Abstract 2733: TYMS as a novel target for AAV-based therapy

The purpose of this study is to develop a strategy for treating pancreatic neuroendocrine tumor (PanNET) through blocking Thymidylate Synthase (TYMS or TS), a DNA metabolic enzyme. Elevated TYMS levels are frequently observed in human PanNET and are associated with worse prognosis and resistance to cytotoxic agents such as 5FU. Elevated TYMS levels directly promote tumorigenesis in vitro and ectopic expression of human TS (hTS) in transgenic mice promotes adenoma development in the endocrine pancreas in vivo. Pancreatic islet tumor formation in hTS transgenic mice occurred with a long latency period, suggesting that additional somatic events are required for PanNET formation and progression. Men1 was shown to be a frequent target for somatic mutation in PanNETs (44% have MEN1 mutations). Therefore, we established a new mouse model designated hTS/Men1-/-, where hTS is overexpressed in pancreatic islet cells carrying conditional Men1 null alleles. We observed that ectopic hTS cooperates with Men1 inactivation to significantly accelerate PanNET progression and shorten survival. Since traditional TYMS inhibitors, such as 5-FU, consistently induce tumor resistance and cannot cure advanced disease, we have now tested the ability of TS-shRNA delivered using adeno-associated viral (AAV) vectors as a pharmacological safe and effective anti-tumor strategy. We packaged TS shRNA under the mouse insulin promoter (mIP) for islet-cell specific expression using capsid optimized Y to F double mutant AAV (AAV8-2M) to generate viral particles of scAAV8-2M-mIP-GFP-hTS-shRNA. We treated hTS/Men1-/- mice with intraperitoneal (IP) injection (1x1011 viral genomes/mice). Treated and control mice were analyzed for PanNET progression, TYMS expression and survival. In addition, we tested a human PanNET tumor cell line (BON) that was isogenic with or without hTS expression for tumor formation in xenograft model. We confirmed sustained reduction of TYMS levels 3 weeks after IP delivery of AA8-2M-mIP-GFP-hTS-shRNA into PanNET tissues of hTS/Men1-/- mice. In addition, AA8-2M-mIP-GFP-hTS-shRNA delivery blocked PanNET tumor progression and enhanced the survival of treated mice as compared to vector controls. We also confirmed that TYMS knock-down in BON cells by hTS-shRNA reduced xenograft tumor growth as compared to non-specific shRNA controls. In conclusion, the ability of AAV-mediated TS shRNA to block PanNET tumor progression directly demonstrates the importance of elevated TYMS in tumorigenesis and offers a novel anti-cancer strategy. Citation Format: Vinod Vijayakurup, Benjamin Meyer, Akbar Nawab, Frederic J. Kaye, Maria V. Guijarro, Maria Zajac-Kaye. TYMS as a novel target for AAV-based therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2733.