Effects of the calcitonin gene-related peptide (CGRP) receptor antagonist BIBN4096BS on alpha-CGRP-induced regional haemodynamic changes in anaesthetised rats

Several studies suggest that a calcitonin gene-related peptide (CGRP) receptor antagonist may have antimigraine properties, most probably via the inhibition of CGRP-induced cranial vasodilatation. We recently showed that the novel selective CGRP receptor antagonist, BIBN4096BS (1-piperidinecarboxamide, -N-[2-[[5-amino-1-[[4-(4-pyridinyl)-1-piperazinyl] carbonyl] pentyl]amino]-1-[(3,5-dibromo-4-hydroxyphenyl) methyl]-2-oxoethyl]-4-(1,4-dihydro-2-oxo-3(2H)-quinazolinyl)-, [[R-(R,(R*,S*)]), attenuated the CGRP-induced porcine carotid vasodilatation in a model predictive of antimigraine activity. In order to evaluate the potential safety of BIBN4096BS in migraine therapy, this study was designed to investigate the effects of intravenous BIBN4096BS on alpha-CGRP-induced systemic and regional haemodynamic changes in anaesthetised rats, using radioactive microspheres. In vehicle-pretreated animals, consecutive intravenous infusions of alpha-CGRP (0.25, 0.5 and 1 microg kg(-1) min.(-1)) dose-dependently decreased mean arterial blood pressure with an accompanying increase in heart rate and systemic vascular conductance whereas cardiac output remained unchanged. Alpha-CGRP also increased the vascular conductance to the heart, brain, gastrointestinal tract, adrenals, skeletal muscles and skin, whilst that to the kidneys, spleen, mesentery/pancreas and liver remained unaltered. The above systemic and regional haemodynamic responses to alpha-CGRP were clearly attenuated in BIBN4096BS (3 mg kg(-1) intravenously)-pretreated animals. These results indicate that exogenously administered alpha-CGRP dilates regional vascular beds via CGRP receptors on the basis of the antagonism produced by BIBN4096BS. Moreover, the fact that BIBN4096BS did not alter baseline haemodynamics suggests that endogenously produced CGRP does not play an important role in regulating the systemic and regional haemodynamics under resting conditions.     

The preclinical pharmacology of BIBN4096BS, a CGRP antagonist

CGRP is an important neuropeptide found throughout the cardiovascular system. However, until recently it has been difficult to define its pharmacology or physiological role because of the lack of suitable antagonists. BIBN4096BS is a high-affinity, nonpeptide antagonist that shows much greater selectivity for human CGRP1 receptors compared to any other drug. Its pharmacology has been defined with studies on transfected cells or cell lines endogenously expressing receptors of known composition. These have allowed confirmation that in many human blood vessels, CGRP is working via CGRP1 receptors. However, it also interacts with other CGRP-activated receptors, of unknown composition. In vivo, clinical studies have shown that BIBN4096BS is likely to be useful in the treatment of migraine. It has also been used to define the role of CGRP in phenomena such as plasma extravasation and cardioprotection following ischemia.     

Clinical data on the CGRP antagonist BIBN4096BS for treatment of migraine attacks

Basal studies have shown that calcitonin gene-related peptide (CGRP) is a major sensory neuronal messenger in the trigeminovascular system, the pathway conveying intracranial pain. In migraine and cluster headache attacks, CGRP is released in parallel with the pain and successful treatment of the attacks abort both the associated pain and the CGRP release. The search for a potent small molecule CGRP antagonist has been successful and such an agent has been tested in preclinical and clinical studies. The aim of the present study was to examine current knowledge on the clinical pharmacology of systemic BIBN4096BS, which has been shown in man to abort acute migraine attacks as well or better than oral sumatriptan. BIBN4096BS is a specific and potent CGRP receptor antagonist in humans. In safety and tolerability studies the substance is well tolerated with no or only mild side effects. In acute migraine attacks the overall response was 66% with the drug and 27% with placebo. A difference as compared to placebo was seen at 30 min; the response was still rising at 4 h suggesting a long duration of action. At 24 h the pain-free rate was better than that with triptans, suggesting a lower grade of rebound and perhaps even a prophylactic possibility.     

