WASHINGTON, March 1 (Xinhua) -- Compounds extracted from green vegetables such as broccoli and cabbage could be a potent drug against melanoma, according to cancer researchers. Tests on mice suggest that these compounds, when combined with selenium, target tumors more safely and effectively than
conventional therapy.
"There are currently no drugs to target the proteins
that trigger melanoma," said Gavin Robertson, associate professor of
pharmacology, pathology and dermatology, Penn State College of Medicine. "We
have developed drugs from naturally occurring compounds that can inhibit the
growth of tumors in mice by 50 to 60 percent with a very low dose."
Robertson and his colleagues previously showed the
therapeutic potential of targeting the Akt3 protein in inhibiting the
development of melanoma. The search for a drug to block the protein led them to
a class of compounds called isothiocyanates.
These naturally occurring chemicals found in
cruciferous vegetables are known to have certain cancer-fighting properties.
However, the potency of these compounds is so low that a successful drug would
require large impractical amounts of these compounds.
Instead, the Penn State researchers rewired the
compounds by replacing their sulfur bonds with selenium. The result, they
believe, is a more potent drug that can be delivered intravenously in low doses.
"Selenium deficiency is common in cancer patients,
including those diagnosed with metastatic melanoma," explained Robertson, whose
findings appear in the March edition of Clinical Cancer Research. "Besides,
selenium is known to destabilize Akt proteins in prostate cancer cells."
To study the effectiveness of the new drug --
isoselenocyanate -- researchers injected mice with 10 million cancer cells. Six
days later, when the animals developed large tumors, they were divided into two
groups and treated separately with either the vegetable compounds or the
compounds supplemented with selenium.
"We found that the selenium-enhanced compounds
significantly reduced the production of Akt3 protein and shut down its signaling
network," explained Robertson, who is also associate director of translational
research and leader of the experimental therapeutics program at Penn State
Hershey Cancer Institute. The modified compounds also reduced the growth of
tumors by 60 percent, compared to the vegetable-based compounds alone.
When the researchers exposed three different human
melanoma cell lines to the two compounds, the selenium-enhanced drug worked
better on some cell lines than others. The efficiency was from 30 to 70 percent
depending on the cell line.
The exact mechanism of how selenium inhibits cancer
remains unclear. However Robertson, who has a filed provisional patent on the
discovery, is convinced that the use of naturally occurring compounds that
target cancer-causing proteins could lead to more effective ways of treating
melanoma.
"We have harnessed something found in nature to
target melanoma," said Robertson. "And since we only need tiny amounts to kill
the cancer cells, it means even less toxic side-effects for the patient."
Human trials of the new drug are still some years
away, but the Penn State researcher envisions a drug that could be delivered
either intravenously to treat melanoma, or added to sunscreen lotion to prevent
the disease.
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