Molecular ‘beacon’ paints tumor margins

Interest in image-guided interventions rests heavily on the ability of MR- and CT-guided devices to paint the outer margins of tumors. Now researchers have come up with an alternative kind of paint: a molecular "beacon" that illuminates tumor margins.

Preclinical tests conducted on mice show that this molecular paint binds selectively with tumor cells, emitting infrared light that can be used to guide surgeons to the outer layer of the tumor.

Its developers at Seattle Children's Hospital Research Institute and Fred Hutchinson Cancer Research Center say that the scorpion-derived peptide, Chlorotoxin:Cy5.5, can enable surgeons to visualize cancer cells at least 500 times better than an MR image.

MR is limited in distinguishing tumors from healthy tissue only if more than one million cancer cells are present, according to the researchers. Results from their animal studies, published in the July 15 issue of Cancer Research, indicate that the molecular dye lights up brain tumors as small as 1 mm in diameter with no residual effect from surrounding normal brain tissue. Tumors with fewer than 2000 cancer cells can be detected. In a prostate cancer model, as few as 200 cancer cells traveling in a mouse lymph channel could be visualized.

"By allowing surgeons to see cancer that would be undetectable by other means, we can give our patients better outcomes," said Dr. James M. Olson, senior author of the paper and an assistant professor of hematology-oncology at Children's Hospital and the Hutchison Center.

The ability to identify tumor margins is particularly important in the brain, where about 80% of malignant cancers recur at the edges of the surgical site, according to the researchers. The chlorotoxin begins binding to cancer cells minutes after injection and illuminates these cells for up to 14 days.

Chlorotoxin:Cy5.5 could be applicable to many cancers, according to Olson. The biomolecule has the potential for use as a noninvasive screening tool for early detection of skin, cervical, esophageal, colon, and lung cancers. It may also be useful in identifying cancer cells in lymph nodes that may have been cast off by breast, prostate, and testicular cancers.

The researchers are now gathering toxicity data to support an FDA application for clinical trials that could begin within 18 months, Olson said.