A preclinical study reports that targeting an enzyme with a crucial role in protein synthesis improves hypersensitivity in rodent models of migraine. The strategy has promising therapeutic potential to treat migraine in people.
It’s a familiar refrain in molecular biology: DNA, which provides the instructions for making proteins, is first transcribed into a single-stranded intermediate, messenger RNA, which in turn is “translated” into proteins. More than evoking memories of high school biology – good memories or bad ones, perhaps depending on your grades – this process is crucial for producing the so-called workhorses of the cell, functioning as enzymes, antibodies, or cell messengers, just to name a few roles for proteins.
But what if you could interrupt the translation of mRNA into proteins to treat disease? It’s an approach that cancer researchers are already notably putting to the test, and now migraine researchers are doing the same.
In a new paper that appeared online October 27, 2022, in the journal Brain, a group led by Greg Dussor, University of Texas at Dallas, US, report that inhibiting one of the isoforms of MNK (MNK1), an enzyme with a fundamental role in the regulation of translation, alleviated hypersensitivity in two different mouse models of migraine. Whether through pharmacological or genetic means, the strategy produced strong effects, improving prospects for developing novel migraine drugs that work differently from calcitonin gene-related peptide (CGRP)-targeted and other established migraine therapies.
“This paper is an important step forward,” said Arkady Khoutorsky, a pain researcher at McGill University, Montreal, Canada, who has studied MNK in the context of learning and memory but was not involved in the current research. “It gives you the opportunity to develop inhibitors of MNK to potentially use in people. I’m really happy to see such robust results.”
A one-two punch
MNK plays an important part in translation regulation by phosphorylating another protein called eIF4E. (Phosphorylation is a chemical modification in which phosphate groups are attached to molecules like proteins.)
In previous work using animals, current study co-author Ted Price and colleagues showed that the phosphorylation of eIF4E results in the translation of mRNA into proteins that drive the excitability of nociceptors and the subsequent development of chronic pain. That finding provided the basis for the current study’s focus on a potential role for the MNK/eIF4E pathway in migraine.
“We know there’s plasticity occurring in the nervous system that contributes to migraine,” said Dussor, referring to the nervous system’s ability to change in response to experience and injury. “Because this particular pathway had been shown to be important in plasticity in other contexts, we wanted to know whether it could be contributing to something relevant to migraine as well.”
So, the investigators, including first author Jacob Lackovic, tested that hypothesis in two different rodent models of migraine, comparing wild-type mice to genetically engineered knockout mice missing MNK1.
For the first model, the group applied interleukin-6 (IL-6), a pro-inflammatory cytokine, onto the dura mater of mice, which caused periorbital hypersensitivity in wild-type animals. The idea behind this model is that after the mice recover from the IL-6, they are “primed” to respond to a second insult, more so than an animal that had not received the IL-6 “first hit” – this is known as hyperalgesic priming.
The scientists showed that, compared to wild-type animals in which MNK1 is still present, knockout mice were less hypersensitive to IL-6. The knockouts also failed to show a priming response, as they had less hypersensitivity to a second hit, in this case application to the dura mater of a synthetic solution at a pH of 7.0 (pH is a measure of how acidic or basic an aqueous solution is. A pH of 7.0 is considered neutral and does not normally cause hypersensitivity). Together, the results implicated MNK1 as a contributor to the hypersensitivity present in this particular migraine model.
For the second model, the researchers again used their hyperalgesic priming method, this time subjecting wild-type and MNK1 knockout animals to repeated restraint stress, as a first hit. Restraining mice in their cages is a common technique used to assess the effects of stress in rodents – and there was a solid rationale to use it in the current study.
“The reason we stress the animals is because stress is the most commonly reported trigger of migraines in humans. So that’s why we developed this preclinical stress model. I think the effects that we’ve shown with regard to stress in MNK1 knockout animals are really important from a translational medicine standpoint,” said Lackovic.
