Painting Tumors

By Alice Park

When treating cancer with surgery, there's nothing as important as making sure that every last bit of the disease has been removed. That's not always possible, since tumors have nasty habits of embedding themselves within healthy tissue and of breaking away and spreading malignancies to other parts of the body. But Researchers at Seattle's Fred Hutchinson Cancer Research Center have come up with an innovative way of giving surgeons the upper hand against these wily tumors. They have created a molecular "paint" that coats cancer cells so doctors can see the wayward cells that they may otherwise miss.

The paint is a blend of chlorotoxin derived from the scorpion (nonpoisonous to humans) and a fluorescent molecule that emits near infrared light. The scorpion-derived peptide homes in on the cancer cells and binds to them, bypassing healthy cells. The fluorescent tag is piggybacked onto the peptide. After doctors remove a tumor, they use a special camera that captures near infrared photons to look at the body and see any stray cells the scalpel left behind. At those wavelengths, light from the fluorescent marker cannot be blocked by blood, other body fluids or even thin bone.

Hutchinson's team, led by Dr. Jim Olson, spent three years developing the compound and has tested it in a variety of human tumors grown in mice. "The target we are hitting is something that most cancer cells use to eat away normal tissue to make space for the cancer to grow," he says. So far the researchers have successfully illuminated five kinds of cancers: gliomas and medulloblastomas in the brain, sarcomas in muscles, and prostate and colon cancers. They expect to begin testing the agent in human patients next year.

That's especially exciting because painting tumors could also help doctors control cancers before they spread from an organ to the lymph nodes and other tissues. Olson's molecular paint can pick up tumors as small as 200 cells, potentially helping doctors identify, for instance, the micrometastases that can make breast cancer so dangerous. Current techniques like magnetic resonance imaging start detecting tumors at 1 million cells. "It's simply a way to extend what we can see," says Olson, making all our tools against cancer more powerful.