Abstract 2468: Genetic metastatic colorectal cancer model with in vivo imaging capabilities
Authors: Leiva Tyler , Griffith James , Guo Shaoxuan , Lerner Megan , McNally Lacey , Berry William , Morris Katherine 
Published: June 2022

Abstract
Introduction: Colorectal cancer (CRC) is the second leading cancer related cause of death worldwide, responsible for nearly 2 million deaths annually, most commonly due to complications from metastasis. A mouse model that reproduces human CRC is critically important to support pre-clinical research in the field. Recently a novel inducible genetically engineered mouse model in an immune competent B6 background was developed that metastasizes to the lung, liver, and peritoneum recapitulating what is seen in CRC patients. This model uses the Lgr5 (L) promoter to drive tamoxifen inducible Cre recombinase with the following conditional alleles: Apc (A), mutant Kras G12D (K), Tgfbr2 (T), and p53 (P) (LAKTP). After establishing the model in our center, we found mice developing tumors in the absence of tamoxifen induction. Because the original model lacked the ability to monitor the tumor development and progression in vivo in real time we created a LAKTP based mouse model that would allow for easy monitoring of tumor growth over time, allowing us to determine the frequency and time course of tumor development in the absence of tamoxifen induction.
Methods: C57BL/6J mice, with each individual mutation (L, A, K, T, and P), were purchased from Jackson Laboratory and used for breeding in-house. Following breeding, congenic C57BL/6J LAKTP mice were characterized prior to breeding in conditional Luciferase (Rosa26 LSL Luciferase) which was also purchased from Jackson Laboratory. Luciferin was provided by intraperitoneal injection prior to capturing the bioluminescence signal using an imager from Spectral Imaging Systems. Tissue samples were fixed in formalin and embedded in paraffin prior sectioning for histology and immunohistochemistry.
Results: Approximately 30% of our LAKTP mice died or required sacrifice due to meeting humane endpoints around 12 weeks of life in the absence of tamoxifen induction. Upon dissection, these mice exhibited large tumors located in the small intestine that led to non-survival bowel obstructions. Ten percent of these mice had liver metastases as well. Breeding in the conditional Luciferase allele allowed for detection of developing, non-induced tumors as early as 6 weeks of life. In addition to being useful for monitoring tumor growth in vivo, immunostaining of tumor tissue with anti-luciferase antibodies allows for detection of cells derived from Lgr5 positive intestinal stem cells.
Conclusion: The LAKTP mouse model is an important tool for studying CRC, but exhibits tumor development due to leaky Cre activity in the absence of tamoxifen in approximately 30% of mice by 12 weeks. Our strategy of breeding in conditional luciferase allows for in vivo imaging such that mice can be partitioned based on bioluminescence for trials that require equivalent tumor burden at the beginning of interventions. In addition, bioluminescence imaging also allows for tumor size to be monitored over time.
Citation Format: Tyler Leiva, James Griffith, Shaoxuan Guo, Megan Lerner, Lacey McNally, William Berry, Katherine Morris. Genetic metastatic colorectal cancer model with in vivo imaging capabilities [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 2468.