Toxic Snail Venoms Yielding New Painkillers, Drugs

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Toxin Factories

In nature, cone snails use their venom to immobilize prey, such as fish, mollusks, and worms. Cone snails harpoon their prey with pointed tongues that are shaped like hypodermic needles. The snails then pump their prey's flesh full of toxins.

"The poor animal, even if it gets away, [it] breaks off the harpoon. The likelihood of it being fatal is 100 percent, basically," Bingham said. "For any [human] who has been stung by a cone shell, the chance of mortality is 90 percent."

The potency and complexity of the venom fascinates scientists. Over millions of years cone snails have evolved toxins that target specific species in specific environments. No one toxin is exactly like another.

In addition, any cone snail can alter the compounds in its venom at will.

Scientists are studying how each cone snail toxin affects its victim. The results are improving our understanding of how cells, such as those that make up the nervous system, interact and communicate. The research is also leading to the development of new drugs.

"We are learning what nature has put in these animals and applying the strategy to other organisms," Bingham said.

Consider, for example, the painkiller ziconotide, the cone-snail-venom-derived drug that was approved by the FDA in December.

The painkiller (brand name: Prialt) is injected through a special pump into the fluid surrounding a patient's spinal cord. The drug blocks nerve channels that ordinarily transmit pain.

Unlike opium-derived painkillers, such as morphine, ziconotide is said to pose a low risk of addiction or increased tolerance and has few side effects. "If you stop using the drug, the pain comes back. And no matter how long you've used [the drug], you don't have to increase the dosage to kill the pain," Bingham said.

Given the potential of snail venom in the development of new drugs, Bingham said he is concerned that the rush to discover more promising toxins may contribute to the decline the world's cone snail species.

Cone Snail Conservation

Chivian, of Harvard Medical School, said the main threat to cone snails is the loss of coral reefs, which he attributes to bleaching (a type of slow death evident when multihued coral reefs turn a ghostly white) and disease outbreaks induced by global warming. Coastal development, pollution, and destructive fishing practices also negatively affect coral reefs.

As for cone snails, their shells are collected and sold by the thousands at curio shops to tourists. Chivian said that additional collecting for biomedical research, if done irresponsibly, could further imperil the snails.

But by far the greatest impact on the snails has been caused by the loss of coral reefs, Chivian said.

Bingham, the Clarkson University researcher, is taking no chances. He advocates responsible use of cone snails, including minimal collection for research. To that end, Bingham and his colleagues are among the few scientists in the world who "milk" cone snails for venom.

Milking involves a tricky—and potentially deadly—process: enticing a captive cone snail to harpoon a condom-covered test tube opening. (Other scientists typically retrieve venom by dissecting the venom glands of dead snails.)

Bingham notes that milking reduces the number of cone snails he needs to take from the wild for research. The process also allows him to study how and why the snails change the compounds in their venom over time.

Each change in venom compounds yields a new toxin with unknown potential.

Once scientists identify the compounds in any given cone snail toxin, researchers can readily make it in synthetic form, Bingham added, noting that this eliminates the need to extract more venom from the snails.

Chivian, meanwhile, said any measure to protect cone snails is appreciated. "We are losing species at a great rate without identifying them and without any knowledge of what value they may have for our health and our lives," he said.

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