Characterization of anti-Frizzled Antibody [Zr-89]18R5 for PET Imaging of Pancreatic Cancer

Objectives Elevated Wnt signaling is associated with various cancers due to its tumorigenic properties by promoting cellular proliferation, epithelial mesenchymal transition, stem cell renewal and metastasis. Frizzled receptor proteins (Fzd) serve as cell surface receptors in the Wnt signalling pathway and have potential as an imaging biomarker for cancer. Herein, we describe the characterization of a human-specific anti-Fzd IgG antibody (Ab) for in vivo PET imaging with potential for real-time visualization of Fzd tumor status as a predictive and pharmacodynamic biomarker of pancreatic cancer.

Methods The anti-pan-Fzd IgG Ab 18R5 (Vantictumab, OncoMed) was screened against numerous human pancreatic cancer cell lines for Fzd expression via flow cytometry. 18R5 was conjugated to desferoxamine and radiolabeled with Zr-89, followed by live-cell ELISA and RIA to confirm binding specificity post modification. Subcutaneous tumour xenografts in nude mice were established with cell lines with mid (Aspc-1) to low (Panc.0504) Fzd-expression levels, and [Zr-89]18R5 tumour and tissue distribution assessed by biodistribution and immuno PET imaging.

Results FACS and ELISA studies show specificity of 18R5 for Fzd in vitro in human pancreatic cell lines. While Zr-89 radiolabeling of 18R5 was suboptimal (75%). Preclinical in vivo studies demonstrate approximately 13-fold higher uptake of [Zr-89]18R5 in Fzd-mid over Fzd-low pancreatic tumours as early as 24 h post intravenous administration. Uptake slowly washes out from Fzd-mid tumours over 144 h. When corrected for residual tumour blood levels, there is significantly more ligand uptake in Fzd-mid versus Fzd-low tumours (P<0.05).

Conclusions Our preliminary results show evidence of high specificity of 18R5 binding to pancreatic tumours with mid-level expression of Fzd-receptors. This work serves as groundwork for exploring anti-Fzd Abs as a potential predictive biomarker for Wnt-targeted drug therapies, such as PORCN inhibitors. Future work will include optimization of radiolabeling as well as larger studies to validate radiolabelled 18R5 as a bona fide imaging probe for various Fzd-expressing cancers. Research Support: NRF Lab@AU Programme (AG/CIVGC70-C/NRF/2013/2) to AMC.

• Download figure
• Open in new tab
• Download powerpoint