Ryan Soderquist1, Evan Sloane2, Scott Johnson1, Linda Watkins2, Erin Milligan3, and Melissa Mahoney1. (1) Chemical and Biological Engineering, University of Colorado at Boulder, ECCH Rm. 111, 424 UCB, Boulder, CO 80309, (2) Department of Psychology and Center for Neuroscience, University of Colorado at Boulder, UCB 345, Boulder, CO 80309, (3) Department of Neurosciences, University of New Mexico, MSC08 4740, Albuquerque, NM 87131-0001
Neuropathic pain caused by inflammation and/or damage to peripheral nerves afflicts millions of people worldwide. Non-viral plasmid DNA (pDNA) encoding for the anti-inflammatory cytokine interleukin-10 (IL-10) can alleviate symptoms of neuropathic pain in animal models for more than 40 days when administered to the spinal cord. This approach, however, requires two high-dose injections over the course of three days which limits its clinical utility. The focus of this study was to improve the clinical feasibility of pDNA-IL-10 therapy by delivering pDNA-IL-10 via degradable PLGA microparticles. We hypothesized that microparticles with sufficient pDNA loading could achieve long-term therapeutic efficacy following a single injection with reduced pDNA dosage requirements by simultaneously eliciting phagocytic immune cell recruitment and providing prolonged pDNA-IL-10 exposure. To test the hypothesis, the extent to which phagocytic cell populations are stimulated by microparticles in vivo was examined by immunohistochemical analysis of cell populations isolated from cerebrospinal fluid and sectioned spinal cord tissue 24 hours after intrathecal delivery of fluorescently labeled microparticles. An increased presence of classically and alternatively activated macrophages (ED1 positive and ED2 positive cells) was observed in the cerebrospinal fluid after microparticle administration. In tissue sections, microparticles were distributed throughout the meningeal tissue surrounding the spinal cord and elevated levels of phagocytic immune cells were identified (MHCII and OX-42 positive) in areas of high microparticle accumulation. Overall, microparticles recruited and activated phagocytic cells in the intrathecal space, which is a previously demonstrated requirement for successful therapy using multiple doses of unencapsulated pDNA. When administered as a single in vivo intrathecal injection, microparticles loaded with a 14-fold lower dose of pDNA alleviated neuropathic pain in animal models for a prolonged time period (> 60 days), greatly enhancing the potential clinical utility of pDNA-IL-10 therapy for neuropathic pain.
Support: NIH grant DA018156