Preclinical testing of A 2B adenosine receptor inhibitor PSB1115 for pancreatic cancer immunoprevention

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignancy with very poor prognosis due to low efficacy of current treatments and late-stage diagnosis. PDAC is characterized by a profoundly immunosuppressive tumor microenvironment (TME), with the adenosine signaling pathway acting as an important mediator of immune suppression. In this pathway, adenosine (an immunosuppressive metabolite) signals via adenosine receptors, including the A 2B receptor. The goal of this study is to test immunopreventative strategies that target the A 2B adenosine receptor to reduce intratumoral adenosine and prevent immune suppression. We hypothesize that the use of small molecule A 2B inhibitors will prevent the progression of PDAC by shifting the immune microenvironment and promoting anti-tumor immunity. Methods: A syngeneic model of PDAC was used with tumor cells derived from Kras G12D ; Trp53 R172H /+; Pdx1:Cre (KPC) mice. Tumor cells were implanted subcutaneously in the flanks of immunocompetent C57BL/6 mice. Oral gavage delivery of PSB1115 (small molecule A 2B inhibitor) began 14 days after KPC implantation, when tumors were palpable. Mice were treated either three days/week or seven days/week at 0.7mg/kg, and tumor sizes were measured twice weekly. After two weeks of treatment, mice were euthanized. Blood and tumors were collected at the time of euthanasia. Histology was analyzed and 10 fields per mouse were quantified using ImageJ. Results: Oral gavage delivery of PSB1115 reduced the growth rate of KPC subcutaneous tumors in the syngeneic model. While mice treated with PSB1115 trended to have smaller final tumor volumes when compared to vehicle controls in both the 3 and 7 days a week treatment groups, these changes were more pronounced in the 7 days/week group (three-fold reduction; p=0.07) as compared to the 3 days/week group (two-fold reduction; p=0.1). Immunohistochemical staining of tumors showed that treatment with PSB1115 induced significant CD8 + T-cell infiltration (p=0.0174) and increased Granzyme B expression (p<0.0001), indicating an activated cytotoxic immune response. There was no significant increase in the amount of NIMPR14+ cells when comparing the vehicle control and PSB1115 treated tumors (p=0.1565). When compared to vehicle controls, tumors treated with PSB1115 had significantly increased levels of CD68 (p<0.0001), with no significant increase in CD163 levels (p=0.1174), indicating infiltration of anti-tumor M1-like macrophages. Conclusions: Oral gavage delivery of PSB1115 and targeting of the adenosine A 2B receptor alters the immune landscape in subcutaneous PDAC tumors, promoting CD8 + T-cell and M1-like macrophage infiltration through reduced A 2B receptor signaling. Small molecule inhibitors targeting the A 2B adenosine receptor are promising candidates for immunoprevention in PDAC. [Supported by NCI 75N91019D00021/75N91023F00003]