Model Introduction
The Orthotopic Xenograft Model involves the inoculation of tumor cells or tissue fragments into the organ or tissue of an experimental animal that corresponds to the primary site of the tumor. The core principle of this model is to simulate the authentic anatomical environment of tumor growth, making it more closely resemble the natural pathological processes of human tumors in terms of local microenvironment, blood supply characteristics, and invasive/metastatic behavior. Compared to subcutaneous xenograft models, orthotopic models offer higher biological relevance in translational medicine research and serve as a critical in vivo platform for studying tumor progression and evaluating drug efficacy.
Research Applications
This model is primarily utilized in the following research areas:
- Tumor Metastasis Mechanisms: Simulating the process of tumor invasion and metastasis from the primary site to distant organs (e.g., liver, lungs, lymph nodes).
- Drug Screening and Efficacy Evaluation: Particularly for the efficacy assessment of anti-metastatic drugs and preclinical translational research.
- Specific Disease Simulation: Including studies on multi-organ metastasis of pancreatic cancer, liver metastasis of colorectal cancer, localized growth of prostate cancer, and central nervous system tumors such as gliomas and brain metastases.
- Drug Resistance Mechanisms: Utilizing drug-resistant cell lines to construct models for exploring the development of tumor resistance and reversal strategies.
Key Points of Experimental Design
- Experimental Animal Selection: Commonly used strains include BALB/c nude mice, SCID mice, or NOD/scid mice. Appropriate strains and ages must be selected based on tumor type and tumorigenicity requirements.
- Preparation of Inoculation Materials:
- Cell Suspension: Use cells in the logarithmic growth phase, digested with trypsin and washed with sterile PBS to remove serum. The inoculation density is typically $5 \times 10^6$ to $1 \times 10^7$ cells per animal.
- Tumor Tissue: Fresh surgical specimens are collected and cut into $1–2 \text{ mm}^3$ fragments under sterile conditions.
- Standardized Surgical Procedures:
- Pancreatic Orthotopic: A subcutaneous tumor may be established first, followed by surgical transplantation of the tumor fragment into the pancreas.
- Colorectal Orthotopic: Tumor tissue fragments are transplanted directly onto the cecal wall to induce liver metastasis.
- Prostate Orthotopic: The prostate is exposed via surgery, and the cell suspension is injected subcapsularly.
- Intracranial Orthotopic: Precise intracranial injection is performed using a stereotaxic instrument.
- Environmental Quality Control: The entire experimental process must be conducted in an SPF (Specific Pathogen Free) barrier environment, with strict control of husbandry parameters to minimize interference from non-experimental factors.
Key Monitoring Indicators
- Pathological Identification: Histomorphological characteristics are analyzed via HE (Hematoxylin and Eosin) staining to confirm the consistency between the xenograft structure (e.g., nested arrangement, adenocarcinoma-like morphology) and the primary tumor.
- Immunohistochemical (IHC) Identification: Detection of epithelial markers (e.g., Cytokeratin, CK) and specific tumor markers (e.g., hCG for choriocarcinoma).
- Metastasis Rate Assessment: Monitoring the occurrence of metastasis in distant organs (e.g., liver, lungs, lymph nodes), such as the distant metastasis rate in pancreatic cancer orthotopic models.
- Functional and Molecular Indicators:
- Utilization of ELISA to detect the secretion levels of characteristic tumor markers in the serum.
- Utilization of Flow Cytometry to analyze cell cycle distribution and apoptosis rates of tumor cells.
- Growth Monitoring: For palpable or imageable sites, tumor volume is measured periodically, or growth kinetics are evaluated through functional imaging modalities.
