Generation and characterization of nanobodies targeting PSMA for molecular imaging of prostate cancer

Nanobodies show attractive characteristics for tumor targeting in cancer diagnosis and therapy. A radiolabeled nanobody binding the prostate‐specific membrane antigen (PSMA) could offer a noninvasive strategy to select prostate cancer patients eligible for PSMA‐targeted therapies. We here describe the generation, production and in vivo evaluation of anti‐PSMA nanobodies. Nanobodies were derived from heavy‐chain‐only antibodies, raised in immunized dromedaries. Binding characteristics were evaluated through ELISA and flow cytometry. Selected nanobodies were radiolabeled with 99mTc at their hexahistidine tail, after which cell binding capacity and internalization were evaluated on PSMApos LNCaP and PSMAneg PC3 cell lines. In vivo tumor targeting was analyzed in both LNCaP and PC3 xenografted mice through SPECT/microCT and tissue sampling. A panel of 72 generated clones scored positive on ELISA, all contributing to three nanobody groups, of which group 3 dominated with 70 clones. ELISA and FACS analysis led to the selection of two dominant nanobodies. 99mTc‐labeled PSMA6 and PSMA30 both showed specific binding on LNCAP cells, but not on PC3 cells. 99mTc‐PSMA30 internalized significantly more in LNCaP cells compared to 99mTc‐PSMA6. Higher absolute tumor uptake and tumor‐to‐normal organ ratios were observed for 99mTc‐PSMA30 compared with 99mTc‐PSMA6 and a 99mTc‐control nanobody in LNCaP but not in PC3 tumor‐bearing mice. PSMA30 nanobody has improved tar...
Source: Contrast Media and Molecular Imaging - Category: Radiology Authors: Tags: Full Paper Source Type: research