Blockade of CGRP Receptors in the Intracranial Vasculature: A New Target in the Treatment of Headache

Abstract

In primary headaches, there is a clear association between the headache and the release of calcitonin gene-related peptide (CGRP) but not with any of the other neuronal messengers. The purpose of this review is to describe the role of CGRP in the intracranial circulation and to elucidate a possible role for a specific CGRP receptor antagonist in the treatment of primary headaches. Acute treatment with a 5-HT_1B/1D agonist (triptan) results in alleviation of the headache and normalization of the cranial venous CGRP levels, in part due to a presynaptic inhibitory effect on sensory nerves. The central role of CGRP in migraine and cluster headache pathophysiology has led to the search for small molecule CGRP antagonists with few cardiovascular side-effects. The initial pharmacological profile of such a group of compounds has recently been disclosed. One of these compounds has been found to be efficacious in the relief of acute attacks of migraine.

Keywords

Migraine cluster headache CGRP VIP trigeminovascular reflex CGRP blockers

Introduction

The functional studies crucial to any hypothesis regarding headache rests on the classic observations of Ray and Wolff (1) who described painful sensations that resulted from mechanical or electrical stimulation of large cerebral arteries, venous sinuses, and dural arteries. The pain-sensitive supratentorial structures (but not subtentorial elements) are supplied by nerve fibres from the trigeminal ganglion, and there have been uncontrolled positive studies of the efficacy of retrogasserian rhizotomy of the trigeminal ganglia in migraine (2). A role of the trigemino-cerebrovascular system in the transmission of nociceptive information to the central nervous system is thus a viable proposition. Antidromic or local mechanical stimulation of sensory nerve endings results in vasodilatation of peripheral vessels via the release of vasoactive materials such as substance P and calcitonin gene-related peptide (CGRP) (3, 4). This vasomotor effect of the sensory nerves in the periphery appears to have a counterpart in the cerebral circulation with the trigeminal system. The cell bodies are located in the trigeminal ganglion, they send sensory fibres to various cranial structures, and connects to the CNS via the trigeminal nerve. The fibres and the cell bodies contain a number of messengers but CGRP is the one most frequently expressed (5).

CGRP immunoreactivity in intracranial vessels was first shown in 1984 (6), and subsequently found to originate in perikarya within the trigeminal ganglia of all species examined, including man (7). CGRP is frequently colocalized in trigeminal neuronal cells with substance P, neurokinin A, pituitary adenylate cyclase activating peptide (PACAP), amylin, neuronal nitric oxide synthase (NOS), although the number of CGRP-containing cells well exceeds the number of the others (5). Four sources of cerebrovascular CGRP have been described:

the ophthalmic division of the trigeminal ganglion, to innervate the circle of Willis and its branches by the nasociliary nerve;

the maxillary division, probably via an extradural branch at the skull base to the internal carotid artery;

the internal carotid miniganglia, via the greater deep petrosal nerve to distribute in the internal carotid artery and distribute proximally in its intracranial ramifications;

in the upper cervical dorsal root ganglia (C₁–C₃) to innervate the caudal third of the basilar artery and the vertebral artery (7–16).

The major cerebral arteries (anterior, middle, and posterior cerebral arteries, vertebral and basilar arteries) and pial arterioles of the cortical surface are invested with fine varicosed nerve fibres that contain CGRP (17). These nerve fibres are present in the adventitia and at the adventitial-medial border of the blood vessels and colocalized in the cerebrovascular nerve fibres with substance P (18, 19), neurokinin A (20), PACAP (8), NOS (8, 21), amylin (22) and nociceptin (23).

CGRP is a 37 amino acid peptide that results from alternative splicing of calcitonin gene transcripts (24). It exists in two forms α– and β– CGRP (25), which show considerable homology with amylin and adrenomedullin. The receptors belong to a family of G-protein coupled receptors that are linked to adenylate cyclase with diverse biological functions both in the peripheral and in the central nervous systems (4, 26, 27). CGRP containing nerves innervate blood vessels in most regions, the peptide is a potent vasodilator that is involved in pain processes (18, 19, 28). The physiological role of CGRP in the brain and in the cardiovascular system is in many pathological states not well understood (26, 27).

In one particular vascular region, the cerebral circulation, there is a particularly dense supply of trigeminal CGRP containing nerve fibres (18, 19). These fibres release CGRP following electrical stimulation (29–32) or administration of capsaicin (33–35) and are activated in primary headaches and in stroke (31, 36–40). Trigeminal fibres mediate dilatation of brain (17, 41–43), meningeal and dural vessels (43–48), mediate increases in cerebral blood flow (32), has no tonic influence on cerebral blood flow or metabolism (49) and has a key role in the trigeminovascular reflex (19, 33, 50). Although CGRP has a number of effects, its most pronounced action is that of vasodilatation (4, 28). The trigeminovascular system has a primary involvement in cranial sensory functions, but also acts as a vasodilator pathway involving antidromic release of the above signal substances but it is still only for CGRP that a functional role has been defined (19, 33, 50, 51).

Neurotransmitter release in primary headaches

The role of the sensory nerves around the intracranial vessels in primary headaches has been elucidated by analysis of neurotransmitter release in man: Activation of the trigeminal ganglion resulted in unilateral blood flow increases, CGRP and substance P release, and facial flushing on the side of stimulation (29).

Migraine

In migraine attacks there are both vascular and neurogenic components (36). Many consider that the disorder is due to mutations in a calcium channel gene rendering neurons unstable and capable of initiating a migraine attack in, e.g. stress; however, it has only been proven for familiar hemiplegic migraine (52). As part of the pathophysiological mechanisms the trigeminovascular system is activated and there is an antidromic release of CGRP, activation of neurons in the TNC with subsequent mediation of pain. The results from trigeminal ganglion stimulation in trigeminal neuralgia patients (neuropeptides are released and can be measured in the jugular vein) led us to examine during the migraine attacks the levels of neuronal messenger molecules (neuropeptides) associated with the autonomic and sensory nerves (29). The concentration of neuropeptide Y (NPY) (marker for the sympathetic nerves), vasoactive intestinal peptide (VIP) (parasympathetic activity), CGRP and substance P (both markers for sensory nerves) were analysed in the cranial venous outflow from the external jugular vein (Table 1). There were no changes in the levels of NPY, VIP or substance P. However, a marked increase in CGRP was observed during migraine headache (37). Two individuals with facial symptoms similar to those seen in cluster headache (e.g. nasal congestion and rhinorrhea), displayed in addition increases in VIP. This suggests the involvement of a parasympathetically mediated event in these two individuals. There was no difference between patients with attacks of migraine with aura or without aura; each subject had marked CGRP release.

Table 1

Overview of changes in perivascular neuropeptide levels occurring in acute attacks of primary headache disorders

	NPY	VIP	Substance P	CGRP
Migraine without aura	± 0	± 0	± 0	↑
Migraine with aura	± 0	± 0	± 0	↑
Trigeminal neuralgia	± 0	± 0	± 0	↑
Cluster headache	± 0	↑	± 0	↑
Chronic paroxysmal headache	± 0	↑	± 0	↑

± 0, no change from before headache;

↑

significant increase in neuropeptide level.

