Prostate cancer tracking system developed

The Borneo Post - Monday, July 29 2002 Page 19

LOS ANGELES: Researchers at UCLA's Jonsson Cancer Center and in the Department of Urology have demonstrated for the first time that they can locate difficult to detect prostate cancer metastases in laboratory models, a discovery that could lead to safer and more effective gene-based treatments for advanced prostate cancer.

UCLA researchers engineered a virus that can identify prostate cancer cells based on the prostate-specific antigen (PSA) protein expressed only in prostate cells. Using the substance that makes fireflies glow, scientists showed through high-tech imaging that the prostatetargeted virus made prostate cancer cells appear as "hot spots," both in primary tumors and in distant metastases that were still too small to cause symptoms or appear on conventional detection scans. The next step, researchers say, will be to attach gene-based therapies to the virus, which would act as a vehicle to deliver the toxic treatment directly to the prostate cancer cells and, it is hoped, kill them.

"Prostate cancer metastases are difficult to detect and hard to treat," said Lily Wu, lead author of the article, a Jonsson Cancer Center researcher and an assistant professor of urology and pediatrics. "With this method, we've shown we can deliver a targeted virus into a lab model and can demonstrate that it is expressed only in prostate cancer cells. That means we can also deliver a targeted therapy to prostate cancer cells. The idea would be to deliver a toxic gene to the cancer that would not harm surrounding healthy cells."

Wu, who also is a member of the Crump Institute for Molecular Imaging, estimates the gene-based delivery system could be tested in humans within three to five years. Doctors administering gene therapy now have no way to determine quickly that it reaches the cancer cells it's targeting. Doctors and patients are forced to wait weeks or months for any positive response to treatment that may indicate the therapy is attacking the cancer.

This discovery, however, could allow doctors to monitor the progress of gene therapy in the human body almost immediately, not only in primary tumors but in distant organs that may be at risk as well. The Nature Medicine article states that "repetitive imaging over a three-week period after injection into tumor-bearing mice revealed that the virus could locate and illuminate metastases in the lung and spine" of laboratory models. Dr. Kenneth J. Pienta, director of Urologic Oncology at the University of Michigan Medical Centre, said Wu's research is important because it "represents a novel and unique way to image prostate cancer cells as they move through the body and grow in various places."

"Although we are only able to do this in animals now, it is only a matter of time before we can do this in people," said Pienta, who also is a professor of medicine and urology. "This discovery allows us to more rapidly assess how cancers that are growing in animals respond to various treatments, and, ultimately, will allow for the more rapid development of therapies to treat advanced prostate cancer."

Harvey Herschman, director of basic research at UCLA's Jonsson Cancer Center, likened Wu's discovery to a tumour specific searchlight and said it will have "tremendous importance" if it can be trap-;listed into humans. '. "One of our problems is that we don't have a way to
find very small metastases in people," Herschman said. "Patients may be carrying small tumors and we may not know it. If we knew they had these small metastases and where they were located, we could treat them when they're still too small to cause any symptoms or show on scans."

The current method and further amplification of the imaging signals that Wu and her colleagues are working on could theoretically find such tiny cancer spreads in patients much earlier than is possible now, and allow doctors to treat these metastases sooner, when the chances of success are greater."This targeted gene delivery method will help us to catch a metastasis when it is still a small group of cells, instead of a tumor on the spine or in the lung," Wu said. "This could make any kind of gene therapy much safer, and we wouldn't be doing it blindly."