ImmunoPET imaging of tissue factor expression in pancreatic cancer with 89Zr-Df-ALT-836

Overexpression of tissue factor (TF) has been associated with increased tumor growth, tumor angiogenesis, and metastatic potential in many malignancies, including pancreatic cancer. Additionally, high TF expression was shown to strongly correlate with poor prognoses and decreased survival in pancreatic cancer patients. Herein, we exploited the potential targeting of TF for positron emission tomography (PET) imaging of pancreatic cancer. The TF-targeted tracer was developed through radiolabeling of the anti-human TF monoclonal antibody (ALT-836) with Zr-89. The tracer was characterized by fluorescence microscopy and flow cytometry assays in BXPC-3 and PANC-1 cells, two pancreatic cancer cell lines with high and low TF expression levels, respectively. Noninvasive PET scans were acquired in tumor-bearing mice injected with Zr-89-Df-ALT-836. Additionally, ex vivo biodistribution, blocking, and histological studies were performed to establish the affinity and specificity of Zr-89-Df-ALT-836 for TF in vivo. Zr-89-labeling of Df-ALT-836 was achieved in high yield and good specific activity. Flow cytometry and microscopy studies revealed no detectable difference in TF-binding affinity between ALT-836 and Df-ALT-836 in vitro. Longitudinal PET scans unveiled a lasting and prominent Zr-89-Df-ALT-836 uptake in BXPC-3 tumors (peak at 31.5 +/- 6.0% ID/g at 48 h post-injection; n = 3), which was significantly abrogated (2.3 +/- 0.5% ID/g at 48 h post-injection; n = 3) when mice were pre-injected with a blocking dose (50 mg/kg) of unlabeled ALT-836. Ex vivo biodistribution data confirmed the accuracy of the PET results, and histological analysis correlated high tumor uptake with in situ TF expression. Taken together, these results attest to the excellent affinity and TF-specificity of Zr-89-Df-ALT-836. With elevated, persistent, and specific accumulation in TF-positive BXPC-3 tumors, PET imaging using Zr-89-Df-ALT-836 promises to open new avenues for improving future diagnosis, stratification, and treatment response assessment in pancreatic cancer patients.