Pharmacological profile of BIBN4096BS, the first selective small molecule CGRP antagonist

Calcitonin gene-related peptide (CGRP) is one of the most potent endogenous vasodilators known. This peptide is increased during migraine attacks and has been implicated in the pathogenesis of migraine headache. Here we report on the first small molecule selective CGRP antagonist: BIBN4096BS. In vitro, this compound is extremely potent at primate CGRP receptors exhibiting an affinity (Ki) for human CGRP receptors of 14.4 +/- 6.3 (n = 4) pM. In an in vivo model, BIBN4096BS in doses between 1 and 30 micrograms kg-1 (i.v.) inhibited the effects of CGRP, released by stimulation of the trigeminal ganglion, on facial blood flow in marmoset monkeys. It is concluded that BIBN4096BS is a potent and selective CGRP antagonist.     

Effects of BIBN4096BS on cardiac output distribution and on CGRP-induced carotid haemodynamic responses in the pig

Calcitonin gene related peptide (CGRP) seems to be involved in the pathogenesis of migraine, since plasma CGRP levels increase during the headache phase. In the present study, we investigated the effects of a novel CGRP receptor antagonist, BIBN4096BS (1-piperidinecarboxamide, N-[2-[[5-amino-1-[[4-(4-pyridinyl)-1-piperazinyl]carbonyl] pentyl] amino]-1-[(3,5-dibromo-4-hydroxyphenyl) methyl]-2-oxoethyl]-4-(1,4-dihydro-2-oxo-3(2H)-quinazolinyl)-, [R-(R*,S*)]-), on the regional cardiac output distribution and on the carotid haemodynamic changes induced by alpha-CGRP in anaesthetised pigs. Treatment with BIBN4096BS (100, 300 and 1000 microg kg(-1), i.v.) did not affect the heart rate, mean arterial blood pressure or systemic vascular conductance, but a small decrease in cardiac output was noticed; the latter was, however, not significantly different from that in vehicle-treated animals. The highest dose of BIBN4096BS moderately decreased vascular conductance in the lungs, kidneys, spleen and adrenals. Vascular conductance in other tissues including the brain, heart, gastrointestinal system, skin and skeletal muscles remained unchanged. Intracarotid artery infusions of alpha-CGRP (10, 30 and 100 pmol kg(-1) min(-1) during 3 min) increased the total carotid blood flow and conductance, but decreased the arterial blood pressure. These responses were dose-dependently blocked by BIBN4096BS. The above results show that BIBN4096BS is a CGRP receptor antagonist in the porcine carotid and systemic circulations, but the endogenous CGRP does not seem to play an important physiological role in regulating basal vascular tone. These findings suggest that BIBN4096BS may have therapeutic usefulness in migraine.     

The calcitonin gene-related peptide (CGRP) receptor antagonist BIBN4096BS blocks CGRP and adrenomedullin vasoactive responses in the microvasculature

Calcitonin gene-related peptide (CGRP) is a potent microvascular dilator neuropeptide that is considered to play an essential role in neurogenic vasodilatation and in maintaining functional integrity in peripheral tissues. We have examined the effect of the nonpeptide CGRP antagonist BIBN4096BS on responses to CGRP and the structurally related peptide adrenomedullin, AM, in murine isolated aorta and mesentery preparations, and in the cutaneous microvasculature in vivo. We show for the first time that BIBN4096BS is an effective antagonist of CGRP and AM responses in the murine mesenteric and cutaneous microvasculature, and of CGRP in the murine aorta. After local administration, BIBN4096BS selectively inhibits the potentiation of microvascular permeability in the cutaneous microvasculature by CGRP and AM, with no effect on responses induced by other microvascular vasodilators. BIBN4096BS reversed both newly developed and established vasoactive responses induced by CGRP. The ability of CGRP to potentiate plasma extravasation was lost when coinjected with compound 48/80 (where mast cells would be activated to release proteases), but regained when soybean trypsin inhibitor was coinjected with compound 48/80. These results demonstrate that BIBN4096BS is a selective antagonist of responses induced by CGRP and AM in the mouse microvasculature, and CGRP in the mouse aorta. The ability of BIBN4096BS to block an established CGRP microvascular vasodilatation indicates that the sustained vasodilator activity of CGRP is due to the retention of the active intact peptide and the continued involvement of the CGRP receptor.     

