ould new treatments for cancer result from research into the function of tumor-suppressor genes? ORNL scientist Craig Dees thinks so. "It's possible to genetically reengineer tumor cells using tumor-suppressor genes so that the normal growth pattern is restored," Dees states. "Here at ORNL, we have done it with rat liver epithelial cells, and other laboratories have been successful using human colon and lung cancer cells. We have also been the first to genetically repair a cell line that had been transformed into tumor cells by a retrovirus that is closely related to the two viruses that cause human T-cell leukemia and AIDS."

In a recent development, Dees conducted an experiment using nude mice. Because nude mice are defective in their ability to reject tumors or transplants of cells from humans or other animals, they can be used to study the effects of antitumor genetic engineering methods. Tumor cells from rat liver or tumor cells formed from normal cells by a retrovirus were injected under the skin of the nude mice. A genetic element, called a plasmid, engineered to contain the human p53 tumor-suppressor gene was injected weekly in each mouse at the site of the tumor cells.

After several weeks Dees found that tumors in treated animals were much smaller than the large tumors found in untreated mice. This difference in tumor size is attributed to insertion of the human p53 tumor suppressor gene into the tumor cells.

"These results are intriguing," Dees says, "because this is the first time that a genetic engineering method has been shown to slow the growth of tumors caused by cells made cancerous by an AIDS-like virus. Secondly, even though liver cancer is less common in humans than other cancers, it almost always results in death only a few months after it is diagnosed. The results suggest that perhaps the method for genetic reengineering of tumor cells employing a tumor-suppressor gene could be used as a cancer treatment for a highly fatal liver cancer as well as tumors caused by certain viruses."

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