489P - Somatic mosaic model of colorectal cancer for translational immune cancer research

Background

The nature of the immune infiltration and the molecular drivers of the immune phenotype in microsatellite stable (MSS) Colorectal Cancer (CRC) are poorly understood. Moreover, Microsatellite instable high (MSI-H) gene expression signature is closely correlated with BRAF-like gene signature and BRAFV600E MSS tumors have features of immune activation that differ from BRAF Wild-Type (WT) MSS tumor.

Methods

To better address the efficacy of immune checkpoint therapy specifically in relation to presence of a BRAFmutation, we developed a novel platform for the generation of somatic mosaic models of CRC enabling (i) high-throughput generation of genetically complex syngeneic models of cancer, (ii) tracing studies through fluorescence reporters.

Results

Cdx2^Cre/+ mice, expressing the Cre recombinase under the control of a human Cdx2 promoter/enhancer sequence have been crossed with the R26 ^LSL-Cas9-Gfp strain to generate models allowing for tissue specific activation of Cas9 and Gfp reporter only in CDX2 positive cells. This strain has been crossed with BRAF ^FSF-V600E mice to generate the final model. 6-8 weeks old mice have then been transduced with AAV constructs expressing the FLPO recombinase that can be activated by Cre recombinase and sgRNAs targeting APC, TP53, MLH1, MSH2 and ARID1A alone or combined, in order to model MSI-H CRC (APC-TP53-MLH1 and ARID1A-MLH1 conditional mosaic knock-outs) and MSS CRC (APC-TP53 conditional mosaic knock-out). Viral particles have been surgically delivered via subserosal cecal injection and mice monitored for tumor formation by IVIS imaging. 80 mice have been injected with 3 combinations of tumor suppressors providing a diverse immunology repertoire. Cell lines and organoids have been isolated from genetically modified mice provide a physiologic relevant and feasible means to study the mechanisms of response and resistance to immunotherapies and to understand biological and molecular differences between BRAF mutated MSI and MSS tumors.

Conclusions

This project will provide new animal models with functioning human immune systems to more accurately evaluate checkpoint blockers delivery, therapeutic response, and to better define biomarker expression.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

MD Anderson Cancer Center.

Funding

MD Anderson Cancer Center.

Disclosure

T. Troiani: Advisory/Consultancy: Amgen; Advisory/Consultancy: Bayer; Advisory/Consultancy: Novartis; Advisory/Consultancy: Merck; Advisory/Consultancy: Roche; Advisory/Consultancy: Sanofi. F. Ciardiello: Advisory/Consultancy: Roche; Advisory/Consultancy: Merck; Advisory/Consultancy: Amgen; Advisory/Consultancy: Servier; Advisory/Consultancy: Pfzier; Advisory/Consultancy: Symphogen; Research grant/Funding (institution): Roche; Research grant/Funding (institution): Merck; Research grant/Funding (institution): Amgen; Research grant/Funding (institution): Bayer; Research grant/Funding (institution): Ipsen; Advisory/Consultancy: Roche; Advisory/Consultancy: Merck; Advisory/Consultancy: Amgen; Advisory/Consultancy: Roche; Advisory/Consultancy: Merck; Advisory/Consultancy: Amgen. S. Kopetz: Advisory/Consultancy: Amgen; Advisory/Consultancy: Array; Advisory/Consultancy: Bayer; Advisory/Consultancy: Genentech; Advisory/Consultancy: Taiho; Advisory/Consultancy: AstraZeneca; Advisory/Consultancy: Boehringer Ingelheim; Advisory/Consultancy: Eli lilly; Advisory/Consultancy: Symphogen; Advisory/Consultancy: Boston Biomedical; Research grant/Funding (institution): AstraZeneca. All other authors have declared no conflicts of interest.