Efficacy endpoints in migraine clinical trials: the importance of assessing freedom from pain

Many efficacy endpoints have been used in clinical trials of acute migraine pharmacotherapy. Headache response or headache relief (i.e., moderate/severe pain reduced to mild/no pain) at a single, specified time-point, traditionally the primary endpoint, and headache recurrence (i.e., return of pain after initial postdose relief) are inadequate. Headache relief does not provide information about pain-free response and counts a partial response as a treatment success. Headache recurrence can reflect sustained efficacy but is confounded by initial response to treatment, because ineffective drugs have low recurrence rates. The International Headache Society (IHS) guidelines state that 2 hour pain-free response and sustained pain-free response (i.e., freedom from pain with no recurrence or use of rescue or study medication 2-24 hours postdose) provide the most clinically relevant information about the efficacy of migraine pharmacotherapy. The pain-free criterion counts partial responses as failures and thus is a more rigorous test of therapeutic benefit than headache relief, and the two endpoints together incorporate the main treatment attributes that determine patient satisfaction. As an example, consider needle-free subcutaneous sumatriptan and oral triptan tablets. An open-label study of needle-free subcutaneous sumatriptan by Cady and colleagues found that 2 hour pain-free response and sustained pain-free response were 64% and 42% respectively. For oral triptan tablets, the 2001 metaanalysis by Ferrari and colleagues reported 2 hour pain-free response rates ranging from 23% to 38% and sustained pain-free response rates ranging from 11% to 26%. The measures of pain-free response 2 hours postdose and sustained pain-free response can differentiate among treatments and be used to guide therapeutic choices.

The triptan formulations : how to match patients and products

The 5-HT(1B/1D) receptor agonists (the 'triptans') are migraine-specific agents that have revolutionised the treatment of migraine. They are usually the drugs of choice to treat a migraine attack in progress. Different triptans are available in various strengths and formulations, including oral tablets, orally disintegrating tablets, nasal sprays and subcutaneous injections. In Europe, sumatriptan is also available as a suppository. Specific differences among the triptans exist, as evidenced by different pharmacological profiles including half-life, time to peak plasma concentrations, peak plasma concentrations, area under the concentration-time curve, metabolism and drug-drug interaction profiles. How or whether these differences translate to clinical efficacy and tolerability advantages for one agent over another is not well differentiated. However, delivery systems may play an important role in onset of action. Given that the clinical distinctions among these agents are subtle, identification of the most appropriate triptan for an individual patient requires consideration of the specific characteristics of the patient and knowledge of patient preference, an accurate history of the efficacy of previous acute-care medications and individual features of the drug being considered. The selection of an acute antimigraine drug also depends upon the stratification of the patient's migraine attack by peak intensity, time to peak intensity, level of associated symptoms such as nausea and vomiting, time to associated symptoms, comorbid diseases and concomitant treatments that might cause drug-drug interactions. Individual patient response to the triptans seems to be idiosyncratic and possibly genetically determined. Therefore, a set of specific questions can be used to determine whether a currently used triptan is optimally effective, whether the dose needs to be increased or whether another triptan should be tried. The clinician has in his/her armamentarium an ever-expanding variety of triptans, available in multiple formulations and dosages, which have good safety and tolerability profiles. Continued clinical use will yield familiarity with the various triptans, and it should become possible for the interested physician to match individual patient needs with the specific characteristics of a triptan to optimise therapeutic benefit. Use of the methods outlined in this review in choosing a triptan for an individual patient is probably more likely to lead to migraine relief than making an educated guess as to which triptan is most appropriate.

Practical approaches to migraine management

Migraine is a recurrent clinical syndrome characterised by combinations of neurological, gastrointestinal and autonomic manifestations. The exact pathophysiological disturbances that occur with migraine have yet to be elucidated; however, cervico-trigemino-vascular dysfunctions appear to be the primary cause. Despite advances in the understanding of the pathophysiology of migraine and new effective treatment options, migraine remains an under-diagnosed, under-treated and poorly treated health condition. Most patients will unsuccessfully attempt to treat their headaches with over-the-counter medications. Few well designed, placebo-controlled studies are available to guide physicians in medication selection. Recently published evidence-based guidelines advocate migraine-specific drugs, such as serotonin 5-HT(1B/1D) agonists (the 'triptans') and dihydroergotamine mesylate, for patients experiencing moderate to severe migraine attacks. Additional headache attack therapy options include other ergotamine derivatives, phenothiazines, nonsteroidal anti-inflammatory agents and opioids. Preventative medication therapy is indicated for patients experiencing frequent and/or refractory attacks.

Triptans: do they differ?

Headache care specialists agree that the introduction of sumatriptan constitutes a major advance in headache therapy, but they differ about whether other triptans offer clinically significant advantages over sumatriptan. This article examines this issue by considering the similarities and differences among triptans.

Triptans: are they all the same?

