Shrew spit is under investigation by Canadian scientists as a potential screening test and treatment for breast, prostate and ovarian cancers.

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The saliva of the northern short-tailed shrew can paralyze prey with one bite. ((Gilles Gonthier/Flickr))

The northern short-tailed shrew, a mouse-like mammal with a long snout, is one of the world's few venomous mammal species. With one bite, its saliva can paralyze prey.

Biochemist Jack Stewart of Mount Allison University in Sackville, N.B., set out to find out how.

Stewart spent several years luring the animals with pepperoni and trapping dozens of shrews in his rural backyard before he eventually identified the chemical in shrew saliva that causes paralysis. Researchers then purified and synthesized it.

At first, Stewart thought the chemical — called soricidin — might be a potential painkiller, because it blocked nerve transmission. When he tested it on a random cell culture that happened to be ovarian cancer cells, however, he found the cells died — which was initially a source of annoyance to him.

"Then a light bulb came on," Stewart recalled. "Oh, they died," he said with a laugh. "That's a good thing in cancer."

It turned out that soricidin also has an anti-cancer effect against breast and prostate tumours in animal models. It works by blocking calcium from going into the cancer cells.

Like a homing device, soricidin targets a receptor that is found in cancer cells and not healthy cells. That difference makes it a potential diagnostic and treatment tool, said Stewart.

Human trials to come

At a laboratory at the Atlantic Cancer Research Institute in Moncton, Dr. Rodney Ouellette oversees research on a number of potential diagnostic tests for cancer, including soricidin. Ouellette is cautious about raising hopes too early, but he was surprised at early test tube results of the peptide.

"It was a very profound effect on virtually all cancer cell lines we tested," said Ouellette, the institute's president and scientific director. "From that point, we started looking at this in a different way and saying maybe this is the real thing, maybe this can work."

A Phase 1 trial in humans is about a year away, Stewart said. Many research and regulatory hurdles need to be cleared before the peptide could ever be used on patients.

Human studies will determine the peptide could help detect ovarian, breast or prostate cancer cells in a blood test, saliva or urine test, said Ouellette, who has seen many promising molecules fail.

Already soricidin has beaten many odds, however, given that only about one per cent of potential cancer treatments make it to human testing. 

Stewart has left his teaching job, and is now the chair and scientific adviser of Soricimed Biopharma Inc., which is hoping to commercialize his discovery to one day detect and treat cancer.