The release of CGRP rather than substance P is due to the fact that the cerebral circulation is innervated by CGRP-containing fibres from the trigeminal ganglion (7, 13, 14, 53). These initial clinical observations have been confirmed in subsequent studies in man (31, 54). In addition, following sumatriptan administration, the plasma levels of CGRP returned to control with successful amelioration of the headache (31). The 5-HT_1B/1D receptors are expressed on trigeminal ganglion cells of man (55) and guinea pig (56) and on human trigeminal sensory fibres (57, 58) thus providing sites for presynaptic inhibition of the CGRP release. Durham and Russo (59, 60) have examined this in detail and shown that sumatriptan causes a markedly prolonged increase in intracellular calcium in trigeminal neurons which suggests potential mechanisms involved in the inhibition of CGRP release.

Cluster headache

Cluster headache is a well-described clear–cut clinical syndrome. Patients with episodic cluster headache, fulfilling the criteria of the International Headache Society, were examined during acute spontaneous attacks of headache to determine the local cranial release of neuropeptides (38). During the attacks, the blood levels of both CGRP and VIP were markedly raised while there was no change in NPY or substance P (Table 1). Treatment with oxygen or subcutaneous sumatriptan aborted the pain and normalized the CGRP levels, while opiate administration did not alter the peptide levels. The results show that activation of the cranial sensory and parasympathetic nerves have a role in acute attacks of cluster headache. It was particularly noteworthy that all subjects responded with release of VIP, being in concert with the extracranial symptoms.

The results are in excellent agreement with those of others, who have shown release of CGRP in nitroglycerine-elicited attacks of cluster headache (38, 61, 62). CGRP was elevated during the attack period and was elevated further at the peak of the provoked attack. There was no alteration in substance P levels. Interestingly, only when the subjects were in an active period was nitroglycerine able to elicit an attack of cluster headache (62). This suggests that the trigeminovascular system is hyperreactive at this stage.

Thus, CGRP, a marker of the trigemino-vascular system, and VIP, a marker of the parasympathetic nerve activity, are both elevated in acute spontaneous attacks of cluster headache. The attacks were terminated with either sumatriptan or oxygen and associated with normalized CGRP levels, reflecting cessation of the activity in the trigeminovascular system (38). The finding of elevated levels of both CGRP and VIP during attacks further suggests that there is activation of a brainstem reflex, the afferent arc of which is the trigeminal nerve and the efferent the cranial parasympathetic outflow from the VIIth nerve (30, 63, 64).

Trigeminal neuralgia

In a comparison of normal individuals and of subjects with trigeminal neuralgia (29), there was no alteration in the resting levels of neuropeptides. Stimulation of the trigeminal ganglion during thermocoagulation caused a marked increase in the blood levels of CGRP and substance P, and this was associated with unilateral facial flushing. After cessation of the stimulation, the peptide levels returned towards normal levels.

Vasoactive substances may be responsible not only in the mechanisms that cause headache but also in neuronally mediated facial flushing. This conclusion was supported by study of an unstable trigeminal system in which the pain attacks were associated with rhinorrhea and facial flushing (65). Conventional pharmacological therapy did not provide lasting relief and local facial stimulation by tapping a painful trigger point led to both pain and flushing (65), associated with a marked increase in CGRP levels during the flushing, but without any change in substance P, NPY or VIP.

Chronic paroxysmal hemicrania

Chronic paroxysmal hemicrania (CPH) is a rare syndrome that is defined by the IHS operational diagnostic criteria as frequent short-lasting attacks of unilateral pain usually in the orbital, supra-orbital or temporal regions that may last for 2–45 min (attack frequency, often five or more each day). The pain is associated with prominent autonomic symptoms such as conjunctival injection, lacrimation, nasal congestion, rhinorrhea, ptosis or eyelid oedema. According to the diagnostic criteria that the attacks should settle rapidly upon treatment with indomethacin.

In one such case, we observed that, during pain, the CGRP level rose 3-times compared to the level while the subject was on indomethacin. The VIP level increased 4 times during an attack and normalized upon indomethacin treatment (66). The case report and the accompanying data show that attacks of CPH are characterized by activation of both sensory and parasympathetic cranial nerve fibres. Thus, in this way CPH resembles cluster headache.

Responses to CGRP

CGRP is a potent cerebral vasodilator in all species tested (17). The relative potency of different forms of CGRP varies among species; in the cat middle cerebral artery all CGRP variants induce relaxation to the same degree and potency and much more than does substance P; in human cerebral arteries, the maximum responses to CGRP, substance P, and neurokinin A are similar, but CGRP induces relaxations at 100–1000 times lower concentrations. In general, CGRP is the most potent known vasoactive constituent of trigemino-vascular nerves, by far superseding substance P, neurokinin A, PACAP, amylin, galanin and dynorphine in efficacy and potency (Table 2). In addition, CGRP is about 25-fold more potent as a vasodilator of cerebral as compared to other cranial arteries (43, 67, 68). We interpret this phenomenon as due to the existence of a higher number of CGRP receptors in cerebral as compared to other arteries. This is supported by both histochemical data (69) and the modelling of receptor dynamics outlined by Black and Leff (70).

Table 2

Potency (pEC₅₀; pD₂) and effiacy (Emax) of neuronal messengers found in the trigeminal ganglion of human cerebral (CMA) and middle meningeal arteries (MMA)

	Emax (%)	MMA pD₂	MMA Rel.pot vs. SP	CMA pD₂	CMA Rel.pot vs. SP
CGRP	85–100	8.7 ± 0.2	0.12	10.1 ± 0.2	25.0
Substance P	60–70	9.6 ± 0.2	1.0	8.7 ± 0.2	1.0
Neurokinin A	43–81	7.6 ± 0.4	0.01	7.7 ± 0.3	0.1
PACAP ∗	30	–	–	7.7 ± 0.9	0.1
VIP	60–80	7.5 ± 0.2	0.01	8.6 ± 0.2	0.8
PHM	63–87	6.8 ± 0.1	0.002	7.2 ± 0.2	0.03
Amylin	82	–	–	8.3 ± 0.2	0.4
Helospectin∗	50	–	–	8.8 ± 0.6	1.3
Nociceptin	0	–	–	–	–
Dynorphin	0	–	–	–	–
Galanin	0	–	–	–	–

∗

cat. Emax value, variation in different human studies; PD₂, means from cited human studies(see text); Rel.pot, relative potency as compared to the value of substance P (SP) set as unity.

