New molecular imaging compound pinpoints cancer spread in mice

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Researchers have created a new imaging compound in mice that showed a 92 percent success rate in accurately detecting small clusters of tumor cells through fluorescence. This cancer-specific fluorescence allowed investigators to visualize very small tumors in the peritoneum in mice with ovarian cancer, according to the US Department of Health and Human Service’s National Institutes of Health (NIH). The study, conducted by researchers at the National Cancer Institute appeared in this week’s Cancer Research.

“The virtue of this study is that other fluorescent compounds have been tested for the detection of small clusters of cancer cells that might otherwise be missed during surgery, but those have drawbacks, including being always fluorescent thereby making it difficult to distinguish tumor cells from normal tissue. This study points to a potential solution to this problem,” said NIH Director Elias A. Zerhouni, MD.

The researchers, led by Hisataka Kobayashi, MD, PhD, from NCI’s Molecular Imaging Program in the Center for Cancer Research, created a new compound, which they called Av-3ROX, using the protein avidin that can only be tested only in mice. They injected the “always on” fluorescent molecule Av-0.5ROX into the peritoneum of tumor-bearing mice, and fluorescence was immediately detectable and more intense than that produced by Av-3ROX. In contrast, three hours after the new Av-3ROX injection, the fluorescence intensity in normal tissues was less than with Av-0.5ROX, and fluorescence intensity in tumor nodules was much higher than with Av-0.5ROX.

After many tests, researchers determined that Av-3ROX was primarily processed by tumor cells. While Av-3ROX cannot be used in people, because the avidin portion of the compound would cause an immune system reaction, Kobayashi and his colleagues are now working on a second-generation compound.