Noncompetitive antagonism of BIBN4096BS on CGRP-induced responses in human subcutaneous arteries

Pharmacology of erenumab in human isolated coronary and meningeal arteries: Additional effect of gepants on top of a maximum effect of erenumab

BACKGROUND AND PURPOSE

Multiple drugs targeting the calcitonin gene-related peptide (CGRP) receptor have been developed for migraine treatment. Here, the effect of the monoclonal antibody erenumab on CGRP-induced vasorelaxation was investigated in human isolated blood vessels, as well as the effect of combining erenumab with the small molecule drugs, namely rimegepant, olcegepant, or sumatriptan.

EXPERIMENTAL APPROACH

Concentration-response curves to CGRP, adrenomedullin or pramlintide were constructed in human coronary artery (HCA) and human middle meningeal artery (HMMA) segments, incubated with or without erenumab and/or olcegepant. pA2 or pKb values were calculated to determine the potency of erenumab in both tissues. To study whether acutely acting antimigraine drugs exerted additional CGRP-blocking effects on top of erenumab, HCA segments were incubated with a maximally effective concentration of erenumab (3 μM), precontracted with KCl and exposed to CGRP, followed by rimegepant, olcegepant, or sumatriptan in increasing concentrations.

KEY RESULTS

Erenumab shifted the concentration-response curve to CGRP in both vascular tissues. However, in HCA, the Schild plot slope was significantly smaller than unity, whereas this was not the case in HMMA, indicating different CGRP receptor mechanisms in these tissues. In HCA, rimegepant, olcegepant and sumatriptan exerted additional effects on CGRP on top of a maximal effect of erenumab.

CONCLUSIONS AND IMPLICATIONS

Gepants have additional effects on top of erenumab for CGRP-induced relaxation and could be effective in treating migraine attacks in patients already using erenumab as prophylaxis.

The effects of CGRP in vascular tissue - Classical vasodilation, shadowed effects and systemic dilemmas

Vascular tissue consists of endothelial cells, vasoactive smooth muscle cells and perivascular nerves. The perivascular sensory neuropeptide CGRP has demonstrated potent vasodilatory effects in any arterial vasculature examined so far, and a local protective CGRP-circuit of sensory nerve terminal CGRP release and smooth muscle cell CGRP action is evident. The significant vasodilatory effect has shadowed multiple other effects of CGRP in the vascular tissue and we therefore thoroughly review vascular actions of CGRP on endothelial cells, vascular smooth muscle cells and perivascular nerve terminals. The actions beyond vasodilation includes neuronal re-uptake and neuromodulation, angiogenic, proliferative and antiproliferative, pro- and anti-inflammatory actions which vary depending on the target cell and anatomical location. In addition to the classical perivascular nerve-smooth muscle CGRP circuit, we review existing evidence for a shadowed endothelial autocrine pathway for CGRP. Finally, we discuss the impact of local and systemic actions of CGRP in vascular regulation and protection from hypertensive and ischemic heart conditions with special focus on therapeutic CGRP agonists and antagonists.

Vascular and molecular pharmacology of the metabolically stable CGRP analogue, SAX

The main purpose of this study was to compare in vitro pharmacological properties of human αCGRP (CGRP) and a recently discovered metabolically stable CGRP analogue, SAX, in isolated rat and human artery segments. In rat, CGRP and SAX induced similar vasodilatory responses in isolated mesenteric artery with the potency of SAX being lower than that of CGRP (vasodilatory pEC₅₀ 8.2 ± 0.12 and 9.0 ± 0.11, respectively). A corresponding difference in receptor binding affinity of SAX and CGRP was determined in rat cerebral membranes (pKi 8.3 ± 0.19 and 9.3 ± 0.14, respectively). CGRP and SAX-induced vasodilation was antagonised with similar potencies by the CGRP receptor antagonist BIBN4096BS supporting a uniform receptor population for the agonists. In human tissue, SAX and CGRP induced similar pharmacological responses with different potencies in subcutaneous artery (vasodilatory pEC₅₀ 8.8 ± 0.18 and 9.5 ± 0.13, respectively) and human recombinant receptors (cAMP signalling pEC₅₀ 9.1 ± 0.16 and 10.2 ± 0.19). Like in the rat mesenteric artery, both SAX and CGRP-responses were inhibited by the CGRP receptor antagonist BIBN4096BS with similar antagonistic potencies. In conclusion, all pharmacological characteristics of SAX and CGRP in human and rat sources points towards action via a uniform BIBN4096BS sensitive receptor population with the potency of SAX being 5-10 fold lower than that of CGRP.