The triptans have provided a major advance in the treatment of the pain and disability associated with migraine headache. With seven triptans in use or in clinical development, the clinician is faced with the decision of which triptan to prescribe to the patient with migraine. Although the triptans are pharmacologically similar, they each have unique attributes. This article focuses on the pharmacologic differences between triptans with regard to their pharmacokinetics and drug interactions, and provides some helpful tips on how to optimize migraine treatment with the triptans.

Neurogenic inflammation in the context of migraine

Despite considerable research into the pathogenesis of idiopathic headaches, such as migraine, the pathophysiological mechanisms underlying them remain poorly understood. Although it is well established that the trigeminal nerve becomes activated during migraine, the consequences of this activation remain controversial. One theory, based on preclinical observations, is that activation of trigeminal sensory fibers leads to a painful neurogenic inflammation within the meningeal (dural) vasculature mediated by neuropeptide release from trigeminal sensory fibres and characterized by plasma protein extravasation, vasodilation, and mast cell degranulation. Effective antimigraine agents such as ergots, triptans, opioids, and valproate inhibit preclinical neurogenic dural extravasation, suggesting that this activity may be a predictor of potential clinical efficacy of novel agents. However, several clinical trials with other agents that inhibit this process preclinically have failed to show efficacy in the acute treatment of migraine in man. Alternatively, it has been proposed that painful neurogenic vasodilation of meningeal blood vessels could be a key component of the inflammatory process during migraine headache. This view is supported by the observation that jugular plasma levels of the potent vasodilator, calcitonin gene-related peptide (CGRP) are elevated during the headache and normalized by successful sumatriptan treatment. Preclinically, activation of trigeminal sensory fibers evokes a CGRP-mediated neurogenic dural vasodilation, which is blocked by dihydroergotamine, triptans, and opioids but unaffected by NK1 receptor antagonists that failed in clinical trials. These observations suggest that CGRP release with associated neurogenic dural vasodilation may be important in the generation of migraine pain, a theory that would ultimately be tested by the clinical testing of a CGRP receptor antagonist.

A systematic review of the use of triptans in acute migraine

OBJECTIVE

A systematic review of the literature was undertaken, to consolidate evidence concerning the efficacy and safety of triptans currently available in Canada (sumatriptan, rizatriptan, naratriptan, zolmitriptan), and to provide guidelines for selection of a triptan.

METHODS

Data from published, randomized, placebo-controlled trials were pooled and a combined number needed to treat (NNT) and number needed to harm (NNH) was generated for each triptan. Direct comparative trials of triptans were also examined.

RESULTS

The lowest NNT for headache response/pain-free at one/two hours is observed with subcutaneous sumatriptan. Among the oral formulations, the lowest NNT is observed with rizatriptan and the highest NNT with naratriptan. The lowest NNH is observed with subcutaneous sumatriptan.

CONCLUSIONS

Triptans are relatively safe and effective medications for acute migraine attacks. However, differences among them are relatively small. Considerations in selecting a triptan include individual patient response/tolerance, characteristics of the attacks, relief of associated symptoms, consistency of response, headache recurrence, delivery systems and patient preference.

pH-mediated field-amplified sample stacking of pharmaceutical cations in high-ionic strength samples

Capillary electrophoretic separation of samples of physiological origin typically have both poor resolution and efficiency due to destacking. We have previously reported a stacking method for concentration of catecholamines in artificial dialysate, or Ringer's solution. However, pH-mediated sample stacking of other cations has not been investigated. In this report, pH-mediated stacking has been extended to eletripan, dofetilide, doxazosin, sildenafil, UK-103,320, UK-202,581, and CP-122,288. These compounds were chosen without prior structural screening except that they were cationic at the pH of our background electrolyte (BGE). Capillary electrophoretic behavior of samples in BGE is compared with those of samples in Ringer's solution with and without pH-mediated acid stacking. Results indicate that the peak heights and efficiencies for acid-stacked samples are increased compared to the unstacked samples in Ringer's solution or BGE. For example, the peak efficiencies for 5 s injections of eletriptan in BGE and Ringer's solution are 138,000 and 72,000 plates, respectively. In contrast, a 10 s injection of eletriptan followed by acid injection for 16 s produces a peak with 246,000 plates. Evaluation of the stacking effect was performed by comparison of the peak height at similar peak efficiencies for samples in Ringer's solution with and without stacking. Using this method, pH-mediated acid stacking provides a 10- to 27-fold sensitivity enhancement for the seven cations.

Triptans. A support to the central link between serotonin and acetylcholine in migraine

Recently synthesized triptans, sumatriptan derivatives, display aborting migraine activity at doses and with plasmatic maximum peak dramatically lower (20-40 times) than sumatriptan, the 5-HT like agonist, which is the original molecule. That triptans easily cross blood-brain barrier strongly supports the central theory of migraine. We recently discovered the anti-migraine prophylactic action of centrally acting anti-cholinesterase agents, that seems a further support to the central theory of migraine. Indeed, acetylcholine is an important analgesia neurotransmitter and is intertwined with 5-HT central pathways.

