1082 AAV-Based Upregulation of Potassium Channels as a Focal Treatment of Chronic Pain

INTRODUCTION: Efforts to treat pain by reducing the excitability of nociceptors (first order pain-sensing neurons), have focused on the NaV1.7 sodium channel, since loss of SCN9A (gene for NaV1.7) leads to congenital insensitivity to pain, whereas NaV1.7 gain-of-function mutation causes the severe painful syndrome familial erythromelalgia. Despite these genetic mutations and their distinct phenotypes, pharmacologic Nav!.7 targeting has not been a successful strategy. Most pain conditions are focal, yet most treatments are systemic and expose patients to potentially unnecessary systemic adverse side effects. METHODS: The effect of nociceptor specific potassium channel expression was confirmed by dissociated dorsal root ganglion (DRG) calcium imaging, and several rodent pain assays: von Frey mechanical threshold (sciatic injection), Hargreaves thermal threshold (sciatic injection), CFA inflammatory paw model (sciatic injection), and trigeminal neuralgia whisker pad mechanical threshold (trigeminal ganglion injection). Animals were either wild-type mice or TrpV1::ChR2-EYFP (expression of Channelorhodopsin-2 in TrpV1 lineage neurons). Treated animals were compared to age-, and sex-matched controls that received GFP-control virus in the same dose RESULTS: Animals treated with therapeutic potassium channels showed increased mechanical and thermal thresholds, decreased inflammatory response (higher mechanical threshold after CFA injection), and increased whisker pad thresholds compared to animals treated with GFP-control viruses. Animals that showed improved behavioral outcomes with potassium channel treatment were sacrificed and the DRGs dissociated. Calcium influx was lower in treated neurons when compared to GFP-controls supporting the hypothesis that hyperpolarization of nociceptors is a viable analgesic strategy. CONCLUSIONS: Our results validate the over-expression of potassium channels as a promising alternative for pain treatment and support the use of spatial restriction to achieve precision in AAV-mediated gene therapies.