Scorpion Protein Illuminates Brain Tumors for Surgeons
Jim Olson, a pediatric neuro-oncologist at Seattle Children’s Hospital, was reviewing with his colleagues the case of a 17-year-old girl several years ago who had just undergone brain surgery to remove a tumor. An MRI scan revealed a thumb-size piece of tumor left behind. In the operating room, the tumor tissue had looked just like healthy brain tissue. During the review meeting, the hospitals’ chief of neurosurgery turned to Olson and said: “Jim, you have to come up with a way to light these cells up.”
So Olson and a neurosurgical resident started searching for a way to highlight cancer cells in the operating room. Eventually, they came across a report of a scorpion toxin that binds to brain tumors but not healthy cells. By linking a synthetic version of this protein to a molecule that glows in near-infrared light, the researchers think they may have found what they call “tumor paint.”
In their very first test, the pair injected the compound into the tail vein of a mouse whose body harbored a transplanted human tumor. “Within 15 to 20 minutes, the tumor started to glow, bright and distinct from the rest of the mouse,” says Olson.
A Seattle company called Blaze Bioscience has licensed the technology from the Fred Hutchinson Cancer Center. Olson says human trials will begin late in 2013.
The scorpion toxin is special not only because it binds to tumor cells, but because it can cross the blood-brain barrier—a cellular and molecular fortification that lines blood vessels in the brain and prevents most compounds from entering.
“Usually, peptides don’t get into the brain unless they bind to something specific that carries it in there,” says Harald Sontheimer, a neurobiologist at the University of Alabama in Birmingham, who first identified the neurological potential of the scorpion protein.
Although derived from venom, the toxin seems to be safe. A biotech company started by Sontheimer showed in early clinical trials that a version of the scorpion toxin tagged with radioactive iodine was safe in patients. However, the company closed before late-stage testing of the iodine-tagged compound, which is now owned by Japanese pharmaceutical company Eisai.
The tumor paint developed by Olson may also light up cancer outside of the brain. Animal studies suggest it could also demarcate prostate, colon, breast, and other tumors. The potential the compound has to save healthy brain tissue and improve patients’ lives is told in a short film called Bringing Light, which is in the running for the Sundance Film Festival.
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