Dual-targeting of tissue factor and CD105 for PET Imaging of Pancreatic Cancer

Objectives Pancreatic adenocarcinoma is a highly aggressive malignant disease, currently treated with limited success and dismal outcomes. Early detection and treatment offer the potential to reduce cancer morbidity and mortality. Developing noninvasive imaging probes with high specificity for targeting malignant lesions is essential to improve diagnostic accuracy and early therapeutic intervention for pancreatic cancer

Methods Herein, we created a bispecific heterodimer by conjugated an anti-tissue factor (TF) Fab with an anti-CD105 Fab via the biorthogonal “click” reaction between tetrazine (Tz) and trans-cyclooctene (TCO). The heterodimers were separated by gel filtration on a HiPrep 16/60 Sephacryl S-100 HR and purity was evaluated by 10% SDS-PAGE gel. Human pancreatic cancer cells (BXPC-3), which express high levels of both TF and CD105, was used to evaluate the binding affinity and bispecificity of the heterodimer. Flow cytometry and competitive binding assays were performed to determine and compare the binding affinities of heterodimer. After labeled with 64Cu, PET imaging and biodistribution studies were performed in nude mice bearing BXPC-3 xenografted tumors. Immunofluorescence staining of resected BXPC-3 tumor sections was carried out to correlate PET-tracer uptake with in situ TF/CD105 expression.

Results Flow cytometry and competitive binding assay demonstrated enhanced binding affinity and specificity of the heterodimer with dual targeting of TF and CD105. Positron emission tomography of mice bearing BXPC-3 (TF/CD105+/+) tumors with 64Cu-labelled heterodimer uncovered significantly enhanced tumor uptake (28.8 ± 3.2 %ID/g; n = 4) and tumor-to-background ratio (tumor/muscle ratio of 75.2 ± 9.4 at 30 h p.i.; n = 4) compared to each of their monospecific Fab tracers. In agreement with its TF/CD105 bivalent property, 64Cu-NOTA-heterodimer staining showed a stronger fluorescent signal that was distributed in both BXPC-3 cells and tumor-associated vasculature in the tissue. This demonstrated dual TF and CD105 targeting provides a synergistic improvement on both affinity and specificity of 64Cu-NOTA-heterodimer. Furthermore, 64Cu-NOTA-heterodimer enabled sensitive detection of orthotopic pancreatic tumor lesions with the uptake of 17.1 ± 4.9 %ID/g at 30 h p.i and tumor/muscle ratio of 72.3 ± 46.7. Overall, small animal PET/CT using 64Cu-NOTA-heterodimer enabled highly specific and sensitive detection of aggressive BXPC-3 pancreatic tumors.

Conclusions The study provided the initial evidence to confirm the benefit of simultaneous targeting of TF and CD105 for potential imaging and therapy of pancreatic cancer, which implicates combined TF and antiangiogenic inhibition therapies may effectively tackle current therapeutic limitations

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