The calcitonin gene-related peptide (CGRP) receptor antagonist BIBN4096BS reduces neurogenic increases in dural blood flow

In an in vivo preparation of the exposed rat cranial dura mater electrical field stimulation causes increases in blood flow that are mainly due to the vasodilatory effect of calcitonin gene-related peptide (CGRP) released from meningeal afferents. In this preparation the effect of BIBN4096BS, a non-peptide competitive antagonist of CGRP receptors, was examined. Additionally, in an in vitro preparation of the hemisected rat skull the effect of BIBN4096BS on CGRP release stimulated by activation of meningeal afferents was analysed. Injection of BIBN4096BS at cumulative doses of 300 microg/kg and 900 microg/kg caused dose-dependent inhibition of the electrically evoked blood flow increases. The basal blood flow and vital parameters were not significantly changed by any dose. In the hemisected skull BIBN4096BS at 10(-6) M did not alter the CGRP release evoked by depolarizing K(+) concentrations or antidromic electrical stimulation of the trigeminal ganglion. We conclude that neurogenic increases in dural blood flow are reduced by BIBN4096BS without changing basal vascular parameters. This peripheral effect may be important with regard to CGRP receptor inhibition as an antimigraine strategy.     

Effect of the CGRP receptor antagonist BIBN4096BS in human cerebral, coronary and omental arteries and in SK-N-MC cells.

Several lines of evidence suggest that a calcitonin-gene related peptide (CGRP) receptor antagonist may serve as a novel abortive migraine treatment. Here we present data on a human cell line and isolated human vessels for such an antagonist, BIBN4096BS. On SK-N-MC membranes, radiolabelled CGRP was displaced by both CGRP-(8-37) and BIBN4096BS, yielding pK(i) values of 8.5 and 11.4, respectively. Functional studies with SK-N-MC cells demonstrated that CGRP-induced cAMP production was antagonised by both CGRP-(8-37) and BIBN4096BS with pA(2) values of 7.8 and 11.2, respectively. Isolated human cerebral, coronary, and omental arteries were studied with a sensitive myograph technique. CGRP induced a concentration-dependent relaxation that was antagonized by both CGRP-(8-37) and BIBN4096BS in a competitive manner. CGRP was a weaker agonist on coronary arteries as compared to intracranial arteries; however, BIBN4096BS was an equally effective antagonist. In human omental arteries, CGRP did not induce relaxation. BIBN4096 had a pA(2) value of 10.1 in cerebral and 10.4 in coronary arteries. The results of clinical trials with BIBN4096BS for acute migraine attacks are awaited with great interest.     

Modelling the anti-migraine effects of BIBN 4096 BS: a new calcitonin gene-related peptide receptor antagonist

BACKGROUND AND OBJECTIVE: Migraine attacks are associated with release of the calcitonin gene-related peptide (CGRP) from trigeminal nerves. BIBN 4096 BS is the first CGRP receptor antagonist tested in humans showing response rates similar to those reported for triptans, together with very good safety and tolerability profiles. The objective of the current study is to develop a population pharmacokinetic/pharmacodynamic model resembling the mechanism of action of BIBN 4096 BS, and to extract by model-based simulations dosage formulations and pharmacodynamic properties that can assist in the development of CGRP receptor antagonists. METHODS: 126 patients with an acute moderate to severe migraine attack lasting not more than 6 hours were enrolled in this phase IIa study. BIBN 4096 BS was given as a single intravenous 10-minute infusion at different dose levels ranging from 0.25 to 10 mg. Severity of headache was measured up to 24 hours. Patients who did not show pain relief by 2 hours were allowed to take rescue medication. Severity of headache and time to rescue medication measurements were fitted simultaneously using logistic regression and time-to-event analysis with nonlinear mixed-effect modelling software NONMEM version V. RESULTS: Severity of headache and time to rescue medication were described as a function of the fraction of the CGRP receptors blocked by BIBN 4096 BS, and controlled by the second- and first-order rate constants representing the onset (k(on)) and offset (k(off)) of the anti-migraine effects. The model predicted a slow rate of offset of the anti-migraine effect (half-life of k(off) = 21 hours). The model developed described the data well and was validated properly. DISCUSSION: A semi-mechanistic population pharmacokinetic/pharmacodynamic model has been developed for the anti-migraine effects of BIBN 4096 BS, characterised by the severity of headache and time to rescue medication. Simulations exploring the effect of the rate of absorption, bioavailability after an extravascular administration and the rate of activation/inactivation of the anti-migraine effect were performed. The rate of absorption seems to play a minor role; however, at least bioavailability fractions of 0.2-0.3 should be obtained. With regard to the kinetics of the anti-migraine effect, and to achieve a response rate of 60% at 2 hours, values of k(on) should be > 0.081 mL/ng/h. At later times after administration higher values of k(off) are associated with faster offset of the response. The simulations showed that molecules with high k(on) and low k(off) values are the most promising.     

