An innovative fluorescence probe and its matching enzyme, which precisely target and illuminate tumours, promise sharper, more accurate visualisation.
This has the potential to transform surgical outcomes.
Researchers have developed a bioorthogonal fluorescence probe and a corresponding reporter enzyme that selectively activate the probe at tumour sites.
A common issue with other tools is that some probes can also be activated in healthy tissues by endogenous enzymes, resulting in background fluorescence that complicates the identification of what to remove.
Conversely, cancer cells may remain unmarked and be missed during surgery, increasing the risk of recurrence.
Associate Professor Ryosuke Kojima, from the Laboratory of Chemical Biology and Molecular Imaging at the University of Tokyo, said: ‘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 tumours and used a fluorescence probe that only turns on when that enzyme is present.
‘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 tumours in the abdominal wall lining and was followed up by the probe, which lit up as expected.
Kojima said: ‘This allowed us to see tiny, millimetre-sized tumour lesions with extremely low background noise, a level of contrast that could be very useful during surgery. In the near term, this system could become a powerful research tool, and in the longer term, it may help surgeons remove tumours 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 types of cancer, beyond the peritoneal cancer used in these trials, the team suggested.
By swapping the tumour-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 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 where needed.
