Successful cancer surgery depends on a surgeon’s ability to remove tumors, while minimizing harm to healthy tissues. Surgeons currently use glowing dyes which mark cancer cells to help differentiate from healthy cells, but these dyes aren’t perfect and will light up some healthy tissues too. For the first time, researchers including those from the University of Tokyo developed what they call a bioorthogonal fluorescence probe and a matching reporter enzyme that can activate the probe selectively at targeted tumor sites. This enables high-contrast tumor visualization with very low background. This study was performed in mice.
Cancer is a universal issue which affects uncountably many people around the world. Many will turn to surgery in the hope a surgeon will be able to completely remove a tumor leaving healthy tissues unaffected. Various tools and techniques have been developed over the years to improve the way these surgeries are performed, and visual imaging methods such as glowing dyes have proven to be very useful. But one drawback is that some probes can also be activated in healthy tissues by endogenous enzymes, creating background fluorescence and making it harder to judge what should be removed. The opposite is also possible, where cancer cells are left unmarked and are missed during surgery, increasing the chance of recurrence.
“Our group acknowledged this current shortcoming and improved upon this way to make cancer cells light up inside the body. In tests on mice, we delivered a special enzyme to tumors and used a fluorescence probe that only turns on when that enzyme is present,” said Associate Professor Ryosuke Kojima from the Laboratory of Chemical Biology and Molecular Imaging at the University of Tokyo. “Older probes often light up healthy tissue by mistake, creating background noise, but our highly selective, or bioorthogonal, dye probe is designed to stay completely off unless it meets its matching engineered enzyme. We essentially trained the enzyme through repeated mutation and selection, a form of directed evolution, so it could activate the probe strongly enough to work inside living animals.”
Kojima, with Professor Yasuteru Urano and their team, created a special fluorescent probe that is not easily activated by natural enzymes in the body, which helps prevent unwanted background glow. This probe was paired with a matching reporter enzyme specially tailored to switch it on, so fluorescence appears mainly where the enzyme is delivered. When tested in mice bearing peritoneal cancer, the engineered enzyme reached the tumors in the abdominal wall lining and was followed up by the probe which lit up as expected.
“This allowed us to see tiny, millimeter-sized tumor lesions with extremely low background noise, a level of contrast that could be very useful during surgery,” said Kojima. “In the near term, this system could become a powerful research tool, and in the longer term, it may help surgeons remove tumors more completely by clearly highlighting cancer cells. A major hurdle for clinical use will be ensuring that the engineered enzyme does not trigger an unwanted immune response in patients.”
The system could be adapted to other kinds of cancers too, beyond the peritoneal cancer used in these trials, as many cancers present corresponding antigens, telltale markers of tumor tissue. By swapping the tumor-targeting component (for example, an antibody or nanobody against a chosen antigen), the same enzyme–probe pair could in principle be redirected to other cancer types. Looking even further ahead, this research could even be helpful in highly targeted drug delivery, where instead of glowing dyes, cancer-fighting drugs would be sent to the sites they’re needed, and nowhere else. But as Kojima stresses, it's still early days, the trials have only been done in mice, and much work is needed before it’s deemed safe enough for human trials.
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Journal: Ziyi Wang, Ryosuke Kojima*, Rikuki Kiji, Kyohhei Fujita, Ryo Tachibana, Reiko Tsuchiya, Taku Uchiyama, Yoshihiro Minagawa, Tadahaya Mizuno, Kiyohiko Igarashi, Hiroyuki Noji, Mako Kamiya, and Yasuteru Urano*, “Low-Background Cancer Imaging with a Bioorthogonal Fluorescence Probe and Engineered Reporter Enzyme Bearing a Targeting Moiety”, Journal of the American Chemical Society , https://doi.org/10.1021/jacs.5c14173
Funding: This work was supported by Grants-in-Aid for Scientific Research (KAKENHI; 20H02874, 24K01642, 24H00868, and 22H04919 to R. Kojima; 19H05632 and 24H00050 to Y.U.), The Mochida Memorial Foundation for Medical and Pharmaceutical Research (grant to R. Kojima), the Toyota Riken Scholarship (to R. Kojima), the Nakatani Foundation Research Grant (to R. Kojima), the Daiichi Sankyo Foundation for Life Science (grant to R. Kojima), the Japan Science and Technology Agency (JST) PRESTO program (JPMJPR17H5 to R. Kojima), the JST FOREST program (JPMJFR214N to R. Kojima), the JST Mirai Program (JPMJMI24G2 to Y.U.), the JST Moonshot Research and Development Program (JPMJMS2022 to Y.U.), and a Grant-in-Aid for JSPS Fellows (to Z.W. and R. Kiji).
Research Contacts:
Associate Professor Ryosuke Kojima
Laboratory of Chemical Biology & Molecular Imaging, Graduate School of Medicine,
The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, JAPAN
kojima@m.u-tokyo.ac.jp
Professor Yasuteru Urano
Laboratory of Chemistry and Biology, Graduate School of Pharmaceutical Sciences,
The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, JAPAN
Graduate School of Medicine: https://www.m.u-tokyo.ac.jp/english/
Graduate School of Pharmaceutical Sciences - https://www.f.u-tokyo.ac.jp/en/
Press contact:
Mr. Rohan Mehra
Strategic Communications Group, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
press-releases.adm@gs.mail.u-tokyo.ac.jp
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Journal of the American Chemical Society
Experimental study
Animals
Low-Background Cancer Imaging with a Bioorthogonal Fluorescence Probe and Engineered Reporter Enzyme Bearing a Targeting Moiety
27-Feb-2026