Grifolic acid, a FFAR4 agonist, identified as a dual antagonist of voltage-gated sodium and CaV2.2 channels with potent antinociceptive effects.

Background and purpose: Chronic pain affects nearly 30% of the global population. Because of significant adverse effects of opioids, alternative therapies are urgently needed. In a drug discovery project, we identified grifolic acid (GA) as a potent Na_V1.7 antagonist. Here, we have evaluated its biophysical properties and efficacy in animal pain models.

Experimental approach: A mechanistic investigation of GA was carried out on dorsal root ganglion (DRG) neurons, and various stable cell lines, using whole-cell patch clamp techniques. Site-directed mutagenesis and molecular docking analyses also were performed to identify the binding pocket of GA on Na_V1.7. The antinociceptive efficacy of GA was evaluated in inflammatory pain models.

Key results: GA exhibited state-dependent blockade of Na_V1.7 channels and modulated channel gating kinetics. It suppressed native Na_V currents and action potential (AP) firing in DRG neurons. GA inhibited the increase in action potential firing frequency in DRG neurons induced by inflammatory mediators. Mutational and molecular docking studies revealed that GA and bupivacaine targeted anaesthetics binding sites, with their use-dependent properties almost abolished in the F1737A mutant. In formalin and CFA-induced inflammatory pain models in male mice, GA demonstrated analgesic effects comparable to, or exceeding, those of the indomethacin, lidocaine and carbamazepine. GA showed minimal effects on skeletal muscle function but exhibited an inhibitory effect on the Ca_V2.2 channel.

Conclusions and implications: GA is a state-dependent sodium channel and Ca_V2.2 channel antagonist with potent analgesic effects. These findings support its potential as an antinociceptive agent in the treatment of chronic pain conditions.