Lily Wu of the University of California at Los Angeles and her colleagues developed a so-called virus vector that contains components that specifically target prostate cancer cells based on their expression of a protein called prostate-specific antigen (PSA). The vector expresses a firefly gene that produces a glowing protein when in the presence of PSA. When the researchers injected it into mice with prostate cancer, only the prostate tumors--even tiny ones--glowed brightly. Additionally, tumors that had metastasized to other areas of the body also lit up. "With this method, we¿ve shown that we can deliver a targeted virus into a lab model and can demonstrate that it is expressed only in prostate cancer cells," Wu says. Using this directed vector, researchers could deliver toxic genes straight to the cancer. The therapy would theoretically not harm the surrounding healthy tissue, and researchers could see whether or not the tumors were shrinking by examining the amount of luminescence in the body.
Wu posits that human testing of her model may not occur for at least three to five years. One problem lies in the fact that the camera that identifies the fluorescing firefly protein in mice cannot be used in humans. Researchers are investigating the use of positron emission tomography, or PET scans, as an alternative. If this approach in fact works in people, the implications could be tremendous. "This targeted gene delivery method will help us catch a metastasis when it is still a small group of cells," Wu notes. "This could make any kind of gene therapy much safer, and we wouldn¿t be doing it blindly. We¿d be able to see that the toxin is getting delivered to the right place."