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

Calcitonin gene-related peptide (CGRP) is a potent vasodilator in brain vessels and it has been implicated in the pathogenesis of migraine headache. Blocking post-junctional CGRP receptors, mediators of trigeminal-induced vasodilation, has been suggested as a potential antimigraine strategy. In this study, we tested the ability of a new non-peptide CGRP receptor antagonist, BIBN4096BS, to inhibit the CGRP-induced dilation in human and/or bovine brain vessels and compared it to that of the antagonist alpha-CGRP(8-37). BIBN4096BS and alpha-CGRP(8-37) both blocked the alpha-CGRP-induced dilation in bovine middle artery segments with respective potency (pK(B) values) of 6.3 and 7.8. In human pial vessels, BIBN4096BS was particularly potent. When tested at 10(-14)-10(-9) M concentrations, it induced a rightward shift in the alpha-CGRP concentration-response curve and yielded a biphasic Schild plot suggesting interaction with more than one receptor population, as was also indicated by the significant best fit of the alpha-CGRP-induced dilation in human brain vessels with a two receptor site interaction. Schild plot analysis in the linear portion of the BIBN4096BS inhibition curve revealed interaction with one high affinity site (pA(2) value approximately 14). In bovine vessels, both alpha-CGRP(8-37) and BIBN4096BS concentration-dependently reversed a pre-established CGRP-induced dilation ( approximately 59 and 85%, respectively), BIBN4096BS being approximately tenfold more potent than alpha-CGRP(8-37) (respective pIC(50) values of 7.5 and 6.75). In human middle cerebral and middle meningeal arteries, BIBN4096BS reversed the alpha-CGRP-induced dilation (> or =70%) by interaction with two different receptor populations: it exhibited a high affinity for one population (pIC(50) value approximately 13) and a lower affinity for the other (pIC(50) value approximately 8). The present data demonstrate that BIBN4096BS is a very potent antagonist that could, depending on its bioavailability and in vivo affinity, be of potential benefit in the acute treatment of migraine headache by blocking and/or reversing the CGRP-mediated dilation of intracranial vessels induced by activation of trigeminovascular afferents.     

Inhibitory effect of BIBN4096BS on cephalic vasodilatation induced by CGRP or transcranial electrical stimulation in the rat

