Abstract A30: Development of an immunogenic and radioresistant orthotopic mouse model to recapitulate the stromal barriers of pancreatic cancer

Pancreatic cancer responds poorly to systemic therapies, including immunotherapy. One of the most important factors responsible for the historically poor response rates of pancreatic cancer is the presence of highly desmoplastic immunosuppressive stroma. Elevated interstitial fluid pressures (IFP) prevent the penetration of systemic therapeutics and immune cells into pancreatic tumor tissue. It has been hypothesized that ablative techniques, such as irradiation (XRT), can overcome these barriers, but only a few studies have specifically focused on pancreatic cancer, which is relatively radioresistant, due to the lack of good preclinical models. Hence, it has become increasingly important to develop mouse models of pancreatic cancer that not only have dense desmoplastic immunosuppressive stroma but also mimic its radioresistant properties. We have developed an immunocompetent mouse model of pancreatic cancer using a cell line derived from a genetically engineered KPC mouse (LSL-KrasG12D/+; LSL-Trp53R172H/+; PDX1Cre/+; LSL-ROSA26 Luc/+). Tumor pieces from subcutaneous tumors grown on C57BL/6 mice were surgically implanted on the pancreatic tails of mice of same background to develop the orthotopic tumors. Eight days post-implantation, the IFP of these tumors were measured to be 40 +/- 16 mm Hg using a microtip pressure catheter. This pressure was higher than the IFP of normal pancreas (8-15 mm Hg) and the capillary-venous blood pressures (15-30 mmHg), which mimicked the difference between pancreatic tumor IFPs and normal tissue IFPs measured in human tumors. Further, second harmonic generation microscopy was used to study the collagen deposition in these tumors, which revealed a 16 +/- 3.2 % collagen accumulation, characteristic of a desmoplastic stroma in contrast to the 1.07 +/- 0.2% in normal pancreas. Further, flow cytometry analysis in these tumors showed an excessive infiltration of immunosuppressive CD11b+, Gr-1+ myeloid-derived suppressor cells (MDSC) that amounted to 11 +/- 2.5% of total cells in the tumor. However, the CD4+ and CD8+ populations were observed to be less than 0.1% of the total tumor, which was confirmed by immunohistochemical analyses. Mice bearing these orthotopic pancreatic tumors of mean tumor volume 58 +/- 6.4 cubic mm (n=5/group) were then subjected to increasing doses of focused XRT (0, 8, 12, and 16 Gy) using a laser-guided stereotactic small-animal X-ray irradiator with 1-mm resolution. The mean tumor volumes (in cubic mm) 14 days post XRT were 612 +/- 38.6, 780 +/- 45.8, 794 +/- 47.6, 508 +/- 40.2 for 0, 8, 12, and 16 Gy of radiation without statistically significant differences between the groups. This study shows the development of a radioresistant orthotopic mouse model of pancreatic cancer with the stromal and microenvironmental characteristic of human tumors, which can be used for the preclinical study of various stromal inhibitors and immunomodulatory agents in combination with ablation techniques. Citation Format: Jayanth Surya Narayanan Shankara Narayanan, Suna Erdem, Phillip Dominick Sanders, Andrew Sharabi, Rebekah White. Development of an immunogenic and radioresistant orthotopic mouse model to recapitulate the stromal barriers of pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr A30.