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Last Updated: Monday, 20 October, 2003, 15:31 GMT 16:31 UK
Drug-hope snails imperilled
Their shells are sought after by collectors

Medical science risks missing out on some remarkable new drugs because of the imperilled status of cone snails.

The marine molluscs, which live in shallow tropical waters, have powerful venoms that will form the basis of a novel class of strong painkillers.

But the animals are now under intense pressure from habitat loss and because their beautiful shells make them the highly prized target for collectors.

Their plight is raised in the current edition of the journal Science.

"Tropical cone snails may contain the largest and most clinically important pharmacopoeia of any genus in Nature, but wild populations are being decimated by habitat destruction and overexploitation," said Dr Eric Chivian, from Harvard Medical School in Boston, US.

"To lose these species would be a self-destructive act of unparalleled folly."

Big markets

Chivian; Professor Callum Roberts of York University, UK; and Aaron Bernstein, of Chicago University, US, believe urgent action is now needed to give the snails better protection.

They say a good first step would be to bring the animals under the aegis of the Convention on International Trade in Endangered Species (Cites).

This would require countries to monitor their trade and prevent unsustainable activity.

"They are exquisite and within easy reach of people," said Professor Roberts. "As a result, they are suffering badly from unregulated, intensive collection."

Hundreds of tonnes of shells are imported into the US and Europe annually.

The ecosystems in which the snails thrive - coral reefs, shallow-water mudflats and mangrove forests - are also under immense pressure.

Hollow tooth

The worry is that the 500 or so species of cone snail will be all gone before science has had the chance to investigate properly the extraordinary properties of their venoms.

These contain so-called conotoxins, which are small peptides constructed from perhaps just 10-40 amino acids.

Cone snails, Callum Roberts
Professor Roberts: Monitoring of all wild-caught species is needed
A snail will defend itself and paralyse its prey - worms, fish, and other molluscs - by injecting a cocktail of these toxins through a proboscis - a hollow, harpoon-like tooth.

Each snail species has its own distinct set of around 100 conotoxins. To date, only about 100 of the estimated 50,000 cone snail toxins have been characterised, and a mere handful tested for their medical potential.

Those that have are already showing remarkable promise.

"Most conotoxins are extremely selective about their receptor binding sites," said Bernstein.

"This makes them powerful tools for understanding how cells work and a rich source for discovery of new medicines."

Chronic pain

Conotoxins that block key neurological pathways have been shown to be effective in the diagnosis and possible treatment of small-cell lung cancer, one of the biggest cancer killers.

A conotoxin-based compound now in clinical trials also has a powerful anti-epileptic effect.

Other research suggests that conotoxins could treat muscle spasticity following spinal cord injury, and prevent cell death when there is inadequate circulation, such as during strokes, head injuries or coronary bypass surgery.

Studies indicate they could also be used to treat clinical depression, heart arrhythmias and urinary incontinence.

But it is in the field of pain relief that the snail venoms have generated huge excitement.

"Because these toxins are so specific in their mode of action, they are far more potent than existing painkillers, such as the opiate-based drugs like morphine," said Professor Roberts.

"What is more, they don't seem to cause addiction and the patient doesn't become tolerant to them over time. This makes them extremely useful for treating people suffering from chronic pain."

All species

One of the snail-derived pain treatments, a synthetic drug called Prialt, is currently undergoing clinical trials.

The researchers tell the journal Science that cone snails should be covered immediately by Appendix 2 of Cites, which would require proper management of the trade in shells.

But they go further in calling for the scope of Cites, or a mechanism like it, to be extended to keep a watchful eye on emerging global markets.

"At the moment, Cites is a reactive mechanism - it kicks in when species have already been depleted. But that is often too late," said Roberts.

"We would prefer to see something that monitors all wild-caught species, not just the species that are currently threatened."

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