Calcitonin gene-related peptide (CGRP) is believed to play a pivotal role in the pathogenesis of migraine via activation of CGRP receptors in the trigeminovascular system. The CGRP receptor antagonist, BIBN4096BS, has proven efficacy in the acute treatment of migraine attacks and represents a new therapeutic principle. We used an improved closed cranial window model to measure changes of the middle meningeal artery (MMA) and cortical pial artery/arteriole diameter (PA) and changes in local cortical cerebral blood flow (LCBF(Flux)) in anaesthetised artificially ventilated rats. The ability of BIBN4096BS (i.v.) to prevent the vasodilatatory actions of rat-alphaCGRP, betaCGRP and endogenously released CGRP following transcranial electrical stimulation (TES) was investigated. BIBN4096BS was per se without vasoactive effect on any of the measured variables and significantly inhibited the hypotension induced by both types of CGRP (P < 0.001). The alphaCGRP induced MMA dilatation was reduced from 97.4 +/- 14 to 2.1 +/- 1.3% (P < 0.001) and the betaCGRP induced dilatation was fully blocked by BIBN4096BS. ID(50) was 5.4 +/- 1.6 microg kg(-1) for alphaCGRP and 16.3 +/- 1.6 microg kg(-1) for betaCGRP. Transcranial electrical stimulation induced a 119.1 +/- 6.9% increase in MMA diameter. BIBN4096BS (333 microg kg(-1)) attenuated this increase (19.8 +/- 2.1%) (P < 0.001). Systemic CGRP and TES induced an increase in PA diameter that was not significantly inhibited by BIBN4096BS. The CGRP induced increase in LCBF(Flux) was similar not prevented by the antagonist. We suggest that systemic BIBN4096BS exerts its inhibitory action mainly on large dural blood vessels (MMA).     

降钙素基因相关肽和BIBN4096BS对麻醉大鼠心肌缺血的作用

INTRODUCTION Calcitonin gene-related peptide (CGRP) is a 37amino acid peptide that is predominantly synthesized andstored in sensory neurons. It can be released from boththe central and peripheral axons of these neurons.CGRP-containing nerve fibers have been identifiedthroughout the cardiovascular system, in association withblood vessels, in particular the coronary arteries, andaround the sinoatrial and atrioventricular nodes.CGRP is a potent vasodilator peptide and it exerts positivechronotropic and inotropic effects in rats and hu-mans. It has been shown to exert extremely potent     

BIBN4096BS is a potent competitive antagonist of the relaxant effects of alpha-CGRP on human temporal artery: comparison with CGRP(8-37)

Release of CGRP during migraine may produce harmful dilatation of cranial arteries, thereby possibly causing pain. We have compared the antagonism by BIBN4096BS and CGRP(8-37) of the relaxant effects of alpha-CGRP on rings of human temporal artery. alpha-CGRP relaxed the arteries precontracted with 9 - 24 mM KCl (-logEC50=9.4) nearly as efficaciously as sodium nitroprusside (10 microM). BIBN4096BS (0.1 - 100 nM) antagonized the effects of alpha-CGRP in surmountable manner with slopes of Schild-plots not different from unity. -LogKB values of 10.1 and 10.4 were estimated for BIBN4096BS when administered before or during the KCl-contracture respectively. BIBN4096BS (1 microM) did not modify the relaxant effects of papaverine and sodium nitroprusside. CGRP(8-37) (1 - 10 microM) antagonized the effects of alpha-CGRP in a surmountable manner with slopes of Schild-plots not different from unity. -LogKB values of 6.6 and 6.7 were estimated for CGRP(8-37) administered before or during the KCl-contracture respectively. The high affinity of BIBN4096BS for CGRP receptors of human temporal artery makes it an excellent tool to explore the hypothesis of CGRP-evoked cerebral vasodilation in migraine.     

Inhibitory effect of BIBN4096BS, CGRP(8-37), a CGRP antibody and an RNA-Spiegelmer on CGRP induced vasodilatation in the perfused and non-perfused rat middle cerebral artery

BACKGROUND AND PURPOSE: A new concept for the inhibition of CGRP signalling has been developed by interaction with the CGRP molecule per se by using a CGRP antibody or a CGRP binding RNA-Spiegelmer (NOX-C89). We have compared these CGRP scavengers with two known receptor antagonists (CGRP8-37 and BIBN4096BS) on CGRP-induced relaxations in the rat middle cerebral artery (MCA). Furthermore, the role of the endothelial barrier has been studied. EXPERIMENTAL APPROACH: We used the luminally perfused MCA in an arteriograph, pressurized to 85 mm Hg and myograph studies of isolated ring segments of the MCA.KEY RESULTS: In myograph studies and in the perfusion system during abluminal application, alphaCGRP and betaCGRP induced concentration-dependent dilatation of the MCA. Given luminally neither peptide was significantly vasodilator. Adrenomedullin and amylin induced weak dilatations. In myograph experiments, relaxation induced by alphaCGRP was prevented by the four CGRP blockers (CGRP8-37, BIBN4096BS, the CGRP antibody and NOX-C89.). In abluminal perfusion experiments, the relaxant response to alphaCGRP was prevented by these agents to a varying degree. Dilatation induced by abluminal application of alphaCGRP was inhibited by luminal CGRP8-37 but not by luminal BIBN4096BS, CGRP antibody or NOX-C89. CONCLUSIONS AND IMPLICATIONS: alpha or betaCGRP acted on smooth muscle cell CGRP receptors in rat MCA and were effectively prevented from reaching these receptors by the endothelial barrier. The CGRP blockers significantly inhibited alphaCGRP induced relaxation but were also prevented from reaching the CGRP receptors by the arterial endothelium.     

