Near-Infrared Dye Could Highlight Cancer Locations

Under development by researchers at Stanford University (CA, USA), the small-molecule fluorophore dye emits light in a portion of the NIR range known as the second window, or NIR-II. Dyes emitting light in that range have long wavelengths, allowing researchers to probe tissues at centimeter depths, as well as achieve micrometer-scale resolution at millimeter depth. But while all currently approved NIR-II fluorophores are excreted slowly from the reticuloendothelial system, the new dye is rapidly eliminated, with about 90% excreted through the kidneys within 24 hours.

In laboratory tests in mice, the fluorophore, which is based on CH1055 (a synthetic 970-Da organic molecule), outperformed indocyanine green in resolving lymphatic vasculature and sentinel lymphatic mapping near a tumor. High levels of uptake of were observed in brain tumors in the mice, suggesting that the dye could be detected at a depth of about four mm. The dye succeeded in resolving blood vessels in the forelimb as well as the peripheral brain with high clarity, but also provided clear resolution of tumors in the center of the mouse's brain.

The CH1055 dye also allows targeted molecular imaging of tumors in vivo when conjugated with an antibody. According to the researchers, this could in the future prove to be an invaluable surgical tool, since the dye provides a superior tumor-to-background signal ratio, and thus could allow precise image-guided real-time excision surgery. The study describing the NIR-II fluorophore and the mouse experiments was published on November 23, 2015, in Nature Materials.

“The difficulty is how to make a dye that is both fluorescent in the infrared and water soluble. A lot of dyes can glow but are not dissolvable in water, so we can't have them flowing in human blood. Making a dye that is both is really the difficulty,” said lead author graduate student Alex Antaris, MSc. “We struggled for about three years or so and finally we succeeded. What's more, the new dye produces images that are sharper and more detailed than before, increasing their potential value to medicine and surgery.”

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