Molecular Imaging of B7-H3-Targeting Bispecific T Cell-Engaging Antibody MGD009 in Glioblastoma Models

Adults diagnosed with glioblastoma (GBM) face an extremely poor prognosis; it is the most aggressive and fatal form of a primary brain tumor. The development of CD3-targeting bispecific antibodies (CD3-bsAbs) has recently gained attention as a promising therapeutic approach for GBM. MGD009, a CD3-bsAb, promotes T-cell-mediated cancer cell death by linking B7-H3 on tumor cells with CD3ε on T cells. The efficacy and relative toxicity of this treatment are closely associated with the tumor uptake and metabolic profile of major organs. However, limited data on the biodistribution and GBM targeting of MGD009 have been reported. In this study, surface plasmon resonance (SPR), flow cytometry, and immunofluorescence assays were carried out to assess the in vitro binding affinities of MGD009 with glioma cells. MGD009 was also labeled with a near-infrared fluorescent dye to evaluate its tumor targeting capacity and biodistribution in subcutaneous GBM models. Moreover, MGD009 was labeled with PET isotope zirconium-89 (⁸⁹Zr) to facilitate noninvasive molecular imaging in subcutaneous and orthotopic GBM models. The fluorescence intensity of Cy5.5-labeled MGD009 peaked at 24 h postinjection (p.i.), with a radiant efficiency of 8.98 × 10⁹ D/s/cm²/sr and a prolonged retention time up to 120 h. Tumor uptake of ⁸⁹Zr-labeled MGD009 peaked at 24 h p.i., with an uptake value of 10.77 ± 1.43% ID/g. In orthotopic U-87MG models, tumor uptake of ⁸⁹Zr-labeled MGD009 reached 18.10 ± 0.87% ID/g at 24 h p.i. Additionally, the liver, spleen, and bone marrow also showed a relatively high radioactivity. These findings provide critical insights into the biodistribution and tumor-targeting of MGD009, supporting its potential clinical application in glioblastoma treatment.