Abstract 719: Preclinical testing of CD73 inhibitors for pancreatic cancer immunoprevention
Authors: Singh Kanchan , Chandra Vidhi , Ballew Lincoln , Mills Tingting , Faraoni Erika Y. , Clark Trent , Vornik Lana A. , Savage Michelle I. , Eltzschig Holger K. , Mohammed Altaf , Sei Shizuko , Brown Powel H. , McAllister Florencia , Bailey-Lundberg Jennifer 
Published: June 2022

Abstract
Introduction: Pancreatic ductal adenocarcinoma (PDAC) is characterized by a profoundly immunosuppressive microenvironment. Innovative therapeutic strategies are urgently needed to stop the progression of precancerous lesions into aggressive PDAC, which remains a lethal malignancy. The goal of this research project is to test the immunopreventive strategies by targeting the ectonucleotidase CD73, one of the gatekeeper enzymes responsible for adenosine production and the formation of immunosuppressive tumor microenvironment in this malignancy. We hypothesize that inhibition of CD73 will prevent pancreatic intraepithelial neoplasia (PanIN) formation and progression to PDAC by reversing immunosuppression.
Materials and methods: A syngeneic PDAC mouse model was employed by injecting 100k murine pancreatic cancer (KPC) cells in flanks of C57BL/6 female mice. Oral gavage of AB680 (small molecule CD73 inhibitor) was given three days/week at 10mg/kg starting the day after KPC injections and tumor sizes were measured weekly. Toxicity was analyzed by serum ALT analysis. At the time of death 6 weeks post-KPC inoculation, tumor volume and mass were recorded. In another experiment, AB680 was administered 3 days/week at 10mg/kg for 5 weeks. CyTOF immunoprofiling of digested tumors from control and AB680 treated mice and HPLC analysis on serum from the time of death were performed.
Results: In experiment 1, by week three of the study, there was a significant difference in tumor volume between the control and AB680 treated groups (P=0.02). However, in weeks 4-5 AB680 reduced tumor growth compared to vehicle controls, but the grouped statistical analysis was not significant. When observing individual tumors, there was a reduction in tumor size in 30% of the AB680 treated mice between weeks 3-5, but the difference was not statistically different. ALT analysis determined AB680 does not induce liver toxicity. For experiment 2 (3x/week treatment with AB680), there was a significant reduction in tumor growth. Activated CD8-positive T cells, dendritic cells, and macrophages were significantly increased in the syngeneic tumors from AB680 treated mice. The intratumoral adenosine levels were significantly decreased in AB680 treated mice compared to vehicle treated mice.
Conclusion: We conclude oral gavage delivery of CD73 inhibitor AB680 at 10mg/kg (6x/week) reduces tumor growth in KPC syngeneic tumor bearing mice. Treatment with AB680 at 10mg/kg 3x/week significantly increases tumor doubling time, significantly alters intratumoral immune cell populations, and results in a significant decrease in intratumoral adenosine levels. In addition, we observed a significant increase in infiltration of activated CD8-positive T cells indicating oral gavage delivery using AB680 reverses immunosuppression in vivo. [Supported by NCI 75N91019D00021/75N91020F00002]
Citation Format: Kanchan Singh, Vidhi Chandra, Lincoln Ballew, Tingting Mills, Erika Y. Faraoni, Trent Clark, Lana A. Vornik, Michelle I. Savage, Holger K. Eltzschig, Altaf Mohammed, Shizuko Sei, Powel H. Brown, Florencia McAllister, Jennifer Bailey-Lundberg. Preclinical testing of CD73 inhibitors for pancreatic cancer immunoprevention [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 719.