Compounds extracted from vegetables, such as broccoli and cabbage, could be a potent drug against melanoma, say 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," says Gavin Robertson, associate professor of pharmacology, pathology and dermatology at the Penn State College of Medicine in University Park. "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 that targeting the Akt3 protein can inhibit melanoma development. The search for a drug to block the protein led them to a class of compounds called isothiocyanates.

These naturally occurring chemicals, which are found in cruciferous vegetables, are known to have cancer-fighting properties. But the potency is so low that a successful drug would require impractical amounts of these compounds, according to a news release.

Instead, the Penn State researchers rewired the compounds by replacing their sulfur bonds with selenium. The result, they say, 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," Robertson says. "Besides, selenium is known to destabilize Akt proteins in prostate cancer cells."

In tests with mice, the reserachers found the selenium-enhanced compounds significantly reduced Akt3 protein production.
The modified compounds also reduced the growth of tumors by 60 percent, compared with 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 perdent to 70 percent, depending on the cell line.

The exact mechanism of how selenium inhibits cancer remains unclear. But Robertson says he is convinced that the use of naturally occurring compounds that target cancer-causing proteins could lead to more effective ways to treat melanoma.

"We have harnessed something found in nature to target melanoma," Robertson says. "And since we only need tiny amounts to kill the cancer cells, it means even less toxic side-effects for the patient."

Human trials are still some years away.