PET of Hypoxia with⁸⁹Zr-Labeled cG250-F(ab′)₂in Head and Neck Tumors

Abstract

Hypoxic tumor cells are resistant to radiotherapy and various chemotherapeutic agents. The pretherapeutic assessment of intratumoral hypoxia may allow selection of patients for intensified treatment regimens. Carbonic anhydrase IX (CAIX) is an endogenous hypoxia-related protein involved in pH regulation and is upregulated in many tumor types. Radionuclide imaging using a monoclonal antibody against CAIX, such as cG250, may allow noninvasive PET of hypoxia in these tumor types. The aims of this study were to investigate whether 89 Zr-labeled cG250-F(ab9) 2 allowed visualization of tumor hypoxia using small-animal PET and whether the tracer showed spatial correlation to the microscopic distribution of CAIX-expressing cells in a human head and neck xenograft tumor model. Methods: Athymic mice with subcutaneous human head and neck carcinoma xenografts (SCCNij3) were imaged with small-animal PET after injection of 89 Zr-cG250-F(ab9) 2 . PET images were parameterized in terms of standardized uptake values (SUVs). After injection with the nitroimidazole hypoxia marker pimonidazole and the perfusion marker Hoechst 33342, the animals were sacrificed, tumors excised, and CAIX-and pimonidazole-marked hypoxia and blood perfusion were analyzed immunohistochemically. 89 Zr-cG250-F(ab9) 2 tumor uptake was analyzed by ex vivo activity counting and by autoradiography of tumor sections. Results: As early as 4 h after administration, accumulation of 89 Zr-cG250-F(ab9) 2 in the tumor had occurred and tumors were clearly visualized by PET, with reduced uptake by 24 h after injection. Pixel-bypixel analysis showed a significant positive spatial correlation between CAIX expression and 89 Zr-cG250-F(ab9) 2 localization (r 5 0.57-0.74; P , 0.0001). Also, significant correlations were found between pimonidazole staining intensity and 89 ZrcG250-F(ab9) 2 activity concentration, although less strong (r 5 0.46-0.68; P , 0.0001). Tumor maximum SUV correlated significantly with tumor uptake determined ex vivo (r 5 0.93; P 5 0.0067), as did fractions of CAIX and pimonidazole in tumor sections (r 5 0.75; P 5 0.03 and r 5 0.78; P 5 0.02, respectively). Conclusion: 89 Zr-labeled cG250-F(ab9) 2 small-animal PET showed rapid accumulation in a head and neck xenograft tumor model with good correlation to CAIX expression on a microscopic level.

A novel CD44v6 targeting antibody fragment with improved tumor-to-blood ratio

“…This has, to our knowledge, never before been reported for CD44v6-binding radioimmunotargeting molecules. For other targets, enzymatically derived divalent F(ab') 2 and monovalent Fab' fragments have shown promising results in animal studies (24)(25)(26)(27)(28) and clinical studies (29,30) and F(ab') 2 fragments against a different target in HNSCC (E48) has been shown to be equally effective as the parent antibody, in tumor and lymph node detection with planar gamma camera (31).…”

PET of EGFR with 64Cu‐cetuximab‐F(ab′)2 in mice with head and neck squamous cell carcinoma xenografts

“…Conversely, F(ab′) 2 fragments demonstrate high tumor-to-background signal ratios at earlier time points, while retaining tumor-binding characteristics similar to those of whole antibodies (11,12). Previous in vivo studies have shown that 111 In-cetuximab-F(ab′) 2 can visualize EGFR accessibility in mice.…”

Imaging of Epidermal Growth Factor Receptor Expression in Head and Neck Cancer with SPECT/CT and 111In-Labeled Cetuximab-F(ab′)2

“…Cetuximab and cetuximab-F(ab9) 2 were conjugated to isothiocyanatobenzyl-diethylenetriaminepentaacetic acid (ITC-DTPA; Macrocyclics) in 0.1 M NaHCO 3 , pH 9.5, for 1 h at room temperature using a 50-fold molar excess of ITC-DTPA (14,15). Unbound ITC-DTPA was removed by dialysis against NH 4 OAc (0.25 M, pH 5.5).…”

“…Antibody F(ab9) 2 fragments of cetuximab IgG have a lower molecular weight and therefore display faster blood-/tissue-clearance kinetics and enable earlier high-contrast molecular imaging (15). In this study, we aimed to characterize and optimize cetuximab-F(ab9) 2 as an EGFR-targeting imaging agent in HNSCC.…”