Two months ago we reported on the first ovarian cancer surgeries performed with fluorescence guidance. As described in the Nature Medicine paper, the international team of researchers from The Netherlands, Germany, and Indiana used folate coupled to fluorescein isothiocyanate (FITC) to make ovarian cancer cells glow so they could be easily identified.
Now, in this week’s issue of Science Translational Medicine, another international team from Japan and Maryland reports their development of a spray-on probe that may provide even better sensitivity and fluorescent contrast than the folate-FITC counterpart. The editors of STM summarize this work well in the following note:
Ovarian cancer is a deadly gynecological disease, considering its propensity for invading the peritoneal cavity and depositing tumors throughout. Surgeons can miss these disseminated tumors during surgical removal of cancerous lesions, owing to their small size (~1 mm) and unclear borders. To help surgeons visualize and eliminate these clandestine killers, Urano et al. have developed a small-molecule aminopeptidase probe that fluoresces upon contact with cancer cells. The probe –g-glutamyl hydroxymethyl rhodamine green (gGlu-HMRG) -is intramolecularly caged, so that it is quenched (nonfluorescent) in its ”off” state. When the probe encounters cancer cells, which overexpress the enzyme g-glutamyltranspeptidase (GGT), the gGlu is cleaved, simultaneously turning ”on” the fluorescent HMRG. Urano and colleagues first tested the probe in 11 human ovarian cancer cell lines in vitro and observed rapid fluorescence within 10 min after addition of the imaging agent to the cell cultures. They next moved into several mouse models of disseminated human peritoneal ovarian cancer, using a spray formulation of the probe that allowed the researchers to topically apply the probe during surgery or endoscopy. Within 1 min of spraying the tumors, gGlu-HMRG was enzymatically cleaved, revealing a bright fluorescent region of the peritoneal cavity in which the cancerous lesions were located. These small nodules were quickly and completely removed from living animals and depositing tumors throughout. Surgeons can miss these disseminated tumors during surgical with forceps, demonstrating the power of rapid fluorescence-guided tumor resection.
This gGlu-based fluorescent probe as well as several other aminopeptidase-based reagents identified by the authors could help surgeons to track down tiny tumors dispersed throughout body cavities, ensuring that no residual tumor is left behind. Complete obliteration of disseminated tumors should improve cancer outcomes after surgery.
In addition to increased sensitivity and contrast, the spray-on probe has the the advantage of being easily interfaced with existing intraoperative and endoscopic procedures, visible within seconds or minutes of spraying, and potentially less toxic given that topical spraying requires a lower dosage (1% in some cases) than currently used intravenous fluorophores.
This platform of course remains to be tested in humans so we look forward to hearing about upcoming clinical trials.
We followed up with senior author, Dr. Hisataka Kobayashi, of the National Cancer Institute:
Shiv Gaglani, Medgadget: Your paper concludes, “Although GGT might not be a specific biomarker for all cancers, other probes similar to gGlu-HMRG can be developed for enzymes known to be located at the surface of tumors.” Can you comment on your plans or current research to develop probes for other tumor surface enzymes?
Dr. Kobayashi: Based on this same mechanism (spirocyclic caging) and others, we have synthesized various peptidase and glycosidase activatable probes. Now we are currently performing screening of those probes for selecting alternative or combinational probes.
Medgadget: What are the next steps for this particular technology? Any plans for clinical trials?
Dr. Kobayashi: We are performing a trial using fresh human cancer samples obtained in the surgery room to validate the efficacy of this gGlu probe for de novo human cancers. We are also planning to synthesize this probe in large scale with GMP-grade for large animal toxicology and phase 0/1, which is necessary for applying IND [Investigational New Drug] to US FDA. We are also planning trials in Japan under the Japanses regulation.
Paper in Science Translational Medicine: Rapid Cancer Detection by Topically Spraying a γ-Glutamyltranspeptidase–Activated Fluorescent Probe
Comment in STM: Glowing Tumors Make for Better Detection and Resection