Abstract SY24-03: Modulating cellular senescence to reinstate natural killer cell immunity for pancreatic cancer immunotherapy
Authors: Ruscetti Marcus 
Published: June 2022

Abstract
Background: Cancer immunotherapies can lead to durable and sometimes curative responses in patients with otherwise treatment-refractory disease, and as such have revolutionized our approach to cancer therapy. Still, there are many roadblocks that must be overcome to make immunotherapies effective across a broader spectrum of patients and cancer types. Immune checkpoint blockade (ICB) therapies that are effective in some malignancies through reactivation of cytotoxic T cell immunity have failed in immunologically “cold” tumors such as pancreatic ductal adenocarcinoma (PDAC) due to poor T cell infiltration and weak antigen presentation necessary for effective anti-tumor T cell responses. We and others have demonstrated that induction of cellular senescence and the senescence associated secretory phenotype (SASP), which leads to production of immunomodulatory cytokines, chemokines, and growth factors, can be a powerful way to not only enhance T cell infiltration into tumors but also reactivate a different type of innate, antigen-independent Natural Killer (NK) cell immunity that can mediate tumor control. Recently, we found that a combination of two RAS pathway targeting therapies- the MEK inhibitor trametinib and CDK4/6 inhibitor palbociclib (T/P)- could induce senescence in genetically engineered mouse models of KRAS mutant lung adenocarcinoma and PDAC (Ruscetti*, Leibold*, Bott* et al. Science 2018; Ruscetti*, Morris*, Mezzadra* et al. Cell 2020). Strikingly, whereas therapy-induced senescence led to NK cell-mediated tumor regressions and long-term survival benefit in KRAS mutant lung cancer, it had little effect on NK cell immunity and tumor progression in PDAC. Here we set out to understand how the pancreas tumor microenvironment (TME) suppresses NK immunity and develop strategies to harness NK cell surveillance for immunotherapy in PDAC.
Results and Discussion: We took advantage of genetically similar Kras mutant, p53 altered PDAC and lung cancer cell lines that could be transplanted into different organs of C57BL/6 mice to study whether and how the pancreas TME may impact senescence-driven immune responses. Syngeneic KRAS mutant lung and PDAC tumor cells transplanted into the pancreas of C57BL/6 mice displayed transcriptional repression and reduced chromatin accessibility of SASP transcriptional activators (NF-KB, IRFs) and factors necessary for NK cell activity (IL-15, IL-18) and chemotaxis (CCL2, CCL7, CCL8, CXCL9, CXCL10) following T/P-induced senescence, and did not undergo anti-tumor NK immune surveillance as compared to tumors propagated in the lungs and liver. Transcriptomic analysis identified induction of EZH2 and epigenetic repression of its targets, including key SASP factors and regulators, specifically in tumor cells grown in the pancreas TME. Genetic or pharmacological inhibition of EZH2 enhanced proinflammatory SASP signaling and resulted in NK cell migration and anti-tumor cytotoxicity in murine and human PDAC lines and transplanted and genetically engineered PDAC mouse models. Remarkably, tumor-intrinsic EZH2 knockdown in combination with T/P treatment led to complete tumor regressions in some PDAC-bearing mice that were reversed following NK cell depletion or suppression of key SASP factors. Pharmacological inhibition of EZH2 methyltransferase activity also enhanced NK cell infiltration and tumor control following therapy-induced senescence in transplanted and genetically engineered PDAC mouse models. Importantly, we found that an EZH2 repression signature was associated with enhanced NK cell infiltration and SASP induction in human PDAC patient samples. These results demonstrate that EZH2 mediates transcriptional repression of the proinflammatory SASP in the pancreas TME, and that EZH2 blockade in combination with senescence-inducing therapies could be a powerful means to reactivate absent NK cell surveillance in PDAC to achieve immune-mediated tumor responses. In the future we plan to test these therapeutic interventions in combination with anti-PD-1/PD-L1 ICB therapy as a means to further activate both NK and T cell immunity to fully eradicate pancreatic cancer. This work highlights the importance of understanding the impact of the resident tumor microenvironment on anti-tumor immune responses to come up with new paradigms to potentiate immunotherapy in this and other immunologically “cold” tumor settings that are historically unresponsive to ICB therapy.
Citation Format: Marcus Ruscetti. Modulating cellular senescence to reinstate natural killer cell immunity for pancreatic cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr SY24-03.