RgIA5474 as a Novel α9α10 Nicotinic Acetylcholine Receptor Antagonist to Treat Migraine - Project Summary Treatment of episodic migraine relies on acute therapies that are often not effective in as many as half of the patients. We wish to test the relevance of α9α10 nicotinic acetylcholine receptors (nAChRs) as a new target for the treatment of migraine. We hypothesize that RgIA5474, a peripherally restricted, highly selective α9α10 nAChR antagonist, may be effective in the treatment of migraine-like pain, especially for patients who don’t respond to CGRP blockers and are contraindicated for triptans. This hypothesis originated from the realization of strong autonomic nature of symptoms associated with migraine. The α9-expressing nAChR is highly permeable to Ca2+. When co-expressed with α10 subunit, the α9 subunit current induced by ACh is increased by about 100-fold. Notably, the expression of α9α10 subunits is highly restricted outside the central nervous system (CNS), mainly at the adrenal gland medullary chromaffin cells and immune cells, besides the inner ear hair cells where they were initially discovered. Activation of α9α10 nAChRs promotes the release of inflammatory mediators from the immune cells and stress hormones from the adrenal medulla. Both could activate trigeminal neurons and elicit release of neuropeptides like calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase-activating polypeptide (PACAP), leading to migraine pain. The release of CGRP and PACAP could further stimulate the release of inflammatory mediators. Therefore, α9α10 nAChR antagonists may represent a viable novel mechanism for acute treatment of migraine-related pain. Importantly, the limited distribution of α9α10 nAChRs may confer a great advantage of limited side effects, especially lack of CNS side effects. RgIA5474 is a 3rd generation peptide modified from a marine snail toxin that has better plasma stability, higher affinity (IC50 at pM range) and selectivity for both rodent and human α9α10 nAChRs than the previously tested analogs including the 2nd generation RgIA4, offering strong translational potential. Our preliminary data demonstrated that one acute dose of RgIA4 blocked the development of evoked cephalic and extracephalic allodynia and spontaneous facial grimace induced by inflammatory mediators in mice and reversed the cutaneous allodynia induced by bright light stress in rats sensitized by sumatriptan. We will evaluate RgIA5474’s dose- and time-dependent effects in alleviating migraine-related pain in female and male CBA/CaJ mice using 2 non-invasive mouse models induced by human migraine triggers. Two specific aims will evaluate pain related behavioral (cephalic allodynia and facial grimace score), neurochemical (plasma release of pro-inflammatory cytokines), as well as immunohistochemical (activation of trigeminal ganglia and trigeminal nucleus caudalis) changes induced by supradural CGRP or PACAP38 (with CGRP receptor antagonist on board) for CGRP- dependent and CGRP-independent mechanisms, respectively. α9 knockout mice will be utilized to verify the contribution of this target to migraine pathology. These studies will help us determine whether blockade of α9α10 nAChRs is a viable strategy for development of a novel therapeutic class for migraine treatment.
