Fluorescent Image-Guided Surgery with an Anti-Prostate Stem Cell Antigen (PSCA) Diabody Enables Targeted Resection of Mouse Prostate Cancer Xenografts in Real Time.

PURPOSE: The inability to visualize cancer during prostatectomy contributes to positive margins, cancer recurrence, and surgical side effects. A molecularly targeted fluorescent probe offers the potential for real-time intraoperative imaging. The goal of this study was to develop a probe for image-guided prostate cancer surgery. EXPERIMENTAL
DESIGN: An antibody fragment (cys-diabody, cDb) against prostate stem cell antigen (PSCA) was conjugated to a far-red fluorophore, Cy5. The integrity and binding of the probe to PSCA was confirmed by gel electrophoresis, size exclusion, and flow cytometry, respectively. Subcutaneous models of PSCA-expressing xenografts were used to assess the biodistribution and in vivo kinetics, whereas an invasive intramuscular model was utilized to explore the performance of Cy5-cDb-mediated fluorescence guidance in representative surgical scenarios. Finally, a prospective, randomized study comparing surgical resection with and without fluorescent guidance was performed to determine whether this probe could reduce the incidence of positive margins.
RESULTS: Cy5-cDb demonstrated excellent purity, stability, and specific binding to PSCA. In vivo imaging showed maximal signal-to-background ratios at 6 hours. In mice carrying PSCA(+) and negative (-) dual xenografts, the mean fluorescence ratio of PSCA(+/-) tumors was 4.4:1. In surgical resection experiments, residual tumors <1 mm that were missed on white light surgery were identified and resected using fluorescence guidance, which reduced the incidence of positive surgical margins (0/8) compared with white light surgery alone (7/7).
CONCLUSIONS: Fluorescently labeled cDb enables real-time in vivo imaging of prostate cancer xenografts in mice, and facilitates more complete tumor removal than conventional white light surgery alone. ©2015 American Association for Cancer Research.