Although new cancers that form after the virus is delivered would not be fluorescent, Hoffman says that any of the original cancer that began to grow again should still express GFP, allowing clinicians the opportunity to monitor the results of the surgery over time.
Hisataka Kobayashi, a scientist in the molecular imaging program at the National Cancer Institute, says the advantages of this method are that it very specifically targets cancer cells and makes it possible to monitor the cancer over time. The method also allows for flexibility; for instance, a gene that would cause the cancer cells to kill themselves could be added to the virus along with GFP, pairing imaging with treatment.
Kobayashi says that one of the key questions of the technology is safety. Giving patients a virus carrying a gene for imaging is very similar to giving them a gene to correct a disease, he says, and consequently “all the problems with gene therapy apply to this method.” Many gene therapy approaches have been stalled because of immune reactions to the treatment. However, Lily Wu, a scientist at the University of California, Los Angeles, who develops cancer therapies, points out that similar gene therapy treatments for cancer have so far been found safe in clinical trials, whereas safety “is still not determined for other synthetic vectors such as quantum dots.” Wu believes that this method offers several advantages over other ways of labeling tumors but says that it will require a more thorough quantitative analysis to demonstrate its effectiveness.
Hoffman says AntiCancer hopes to complete further safety testing that will allow it to bring the technology into clinical trials. Although fluorescence in mice can be visualized throughout the body, in humans the task will be more difficult, because the light scatters easily and doesn’t penetrate very far into tissues. For that reason, the researchers envision this technique being used during surgery where the tumor can be seen directly.