No acute antimigraine efficacy of CP-122,288, a highly potent inhibitor of neurogenic inflammation: results of two randomized, double-blind, placebo-controlled clinical trials

CP-122,288 is a highly potent inhibitor of neurogenic plasma extravasation in animal models at doses without vasoconstrictor effect. We evaluated the acute antimigraine efficacy of intravenous and oral CP-122,288 in two double-blind studies. In a crossover design, patients randomly received 31.25 microg of CP-122,288 intravenously, placebo, or both. In the oral study, patients received placebo or one of four doses of CP-122,288 between 3.125 and 312.5 microg, using a novel "up and down" design for randomization. Both studies were stopped prematurely when target efficacy could not be achieved. Responder rates were 29% for CP-122,288 versus 30% for placebo (difference, -1%; 95% CI, -24-22%; intravenous study) and an overall rate of 25% for CP-122,288 versus 0% for placebo (difference, 25%; 95% CI; 10-40%; oral study). CP-122,288 was not clinically effective at doses and plasma concentrations in excess of those required to inhibit neurogenic plasma extravasation in animals. Neurogenic plasma extravasation is unlikely to play a crucial role in the pathophysiology of migraine headache.

Differential effects of low dose CP122,288 and eletriptan on fos expression due to stimulation of the superior sagittal sinus in cat

CP122,288, a conformationally restricted analogue of sumatriptan, is a highly potent inhibitor of neurogenic plasma protein extravasation (PPE) in rat and guinea pig at low doses where it has no 5HT1B-mediated vascular actions. We have examined its effect on a model of trigeminovascular nociception to assess the relative importance of vasoconstrictor and serotonin (5HT)(1B/1D) agonist activity to the modulation trigeminal neuronal activation. For comparison to activate relevant 5HT receptors, the clinically effective relatively lipophilic 5HT(1B/1D) agonist eletriptan was studied in parallel. The superior sagittal sinus was isolated in the alpha-chloralose (60 mg/kg, i.p. and 15-20 mg/kg i.v. supplement every 2 h) anaesthetized cat. Animals were prepared for stimulation and then maintained for 24 h before stimulation and perfusion for Fos immunohistochemistry. Stimulation of the superior sagittal sinus (250 micros, 100 V, 0.3 Hz) resulted in Fos expression in cells in the trigeminal nucleus caudalis and superficial laminae of the dorsal horns of C(1-2). Administration of low dose CP122,288 (100 ng/kg) had no effect on Fos expression after sinus stimulation either when administered alone or in combination with mannitol; the latter to ensure access to the trigeminocervical complex. The number of cells in the superficial laminae of the trigeminal nucleus caudalis with stimulation being a median of 50 (quartile range: 47-53) and 48 (35-48) after CP122,288, and after CP122,288 and mannitol 45 (41-53). In comparison, the clinically effective 5HT(1B/1D) agonist, eletriptan, reduced Fos expression in the trigeminocervical complex to a median of 24 (21-33). These data demonstrate that the potent inhibitor of neurogenic plasma protein extravasation (PPE) CP122,288 has no effect on Fos expression in central trigeminal neurons when administered at a dose which blocks PPE in rat and guinea pig, but has no vasoconstrictor 5HT(1B/1D) activity, and while ensuring its access to central trigeminal neurons. The data suggest that activation of the 5HT(1B/1D) receptor is important for the clinical action of this class of compounds and is consistent with the fact the CP122,288 is ineffective in the treatment of the acute attack of migraine.

Present and future of 5-HT receptor agonists as antimigraine drugs

Serotonin (5-hydroxytryptamine; 5-HT) is thought to play an important role in the pathogenesis of migraine. The discovery of the 5-HT1B/1D/1F agonist sumatriptan constitutes a substantial advance in the acute treatment of migraine, though it displays a number of nonnegligible shortcomings. Today, a number of second-generation drugs derived from tryptamine are under advanced clinical development or are about to be marketed worldwide for the acute treatment of migraine. These tryptamine derivatives display partial agonist properties at 5-HT1B/1D receptors. It is not yet clearly established whether these agents represent a major improvement over sumatriptan in therapeutic effectiveness. Most of them also show affinity for 5-ht1F binding sites and have better oral pharmacokinetics than sumatriptan. The acute antimigraine effects of this second-generation of triptans seem to be obtained in largely the same way as with sumatriptan: by cranial vasoconstriction and inhibition of trigeminovascular activation from both peripheral and central projections. Future directions in migraine therapy should focus on agents that exhibit high intrinsic activity at 5-HT1B/1D receptors, offer a good safety profile, and demonstrate long-lasting action which might also be considered in migraine prophylaxis.