The relaxant effect of CGRP remains after removal of the endothelium, is paralleled by an increase in adenylate cyclase activity (71) and both effects are blocked by CGRP antagonists (34). CGRP induces a greater dilatation of pial arterioles in situ than substance P (19). Unlike substance P, CGRP does not provoke dilatation of pial veins when given abluminally. The pial arteriolar responses after a single application of CGRP are sustained for several minutes, particularly at high concentrations (19, 50). The potency of CGRP as a cerebrovascular dilator, its sustained action in vivo, its release by capsaicin, the lack of effect of neurokinin antagonists or nitric oxide synthase inhibitors while a CGRP blocker has effect, all point to the involvement of CGRP in the restoration of vascular calibre after vasoconstriction. To understand the role of CGRP released from perivascular nerves relative to circulating CGRP, we used the pressurized middle cerebral artery (MCA) method, a technique allowing discrete investigation of the relative contribution of endothelial and smooth muscle cells to vascular tone. MCAs from Sprague-Dawley rats were mounted onto two glass micropipettes, pressurized to 85 mmHg and luminally perfused. The diameter responses to luminally and abluminally applied α- and β-CGRP, adrenomedullin and amylin were compared relative to the resting diameter. Only abluminally administrated α- and β-CGRP showed significant dilatory effects, mediated through the CGRP receptor (72). The endothelial barrier in the pressurized arteriograph may mimic the in vivo situation preventing the peptides from reaching their receptors in the medial layer.

Some aspects on the activation of the trigeminovascular afferents have been studied using an intravital microscope preparation. Thus, electrical stimulation of the dura mater elicits dilatation of dural blood vessels, a response that is due mainly to the release of CGRP since it can be abolished by CGRP antagonists but not by neurokinin agonists or blockers (73). This and other data have pointed out that substance P is not involved in vascular nociception in man (74).

A recent study in man using SPECT to determine regional cerebral blood flow (rCBF) revealed that systemic infusion of CGRP had minor effects on rCBF (75, 76). Transcranial Doppler used in parallel to determine blood flux velocity in the MCA was seen to result in a reduction during the CGRP infusion, suggesting that CGRP dilated the MCA in vivo. This agrees well with studies in rat, guinea-pig and rabbit where at most minor effects were seen upon CGRP administration (77–79). Chronic surgical division of the trigeminal nerve in cats does not modify local cerebral blood flow, glucose utilization, or the magnitude of the arteriolar responses to perivascular microapplication of either vasconstrictor or vasodilatory agents (49) while stimulation results in local CBF increases that is blocked by a CGRP antagonist (31, 32, 80, 81). However, trigeminal lesion prolongs the duration of the cerebral arteriolar vasoconstriction induced by noradrenaline, prostaglandin F ₂α, barium chloride, alkaline pH and blood without altering the duration of vasodilatatory responses (19, 50). The cerebrovascular trigeminal neuronal system, in which CGRP is the most potent vasoactive constituent, appears to be involved in a reflex or local response to excessive cerebral vasoconstriction that facilitates the restoration of normal diameter (19). It is unclear whether this mechanism is a local response, resulting from direct mechanical stimulation of sensory nerve endings, or whether it is part of a reflex arc with the trigeminal nerve constituting the afferent or efferent limb (Fig. 1).

Figure 1

Schematic illustration of the trigeminovascular reflex as shown by experiments in the cat (19, 50, 51). Irrespective which vasoconstrictor that was used the cortex arterioles dilated back to original diameter in the sensory innervated vessel within one minute but it was markedly prolonged in the trigeminal lesioned animal (CGRP was depleted from these vessels as shown both by immunocytochemistry and radioimmunoassay).

A protective mechanism such as the trigeminovascular reflex may have considerable pathological significance and is supported by clinical data:

Experimental data suggest depletion of CGRP from cerebral vessels in subarachnoid haemorrhage (SAH) (82);

The CGRP levels in cranial venous blood and in CSF correlate with the degree of cerebrovascular constriction in SAH that can be seen with transcranial Doppler (39, 83);

CGRP cannot be detected in cerebral blood vessels of patients that have died due to SAH (84), putatively because the peptide has been released in an unsuccessful attempt to maintain adequate levels of blood flow. In the same patients, cerebrovascular levels of other perivascular vasoactive peptides were close to the levels found in normal subjects.

Administration of CGRP to patients with symptomatic vasospasm can reverse the contraction if the blood pressure is carefully monitored (40) or in primates the administration of CGRP prevents cerebral vasospasm after a subsequent experimental SAH (85).

Thus, a vasomotor role in the trigemino-cerebrovascular system would not be to the exclusion of its involvement in nociception since intense pain often accompanies a SAH. The role of the trigemino-vascular system is almost the exact counterpart of the role of perivascular sympathetic fibres; the function of the vasoconstrictor system is not to reduce cerebral blood flow but rather to attenuate or prevent excessive vasodilatation, for example, extreme hypertension (86). The function of the vasodilatory trigeminal system is not to increase cerebral blood flow but rather to attenuate excessive cerebral vasoconstriction. The involvement of cerebrovascular autonomic fibres in situations where extremes of cerebral perfusion threatens the survival of neurons in the CNS does not require any reappraisal of the primacy of cerebral metabolism rather than neurogenic factors in determining tissue perfusion on a moment-to-moment basis.

CGRP receptors

CGRP is present in two forms α- and β-CGRP. Calcitonin and α-CGRP are transcribed from the same gene, while β-CGRP is formed from a separate CGRP gene (24, 25, 87, 88). Early pharmacological studies of CGRP receptors focused on the use of CGRP agonists and the CGRP fragment CGRP_8-37 to discriminate between the CGRP receptor subtypes (27). The use of peptide antagonists to classify CGRP receptors has been criticized since experimental conditions may sometimes change the actions of these peptides and thereby limit their ability to reliably discriminate CGRP receptor subtypes (89).

Subsequent cloning efforts have resulted in the molecular identification of the CGRP receptor (Fig. 2) (90). Calcitonin receptor like receptor (CRLR) is a G_s-coupled seven-transmembrane domain G-protein-coupled receptor (GPCR) that shares 55% sequence identity with the calcitonin receptor. McLatchie et al. (91) demonstrated that functional CGRP and adrenomedullin receptors are both derived from CRLR and that the phenotype is determined by co-expression with a particular receptor activity modifying protein, RAMP. Co-expression of CRLR with RAMP1 results in CGRP receptor pharmacology while CRLR and RAMP2 or RAMP3 co-expression form adrenomedullin receptors. RAMPs are relatively small proteins(148–175 amino acids) containing a single membrane spanning domain, a large extracellular domain, and a short cytoplasmic domain (92). Three biological functions have been defined for RAMPs:

Figure 2

Demonstration of the RT-PCR product (339 base pair long) corresponding to mRNA encoding the human CGRP₁ receptor in human cerebral (C), middle meningeal (M) and temporal arteries (T) (99).

They enable expression of CRLR on the cell surface and thereby determine the relative affinity of this receptor for CGRP and adrenomedullin (92);

CRLR internalization following CGRP stimulation has been shown to occur together with RAMP1, and both proteins are targeted to the protein degradation pathway (93). Although the receptors resulting from co-expression of CRLR with either RAMP1 or RAMP2/3 are functionally distinct, CGRP and adrenomedullin displayed some cross-reactivity for the opposite receptor (91);

RAMP proteins have, in addition, been shown to modulate the pharmacology of the calcitonin receptor, which in combination with RAMP1 or RAMP3, will bind amylin with high affinity (94, 95).

