Faculty of Medicine

In the Fight Between Viruses and Bacteria, New Anti-Cancer Possibilities

Dec 5, 2018
Heidi Singer

University of Toronto researchers, studying the evolutionary arms race between bacteria and the viruses that infect them, have stumbled into a discovery that could open new avenues in the search for cancer treatments.

Professors Justin Nodwell and Karen MaxwellProfessors Justin Nodwell and Karen Maxwell

A few years ago, professors Karen Maxwell and Justin Nodwell were researching the way Streptomyces, a common bacterium in soil, interacts with viruses. By accident, they found that Streptomyces produces chemicals that stop viruses from attacking them.

“We were surprised by the finding,” says Maxwell, an assistant professor in the Department of Biochemistry. “This is a whole new category for understanding the dance between viruses and bacteria that is essential to human life.”

Viruses that attack bacteria are called phages. Scientists already knew that bacteria can fight back against phages, but only using protein-based mechanisms like the now-famous CRISPR system. Until now, nobody knew that Streptomyces produced chemicals that could do the same thing.

Several of these anti-phage chemicals have been used for decades to fight cancer in people. One of them, daunorubicin, is among the most important anti-cancer drugs in use. These are ancient molecules – bacteria have produced them for hundreds of millions of years. Why they do so has been an open question since they were first discovered in the 1960s.

It’s not surprising that these molecules work on both, says Maxwell, because a chemical designed to shut down the fast replication of viruses might also work on cancer cells, which grow uncontrollably. Because these anti-viral molecules are so numerous and common, and because they may occur in other bacteria, not just Streptomyces, they offer many possibilities for cancer research.

Looking back, Maxwell is amazed nobody discovered the anti-phage power of bacteria before. Streptomyces live in the soil, so scientists already knew they produce compounds to fight off fungus, parasites and bacteria.

“Nobody ever looked to see whether they make molecules to protect against another kind of predator – the virus,” Maxwell says. “We’ve known since the 60s that Streptomyces produce compounds that can be turned into anti-cancer drugs. But nobody ever thought about the biology of it and questioned why it worked.”

Now that they know that this bacterium is a potentially rich source of anti-viral activity, the team will look to see if all bacteria produce anti-phage chemicals, says Maxwell. And cancer researchers can begin to examine these bacteria to understand how they shut down fast replication. Even understanding how they fail to do so could help in the fight against cancer.

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