U.S. National Institute of HealthNational Cancer Institute
 
Research Article # 3

Utilization of mice in experiments.

In the previous article, we presented results demonstrating that an experimental agent works well in stopping the growth of tumor cells in a dish. The next step is to test it in mice. We start by asking the question, it is safe to give the experimental agent to mice, or is it so toxic that the mice become sick? So we administer the experimental agent to several mice for several weeks and see that they do well. They do not stop drinking water or eating food, they do not lose weight, they do not stop running around, a check of their blood shows normal levels, and they do not show any signs that concerns the animal care giver.

We can now ask other questions, such as, "Does the experimental agent stop the growth of tumors?" One way to perform these experiments is by using cell lines. Again, if we had a wildtype GIST tumor cell line, there is no doubt that a host of researchers would have already performed the types of experiments that are described below. For the images that follow, all experiments utilized an osteosarcoma (bone tumor) cell line.

Since half of all osteosarcomas occur around the knee, we take 2 million osteosarcoma tumor cells and inject them into the area just below the knee in mice (Picture 1). The mice that we use are very expensive, approximately $100 each. This is because they have been specially generated to have weak immune systems. In normal mice, cells that make up the immune system do an excellent job of recognizing human tumor cells as foreign and destroying them, thereby preventing the formation of tumors. Since the mice that we use have a weakened immune system, there is a greater chance that human tumor cells will go on to form tumors in these mice.
being injected with tumor cells
Picture 1
After a period of 3-6 weeks, sometimes much longer depending on the type of cell line used, some mice develop tumors (Picture 2). Notice the size of the normal leg (shown on the right) compared to the other leg, which was injected with tumor cells that went on to form a large osteosarcoma tumor (shown on the left). When the tumor approaches two centimeters (less than one inch), mice are euthanized. Every animal research facility has an Animal Care and Use Committee, that provide very strict guidelines about how large a tumor can get. This is to minimize any suffering that the mice may experience. With a very aggressive cell line, approximately 50-90% of mice develop tumors. Because not all mice develop tumors, we usually use ten mice per group in our experiments.
A mouse with a bone tumor Picture 2

Following are the results of one of our experiments. We took 20 immune weakened mice and injected each of them with 2 million osteosarcoma cells into the area just below the knee. The following day, we randomized the mice into two groups of ten mice each. Group One began treatment with an experimental agent, given once a day, Monday through Friday. Mice in Group Two were treated exactly the same as the mice in Group One, but they received salt water instead of the experimental agent. The mice were then monitored for tumor formation. After four weeks, mice in Group Two started to develop small tumors. These increased in size over the next two weeks. When the tumor approached 2 centimeters in size, that mouse was euthanized.

Six weeks after the start of treatment, we obtained the following results:

Group Treatment Administered Result
     
One Experimental Agent 2 of 10 mice had large tumors
Two Salt Water 8 of 10 mice had large tumors

All of the mice that did not develop tumors were monitored for an additional 15 weeks to guarantee that they did not form tumors later. A statistical analysis showed that these results would not have occurred by chance alone, suggesting that the experimental agent was effective in preventing the formation of osteosarcoma tumors. These results, and many others, prompted us to pursue this agent further in Phase I human clinical trials.

Attached is a powerpoint presentation  that demonstrates some of the innovative techniques that we have utilized to track the early stages of tumor formation, before we can feel them by touch or detect them by eye.



Tumor xenografts

A xenograft is a surgical transfer of tissue from one species to another. In cancer research, the xenograft utilized most often is the transfer of a human tumor into a mouse. Most xenografts do not go on to form tumors, but some do. Frequently, the tumor is implanted directly under the skin of the mouse. Although this procedure is much easier, it is probably not the best place to implant the tumor. A much more relevant model is to place the tumor into the same location from which it came (also known as an orthotopic injection). For bone tumors, we perform surgery to expose a bone in the mouse, and then place the tumor there. For GIST, the ideal locations would be the stomach, intestines, or the liver in the mouse, depending on where the tumor was taken from.

Shown on another website, is a video of the orthotopic implantation of a colon cancer tumor into the large colon of a mouse http://www.jove.com/index/Details.stp?ID=484



What Can I Do To Help?

If you are about to undergo surgery to remove a tumor, please inform your doctor that you would like any tumor sample that is left over, to be implanted into a mouse. This procedure can be performed at all CPGR member institutions.


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