New drugs for the prevention and treatment of migraine: topiramate and BIBN 4096 BS

Migraine is one of the leading causes of disability. Topiramate has multiple mechanisms and may reduce neurotransmission through the trigeminocervical complex to prevent migraine. In clinical trials for the prevention of migraine, the mean monthly migraine frequency decreased from 5.6 to 4.5 in the placebo group and larger decreases were observed with topiramate (100 mg/day, 5.8 to 3.5; 200 mg/day, 5.1 to 3.0). However, topiramate use is associated with a high incidence of adverse events (paraesthesia, fatigue, anorexia, diarrhoea), which may limit the willingness of patients to use topiramate for the prevention of migraine. BIBN 4096 BS is a non-peptide calcitonin gene-related peptide-receptor antagonist that has recently been trialled in migraine attacks. The primary efficacy end point was the reduction of severe or moderate headache prior to treatment to mild or no headache at 2 h. This endpoint was achieved in 21 of 32 (66%) patients with BIBN 4096 BS 2.5 mg, compared to 27% of patients given placebo. Although BIBN 4096 BS is a non-peptide, it is still administered intravenously, which will probably limit its use to medical centres.     

New drugs for the prevention and treatment of migraine: topiramate and BIBN 4096 BS

Migraine is one of the leading causes of disability. Topiramate has multiple mechanisms and may reduce neurotransmission through the trigeminocervical complex to prevent migraine. In clinical trials for the prevention of migraine, the mean monthly migraine frequency decreased from 5.6 to 4.5 in the placebo group and larger decreases were observed with topiramate (100 mg/day, 5.8 to 3.5; 200 mg/day, 5.1 to 3.0). However, topiramate use is associated with a high incidence of adverse events (paraesthesia, fatigue, anorexia, diarrhoea), which may limit the willingness of patients to use topiramate for the prevention of migraine. BIBN 4096 BS is a non-peptide calcitonin gene-related peptide-receptor antagonist that has recently been trialled in migraine attacks. The primary efficacy end point was the reduction of severe or moderate headache prior to treatment to mild or no headache at 2 h. This endpoint was achieved in 21 of 32 (66%) patients with BIBN 4096 BS 2.5 mg, compared to 27% of patients given placebo. Although BIBN 4096 BS is a non-peptide, it is still administered intravenously, which will probably limit its use to medical centres.     

Population pharmacokinetic modelling of BIBN 4096 BS, the first compound of the new class of calcitonin gene-related peptide receptor antagonists.

Pharmacokinetics (PK) of the calcitonin gene-related (CGRP) peptide receptor antagonist BIBN 4096 BS, the first compound of this new class tested in humans, has been evaluated combining the data from a phase I study performed in healthy volunteers and a phase IIa study conducted in migraine patients. A total of 94 individuals with a total of 556 plasma samples contributed to the analysis. Subjects received a single dose of 0.25, 0.5, 1, 2.5, 5 or 10 mg BIBN 4096 BS administered in a 10 min i.v. infusion. Blood samples were obtained at selected times up to 12 h. Disposition of BIBN 4096 BS was best described with a three compartment body model with first order elimination. BIBN 4096 BS showed a moderate degree (between 30 and 50%) of inter-subject variability in the apparent volume of distribution of the central compartment (V1), total plasma clearance (CL), distribution clearance between the central and deep compartment, and the apparent volume of distribution of the shallow compartment. Typical estimates of V1 were significantly (P <0.01) lower in healthy volunteers (7.16 versus 9.95 L), and typical estimates of CL were significantly lower in subjects receiving oral contraceptives (11.4 versus 17.1 L/h), although the absolute reduction in the unexplained inter-subject variability was negligible (4%). Computer simulations showed that the above mentioned covariates lack clinical significance. In conclusion, the pharmacokinetics of BIBN 4096 BS was independent of the dose and not altered by the tested covariates to a clinically significant degree.     

