Abstract 700: Systemic administration of DNA nanoparticles containing the diphtheria toxin gene reduces pancreatic tumor load in mice
Authors: Sawicki Janet A. , Peng Weidan , Rhodes Kelly , Getts Robert 
Published: May 2015

Abstract
Despite years of research and hundreds of clinical trials, our ability to treat metastatic pancreatic ductal adenocarcinoma (PDA) effectively has been thwarted due to the numerous genetic mutations in multiple core pathways that are characteristically present in pancreatic tumors, as well as the ability of tumors to develop resistance to chemotherapeutic drugs and small molecules. To avoid these complications, we have developed a suicide gene therapy that targets the death of PDA tumor cells regardless of their genetic mutation profile while avoiding unwanted harmful effects to healthy cells. A novel DNA nanoparticle, 3DNA, serving as a delivery vector is derivatized by conjugation to a DNA construct (MSLN promoter-driven diphtheria toxin A, pMSLN/DTA) as well as to a tumor-targeting molecule. Targeted DTA-induced tumor cell death is achieved in two ways: targeted nanoparticle delivery to tumor cells via docking and internalization, and targeted expression to cells that have an active mesothelin (MSLN) promoter (MSLN is highly overexpressed in ∼50% of PDA tumors). In preclinical tests, these formulations are systemically administered to PDA tumor-bearing mice. In an initial experiment, after confirming that MSLN is highly expressed in murine Pan02-luc PDA cells, we generated Pan02-luc orthografts in C57BL/6 mice and treated mice 2X/week with ∼50μg cargo DNA/i.v. injection for 4 weeks with either MSLN/DTA-TFP (n=7) or with MSLN/XX-TFP (n=5) dendrimer formulations (TFP is a peptide with strong affinity for the human transferrin receptor (TR), and weaker affinity for murine TR; XX = no coding sequence). Tumor load was assessed weekly by optical imaging and luciferase bioluminescence quantitation. Fold increase in relative light units (RLU) (baseline to 4 days after the last injection) was used to measure therapeutic efficacy. After 4 weeks of treatment, the mean RLU ratio for the MSLN/DTA-TFP treated mice was 0.51 +/-0.20 while that of the MSLN/XX-TFP treated mice was 7.1 +/-8.22, a significant 15-fold difference in tumor load (p=0.04). This quantitative analysis of tumor load as well as gross observations of tumors upon sacrifice of the mice showed that tumors in mice systemically treated with MSLN/DTA-TFP dendrimer formulation shrunk significantly to the point where tumor load was negligible in contrast to rapid growth of tumors in mice treated with the MSLN/XX-TFP formulation. This experiment demonstrates that systemically-administered DNA nanoparticle-delivered DTA effectively kills tumor cells with little to no apparent systemic toxicity as assessed by body weight and TUNEL assays of multiple normal tissues. In ongoing experiments to further validate this approach for the treatment of metastatic PDA, other targeting molecules such as folate and TFP are being used to target delivery to Pan02-luc orthografts and human BxPC3-luc2 xenografts.
Citation Format: Janet A. Sawicki, Weidan Peng, Kelly Rhodes, Robert Getts. Systemic administration of DNA nanoparticles containing the diphtheria toxin gene reduces pancreatic tumor load in mice. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 700. doi:10.1158/1538-7445.AM2014-700