Of mice and men

    Mice -- our best bet against cancer?.
In trying to evaluate whether mouse cancer research will apply to humans, we'll look first at the positive side of the ledger. Why use mice when you're interested in curing human cancer?

This "nude" mouse lacks a thymus gland, needed for the development of the immune system. Since its immune systems is so defective, this mouse does not reject transplanted human cancers, so it is widely used to test cancer drugs. Courtesy of Jackson Laboratory, Bar Harbor, Maine.

  bullet They're available. Candidate drugs just can't be tested on people. "You obviously can't take an unknown drug and inject it into a patient," says Robert Evans, senior staff scientist at the Jackson Laboratory, Bar Harbor, Maine. "It's unethical, immoral, and probably illegal." Before a new drug can be tested, he says, "you have to have some guidelines to say what it will do." And these guidelines can only come from mice and other animal models.

    bullet They're similar. Mice share many common features with humans, says Evans. "Mice develop all the types of cancer that humans develop. They also have the same genes involved in a lot of these cancers."

    bullet They can "get" human cancers. Furthermore, human tumors can be implanted in mice, as was done in the angiogenesis studies we've been discussing.

    bullet They have simpler genetics. Genetically identical mice simplify experiments by minimizing the confusion that arises when testing drugs on mixed populations.

mouse xing
  "In theory, [genetically identical mice] should all respond the same to a given form of treatment," Evans says. By adding or deleting genes from mice, scientists can learn how that gene's products influence a treatment and thus obtain valuable clues to the biochemistry of cancer. For example, by adding genes that produce an angiogenesis inhibitor, scientists are hoping to increase the animals' own production of the valuable protein, and see how that affects the course of cancer.

This genetic uniformity in mice contrasts to the situation in people, Evans says. "When you come to cancer patients, you are dealing with individuals. Even if you have 100 melanoma patients, they will not respond the same -- all their genes are different."

But even Evans, who, after all, works for a laboratory built on mouse research, does not argue that mice are men. Making the transition from lowly lab rodent to the organism that is obsessed with inventing a better mousetrap is a big jump. "You have to learn every time -- you can't generalize about the individual drugs," he says. "Each new drug is new -- you have to go through the process" of testing toxicity and effectiveness.

I bet there's a counterargument here. Are animals really such great "models" for human disease?

The Why Files
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