Bacterial
protein azurin can kill human melanoma cells in mice without causing
clinically apparent adverse effects
A protein secreted by bacteria can
kill cancer cells without any apparent adverse side effects, according
to animal research published in the October 29th issue of the Proceedings
of the National Academy of Sciences. The
researchers isolated azurin, a well-known protein that is involved
in cellular metabolism, from the growth medium of Pseudomonas aeruginosa.
When the protein was tested in mice injected with human melanoma
cells, the protein shrank tumors; however, in contrast to other
studies, which have used whole bacteria, the experiments caused
no deaths or apparent adverse reactions in the lab animals.
"Bacterial proteins could well be a new
weapon in the war against cancer," said Ananda Chakrabarty,
a microbiologist and immunologist.
Specially-bred immunodeficient mice implanted
with human melanoma were treated with 0.5 mg azurin daily for 22
days. At the conclusion of the trial, the average size of the tumors
in treated mice was 60 percent smaller than the average tumor size
in untreated mice. None of the mice showed signs of illness or loss
of weight.
The researchers said that azurin appears to
work as an anticancer agent by stabilizing the p53 protein, product
of the p53 tumor suppressor gene. Normally, the p53 protein is short-lived,
surviving just a few minutes before degradation. However, azurin
enters the nucleus, binding to the p53 protein and protecting it
from degradation.
According to Dr. Tapas Das Gupta, a co-investigator,
preliminary data show that azurin kills several types of cancer
cells, including breast and colon cancer.
"These results suggest that azurin could
be a useful anticancer agent not just for melanoma but for different
kinds of tumors," Das Gupta said. However, he cautioned that
extensive studies are needed to confirm the initial laboratory results.
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