Taking a Closer Look at Common Animal Models for Tumor Diseases: Colorectal Cancer

Colorectal cancer is a common malignancy that occurs in the colon, a part of the digestive tract. It is typically found at the junction of the rectum and sigmoid colon and has the highest incidence in the 40 to 50-year-old age group. The male-to-female ratio is 2-3:1, and it is the third most common gastrointestinal tumor. Colorectal cancer mainly includes adenocarcinoma, mucinous adenocarcinoma, and undifferentiated carcinoma. Its gross morphology can appear as polypoid or ulcerative types, along with other forms. Individuals at higher risk include those with chronic colitis, colon polyps, and male obesity.

Animal models of colorectal cancer can simulate the development of human colorectal cancer to a certain extent, and they provide a valuable platform for studying the occurrence, progression, biological characteristics, and treatment of colorectal cancer in humans. As such, understanding the classification, characteristics, and applications of colorectal cancer models holds substantial significance for research into the pathogenesis and clinical drug treatment of colorectal cancer.

Figure 1. Schematic Representation of Mouse Models of Colorectal Cancer ^[1]

Common Animal Models of Colorectal Cancer

Tumor Transplantation Models

Cyagen has developed a variety of effective tumor transplantation models, including colorectal cancer, breast cancer, liver cancer, and more. These models involve:

1. Successful xenotransplantation of over 300 human cell lines using immunodeficient mice such as C-NKG (severe immunodeficiency mice), NOD-Scid, BALB/c nude (nude mice), etc., as recipients.

2. Homologous tumor transplantation typically employs wild-type mice like C57BL/6 or BALB/c as recipients.

(1) Heterotopic/Subcutaneous Xenograft CDX Model

In heterotopic transplantation models, subcutaneous implantation on the back or under the armpit is a commonly used method. Due to its short tumor model construction time and ease of detection, cell line-derived xenograft (CDX) models  are utilized for preclinical evaluation of anti-colorectal cancer treatments. This method offers a high tumor formation rate, short tumor growth cycle, easy control over tumor size and location, minimal individual variation, consistent impact on the host, and facilitates objective assessment of therapeutic efficacy.  However, CDX models cannot fully simulate the tumor microenvironment.

Cyagen's Selected Colorectal Cancer Cell Line Xenograft Models

(2) Orthotopic/Homologous Transplantation Model

Compared to heterotopic transplantation models, orthotopic transplantation offers a more accurate reflection of the real-life tumor scenario, which enhances the reliability of tumor models. In orthotopic transplantation models, metastasis can be induced to demonstrate the interaction between tumor cells and organ-specific factors, which is significant to the development of conditions like liver cancer. Orthotopic transplantation can also simulate the tumor's immune microenvironment. As a result, most results based on heterotopic models often require further validation through orthotopic transplantation models. Orthotopic growth more accurately replicates the microenvironment in which tumor cells grow in the body, leading to more accurate predictions of drug efficacy.

(3) Patient-Derived Xenograft Model

Patient-derived xenograft (PDX) models have two primary issues:

1. The success rate of PDX models worldwide is currently less than 20%.

2. Due to the defective T-cell immune system in immunodeficient mice, this model is not suitable for immunological research.

While orthotopic tumors in PDX models tend to form single tumors, the overall homogeneity of tumor masses is still relatively poor. Furthermore, quality control methods are not as well-established as those for heterotopic models. Additionally, it is challenging to incorporate fluorescent reporter gene markers in orthotopic models. Monitoring of tumor growth and drug responses in orthotopic colon transplantation models is also not as straightforward as in heterotopic colon transplantation models.

Spontaneous Tumor Models

Spontaneous tumors refer to tumors that occur naturally in experimental animals without any artificial intervention. These tumors develop and progress similarly to human tumors and are not influenced by any deliberate factors. As a result, they closely resemble the true state of tumors within the human body. However, spontaneous colorectal cancer animal models are relatively rare and their incidence rate is not high. Consequently, it is challenging to obtain a sufficient number of suitable animal models within a short timeframe. Additionally, the observation period for these models can be lengthy, resulting in substantial experimental costs. Therefore, spontaneous tumor animal models are rarely used in research.

Chemically Induced Tumor/Cancer Model

Chemically induced tumor animal models involve the deliberate application of various carcinogenic agents under controlled experimental conditions to induce tumor formation in animals. Tumors can be induced through methods such as oral administration, injection, implantation, and topical application. These models are relatively simple to create, exhibit good reproducibility, can be generated in large numbers within a short period, and closely mimic the process of carcinogenesis.

