March 1, 2009 (foodconsumer.org) -- Compounds extracted from green vegetables when used along with selenium could be a potent treatment for melanoma, a deadly skin cancer, according to a new study published in the March 2009 issue of Clinical Cancer Research.

The study led by researchers at Penn State College of medicine showed the treatment targeted tumors more safely and effectively than conventional therapy.

"There are currently no drugs to target the proteins that trigger melanoma," said Dr. Gavin Robertson. "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."

In previous studies, Robertson and his colleagues found targeting the Akt3 protein may potentially inhibit development of melanoma. The finding led them to a class of compound called isothiocyanates, which are commonly found in cruciferous vegetables such as broccoli.

Isothiocyanates have been known to have certain chemo-preventative properties. The problem is that the potency of these compounds is too low to be used as therapeutic agents to treat cancer.

In the current study, the researchers compared the therapeutic efficacy of isothiocyanates and isoselenocyanates in tumor-bearing mice. Isoselenocyanate is a drug in which the sulfur bonds were replaced with selenium, according to a press release by Penn State.

"Selenium deficiency is common in cancer patients, including those diagnosed with metastatic melanoma," explained Robertson. "Besides, selenium is known to destabilize Akt proteins in prostate cancer cells."
 
For the study, the researchers injected mice with 10 million cancer cells and six days later when large tumors developed in the mice, they treated the animals either with isothiocyanates or isoselenocyanates.

"We found that the selenium-enhanced compounds significantly reduced the production of Akt3 protein and shut down its signaling network," explained Robertson.

In addition, isoselenocyanates also reduced the growth of tumors by 60 percent, compared to the isothiocyanates alone.

Different human melanoma cell lines responded to the selenium enhanced drug differently with the efficiency ranging from 30 to 70 percent depending on the cell lines.

The mechanism behind the therapeutic effect of isoselenocyanates remains unknown, but the researchers believe that the use of naturally occurring compounds that target cancer-causing proteins may lead to discovery of more effective ways to treat melanoma.