Hypomethylation Therapy Leads To Immune Polarization And Improved Efficacy Of Immunotherapy In Transgenic Model Of Pancreatic Cancer

BACKGROUND Despite significant activity of immunotherapies in several malignancies, their efficacy in pancreatic cancer has been limited. One possible explanation may be the absence of a tumor microenvironment and immune cells that are necessary. We have demonstrated that 5-aza-2-deoxycitidine (DAC) had a profound effect on pancreatic cancer associated stroma and up-regulated many immune pathways. Therefore we proposed that hypomethylating therapy may alter the microenvironment to allow immue checkpoint inhibitors greater therapeutic efficacy. METHODS Transgenic mice that spontaneously develop pancreatic cancer (Kras, Trp53, Pdx-1 Cre [KPC]) underwent weekly transabdominal ultrasound to detect mice initially with larger (6-8 mm) and subsequently with smaller (3-5 mm) tumors. PBS or DAC (5 mg/kg) and anti -PD1H or isotype control antibody were administered every 72 hours intraperitoneally for 3 doses. Tumor size was monitored biweekly and 3D tumor volume reconstruction was used to estimate size. The immune cell infiltrate was characterized by quantitative immunohistochemistry or by FACS. RESULTS Mice treated with DAC with 6-8 mm tumors demonstrated a significantly increased survival and tumor necrosis as well as polarization of the infiltrating macrophages towards an M1 (CD86, CD163) phenotype and a trend towards an increase in infiltrating CD8 cells compared with controls. The shift in the T cell population and the macrophage phenotypes was not seen in the spleen or peripheral blood of either wild type or tumor bearing animals treated with DAC compared with controls. We subsequently treated mice with 3 doses of DAC followed by 3 doses of anti -PD1H and compared them to anti-PD1H alone in KPC mice with smaller (3-5 mm) tumors. In DAC + anti-PD1H we noted a decrease in the growth rate of tumors, an increased survival and a significant increase in necrosis and CD8 infiltrates, as well as a significant decrease in Ki67 and increase in Tunel staining compared with anti-PD1H alone. CONCLUSIONS Our results suggest that DAC pre-treatment prior to checkpoint inhibitors may favorably polarize the tumor infiltrating immune cell population, lead to increased recruitment of CD8 positive T cells, result in marked tumor necrosis and slow tumor growth. These effects ultimately contribute to increased therapeutic efficacy of checkpoint inhibitors in pancreatic cancer. We plan to optimize the efficacy of epigenetic therapy and checkpoint inhibitors by using other monoclonal antibodies (anti-PD1, PD1L)and different dosing regimens. Citation Format: Tamas Gonda, Jarwei Fang, Catheine Do, Anna Zhukovskaya, Martha Salas, Benjamin Tycko. Hypomethylation therapy leads to immune polarization and improved efficacy of immunotherapy in transgenic model of pancreatic cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3213.