This article describes a method for establishing a mouse model of brain metastasis, where cancer cells from other organs spread to the brain. The procedure involves surgical techniques to inject cancer cells into the carotid artery of an anesthetized mouse.
In brain metastasis, cancer cells from other affected organs, or the primary site of origin, spread into the central nervous system to form secondary tumors. To generate a mouse brain metastasis model, prep an anesthetized mouse in the supine position. Make a small incision in the neck region.
Dissect the muscles to expose one of the underlying carotid arteries. Carotid arteries are a pair of major blood vessels in the neck, supplying blood to the brain and head. Separate the carotid artery from the adjacent vagus nerve. Next, place suture knots around the proximal and distal ends of the artery.
Tighten the proximal knot to obstruct the blood flow into the target injection site. Then, place a buffer-soaked cotton ball under the target injection site to immobilize and stretch the artery for additional support. Take a syringe filled with green fluorescent protein or GFP-labeled cancer cell suspension.
Gently inject the cell suspension into the lumen of the carotid artery. Retract the needle and tighten the distal knot to prevent leakage of cancer cells. Lastly, suture the incision. Allow the mouse to recover. Over time, cancer cells begin to migrate and form secondary tumors in the brain, confirming the successful establishment of a brain metastasis model.
In this procedure, anesthetize the mouse with ketamine/xylazine cocktail by intraperitoneal injection. Confirm complete anesthesia by pinching the animal's feet and observe the lack of response. Next, remove the neck hair by shaving or using a small amount of hair removal product.
Then, place the mouse on a glass plate and secure with rubber bands. Clean the skin by applying 70% alcohol and povidone-iodine. Now, make an incision in the skin about 1 centimeter long with a surgical scalpel. Then, bluntly dissect the muscle with surgical forceps to expose the carotid artery underneath.
Separate the carotid artery from the adjacent vagus nerve with surgical forceps. Afterward, place two sutures - one distal and the other proximal to the cotton ball - and make loose knots. Tighten the proximal knot to block the blood flow into the injection site.
After that, moisten a small cotton ball with buffer and place it underneath the carotid artery of the intended site of injection. Then, proceed to cancer cell injection if the carotid artery on the cotton ball appears fully pressurized with fresh red blood.
In this step, vortex and draw 100 microliters of cancer cells into the syringe. Under the dissecting microscope, slowly insert the 31-gauge needle with bevel up into the lumen of the carotid artery sitting on top of the cotton ball. Slowly inject the cells from the syringe into the carotid artery.
Successful injection can be observed by the changing color of nearby blood vessels and musculature when the buffered cancer cells are pushed into the circulation. When the injection is complete, lift the distal ligature gently to prevent regurgitation. Then, quickly tighten the distal knot to complete the injection process.
After completing the injection, tighten the ligatures and trim the excess silk suture with micro-scissors. Move back the separated muscle to cover the wound site and close the skin with two staples.
For recovery, transfer the animal onto a heating pad. Then, administer buprenorphine via subcutaneous injection as post-surgical analgesia. Once it regains consciousness and resumes normal behavior, return the mouse to its housing location. Provide the animal with gel food for several days post-surgery.
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