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Study: Pot slows lung cancer in mice


April 18, 2007

Giving marijuana to mice with cancer shrank their lung tumors by half and slowed spread of the disease, findings that may one day expand legal use of the substance as a treatment, researchers said.

The research is the first to show that marijuana's active ingredient, tetrahydrocannabol, or THC, blocks a known cancer-related protein that's already the target of drugs such as ImClone System Inc.'s Erbitux and Amgen Inc.'s Vectibix.

The findings, presented yesterday at the American Association for Cancer Research meeting in Los Angeles, add to evidence that marijuana may have anti-tumor properties, researchers said. Scientists speculate THC may activate biological pathways that halt cancer cell division or block development of blood vessels that feed tumors.

"THC can have a potential therapeutic role," said Anju Preet, the study's lead author and a researcher at Harvard University's division of experimental medicine. "Maybe THC is killing cells. The preliminary studies are promising."

Tumor cells dosed with THC also showed a reduction in epidermal growth factor receptor, or EGFR, which means the substance may be acting similarly to Erbitux and Vectibix, which block the protein, Preet said.

The group includes Erbitux, which treats colon and head and neck cancers; Vectibix, which treats colon cancer; OSI Pharmaceuticals' Tarceva, approved for lung and pancreatic cancer; and AstraZeneca Plc's Iressa, which treats lung cancer.

Lung cancer cells with high levels of EGFR are generally very aggressive and treatment-resistant, researchers said.

In addition to reducing tumor size by half, THC was also associated with a 60 percent reduction in cancer lesions in the lungs of mice. More work needs to be done to understand how THC prevents tumor growth and to find the right dose before starting clinical trials, Preet said. Previous research has shown that too much THC can stimulate cancer growth, she said.

"Before jumping into clinical study, we need to understand how it works, which can help us design a better therapeutic," Preet said.

In the United States, 11 states allow patients to use marijuana for medical purposes. Only one THC drug, Marinol, is approved in this country. The treatment, made by Solvay Pharmaceuticals, is used as an appetite stimulant for cancer patients.