Poster CC8 - Delivery of Unmethylated Plasmid DNA Boosts Survival in Murine Melanoma Challenged Mice

Introduction: Melanoma poses a major burden on the healthcare industry with about 1.5 million cases annually reported worldwide. Currently, therapeutic approaches, including immunotherapy and chemotherapy, are faced with a myriad of challenges like difficulty in biomarker identification, and resistance to drug treatment. The lack of effective strategies in combating the disease necessitates the development of novel alternatives to conventional therapeutic modalities. In our previous studies, we observed that unmethylated plasmid DNA (UMpDNA) when delivered intradermally and subcutaneously, led to the activation of innate immune system, causing enhanced wound healing outcomes in healthy and diabetic mice. Based on these findings, we hypothesized that delivering UMpDNA expressing a model melanoma antigen – ovalbumin (OVA) – will lead to its enhanced transgene expression, facilitating the development of an effective strategy to combat murine B16F10-OVA melanoma tumors. We expected that the increased transgene expression of OVA would stimulate the activity of antigen-presenting cells in the skin, which, in turn, would educate the adaptive immune cells in the regional lymph nodes, ultimately resulting in antigenic immunity.

Materials and

Methods: A murine excisional wounding model was created on the dorsum in C57BL6/J mice. The pDNA was delivered through intradermal and subcutaneous routes near the wound site in these mice. The mice were treated with either methylated or unmethylated plasmid DNA (n=6 per group), followed by boosting with the same plasmid DNA after 14 days. The boosted mice were then inoculated with murine melanoma cells (B16F10-OVA or parental B16F10) post-booster administration. The tumor growth rate and survival were monitored over a period of 90 days in these mice. Upon euthanasia, blood, end organs, and tumors were collected and subjected to immunohistochemical analysis. Levels of anti-OVA IgG antibodies were examined in the collected blood. Tumors were analyzed for the presence of tumor-infiltrating immune cells, and end organs were tested for the presence of metastasizing melanoma cells.

Results, Conclusions, and Discussions: Our studies indicate that administering UMpDNA in mice enhances survival probability as compared to mice that did not receive this treatment. Tumor onset and progression were delayed in mice receiving the pDNA treatment with or without wounding. This could be attributed to the presence of antibodies generated against OVA in the mice that received the pDNA treatment. Moreover, plasma samples collected during ante-mortem blood draw pre-boosting showed the presence of antibodies against OVA (14 days after the initial treatment). This study demonstrated the efficacy of unmethylated plasmid DNA as a prophylactic treatment for melanoma cancer.

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