In addition to the RAMPs, the CGRP receptor may require another accessory protein for its function, the receptor component protein (RCP) (96). By using cell lines which express antisense RCP mRNA, it was demonstrated that the ability of CGRP to stimulate cAMP production was attenuated, although ¹²⁵I-CGRP binding was unaffected (97). These observations suggest that RCP does not function as a molecular chaperone, but may instead be involved in coupling of the receptor to downstream signalling pathways. RAMP1 is required for glycosylation and proper transport of CRLR to the plasma membrane and RCP is necessary for coupling of the receptor to the cellular signal transduction machinery. Whether RCP is utilized by other GPCRs for G-protein signalling remains to be determined.

Pharmacological studies of cerebral and meningeal vessels from laboratory animals and man early revealed that CGRP-receptors dominate by inducing maximum dilatation while the responses to amylin and adrenomedullin are minor and mediated by the CGRP₁ receptor (17, 22, 42, 98). The CGRP induced relaxation is endothelium independent and occurs in parallel with activation of adenylyl cyclase both in man (35, 41, 42, 68, 98) and in the cat (71). CGRP receptor mRNA has been demonstrated in human cranial arteries and in the human trigeminal ganglion (53, 99), thus demonstrating possible post- and pre-junctional CGRP receptors. Studies have, in addition demonstrated the expression of mRNAs encoding CRLR and all three RAMPs in the smooth muscle cell layer of human cranial arteries (69, 100). However, functionally it is the CGRP₁ receptor profile that dominates.

Non-Peptide CGRP Receptor Antagonists

A breakthrough in the CGRP field came recently when researchers at Boehringer Ingelheim developed small molecules that were proven to be potent antagonists for the CGRP receptor; BIBN4096BS and compound 1 (101–107). The more potent of these, BIBN4096BS demonstrates extremely high affinity for human CGRP receptors expressed in SK-NM-C cells with an apparent pA₂ value in the pM range. Interestingly, both antagonists are 2 or 3 log units more potent in human tissues as compared to that seen in experimental animals. The high affinity of BIBN4096BS and compound 1 for hCRLR/hRAMP1 was unusual and therefore analysed in detail. It was observed that this species selectivity was dictated strictly by hRAMP1 (108). The region between amino acids 66–112 was seen to be critical for determining the pharmacology. The exact molecular mechanisms by which RAMP1 modulates the antagonist binding apparently resides in a mutation of only one amino acid (108).

BIBN4096BS dose-dependently inhibits vasodilatation induced by electrical stimulation of the trigeminal ganglion in the marmoset (101). The results demonstrated that BIBN4096BS is a potent inhibitor of neurogenic vasodilatation, a putative model for antimigraine potential. In a separate report, BIBN4096BS and CGRP_8-37 were shown to block the development of tolerance to morphine (109), further supporting the role of CGRP receptors in nociception. α-CGRP is, in human cerebral vessels, significantly more potent as a vasodilator than it is in peripheral, coronary, meningeal and temporal arteries (41, 68) and in addition BIBN4096BS acts as an excellent antagonist (102, 110, 111) (Fig. 3).

Figure 3

Relaxant effect of α-CGRP in human cerebral arteries (○, control) and the inhibition of this response by BIBN4096BS in increasing concentrations (shown as log M concentration); □ BIBN 10⁻¹⁰ M, ▪ BIBN 3 10⁻⁹ M, • BIBN 10⁻⁹ M. A clear parallel shift to the right indicate the competitive nature of the antagonist at the CGRP receptor (102).

The second small molecule, Compound 1, has been studied on CGRP induced responses in human cranial arteries (103). Compound 1 displaced ¹²⁵I-CGRP from SK-N-MC cells and antagonized CGRP-induced cAMP production in the same cells with pA₂ values of about 8. On human isolated cerebral arteries, Compound 1 caused a parallel shift to the right of the concentration-effect curve to CGRP without changing the maximum response, yielding a pA₂ value of 10 nm. In the same type of tests BIBN4096BS was about 2 log units more potent than Compound 1 as CGRP receptor antagonist (102). Based on these observations, it is likely that both compounds act at CGRP₁ receptors, composed of CRLR and RAMP1 on human cerebral arteries.

A third small CGRP antagonistic molecule was recently presented, SB-(+)-273779, a selective nonpeptide antagonist of the CGRP₁ receptor (112). SB-(+)-273779 inhibited CGRP binding to SK-N-MC, the human cloned CGRP₁ receptor and the CGRP(3 nm)-activated adenylyl cyclase. Experiments on SK-N-MC cells with SB-(+)-273779 resulted in reduction in maximum CGRP-mediated adenylyl cyclase activity, which suggests that this compound has irreversible binding characteristics. In addition, SB-(+)-273779 antagonized the CGRP-mediated increase in intracellular calcium ions in recombinant CGRP receptors in HEK-293 cells, inhibition of insulin-stimulated deoxyglucose uptake in L6 cells, vasodilation in rat pulmonary artery, and decrease in blood pressure in anaesthetized rats. SB-(+)-273779, tested at 3 µm, had no significant affinity for calcitonin, endothelin, angiotensin II, and α-adrenergic receptors, or on responses to forskolin or PACAP. Thus, SB-(+)-273779 is a valuable tool for studying CGRP-mediated functional responses in various biological systems since it did not appear selective for human CGRP receptors as are BIBN 4096BS and Compound 1.

Is there a need for a CGRP antagonist in migraine?

CGRP has long been regarded as a useful target for the development of novel antimigraine therapies. The excellent correlation between CGRP release and migraine headache has long pointed to the potential usefulness of a specific CGRP antagonist in the treatment of primary headache (36). It was observed that the triptans have the ability to inhibit the release of CGRP (30, 31, 38) via 5-HT_1B/1D receptors on the sensory nerves (55–57,113) but these agents all suffer from cardiovascular side-effects of 3–5% in clinical trials to mild chest symptoms in up to 30–40% in clinical practice (114). The recent progress in the demonstration of the unique molecular biology and functional organization of the CGRP family of receptors has provided a detailed and unique understanding of the various elements of the receptor function. The development of small nonpeptide molecules with selectivety for human CGRP receptors has opened up the possibility to examine this in clinical studies.

At present CGRP is the only transmitter reliably found to be released in primary headaches. From our histochemical studies of human cranial arteries and trigeminal ganglia it has been shown that at least half of the cell bodies contain CGRP (53), but several other peptides and nitric oxide synthase are present in the trigeminal ganglion. In addition, the human CGRP-containing neurons express 5-HT_1B/1D receptors (55), the activation of these reduce the CGRP release via a presynaptic inhibition via 5-HT_1B/1D receptors which then can ameliorate the headache (31, 38). Ongoing clinical trials with BIBN4096BS in man have provided some answers; CGRP antagonism is effective in the treatment of acute migraine attacks and has no significant site effects (115). In a recent study the blocker was seen to have an efficacy similar to that of oral sumatriptan study; thus, BIBN4096BS had an effect of about 60% in doses up to 10 mg/patient given intravenously (116). Since there is at present no evidence that the novel CGRP receptor antagonists have direct contractile effects on human vasculature (101–103, 110, 111, 117) this may prove to be a significant advantage over the triptans given they have similar efficacy on the acute attacks.