As a result, they are widely used in experiments. Chemical methods are frequently utilized for the induction of colorectal cancer models. Common chemical inducers for colorectal cancer include dimethylhydrazine (DMH), azoxymethane (AOM), and the inflammatory agent dextran sulfate sodium (DSS), among others.

Colorectal Cancer Model Validation Data

1. Construction of Subcutaneous/Heterotopic CDX Model Based on Immunodeficient C-NKG Mice.

Severe Cachexia Mouse Model of Colo205/COLO 205 Colorectal Cancer

Figure 2. Subcutaneously Transplanted (Heterotopic transplantation) Tumor and Body Weight Growth Curve of Colo205 Colorectal Cancer Cells.

The cells were inoculated subcutaneously into C-NKG and BALB/c nude mice, and tumor volumes were measured at various time points. Cell inoculation was carried out at doses of 5×10⁶/each and 3×10⁶/each, and the data are presented as Mean±SEM. The results demonstrate that Colo205 (COLO 205) readily forms tumors in both C-NKG and BALB/c nude mice, accompanied by a decrease in body weight. This model represents a severe cachexia model.

Mild Cachexia Mouse Model of HT29 Colorectal Cancer

Figure 3. Subcutaneously Transplanted Tumor and Body Weight Growth Curve of HT29 Colorectal Cancer Cells.

The cells were subcutaneously injected into C-NKG and BALB/c nude mice, and tumor volumes were measured at different time points. Cell inoculation was done at doses of 1×10⁶/each and 3×10⁶/each, and the data is presented as Mean±SEM. The results indicate that HT29 readily forms tumors in both C-NKG and BALB/c nude mice, accompanied by a decrease in body weight. This model represents a mild cachexia model.

Heterotopic Mouse Model of LOVO Colorectal Cancer

Figure 4. Subcutaneously Transplanted Tumor and Body Weight Growth Curve of LOVO Colorectal Cancer Cells.

The cells were subcutaneously injected into C-NKG and BALB/c nude mice, and tumor volumes were measured at different time points. Cell inoculation was performed at doses of 5×10⁶/each and 10×10⁶/each, and the data is presented as Mean±SEM. The results demonstrate that LOVO readily forms tumors in both C-NKG and BALB/c nude mice.

Heterotopic Mouse Model of HCT116 Colorectal Cancer

Figure 5. Subcutaneously Transplanted Tumor and Body Weight Growth Curve of HCT116 Colorectal Cancer Cells.

The cells were subcutaneously injected into C-NKG, NOD-Scid, and BALB/c nude mice, and tumor volumes were measured at different time points. Cell inoculation was carried out at a dose of 5×10⁶/each, and the data is presented as Mean±SEM. The results indicate that HCT116 readily forms tumors in C-NKG, NOD-Scid, and BALB/c nude mice.

2. Orthotopic CDX Mouse Models Exhibit Tumor Metastasis Based on LUC Fluorescent Reporter Gene Cells.

Figure 6. In Vivo Fluorescent Imaging of Orthotopically Transplanted Colon Tumor with HCT116-luc Colorectal Cancer Cells, along with Fluorescence Intensity Changes and Mouse Survival Curve.

The results indicate that HCT116-luc readily forms tumors in C-NKG mice with a relatively short survival period. Tumor tissue exhibits intra-abdominal metastasis, and after a certain period of proliferation (Day 25), calcifications are observed within the tumor tissue, corresponding to a decrease in the fluorescence signal from the mice.

C-NKG Severe Immunodeficient Mice at Cyagen

C-NKG mice are a severe immunodeficient strain developed by Cyagen through the knockout of the Il2rg gene on the NOD-Scid background strain. These models are currently recognized as an excellent model for research in areas such as cancer, human immune function, immunology, autoimmune diseases, immunotherapy, infectious disease/vaccines, graft versus host disease (GvHD), safety assessment, stem cell biology, and more. Additionally, Cyagen can provide services tailored to your project requirements, including human immune system reconstitution and xenotransplantation of human tumor cell lines.

Reference:

[1] Kucherlapati, Melanie Haas.,  and Kucherlapati, Melanie Haas.. "Mouse models in colon cancer, inferences, and implications." iScience.