α6GABA_A receptor positive allosteric modulators targeting trigeminal ganglia for preventing and aborting chronic periorbital allodynia and cephalic pain in both sexes: A mechanistic and comparative preclinical study

Migraine remains an unmet medical need, even with new calcitonin gene-related peptide (CGRP)-targeting treatments. The α6 subunit (Gabra6)-containing GABA_A receptors (α6GABA_ARs) are abundant in trigeminal ganglia (TG). We evaluated the possible anti-migraine efficacy and mechanism of DK-I-56–1, a druggable α6GABA_AR-selective positive allosteric modulator (PAM), using a chronic migraine model induced by repeated intermittent nitroglycerin (riNTG) injections (10 mg/kg, i.p., every 2 days for a total of 5 doses). Chronic and acute allodynic responses of riNTG-treated ICR mice of both sexes were assessed by reduced mechanical withdrawal thresholds in their periorbital areas, and their chronic cephalic pain by elevated grimace scores. riNTG induced long-lasting chronic periorbital allodynia and cephalic pain, and one NTG injection caused acute allodynia. Daily DK-I-56–1 prevented chronic allodynia and cephalic pain, and abolished acute allodynia in both sexes. Anti-allodynic and cephalic pain-relieving effects of DK-I-56–1 (10 mg/kg, i.p.) were mimicked by topiramate (30 mg/kg, i.p.), antagonized by i.p. furosemide, an α6GABA_AR antagonist, and nullified in Gabra6-knockout ICR mice. However, olcegepant (1 mg/kg, i.p.) only partially prevented cephalic pain. In dissociated TG neurons, DK-I-56–1 induced a furosemide-sensitive potentiation of GABA-induced current and depolarization. However, DK-I-56–1 did not altered increased inflammatory cytokines, down-regulated glutamate decarboxylase 65 kDa (GAD65), and Gabra6 protein levels in TG of riNTG-treated mice. Therefore, DK-I-56–1 may have the potential to prevent and abort migraines by potentiating GABA-induced depolarization in TG neurons via α6GABA_ARs, offering efficacy comparable to that of topiramate but superior to olcegepant as a novel migraine therapy.