644. Gene Delivery for Chronic Pain Control: Micrcroencapsulated Plasmid DNA Encoding the Anti-Inflammatory Cytokine Gene, Interleukin-10 (IL-10)

Abstract

Chronic pain control is a major unresolved clinical problem. Spinal cord astrocytes & microglia are critically involved in the creation & maintenance of diverse enhanced pain states via the release of proinflammatory cytokines. Interleukin-10 (IL-10), a potent anti-inflammatory cytokine, suppresses proinflammatory cytokine production & activity. We have previously shown that administration of IL-10 protein directly or via a viral vector encoding it into the spinal cord (intrathecal, i.t.) reverses neuropathic pain in the rat; although direct administration of IL-10 protein showed a very short-term reversal. We sought to determine whether neuropathic pain (hypersensitivity to light touch [allodynia] produced by chronic constriction injury [CCI] of the sciatic nerve) could be reversed by: 1) single or repeated i.t. delivery of naked plasmid DNA encoding rat IL-10 (pIL10), 2) single or repeated i.t. delivery of pIL10 treated with the cationic polymer, polyethyleneimine (PEI- pIL10), and 3) single or repeated i.t. pIL10 encapsulated in micro-particles prepared from FDA-approved biodegradable copolymers of polylactide and polyglycolide (PLGA) (PLGA- pIL10). Lastly, we examined whether i.t. rhodamine-labeled PLGA-micro-particles could be visualized in spinal cord using confocal microscopy in naive rats. Behavioral measures were assessed prior to & at 3 & 10 days post CCI. I.t. injections were given on day 10 post-CCI, consisting of pIL10 (100 ug/injection), control plasmid encoding jellyfish green fluorescent protein (pGFP; 100 ug/injection), vehicle (3% sucrose in phosphate buffered saline), PEI- pIL10 (10 ug/injection) or PLGA- pIL10 (350 ug PGLA/injection). For repeated injections, a 2nd injection was given on day 13. Allodynia was reassessed every 1 to 4 days. Allodynia was stable in control treated rats but was reversed (prolonged reversal lasting 40+ days), in rats given 2 i.t. injections of: 1) pIL10 2) PEI- pIL10 & 3) PLGA-IL10. Single i.t. injections of pIL10, PEI- pIL10 or PLGA- pIL10 produced a brief 3-6 day reversal of allodynia. Importantly, rhodamine-labeled PLGA-micro-particles were visible immediately & at 3 days after i.t. injection. Ongoing studies using i.t. rhodamine-labeled PLGA-micro-particles (either without DNA or with pGFP DNA) are aimed at examining the spread, the distribution in superficial spinal cord or deeper parenchymal layers & gene expression. This approach to pain control represents a dramatic departure from all other available therapies. Support: Avigen & NIH HL56510, DA015656, DA018156 & DA015642.