Painting Tumors

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When treating cancer with surgery, it's crucial that every bit of the disease has been removed; but spotting cancer cells left behind after a tumor has been removed is difficult. Now, however, researchers at Seattle's Fred Hutchinson Cancer Research Center have created a molecular "paint" that coats cancer cells so doctors can see the wayward ones that they might 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, while the fluorescent tag is piggybacked on to the peptide. After doctors excise a tumor, they use a special camera that captures nearinfrared photons to then 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 tested it in a variety of human tumors grown in mice. So far, the researchers have successfully illuminated five kinds of cancers, and 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 a way to extend what we can see," says Olson, making all our tools against cancer more powerful.