Dual-Modality ImmunoPET/Fluorescence Imaging of Prostate Cancer with an Anti-PSCA Cys-Minibody

Theranostics. 2018 Nov 12;8(21):5903-5914. doi: 10.7150/thno.27679. eCollection 2018.

Abstract

Inadequate diagnostic methods for prostate cancer lead to over- and undertreatment, and the inability to intraoperatively visualize positive margins may limit the success of surgical resection. Prostate cancer visualization could be improved by combining the complementary modalities of immuno-positron emission tomography (immunoPET) for preoperative disease detection, and fluorescence imaging-guided surgery (FIGS) for real-time intraoperative tumor margin identification. Here, we report on the evaluation of dual-labeled humanized anti-prostate stem cell antigen (PSCA) cys-minibody (A11 cMb) for immunoPET/fluorescence imaging in subcutaneous and orthotopic prostate cancer models. Methods: A11 cMb was site-specifically conjugated with the near-infrared fluorophore Cy5.5 and radiolabeled with 124I or 89Zr. 124I-A11 cMb-Cy5.5 was used for successive immunoPET/fluorescence imaging of prostate cancer xenografts expressing high or moderate levels of PSCA (22Rv1-PSCA and PC3-PSCA). 89Zr-A11 cMb-Cy5.5 dual-modality imaging was evaluated in an orthotopic model. Ex vivo biodistribution at 24 h was used to confirm the uptake values, and tumors were visualized by post-mortem fluorescence imaging. Results: A11 cMb-Cy5.5 retained low nanomolar affinity for PSCA-positive cells. Conjugation conditions were established (dye-to-protein ratio of 0.7:1) that did not affect the biodistribution, pharmacokinetics, or clearance of A11 cMb. ImmunoPET using dual-labeled 124I-A11 cMb-Cy5.5 showed specific targeting to both 22Rv1-PSCA and PC3-PSCA s.c. xenografts in nude mice. Ex vivo biodistribution confirmed specific uptake to PSCA-expressing tumors with 22Rv1-PSCA:22Rv1 and PC3-PSCA:PC3 ratios of 13:1 and 5.6:1, respectively. Consistent with the immunoPET, fluorescence imaging showed a strong signal from both 22Rv1-PSCA and PC3-PSCA tumors compared with non-PSCA expressing tumors. In an orthotopic model, 89Zr-A11 cMb-Cy5.5 immunoPET was able to detect intraprostatically implanted 22Rv1-PSCA cells. Importantly, fluorescence imaging clearly distinguished the prostate tumor from surrounding seminal vesicles. Conclusion: Dual-labeled A11 cMb specifically visualized PSCA-positive tumor by successive immunoPET/fluorescence, which can potentially be translated for preoperative whole-body prostate cancer detection and intraoperative surgical guidance in patients.

Keywords: antibody fragment; fluorescence; immunoPET; molecular imaging; prostate cancer.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Antigens, Neoplasm / analysis*
  • Carbocyanines / administration & dosage
  • Disease Models, Animal
  • Fluorescent Dyes / administration & dosage
  • GPI-Linked Proteins / analysis
  • Heterografts
  • Humans
  • Immunoglobulins / administration & dosage*
  • Male
  • Mice, Nude
  • Molecular Imaging / methods*
  • Neoplasm Proteins / analysis*
  • Neoplasm Transplantation
  • Optical Imaging / methods*
  • Positron-Emission Tomography / methods*
  • Prostatic Neoplasms / diagnostic imaging*
  • Prostatic Neoplasms / surgery
  • Radiopharmaceuticals / administration & dosage
  • Surgery, Computer-Assisted / methods

Substances

  • Antigens, Neoplasm
  • CY5.5 cyanine dye
  • Carbocyanines
  • Fluorescent Dyes
  • GPI-Linked Proteins
  • Immunoglobulins
  • Neoplasm Proteins
  • PSCA protein, human
  • Radiopharmaceuticals