Discovery of MK-3207: A Highly Potent, Orally Bioavailable CGRP Receptor Antagonist

Elucidating the Interactome of G Protein-Coupled Receptors and Receptor Activity-Modifying Proteins

G protein-coupled receptors (GPCRs) are known to interact with several other classes of integral membrane proteins that modulate their biology and pharmacology. However, the extent of these interactions and the mechanisms of their effects are not well understood. For example, one class of GPCR-interacting proteins, receptor activity-modifying proteins (RAMPs), comprise three related and ubiquitously expressed single-transmembrane span proteins. The RAMP family was discovered more than two decades ago, and since then GPCR-RAMP interactions and their functional consequences on receptor trafficking and ligand selectivity have been documented for several secretin (class B) GPCRs, most notably the calcitonin receptor-like receptor. Recent bioinformatics and multiplexed experimental studies suggest that GPCR-RAMP interactions might be much more widespread than previously anticipated. Recently, cryo-electron microscopy has provided high-resolution structures of GPCR-RAMP-ligand complexes, and drugs have been developed that target GPCR-RAMP complexes. In this review, we provide a summary of recent advances in techniques that allow the discovery of GPCR-RAMP interactions and their functional consequences and highlight prospects for future advances. We also provide an up-to-date list of reported GPCR-RAMP interactions based on a review of the current literature. SIGNIFICANCE STATEMENT: Receptor activity-modifying proteins (RAMPs) have emerged as modulators of many aspects of G protein-coupled receptor (GPCR)biology and pharmacology. The application of new methodologies to study membrane protein-protein interactions suggests that RAMPs interact with many more GPCRs than had been previously known. These findings, especially when combined with structural studies of membrane protein complexes, have significant implications for advancing GPCR-targeted drug discovery and the understanding of GPCR pharmacology, biology, and regulation.

Single-Dose Pharmacokinetics and Safety of Ubrogepant in Adults With Hepatic Impairment: Results From an Open-Label, Phase 1 Trial

Ubrogepant is an oral calcitonin gene–related peptide receptor antagonist approved for the treatment of acute migraine headaches. Ubrogepant demonstrated efficacy and safety in 2 pivotal phase 3 studies (N = 2240) that led to its approval. Here, we report the pharmacokinetics and safety results from a phase 1 study in which participants with severe (n = 4), moderate (n = 8), or mild (n = 8) hepatic impairment and matched participants with normal hepatic function (n = 8) were administered a single dose of 100 mg of ubrogepant. Twenty‐eight participants aged 36 to 70 years were enrolled and completed the study. In participants with mild, moderate, or severe hepatic impairment, ubrogepant systemic exposure (area under the plasma concentration–time curve) increased by 7%, 52%, and 115%, respectively, compared with participants with normal hepatic function (≈1600 ng • h/mL). Peak exposure increased by 1%, 18%, and 26%, respectively, in participants with mild, moderate, or severe hepatic impairment compared to those with normal hepatic function (≈400 ng/mL). Plasma protein binding did not change significantly across groups. No dose adjustment is recommended for patients with mild or moderate hepatic impairment. Dose adjustment (50 mg) is recommended for patients with severe hepatic impairment. Single doses of ubrogepant 100 mg were safe, and all the enrolled participants, regardless of hepatic function, completed the study.

Discovery of a First-In-Class Small Molecule Antagonist against the Adrenomedullin-2 Receptor: Structure-Activity Relationships and Optimization

Class B G-protein-coupled receptors (GPCRs) remain an underexploited target for drug development. The calcitonin receptor (CTR) family is particularly challenging, as its receptors are heteromers comprising two distinct components: the calcitonin receptor-like receptor (CLR) or calcitonin receptor (CTR) together with one of three accessory proteins known as receptor activity-modifying proteins (RAMPs). CLR/RAMP1 forms a CGRP receptor, CLR/RAMP2 forms an adrenomedullin-1 (AM1) receptor, and CLR/RAMP3 forms an adrenomedullin-2 (AM2) receptor. The CTR/RAMP complexes form three distinct amylin receptors. While the selective blockade of AM2 receptors would be therapeutically valuable, inhibition of AM1 receptors would cause clinically unacceptable increased blood pressure. We report here a systematic study of structure-activity relationships that has led to the development of first-in-class AM2 receptor antagonists. These compounds exhibit therapeutically valuable properties with 1000-fold selectivity over the AM1 receptor. These results highlight the therapeutic potential of AM2 antagonists.

