Prostate-specific Membrane Antigen (PSMA) is overexpressed in prostate cancer (PCa) and a promising target for molecular imaging and therapy. Nanobodies (single domain antibodies, VHH) are the smallest antibody-based fragments possessing ideal molecular imaging properties, such as high target specificity and rapid background clearance. We developed a novel anti-PSMA nanobody (JVZ-007) for targeted imaging and therapy of PCa. Here, we report on the application of the 111In-radiolabeled nanobody for SPECT/CT imaging of PCa.

METHODS:

A nanobody library was generated by immunization of a llama with four human PCa cell lines. Anti-PSMA nanobodies were captured by biopanning on PSMA overexpressing cells. JVZ-007 was selected for evaluation as imaging probe. JVZ-007 was initially produced with a c-myc-hexahistidine (his) tag allowing purification and detection. The c-myc-his tag was subsequently replaced by a single cysteine at the C-terminus, allowing site-specific conjugation of chelates for radiolabeling. JVZ-007-c-myc-his was conjugated to p-SCN-DTPA via the lysines, while JVZ-007-cys was conjugated to maleimide-DTPA via the C-terminal cysteine. PSMA-targeting was analyzed in vitro by cell binding experiments using flow cytometry, autoradiography and internalization assays using various PCa cell lines and patient-derived xenografts (PDXs). Targeting properties of radiolabeled nanobodies were evaluated in vivo in biodistribution and SPECT/CT imaging experiments, using nude mice bearing PSMA-positive PC-310 and PSMA-negative PC-3 tumors.

 

(후략)