Experimental Research on Spinal Metastasis with Mouse Models
The spine is a common site for tumor metastasis, and patients with spinal metastases often experience pain, pathological fractures, and spinal deformities due to tumor invasion of spinal bones. Mouse models have become a crucial tool in studying spinal metastases, aiding in the elucidation of pathophysiological mechanisms, improvement of diagnosis and treatment guidelines, and development of new therapeutic methods. This article provides a comprehensive overview of various mouse spinal metastasis models, their applications, and the methodologies used in their development and evaluation.
Mouse models of spinal metastasis are primarily developed using human and murine tumor cell lines. Human tumor cell lines include prostate cancer PC-3, lung cancer cell lines (PC-9, A549, NCI-H1299, NCI-H460, H2030, SPCA-1, and PC-14), melanoma A2058, kidney cancer ACHN, and breast cancer. Murine-derived tumor cell lines include BALB/c mouse breast cancer TM40D, breast cancer 4T1, melanoma B16, melanoma B16-luc, melanoma mB16-luc, melanoma B16-F1, prostate cancer MBT-2, prostate cancer TRAMP-C2, and lung cancer LLC1. Murine tumor cell lines are advantageous as they avoid excessive host versus graft reaction, making them suitable for studying the pathophysiological processes and molecular mechanisms at various stages of primary tumor metastasis and colonization in the spine. However, due to species differences between mice and humans, models using murine tumor cells are not entirely suitable for developing new therapies for human metastatic tumors. Therefore, models using human-derived tumor cells in immunodeficient mice are essential.
Models using murine-derived tumor cells are established using non-immunodeficient mice, such as BALB/C mice, C57BL/6J, and C3H/He. In contrast, models using human tumor cells require immunodeficient mice, with T lymphocyte dysfunction mice being the most commonly used. Severe combined immunodeficient non-obese diabetic/severe combined immunodeficient (NOD/SCID) mice are also used as carrier animals, offering a higher success rate for tumor modeling. However, NOD/SCID mice require more demanding conditions and are more prone to disease and death.
Several methods are employed to establish spinal metastasis models in mice, including circulatory system injection, spine injection, and spontaneous spine metastasis. The circulatory system injection method involves injecting a certain amount of tumor cell suspension into the blood circulation system of mice to simulate the spread of tumor cells to the spine. The spine injection method involves directly injecting tumor mass or cells into the spine through surgery or percutaneous injection. The spontaneous spine metastasis method involves implanting tumor cell suspension in the corresponding in situ organ or subcutaneous tumors in mice, allowing cancer cells to spontaneously metastasize to the spine over time.
Various imaging techniques are used to evaluate and monitor spinal metastasis mouse models, including in vivo bioluminescent imaging (BLI), micro-computed tomography (micro CT), magnetic resonance imaging (MRI), and positron emission tomography-CT (PET-CT). BLI can evaluate the activity of inoculated tumor tissues or cells immediately after injection, detect metastatic tumors in the initial stage before bone damage occurs, and record the occurrence time of metastatic tumors. Micro CT is used to evaluate osteoblastic or osteolytic changes in spinal metastases, quantitatively analyze bone volume, density, and surface area, and reconstruct 3-dimensional images of bone tumors. MRI can perform multiple imaging tests on all soft tissues with high sensitivity. PET-CT using fluorodeoxyglucose has better sensitivity and accuracy for detecting spinal metastases in mice than MRI, as it can detect smaller tumor tissues earlier due to increased tracer uptake levels in tumor lesions before bone destruction.
Extensive spinal metastases can compress the spinal cord, leading to neurological dysfunction. Current studies focus on evaluating neuromotor and sphincter dysfunction in mouse models of metastatic spinal tumors. The Basso Mouse Scale (BMS) for Locomotion is the most commonly used method for evaluating neuromotor function, providing a sensitive, reliable, and effective assessment of motor function changes in mice with spinal cord injury. Researchers have also proposed classifying motor nerve function injury caused by tumor compression in mice into four stages: tail dragging, dorsal stepping, hind-limb sweeping, and paralysis. Gait analysis is another method used to evaluate neurological functions in mice with spinal metastases, offering a more objective assessment of motor functions.
Spontaneous spinal metastasis models can completely simulate the process of primary tumor metastasis to the spine, allowing researchers to study each step of the multi-step cascade of tumor metastasis, including the formation of a microenvironment before metastasis, organ-targeting of tumor metastasis to the spine, dormancy of tumor cells, the effect of surgical resection of primary tumors on metastasis, and the regulatory function of the immune system on the formation of spinal metastasis. Studies using the circulatory injection method focus on the key steps of the early formation of spinal metastases, including the mechanisms of tumor cell propagation, circulation, and extravasation. However, this method cannot model specific vertebral segments and often results in tumors in multiple organs, leading to mice dying of infection and excessive tumor load before developing neurological damage caused by spinal metastatic compression. Transplanting tumors directly into the spine can produce highly consistent, reproducible, and stable spinal metastatic tumor models, allowing researchers to study the microenvironment of spinal metastases, the effects of metastatic tumors on the spinal peripheral nervous system, mechanisms related to metastatic tumor growth in the spine, the invasion of spinal bone tissues, the differences in the biological behavior of different tumor cell types in the spine, and the neurological dysfunction caused by spinal cord compression due to tumors. However, this method cannot be used to study tumor metastasis mechanisms.
The pathways of primary tumor metastasis to the spine include hematogenous spread, direct extension, and cerebrospinal fluid (CSF) spread. Hematogenous spread involves tumor cells metastasizing from the primary tumor to the spine through blood flow. Direct extension involves primary tumors in soft tissues adjacent to vertebrae directly invading and spreading to the spine. CSF spread involves brain tumors metastasizing to the spine via CSF. Currently, no mouse model of spinal metastasis simulates the pathways of direct extension and CSF spread, highlighting the need for new models to simulate these processes.
In conclusion, mouse models of spinal metastasis are invaluable tools for studying the mechanisms, diagnosis, and treatment of spinal metastases. Various modeling methods and imaging techniques provide insights into the pathophysiological processes and molecular mechanisms involved in spinal metastasis. However, the development of new models to simulate the pathways of direct extension and CSF spread is essential for advancing our understanding and treatment of spinal metastases.
doi.org/10.1097/CM9.0000000000002922
Was this helpful?
0 / 0