Structure-Based Drug Discovery of N-((R)-3-(7-Methyl-1H-indazol-5-yl)-1-oxo-1-(((S)-1-oxo-3-(piperidin-4-yl)-1-(4-(pyridin-4-yl)piperazin-1-yl)propan-2-yl)amino)propan-2-yl)-2'-oxo-1',2'-dihydrospiro[piperidine-4,4'-pyrido[2,3-d][1,3]oxazine]-1-carboxamide (HTL22562): A Calcitonin Gene-Related Peptide Receptor Antagonist for Acute Treatment of Migraine

Structure-based drug design enabled the discovery of 8, HTL22562, a calcitonin gene-related peptide (CGRP) receptor antagonist. The structure of 8 complexed with the CGRP receptor was determined at a 1.6 Å resolution. Compound 8 is a highly potent, selective, metabolically stable, and soluble compound suitable for a range of administration routes that have the potential to provide rapid systemic exposures with resultant high levels of receptor coverage (e.g., subcutaneous). The low lipophilicity coupled with a low anticipated clinically efficacious plasma exposure for migraine also suggests a reduced potential for hepatotoxicity. These properties have led to 8 being selected as a clinical candidate for acute treatment of migraine.

Discovery of a First-in-Class Potent Small Molecule Antagonist against the Adrenomedullin-2 Receptor

The hormone adrenomedullin has both physiological and pathological roles in biology. As a potent vasodilator, adrenomedullin is critically important in the regulation of blood pressure, but it also has several roles in disease, of which its actions in cancer are becoming recognized to have clinical importance. Reduced circulating adrenomedullin causes increased blood pressure but also reduces tumor progression, so drugs blocking all effects of adrenomedullin would be unacceptable clinically. However, there are two distinct receptors for adrenomedullin, each comprising the same G protein-coupled receptor (GPCR), the calcitonin receptor-like receptor (CLR), together with a different accessory protein known as a receptor activity-modifying protein (RAMP). The CLR with RAMP2 forms an adrenomedullin-1 receptor, and the CLR with RAMP3 forms an adrenomedullin-2 receptor. Recent research suggests that a selective blockade of adrenomedullin-2 receptors would be therapeutically valuable. Here we describe the design, synthesis, and characterization of potent small-molecule adrenomedullin-2 receptor antagonists with 1000-fold selectivity over the adrenomedullin-1 receptor, although retaining activity against the CGRP receptor. These molecules have clear effects on markers of pancreatic cancer progression in vitro, drug-like pharmacokinetic properties, and inhibit xenograft tumor growth and extend life in a mouse model of pancreatic cancer. Taken together, our data support the promise of a new class of anticancer therapeutics as well as improved understanding of the pharmacology of the adrenomedullin receptors and other GPCR/RAMP heteromers.

Potential Drugs Targeting Early Innate Immune Evasion of SARS-Coronavirus 2 via 2'-O-Methylation of Viral RNA

