Snail toxin could ease chronic pain

New painkiller may be 10,000 times stronger than morphine.
19 July 2002

INGRID HOLMES

Sea-snail's prey paralyser also eases pain. © D. Paul

A sea-snail toxin could relieve chronic pain¹ . Tests on rats hint the chemical could be 10,000 times more potent than morphine, non-addictive and not cause side-effects.

A team from the University of Melbourne led by Bruce Livett extracted the 'conotoxin' from a cone-shell snail. They will announce their patented discovery, called ACV1, this week at the Venoms to Drugs 2002 conference on Heron Island, Australia.

More than 60% of us will suffer long-term pain at some time. Despite the addictive nature of morphine, many patients suffering from chronic pain eventually receive it, as there are few effective alternatives.

"We are confident not only that ACV1 inhibits pain, but also that it accelerates the recovery of injured nerves - a unique property not previously documented for an analgesic," says one of the research team, Zeinab Khalil. Moreover, says Khalil, "the universal way in which the drug blocks pain should mean it is effective in treating all types of chronic pain".

The researchers are currently seeking a commercial partner to take the compound through the next round of animal trials. "It is a long road ahead of us, but the results we have indicate we will be there sooner rather than later," says Khalil.

Experiments on the standard rat model for chronic pain lead them to believe that ACV1 stops sensations of hurt and touch as they start to make their way through the nervous system. They suspect that it does this by blocking receptors on the primary nerves involved in pain transmission, called nicotinic acetylcholine receptors.

Pain researcher David Borsook of Mass General Hospital, Boston agrees that the results look promising. Alternative relief for the kinds of pain associated with cancer, arthritis and spinal injury is needed desperately, he explains. "Current treatments are either ineffective or have significant side-effects. There is no medication for this type of neuropathic pain that is as effective as, say, an antibiotic is for a specific infection."

But others caution that, without fully understanding the mechanism of ACV1, it is impossible to know if it will be as broadly applicable, non-addictive or free of side-effects as the researchers claim.

"No one has ever found a drug that is truly a strong painkiller and is non-addictive," says chronic pain management specialist Jennifer Schneider of Arizona Community Physicians practice in Tuscon. "But there is always room for new drugs that act by different mechanisms, so it will be great if ACV1 is proven to work."

Cone-shell snails (Conus spp.) dwell in coral reefs. They use their mouthparts to harpoon small fish and shoot conotoxins into them. These toxins paralyse prey by preventing nerve communication; in small doses the chemicals block pain.

Several other groups are trying to isolate components of cone-shell venom that may have pharmacological uses. Another conotoxin, called Prialt, is currently awaiting approval from the US Food and Drug Administration. It is intended as an alternative to morphine, but its side-effects include blurred vision and confusion.

ACV1 targets a different class of receptors, so may not cause the same effects.

1. Satkunanathan, N. et al. An alpha-conotoxin from an Australian Conus is a potent analgesic in a rat model of neuropathic pain. Presented at the Venoms to Drugs Conference, Heron Island, Australia (2002).