Abstract A040: Assessing the ability of Fc3TSR to remodel the tumor microenvironment and enhance efficacy of immunotherapies and chemotherapy in a murine model of pancreatic ductal adenocarcinoma
Authors: Garlisi Bianca , Aitken Caroline , Lauks Sylvia , Stewart Julia , Petrik Duncan , Lawler Jack , Petrik Jim 
Published: January 2024

Abstract
Introduction: Pancreatic Ductal Adenocarcinoma (PDAC) has a poor survival rate due to late diagnosis where metastasis has often occurred. Angiogenesis, the process by which new vessels form from pre-existing vasculature, is crucial for tumor growth and metastasis. Tumors aggressively upregulate expression of pro-angiogenic factors, stimulating rapid vessel formation. These vessels often lack pericyte coverage and have dysfunctional morphology, leading to high interstitial fluid pressure (IFP). Impaired perfusion and high IFP impede therapy uptake. Fc3TSR is a novel fusion protein derived from the potent angiogenic inhibitor thrombospondin 1, which we have shown to normalize vasculature in ovarian cancer, significantly decreasing tumor size and improving uptake of many therapies. In this study, we evaluated Fc3TSR’s ability to remodel the tumor microenvironment to induce tumor regression and to enhance efficacy of other therapies. Methods: We developed an orthotopic syngeneic murine model of PDAC, whereby we surgically injected 2.5 × 104 murine PDAC cells (KPC) into the tail of the pancreas of C57BL/6 mice. Tumors were allowed to progress for 14 days before intraperitoneal (IP) administration of Fc3TSR (0.158mg/kg) or PBS (control) on day 14 and 21. Gemcitabine (GEM) chemotherapy treated mice received either daily, metronomic dosages of GEM, or weekly, maximum tolerated dosages GEM starting on day 23. Checkpoint inhibitor mice received either PD-L1 (25ug) or CTLA4 (25ug) checkpoint inhibitors on day 23 and 26. Mice were euthanized on day 30 and tumors and the draining lymph nodes were collected and weighed. 1 hour before euthanasia, Fc3TSR and PBS mice were IP injected with Hypoxyprobe (Pimonidazole Hydrochloride) and tumors were immunostained for markers of blood vessels and tumor hypoxia. Results: Fc3TSR induced tumor regression when compared to PBS, but GEM at either dosage did not further enhance this effect. Following Fc3TSR, PD-L1, but not CTLA-4 checkpoint inhibitors significantly reduced tumor size when compared to mice pre-treated with PBS. Fc3TSR treatment also reduced the area of tumor hypoxia. Tumor vasculature is currently being imaged and analyzed for Fc3TSR’s effect on vessel morphology. Conclusion: Our data suggests that normalizing the tumor microenvironment can enhance the uptake and efficacy of combination therapies. Enhanced perfusion could facilitate the migration of activated immune cells and may enhance immune responses in PDAC patients. Here we demonstrate a novel approach to optimize therapeutic efficacy in advanced stage PDAC.
Citation Format: Bianca Garlisi, Caroline Aitken, Sylvia Lauks, Julia Stewart, Duncan Petrik, Jack Lawler, Jim Petrik. Assessing the ability of Fc3TSR to remodel the tumor microenvironment and enhance efficacy of immunotherapies and chemotherapy in a murine model of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr A040.