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) causing the COVID-19 respiratory disease pandemic utilizes unique 2'-O-methyltransferase (2'-O-MTase) capping machinery to camouflage its RNA from innate immune recognition. The nsp16 catalytic subunit of the 2'-O-MTase is unusual in its requirement for a stimulatory subunit (nsp10) to catalyze the ribose 2'-O-methylation of the viral RNA cap. Here we provide a computational basis for drug repositioning or de novo drug development based on three differential traits of the intermolecular interactions of the SARS-CoV-2-specific nsp16/nsp10 heterodimer, namely: (1) the S-adenosyl-l-methionine-binding pocket of nsp16, (2) the unique "activating surface" between nsp16 and nsp10, and (3) the RNA-binding groove of nsp16. We employed ≈9000 U.S. Food and Drug Administration (FDA)-approved investigational and experimental drugs from the DrugBank repository for docking virtual screening. After molecular dynamics calculations of the stability of the binding modes of high-scoring nsp16/nsp10-drug complexes, we considered their pharmacological overlapping with functional modules of the virus-host interactome that is relevant to the viral lifecycle, and to the clinical features of COVID-19. Some of the predicted drugs (e.g., tegobuvir, sonidegib, siramesine, antrafenine, bemcentinib, itacitinib, or phthalocyanine) might be suitable for repurposing to pharmacologically reactivate innate immune restriction and antagonism of SARS-CoV-2 RNAs lacking 2'-O-methylation.

Blocking the CGRP Pathway for Acute and Preventive Treatment of Migraine: The Evolution of Success

The pivotal role of calcitonin gene-related peptide (CGRP) in migraine pathophysiology was identified over 30 years ago, but the successful clinical development of targeted therapies has only recently been realized. This Perspective traces the decades long evolution of medicinal chemistry required to advance small molecule CGRP receptor antagonists, also called gepants, including the current clinical agents rimegepant, vazegepant, ubrogepant, and atogepant. Providing clinically effective blockade of CGRP signaling required surmounting multiple challenging hurdles, including defeating a sizable ligand with subnanomolar affinity for its receptor, designing antagonists with an extended confirmation and multiple pharmacophores while retaining solubility and oral bioavailability, and achieving circulating free plasma levels that provided near maximal CGRP receptor coverage. The clinical efficacy of oral and intranasal gepants and the injectable CGRP monoclonal antibodies (mAbs) are described, as are recent synthetic developments that have benefited from new structural biology data. The first oral gepant was recently approved and heralds a new era in the treatment of migraine.

Applications of fluorine-containing amino acids for drug design

Fluorine-containing amino acids are becoming increasingly prominent in new drugs due to two general trends in the modern pharmaceutical industry. Firstly, the growing acceptance of peptides and modified peptides as drugs; and secondly, fluorine editing has become a prevalent protocol in drug-candidate optimization. Accordingly, fluorine-containing amino acids represent one of the more promising and rapidly developing areas of research in organic, bio-organic and medicinal chemistry. The goal of this Review article is to highlight the current state-of-the-art in this area by profiling 42 selected compounds that combine fluorine and amino acid structural elements. The compounds under discussion represent pharmaceutical drugs currently on the market, or in clinical trials as well as examples of drug-candidates that although withdrawn from development had a significant impact on the progress of medicinal chemistry and/or provided a deeper understanding of the nature and mechanism of biological action. For each compound, we present features of biological activity, a brief history of the design principles and the development of the synthetic approach, focusing on the source of tailor-made amino acid structures and fluorination methods. General aspects of the medicinal chemistry of fluorine-containing amino acids and synthetic methodology are briefly discussed.

CGRP Is Critical for Hot Flushes in Ovariectomized Mice

Hot flushes are common and troublesome symptoms of menopause. The neuropeptide calcitonin gene-related peptide (CGRP) is increased in plasma during hot flushes but it has not been clear if CGRP is causally involved in the mechanism underpinning the flushes. Here, we examined the effect of interventions with CGRP in a mouse model of hot flushes based on flush-like temperature increases triggered by forced physical activity in ovariectomized mice. Compared to normal mice, ovariectomized mice reacted with an exaggerated, flush-like, temperature increase after physical exercise. This increase was completely blocked by the non-peptide CGRP-antagonist MK-8825 (-0.41 degrees Celsius, 95% CI: -0,83 to 0,012, p < 0.0001) at a dose that had no obvious effects on locomotor activity (50 mg/kg). Further, the flush-like temperature increases were strongly attenuated in ovariectomized mice lacking αCGRP due to a genetic modification. Collectively, our findings suggest that CGRP is an important mediator of experimentally induced hot flushes and they identify CGRP antagonists as promising treatment candidates for women and possibly also men with hot flushes.

