A Novel 111In-Labeled Anti–Prostate-Specific Membrane Antigen Nanobody for Targeted SPECT/CT Imaging of Prostate Cancer

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 im-aging properties, such as high target specificity and rapid back-ground 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 4 human PCa cell lines. Anti-PSMA Nanobodies were captured by biopanning on PSMA-overexpressing cells. JVZ-007 was selected for evaluation as an imaging probe. JVZ-007 was initially produced with a c-myc-hexahistidine (his) tag allowing purification and detection. The c-myc-his tag was sub-sequently replaced by a single cysteine at the C terminus, allowin