nw-1029 and Neuralgia

Neuropathic pain is among the most common and difficult-to-treat types of chronic pain and is associated with sodium channel malfunction. The sodium channel blocker ralfinamide has exhibited potent analgesic effects in several preclinical pain models and in patients with mixed neuropathic pain syndromes (Phase II trials), but it failed to ameliorate neuropathic low back pain in Phase III trials. It is unclear whether ralfinamide is effective against neuropathic pain induced by specified etiologies. In the present study, the antinociceptive effects of ralfinamide in neuropathic pain models induced by spared nerve injury and chemotherapy were compared in a gabapentin-controlled manner. The effects of ralfinamide on physiological pain were evaluated in mechanical withdrawal, hot plate, and acetic acid writhing tests. We also investigated the effects of ralfinamide on cardiovascular function and locomotor activity. Oral ralfinamide dose-dependently alleviated spared nerve injury-induced allodynia in rats and mice. Ralfinamide increased mechanical withdrawal thresholds in oxaliplatin-induced and paclitaxel-induced neuropathic pain. Ralfinamide did not affect physiological pain, locomotion, or cardiovascular function. Together, ralfinamide attenuated mechanical allodynia in all the neuropathic pain models tested, with subtle differences in efficacy. The effect of ralfinamide is comparable to that of gabapentin, but with no interference in basal mechanical sensitivity. The present study supports the effectiveness of selective sodium channel blockade as an analgesic strategy, as well as the development of compounds similar to ralfinamide.

Topics: Amines; Analgesics; Animals; Antineoplastic Agents; Blood Pressure; Cyclohexanecarboxylic Acids; Disease Models, Animal; Fluorobenzenes; Gabapentin; gamma-Aminobutyric Acid; Heart Rate; Locomotion; Male; Neuralgia; Organoplatinum Compounds; Oxaliplatin; Paclitaxel; Peripheral Nervous System; Rats; Rats, Sprague-Dawley

Ralfinamide is analgesic when applied as a single dose in rodent models of stimulus-evoked chronic pain. However, it is unknown whether its chronic application after nerve injury can suppress spontaneous chronic pain, the main symptom driving patients to seek treatment. In this study ralfinamide was administered to rats at doses producing plasma levels similar to those causing analgesia in pain patients. The analgesic effect was tested on autotomy, a behavior of self-mutilation of a denervated paw that models spontaneous neuropathic pain. Sprague-Dawley male rats (N=10-20/group) underwent transection of the sciatic and saphenous nerves unilaterally. Ralfinamide or its vehicle were administered per os for 7 days preoperatively (80 mg/kg; bid), followed by the vehicle or Ralfinamide, until postoperative d42. Autotomy was scored daily until d63. Lasting 'preemptive analgesia' was found in rats treated with ralfinamide preoperatively, expressed by delayed autotomy onset (P=0.009) and reduced scores on d63 (P=0.01). Rats treated with ralfinamide (30 or 60 mg/kg; bid) from the operation till d42, but not preoperatively, also showed delayed autotomy (P=0.05, P=0.006), and reduced autotomy scores lasting till d63 (P=0.02, P=0.01), for the two doses, respectively. Combining ralfinamide treatments for 7 days preoperatively and 42 days postoperatively also resulted in significantly suppressed scores on d42 and d63 (P=0.005, P=0.001, respectively). Suppression of neuropathic pain-related behavior was likely caused by a combination of mechanisms reported for ralfinamide, including inhibition of Na+ and Ca++ currents in Nav1.3, Nav1.7, Nav1.8, and Cav2.2 channels in rat DRG neurons, inhibition of substance P release from spinal cord synaptosomes, NMDA receptor antagonism and neuroprotection.

Topics: Administration, Oral; Analgesics; Animals; Behavior, Animal; Fluorobenzenes; Hindlimb; Neuralgia; Pain Measurement; Pain Threshold; Pain, Postoperative; Premedication; Rats