Study on the Alkylation Reactions of N(7)-Unsubstituted 1,3-Diazaoxindoles

The chemistry of the 5,7-dihydro-6H-pyrrolo[2,3-d]pyrimidin-6-one (1,3-diazaoxindole) compound family, possessing a drug-like scaffold, is unexplored. In this study, the alkylation reactions of N(7)-unsubstituted 5-isopropyl-1,3-diazaoxindoles bearing various substituents at the C(2) position have been investigated. The starting compounds were synthesized from the C(5)-unsubstituted parent compounds by condensation with acetone and subsequent catalytic reduction of the 5-isopropylidene moiety. Alkylation of the thus obtained 5-isopropyl derivatives with methyl iodide or benzyl bromide in the presence of a large excess of sodium hydroxide led to 5,7-disubstituted derivatives. Use of butyllithium as the base rendered alkylation in the C(5) position possible with reasonable selectivity, without affecting the N(7) atom. During the study on the alkylation reactions, some interesting by-products were also isolated and characterized.

Synthesis of Chiral Piperazinones Using Amphoteric Aziridine Aldehyde Dimers and Functionalized Isocyanides

We have evaluated a range of functionalized isocyanides in the aziridine aldehyde-driven multicomponent synthesis of piperazinones. High diasteroselectivity for each isocyanide was observed. A theoretical evaluation of the reaction course corroborates the experimental data. Moreover, the reactivity of cis- and trans-configured aziridine aldehyde dimers has been compared. This study further probes the dimer-driven mechanism of cyclization and enables an efficient access to a wide range of chiral piperazinones bearing functionalized side chains.

Novel oxazolidinone calcitonin gene-related peptide (CGRP) receptor antagonists for the acute treatment of migraine

In our efforts to develop CGRP receptor antagonists as backups to MK-3207, 2, we employed a scaffold hopping approach to identify a series of novel oxazolidinone-based compounds. The development of a structurally diverse, potent (20, cAMP+HS IC50=0.67 nM), and selective compound (hERG IC50=19 μM) with favorable rodent pharmacokinetics (F=100%, t1/2=7h) is described. Key to this development was identification of a 3-substituted spirotetrahydropyran ring that afforded a substantial gain in potency (10 to 35-fold).

Mechanistic investigation of aziridine aldehyde-driven peptide macrocyclization: the imidoanhydride pathway

Aziridine aldehydes participate in a multicomponent reaction with α-amino amides and isocyanides to generate reactive imidoanhydride intermediates.

Aziridine aldehyde dimers, peptides, and isocyanides participate in a multicomponent reaction to yield peptide macrocycles. We have investigated the selectivity and kinetics of this process and performed a detailed analysis of its chemoselectivity. While the reactants encompass all of the elements of the traditional Ugi four-component condensation, there is a significant deviation from the previously proposed mechanism. Our results provide evidence for an imidoanhydride pathway in peptide macrocyclization and lend justification for the diastereoselectivity and high effective molarity observed in the reaction.

Stereocontrolled disruption of the Ugi reaction toward the production of chiral piperazinones: substrate scope and process development

The factors determining diastereoselectivity observed in the multicomponent conversion of amino acids, aziridine aldehyde dimers, and isocyanides into chiral piperazinones have been investigated. Amino acid-dependent selectivity for either trans- or cis-substituted piperazinone products has been achieved. An experimentally determined diastereoselectivity model for the three-component reaction driven by aziridine aldehyde dimers has predictive value for different substrate classes. Moreover, this model is useful in reconciling the previously reported observations in multicomponent reactions between isocyanides, α-amino acids, and monofunctional aldehydes.

