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The fine art of brain tumor painting

Oct 2009
Krista D. Zanolli,

SEATTLE – According to the American Cancer Society, 22,070 malignant tumors of the brain or spinal cord will be diagnosed in the US this year. Of that number, roughly 12,920 patients will die this year from the tumors.

Cancerous tumors in the brain are one of the most difficult to treat because there currently are no blood tests or screening exams to detect them before they begin to cause symptoms. These tumors typically invade surrounding tissue, making it difficult to determine a clear boundary between normal brain tissue and that of a cancerous tumor. However, a new imaging technique is producing promising results.

In a study published in the journal Small, researchers at the University of Washington, led by Miqin Zhang, professor of materials science and engineering, reported that they have found a way to illuminate brain tumors by injecting fluorescent nanoparticles into the bloodstream that can safely cross the blood-brain barrier. This barrier, which protects the brain from infection by preventing passage of disease-causing organisms such as viruses into nerve tissue of the central nervous system, is almost impenetrable.


Shown is a mouse brain tumor imaged using nanoparticles. Courtesy of the University of Washington.

Using mouse brains, the team injected fluorescent nanoparticles into the bloodstream, where they crossed the blood-brain barrier. The nanoparticles illuminated the tumors for up to five days without any sign of damaging the barrier and actually improved the contrast between normal and diseased tissue in MRI and optical imaging techniques, both of which are used during surgery.

“If we can inject these nanoparticles with infrared dye, they will increase the contrast between the tumor tissue and the normal tissue,” Zhang said. “So, during the surgery, the surgeons can see the boundary more precisely.

“We call it ‘brain tumor illumination or brain tumor painting.’ The tumor will light up.”

The fluoro-nanoparticle targets tumors using a derivative of scorpion venom called chlorotoxin, enabling precise imaging of the size and location of cancerous tumors. For more than a decade, scientists have been exploring chlorotoxin for its tumor-targeting abilities because it binds to surface proteins overexpressed by many types of tumors, including brain cancer.

Zhang said that, until now, no nanoparticle used for imaging has been able to cross the blood-brain barrier and specifically bind to brain tumor cells. Current techniques use dyes and drugs to temporarily open the blood-brain barrier, risking infection to the brain.

The researchers overcame this problem by building a nanoparticle that remains small, even in wet conditions. The particle was roughly 33 nm when wet, about a third the size of smaller particles used in other parts of the body.

Because current imaging techniques have a maximum resolution of 1 mm, the use of nanoparticles could improve the resolution by a factor of 10 or more, allowing for the detection of smaller tumors and earlier treatment.

“Precise imaging of brain tumors is phenomenally important. We know that patient survival for brain tumors is directly related to the amount of tumor that you can resect,” said co-author Richard Ellenbogen, professor and chairman of neurological surgery at the university’s School of Medicine. “This is the next generation of cancer imaging.”

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