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

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 124 I or 89 Zr. 124 I-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 124 I-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, 89 Zr-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.