The deathstalker scorpion's venom may help surgeons see brain tumours
The deathstalker is among the most dangerous scorpions alive, a pale yellow desert hunter whose venom resists even large doses of antivenom. Yet one peptide from that venom, chlorotoxin, clings to brain tumour cells. Tagged with a fluorescent dye, it has been tested as a tumour paint that makes cancer glow during surgery.
Its scientific name, Leiurus quinquestriatus, means roughly five-striped smooth-tail. The pet trade has given it a confusing pile of common names, among them Omdurman scorpion and Naqab desert scorpion, so specialists stick to the Latin. Adults average about 58 millimetres. The species ranges across desert and scrubland from Algeria and Mali through Egypt, Ethiopia and Arabia to western India and Kazakhstan. In 2014 a population once treated as a subspecies was split off as Leiurus hebraeus, the Hebrew deathstalker.
The venom is a cocktail of neurotoxins with a low lethal dose. One ingredient, charybdotoxin, blocks potassium channels that respond to calcium, and another, Lq2, is named after the scorpion itself. A sting is excruciating but seldom kills a healthy adult; children, older people and those with heart conditions or allergies face much greater danger, and when death occurs it usually comes from fluid in the lungs. An Israeli study also found frequent pancreatitis after stings.
Antivenom is made by AbbVie, Sanofi Pasteur and a national centre in Riyadh, but outside the scorpion's range none of these is approved by regulators such as the US Food and Drug Administration. The US military keeps an investigational application for the Riyadh product, and a Miami-Dade fire rescue unit runs the Florida Antivenin Bank, which stocks Sanofi Pasteur's Scorpifav.
Chlorotoxin is the medical surprise. Clinical trials of a fluorescent version, BLZ-100, began in 2015, aiming to help surgeons remove as much cancer as possible while sparing healthy brain. In animal tests it lit up clusters of just 200 cancer cells, whereas MRI typically needs more than 500,000 to register. Other venom components have hinted at uses in regulating insulin. Many places now require permits to keep the scorpion, and some restrict it to licensed zoos.
Source: Deathstalker
