knowledge of 5-HT(1F) receptor-mediated effects, in part by comparing them to triptans, and we also summarize data from basic research and clinical trials.

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.

New drugs for migraine

After the triptans, a calcitonin gene-related peptide blocker (telcagepant) is the first acute medicine that has been developed primarily for treatment of acute migraine. Otherwise, the new drugs have been developed first for other purposes, like anticonvulsants, antihypertensives and antidepressants used for migraine prophylaxis. For acute attacks, a new way to administer a traditional drug like dihydroergotamine is under way, and documentation of efficacy in migraine has been gained for some commonly used painkillers and anti-inflammatory drugs, and for some herbal extracts. Based on insights into the basic pathophysiological mechanisms of the disorder, some drugs have been developed which seem promising in early phase II studies (NOS inhibitors and 5HT1F-receptor agonists). In the future, development and enhancements of existing medicines must be accompanied by increased efforts to develop truly new migraine drugs based on knowledge of the pathophysiology if one wishes to reduce substantially the great burden migraine poses on patients and society.

Migraine

Migraine is a neurovascular disorder which affects one fifth of the general population. Disability due to migraine is severe and involves patients from infancy through senescence and it is aggravated by the fact there is no complete cure. However, various drugs for the symptomatic or prophylactic treatment of the disease are available. Recently, better knowledge of the neurobiological and pharmacological aspects of a subset of trigeminal primary sensory neurons has provided key information for the development of effective molecules that specifically target the activation of the trigeminovascular system and may represent a significant advancement in the treatment of the disease. These novel antagonists block the receptor for the sensory neuropeptide calcitonin gene-related peptide (CGRP), which upon release from peripheral terminals of trigeminal perivascular neurons dilates cranial arterial vessels. Whether neurogenic vasodilatation is the major contributing factor to generate the pain and the associated symptoms of the migraine attack or whether other sites of action of CGRP receptor antagonists are responsible for the antimigraine effect of these compounds is the subject of current and intense research.

Current and prospective pharmacological targets in relation to antimigraine action

Migraine is a recurrent incapacitating neurovascular disorder characterized by unilateral and throbbing headaches associated with photophobia, phonophobia, nausea, and vomiting. Current specific drugs used in the acute treatment of migraine interact with vascular receptors, a fact that has raised concerns about their cardiovascular safety. In the past, alpha-adrenoceptor agonists (ergotamine, dihydroergotamine, isometheptene) were used. The last two decades have witnessed the advent of 5-HT(1B/1D) receptor agonists (sumatriptan and second-generation triptans), which have a well-established efficacy in the acute treatment of migraine. Moreover, current prophylactic treatments of migraine include 5-HT(2) receptor antagonists, Ca(2+) channel blockers, and beta-adrenoceptor antagonists. Despite the progress in migraine research and in view of its complex etiology, this disease still remains underdiagnosed, and available therapies are underused. In this review, we have discussed pharmacological targets in migraine, with special emphasis on compounds acting on 5-HT (5-HT(1-7)), adrenergic (alpha(1), alpha(2,) and beta), calcitonin gene-related peptide (CGRP(1) and CGRP(2)), adenosine (A(1), A(2), and A(3)), glutamate (NMDA, AMPA, kainate, and metabotropic), dopamine, endothelin, and female hormone (estrogen and progesterone) receptors. In addition, we have considered some other targets, including gamma-aminobutyric acid, angiotensin, bradykinin, histamine, and ionotropic receptors, in relation to antimigraine therapy. Finally, the cardiovascular safety of current and prospective antimigraine therapies is touched upon.

Examining the essence of migraine--is it the blood vessel or the brain? A debate

A debate is presented that examines whether it is the blood vessel or the brain that determines the essence of migraine.

Cardiovascular responses produced by 5-hydroxytriptamine:a pharmacological update on the receptors/mechanisms involved and therapeutic implications

