Intrathecal administration of the Nav1.7 inhibitor PF-05089771 produces rapid and side-effect-free analgesia in mice

ABSTRACT: Nav1.7 has emerged as a promising target for developing novel analgesics that avoid central side effects, yet clinical trials involving systemically administered Nav1.7 inhibitors have thus far yielded disappointing outcomes. In this study, we explored whether delivering PF-05089771-a highly selective Nav1.7 inhibitor previously tested in clinical settings-directly into the intrathecal space could elicit potent analgesic effects. We assessed pain responses using a range of behavioral assays, including the Hargreaves, hot plate, von Frey hair, and Randall-Selitto tests, while evaluating motor coordination and gastrointestinal transit through the rotarod test and a charcoal meal gavage method, respectively. Intrathecal administration of PF-05089771 produced rapid (within 15 minutes) and long-lasting (>4 hours) analgesia across multiple pain models, including nociceptive, inflammatory, neuropathic, and morphine-tolerant pain, as well as both acute and chronic itch. However, no significant effect was observed in a visceral pain model. The analgesic effects were abolished by naloxone pretreatment, implicating endogenous opioid signaling in the mechanism of action. Importantly, repeated intrathecal injections did not lead to analgesic tolerance, and no adverse effects on motor function or gastrointestinal motility were detected. These results indicate that changing the delivery route of Nav1.7 inhibitors may overcome limitations seen with systemic administration and highlight the potential of intrathecal PF-05089771 as a powerful and well-tolerated analgesic.