Snake Venom May Slow Cancer Growth, Studies Hint

Jennifer Hile
National Geographic Channel,June 1, 2004

Preliminary research shows a natural compound in some snake venoms may prevent the growth of cancerous tumors, potentially transforming one of nature's deadliest toxins into a curative agent.

"Snakes use venom to alter biological functions, and that's what medicine does too," explained John Perez, director of the Natural Toxins Research Center at Texas A&M University-Kingsville. "This is why venoms have always been of interest to medical researchers."

Today roughly a dozen diagnostic tests and drugs are derived from snake venom, according to Zoltan Takacs, a toxinologist (natural-toxins scientist) and herpetologist based at the Yale University School of Medicine in New Haven, Connecticut.

ACE inhibitors, a class of drugs used to treat high blood pressure and other cardiovascular disorders, were developed from the venom of a Brazilian snake. Scientists anticipate that this is just the beginning.

Of the nearly 3,000 species of snakes in the world, about 650 are venomous. Ten of the most deadly live in Australia, making it a logical base for new experiments.

"We knew Australia could be a rich source of drugs because there are so many venomous creatures here," said Tony Woods, a biologist at the University of South Australia in Adelaide. Woods is co-leader of a project to investigate whether the toxins in venom can be used to destroy blood vessels that feed cancerous tumors.

The Power of Nature's Toxins

Venoms are exquisitely complex, composed of as many as a hundred different peptides, enzymes, and toxins. Not only are the venoms of every snake species different, there are also subtle variations within each species.

"There are differences between [venoms of] juveniles and adults, and even among different geographic regions," Takacs said. "These differences may be due to different evolutionary pressures, like different ancestry, prey, and environments."

The variations between venom types and the number of venomous snakes worldwide create a rich molecular hunting ground for researchers, like Woods, seeking to design new drugs.

"A tumor is made of tissue," Woods said. "Like tissue in any part of the body, if you can prevent it from developing a blood supply, or interfere with that supply, then you will have an effect on the growth of that tissue."
Woods is working with Michael Venning, a pharmacologist at the University of South Australia, and graduate student Emma Bateman. Peter Mirtschin, a toxinologist at Venom Supplies in Tanunda, South Australia, is providing the venom directly from the snakes.

Woods's group has found a compound in snake venom that disrupts endothelial cells, which line the inner surface of blood vessels. "It causes the cells to separate from one another, which kills them," Woods said. "When that happens, the function of the blood vessel is inhibited, preventing or at least interfering with blood flow to the tumor [effectively starving it of nutrients]."

Woods will not specify which snake venoms his team is studying, because the compounds have not yet been patented.

The Cure That Doesn't Kill

The advantage of these venom-derived toxins is that they seem to act only on certain types of cells.

Chemotherapy and many other drug treatments do not distinguish between tumor cells and other healthy cells, causing debilitating side effects. But natural toxins have evolved to impact very specific targets.

"We believe the cells that line blood vessels in tumors are different in subtle ways from similar cells elsewhere in the body, because they are exposed to different stimulation and chemicals," Woods said. That means toxins inhibiting tumor blood vessels may not effect surrounding healthy cells, which would theoretically leave patients using these toxins feeling better than those who go through chemotherapy.

Woods anticipates that he will begin testing the venom-derived toxin in animals within the year. Those results will reveal whether the drug is suitable for human clinical trials.

"I don't actually like snakes, they scare me to death, but I'm fascinated by their venom," Woods said. "So long as it's provided to me in nice plastic tubes, I'm very comfortable with handling it."