Abstract 2788: Characterization of a panel of orthotopic syngeneic models using bioluminescent imaging for the evaluation of immuno oncology therapeutics

Background: The rapid development of immuno-oncology (I/O) therapies for various cancer types has transformed the paradigm of cancer treatment from targeting the tumor to targeting the immune system, and now to combination strategies. Numerous Phase I-III trials with immunotherapeutics and combinations are being conducted; however, a lot of these are failing. More preclinical models are required to help investigate efficacy, uncover mechanisms of action, and to design more rational combination strategies. The most widely used models for immunotherapy evaluation are models with functional murine immunity such as syngeneic allograft models and genetically engineered mouse models (GEMMs). Syngeneic models are used in nearly all I/O therapy programs as these are well-characterized and straightforward to set-up as subcutaneous models. However, one of the major disadvantages of subcutaneous models is the lack of a clinically relevant tumor microenvironment (TME) including stromal cells, immune cells, extracellular matrix etc. The dynamic interplay of these cells drive alterations in cellular functions and impact study outcomes. Using bioluminescent imaging (BLI), we have developed and characterized a panel of orthotopic models where tumor cells are inoculated in a relevant organ-specific location to recapitulate the immune and stromal component interactions with the tumor, which can also facilitate metastatic spread. These models can be used to evaluate various therapies in both the orthotopic and metastatic settings. Method: A panel of syngeneic cell lines were labeled with bioluminescence by transducing the cell lines with a lentiviral vector carrying the firefly luciferase gene. This panel represents a diverse range of cancer types including liver (Hepa 1-6 and HT22), breast (4T1), colon (CT26.WT), brain (GL261), prostate (RM-1), and pancreas (Pan02). These bioluminescent cells were orthotopically implanted into immune competent mice. In-life tumor growth and metastasis were assessed using the IVIS® Spectrum In Vivo Imaging System. Tumor-infiltrating lymphocytes were assessed by flow cytometry (BD LSRFortessa™) and multiplex IHC. Results: Orthotopic implantation of syngeneic models was successfully demonstrated for all models as confirmed by in-life imaging and ex vivo imaging at termination. Baseline response towards various checkpoint inhibitors and chemotherapies were established. For the Hepa 1-6 liver model, response to an anti-PD-1 antibody was significant in both the subcutaneous and orthotopic setting. In contrast, the H22 liver model responded to both sorafenib and anti-mCTLA-4 antibody in the subcutaneous model but not in the orthotopic setting. In addition, anti-mCTLA-4 treatment led to more significant inhibition of pancreatic Pan02 tumor growth in the orthotopic model in comparison with its corresponding subcutaneous setting. Conclusion: Bioluminescent syngeneic models in the orthotopic setting provide a valuable tool for testing immunotherapies, with a more clinically relevant TME in comparison to the corresponding subcutaneous model. The establishment of a range of models covering diverse cancer types allows for a thorough interrogation of immunotherapeutic potential. Citation Format: Diandong Jiang, Bryan Miller, Yanrui Song, Rajendra Kumari, Annie An, Jie Cai, Davy Xuesong Ouyang, Henry Qixiang Li, Yinfei Yin. Characterization of a panel of orthotopic syngeneic models using bioluminescent imaging for the evaluation of immuno oncology therapeutics [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2788.