Differential inhibitory response to telcagepant on αCGRP induced vasorelaxation and intracellular Ca2+ levels in the perfused and non-perfused isolated rat middle cerebral artery

Background

Calcitonin gene-related peptide (CGRP) is one of the most potent endogenous vasodilators identified to date. The present study elucidates the differential interaction of CGRP, its receptor and the effect of the CGRP-receptor antagonist telcagepant on intracellular Ca²⁺ -levels and tension in rat middle cerebral arteries (MCA) by pressurized arteriography, FURA-2/wire myography and immunohistochemistry.

Methods

A pressurized arteriograph system was used to evaluate changes in MCA tension when subjected to CGRP and/or telcagepant. Intracellular calcium levels were evaluated using a FURA-2/wire myograph system. Localization of the CGRP-receptor components was verified using immunohistochemistry.

Results

Abluminal but not luminal αCGRP (10^-12-10^-6 M) caused concentration-dependent vasorelaxation in rat MCA. Luminal telcagepant (10^-6 M) failed to inhibit this relaxation, while abluminal telcagepant inhibited the relaxation (10^-6 M). Using the FURA-2 method in combination with wire myography we observed that αCGRP reduced intracellular calcium levels and in parallel the vascular tone. Telcagepant (10^-6 M) inhibited both vasorelaxation and drop in intracellular calcium levels. Both functional components of the CGRP receptor, CLR (calcitonin receptor-like receptor) and RAMP1 (receptor activity modifying peptide 1) were found in the smooth muscle cells but not in the endothelial cells of the cerebral vasculature.

Conclusions

This study thus demonstrates the relaxant effect of αCGRP on rat MCA. The vasorelaxation is associated with a simultaneous decrease in intracellular calcium levels. Telcagepant reduced relaxation and thwarted the reduction in intracellular calcium levels localized in the vascular smooth muscle cells. In addition, telcagepant may act as a non-competitive antagonist at concentrations greater than 10^-8 M.

Binding and functional pharmacological characteristics of gepant-type antagonists in rat brain and mesenteric arteries

AIM

The neuropeptide calcitonin gene-related peptide (CGRP) is found in afferent sensory nerve fibers innervating the resistance arteries and plays a pivotal role in a number of neurovascular diseases such as migraine and subarachnoid bleedings. The present study investigates the binding and antagonistic characteristics of small non-peptide CGRP receptor antagonists (i.e. gepants) in isolated rat brain and mesenteric resistance arteries.

METHODS

The antagonistic behavior of gepants was investigated in isolated rat mesenteric arteries using a wire myograph setup while binding of gepants to CGRP receptors was investigated in rat brain membranes using a radioligand competitive binding assay. Furthermore, the histological location of the key components of CGRP receptor (RAMP1 and CLR) was assessed by immunohistochemistry.

RESULTS

Our functional studies clearly show that all gepants are reversible competitive antagonists producing Schild plot slopes not significantly different from unity and thus suggesting presence of a uniform CGRP receptor population in the arteries. A uniform receptor population was also confirmed by radioligand competitive binding studies showing similar affinities for the gepants in rat brain and mesenteric arteries, the exception being rimegepant which had 50-fold lower affinity in brain than mesenteric arteries. CLR and RAMP1 were shown to be located in both vascular smooth muscle and endothelial cells of rat mesenteric arteries by immunohistochemistry.

CONCLUSION

The present results indicate that, despite species differences in the CGRP receptor affinity, the antagonistic nature of these gepants, the distribution pattern of CGRP receptor components and the mechanism behind CGRP-induced vasodilation seem to be similar in resistance-sized arteries of human and rats.

Differential localization and characterization of functional calcitonin gene-related peptide receptors in human subcutaneous arteries

AIM

Calcitonin gene-related peptide (CGRP) and its receptor are widely distributed within the circulation and the mechanism behind its vasodilation not only differs from one animal species to another but is also dependent on the type and size of vessel. The present study examines the nature of CGRP-induced vasodilation, characteristics of the CGRP receptor antagonist telcagepant and localization of the key components calcitonin receptor-like receptor (CLR) and receptor activity modifying protein 1 (RAMP1) of the CGRP receptor in human subcutaneous arteries.

METHODS

CGRP-induced vasodilation and receptor localization in human subcutaneous arteries were studied by wire myograph in the presence and absence of the CGRP receptor antagonist telcagepant and immunohistochemistry respectively.

RESULTS

At concentrations of 1, 3, 5, 10 and 30 nm, telcagepant had a competitive antagonist-like behaviour characterized by a parallel rightwards shift in the log CGRP concentration-tension/calcium curve with no depression of the maximal relaxation. CGRP-induced vasodilation was not affected by mechanical removal of the endothelium or addition of L-NG-nitroarginine methyl ester and indomethacin, antagonists for synthesis of nitric oxide and prostaglandins, respectively. CLR and RAMP1 were localized in the vascular smooth muscle and endothelial cells.

