Experimental Metastatic Melanoma Mouse Model: A Platform to Study the Metastatic Potential of Melanoma Cells in the Lungs

- Experimental metastasis models help evaluate the tumor cells potential to extravasate and proliferate in particular sites following intravascular injection. To begin, prepare a single-cell suspension of melanoma cells in the desired concentration using an appropriate medium. Load the suspension into a syringe.

Next, restrain a mouse in a chamber and secure it such that its tail is accessible. Rotate the mouse 90 degrees to visualize its lateral vein. Use a heat lamp to increase the ambient temperature to dilate the tail vein. Now, insert the needle towards the distal end of the tail and inject the prepared melanoma cell suspension into the dilated vein.

The injected metastatic tumor cells migrate through the circulatory system. Eventually, some of these cells extravasate from the circulation into distant organs like the lungs. These tumor cells adapt to their new microenvironment to proliferate and establish experimental metastatic foci.

In the following protocol, we will demonstrate the tail vein injection of B16-BL6 melanoma cells into a mouse model to study their metastatic potential.

- After all B16-BL6 cell suspensions have been prepared, select a mouse. Holding it by the tail, guide the animal, rear first, into a restrainer. When the mouse's torso is in the main chamber and its tail outside of the apparatus, proceed to pull the animal towards the end of the restrainer.

Next, insert the restrainer-plunger and continue to push on the plunger until the mouse is secure. Once the animal is in place, rotate the mouse 90 degrees such that one of the lateral tail veins is facing upwards. Then, use an alcohol pad to vigorously clean the side of the mouse's tail where the vein is most visible.

To prepare for injection, first, collect 300 microliters of the 0.5 million cells per milliliter suspension into a syringe. Afterwards, eject bubbles from the syringe by inverting it, flicking its side, and pushing the plunger. Once bubbles have been removed, eject the cell culture to yield a final volume of 250 microliters in the syringe.

Proceed to extend the mouse tail with the non-dominant hand. Hold it so that the forefinger elevates the proximal end of the tail and the thumb depresses the distal portion. With the dominant hand, insert the needle into the vein towards the distal end of the tail, at a minute downward angle. Then, insert the needle further, adjusting it so that it matches the angle of the tail vein.

After the needle has been inserted, approximately 1 centimeter into the tail vein, begin to push the plunger while holding the syringe steady. Stop any bleeding by holding gauze against the entry site. Once the cell suspension has been ejected, remove the needle from the vein and discard it. Next, remove the plunger from the restrainer and place the mouse in a recipient cage.