Increased Incidence of Colon Tumors in AOM-Treated Apc1638N/+ Mice Reveals Higher Frequency of Tumor Associated Neutrophils in Colon Than Small Intestine

Abstract

Colorectal cancer (CRC) is one of the most common cancers and a major cause of mortality. Mice with truncating Apc germline mutations have been used as a standard model of CRC, but most of the Apc-mutated lines develop multiple tumors in the proximal small intestine and rarely in the colon precluding detailed analysis of colon tumor microenvironment. Our aim was to develop a model with higher resemblance to human CRC and to characterize tumor infiltrating immune cells in spontaneously developing colon tumors compared to small intestinal tumors. Therefore, the Apc1638N/+ line was treated repeatedly with azoxymethane (AOM) and 90% colon tumor incidence and 4 to 5 colon tumors per mouse were achieved. Of note, AOM treatment specifically increased the tumor burden in the colon, but not in the small intestine. Histological grading and WNT-signaling activity did not differ significantly between small intestinal and colon tumors with some lesions progressing to invasive adenocarcinoma in both locations. However, characterization of the intratumoral myeloid cell compartment revealed a massive infiltration of colon tumors with neutrophils − 6-fold higher than in small intestinal tumors. Moreover, CCL17-expressing macrophages and dendritic cells accumulated in the tumors indicating the establishment of a tumor-promoting immunosuppressive environment. Thus, Apc1638N/+ mice treated with AOM are a suitable and straightforward model to study the influence of immune cells and chemokines on colon carcinogenesis.

Macrophages, as a Promising Strategy to Targeted Treatment for Colorectal Cancer Metastasis in Tumor Immune Microenvironment

“…Activation of the wnt signaling pathway leads to granulocyte recruitment and tumor invasion, and abnormal wnt signaling directly alters the antineoplastic activities of effector T cells, helper T cells, and Tregs, suppressing tumor immunity (69). In highly proliferative colorectal tumors, wnt/b-catenin signaling is activated and abundant b-catenin accumulates in the nucleus, accompanying the immune cell infiltrates including TAMs (70).…”

“…Studies have revealed that complex chemokine networks can affect cancer progression via the recruitment and activation of TAMs. The increased expression of CCL17 in DCs and M2-like TAMs in tumors induces an immunosuppressive environment; CCL17 expression has been used as a marker for M2-like immunosuppressive macrophage polarization (133). CCL5, secreted by TAMs, inhibits T-cell-mediated killing of CRC cells and promotes immune escape by stabilizing PD-L1 (113).…”

Risk factors for small intestinal adenocarcinomas that are common in the proximal small intestine

“…In other words, the content of the intestinal tract did not significantly influence the development of tumors in the intestinal tract, and this experiment showed that the properties of the intestinal tract are involved in the development of tumors. This azoxymethane administration experiment was conducted again recently, and the results did not show carcinogenicity in the small intestine[ 13 ]. In the 1980s, an experiment was conducted in which dimethylhydrazine was administered to rats to examine the reproducibility of the above experiment, and the results were similar[ 14 ].…”