CONCLUSION

The present results indicate that CGRP exerts its vasodilatory effect in human subcutaneous arteries by binding to its receptors located on the smooth muscle cells and is suggested to be endothelium-independent. In conclusion, these results underline the dynamic distribution of CGRP receptor components in the human circulation reflecting the important role of CGRP in fine tuning of the blood flow in resistance arteries.

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.

Characterisation of CGRP receptors in the human isolated middle meningeal artery

Although the understanding of migraine pathophysiology is still incomplete, there seems to be little doubt that dilatation of cranial blood vessels, including meningeal arteries, is involved in the headache phase of migraine. Since calcitonin gene-related peptide (CGRP) has been implicated in this vasodilatation, the present study set out to compare the relaxant effects of the endogenous ligand h-alphaCGRP, and [ethylamide-Cys(2,7)]h-alphaCGRP ([Cys(Et)(2,7)]h-alphaCGRP), a CGRP(2) receptor agonist, on human isolated middle meningeal artery segments, precontracted with KCl. Classical Schild plot analysis was used to characterise the receptor population in this artery using BIBN4096BS and h-alphaCGRP(8-37) as antagonists. h-alphaCGRP relaxed arterial segments more potently than [Cys(Et)(2,7)]h-alphaCGRP (pEC(50): 8.51+/-0.16 and 7.48+/-0.24, respectively), while the maximal responses to these agonists were not significantly different. BIBN4096BS equipotently blocked the relaxations induced by both agonists with a pA(2) of approximately 10 and with a Schild plot slope not significantly different from unity. h-alphaCGRP(8-37) also antagonised the response to h-alphaCGRP with a pA(2) of 6.46+/-0.16 and a Schild plot slope not different from unity. Furthermore, the results obtained from RT-PCR studies confirmed the presence of all the essential components required for a functional CGRP(1) receptor in these arteries. Considering the high antagonist potency of BIBN4096BS, coupled to the lower agonist potency of [Cys (Et)(2,7)]h-alphaCGRP, it is reasonable to suggest a predominant role of CGRP(1) receptors in the human middle meningeal artery. This view is reinforced by Schild plot analysis, which revealed a slope of unity in all experiments, giving further evidence for a homogeneous CGRP receptor population in this vascular preparation.

Characterisation of CGRP receptors in human and porcine isolated coronary arteries: evidence for CGRP receptor heterogeneity

This study sets out to characterise calcitonin gene-related peptide (CGRP) receptors in human and porcine isolated proximal and distal coronary arteries using BIBN4096BS. Human (h)-alphaCGRP induced relaxations that were blocked by BIBN4096BS in all arteries studied. In contrast to the other vessels, the Schild plot slope in the human distal coronary artery segments (0.68 +/- 0.07) was significantly less than unity and BIBN4096BS potently blocked these responses (pK(b) (10 nM): 9.29 +/- 0.34, n = 5). In the same preparation, h-alphaCGRP(8-37) behaved as a weak antagonist of h-alphaCGRP-induced relaxations (pK(b) (3 microM): 6.28 +/- 0.17, n = 4), with also a Schild plot slope smaller than unity. The linear agonists, [ethylamide-Cys(2,7)]-h-alphaCGRP ([Cys(Et)(2,7)]-h-alphaCGRP) and [acetimidomethyl-Cys(2,7)]-h-alphaCGRP ([Cys(Acm)(2,7)]-h-alphaCGRP), had a high potency (pEC(50): 8.21 +/- 0.25 and 7.25 +/- 0.14, respectively), suggesting the presence of CGRP(2) receptors, while the potent blockade by BIBN4096BS (pK(b) (10 nM): 10.13 +/- 0.29 and 9.95 +/- 0.11, respectively) points to the presence of CGRP(1) receptors. Using RT-PCR, mRNAs encoding for the essential components for functional CGRP(1) receptors were demonstrated in both human proximal and distal coronary artery. Further, h-alphaCGRP (100 nM) increased cAMP levels, and this was attenuated by BIBN4096BS (1 microM). The above results demonstrate the presence of CGRP(1) receptors in all coronary artery segments investigated, but the human distal coronary artery segments seem to have an additional population of CGRP receptors not complying with the currently classified CGRP(1) or CGRP(2) receptors.

GPCR modulation by RAMPs

Our conceptual understanding of the molecular architecture of G-protein coupled receptors (GPCRs) has transformed over the last decade. Once considered as largely independent functional units (aside from their interaction with the G-protein itself), it is now clear that a single GPCR is but part of a multifaceted signaling complex, each component providing an additional layer of sophistication. Receptor activity-modifying proteins (RAMPs) provide a notable example of proteins that interact with GPCRs to modify their function. They act as pharmacological switches, modifying GPCR pharmacology for a particular subset of receptors. However, there is accumulating evidence that these ubiquitous proteins have a broader role, regulating signaling and receptor trafficking. This article aims to provide the reader with a comprehensive appraisal of RAMP literature and perhaps some insight into the impact that their discovery has had on those who study GPCRs.