'Scorpion venom' zaps aggressive brain tumours

Jul 31 2006

Researchers in the U.S. have come up with a "man-made" scorpion venom which they say targets deadly brain tumours called gliomas without affecting neighboring tissue or body organs.

As many as 17,000 Americans are diagnosed with gliomas each year; the tumors are extremely aggressive and deadly, with only eight percent of patients surviving two years and three percent surviving five years from time of diagnosis.

Even after surgery is performed to remove a glioma, and despite the development of advanced treatments in radiotherapy, chemotherapy and surgery, some cancer cells invariably remain behind and proliferate.

The researchers say the venom can be used as a carrier to deliver radioactive iodine into tumour cells left behind, after surgery has removed the bulk of the tumour and can be used in conjunction with other treatments.

The technique has already been trialled in 18 patients and the initial findings suggest the treatment is well-tolerated and may be effective.

Further trials are under way and study leader, Dr. Adam Mamelak a neurosurgeon at Cedars-Sinai Medical Center, says a synthetic version of a peptide, or protein particle, that naturally occurs in the venom of the Giant Yellow Israeli scorpion, TM-601 was used on the participants, who had already undergone surgery to remove their tumour.

The researchers carried out a study using TM-601, a synthetic version of a peptide, that naturally occurs in the venom of the Giant Yellow Israeli scorpion.

The peptide has the unusual ability to pass through the blood-brain barrier that blocks most substances from reaching brain tissue from the bloodstream and can bind to glioma cells.

A single, low dose of TM-601 with radioactive iodine attached was injected into the cavity from which the tumour had been removed 14 to 28 days after surgery with very few adverse effects.

Six patients agreed to receive additional doses at one of three different levels of the drug.

The trial aimed to assess the tolerance of the dose and the researchers say the median length of survival for all patients was 27 weeks.

However two patients had no evidence of tumour and were still alive 33 and 35 months after surgery and most of the radioactivity delivered by the drug had disappeared after 24 hours.

Any residual radiation remained in the tumour cavity, which the researchers say suggests the drug binds to the tumour cells rather than normal brain cells.

The drug also appears to bind to other types of tumours and the researchers are planning further studies.

The drug was eliminated primarily through the urine, and radiation doses to the thyroid and other vital organs were extremely low and harmless.

Dr. Mamelak says although they were using TM-601 primarily as a carrier to transport radioactive iodine to glioma cells, the data suggests that it's ability to impede cancer growth could mean reduced doses of chemotherapy could be used.

Mamelak says if further studies confirm this, TM-601 may possibly be used in conjunction with other treatments, such as chemotherapy, because there may be a synergistic effect.