NEW YORK (Reuters Health) - Some components of green tea may counteract the beneficial effects of a widely used anti-cancer agent called Velcade, also known as bortezomib.

"We know that cancer patients look to green tea extracts among other natural supplements to complement their therapeutic regimens," Dr. Axel Schonthal, said in a statement. "We wanted to better understand how the compounds in green tea interact with a cytotoxic chemical therapy and how that may affect patient outcomes."

In lab studies, Schonthal, from the University of Southern California Keck School of Medicine, Los Angeles, and colleagues evaluated the impact of green tea compounds on the efficacy of bortezomib against multiple myeloma, a blood cancer, and glioblastoma, a malignant brain tumor.

Bortezomib normally fights cancer by inducing tumor cell death. However, Schonthal and colleagues were surprised to find that some of the green tea polyphenols and other components actually prevented bortezomib from killing tumor cells.

"Our surprising results indicate that green tea polyphenols may have the potential to negate the therapeutic efficacy of bortezomib," Schonthal said.

"The current evidence," Schonthal said, "is sufficient enough to strongly urge patients undergoing bortezomib therapy to abstain from consuming green tea products, particularly the widely available, highly concentrated green tea and EGCG (epigallocatechin gallate) products that are sold in liquid or capsule form."

The findings of this study, the investigators emphasize, are specific for patients taking bortezomib as opposed to any other common cancer drug.

"Although the study has exposed detrimental effects of great tea in specific combination with Velcade, this should not minimize the previously reported potentially beneficial effect of this herb," Schonthal said. "Related studies with other types of cancer therapies are promising and green tea extract may actually improve the anticancer effects of other drugs."

SOURCE: Blood, online February 3, 2009.

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