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

1. The ability of the CGRP antagonist BIBN4096BS to antagonize CGRP and adrenomedullin has been investigated on cell lines endogenously expressing receptors of known composition. 2. On human SK-N-MC cells (expressing human calcitonin receptor-like receptor (CRLR) and receptor activity modifying protein 1 (RAMP1)), BIBN4096BS had a pA(2) of 9.95 although the slope of the Schild plot (1.37 +/- 0.16) was significantly greater than 1. 3. On rat L6 cells (expressing rat CRLR and RAMP1), BIBN4096BS had a pA(2) of 9.25 and a Schild slope of 0.89 +/- 0.05, significantly less than 1. 4. On human Colony (Col) 29 cells, CGRP(8-37) had a significantly lower pA(2) than on SK-N-MC cells (7.34 +/- 0.19 (n = 7) compared to 8.35 +/- 0.18, (n = 6)). BIBN4096BS had a pA(2) of 9.98 and a Schild plot slope of 0.86 +/- 0.19 that was not significantly different from 1. At concentrations in excess of 3 nM, it was less potent on Col 29 cells than on SK-N-MC cells. 5. On Rat 2 cells, expressing rat CRLR and RAMP2, BIBN4096BS was unable to antagonize adrenomedullin at concentrations up to 10 microM. CGRP(8-37) had a pA(2) of 6.72 against adrenomedullin. 6. BIBN4096BS shows selectivity for the human CRLR/RAMP1 combination compared to the rat counterpart. It can discriminate between the CRLR/RAMP1 receptor expressed on SK-N-MC cells and the CGRP-responsive receptor expressed by the Col 29 cells used in this study. Its slow kinetics may explain its apparent 'non-competitive' behaviour. At concentrations of up to 10 micro M, it has no antagonist actions at the adrenomedullin, CRLR/RAMP2 receptor, unlike CGRP(8-37).     

Inhibition of capsaicin-induced increase in dermal blood flow by the oral CGRP receptor antagonist, telcagepant (MK-0974)

AIMS

To evaluate inhibition of capsaicin-induced increase in dermal blood flow (DBF) following telcagepant (MK-0974), a potent and selective orally bioavailable calcitonin gene-related peptide (CGRP) receptor antagonist being developed for the acute treatment of migraine.

METHODS

A three-period crossover study in 12 healthy adult men. Each subject received a single oral dose of telcagepant 300 mg, telcagepant 800 mg or placebo at 0 h, followed 0.5 and 3.5 h later by two topical doses of 300 and 1000 µg capsaicin per 20 µl water–ethanol mixture. Capsaicin was applied at two sites on the volar surface of the subjects'' left and right forearms. DBF was assessed by laser Doppler perfusion imaging immediately before (‘baseline’), and 0.5 h after each capsaicin application at 1 and 4 h. Plasma samples to determine telcagepant concentrations were collected immediately after laser Doppler perfusion imaging. A pharmacodynamic model was developed to explore the relationship between plasma concentration and inhibition of capsaicin-induced increase in DBF.

RESULTS

Geometric mean plasma concentrations after dosing with 300 mg and 800 mg telcagepant were 720 and 1146 nm, respectively, at 1 h, vs. 582 and 2548 nm, respectively, at 4 h. The pharmacodynamic model suggested that the EC₉₀ for telcagepant inhibition of capsaicin-induced increases in DBF was 909 nm.

CONCLUSIONS

Telcagepant inhibits the increases in DBF induced by the topical application of capsaicin on the human forearm. This experimental medicine model may have utility to assist in dose selection for the development of CGRP receptor antagonists.