Blockade of calcitonin gene-related peptide release after superior sagittal sinus stimulation in cat: a comparison of avitriptan and CP122,288

The pathophysiological basis for the pain of migraine has been the subject of substantial attention and must include activation of elements of the trigeminal innervation of the cranial vessels, the trigeminovascular system. Recently, consideration of trigeminal-evoked neurogenic plasma protein extravasation (PPE) as a model for the pain has driven the search for compounds with specific anti-extravasation properties. Calcitonin gene-related peptide (CGRP) is a marker for trigeminovascular activation and is released during the headache phase of migraine and cluster headache. CGRP may have a role in migraine through its potent cranial vasodilator effects or by an action on trigeminal nerve activity, both of which are targeted by 5HT(1B/1D)agonist drugs but does not itself produce PPE. It has been suggested that 5HT(1B/1D)agonists may have an anti-migraine effect via inhibition of PPE in the dura mater. Avitriptan and CP122,288 both have strong binding affinities for 5HT(1B/1D)receptors, but only CP122,288 is a potent inhibitor of PPE. In this study we sought to compare the effects of CP122,288 and avitriptan on jugular vein CGRP release after stimulation of the superior sagittal sinus (SSS) in the cat. In eleven anaesthetized cats external jugular vein blood samples were analyzed by radioimmunoassay for CGRP levels in three settings: a) control, b) 1 min after SSS stimulation and c) 1 min after SSS stimulation in presence of drug. Stimulation of the SSS resulted in release of CGRP from the external jugular vein (77+/-1 pmol/L). At a PPE-inhibitory dose in rat (100 ng/kg intravenously) CP122, 288 had no effect on CGRP release (77+/-6 pmol/L) whereas at a clinically relevant dose (50 microgram/kg intravenously) avitriptan blocked CGRP release. This study demonstrates that the potent inhibitor of PPE, CP122, 288, which has been shown in clinical trials to be ineffective in treating acute migraine attacks, had no effect on CGRP release, whereas the effective anti-migraine drug and relatively impotent inhibitor of PPE, avitriptan, blocked CGRP release. These data emphasize the importance of CGRP release and its possible independence from PPE in migraine and more importantly suggest that other non-5HT-based pharmacological targets may account for PPE blockade in animal studies.

A fluorescence-based method for assessing dural protein extravasation induced by trigeminal ganglion stimulation

Neurogenic dural inflammation has been proposed as a source of pain during migraine. Unilateral electrical stimulation of the trigeminal ganglion causes the ipsilateral release of inflammatory neuropeptides and subsequent dural plasma protein extravasation, a component of neurogenic inflammation. We measured the amount of protein leaking into the dural tissue of guinea pigs following trigeminal ganglion stimulation by exploiting the complexation reaction of endogenous proteins with the fluorescent dye Evans Blue, instead of utilizing exogenous radiolabeled albumin as commonly done in the literature. The amount of Evans Blue trapped in dural tissue following electrical stimulation of the trigeminal ganglion was measured using a fluorescence microscope equipped with a spectrophotometer. This method utilized multiple measurements on each dura sample which resulted in very precise values using a small number of animals per point (n = 3). Sumatriptan and CP-122,288 were found to dose-dependently prevent neurogenic dural extravasation. The potencies of CP-122,288 and sumatriptan were found to be similar to those reported in the literature when similar experimental protocols were used.

Naratriptan: biological profile in animal models relevant to migraine

The biological profile of naratriptan (N-methyl-3-(1-methyl-4-piperidinyl)-1H-indole-5-ethane-sulphonamide), a novel 5HT1B/1D receptor agonist, was investigated in a variety of experimental models of relevance to migraine. Naratriptan has high affinity for human recombinant 5HT1B and 5HT1D receptors (pKi = 8.7 +/- 0.03 and 8.3 +/- 0.1, respectively) and causes contractions of dog isolated basilar and middle cerebral artery (EC50 values of 0.11 and 0.07 microM, respectively). Naratriptan causes small contractions of human isolated coronary arteries (EC50 value of 0.17 microM; maximum contraction equivalent to 33% of 5HT maximum). In anaesthetized dogs, naratriptan causes selective vasoconstriction of the carotid arterial bed (CD50 dose = 19 +/- 3 micrograms kg-1) and, in anaesthetized rats, naratriptan selectively inhibits neurogenic plasma protein extravasation in the dura (ID50 = 4.1 micrograms kg-1). In a variety of antinociceptive tests, naratriptan has no effect even at high doses. In conscious rats and dogs, naratriptan has high oral bioavailability (71% and 95%, respectively). The data show that naratriptan is a selective agonist at 5HT1B/1D receptors, with a pharmacological profile very similar to that of sumatriptan, albeit 2-3 fold more potent. These observations, coupled with high oral bioavailability in animals, suggest that naratriptan has the profile of an orally effective anti-migraine drug.