The complexity of cardiovascular responses produced by 5-hydroxytryptamine (5-HT, serotonin), including bradycardia or tachycardia, hypotension or hypertension, and vasodilatation or vasoconstriction, has been explained by the capability of this monoamine to interact with different receptors in the central nervous system (CNS), on the autonomic ganglia and postganglionic nerve endings, on vascular smooth muscle and endothelium, and on the cardiac tissue. Depending, among other factors, on the species, the vascular bed under study, and the experimental conditions, these responses are mainly mediated by 5-HT(1), 5-HT(2), 5-HT(3), 5-HT(4), 5-ht(5A/5B), and 5-HT(7) receptors as well as by a tyramine-like action or unidentified mechanisms. It is noteworthy that 5-HT(6) receptors do not seem to be involved in the cardiovascular responses to 5-HT. Regarding heart rate, intravenous (i.v.) administration of 5-HT usually lowers this variable by eliciting a von Bezold-Jarisch-like reflex via 5-HT(3) receptors located on sensory vagal nerve endings in the heart. Other bradycardic mechanisms include cardiac sympatho-inhibition by prejunctional 5-HT(1B/1D) receptors and, in the case of the rat, an additional 5-ht(5A/5B) receptor component. Moreover, i.v. 5-HT can increase heart rate in different species (after vagotomy) by a variety of mechanisms/receptors including activation of: (1) myocardial 5-HT(2A) (rat), 5-HT(3) (dog), 5-HT(4) (pig, human), and 5-HT(7) (cat) receptors; (2) adrenomedullary 5-HT(2) (dog) and prejunctional sympatho-excitatory 5-HT(3) (rabbit) receptors associated with a release of catecholamines; (3) a tyramine-like action mechanism (guinea pig); and (4) unidentified mechanisms (certain lamellibranch and gastropod species). Furthermore, central administration of 5-HT can cause, in general, bradycardia and/or tachycardia mediated by activation of, respectively, 5-HT(1A) and 5-HT(2) receptors. On the other hand, the blood pressure response to i.v. administration of 5-HT is usually triphasic and consists of an initial short-lasting vasodepressor response due to a reflex bradycardia (mediated by 5-HT(3) receptors located on vagal afferents, via the von Bezold-Jarisch-like reflex), a middle vasopressor phase, and a late, longer-lasting, vasodepressor response. The vasopressor response is a consequence of vasoconstriction mainly mediated by 5-HT(2A) receptors; however, vasoconstriction in the canine saphenous vein and external carotid bed as well as in the porcine cephalic arteries and arteriovenous anastomoses is due to activation of 5-HT(1B) receptors. The late vasodepressor response may involve three different mechanisms: (1) direct vasorelaxation by activation of 5-HT(7) receptors located on vascular smooth muscle; (2) inhibition of the vasopressor sympathetic outflow by sympatho-inhibitory 5-HT(1A/1B/1D) receptors; and (3) release of endothelium-derived relaxing factor (nitric oxide) by 5-HT(2B) and/or 5-HT(1B/1D) receptors. Furthermore, central administration of 5-HT can cause both hypotension (mainly mediated by 5-HT(1A) receptors) and hypertension (mainly mediated by 5-HT(2) receptors). The increasing availability of new compounds with high affinity and selectivity for the different 5-HT receptor subtypes makes it possible to develop drugs with potential therapeutic usefulness in the treatment of some cardiovascular illnesses including hypertension, migraine, some peripheral vascular diseases, and heart failure.

The phe-124-Cys and A-161T variants of the human 5-HT1B receptor gene are not major determinants of the clinical response to sumatriptan

BACKGROUND

The 5-HT(1B/1D) receptor agonist sumatriptan is highly effective in the treatment of migraine. However, some patients do not respond to sumatriptan or experience recurrence of the headache after initial relief. In addition, some patients report chest symptoms after the use of sumatriptan.

OBJECTIVE

To assess whether 2 genetic variants (F124C changing a phenylalanine for a cysteine and polymorphism A/T at nucleotide position -161 in the 5' regulatory region) of the 5-HT(1B) receptor play a major role in the therapeutic response to sumatriptan. The 5-HT(1B) receptor most likely mediates the therapeutic action and coronary side effects of sumatriptan, and both F124C and A-161T have relevant functional consequences on either the affinity of sumatriptan to bind to the 5-HT(1B) receptor or on receptor expression level itself, respectively.

METHOD

Genomic DNA of a relatively small but very well-characterized set of migraine patients with consistently good response to sumatriptan (n = 14), with no response (n = 12), with recurrence of the headache (n = 12), with chest symptoms (n = 13), and patients without chest symptoms (n = 27) was available for the genetic analyses and screened for the F124C variant and the A-161T polymorphism in the human 5-HT(1B) receptor gene.

RESULTS

F124C was not detected in any of the patients studied. In addition, we did not observe drastic changes in allele frequencies of the A-161T polymorphism that might hint to a causal relation with the therapeutic effect of sumatriptan.

CONCLUSION

We have not obtained any evidence that variants F124C and A-161T of the 5-HT(1B) receptor are major determinants in the clinical response to sumatriptan.

The Discovery of a New Drug Class for the Acute Treatment of Migraine

The history of the scientific ideas and events that led to the discovery of sumatriptan is outlined with personal reminiscences about individuals who influenced the approach. The development of sumatriptan revolutionized the acute treatment of migraine and led to the availability of a number of other triptans. The anti-migraine effects of all the triptans are mediated via 5-HT(1B), and possibly 5-HT(1D) receptors, which transduce their effects via G; proteins. This suggests that agonists at other G(i) protein-coupled receptor types appropriately located (eg, somatostatin sst(2), adenosine A(1)) should be examined for their effects on the trigeminovascular system, Studies on such receptor targets may provide insight into a novel approach towards the design of new anti-migraine drugs.

New Migraine and Pain Research

An understanding of the pathophysiology and pharmacology of migraine has been driven by astute clinical observations, elegant experimental medicine studies and importantly by the introduction of highly effective selective anti-migraine agents such as the Triptan 5-HT(1B/1D) agonists. New investigational migraine therapies such CGRP antagonists target key components of the trigeminal sensory neuroinflammatory response and show promise for the future. Cutting edge molecular profiling studies looking at gene expression during chronic pain are now being used to reveal the cell biology of pain and new potential therapeutic targets. Translational neuroimaging research can link the laboratory and the clinic and is now being used to help understand the neural systems biology of migraine. Research into migraine has generated sophisticated hypotheses that encompass primary CNS dysfunction, trigeminovascular activation, pain perception and activation of associated neural circuits involved in affective functions providing a rich framework within which to design and test future migraine treatment strategies.