Abstract PR15: Adenosine inhibits STING driven anti-tumor immunity in pancreatic cancer
Authors: Premji Alykhan , Link Jason , Yamao Takanobu , Rashid Khalid , Abt Evan , Labora Amanda , Chan Charlotte , Le Thuc , Wainberg Zev , Radu Caius , Donahue Timothy 
Published: January 2024

Abstract
Pancreatic ductal adenocarcinoma (PDAC) is characterized by an immunosuppressed tumor immune microenvironment (TIME) where combinations of chemotherapy and immune checkpoint blockade (ICB) have shown limited efficacy. Standard of care FOLFIRINOX chemotherapy promotes replication stress associated cell death leading to an increase in extracellular ATP in the TIME and subsequent inflammation that favors anti-tumor immunity. Concomitantly, replication stress from chemotherapy also generates aberrant cytosolic DNA, which stimulates the production of 2’-3’ cGAMP, an immunotransmitter that activates STING in cells in the TIME. STING activation leads to the induction of Type 1 Interferon and a host of anti-tumor immune responses. Moreover, ATP augments leukocyte uptake of cGAMP, further increasing STING activation and promoting tumor immunity. However, acute ATP-dependent inflammation is self-limiting when ATP is inevitably converted to immunosuppressive adenosine (Ado) by extracellular ectonucleotidases (notably, CD39 and CD73) which are highly expressed in PDAC. As evidence of the tumor-promoting role of Ado in PDAC, we show in a Phase I neoadjuvant clinical trial for borderline resectable tumors (n=20) that resistance to neoadjuvant FOLFIRINOX and PD-1 inhibition is associated with an increase in adenosine-related gene expression. We deciphered a novel mechanism of adenosine-mediated immunosuppression whereby signaling through Ado receptors interrupts STING activation by cGAMP. Specifically, we show that NECA, a potent adenosine receptor agonist, inhibits phosphorylation of IRF3 downstream of STING activation and consequently blocks transcription of STING-driven IFNB1 in RAW264.7 macrophages, murine bone marrow-derived macrophages, and CD14+ human PBMCs. Under these same conditions, NECA increases IL-6 and IL-1B, highlighting a complex cytokine milieu controlled by ATP metabolism and STING signaling. These effects are reversed with the addition of AB928, an adenosine receptor antagonist. We considered that boosting cGAMP in the PDAC TIME might be sufficient to offset the effects of Ado signaling. In support of this approach, we show that blocking hydrolysis of cGAMP by inhibiting ENPP1 augments the efficacy of FOLFIRINOX against syngeneic murine PDAC tumors, despite the likely presence of adenosine. These findings support the conclusion that adenosine signaling interrupts anti-tumor STING signaling and demonstrate that ENPP-1 inhibition may provide therapeutic benefits by boosting STING and reducing adenosine during chemotherapy treatment in PDAC patients.
Citation Format: Alykhan Premji, Jason Link, Takanobu Yamao, Khalid Rashid, Evan Abt, Amanda Labora, Charlotte Chan, Thuc Le, Zev Wainberg, Caius Radu, Timothy Donahue. Adenosine inhibits STING driven anti-tumor immunity in pancreatic cancer [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 PR15.