Emerging targets in migraine

Migraine is a common and highly disabling neurological disorder. Despite the complexity of its pathophysiology, substantial advances have been achieved over the past 20 years in its understanding, as well as the development of pharmacological treatment options. The development of serotonin 5-HT(1B/1D) receptor agonists ("triptans") substantially improved the acute treatment of migraine attacks. However, many migraineurs do not respond satisfactorily to triptans and cardiovascular co-morbidities limit their use in a significant number of patients. As migraine is increasingly considered to be a disorder of the brain, and preclinical and clinical data indicate that the observed vasodilation is merely an epiphenomenon, research has recently focused on the development of neurally acting compounds that lack vasoconstrictor properties. This review highlights the most important pharmacological targets for which compounds have been developed that are highly likely to enter or have already advanced into clinical trials for the acute and preventive treatment of migraine. In this context, preclinical and clinical data on compounds acting on calcitonin gene-related peptide or its receptor, the 5-HT(1F) receptor, nitric oxide synthase, and acid-sensing ion channel blockers are discussed.

[(11)C]MK-4232: The First Positron Emission Tomography Tracer for the Calcitonin Gene-Related Peptide Receptor

Rational modification of the potent calcitonin gene-related peptide (CGRP) receptor antagonist MK-3207 led to a series of analogues with enhanced CNS penetrance and a convenient chemical handle for introduction of a radiolabel. A number of (11)C-tracers were synthesized and evaluated in vivo, leading to the identification of [(11)C]8 ([(11)C]MK-4232), the first positron emission tomography tracer for the CGRP receptor.

Discovery of (R)-N-(3-(7-methyl-1H-indazol-5-yl)-1-(4-(1-methylpiperidin-4-yl)-1-oxopropan-2-yl)-4-(2-oxo-1,2-dihydroquinolin-3-yl)piperidine-1-carboxamide (BMS-742413): a potent human CGRP antagonist with superior safety profile for the treatment of migraine through intranasal delivery

Calcitonin gene-related peptide (CGRP) receptor antagonists have been shown to be efficacious as abortive migraine therapeutics with the absence of cardiovascular liabilities that are associated with triptans. Herein, we report the discovery of a highly potent CGRP receptor antagonist, BMS-742413, with the potential to provide rapid onset of action through intranasal delivery. The compound displays excellent aqueous solubility, oxidative stability, and toxicological profile. BMS-742413 has good intranasal bioavailability in the rabbit and shows a robust, dose-dependent inhibition of CGRP-induced increases in marmoset facial blood flow.

Discovery of (5S,6S,9R)-5-amino-6-(2,3-difluorophenyl)-6,7,8,9-tetrahydro-5H-cyclohepta[b]pyridin-9-yl 4-(2-oxo-2,3-dihydro-1H-imidazo[4,5-b]pyridin-1-yl)piperidine-1-carboxylate (BMS-927711): an oral calcitonin gene-related peptide (CGRP) antagonist in clinical trials for treating migraine

Calcitonin gene-related peptide (CGRP) receptor antagonists have demonstrated clinical efficacy in the treatment of acute migraine. Herein, we describe the design, synthesis, and preclinical characterization of a highly potent, oral CGRP receptor antagonist BMS-927711 (8). Compound 8 has good oral bioavailability in rat and cynomolgus monkey, attractive overall preclinical properties, and shows dose-dependent activity in a primate model of CGRP-induced facial blood flow. Compound 8 is presently in phase II clinical trials.

Targeting a family B GPCR/RAMP receptor complex: CGRP receptor antagonists and migraine

The clinical effectiveness of antagonizing the calcitonin gene-related peptide (CGRP) receptor for relief of migraine pain has been clearly demonstrated, but the road to the development of these small molecule antagonists has been daunting. The key hurdle that needed to be overcome was the CGRP receptor itself. The vast majority of the current antagonists recognize similar epitopes on the calcitonin receptor-like receptor (CLR) and receptor activity-modifying protein 1 (RAMP1). RAMP1 is a relatively small, single, transmembrane-spanning protein and along with the G-protein-coupled receptor CLR comprise a functional CGRP receptor. The tri-helical extracellular domain of RAMP1 plays a key role in the high affinity binding of CGRP receptor antagonists and drives their species-selective pharmacology. Over the years, a significant amount of mutagenesis data has been generated to identify specific amino acids or regions within CLR and RAMP1 that are critical to antagonist binding and has directed attention to the CLR/RAMP1 extracellular domain (ECD) complex. Recently, the crystal structure of the CGRP receptor ECD has been elucidated and not only reinforces the early mutagenesis data, but provides critical insight into the molecular mechanism of CGRP receptor antagonism. This review will highlight the drug design hurdles that must be overcome to meet the desired potency, selectivity and pharmacokinetic profile while retaining drug-like properties. Although the development of these antagonists has proved challenging, blocking the CGRP receptor may one day represent a new way to manage migraine and offer hope to migraine sufferers.

