Intranasal delivery of siRNA targeting NR2B attenuates cancer-associated neuropathic pain

Purpose: This study aimed to reduce cancer-associated pain by blocking pain signals through the intranasal administration of siRNA targeting the NMDA subunit NR2B (siNR2B). Methods: Cancer pain models were established by injecting 3 × 10⁵ B16F10 melanoma cells into the left hind paws of C57BL/6 mice. To evaluate pain reduction, 600 pmol of siNR2B was complexed with the RVG9R peptide at a 20:1 molar ratio, or 5 mg/kg NR2B receptor antagonist Ro25-6981 was used as a positive control. Melanoma-xenografted mice were intranasally administered the peptide/siRNA complex or intraperitoneally inoculated with Ro25-6981 three times a week for 3 weeks. The mechanical withdrawal threshold was determined using an electronic von Frey apparatus. Results: The therapeutic effect of intranasally administered siNR2B was observed 21 days after cancer cell implantation in a hind paw melanoma model. NR2B expression in the cancer model was approximately twice that in the normal animals. The groups treated with siNR2B or Ro25-6981 exhibited approximately 60 and 50% of NR2B expression in the thalamus, respectively. This reduced pain signaling in the thalamic region, as evidenced by a decrease in phosphorylated extracellular signal-regulated kinase. In addition, the siNR2B-treated group displayed significant behavioral improvements, a marked reduction in cancer-induced pain, compared with controls. siNR2B treatment in a cancer-induced murine model did not affect the general cognitive function. Conclusion: This study demonstrated that the intranasal delivery of siNR2B in a murine model effectively reduced cancer-induced neuropathic pain by downregulating overexpressed NMDA receptor-mediated pain signaling in the thalamus.