Scorpion venom offers improved cancer surgery

A substance derived from scorpion venom could be the key to more effective treatment for a wide range of cancers, researchers say.

Turned into a "paint" which can distinguish even a small number of cancerous cells from healthy tissue, the venom would vastly improve surgeons' accuracy when removing tumours.

Scientists found that chlorotoxin, a chemical in the venom, would attach itself to cancer cells. Joined to a fluorescent marker, Cy5.5, it becomes a molecular beacon which emits light near the infra-red spectrum, illuminating whole tumours or even clusters of only a few hundred cancerous cells. When injected, it sticks to cancer cells within two minutes.

Precision is paramount in operations to remove tumours, when cancerous cells can be missed and left behind. It is especially important when dealing with the brain, where some 80 per cent of malignant cancers return at the edge of surgical sites and where surrounding neurons must not be damaged.

At the moment, surgeons use colour, texture and blood supply to tell cancerous from healthy tissue. The paint marks tumours with at least 500 times more sensitivity than a magnetic resonance imaging scan, which will only work if more than a million cancer cells are present. Lasting for two weeks, it also massively outperforms contrast agents currently used to show up cancers, which last only a few minutes.

The research team, from Seattle Children's Hospital and the Fred Hutchinson Cancer Research Centre in Washington, found in tests on mice that they could illuminate brain tumours as small as 1mm in diameter. In another case they detected 200 prostate cancer cells travelling through a mouse's lymph system.

Dr James Olson, who led the team, said: "My greatest hope is that tumour paint will fundamentally improve cancer therapy. By allowing us to see cancer that would be undetectable by other means, we can give our patients better outcomes."

Dr Richard Ellenbogen, a paediatric neurosurgeon at Seattle Children's Hospital, co-wrote the study, which was published in the journal Cancer Research. He said: "This development has the potential to save lives and make brain tumour resection safer."

The researchers are due to start clinical trials in humans and say the paint could be used in surgery in as little as 18 months.

Experts in the UK say more research is needed into why the molecule only binds to tumour cells, and to ensure it is not toxic in humans. Professor John Griffiths, head of molecular imaging at Cancer Research UK's Cambridge Research Institute, said: "The big problem with surgery for brain cancer is that tumours can infiltrate normal brain tissue, making it very hard to tell where the tumour ends and the normal tissue begins. If you could light up the tumour cells by shining an infra-red beam on them, it might be very helpful."

Chlorotoxin:Cy5.5 could be used as a non-invasive screening tool for the early detection of skin, cervical, oesophageal, colon and lung cancers, and may help identify positive lymph nodes in patients with breast, prostate and testicular cancers.