Shifting Attention from the Outside to the Inside of the Cell during Migraine

By Neil Andrews | November 7, 2023 | Posted in

New research shows that second messenger signaling spurs migraine attacks even in the presence of CGRP receptor blockade.

The development of drugs that target calcitonin gene-related peptide (CGRP) has been a huge success for migraine treatment, providing relief to many people living with migraine who don’t respond to older acute care drugs like triptans or preventive drugs like epilepsy medications. But not everyone who receives anti-CGRP treatment benefits from it, adding to data that there are other molecular mechanisms driving this headache disorder. A new study now provides further evidence that researchers and drug developers should look beyond the CGRP receptor – and into the cell itself.

Investigators led by Messoud Ashina, Copenhagen University Hospital – Rigshospitalet and the University of Copenhagen in Denmark, used cilostazol in patients who had been treated with the anti-CGRP antibody erenumab. Cilostazol is a drug that increases intracellular levels of cyclic adenosine monophosphate (cAMP), a so-called second messenger molecule with numerous functions inside the cell including the regulation of ion channels.

The researchers found, in this randomized, double-blind, placebo-controlled trial, that cilostazol, which their previous work showed can spur migraine attacks in patients, still caused attacks even in those who had received erenumab preventively, just as it spurred attacks in those randomized to placebo. That finding not only underscores the complex pathophysiology of migraine but also highlights intracellular mechanisms, downstream of the CGRP receptor, as promising places to look for the next generation of migraine treatments.

“This study shows that even when you block the CGRP receptor, you can cause migraine by giving cilostazol and increasing cAMP in the cytoplasm,” said Alan Rapoport, David Geffen School of Medicine at University of California, Los Angeles, US, in an interview with Migraine Science Collaborative.

Rapoport, who called the research “provocative and elegant,” was enthusiastic about the clinical potential of targeting intracellular mechanisms to develop new treatments.

“People have been looking at these intracellular mechanisms for a long time, but from my point of view, this is the first time we see that it’s probably going to be clinically important going forward,” he said.

The study appeared in Brain online ahead of print on August 4, 2023.

Putting a human provocation model to a new test
The new study follows an approach – using different signaling molecules to trigger migraine attacks in people, also known as a human provocation model – that has long been a part of Ashina’s research.

“Studying migraine is different than studying multiple sclerosis, dementia, or Parkinson disease, for example, because migraine is a disease characterized by recurrent attacks that come and go; between the attacks you are asymptomatic,” Ashina told Migraine Science Collaborative. “This provides a quite unique opportunity to express the disease for a certain duration of time using signaling molecules,” he said of the human provocation model.

Ashina’s previous work had focused on signaling molecules like CGRP and cilostazol. But while CGRP acts on a receptor at the cell surface, cilostazol works intracellularly, bypassing the CGRP receptor. It does so by inhibiting phosphodiesterase-3 (PDE3), an enzyme that metabolizes cAMP. By keeping PDE3 in check, cilostazol increases the amount of cAMP within the cell, which can eventually affect the activity of ion channels that may contribute to migraine.

For their new study, Ashina and colleagues were interested in learning more about the contribution of intracellular mechanisms to migraine and used cilostazol for that purpose. The researchers were especially curious to learn whether cilostazol would cause headache independently of CGRP receptor blockade.

Second messenger signaling and migraine

Study design. Participants were enrolled in a randomized, double-blind, placebo-controlled, parallel trial. Participants were randomly allocated to a subcutaneous administration of 140 mg of erenumab or placebo (isotonic saline). Seven to 21 days after study drug administration, participants were randomly allocated to receive a continuous intravenous infusion of 1.5 μg/min of calcitonin gene-related peptide (CGRP) over 20 min or oral intake of 200 mg cilostazol on separate experimental study days. Credit: Image and caption from Do et al. Brain. 2023 Aug 4; Online ahead of print.