Conclusion

Migraine is a common health problem that afflicts up to 15% of the adult population worldwide, it is present in children and the elderly but at lower frequency. It poses a considerable socio-economic burden to the individual and to society. The scientific work in the last decade has unravelled much of the pathophysiological background and suggests that it is a neurovascular disease. The developments of drugs of the triptan class has provided relief for the acute attacks at the cost of some side-effects, thus there still exists ample possibilities for improvements in the treatment. The discovery that the trigemino-vascular system is involved with release of CGRP, associated with the pain, during acute migraine and cluster headache attacks, provides the opportunity to directly block this receptor as a new target. Furthermore, CGRP administration in man may result in migraine attacks (118) and this response can be effectively aborted by administration of BIBN4096BS (76). The triptans have been found to act in part via presynaptic blockade of the release of CGRP. This has prompted the development of CGRP antagonists and in fact it has now been disclosed that one CGRP antagonist (BIBN4096BS) works to alleviate the acute migraine attack without significant side-effects and thus proves the concept. Further development of drugs against this receptor type will provide a significant therapeutic advance in the field of antimigraine drugs.

Footnotes

Acknowledgements

The studies of the authors’ reviewed have been supported by the Swedish Research Council (project no. 5958).

References

Ray

Wolff

HG.

Experimental studies on headaches, pain sensitive structures of the head and their significance in headaches. Arch Surg 1940; 41: 813–56.

Olesen

Tfelt-Hansen

Welch

KMA.

The Headaches. Philadelphia: Lippincott Williams & Wilkins, 2000.

Lembeck

Gamse

Substance P in peripheral sensory processes. Ciba Found Symp 1982: 35–54.

Brain

Cambridge

Calcitonin gene-related peptide: vasoactive effects and potential therapeutic role. General Pharmacol 1996; 27: 607–11.

Gulbenkian

Uddman

Edvinsson

Neuronal messengers in the human cerebral circulation. Peptides 2001; 22: 995–1007.

Edvinsson

Functional role of perivascular peptides in the control of cerebral circulation. Trends Neurosci 1985; 8: 126–31.

Edvinsson

Hara

Uddman

Retrograde tracing of nerve fibers to the rat middle cerebral artery with true blue: colocalization with different peptides. J Cereb Blood Flow Metab 1989; 9: 212–8.

Edvinsson

Elsas

Suzuki

Shimizu

Lee

TJ.

Origin and Co-localization of nitric oxide synthase, CGRP, PACAP, and VIP in the cerebral circulation of the rat. Microsc Res Tech 2001; 53: 221–8.

Keller

Marfurt

CF.

Peptidergic and serotoninergic innervation of the rat dura mater. J Comp Neurol 1991; 309: 515–34.

10.

Kawaja

MD.

Sympathetic and sensory innervation of the extracerebral vasculature. roles for p75NTR neuronal expression and nerve growth factor. J Neurosci Res 1998; 52: 295–306.

11.

Messlinger

Hanesch

Baumgartel

Trost

Schmidt

RF.

Innervation of the dura mater encephali of cat and rat: ultrastructure and calcitonin gene-related peptide-like and substance P-like immunoreactivity. Anat Embryol (Berl) 1993; 188: 219–37.

12.

Nakakita

Peptidergic innervation in the cerebral blood vessels of the guinea pig: an immunohistochemical study. J Cereb Blood Flow Metab 1990; 10: 819–26.

13.

Uddman

Edvinsson

Hara

Axonal tracing of autonomic nerve fibers to the superficial temporal artery in the rat. Cell Tissue Res 1989; 256: 559–65.

14.

Uddman

Hara

Edvinsson

Neuronal pathways to the rat middle meningeal artery revealed by retrograde tracing and immunocytochemistry. J Auton Nerv Syst 1989; 26: 69–75.

15.

You

Gulbenkian

Jansen Olesen

Marron

Wharton

Barroso

, Peptidergic innervation of guinea-pig brain vessels: comparison with immunohistochemistry and in vitro pharmacology in rostrally and caudally located arteries. J Auton Nerv Syst 1995; 55: 179–88.

16.

Suzuki

Hardebo

Owman

Origins and pathways of cerebrovascular nerves storing substance P and calcitonin gene-related peptide in the rat. Neuroscience 1989; 31: 427–38.

17.

Edvinsson

Ekman

Jansen

McCulloch

Uddman

Calcitonin gene-related peptide and cerebral blood vessels. distribution and vasomotor effects. J Cereb Blood Flow Metab 1987; 7: 720–8.

18.

Uddman

Edvinsson

Ekman

Kingman

McCulloch

Innervation of the feline cerebral vasculature by nerve fibers containing calcitonin gene-related peptide. trigeminal origin and co-existence with substance P. Neurosci Lett 1985; 62: 131–6.

19.

McCulloch

Uddman

Kingman

Edvinsson

Calcitonin gene-related peptide: functional role in cerebrovascular regulation. Proc Natl Acad Sci U S A 1986; 83: 5731–5.

20.

Edvinsson

Brodin

Jansen

Uddman

Neurokinin

in cerebral vessels: characterization localization and effects in vitro. Regul Pept 1988; 20: 181–97.

21.

Barroso

Edvinsson

Zhang

Cunha e Sa

Springall

Polak

, Nitroxidergic innervation of guinea pig cerebral arteries. J Auton Nerv Syst 1996; 58: 108–14.

22.

Edvinsson

Goadsby

Uddman

Amylin. localization, effects on cerebral arteries and on local cerebral blood flow in the cat. Thescientificworld 2001; 1: 168–80.

23.

Hou

Uddman

Tajti

Edvinsson

Nociceptin immunoreactivity and receptor mRNA in the human trigeminal ganglion. Brain Res 2003; 964: 179–86.

24.

Amara

Jonas

Rosenfeld

Ong

Evans

Alternative

RNA.

processing in calcitonin gene expression generates mRNAs encoding different polypeptide products. Nature 1982; 298: 240–4.

25.

Steenbergh

Höppener

JWM

Zandberg

Lips

CJM

Jansz

second human calcitonin/CGRP gene. FEBS Lett 1985; 183: 403–7.

26.

Sexton

PM.

Central nervous system binding sites for calcitonin and calcitonin gene-related peptide. Mol Neurobiol 1991; 5: 251–73.

27.

The CGRP Family: Calcitonin Gene-Related Peptide (CGRP), Amylin and Adrenomedullin. In: Poyner

Marshall

Brain

, editors. Georgetown: Landes Bioscience, 2000: 1–261.

28.

Uddman

Edvinsson

Ekblad

Hakanson

Sundler

Calcitonin gene-related peptide (CGRP): perivascular distribution and vasodilatory effects. Regul Pept 1986; 15: 1–23.

29.

