A peptide-derived paint that illuminates cancerous cells could help surgeons see where a tumor begins and ends more precisely, says a new study.

Researchers at Seattle Children’s Hospital Research Institute (WA, USA) and the Fred Hutchinson Cancer Research Center (Seattle, WA, USA) developed the paint, a scorpion-derived peptide called chlorotoxin that is linked to Cy5.5, a fluorescent molecular beacon that emits photons in the near infrared spectrum. Chlorotoxin:Cy5.5 activates within hours and it begins binding to cancer cells within minutes; the signal lasts for 14 days. Cy5.5 can identify tumors with as few as 2000 cancer cells, making it 500 times more sensitive than magnetic resonance imaging (MRI). In mouse models, the team demonstrated that they could light up brain tumors as small as 1 millimeter in diameter without lighting up the surrounding normal brain tissue; while in a prostate cancer model as few as 200 cancer cells traveling in a mouse lymph channel could be detected.

This illumination gives surgeons a better chance of removing all of the cancerous cells during surgery without injuring surrounding healthy tissue. This is particularly significant in the brain, where approximately 80% of malignant cancers recur at the edges of the surgical site. The study was published in the July 15, 2007, issue of Cancer Research.

“My greatest hope is that tumor paint will fundamentally improve cancer therapy,” said senior author James M. Olson, M.D., Ph.D. “By allowing surgeons to see cancer that would be undetectable by other means, we can give our patients better outcomes.”

The researchers believe that Chlorotoxin:Cy5.5 has the potential to be used in the future as a non-invasive screening tool for early detection of skin, cervical, esophageal, colon and lung cancers. It is also useful in identifying positive lymph nodes, which could mean a significant advancement for breast, prostate, and testicular cancers.

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