Cilostazol causes headache even in patients who received erenumab
To test the idea, the investigators performed a clinical trial, at a single center in Denmark, that ultimately included 75 participants aged 18 to 65 years (an average of 33 years of age) for analysis. The participants all had a previous diagnosis of migraine, with half randomized to receive subcutaneous erenumab or placebo. Then, one to three weeks later, half of participants received intravenous CGRP, while the other half received oral cilostazol.

As expected, erenumab improved the incidence of migraine attacks after CGRP administration, with 27% of the 37 subjects receiving erenumab having an attack, compared to 53% of the 38 subjects who received placebo.

However, the key finding from the study was that there were no significant differences in attack incidence after cilostazol in the erenumab group versus those in the placebo group – showing that cilostazol caused headache independently of CGRP receptor blockade. Along these lines, in the placebo group, all (but one) participant who experienced a migraine attack after CGRP had an attack after cilostazol, but, similarly, for the erenumab group, all of those who had an attack after CGRP still had an attack after cilostazol.

“There was no effect of prior erenumab treatment on the cilostazol-induced migraine attacks. suggesting that these intracellular mechanisms are very important in the migraine cascade,” Ashina said.

“Everything taking place in migraine is quite complex, and in this puzzle, the intracellular mechanisms, when they are strong enough, are taking over and that’s why you get an eruption of the attacks even if you get the medication [erenumab],” he added.

The investigators also looked at parameters of blood vessel function. As anticipated, they saw that erenumab reduced dilation of the superficial temporal artery, and of the radial artery, after CGRP. The anti-CGRP drug also lessened changes in mean arterial blood pressure and heart rate after CGRP. But, consistent with the earlier results on migraine attacks, there were no such differences between the erenumab and placebo groups after cilostazol administration. Once again, the results pointed to effects of cilostazol that are independent of CGRP receptor blockade.

Targeting intracellular mechanisms
If intracellular mechanisms involving cAMP contribute to headache, is it possible to target them as a way to prevent migraine attacks?

“Wow, this is a tough question,” Ashina said. He noted that with the traditional pharmacological approach, which targets receptors on the cell surface, there is a lower risk of side effects than when manipulating intracellular mechanisms downstream of those receptors. The answer, he said, depends on whether it will be possible to target specific ion channels affected by cAMP based on features such as the type of channel or where the channel is located. Ashina is now pursuing that research.

“The question is whether we can find a selective channel and a selective drug that we can use to prevent migraine attacks,” he said.

If the research proves that manipulating the intracellular cAMP system is feasible, the therapeutic payoff would be considerable, in light of the variability in patient responses to existing therapies.

“Even though I have many medications to use right now that often work for my migraine patients, I don’t always have the right one for any individual patient,” Rapoport said. “We need this diversity of treatments, and we sometimes even use two treatments together, with separate mechanisms of action, that work better than one alone. So I’m really excited about targeting these novel intracellular mechanisms.”

As for Ashina, he hopes that one message readers will take away from his paper is the importance of human provocation models as a way to understand the pathophysiology of migraine.

“I don’t want to exaggerate, but maybe these models are the most important way to study migraine, and not many people appreciate that because it is unique that we can do that for this condition. The human models allow us to discover the whole complexity of migraine and map the signaling pathways responsible for it.”

Neil Andrews is a science journalist and executive editor of the Migraine Science Collaborative. Follow him on Twitter @NeilAndrews

Reference
Second messenger signaling bypasses CGRP receptor blockade to provoke migraine attacks in humans.
Do et al.
2023 Aug 4; Online ahead of print.

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Neil Andrews is a science journalist and editor based in New York City. He has over two decades of experience covering science and medicine for expert and non-expert audiences alike. He is also the executive editor of the Migraine Science Collaborative, where he manages the day to day operations of the site. Previously he was the executive editor of the Pain Research Forum.

When not thinking and writing about neuroscience, Neil spends much of his free time on his Peloton and exploring NYC. He is also on a quest to satisfy his coffee cravings by visiting every independent coffee shop in the city. Follow him on Twitter @NeilAndrews.

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