MicroPET/CT imaging of patient-derived pancreatic cancer xenografts implanted subcutaneously or orthotopically in NOD-scid mice using 64Cu-NOTA-panitumumab F(ab')2 fragments

Introduction: Our objective was to study microPET/CT imaging of patient-derived pancreatic cancer xenografts in NOD-scid mice using F(ab')(2) fragments of the fully-human anti-EGFR monoclonal antibody, panitumumab (Vectibix) labeled with Cu-64. More than 90% of pancreatic cancers are EGFR-positive. Methods: F(ab')(2) fragments were produced by proteolytic digestion of panitumumab IgG or non-specific human IgG, purified by ultrafiltration then modified with NOTA chelators for complexing Cu-64. Panitumumab IgG and Fab fragments were similarly labeled with Cu-64. EGFR immunoreactivity was determined in competition and direct (saturation) cell binding assays. The biodistribution of Cu-64-labeled panitumumab IgG, F(ab')(2) and Fab was compared in non-tumor-bearing Balb/c mice. MicroPET/CT and biodistribution studies were performed in NOD-scid mice engrafted subcutaneously (s.c.) or orthotopically with patient-derived OCIP23 pancreatic tumors, or in NOD-scid with s.c. PANC-1 human pancreatic cancer xenografts. Results: Panitumumab F(ab')(2) fragments were produced in high purity (>90%), derivitized with 32 +/- 0.7 NOTA/F(ab')(2), and labeled with Cu-64 (03-3.6 MBg/mu g). The binding of Cu-64-NOTA-panitumumab F(ab')(2) to OCIP23 or PANC-1 cells was decreased significantly by an excess of panitumumab IgG. The K-d for binding of Cu-64-NOTA-panitumumab F(ab')(2) to EGFR on PANC-1 cells was 0.14 +/- 0.05 nmol/L F(ab')(2) fragments exhibited more suitable normal tissue distribution for tumor imaging with Cu-64 than panitumumab IgG or Fab. Tumor uptake at 48 h post injection (p.i.) of Cu-64-NOTA-panitumumab F(ab')(2) was 12.0 +/- 0.9% injected dose/g (ID/g) in s.c. and 11.8 +/- 0.9% ID/gin orthotopic OCIP23 tumors vs. 6.1 +/- 1.1% ID/gin s.c. PANC-1 xenografts. Tumor/Blood (T/B) ratios were 5:1 to 9:1 for OCIP23 and 2.4:1 for PANC-1 tumors. Tumor uptake of Cu-64-NOTA-non-specific F(ab')2 in OCIP23 xenografts was 5-fold lower than Cu-64-panitumumab F(ab')(2). All tumor xenografts were clearly imaged by microPET/CT at 24 or 48 h p.i. of Cu-64-NOTA-panitumumab F(ab')(2). Conclusions: Cu-64-panitumumab F(ab.)(2) fragments bound with high affinity to EGFR on pancreatic cancer cells in vitro and localized specifically in patient-derived pancreatic cancer xenografts in mice in vivo, allowing tumor visualization by microPET/CT at 24 or 48 h p.i. (C) 2014 Elsevier Inc. All rights reserved.