Chlorotoxin

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Chlorotoxin is a 36-amino acid peptide found in the venom of the deathstalker scorpion (Leiurus quinquestriatus). A synthetically modified version, 131I-chlorotoxin or TM-601, is under investigation for the treatment of gliomas, because it specifically binds to glial tumor cells, but not normal cells.

Researchers at Seattle Children’s Hospital Research Institute and Fred Hutchinson Cancer Research Center have recently used Chlorotoxin in combination with fluorescent material named, Cy5.5 to demarcate cancer cells from the surrounding normal cells. Chlorotoxin:Cy5.5 is a fluorescent molecule emitting photons in the near infrared spectrum and hence can be visualized in the operating room with the aid of infrared glasses. Current technology (such as MRI with contrast agent) can distinguish tumors from healthy tissue only if more than 1 million cancer cells are present. Studies in mouse models have shown that Cy5.5 can identify tumors with as few as 2000 cancer cells, making it 500 times more sensitive than MRI. This gives surgeons a better chance of removing all of the cancerous cells without injuring the surrounding healthy tissue. There are plans to conduct a clinical trial, so Chlorotoxin:Cy5.5 could be used in operating rooms in as little as 18 months.