Snail venom could help develop powerful painkiller

Snail venom may be used to develop powerful nonaddictive painkillers which could potentially be stronger than morphine, scientists claim.
Scientists have created at least five new experimental substances - based on a tiny protein found in cone snail venom - that could lead to the development of safe and effective oral medications for treatment of chronic nerve pain.
The substances could potentially be stronger than morphine, with fewer side effects and lower risk of abuse. researchers said.
"This is an important incremental step that could serve as the blueprint for the development of a whole new class of drugs capable of relieving one of the most severe forms of chronic pain that is currently very difficult to treat," said David Craik from the University of Queensland.

Craik, who led the study, said that acute pain occurs when the nervous system is stimulated by a wound or injury and naturally subsides over time.
In contrast, chronic neuropathic pain kicks in when the nervous system itself is damaged.

This type of pain - which is often triggered by diabetes, multiple sclerosis and other diseases - can last for months, years or even decades.
Current treatments for chronic neuropathic pain have serious side effects and provide relief to only about one in every three patients, Craik said.
Cone snails are marine animals that use venom to paralyse their prey.

This venom contains hundreds of peptides (small proteins) known as conotoxins. But in humans some of these conotoxins appear to have analgesic effects, Craik said.
However, so far only one conotoxin-derived medication has been approved for human use. This drug, ziconotide, has one big drawback: It has to be infused directly into the lower part of the spinal cord - a clearly invasive procedure.
The team is working to develop a conotoxin-based drug that can be taken orally, which would be much more practical for patients.
They found a way to modify conotoxin peptides so they formed circular chains of amino acids. As a result, the modified peptides - which are essentially tied into a loop - are extremely stable and resistant to enzymes in the body.

In laboratory rats, a single, small oral dose of a prototype drug based on one of these looped conotoxins appeared to significantly reduce pain, as measured by a standard protocol, researchers said.
Scientists concluded that this prototype drug was about 100 times more potent than morphine or gabapentin, the two drugs that are considered the "gold standard" treatments for chronic nerve pain.
Addiction is less of a concern because conotoxins act on different receptors in the brain than morphine and other opiate drugs, Craik said.
The finding was presented at the National Meeting & Exposition of the American Chemical Society (ACS) in Dallas.