(233g) Unmethylated Plasmid DNA Delivery Boosts Survival Against Murine Melanoma

Melanoma is a major healthcare burden with 1.5 million cases reported annually globally. Current therapeutic approaches include chemotherapy and immunotherapy, but low response rates and outgrowth of drug-resistant disease necessitate novel therapeutic approaches. We found that intradermal and sub-cutaneous delivery of plasmids without prokaryotic methylation (‘unmethylated plasmid DNA’ or ‘UMpDNA’) activate the innate immune system and lead to closure of full thickness wounds in healthy and diabetic, obese mice. Although transgene expression was similar with methylated plasmid DNA (‘MpDNA), immune activation and wound closure were seen only with UMpDNA. Interestingly, wounding enhanced transgene expression from both MpDNA and UMpDNA in mice Building on these, we hypothesized that delivery of UMpDNA which expresses a model melanoma antigen - ovalbumin (OVA) - will activate the immune system and simultaneously act as a vaccine to combat B16F10 OVA melanoma tumors in immunocompetent mice. We hypothesized that local expression of transgene (OVA) will stimulate antigen presenting cells present in the skin, educating adaptive immune cells in regional lymph nodes, which will ultimately result in antigenic immunity. In order to test these hypotheses, delivered OVA-expressing UMpDNA or MpDNA intradermally and sub-cutaneously in C57/BL6 mice with or without 5 mm diameter splinted full-thickness wounds. DNA was administered immediately upon wound and a booster was administered on day 14 following wounding at which point, the mice were challenged with B16F10-OVA cells. Tumor growth and survival was monitored over a period of 90 days. (Figure A-D) Plasma samples (n=2) collected through submandibular bleeds showed antibodies against OVA generated after 2 weeks from the initial treatment. (Figure E) Our studies demonstrated that UMpDNA treatment resulted in significantly higher survival than seen in untreated mice (Figure F). In addition, wounding significantly enhanced survival in mice and retarded tumor progression compared to untreated mice and unwounded mice treated with OVA-UMpDNA. This study demonstrates the efficacy of plasmid DNA with unmethylated prokaryotic sites as a potential vaccine for melanoma, particularly after excision of the primary tumor.