Arthritis drugs like Celebrex and the recently withdrawn Vioxx may boost the immune system’s ability to attack brain tumors, and possibly other types of cancer, researchers said on Friday.

Doctors at Cedars-Sinai Medical Center in Los Angeles have shown that the COX-2 enzyme is responsible for triggering a cellular process that disrupts the body’s immune response, allowing cancer cells to multiply.

COX-2 blockers - a class that includes Pfizer Inc.‘s Celebrex and Merck & Co Inc.‘s late Vioxx - work to fight arthritis pain by blocking the inflammation-causing COX-2 enzyme.

Results of the Cedars-Sinai study, which appear in the Oct. 1 issue of the Journal of Immunology, support the idea that medications attacking the enzyme may also boost the immune system’s ability to recognize and target cancer cells.

“When secreted, COX-2 shuts down the immune system,” said Dr. John Yu, the study’s principal investigator. “We would hope to incorporate use of COX-2 inhibitors in all patients with brain tumors.”

Vioxx was withdrawn from the market last month after twice as many patients taking it for at least 18 months suffered heart attacks and strokes during a 2,600-patient trial of the drug’s ability to curb precancerous colon polyps.

Merck also halted two other cancer-related studies of the drug - one in men at risk of prostate cancer and another related to preventing colon cancer.

Using brain cancer cells, the Cedars-Sinai researchers said laboratory tests showed that COX-2 set in motion a series of interactions that altered messages sent to dendritic cells, which are responsible for detecting foreign matter and instructing cancer-killing cells to attack the tumor.

But T-cells circulating in the bloodstream showed a regulatory response against the patient’s cancer cells, the study found.

“By using COX-2 inhibitors, these tumors may become more detectable and therefore more vulnerable to destruction by the immune system,” Yu said.

He said Cedars-Sinai plans to add drugs like Celebrex to its clinical trials for brain tumors.

“Studies need to be done to see if there is relevance to other cancers,” Yu added.