Discovery of a potent, orally bioavailable and highly selective human neuronal nitric oxide synthase (nNOS) inhibitor, N-(1-(piperidin-4-yl)indolin-5-yl)thiophene-2-carboximidamide as a pre-clinical development candidate for the treatment of migraine

We recently reported a series of 1,6-disubstituted indoline-based thiophene amidine compounds (5) as selective neuronal nitric oxide synthase (nNOS) inhibitors to mitigate the cardiovascular liabilities associated with hERG K(+) channel inhibition (IC(50) = 4.7 μM) with previously reported tetrahydroquinoline-based selective nNOS inhibitors (4). The extended structure-activity relationship studies within the indoline core led to the identification of 43 as a selection candidate for further evaluations. The in vivo activity in two different pain (spinal nerve ligation and migraine pain) models, the excellent physicochemical and pharmacokinetic properties, oral bioavailability (F(po) = 91%), and the in vitro safety profile disclosed in this report make 43 an ideal candidate for further evaluation in clinical applications related to migraine pain.

MK-8825: a potent and selective CGRP receptor antagonist with good oral activity in rats

Rational modification of the clinically tested CGRP receptor antagonist MK-3207 (3) afforded an analogue with increased unbound fraction in rat plasma and enhanced aqueous solubility, 2-[(8R)-8-(3,5-difluorophenyl)-8-methyl-10-oxo-6,9-diazaspiro[4.5]dec-9-yl]-N-[(6S)-2'-oxo-1',2',5,7-tetrahydrospiro[cyclopenta[b]pyridine-6,3'-pyrrolo[2,3-b]pyridin]-3-yl]acetamide (MK-8825) (6). Compound 6 maintained similar affinity to 3 at the human and rat CGRP receptors but possessed significantly improved in vivo potency in a rat pharmacodynamic model. The overall profile of 6 indicates it should find utility as a rat tool to investigate effects of CGRP receptor blockade in vivo.

Identification of a novel RAMP-independent CGRP receptor antagonist

Identification of an HIV integrase inhibitor with micromolar affinity for the CGRP receptor led to the discovery of a series of structurally novel CGRP receptor antagonists. Optimization of this series produced compound 16, a low-molecular weight CGRP receptor antagonist with good pharmacokinetic properties in both rat and dog. In contrast to other nonpeptide antagonists, the activity of 16 was affected by the presence of divalent cations and showed evidence of an alternative, RAMP-independent CGRP receptor binding site.

What has polar surface area ever done for drug discovery?

Over the last decade, polar surface area (PSA) has become a ubiquitous term in medicinal and computational chemistry circles. This article charts the development of the increasingly efficient methods for the calculation of PSA before illustrating its usefulness through selected examples drawn from the medicinal chemistry literature. Consideration of PSA is shown to assist in the improvement of cellular potency, intestinal absorption and blood-brain barrier permeation or restriction to the peripheral circulation.

Randomized controlled trial of the CGRP receptor antagonist MK-3207 in the acute treatment of migraine

Background: This study evaluated the CGRP receptor antagonist MK-3207 for acute treatment of migraine.

Methods: Multicenter, double-blind, randomized, placebo-controlled, parallel-group, two-stage adaptive study with two interim efficacy analyses to facilitate optimal dose selection. Migraine patients were initially randomized to MK-3207 2.5, 5, 10, 20, 50 and 100 mg or placebo to treat a moderate/severe migraine. One or more doses were to be discontinued based on the first interim analysis and a lower or higher dose could be added based on the second interim analysis. The primary endpoint was two-hour pain freedom.

