Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Prostate stem-cell antigen (PSCA) is a cell-surface antigen expressed in the normal prostate and overexpressed in over 80% of prostate cancer tissues. PSCA overexpression is associated with increased tumor stage, grade, and bone metastasis, as well as androgen independence and higher resistance to treatment. The aim of this work was to prepare and characterize a humanized monoclonal anti PSCA antibody (anti-PSCA mAb) for near infrared fluorescence (NIRF) and PET imaging using a near infrared (NIR) dye Alexa Fluor 750 (AF) and [64Cu]Cu-NOTA as a prerequisite for combination of both imaging methods. We evaluated the imaging potential of the [64Cu]Cu-NOTA-AF-anti-PSCA mAb in human prostate cancer xenograft mouse models by using the androgenindependent recombinant cell line PC3-PSCA as target and the non-transfected cell line as control. anti-PSCA mAb was conjugated with the bifunctional chelator 2-(p-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (SCN-Bz-NOTA) and Alexa Fluor succinimidyl carboxic acid (Ex 752 nm; Em 776 nm; AF). NOTA-AF-anti-PSCA mAb was labeled with 64Cu within 30 min with high
radiolabeling yield and radiochemical purity. The [64Cu]Cu-NOTA- AF-anti-PSCA mAb showed high accumulation in xenotransplanted prostate carcinomas in mice after 24 hours demonstrated with both small animal PET and NIRF. The comparison of both methods in living animals showed the high signal intensity and accumulation of the probe in tumors; however only PET allowed the quantitative characterization of the probe distribution in vivo. Subsequent whole body cryosectioning of the animals into 40-micrometer sections permitted the direct comparison of the autoradiograms and NIRF images of the tissue cuts. The quantitative comparison of the registered autoradiograms and the NIRF images showed a good correlation of the pixel intensities, however, the different geometric resolution did not allow a pixel vise comparison. The NIRF images showed a higher differentiation than the autoradiograms. This was used to study the stability of the radio- and NIR-label on the mAbs. Dual labeling of antibodies is a promising tool for quantitative evaluation of the long time distribution in animals using also NIRF of cryosections beyond the decay of the radionuclide used.
Acknowledgement: This project was partially supported by FP7 project “GIPIO”, Project Reference: 223057