Comparative analysis of radiolabeled monoclonal antibodies and antibody fragments for immunotherapy of Prostate Stem Cell Antigen expressing tumors


Comparative analysis of radiolabeled monoclonal antibodies and antibody fragments for immunotherapy of Prostate Stem Cell Antigen expressing tumors

Oertel, F.; Arndt, C.; Feldmann, A.; Bachmann, M.; Bergmann, R.; Steinbach, J.; Pietzsch, H.-J.

Aim: Advances in antibody engineering have led to the development of a multiplicity of antibody types for radioimmunotherapy. Predominantly, this development was concentrated on generating variations in the antibody size, which evidently influences the pharmacokinetics and tumor uptake. However, it is still discussed, which size has most suitable properties for radioimmunotherapy approaches. Here, two different antibody types, monoclonal antibodies (mAbs, 150 kDa) and thereof derived single-chain variable fragments (scFv, 35 kDa), were compared, that are directed against the prostate stem cell antigen (PSCA). Due to its overexpression on the surface of various cancers, including prostate, pancreas and bladder cancer, PSCA is proposed to be a promising tumor target structure for antibody-based immunotherapy.

Methods: In this study, two different anti-PSCA mAb clones, RD1 and RD2, as well as their respective anti-PSCA scFvs were compared with regard to their binding properties towards PSCA, using flow cytometry analysis. Above, the anti-PSCA mAbs were conjugated with the radionuclide chelating agent CHX-A’'-DTPA and subsequently radiolabeled with 177Lu. The radiolabeled mAb-conjugates were, then, characterized regarding binding properties on PC3-PSCA cells in vitro.

Results: As determined by flow cytometry, non-radiolabeled anti-PSCA mAbs RD1 and RD2 show a high affinity, with a dissociation constant of 10 and 6 nM, respectively. Even though, the scFvs of RD1 and RD2 exhibit a lower affinity in comparison to their mAbs counterpart, they maintain a moderate Kd-value (170 and 98 nM) that is sufficient to proceed with conjugation and radiolabeling analogous to the mAbs. Conjugation of three CHX-A’’-DTPA-chelators to the mAbs had no influence on binding affinity towards the PSCA. Subsequent radiolabeling of the mAb-conjugates could be performed with high radiochemical purity (> 95%). Similar to the non-radiolabeled mAbs, the binding affinity of 177Lu-labeled (CHX-A’’-DTPA)3-RD1 or RD2 was high with 12 and 19 nM, respectively. Summing up, both anti-PSCA mAb were successfully radiolabeled with 177Lu without losing their binding properties to PSCA. Thus, these molecules are attractive candidates for radioimmunotherapy of PSCA-positive cancers.

  • Lecture (Conference)
    24. Jahrestagung der Arbeitsgemeinschaft Radiochemie/Radiopharmazie 2016, 29.09.-01.10.2016, Morschach, Schweiz

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Publ.-Id: 25074