Goadsby

Edvinsson

Ekman

Release of vasoactive peptides in the extracerebral circulation of humans and the cat during activation of the trigeminovascular system. Ann Neurol 1988; 23: 193–6.

30.

Goadsby

Edvinsson

Joint 1994 Wolff Award Presentation. Peripheral and central trigeminovascular activation in cat is blocked by the serotonin (5HT) -1D receptor agonist 311C90. Headache 1994; 34: 394–9.

31.

Goadsby

Edvinsson

The trigeminovascular system and migraine. studies characterizing cerebrovascular and neuropeptide changes seen in humans and cats. Ann Neurol 1993; 33: 48–56.

32.

Goadsby

PJ.

Inhibition of calcitonin gene-related peptide by h-CGRP (8–37) antagonizes the cerebral dilator response from nasociliary nerve stimulation in the cat. Neurosci Lett 1993; 151: 13–6.

33.

Edvinsson

Jansen

Kingman

McCulloch

Cerebrovascular responses to capsaicin in vitro and in situ. Br J Pharmacol 1990; 100: 312–8.

34.

Jansen-Olesen

Mortensen

Edvinsson

Calcitonin gene-related peptide is released from capsaicin-sensitive nerve fibres and induces vasodilatation of human cerebral arteries concomitant with activation of adenylyl cyclase. Cephalalgia 1996; 16: 310–6.

35.

Jansen

Alafaci

Uddman

Edvinsson

Evidence that calcitonin gene-related peptide contributes to the capsaicin-induced relaxation of guinea pig cerebral arteries. Regul Pept 1990; 31: 167–78.

36.

Edvinsson

Aspects on the pathophysiology of migraine and cluster headache. Pharmacol Toxicol 2001; 89: 65–73.

37.

Goadsby

Edvinsson

Ekman

Vasoactive peptide release in the extracerebral circulation of humans during migraine headache. Ann Neurol 1990; 28: 183–7.

38.

Goadsby

Edvinsson

Human in vivo evidence for trigeminovascular activation in cluster headache. Neuropeptide changes and effects of acute attacks therapies. Brain 1994; 117: 427–34.

39.

Juul

Edvinsson

Gisvold

Ekman

Brubakk

Fredriksen

TA.

Calcitonin gene-related peptide-LI in subarachnoid haemorrhage in man. Signs of activation of the trigemino-cerebrovascular system?

Br J Neurosurg 1990; 4: 171–9.

40.

Juul

Aakhus

Bjornstad

Gisvold

Brubakk

Edvinsson

Calcitonin gene-related peptide (human alpha-CGRP) counteracts vasoconstriction in human subarachnoid haemorrhage. Neurosci Lett 1994; 170: 67–70.

41.

Edvinsson

Ekman

Jansen

Ottosson

Uddman

Peptide-containing nerve fibers in human cerebral arteries: immunocytochemistry, radioimmunoassay, and in vitro pharmacology. Ann Neurol 1987; 21: 431–7.

42.

Jansen

Mortensen

Edvinsson

Characterization of calcitonin gene-related peptide receptors in human cerebral vessels. Vasomotor responses and cAMP accumulation. Ann NY Acad Sci 1992; 657: 435–40.

43.

Jansen

Uddman

Ekman

Olesen

Ottosson

Edvinsson

Distribution and effects of neuropeptide Y, vasoactive intestinal peptide, substance P, and calcitonin gene-related peptide in human middle meningeal arteries: comparison with cerebral and temporal arteries. Peptides 1992; 13: 527–36.

44.

Akerman

Williamson

Kaube

Goadsby

PJ.

Nitric oxide synthase inhibitors can antagonize neurogenic and calcitonin gene-related peptide induced dilation of dural meningeal vessels. Br J Pharmacol 2002; 137: 62–8.

45.

Messlinger

Suzuki

Pawlak

Zehnter

Schmidt

RF.

Involvement of nitric oxide in the modulation of dural arterial blood flow in the rat. Br J Pharmacol 2000; 129: 1397–404.

46.

Strecker

Dux

Messlinger

Increase in meningeal blood flow by nitric oxide – interaction with calcitonin gene-related peptide receptor and prostaglandin synthesis inhibition. Cephalalgia 2002; 22: 233–41.

47.

Williamson

Shepheard

Hill

Hargreaves

RJ.

The novel anti-migraine agent rizatriptan inhibits neurogenic dural vasodilation and extravasation. Eur J Pharmacol 1997; 328: 61–4.

48.

Williamson

Hargreaves

Hill

Shepheard

SL.

Sumatriptan inhibits neurogenic vasodilation of dural blood vessels in the anaesthetized rat – intravital microscope studies. Cephalalgia 1997; 17: 525–31.

49.

Edvinsson

McCulloch

Kingman

Uddman

On the functional role of the trigemino-cerebrovascular system in the regulation of cerebral circulation. In: Owman

Hardebo

, editors. Neural Regulation of the Cerebral Circulation. Amsterdam: Elsevier Science, 1986: 407–18.

50.

Edvinsson

Jansen Olesen

Kingman

McCulloch

Uddman

Modification of vasoconstrictor responses in cerebral blood vessels by lesioning of the trigeminal nerve: possible involvement of CGRP. Cephalalgia 1995; 15: 373–83.

51.

Edvinsson

Jansen

Kingman

McCulloch

Cerebrovascular responses to capsaicin in vitro and in situ. Br J Pharmacol 1990; 100: 312–31.

52.

Kors

van den Maagdenberg

Plomp

Frants

Ferrari

MD.

Calcium channel mutations and migraine. Curr Opin Neurol 2002; 15: 311–6.

53.

Tajti

Uddman

Moller

Sundler

Edvinsson

Messenger molecules and receptor mRNA in the human trigeminal ganglion. J Auton Nerv Syst 1999; 76: 176–83.

54.

Gallai

Sarchielli

Floridi

Franceschini

Codini

Glioti

, Vasoactive peptide levels in the plasma of young migraine patients with and without aura assessed both interictally and ictally. Cephalalgia 1995; 15: 384–90.

55.

Hou

Kanje

Longmore

Tajti

Uddman

Edvinsson

5-HT (1B) and 5-HT (1D) receptors in the human trigeminal ganglion. co-localization with calcitonin gene-related peptide, substance P and nitric oxide synthase. Brain Res 2001; 909: 112–20.

56.

Hill

Sirinathsinghji

Colocalization of CGRP with 5-HT1B/1D receptors and substance P in trigeminal ganglion neurons in rats. Eur J Neurosci 2001; 13: 2099–104.

57.

Smith

Hill

Edvinsson

Longmore

An immunocytochemical investigation of human trigeminal nucleus caudalis: CGRP, substance P and 5-HT1D-receptor immunoreactivities are expressed by trigeminal sensory fibres. Cephalalgia 2002; 22: 424–31.

58.

Uddman

Tajti

Hou

Sundler

Edvinsson

Neuropeptide expression in the human trigeminal nucleus caudalis and in the cervical spinal cord C1 and C2. Cephalalgia 2002; 22: 112–6.