Differential effects of 5-HT1B/1D receptor agonists on neurogenic dural plasma extravasation and vasodilation in anaesthetized rats

These studies compared the effects of the 5-HT1B/1D receptor agonists sumatriptan, CP-122 288 ((R)-N-methyl-[3-(1-methyl-2-pyrrolidinylmethyl)-1H-indol-5-yl] methanesulphonamide succinate) and CP-93 129 (3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one dihydrochloride) on neurogenic dural extra-vasation and vasodilation in anaesthetized rats. Dural extravasation, evoked by high intensity (1.2 mA) stimulation of the trigeminal ganglion, was measured using the radioactive plasma marker 125I-labelled bovine serum albumin. Dural vasodilation produced by lower intensity (50-300 microA) stimulation of trigeminal fibres, was measured through a closed cranial window using intravital microscopy. All compounds inhibited dural extravasation (rank order of potency: CP-122 288 > > sumatriptan > CP-93 129) and dural vasodilation (rank order of potency: CP-93 129 > > sumatriptan = CP-122 288). Comparison of the potency of these compounds with their potencies in an in vitro functional model, agonist-induced [35S]GTP gamma S binding, suggests that blockade of dural extravasation was consistent with an action at rat 5-HT1D receptors, but activity at another, unknown, "extravasation receptor" could also be involved. In contrast, inhibition of dural vasodilation was consistent with an action at rat 5-HT1B receptors. We suggest that in our preparations, production of dural vasodilation involves activation of trigeminal A delta-fibres whereas production of dural extravasation involves activation of trigeminal C-fibres. The differential effects of compounds on dural extravasation and vasodilation may therefore be due to the different receptor subtypes involved and to the selective localization of these subtypes on different populations of trigeminal sensory fibre.

The 5-HT1D receptor antagonist GR-127,935 prevents inhibitory effects of sumatriptan but not CP-122,288 and 5-CT on neurogenic plasma extravasation within guinea pig dura mater

The aim of this study was to examine whether GR-127,935, a 5-HT1B/1D receptor antagonist, blocks the inhibitory effects of sumatriptan, CP-122,288 and 5-carboxamidotryptamine (5-CT) on plasma protein extravasation, within guinea pig and rat dura matter, following electric stimulation of the trigeminal ganglion. Binding studies first established that GR-127,935 shows a 500-fold selectivity for 5-HT1D binding sites (labeled by [3H]L-694,247) versus 5-HT1F binding sites (labeled by [3H]sumatriptan in the presence of 50 nM 5-carboxamidotryptamine) in guinea pig forebrain homogenates (pKD +/- SD = 7.0 +/- 0.2 at 5-HT1F sites and 9.7 +/- 0.1 at 5-HT1D sites). In guinea pigs, GR-127,935 showed partial agonist activity and inhibited dural plasma protein extravasation. Increasing doses of GR-127,935 reversed the effect of sumatriptan, but did not affect the action of 5-CT and CP-122,288 (at a dose as high as 2 mumol/kg). Sumatriptan, CP 122,288 and 5-CT dose-responsively inhibited plasma protein extravasation. At a dose of 2 mumol/kg (but not at 0.2 mumol/kg), GR-127,935 right-shifted the dose-response curve of sumatriptan. No significant rightward shift was observed in the dose-response of CP-122,288 and 5-CT. In rats, GR-127,935 did not show any significant partial agonist activity. A dose of 0.2 mumol/kg was sufficient to right-shift the dose-response curve of sumatriptan. These data suggest that sumatriptan inhibits neurogenic inflammation via 5-HT1D alpha receptors in guinea pigs and 5-HT1D beta (5-HT1B) receptors in rats. Additional receptor subtypes are likely to be involved in the inhibition of plasma extravasation by CP-122,288 and 5-CT. Pertussis toxin reduced the inhibitory effects of both sumatriptan and 5-CT, but not of muscimol, known to act at GABAA receptors. These results suggest that 5-CT, as well as sumatriptan, act at a receptor linked to an inhibitory G-protein.

Effects of S20749, a close analogue of sumatriptan, on porcine carotid haemodynamics and human isolated coronary artery

Several acutely acting antimigraine drugs, including sumatriptan and other second generation 5-HT1D receptor agonists, have the ability to constrict porcine arteriovenous anastomoses. Sumatriptan also constricts the human isolated coronary artery. These two experimental models seem to serve as indicators, respectively, for the therapeutic and coronary side-effect potential of the compounds. Using these two models, we have now investigated the effects of S20749 (1-[2-(dimethylamino)ethyl]-naphthalene-7-methylsulfonamide), a close analogue of sumatriptan. S20749 (30, 100, 300 and 1000 micrograms.kg-1) decreased the total carotid blood flow by exclusively decreasing arteriovenous anastomotic blood flow; capillary blood flow was moderately increased. These changes were statistically significant with the highest two doses. S20749 moderately constricted the human isolated coronary artery (pD2: < or = 4.5: Fmax: > 11% of the contraction to 100 mM K+). The above results suggest that S20749 should be able to abort migraine headaches in patients.

