Abstract 2921: Characterization of orthotopically implanted syngeneic cell lines as more clinically relevant in vivo models
Authors: Urs Sumithra , Germain Derrik , Baugher Meridith , Trachet Erin , Franklin Maryland 
Published: July 2021

Abstract
Preclinical oncology studies aim to model human disease in animal settings. To this effect, the site of tumor implant is thought to impact critical parameters that determine response to treatment. The more frequently used subcutaneous (SC) models have advantages; speed, cost efficiency and ability to monitor growth by caliper measurements but they lack heterogeneous tumor morphology, vessel density and immune cell infiltrates comparable to human disease. Orthotopic (OT) tumor models may allow for tumor modeling in the organ of origin by mimicking many human disease parameters such as vascularization, tumor architecture, metastatic potential, immune profile and tumor microenvironment. OT models may better represent clinical disease but are more challenging to monitor in vivo. Thus, we stably transfected several mouse syngeneic cell lines with luciferase (Luc). The Luc enabled cells facilitate non-invasive monitoring of tumor progression, potential metastasis and response to treatment via bioluminescence imaging (BLI). Here, we focus on pancreas (Pan02-Luc) and lung (LL/2-Luc) models. All animal work was performed in an AAALAC accredited facility, in alignment with applicable animal welfare regulations and with predetermined humane euthanasia criteria on all studies. Surgical procedures were used with minimal invasion to the respective organs followed by monitoring of tumor take and progression using BLI. Both the LL/2-Luc and Pan02-Luc models showed 90-100% tumor take and successful growth in their respective organs. The OT LL/2-Luc model showed mild response to paclitaxel and cisplatin with an increased time to progression (ITP) of 23% and 46%, respectively, 30% and 46% ITP to checkpoint inhibitors anti-PD-1 and anti-PD-L1 respectively, and 20% ITP to focal radiation (Xstrahl). In comparison, the SC LL/2 model showed 5%, 10%, 4.5% and 1% ITP to cisplatin, paclitaxel, anti-PD-1 and anti-PD-L1, respectively. This demonstrates the potential for the OT model to be more translatable than the SC model. Immune profile of the OT tumors by flow cytometry showed a high percentage of B cells and macrophages in the LL/2-Luc tumors. The OT Pan02-Luc model responded well to gemcitabine treatment with &gt;96% ITP and 62% tumor free survivors while anti-PD-1 treatment resulted in 25% ITP. The SC Pan02 model showed 85% and 9% ITP to gemcitabine and anti-PD1 treatments, respectively. The baseline immune profile of Pan02-Luc tumors showed very few CD4+ and CD8+ T cells and a large myeloid cell population of M-MDSC & M2 TAMs. The poor lymphoid cell infiltration and presence of large numbers of myeloid suppressor cells, characteristic of non-immunogenic tumors corresponds to the lack of robust response to checkpoint inhibitor treatment. The use of OT models may provide an important bridge between the more standard SC models and further clinical approaches.
Citation Format: Sumithra Urs, Derrik Germain, Meridith Baugher, Erin Trachet, Maryland Franklin. Characterization of orthotopically implanted syngeneic cell lines as more clinically relevant in vivo models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2921.