An immunosuppressant normally used to prevent rejection of transplanted organs appears to prevent tobacco-related lung-cancer tumors from growing in mice, according to new research from the National Cancer Institute (NCI).

Mice given the immune-suppressing drug rapamycin -- typically prescribed to patients receiving organ or bone-marrow transplants, and also used to coat cardiac stents -- had 90 percent fewer tumors after being exposed to known carcinogens than mice that did not receive the drug. The rapamycin group also experienced a 74-percent decrease in tumor size and fewer abnormalities within their cancer cells.

Researchers said that mTOR, a protein targeted by rapamycin, appears to play an important role in early development of lung tumors. "Our studies provide an exciting link between exposure to an important tobacco carcinogen, NNK, and mTOR," said Phillip A. Dennis, M.D., Ph.D., head of the Signal Transduction Section at NCI's Center for Cancer Research. "The critical question is whether this approach would be safe and effective in smokers at high risk to develop lung cancer. Given that rapamycin is relatively inexpensive and FDA-approved for other indications, we are designing clinical trials in humans to address these questions and hope to have these answers in the near future."

The study was published in the April 1, 2007 issue of the journal Clinical Cancer Research.