59.

Durham

Russo

AF.

Regulation of calcitonin gene-related peptide secretion by a serotonergic antimigraine drug. J Neurosci 1999; 19: 3423–9.

60.

Durham

Sharma

Russo

AF.

Repression of the calcitonin gene-related peptide promotor by 5-HT₁ receptor activation. J Neurosci 1997; 17: 9545–53.

61.

Fanciullacci

Alessandri

Figini

Geppetti

Michelacci

Increase in plasma calcitonin gene-related peptide from the extracerebral circulation during nitroglycerin-induced cluster headache attack. Pain 1995; 60: 119–23.

62.

Fanciullacci

Alessandri

Sicuteri

Marabini

Responsiveness of the trigeminovascular system to nitroglycerine in cluster headache patients. Brain 1997; 120: 283–8.

63.

Zagami

Goadsby

Edvinsson

Stimulation of the superior sagittal sinus in the cat causes release of vasoactive peptides. Neuropeptides 1990; 16: 69–75.

64.

Bolay

Reuter

Dunn

Huang

Boas

Moskowitz

MA.

Intrinsic brain activity triggers trigeminal meningeal afferents in a migraine model. Nat Med 2002; 8: 136–42.

65.

Goadsby

Edvinsson

Ekman

Cutaneous sensory stimulation leading to facial flushing and release of calcitonin gene-related peptide. Cephalalgia 1992; 12: 53–6.

66.

Goadsby

Edvinsson

Neuropeptide changes in a case of chronic paroxysmal hemicrania – evidence for trigemino-parasympathetic activation. Cephalalgia 1996; 16: 448–50.

67.

Jansen

Uddman

Hocherman

Ekman

Jensen

Olesen

, Localization and effects of neuropeptide Y, vasoactive intestinal polypeptide, substance P, and calcitonin gene-related peptide in human temporal arteries. Ann Neurol 1986; 20: 496–501.

68.

Edvinsson

Gulbenkian

Barroso

Cunha e Sa

Polak

Mortensen

, Innervation of the human middle meningeal artery: immunohistochemistry, ultrastructure, and role of endothelium for vasomotility. Peptides 1998; 19: 1213–25.

69.

Oliver

Wainwright

Edvinsson

Pickard

Hill

RG.

Immunohistochemical localization of calcitonin receptor-like receptor and receptor activity-modifying proteins in the human cerebral vasculature. J Cereb Blood Flow Metab 2002; 22: 620–9.

70.

Black

Leff

. Operational models of pharmacological agonism. Proc R Soc Lond 1983; 220: 141–62.

71.

Edvinsson

Fredholm

Hamel

Jansen

Verrecchia

Perivascular peptides relax cerebral arteries concomitant with stimulation of cyclic adenosine monophosphate accumulation or release of an endothelium-derived relaxing factor in the cat. Neurosci Lett 1985; 58: 213–7.

72.

Petersen

Nilsson

Olesen

Edvinsson

Only abluminally applied CGRP induces rat pial artery dilatation in vitro and in vivo. Cephalalgia 2003; 23: 647.

73.

Williamson

Hargreaves

Hill

Shepheard

SL.

Intravital microscope studies on the effects of neurokinin agonists and calcitonin gene-related peptide on dural blood vessel diameter in anaesthetized rat. Cephalalgia 1997; 17: 518–24.

74.

Holfhusen

Kindgen-Milles

Ding

ZP.

Substance P is not involved in vascular nociception in humans. Neuropeptides 1997; 31: 445–8.

75.

Lassen

Jacobsen

Haderslev

Sperling

Iversen

Olesen

The effect of intravenous infusion of hCGRP on cerebral arteries and regional cerebral blood flow in man. Cephalalgia 2004 in press.

76.

Petersen

Lassen

Birk

Olesen

The effect of the nonpeptide CGRP-antagonist, BIBN4096BS on human-alphaCGRP induced headache and hemodynamics in healthy volunteers. Cephalalgia 2003; 23: 725.

77.

Beattie

McNeil

Conner

HE.

The influence of neurokinins and calcitonin gene-related peptide on cerebral blood flow in anaesthetized guinea-pigs. Neuropeptides 1993; 24: 343–9.

78.

Suzuki

Satoh

Ikegaki

Okada

Shibuya

Sugita

, Effects of neuropeptide Y and calcitonin gene-related peptide on local cerebral blood flow in rat striatum. J Cereb Blood Flow Metab 1989; 9: 268–70.

79.

Martin

Nelson

Perry

Pickard

JD.

The cerebrovascular and cardiovascular effects of calcitonin gene-related peptide (CGRP) in anaesthetied rabbit. J Physiol 1990; 427: 34.

80.

Tsukahara

Fukuda

Suzuki

Maruyama

Sakai

Role of CGRP receptors in cerebral blood flow increase upon trigeminovascular activation in rats. Cephalalgia 2003; 23: 651.

81.

Edvinsson

Mulder

Goadsby

Uddman

Calcitonin gene-related peptide and nitric oxide in the trigeminal ganglion: cerebral vasodilatation from trigeminal nerve stimulation involves mainly calcitonin gene-related peptide. J Auton Nerv Syst 1998; 70: 15–22.

82.

Edvinsson

Delgado-Zygmunt

Ekman

Jansen

Svendgaard

Uddman

Involvement of perivascular sensory fibers in the pathophysiology of cerebral vasospasm following subarachnoid hemorrhage. J Cereb Blood Flow Metab 1990; 10: 602–7.

83.

Juul

Hara

Gisvold

Brubakk

Fredriksen

Waldemar

, Alterations in perivascular dilatory neuropeptides (CGRP, SP, VIP) in the external jugular vein and in the cerebrospinal fluid following subarachnoid haemorrhage in man. Acta Neurochir (Wien) 1995; 132: 32–41.

84.

Edvinsson

Ekman

Jansen

McCulloch

Mortensen

Uddman

Reduced levels of calcitonin gene-related peptide-like immunoreactivity in human brain vessels after subarachnoid haemorrhage. Neurosci Lett 1991; 121: 151–4.

85.

Inoue

Shimizu

Kaminuma

Tajima

Watabe

Yoshimoto

Prevention of cerebral vasospasm by calcitonin gene-related peptide slow-release tablet after subarachnoid hemorrhage in monkeys. Neurosurgery 1996; 39: 984–90.

86.

Edvinsson

Krause

DN.

Cerebral Blood Flow and Metabolism. Philadelphia: Lippincott Williams & Wilkins, 2002.

87.

Rosenfeld

Mermod

Amara

Swanson

Sawchenko

Rivier

, Production of a novel neuropeptide encoded by the calcitonin gene via tissue-specific RNA processing. Nature 1983; 304: 129–35.

88.

Rosenfeld

Amara

Roos

Ong

Evans

RM.

Altered expression of the calcitonin gene associated with RNA polymorphism. Nature 1981; 290: 63–5.

89.

Waugh

Bockman

Smith

Abel

PW.

Limitations in using peptide drugs to characterize calcitonin gene-related peptide receptors. J Pharmacol Exp Ther 1999; 289: 1419–26.

