SUMMARY Glutamine is thought to play an important role in cancer cells by being deaminated via glutaminolysis to α-ketoglutarate (aKG) to fuel the tricarboxylic acid (TCA) cycle. Supporting this notion, aKG supplementation can restore growth/survival of glutamine-deprived cells. However, pancreatic cancers are often poorly vascularized and limited in glutamine supply, in alignment with recent concerns on the significance of glutaminolysis in pancreatic cancer. Here, we show that aKG-mediated rescue of glutamine-deprived pancreatic ductal carcinoma (PDAC) cells requires glutamate ammonia ligase (GLUL), the enzyme responsible for de novo glutamine synthesis. GLUL-deficient PDAC cells are capable of the TCA cycle but defective in aKG-coupled glutamine biosynthesis and subsequent nitrogen anabolic processes. Importantly, GLUL expression is elevated in pancreatic cancer patient samples and in mouse PDAC models. GLUL ablation suppresses the development of KrasG12D-driven murine PDAC. Therefore, GLUL-mediated glutamine biosynthesis couples the TCA cycle with nitrogen anabolism and plays a critical role in PDAC.

The presence of tumor-infiltrating T cells is associated with favorable patient outcomes, yet most pancreatic cancers are immunologically silent and resistant to currently available immunotherapies. Here we show using a syngeneic orthotopic implantation model of pancreatic cancer that Pik3ca regulates tumor immunogenicity. Genetic silencing of Pik3ca in Kras G12D /Trp53 R172H -driven pancreatic tumors resulted in infiltration of T cells, complete tumor regression, and 100% survival of immunocompetent host mice. By contrast, Pik3ca -null tumors implanted in T cell–deficient mice progressed and killed all of the animals. Adoptive transfer of tumor antigen–experienced T cells eliminated Pik3ca -null tumors in immunodeficient mice. Loss of PIK3CA or inhibition of its effector AKT increased the expression of MHC class I and CD80 on tumor cells. These changes contributed to the increased susceptibility of Pik3ca -null tumors to T cell surveillance. Our results indicate that tumor cell PIK3CA-AKT signaling limits T cell recognition and clearance of pancreatic cancer cells. Strategies that target this pathway may yield an effective immunotherapy for this cancer.

The presence of tumor-infiltrating T cells is associated with favorable patient outcomes, yet most pancreatic cancers are immunologically silent and resistant to currently available immunotherapies. Here we show using a syngeneic orthotopic implantation model of pancreatic cancer that Pik3ca regulates tumor immunogenicity. Genetic silencing of Pik3ca in Kras G12D /Trp53 R172H -driven pancreatic tumors leads to infiltration of T cells, complete tumor regression, and 100% survival of immunocompetent host mice. By contrast, Pik3ca-null tumors implanted in T cell-deficient mice progress and kill all of the animals. Adoptive transfer of tumor antigen-experienced T cells eliminates Pik3ca-null tumors in immunodeficient mice. Loss of PIK3CA or inhibition of its effector, AKT, increases the expression of MHC Class I and CD80 on tumor cells. These changes contribute to the increased susceptibility of Pik3ca-null tumors to T cell surveillance. These results indicate that tumor cell PIK3CA-AKT signaling limits T cell recognition and clearance of pancreatic cancer cells. Strategies that target this pathway may yield an effective immunotherapy for this cancer. 3 SIGNIFICANCE PIK3CA-AKT signaling in pancreatic cancer cells limits T cell infiltration and clearance of tumors by suppressing the surface expression of MHC Class I and CD80. Targeting the PIK3CA-AKT pathway in tumor cells provides a new avenue for discovery of novel pancreatic cancer immunotherapies.

The presence of tumor-infiltrating T cells is associated with favorable patient outcomes, yet most pancreatic cancers are immunologically silent and resistant to currently available immunotherapy. In this study, a syngeneic orthotopic implantation model of pancreatic cancer was used to show that PI3K/Akt signaling in tumor cells down-regulate immunogenicity to evade T cell surveillance. Genetic silencing of PI3K catalytic isoform Pik3ca in KrasG12D/Trp53R172H-driven pancreatic tumors leads to infiltration of T cells, complete tumor regression, and 100% survival of immunocompetent host mice. By contrast, Pik3ca-null tumors implanted in T cell-deficient mice progress and kill 100% of the animals. Adoptive transfer of tumor antigen-experienced T cells eliminates Pik3ca-null tumors in immunodeficient mice. Pik3ca silencing or inhibition of its effector, Akt, increases the expression of MHC Class I and CD80 on the surface of murine and human pancreatic cancer cells. Down-regulating MHC Class I and CD80 expression, or increasing Akt activity, in Pik3ca-null tumors increases their susceptibility to T cell-mediated regression in vivo. These results indicate that PI3K/Akt signaling in tumor cells limits T cell recognition and clearance of pancreatic cancer. Strategies that selectively target the PI3K/Akt signaling pathway in tumor cells may improve immunotherapy for pancreatic cancer. Citation Format: Nithya Sivaram, Patrick McLaughlin, Ya-Ping Jiang, Lisa Ballou, Kien Pham, Chen Liu, Adrianus van der Velden, Richard Lin. PI3K/Akt signaling in tumor cells promotes immune evasion by limiting infiltration, recognition and killing by T cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 522.