Donitriptan

Abstract: Calcitonin gene related peptide (CGRP) released from the C-fibers projecting from the trigeminal ganglion to the meninges has been suggested to play a crucial role in the pathophysiology of headache, particularly migraine. In humans it has been shown that CGRP is released during migraine-attacks, and this is attenuated by the administration of typical anti-migraine drugs such as dihydroergotamine or sumatriptan. We describe a new rat model which allows the study of CGRP release from the meninges into venous blood following activation of the trigeminal vascular system. The effects of classical and new anti-migraine drugs such as acetylsalicylic acid (ASA), sumatriptan and the new high efficacy 5-HT1B/1D agonist donitriptan (4-[4-[2-(2-aminoethyl)-1H-indol-5-yloxyl]acetyl]piperazinyl-1-yl]benzonitrile) were evaluated in comparison with the established model of neurogenic inflammation in the meninges. Sumatriptan and donitriptan inhibited CGRP release as well as neurogenic inflammation. ASA, however, attenuated neurogenic inflammation, but not CGRP release, confirming the concept of prejunctional inhibition of CGRP release by 5-HT1B/1D receptors. This new model allows the further study of prejunctional pharmacology and mechanisms of neuropeptide release in the trigeminal vascular system, which might be crucial for the further development of potent, more effective anti-migraine drugs.

Abstract: Background and purpose: It has been suggested that during a migraine attack capsaicin-sensitive trigeminal sensory nerves release calcitonin gene-related peptide (CGRP), resulting in cranial vasodilatation and central nociception; hence, trigeminal inhibition may prevent this vasodilatation and abort migraine headache. This study investigated the effects of the agonists sumatriptan (5-HT1B/1D water-soluble), donitriptan (5-HT1B/1D lipid-soluble), PNU-142633 (5-HT1D water-soluble) and PNU-109291 (5-HT1D lipid-soluble) on vasodilator responses to capsaicin, α-CGRP and acetylcholine in dog external carotid artery.

Abstract: We hypothesized that the limited acute therapeutic effectiveness of tryptamine derivatives in alleviating migraine headache could be explained by the relatively low intrinsic activity of these agents at 5-HT1B/1D receptors. Donitriptan is a novel arylpiperazide 5-hydroxytryptamine (5-HT) derivative which was designed to exploit the higher potency and efficacy properties of 5-HT compared to tryptamine at 5-HT1B/1D receptors. In vitro, donitriptan has subnanomolar affinity for nonhuman and human 5-HT1B/1D receptors and micromolar affinity for the 5-HTip subtype. Donitritpan potently inhibited forskolin-induced cAMP formation and enhanced specific GTP35γS specific binding to a greater extent than tryptamine derivatives and equivalent to 5-HT in C6 cells expressing human 5-HT1B or 5-HT1D receptors. Donitriptan produced more potent and larger amplitude increases in hyperpolarizing Ca2+-dependent K+ current than sumatriptan in guinea pig isolated trigeminal ganglion neurons, and was more potent than tryptamine derivatives in eliciting contractile responses in rabbit isolated saphenous vein rings. In vivo, donitriptan evoked more potent, longer-lasting and greater amplitude carotid vasoconstrictor responses than tryptamine derivatives in anesthetized pigs; and in contrast to sumatriptan, naratriptan or zolmitriptan, produced long-lasting, dose-dependent decreases in unilateral carotid blood flow in conscious dogs at doses from 0.63 mg/kg p.o. without affecting heart rate or behavior. Oral donitriptan also evoked hypothermic responses in guinea pigs suggesting that the compound gains access to the brain. Donitriptan is thus a selective, potent 5-HT1B/1D receptor agonist which can be distinguished from tryptamine derivatives in consistently exerting high intrinsic activity at these receptors in a series of vascular and neuronal models relevant to migraine. Advantages in terms of therapeutic effectiveness in the acute relief of migraine headache over currently available triptans can be expected to include greater response rates and consistency of pain relief, a lower incidence of migraine recurrence and better tolerability. The acute anti-migraine potential of the first high efficacy 5-HT1B/1D agonist of its kind, donitriptan, is currently being investigated in man.