FINAL REPORT: Targeting TRPA1 Channels For Novel Migraine Therapeutics

Summary

TRPA1 is emerging as a novel target for the development of drugs for migraine treatment. The transient receptor potential Ankyrin 1 (TRPA1), a cation channel expressed by nociceptors, plays a critical role in migraine. TRPA1 is activated by a series of pain provoking exogenous and endogenous agents which are responsible for the release of calcitonin gene-related peptide (CGRP). While some known TRPA1 activators have been identified as migraine triggers, a series of antimigraine medicines have been shown to inhibit/desensitize the channel.

We focused our research for this grant on the pharmacological profile of dipyrone, antipyrine and propyphenazone, pyrazolone derivatives (PDs), successfully used for more than a century in a number of painful diseases. We discovered that the PDs dipyrone and propyphenazone, but not their main metabolites, display a TRPA1-dependent analgesic profile, behaving as TRPA1 antagonists. We then synthetized a small library of PD analogues that have been designed with the aim of preventing the production of undesired metabolites that may be responsible for the worst side effects of PDs. We also set up and validated the experimental conditions for the in vitro and in vivo pharmacological characterization of the synthetized ligands.

Hypothesis vs. Findings

There is evidence suggesting that the analgesic activity of PDs could be improved by the chemical manipulation of the pyrazolone scaffold aimed at enhancing their potency in blocking the TRPA1 opening. We were able to identify two PDs (T1-05 and T1-13) that display TRPA1 antagonist activity with significantly higher potency (10-fold) than dipyrone in the in vitro calcium mobilization assay. We tried to validate the dynamic mass redistribution assay (DMR) for the in vitro characterization of our compounds; however, the results obtained comparing DMR with calcium mobilization experiments demonstrated that the latter assay is more sensitive, and therefore more suitable for screening purposes.

Unanswered Questions

The next step will be to test selected compounds by using the TRPA1-depedent component of the formalin assay in mice, which we validated in this study. In addition, we plan to set up and validate a mouse model predictive for migraine by using the home cage wheel running test after the chemical intracranial dural stimulation with inflammatory soup. This model mimics the reduction in routine physical activity commonly caused by migraine in humans. The anti-migraine therapeutic potential of the best TRPA1 antagonists identified in this study will be assessed using these in vivo assays.

 What This Research Means to You

The Migraine Research Foundation grant has allowed us to obtain a series of PD analogs with improved in vitro profile as TRPA1 inhibitors that are potentially devoid of the metabolic instability of dipyrone, our reference analgesic. The synthetized compounds identified a new and previously unexplored chemotype in the current scenario of TRPA1 ligands. Although more preliminary work is required, we are confident that our research effort will pave the way for the development of anti-migraine agents with a new mechanism of action.