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


METHODS
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.
Department of Urology, University of California, Los Angeles, California.
Geoffrey A
GA
Sonn
Department of Urology, University of California, Los Angeles, California.
Andrew S
AS
Behesnilian
Department of Urology, University of California, Los Angeles, California.
Ziyue Karen
ZK
Jiang
Molecular and Medical Pharmacology, University of California, Los Angeles, California. Crump Institute for Molecular Imaging, University of California, Los Angeles, California.
Kirstin A
KA
Zettlitz
Molecular and Medical Pharmacology, University of California, Los Angeles, California. Crump Institute for Molecular Imaging, University of California, Los Angeles, California.
Eric J
EJ
Lepin
Deparment of Chemistry and Biochemistry, University of California, Los Angeles, California. California NanoSystems Institute, University of California, Los Angeles, California.
Laurent A
LA
Bentolila
Molecular and Medical Pharmacology, University of California, Los Angeles, California. Crump Institute for Molecular Imaging, University of California, Los Angeles, California.
Scott M
SM
Knowles
Molecular and Medical Pharmacology, University of California, Los Angeles, California.
Daniel
D
Lawrence
Molecular and Medical Pharmacology, University of California, Los Angeles, California. Crump Institute for Molecular Imaging, University of California, Los Angeles, California.
Anna M
AM
Wu
Department of Urology, University of California, Los Angeles, California. Rreiter@mednet.ucla.edu.
Robert E
RE
Reiter
D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D000951:Antigens, Neoplasm / Q000378:metabolism; D004195:Disease Models, Animal; D005456:Fluorescent Dyes; D058851:GPI-Linked Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D007128:Immunoglobulin Fragments / Q000494:pharmacology*; D008297:Male; D051379:Mice; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D061848:Optical Imaging / Q000379:methods; D011471:Prostatic Neoplasms / Q000188:drug therapy* / Q000276:immunology / Q000378:metabolism / Q000601:surgery*; D025321:Surgery, Computer-Assisted / Q000379:methods; D023041:Xenograft Model Antitumor Assays
D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; D005456:Fluorescent Dyes; D058851:GPI-Linked Proteins; D007128:Immunoglobulin Fragments; D009363:Neoplasm Proteins; C110843:PSCA protein, human