Abstract 87: Recapitulating the orthotopic tumor microenvironment using bioluminescent syngeneic models in immune competent mice for checkpoint inhibitor interrogation
Authors: Obeng Joyce Afrakoma , Jetha Maya , Wrigley Jane , Jiang Simon , King Jason , Kumari Rajendra , Yin Yinfei 
Published: August 2019

Abstract
BACKGROUND: Checkpoint inhibitors have shown promising therapeutic benefit in various cancer types, but more advanced preclinical models are required to combat resistance and evaluate opportunities for combination treatments. Subcutaneous syngeneic models are routinely used to evaluate the impact of immunotherapies on tumour growth as well as tumour invading leucocytes (TILs). However, the tumour microenvironment of orthotopic models is more comparable to the patient due to the organ-specific location of the tumour which facilitates metastatic spread and also recapitulates the immune and stromal component interactions with the tumour. Bioluminescent imaging (BLI) enables non-invasive longitudinal monitoring of orthotopic tumour burden and end stage quantification of tumour spread. Here we report the generation of a panel of bioluminescent syngeneic cell lines for orthotopic and metastatic modeling with an aim to assess the impact of standard of care agents, immune checkpoint therapies and combinations in a more clinically relevant environment.
METHODS: Bioluminescent variants of syngeneic cell lines were established by lentiviral transduction. Orthotopic models were established via direct implantation into various organs e.g. liver, breast, pancreas and bladder and tumour growth assessed by BLI in-life as well as end stage (Spectrum CT; PerkinElmer). Response to standard of care agents such as sorafenib, gemcitabine, docetaxel and immune checkpoint therapy (anti-CTLA-4, anti-PD-1) was also evaluated and TIL infiltration was assessed by flow cytometry analysis and IHC.
RESULTS: The success rate of tumour transplantation into different organs ranged from 60-100% as confirmed by both in-life imaging and ex vivo imaging at termination. For example, Hepa 1-6 appeared to grow within the parenchyma of the liver whereas 4T1 metastasized to the lungs and bone from the mammary fat pad, which was easily quantified by BLI. Real-time quantification of tumour size could be correlated with biomarkers and end stage assessment, for example, treatment with Sorafenib and check point inhibitors was correlated with alpha-fetoprotein (AFP) and end stage tumour burden, showing significant response in the orthotopic setting (p&lt;0.001, Two way ANOVA). Different responses to check point inhibitors were observed between tumors inoculated at subcutaneous sites and orthotopic sites.
CONCLUSIONS: Bioluminescent syngeneic models enables clinically relevant interrogation of standard of care agents, immunotherapies and combination which is distinct from the subcutaneous setting. The orthotopic microenvironment influences the tumour growth and response to immuno therapy. These models also enable the assessment of disease progression and modelling the metastatic environment.
Citation Format: Joyce Afrakoma Obeng, Maya Jetha, Jane Wrigley, Simon Jiang, Jason King, Rajendra Kumari, Yinfei Yin. Recapitulating the orthotopic tumor microenvironment using bioluminescent syngeneic models in immune competent mice for checkpoint inhibitor interrogation [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 87.