Investigations with GMC2021 in experimental models predictive of antimigraine activity and coronary side-effect potential

Several acutely acting antimigraine drugs, including sumatriptan and other second generation 5-HT1D receptor agonists, have the ability to constrict porcine carotid arteriovenous anastomoses as well as the human isolated coronary artery. These two experimental models seem to serve as indicators, respectively, for the therapeutic and coronary side-effect potential of the compounds. Using these two models, we have now investigated the effects of GMC2021 (3-[2-(dimethylanimo)ethyl]-5-[(trifluoromethyl)sulfonyl]oxy][1 H]indole oxalate, a close analogue of sumatriptan. GMC2021 (30, 100, 300 and 1000 micrograms.kg-1, i.v.) decreased the total carotid blood flow by exclusively decreasing arteriovenous anastomotic blood flow; capillary blood flow to the skin and ears was moderately increased. The mean +/- S.E.M. dose of GMC2021 eliciting a 50% decrease (ED50) in the porcine carotid arteriovenous anastomotic blood flow was found to be 1.1 +/- 0.3 mumol.kg-1 and the highest dose (1000 micrograms.kg-1) produced a 67 +/- 4% reduction. The carotid haemodynamic effects of GMC2021 were reduced by the selective 5-HT1D receptor antagonist, GR127935 (N-[methoxy-3-(4-methyl-1- piperazinyl)phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)[1 , 1-biphenyl]-4-carboxamide hydrochloride), which completely antagonizes porcine carotid haemodynamic responses to sumatriptan (ED50: 0.16 mumol.kg-1, i.v.). Compared to sumatriptan (pD2: 6.12 +/- 0.15; Emax: 31.3 +/- 12.3% of contractions to 100 mM K+), GMC2021 was less potent in constricting the human isolated coronary artery (pD2: 5.45 +/- 0.2; Emax: 21.0 +/- 4.8% of contractions to 100 mM K+). The above results suggest that GMC2021 constricts carotid arteriovenous anastomoses partly by a 5-HT1D receptor and partly by another, probably novel, receptor and that GMC2021 should be able to abort migraine headaches in patients, with perhaps a less propensity for coronary side effects.

5-Carboxamido-tryptamine, CP-122,288 and dihydroergotamine but not sumatriptan, CP-93,129, and serotonin-5-O-carboxymethyl-glycyl -tyrosinamide block dural plasma protein extravasation in knockout mice that lack 5-hydroxytryptamine1B receptors

We studied the dural plasma protein extravasation response after unilateral electrical stimulation of the trigeminal ganglion in mice lacking serotonin 5-HT1B (5-HT1D beta) receptors by modifying a technique previously described in rats or guinea pigs. We investigated the inhibitory effects of six 5-HT1 receptor agonists in this model: 3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one (CP-93,129), sumatriptan, serotonin-5-O-carboxymethyl-glycyl -tyrosinamide (GTI), 5-methylaminosulfonylmethyl-3-(N-methylpyrrolidin-2R -ylmethyl)-1H-indole (CP-122,288), 5-carboxamido-tryptamine (5-CT), and dihydroergotamine. The plasma extravasation response did not differ between wild-type and mutant after vehicle injection. The potency of sumatriptan, CP-122,288, CP-93,129, and 5-CT in wild-type mice was similar to that previously reported for rats. CP-122,288 (1 nmol kg), 5-CT (1 nmol/kg), and dihydroergotamine (72 nmol/kg) inhibited plasma protein extravasation within dura mater after electrical trigeminal ganglion stimulation in both wild-type and knockout mice, which suggests that these agonists act predominantly via receptors other than 5-HT1B. Unlike the wild-type mice, CP-93,129 (1.4 mumol/kg), a specific 5-HT1B receptor agonist, had no effect in knockout mice. The same held true for sumatriptan (0.7 mumol/kg) and GTI (0.6 mumol/kg). These results suggest that CP-93,129, sumatriptan, and GTI exert their effects via 5-HT1B (5-HT1D beta) receptors in mice.

The in vivo pharmacological profile of a 5-HT1 receptor agonist, CP-122,288, a selective inhibitor of neurogenic inflammation