Indeed, compared to wild-type animals experiencing restraint stress, MNK1 knockout animals subjected to it did not show priming in response to a second hit to the dura mater, in this instance sodium nitroprusside (a chemical called a nitric oxide donor that generates nitric oxide, which is known to cause headaches). This again pointed to a role for MNK enzymes and translation in the development of hypersensitivity in a preclinical migraine model.
Interestingly, Dussor said that the hyperalgesic priming strategy is a more suitable fit for headache research, compared to pain research where it has been used more often.
“I think hyperalgesic priming is a much better model for headache because this is exactly what happens in people with migraine: Something happened to them in the past to sensitize them but between attacks, they look entirely normal; there’s nothing wrong with them. Then they’re exposed to something that typically does not cause problems, like a stressor, a certain food or a change in a sleep habit – something that shouldn’t cause a migraine attack and doesn’t in people without migraine. So this two-hit model is really nice for looking at mechanisms that cause sensitization to otherwise normal or subthreshold stimuli,” Dussor said.
A new type of migraine drug?
To confirm and extend their findings, the scientists took an additional step: Instead of knocking out MNK genetically, they now used a chemical inhibitor of MNK and tested what effects that manipulation had on hyperalgesic priming.
An hour after receiving the inhibitor, mice received either IL-6 or the pH 7.0 solution. Compared to animals given a control substance, those given the MNK inhibitor showed less periorbital hypersensitivity in response to both agents. They also grimaced less, another clue that these animals were less hypersensitive.
“The effects are very robust, especially for the second phase of the priming model, both with the pharmacology and with the MNK1 knockouts. It’s a good sign” for future development of MNK inhibitors, said Khoutorsky.
Speaking of drug development, 4E Therapeutics is a company developing MNK inhibitors to treat pain and migraine. The company, which was co-founded by current study co-author Price, is now working to improve upon the particular inhibitor used in the study.
“We at 4E have optimized new MNK inhibitors to be more specific, not get into the brain, and to have optimized pharmacokinetics for pain and migraine treatment,” Price wrote to MSC in an email. “We are racing forward to the clinic as fast as possible, and we are hopeful to begin phase 1 clinical trials when we have approval to do so.” (Editor’s note: Price, Dussor, and Lackovic have filed a provisional patent based on the new study results. The patent is licensed to 4E.)
Interestingly, there is an inhibitor of MNK in clinical trials for cancer treatment, which further builds the case for MNK inhibition as a therapeutic avenue to treat other human diseases.
“This approach might be rapidly translated if that compound ultimately ends up being approved by the FDA and is safe to use outside of cancer. So, we may not be that far away from having something that would target this mechanism for migraine treatment,” Dussor said.
Dussor added that researchers will need to figure out when to administer an inhibitor of MNK if they want to target translation as a potential migraine therapy.
“Do you give it at the time of a migraine attack? Do you give it between migraine attacks to try to quiet down the plasticity that has developed, that is allowing the sensitization that occurs in migraine? Those are good questions we don’t know the answers to,” he said.
Important research questions remain, too, including how stress engages the MNK/eIF4E pathway, which mRNAs are translated into proteins, and where in a neuron – at the terminals of axons or within the cell body – the translation takes place. Perhaps even non-neuronal cells play a role. Grappling with whether an inhibitor of the MNK/eIF4E pathway wields its effects in the peripheral or central nervous system, or both, and whether the new findings broadly apply beyond the two migraine models used in the current study should also keep researchers busy for a while.
Dussor also emphasized that the study serves as a good example of the benefits that come from a cross-pollination of ideas from different research areas.
“This is a mechanism that has been explored in other contexts. I think this is a nice example of how people can pull things from other fields and test whether or not they might be relevant in the context of migraine.”
Neil Andrews is a science journalist and executive editor of the Migraine Science Collaborative. Follow him on Twitter @NeilAndrews
MNK1/2 contributes to periorbital hypersensitivity and hyperalgesic priming in preclinical migraine models.
Lackovic et al.
Brain. 2022 Oct 27;awac386. Online ahead of print.
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
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