New PET tracer enables rapid imaging of aggressive breast and bladder cancers

A promising new PET tracer can visualize a protein that is commonly overexpressed in triple-negative breast and urothelial bladder cancers within four hours, according to new research published in the September issue of The Journal of Nuclear Medicine. This same-day imaging approach has the potential to save valuable time in guiding treatment decisions and reduce unnecessary exposure to ineffective therapies.

Triple-negative breast cancer (TNBC) is an aggressive subtype that accounts for approximately 24 percent of newly diagnosed breast cancer cases. Similarly, urothelial bladder carcinoma (UBC) represents the most prevalent malignancy of the urinary tract, with urothelial bladder cancer comprising about 90 percent of cases. Many patients are diagnosed at advanced stages, underscoring the urgent need for reliable methods for early detection and longitudinal monitoring.

Nectin-4 is a protein that is overexpressed in both TNBC and UBC and is a potential target to treat these diseases. However, challenges remain in stratifying patients who are most likely to benefit from nectin-4 therapies. We sought to develop a PET tracer that allowed for rapid, high-contrast visualization of nectin-4 expression, providing a clinically translatable approach for patient stratification and real-time therapeutic monitoring."

Weibo Cai, PhD, professor of radiology and medical physics, University of Wisconsin Madison

A comprehensive evaluation of two PET tracers, ⁶⁴Cu-NOTA-EV (conjugated with a full-length antibody) and ⁶⁴Cu-NOTA-EV-F(ab′)₂ (conjugated with a fragmented antibody) was performed using various analytic methods. Nectin-4 expression in human TNBC and UBC cell lines was assessed by flow cytometry and immunofluorescence. Binding affinity and specificity were evaluated via cell uptake and binding assays. Next, immuno-PET imaging and biodistribution studies were conducted in mice bearing subcutaneous xenografts with varying levels of nectin-4 expression. 

⁶⁴Cu-NOTA-EV-F(ab′)₂ exhibited rapid tumor accumulation and high specificity in nectin-4 positive tumors, with peak uptake observed at 4 hours after injection. EV-F(ab′)₂ demonstrated superior tumor-to-background ratios compared with ⁶⁴Cu-NOTA-EV, particularly in nectin-4 expressing models. Favorable pharmacokinetics of EV-F(ab′)₂ allowed for same-day imaging and reduced radiation exposure relative to intact antibodies. 

"This study demonstrates that ⁶⁴Cu-NOTA-EV-F(ab′)₂ exhibits rapid, specific, and sustained accumulation in tumor tissues in TNBC and UBC models, enabling accurate, noninvasive visualization of nectin-4 expression," noted Lei Kang, MD, PhD, professor of nuclear medicine at Peking University First Hospital in Beijing, China. "In the future, this approach could expand to many other cancers, targets, and PET isotopes, making molecular imaging faster, safer, and more patient-friendly."