Could this tracer agent allow surgeons to see and 'hear' prostate cancer?

Canadian researchers believe a preclinical evaluation of a new ‘dual-mode’ tracer agent — published in advance in the Journal of Medical Chemistry — shows promise to enable surgeons to both see and ‘hear’ prostate cancer.

How it works

For diagnostic imaging, the agent uses a single tracer molecule labelled with Fluorine-18 — a common isotope used in positron emission tomography (PET) scans. It also provides a one-step, widely accessible solution that would enable combined fluorescence-guided and radio-guided surgery.

Targeting and binding to prostate-specific membrane antigen (PSMA) — a protein that is highly expressed on the surface of prostate cancer cells — the tracer not only has a high uptake by the tumour for PET images, but also high optical brightness in the fluorescent mode without requiring special visual equipment.

Its promise

“Precision medicine is increasingly being practised and developed to address the sophisticated treatment methods for diseases like cancer,” said University of British Columbia (UBC) chemist Dr David M Perrin, senior author on the paper.

“Our tracer provides high-resolution visual guidance, but would also allow a surgeon to use a handheld Geiger counter probes to ‘hear’ areas of high radiation density that would accumulate in cancerous tissue not immediately visible — whether it’s a lymph node, or distant metastasis, or local invasion in the like the bowel or the gut.”

Perrin also said that as there is a lack of good clinical options when it comes to dual-mode PSMA tracers, “we feel this could fill an incredibly useful function in the treatment spectrum for prostate cancer, and potentially other diseases like larynx and ovarian cancer if the same approach can be applied to these”.

In Canada, around one in eight men will develop prostate cancer during their lifetime and one in 30 will die from it. As to treatment, this often involves trade-offs between complete tumour removal and preserving critical structures like nerves, the seminal vesicle, bowel and bladder — particularly in cases of advanced localised disease.

In the surgical field, Dr Larry Goldenberg, a professor with the Department of Urologic Sciences at UBC, who was not involved in the study, described the implementation of the new tracer in the surgical field as “an exciting new approach to maximise benefit and minimise harm associated with more extended lymph node removal as well as to decrease the rate of positive surgical margins of a radical prostatectomy”.

Next steps

Perrin’s team and colleagues with the Department of Molecular Oncology at BC Cancer tested the tracer on mice with human tumours implanted in them. The next steps for the research includes Good Manufacturing Practice assessments, toxicity testing and validation runs.

“By combining the technology of 18F-organotrifluoroborates with fluorescein, we have a very bright future in bringing dual-mode tracers closer to clinical applications,” said radiochemist Jerome Lozada, first author on the paper, who conducted the experiments while at UBC. “The tracer is highly translatable to a larger variety of healthcare settings and smaller hospitals that typically have access to more standard suites of equipment.”

Image: University of British Columbia chemists tested the tracer on mice with human tumour implants. Source: University of British Columbia.