259. Plasmid DNA Encoding the Anti-Inflammatory Cytokine Gene, Interleukin-10 (IL-10) for Chronic Pain Control: Taking Advantage of Nuclear Scaffold/Matrix Attachment Regions*

Chronic pathological pain is a major unresolved clinical problem. Spinal cord glial cells are important in diverse forms of enhanced pain states via their release of proinflammatory cytokines. Interleukin-10 (IL-10), a potent anti-inflammatory cytokine, suppresses proinflammatory cytokine production & activity. We have shown that spinal delivery (intrathecal; i.t.) of IL-10 protein resolves animal models of pathological pain. Both i.t. IL-10 protein or i.t. viral vector-delivered IL-10 gene lead to transient therapeutic effects (2hr & 2 wk, respectively). We have recently reported that i.t. naked plasmid DNA encoding IL-10 (pDNA-IL-10) leads to a substantial improvement in the duration of therapeutic pain control (40 days). However, transgene IL-10 may be compromised &/or cleared by cell division. Recently, a chromosomal scaffold/matrix- attached region (S/MAR) linked to the simian virus 40 origin of replication was reported to stably propagate episomally in mammalian cells. Mitotic stability occurs via specific interactions with nuclear matrix proteins. We sought determine if S/MAR inserted into our current plasmid (pDNA-S/MARS-IL10) could improve upon the therapeutic duration of pain control in an animal model of neuropathic pain. The model we use is hypersensitivity to light touch [allodynia] produced by chronic constriction injury [CCI] of the sciatic nerve. Naked pDNA-S/MARS-IL10 was injected peri- spinally (intrathecally; i.t.) after CCI-sensitivity was induced. Behavioral measures were assessed in rats prior to & at 3 & 10 days after induction of CCI. Intrathecal injections were given on Day 10 & Day 12 post-CCI consisting of pDNA-S/MARS-IL10 (100 ug/injection in 18 ul), or pDNA-IL-10 (100 ug/injection in 18 ul). A second i.t. pDNA-S/MARS-IL10 (1 or 25 ug/injection in 5 ul), or pDNA-IL10 (25 ug in 5 ul) injection was given 2 days later. Allodynia was reassessed every 4 days following the second DNA injection. Allodynia was stable through day 10 after CCI induction. An immediate & robust improvement of pain reversal was observed within 24 hr after the first injection of pDNA-S/MARS-IL10 vs pDNA-IL-10. Animals have remained reversed from CCI-induced allodynia after the second i.t. pDNA-S/MARS-IL10 and 25 ug is most effective.Studies are ongoing and will be terminated 90 days after CCI or when CCI-induced allodynia returns. Simultaneous studies are determining whether 1) a single i.t. injection of pDNA-S/ MARS-IL10 is sufficient for long-term pain control, 2) transgene expression by protein analysis can be detected at 1, 2 &/or 3 months in cerebrospinal fluid after injection in behaviorally verified rats, and 3) the distribution of transgene expression in superficial spinal cord or deeper parenchymal layers.