1. The aim of the present study was to investigate the in vivo pharmacological profile of CP-122,288, an indole-derivative with a conformationally restricted N-methylpyrrolidinyl basic side chain in the C-3 position. This C-3 substituent structurally differentiates CP-122,288 from the 5-HT1D receptor agonist sumatriptan, which possesses an N,N-dimethylaminoethyl group. [Formula: see text] 2. When administered prior to electrical stimulation of the trigeminal ganglion, CP-122,288 (0.3-300 ng kg-1, i.v.) produced a dose-related inhibition of plasma protein extravasation in rat dura mater (minimum effective dose, MED, 3 ng kg-1 i.v., P < 0.05; maximal inhibition of plasma extravasation at 30 ng kg-1 i.v., P < 0.01). Sumatriptan produced a similar inhibition of plasma leakage in the dura, but at much higher dose levels (MED, 100 micrograms kg-1 i.v., P < 0.05). Thus, CP-122,288 is of the order of 10(4) fold more potent than sumatriptan. 3. At all doses tested, CP-122,288 did not inhibit plasma protein extravasation measured in extracranial tissues such as the lower lip, eyelid, and conjunctiva. 4. In a separate series of studies in the anaesthetized rat, CP-122,288 (0.003-3 micrograms kg-1 i.v.) produced no change in either heart rate or mean arterial blood pressure, thus demonstrating that doses of CP-122,288 which inhibit plasma protein leakage in rat dura, are devoid of hemodynamic effects. 5. Following a 5 min period of electrical stimulation of the trigeminal ganglion, a 20 min period of sustained neurogenically-driven plasma extravasation, occurring in the absence of electrical stimulation, was initiated. By administration of the compound 5 min after completing the phase of electrical stimulation, this protocol permitted the evaluation of the activity of CP-122,288 on an ongoing and established inflammatory event. CP-122,288 (30 and 300 ng kg-1, i.v., P < 0.01 and P < 0.05, respectively) produced a complete inhibition of plasma protein leakage which was consistent with its effects when administered prior to trigeminal ganglion stimulation. 6. In the anaesthetized dog, CP-122,288 and sumatriptan, at 1-300 micrograms kg-1, i.v., produced a dose-dependent reduction in carotid arterial blood flow and coronary arterial diameter. These data demonstrate that sumatriptan inhibits neurogenic inflammation in the rat (MED, 100 micrograms kg-1, i.v.), and produces vasoconstriction in the dog, over a similar dose-range. Interestingly, doses of CP-122,288 that inhibit neurogenic inflammation in rat dura mater (0.3-300 ng kg-1) were demonstrated to be devoid of vasoconstrictor activity in either the carotid or coronary vascular beds of dog. 7. These data demonstrate that in the rat, CP-122,288 is a highly potent and selective inhibitor of neurogenic inflammation in intracranial tissues, at doses which are devoid of vasoconstrictor activity in dog. Potentially, CP-122,288 may be of use for the acute treatment of migraine, without the risk of cardiovascular side-effects.

[3H]sumatriptan labels both 5-HT1D and 5-HT1F receptor binding sites in the guinea pig brain: an autoradiographic study

We have used in vitro autoradiography to visualize [3H]sumatriptan binding sites in sections of guinea-pig and rat brain. In saturation studies, this ligand recognized a single saturable population of high affinity binding sites in all regions examined (pKD = 8.3-9.3). While 5-HT and the sumatriptan derivative CP-122,288 (5-methyl-aminosulfonylmethyl-3-(N-methylpyrrolidin-2R-yl-me thyl)- 1 H-indole) competed for [3H]sumatriptan binding sites with a high affinity and monophasic profile, displacement experiments with 5-carboxamidotryptamine revealed the existence of 2 classes of binding sites. The high affinity component (pKD = 9.2-9.9) probably corresponded to 5-HT1B (rat) or 5-HT1D (guinea-pig) receptors. The intermediate affinity (pKD = 5.7-7.3) of the other component, taken together with their high affinity for [3H]sumatriptan, was similar to that of the cloned 5-HT1F receptor. The regional distribution of the 5-HT1B/1D [3H]sumatriptan binding sites was in agreement with previously published studies (striatonigral system, hypothalamus, central gray, superficial layer of the superior colliculus) and corresponded to the pattern of serotonin-5-O-carboxymethyl-glycyl [125I]tyrosinamide labeling in consecutive sections. [3H]sumatriptan binding sites with a low affinity for 5-CT predominated in the intermediate neocortical layers, the claustrum (in the guinea-pig only), the mammillary nuclei, most of the thalamic nuclei and the principal oculomotor nucleus (in the guinea-pig only). This distribution is very similar to that of 5-HT1F mRNA, indicating further the identity of these sites with 5-HT1F receptors. Very high densities of 5-HT1F sites were also found in the rat parafascicular nucleus. Some regions, such as the caudate/nucleus, the lateral geniculate nuclei and the spinal trigeminal nucleus appeared to contain both 5-HT1B/1D and 5-HT1F binding sites. Ketanserin had a low affinity for [3H]sumatriptan binding sites in all guinea-pig brain regions, compatible with the presence of the 5-HT1D beta subtype. An exception was the substantia nigra, where a significant proportion of sites displayed an intermediate affinity for this compound, suggesting the presence of 5-HT1D chi receptors. [3H]5-HT labeled 5-HT1F sites in the claustrum and intermediate cortical layers in the guinea-pig. However these data show that [3H]sumatriptan, in the presence of 10 nM 5-carboxamidotryptamine, is a more suitable radioligand to study the distribution of 5-HT1F binding sites.

