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Salmonella
Slows Skin Cancer Growth
The bacterium
that makes you throw up after eating bad food may offer hope for
skin cancer patients.
Skin cancer
tumor growth was significantly slowed when mice were injected
with non-toxic salmonella and radiated, researchers report in
a recent issue of the European Journal of Cancer. The strategy
could be effective with other cancers, researchers add.
"Salmonella
treatment represents a completely new approach to cancer therapy
with many different possibilities, including delivery of specific
toxins and combination with X-ray therapy," says lead author John
M. Pawelek. "Salmonella-injected mice live significantly longer
than untreated controls."
The treatment
is now being tested on people in early clinical trials, Pawelek
says. So far, researchers have found there is a limit to how toxic
a level of salmonella people can tolerate and that salmonella
can "colonize" tumors.
Most of the
work done so far has been on mice, so it's unclear how successful
the treatments would be with people, says T.J. Koerner, scientific
program director for the American Cancer Society. "That's what
clinical trials are all about, weeding out what works."
Research has
been done using other bacteria to boost the body's immune system
to fight cancer, and this study follows along those promising
lines, he says.
"The logic
makes sense," Koerner says. "It's not off-the-wall research, but
it's also not one you'd want to highlight to the public."
While mice
treated just with salmonella or just with radiation lived longer
than control mice, those treated with both lived even longer than
expected, Pawelek says, and researchers aren't sure why.
"Superadditive
means that the two effects were more than the sum. It implies
that in some fashion the two treatments are interacting to help
one another. We don't understand the mechanism at this point,"
he explains.
With just
salmonella injections or just radiation, tumor growth in the mice
was postponed for two to three weeks. But with a dose of salmonella
and a dose of radiation, growth was delayed 100 days. While the
tumors eventually began growing again, the delay is significant
when you consider the average lifespan of a mouse is about 2 years.
"It prolongs
survival," Pawelek says.
The study
was funded in part by Vion Pharmaceutical Inc. in New Haven, Conn.
The mice were
injected with melanoma tumors, which began to metastasize, or
grow and relocate. They were then injected with salmonella that
had been made tolerable to the mice, or X-rayed, or treated with
both. Significantly, the salmonella were able to move to the tumor's
sites to "colonize" -- an important ability when fighting cancer
that has spread.
Melanoma,
Pawelek says, is curable if found and treated early. The problem
comes when it is discovered after it has metastasized. Further
from its original site, it's more difficult to treat, he says.
The researchers
have been working with melanoma and other tumors for years. They
became interested in salmonella when they realized it attacks
microphages, which are small cells that engulf other cells or
materials.
"Metastatic
cells, in order to leave their primary site of origin and move
about the body, express traits normally associated with microphages,"
Pawelek explains. Perhaps, they thought, "Salmonella may attack
tumor cells as well."
Though the
researchers don't know why salmonella and radiation work so well
together, they have some ideas. It's possible salmonella releases
molecules that increase the tumor cells' sensitivity to X-rays,
the study says. Or the X-ray may weaken the tumor cells so they're
more vulnerable to the salmonella. Another theory is that the
salmonella may recruit immune cells to the sites of the tumors
to launch an attack.
SOURCES:
Interviews with John M. Pawelek, Ph.D., senior research scientist,
Yale School of Medicine, New Haven, Conn.; T.J. Koerner, Ph.D.,
scientific program director, American Cancer Society, Atlanta;
December 2000 European Journal of Cancer
Reference
Source 89
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