90.

Aiyar

Rand

Elshourbagy

Zeng

Adamou

Bergsma

, encoding the calcitonin gene-related peptide type 1 receptor. J Biol Chem 1996; 271: 11325–9.

91.

McLatchie

Fraser

Main

Wise

Brown

Thompson

, Ps. regulate the transport and ligand specificity of the calcitonin-receptor-like receptor. Nature 1998; 393: 333–9.

92.

Foord

Marshall

FH.

RAMPs. accessory proteins for seven transmembrane domain receptors. Trends Pharmacol Sci 1999; 20: 184–7.

93.

Kuwasako

Shimekake

Masuda

Nakahara

Yoshida

Kitaura

, Visualization of the calcitonin receptor-like receptor and its receptor activity-modifying proteins during internalization and recycling. J Biol Chem 2000; 275: 29602–9.

94.

Armour

Foord

Kenakin

Chen

WJ.

Pharmacological characterization of receptor-activity-modifying proteins (RAMPs) and the human calcitonin receptor. J Pharmacol Toxicol Meth 1999; 42: 217–24.

95.

Christopoulos

Perry

Morfis

Tilakaratne

Gao

Fraser

, Multiple amylin receptors arise from receptor activity-modifying protein interaction with the calcitonin receptor gene product. Mol Pharmacol 1999; 56: 235–42.

96.

Luebke

Dahl

Roos

Dickerson

IM.

Identification of a protein that confers calcitonin gene-related peptide responsiveness to oocytes by using a cystic fibrosis transmembrane conductance regulator assay. Proc Natl Acad Sci USA 1996; 93: 3455–60.

97.

Evans

Rosenblatt

Mnayer

Oliver

Dickerson

IM.

CGRP-RCP, a novel protein required for signal transduction at calcitonin gene-related peptide and adrenomedullin receptors. J Biol Chem 2000; 275: 31438–43.

98.

Jansen-Olesen

Kaarill

Edvinsson

Characterization of CGRP(1) receptors in the guinea pig basilar artery. Eur J Pharmacol 2001; 414: 249–58.

99.

Edvinsson

Cantera

Jansen Olesen

Uddman

Expression of calcitonin gene-related peptide 1 receptor mRNA in human trigeminal ganglia and cerebral arteries. Neurosci Lett 1997; 229: 209–11.

100.

Sams

Jansen-Olesen

Expression of calcitonin receptor-like receptor and receptor-activity-modifying proteins in human cranial arteries. Neurosci Lett 1998; 258: 41–4.

101.

Doods

Hallermayer

Entzeroth

Rudolf

Engel

, Pharmacological profile of BIBN4096BS, the first selective small molecule CGRP antagonist. Br J Pharmacol 2000; 129: 420–3.

102.

Edvinsson

Alm

Shaw

Rutledge

Koblan

Longmore

, Effect of the CGRP receptor antagonist BIBN4096BS in human cerebral, coronary and omental arteries and in SK-N-MC cells. Eur J Pharmacol 2002; 434: 49–53.

103.

Edvinsson

Sams

Jansen-Olesen

Tajti

Kane

Rutledge

, Characterisation of the effects of a non-peptide CGRP receptor antagonist in SK-N-MC cells and isolated human cerebral arteries. Eur J Pharmacol 2001; 415: 39–44.

104.

Hay

Howitt

Conner

Doods

Schindler

Poyner

DR.

A comparison of the actions of BIBN4096BS and CGRP (8–37) on CGRP and adrenomedullin receptors expressed on SK-N-MC, L6, Col 29 and Rat 2 cells. Br J Pharmacol 2002; 137: 80–6.

105.

Hasbak

Opgaard

Eskesen

Schifter

Arendrup

Longmore

, Investigation of CGRP receptors and peptide pharmacology in human coronary arteries. Characterization with a nonpeptide antagonist. J Pharmacol Exp Ther 2003; 304: 326–33.

106.

Moreno

Terron

Stanimirovic

Doods

Hamel

Characterization of calcitonin gene-related peptide (CGRP) receptors and their receptor-activity-modifying proteins (RAMPs) in human brain microvascular and astroglial cells in culture. Neuropharmacology 2002; 42: 270–80.

107.

van Zwieten

Doods

HN.

Effects of calcitonin gene-related peptide and BIBN4096BS on myocardial ischemia in anesthetized rats. Acta Pharmacol Sin 2001; 22: 588–94.

108.

Mallee

Salvatore

LeBourdelles

Oliver

Longmore

Koblan

, Receptor activity-modifying protein 1 determines the species selectivity of non-peptide CGRP receptor antagonists. J Biol Chem 2002; 277: 14294–8.

109.

Powell

Sutak

Doods

Quirion

Jhamandas

Blockade and reversal of spinal morphine tolerance by peptide and non-peptide calcitonin gene-related peptide receptor antagonists. Br J Pharmacol 2000; 131: 875–84.

110.

Moreno

Abounader

Hebert

Doods

Hamel

Efficacy of the non-peptide CGRP receptor antagonist BIBN4096BS in blocking CGRP-induced dilations in human and bovine cerebral arteries: potential implications in acute migraine treatment. Neuropharmacology 2002; 42: 568–76.

111.

Verheggen

Bumann

Kaumann

AJ.

BIBN4096BS is a potent competitive antagonist of the relaxant effects of a-CGRP on human temporal artery: comparison with CGRP (8–37). Br J Pharmacol 2002; 136: 120–6.

112.

Aiyar

Daines

Disa

Chambers

Sauermelch

Quiniou

, Pharmacology of SB-273779, a nonpeptide calcitonin gene-related peptide 1 receptor antagonist. J Pharmacol Exp Ther 2001; 296: 768–75.

113.

Longmore

Shaw

Smith

Hopkins

McAllister

Pickard

, Differential distribution of 5-HT1D- and 5-HT1B-immunoreactivity within the human trigemino-cerebrovascular system: implication for the discovery of new antimigraine drugs. Cephalalgia 1997; 17: 833–42.

114.

Visser

Jaspers

de Vriend

Ferrari

MD.

Chest symptoms after sumatriptan: a two-year clinical practice review in 735 consecutive migraine patients. Cephalalgia 1996; 16: 554–9.

115.

Petersen

Birk

Lassen

Kruuse

Jonassen

Olesen

The novel CGRP-antagonist, BIBN4096BS does not affect cerebral hemodynamics in healthy volunteers. Cephalalgia 2003; 23: 729.

116.

Olesen

Diener

Husstedt

Goadsby

Hall

Meier

, Calcitonin gene-related peptide receptor antagonist BIBN4096BS for the acute treatment of migraine. N Engl J Med 2004; 350: 1104–10.

117.

Doods

Development of CGRP antagonists for the treatment of migraine. Curr Opin Invest Drugs 2001; 2: 1261–8.

118.

Lassen

Haderslev

Jacobsen

Iversen

Sperling

Olesen

CGRP may play a causative role in migraine. Cephalalgia 2002; 22: 54–61.