Effect of a 5-HT1 receptor agonist, CP-122,288, on oedema formation induced by stimulation of the rat saphenous nerve

Neurogenic oedema formation in the rat hind paw skin induced by electrical stimulation of the saphenous nerve and measured by extravasation of [125I]-albumin, was inhibited by the 5-HT1B receptor agonist, CP-93,129, and the novel tryptamine analogue, CP-122,288. Significant inhibition of up to 66% of control was observed with CP-122,288 (2 x 10(-14) - 2 x 10(-7) mol kg-1) and CP-93,129 (5 x 10(-7) - 5 x 10(-6) mol kg-1), with the minimum effective dose for CP-122,288 being about 10(7) fold less than that for CP-93,129. Oedema formation induced by the intradermal administration of exogenous mediators (substance P and histamine) in rat dorsal skin was not inhibited by CP-122,288 (2 x 10(-10) mol kg-1). These results suggest that CP-122,288 is a potent inhibitor of neurogenic inflammation in rat skin and that the effect may be due to a prejunctional inhibition of neuropeptide release.

The pre- and postjunctional activity of CP-122,288, a conformationally restricted analogue of sumatriptan

The present study investigated the pre- and postjunctional of CP-122,288 (5-methyl-aminosulphonylmethyl-3-(N-methylpyrrolidin-2R-yl-m ethyl)-1H-indole), an analogue of the vascular 5-HT1 receptor agonist, sumatriptan. CP-122,288 inhibited neurogenic plasma protein extravasation in rat dura with a potency approximately 40,000-fold greater than sumatriptan (ID50 values of 0.3 pmol/kg and 13.9 nmol/kg i.v. respectively). However, CP-122,288 was only approximately 2-fold more potent than sumatriptan at inhibiting neurogenically mediated contractions of the dog saphenous vein. CP-122,288 contracted the dog saphenous vein and basilar artery with a potency approximately 2-fold greater than that of sumatriptan. Both compounds possessed similar affinities at either human 5-HT1D alpha or 5-HT1D beta receptors. It is concluded that CP-122,288 exhibits a prejunctional selectivity in the meninges to inhibit dural plasma protein extravasation independent of 5-HT1D alpha and 5-HT1D beta receptor activation.

Suppression by the sumatriptan analogue, CP-122,288 of c-fos immunoreactivity in trigeminal nucleus caudalis induced by intracisternal capsaicin

1. The effects of an intravenously administered sumatriptan analogue were examined on c-fos-like immunoreactivity (c-fos-LI), a marker of neuronal activation, evoked within trigeminal nucleus caudalis (TNC) and other brain stem regions 2 h after intracisternal injection of the irritant, capsaicin (0.1 ml, 0.1 mM), in pentobarbitone-anaesthetized Hartley guinea-pigs. 2. C-fos-LI was assessed in eighteen serial sections (50 microns) using a polyclonal antiserum. A weighted average, reflecting total expression within lamina I, IIo of TNC was obtained from three representative levels (i.e., at -0.225 mm, -2.475 mm and -6.975 mm.). 3. Capsaicin caused significant labelling within lamina I, IIo, a region containing axonal terminations of small unmyelinated C-fibres, as well as within the nucleus of the solitary tract, area postrema and medial reticular nucleus. A similar distribution of positive cells was reported previously after intracisternal injection of other chemical irritants such as autologous blood or carrageenin. 4. Pretreatment with a conformationally restricted sumatriptan analogue (with some selectivity for 5-HT1B and 5-HTID receptor subtypes) CP-122,288, reduced the weighted average by approximately 50-60% (P < 0.05) in lamina I, IIo at > or = 100 pmol kg-1, i.v., but did not decrease cell number within area postrema, nucleus of the solitary tract or medial reticular nucleus. A similar pattern was reported previously following sumatriptan, dihydroergotamine or CP-93,129 administration after noxious meningeal stimulation. 5. We conclude that modifications at the amino-ethyl side chain of sumatriptan dramatically enhance the suppression of c-fos expression within TNC, a finding consistent with its remarkable potency against neurogenic plasma protein extravasation within dura mater. CP-122,288 and related analogues may serve as an important prototype for drug development in migraine and related headaches.

Conformationally restricted sumatriptan analogues, CP-122,288 and CP-122,638 exhibit enhanced potency against neurogenic inflammation in dura mater

CP-122,288 and CP-122,638 blocked plasma protein extravasation response within dura mater following trigeminal ganglion stimulation. The threshold (1 and 0.1 pmol/kg, respectively) was remarkably lower than for sumatriptan (7 nmol/kg), as was the dose at maximum response. As with sumatriptan, substance P-induced plasma leakage was unaffected by either compound, and metergoline only partially (27%) reversed the effects of CP-122,288. The data suggest the importance of modifications at the aminoethyl side chain to the actions of sumatriptan and possibly to the treatment of migraine headache.