Abstract 5945: Transcriptional analysis of TME in MC38 colon carcinoma model following checkpoint inhibition
Authors: Singh Priyanka , Saims Dan , Draper David , Barnes Sheri 
Published: April 2023

Colorectal cancer (CRC) is one of the most common cancers with 200,000 US cases per year. Adenocarcinoma is the most common type of CRC, making up 95 percent of all CRC cases. Checkpoint inhibitors used for CRC have shown efficacy for a specific subset of patients. MC38 is a very popular tumor model due to its characteristics as an immunologically warm tumor and response to some immunotherapies. To identify underlying factors that influence differences in treatment response, the tumor microenvironment (TME) of the MC38 model was analyzed following the treatment with anti-programmed cell death protein 1 (PD-1) and anti-cytotoxic T lymphocyte associated protein 4 (CTLA-4). The minimal tumor growth inhibition was observed in MC38 tumors treated with anti-PD-1 or anti-CTLA-4. The NanoString® nCounter system and flow cytometry were used to provide gene and cell-specific signatures of TME in response to immunomodulatory agents. NanoString® nCounter and flow cytometry analyses were complementary and demonstrated evidence of T cell recruitment and upregulation of genes associated with several immune-related pathways following treatment. Cytotoxic CD8+ T cells, CD4+ T cells, and NK cells in MC38 tumors following treatment with anti-PD-1, suggesting activation of an immune response. With treatment of anti-CTLA-4, tumors did not have demonstrable alterations to immune cell subset distribution which supports evidence that anti-CTLA-4 treatment show minimal activation of the immune system in MC38 tumors. Further, transcriptome analysis with NanoString® nCounter system revealed that the immune pathways related to signatures such as interferon signaling, cytotoxicity, antigen presentation, cytokine signaling, and chemokine signaling were upregulated with anti-PD-1 treatment compared to control or anti-CTLA-4 treatment of MC38 tumors. The transcriptome analysis also demonstrated 2-5-fold increases of interferon, cytotoxicity, cytokine, and chemokine genes such as, Gbp2, Gbp3, Irf1, Irf7, Irf8, Ifit1, Ifit2, Ifit3, Tnfsf10, Ccl2, Ccl5, Ccl7, Ccl12, Cxcl9, Cxcl10, and Cxcl11 over control in the case of anti-PD-1 treatment. In summary, anti-PD-1 treatment increased T cell recruitment into the tumor and upregulated genes in TME. Anti-CTLA-4 treatment known to enable combination activity with anti-PD-1, but not enough to show notable monotherapy activity. Immune cell subset distribution in TME and relative gene expression are two potential types of analyses to predict anti-tumor response. These data can be used mechanistically as well as to inform rational combination strategies for checkpoint inhibitors in colon adenocarcinoma.

Citation Format: Priyanka Singh, Dan Saims, David Draper, Sheri Barnes. Transcriptional analysis of TME in MC38 colon carcinoma model following checkpoint inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5945.