Abstract
Many cancers metastasize to the bones, particularly in cases of breast and prostate cancers. Due to the “vicious cycle” of cancer cells inducing bone resorption, which promotes further tumor growth, they are difficult to treat and may lead to extreme pain. These factors increase the urgency for emerging therapeutics that target bone metastases more specifically and effectively. Animal studies are essential to the development of any therapeutics, but also require robust animal models of human diseases. Robust animal models are often challenging to develop in the case of bone metastasis studies. Previous methods to induce bone metastasis include intracardiac, intravenous, subcutaneous via mammary fat pad, and intraosseous cancer cell injections, but these methods all have limitations. By contrast, the caudal artery route of injection offers more robust bone metastasis, while also resulting in a lower rate of vital organ metastases than that of other routes of tumor implantation. A syngeneic animal model of bone metastasis is necessary in many cancer studies, because it allows the use of immunocompetent animals, which more accurately mimic cancer development observed in immunocompetent humans. Here we present a detailed method to generate robust and easily monitored 4T1-CLL1 syngeneic bone metastases with over 95% occurrence in BALB/c mice, within two weeks. This method can potentially increase consistency between animals in bone cancer metastasis studies and reduce the number of animals needed for studying bone metastases in mice.
Highlights
Over 90% of cancer mortalities can be attributed to metastasis, the dissemination of cancer cells from the primary tumor site to other tissues in the body [1,2]
The caudal artery injection method combined with 4T1-CLL1 bone localizing cells produced higher rates of bone metastasis and generally lower rates of vital organ metastasis than other standard methods (Table 2)
Two rounds of in vivo selection were used to produce a 4T1 derivative cell line “4T1-CLL1” (Fig. 1ii1ix), which we have shown can generate bone metastasis at high rates when used in combination with a caudal artery injection, in BALB/cJ mice (Table 2)
Summary
Over 90% of cancer mortalities can be attributed to metastasis, the dissemination of cancer cells from the primary tumor site to other tissues in the body [1,2]. Intravenous injections (IV) tend to produce lung tumors that can metastasize to bones, and commonly metastasize to the liver, spleen, or brain Another pitfall of IV injections is that the relatively large lung tumors, that inevitably develop, can mask weaker signals located in other parts of the body, due to signal detector saturation. This issue is exaggerated for subcutaneous injections to the mammary fat pads (subsequently referred to as just “fat pads”) due to the large primary tumors which form before metastasis, and the fact that the fat pads are in close proximity to the bones of the leg, pelvis, and spine. Intraosseous ( known as intratibial) injections are consistent and well controlled in terms of cell quantity/growth but require an invasive bone drilling procedure that creates local inflammation and fails to accurately mimic the natural
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