Abstract PR-004: Inhibition of focal adhesion kinase (FAK) improves pancreatic ductal adenocarcinoma’s response to immunotherapy by targeting cancer stem cells (CSCs)

Background: Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers with a 5-year survival rate less than 10%. Current therapies consisting of cytotoxic chemotherapeutic agents are not effective in most patients with metastatic PDAC, and the impact of new strategies, including immunotherapies, has not been established. Previous studies have shown that inhibition of focal adhesion kinase (FAK) modulates the PDAC immunosuppressive tumor microenvironment (TME), and sensitizes tumors to immune checkpoint blockade. However, the role of FAK in regulating tumor cell intrinsic resistance to immunotherapy is not well understood. We and others previously demonstrated FAK regulates PDAC cancer stem cells (CSCs) activity including self-renewal, tumor initiation, and drug resistance. These CSCs are responsible for metastatic dissemination and resistance to multiple therapies, including immunotherapy. In this study, we evaluated the sensitivity of PDAC cells, including CSCs to cytotoxic T cells, and we also analyzed the impact of FAK inhibition on the immunogenicity and the response to cytotoxic T cell activity of PDAC CSCs. Methods: To understand how FAK regulates tumor intrinsic resistance to antigen-specific cytotoxic T cells, we utilized OT-I T cells (OT-I cells) that specifically recognize a peptide fragment of ovalbumin (ova) within the context of MHC-I. Mouse KPC pancreatic cancer cell lines expressing ova were generated and co-cultured with cytotoxic CD8+ OT-I cells in vitro. We analyzed the effect of FAK in regulating bulk cells sensitivity to antigen-specific cytotoxic T cells and clonogenic growth of CSCs by flow cytometry, MTT assay and colony formation assay using CRISPR-Cas9 and small molecule FAK inhibitors. We also analyzed the expression of surface proteins that mediate interactions with T cells (class I MHC) in bulk cells and CSCs after FAK inhibition. Results: Loss of FAK activity decreased CSCs activity (self-renewal, colony formation) in PDAC mouse cell lines, which is consistent with our previous data. Using antigen-specific OT-I co-culture model, we found that CSCs are resistant to cytotoxic T cells anti-tumor activity compared to bulk tumor cells. We also found inhibition of FAK activity not only enhances PDAC cells to cytotoxic T cell activity, but also sensitized CSCs to T cell killing. Studies in both human and mouse PDAC cell lines demonstrated decreased MHC-I expression in CSCs compared to the bulk tumor cells which could be reversed by FAK inhibition. Conclusion: We have demonstrated that CSCs are resistant to antigen-specific cytotoxic T cells, and FAK inhibition in CSCs can sensitize these cells to anti-tumor T cell activity that is associated with changes in the expression of factors involved in antigen presentation. Our study provides novel insights into the unique immunogenicity of CSCs and the role of CSCs in regulating tumor intrinsic immunotherapy resistance in PDAC. Our findings also lead to the identification of FAK as a novel therapeutic target for CSCs to improve immunotherapy efficacy in PDAC. Citation Format: Yezi Zhu, Lyndsey Sandow, William Matsui. Inhibition of focal adhesion kinase (FAK) improves pancreatic ductal adenocarcinoma’s response to immunotherapy by targeting cancer stem cells (CSCs) [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PR-004.