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.

Natural polysaccharides regulate intestinal microbiota for inhibiting colorectal cancer

“…E. coli carrying the polyketide synthase (pks) gene synthesizes colibactin, which induces colorectal carcinogenesis by causing DNA damage, dysfunctional DNA repair, genomic alterations, and instability [ 27 , 28 ]. Moreover, the tumor-promoting effect of E. coli was also verified in vivo , including Apc Min/+ mice, azoxymethane (AOM)-treated IL10 −/− mice, and Apc Min/+ /IL10 −/− mice [ [29] , [30] , [31] ]. These results also confirmed that IBD in IL-10-deficient mice promoted a specific phenotype of dysbacteriosis, and that mono-colonization with E. coli enhanced tumorigenesis in CRC.…”

Experimental Murine Models for Colorectal Cancer Research

“…The histological analysis of Apc mutation-induced tumors of the colon revealed that they are benign adenomas, making this model appropriate for investigating the premalignant rather than malignant phases of CRC. Nevertheless, tumor malignancy increases, and latency time shortens when AOM or other carcinogenic compound is administered [117,119,120]. Despite the fact that additional Apc-targeting murine models have been developed (Apc ∆716 , Apc ∆14 , Apc 1638N , among others), Apc Min/+ continues to be the most widely employed transgenic murine model of CRC [43].…”

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).…”