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tumors – by injecting them with a bacterium found in soil. So far, the
experimental treatment has mostly been tested in pet dogs, but
investigators hope they have found an effective anti-cancer therapy for
people.
Using bacteria to treat cancer is not a new concept. It was first
tried about a century ago. But despite promising results, the microbial
therapy fell out of favor with the advent of powerful chemotherapy drugs
and radiation.
Now, researchers are bringing back the use of bacteria to treat solid tumors. In a study published in the journal Science Translational Medicine,
scientists report how the genetically modified spores of a soil
bacterium – called C. novyi – were directly injected into
naturally-occurring tumors in a group of 16 dogs … and shrank or
completely eliminated them.
In three of the dogs, the tumors were completely eradicated within 21
days of having the spores injected. There was at least a 30 percent
reduction in the size of the cancerous tumors in three other dogs in the
group.
Meanwhile, in one human patient with an advanced soft tissue tumor
that had spread to her abdomen, the spore treatment significantly
reduced the tumor in and around the bone in the woman’s arm where the
cancer originated.
Scientists genetically modified the C. novyi bacterium, because at full strength, an infection could be fatal.
Shibin Zhou is head of experimental therapeutics at John Hopkins University School of Medicine in Baltimore, Maryland.
He says the C. novyi spores thrive in oxygen-poor environments, such
as the middle of a bulky tumor. Once injected, the spores begin to
destroy the tumor cells that traditional cancer treatments can not
reach.
“When the bacteria grow, they will deprive the tumor cells of their
normal nutrients. And also we have found that these bacteria do secrete
enzymes that can degrade proteins and other things that tumors may rely
on,” said Zhou.
More important, Zhou says, is that the microbe can also prompt a strong immune response against the tumor.
“And the immune response will attack not only the bacteria themselves, but also the tumor cells,” he said.
In experiments with mice, the bacterial therapy appeared to stimulate
a lingering immune response against cancer cells that had spread.
Such a response has not yet been seen in the dog or human studies.
Rats with brain tumors that had the microbial therapy survived 33 days
after treatment compared to 18 days for rats that did not receive C.
novyi spores.
Zhou says researchers are now trying to engineer the bacterium so it
causes milder side effects from infection, as well as looking for other
microbes that might work against cancer.
It’s possible,he says, that the bacterial therapy can be combined
with chemotherapy and radiation for a more powerful anti-cancer effect.
[Jessica Berman]