Results: A total of 547 patients took study medication. After the first interim analysis, the two lowest MK-3207 doses (2.5, 5 mg) were identified as showing insufficient efficacy. Per the pre-specified adaptive design decision rule, only the 2.5-mg group was discontinued and the five highest doses (5, 10, 20, 50, 100 mg) were continued into the second stage. After the second interim efficacy analysis, a 200 mg dose was added due to insufficient efficacy at the top three (20, 50, 100 mg) doses. A positive dose-response trend was demonstrated when data were combined across all MK-3207 doses for two-hour pain freedom ( p < .001). The pairwise difference versus placebo for two-hour pain freedom was significant for 200 mg ( p < .001) and nominally significant for 100 mg and 10 mg ( p < .05). The incidence of adverse events appeared comparable between active treatment groups and placebo, and did not appear to increase with increasing dose.

Conclusions: MK-3207 was effective and generally well tolerated in the acute treatment of migraine.

Calcitonin gene-related peptide receptor antagonists for migraine

IMPORTANCE OF THE FIELD

Migraine is a highly prevalent disabling condition, and the current treatment options are not satisfactory. The role of calcitonin gene-related peptide (CGRP) in migraine pathophysiology is well established. CGRP receptor antagonists address this new target and have the potential to improve therapy for both responders and non-responders to previous options.

AREAS COVERED IN THIS REVIEW

This review describes CGRP, its receptors and their role in the pathophysiology of migraine. CGRP receptor antagonists are a recent development; all reported antagonists are reported in chronological order. The experimental evidence, as well as all clinical trials since the first proof-of-concept study in 2004, is discussed.

WHAT THE READER WILL GAIN

An overview of the CGRP system and why it provides an attractive drug target for headache. The main focus is on the currently presented CGRP receptor antagonists and clinical evidence for this new therapeutic option.

TAKE HOME MESSAGE

CGRP receptor antagonists will provide an additional and valuable therapeutic option for the treatment of headaches.

Pharmacological properties of MK-3207, a potent and orally active calcitonin gene-related peptide receptor antagonist

Calcitonin gene-related peptide (CGRP) has long been hypothesized to play a key role in migraine pathophysiology, and the advent of small-molecule antagonists has clearly demonstrated a clinical link between blocking the CGRP receptor and migraine efficacy. 2-[(8R)-8-(3,5-Difluorophenyl)-10-oxo-6,9-diazaspiro[4.5]dec-9-yl]-N-[(2R)-2'-oxo-1,1',2',3-tetrahydrospiro[indene-2,3'-pyrrolo[2,3-b]pyridin]-5-yl]acetamide (MK-3207) represents the third CGRP receptor antagonist to display clinical efficacy in migraine trials. Here, we report the pharmacological characterization of MK-3207, a potent and orally bioavailable CGRP receptor antagonist. In vitro, MK-3207 is a potent antagonist of the human and rhesus monkey CGRP receptors (K(i) = 0.024 nM). In common with other CGRP receptor antagonists, MK-3207 displays lower affinity for CGRP receptors from other species, including canine and rodent. As a consequence of species selectivity, the in vivo potency was assessed in a rhesus monkey pharmacodynamic assay measuring capsaicin-induced changes in forearm dermal blood flow via laser Doppler imaging. MK-3207 produced a concentration-dependent inhibition of dermal vasodilation, with plasma concentrations of 0.8 and 7 nM required to block 50 and 90% of the blood flow increase, respectively. The tritiated analog [3H]MK-3207 was used to study the binding characteristics on the human CGRP receptor. [3H]MK-3207 displayed reversible and saturable binding (K(D) = 0.06 nM), and the off-rate was determined to be 0.012 min(-1), with a t(1/2) value of 59 min. In vitro autoradiography studies on rhesus monkey brain slices identified the highest level of binding in the cerebellum, brainstem, and meninges. Finally, as an index of central nervous system penetrability, the in vivo cerebrospinal fluid/plasma ratio was determined to be 2 to 3% in cisterna magna-ported rhesus monkeys.