Abstract A46: CD73 inhibition enhances the effect of anti-PD-1 therapy on KRAS-mutated pancreatic cancer model
Authors: Le Thuc M. , Udyavar Akshata , Kim Woosuk , Cho Arthur E. , Li Luyi , DiRenzo Daniel , Rosen Brandon , Walters Matthew J. , Tan Joanne B.L. , Radu Caius G. 
Published: March 2020

Abstract
Background: CD73 catalyzes the extracellular generation of adenosine (ADO) from adenosine monophosphate (AMP). High levels of ADO, found in the tumor microenvironment (TME), have been shown to suppress immune responses and curtail T-cell activation in the presence of anti-PD-1/PD-L1 blocking antibodies. Oncogenic drivers resulting from activating mutations, such as KRAS, BRAF, and EGFR mutations, are commonly treated with tyrosine kinase inhibitors that result in robust but nondurable responses. We show here that KRAS mutations, of which 60% were derived from pancreatic adenocarcinoma (PDAC) samples, significantly upregulated CD73 expression and resulted in worsening prognosis. In a murine model of pancreatic cancer bearing KRASG12C mutation, coadministration of CD73 inhibitor with anti-PD-1 in established tumors resulted in significant tumor growth retardation, comparable to KRAS inhibitor alone. These data support the rationale for the clinical development of CD73 inhibitors in pancreatic cancer.
Methods: Linear models were used to evaluate the ability of 299 pan-cancer consensus oncogenic drivers to predict CD73 expression independent of tumor type in the TCGA dataset. Immunohistochemistry (IHC) on formalin-fixed, paraffin-embedded (FFPE) samples was performed using CD73 (Cell Signaling, D7F9A) primary antibody and detected using anti-rabbit HRP. CD73 expressing cells were detected by DAB chromogen and quantified using QuPath Software. CD73 activity in fresh frozen tissues were detected using the Wachstein-Meisel method. C57BL/6J mice bearing established KP4662-G12C tumors (&gt;150 mm3) were treated with A0001421 (CD73i), 30 mg/kg; once a day; s.c. and anti-PD1 (Clone RMP 1-14): 10 mg/kg; twice a week; i.p. Mice were treated for two weeks starting from day 10 post-tumor. Treatment efficacy was monitored using micro-computed tomography (Genisys PET/CT G8 (Sofie Biosciences). All small-molecule inhibitors were synthesized by Arcus Biosciences, Inc.
Results: Out of the 299 oncogenes, alterations in KRAS, BRAF, and EGFR were the top 3 oncogenes upregulating CD73 expression. Increase in CD73 expression in KRAS-mutated tumors was further confirmed by IHC. Data extrapolated from Koyama et al. suggest that PD-1 nonresponsive mice express higher levels of adenosine pathway genes, including CD73 and CD39. Coadministration of CD73 inhibitor with anti-PD-1 was superior to anti-PD-1 alone in limiting tumor growth of an aggressive model of pancreatic cancer. Global changes in immune contexture and TME were also observed, consistent with the immune modulatory effects of inhibiting CD73 activity.
Conclusion: CD73 is a highly efficient ecto-enzyme that catalyzes the hydrolysis of AMP to immune-suppressive ADO and is associated with worsening prognosis across multiple malignancies. AB680, a potent and selective CD73 inhibitor with excellent safely and pharmacokinetic profile, is currently undergoing clinical evaluation in 1L metastatic PDAC in combination with AB122 and chemotherapy.
Citation Format: Thuc M. Le, Akshata Udyavar, Woosuk Kim, Arthur E. Cho, Luyi Li, Daniel DiRenzo, Brandon Rosen, Matthew J. Walters, Joanne B.L. Tan, Caius G. Radu. CD73 inhibition enhances the effect of anti-PD-1 therapy on KRAS-mutated pancreatic cancer model [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A46.