Imaging of tumor angiogenesis using 99mTc-labeled human recombinant anti-ED-B fibronectin antibody fragments
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Published on: September 16, 2019
Dietmar Berndorff1, Sandra Borkowski, Dieter Moosmayer
1Research Laboratories, Schering AG, Berlin, Germany. dietmar.berndorff@schering.de
Unlabelled:
The aim of this study was to target the angiogenesis-associated extracellular matrix protein ED-B fibronectin for molecular imaging of solid tumors. Recombinant and chemically modified derivatives of the single-chain antibody fragment (scFv) L19, capable of being labeled with 99mTc, were synthesized and radiolabeled. The resulting compounds 99mTc-AP39, 99mTc-L19-His, and 99mTc-L19-Hi20 were assessed for their imaging properties in vivo.
Methods:
L19 was genetically modified by inserting either the (Gly)3-Cys-Ala (AP39) or a (His)6 tag (L19-His) sequence at the C-terminal end. Chemical modifications were performed by conjugating the bifunctional chelator Hi20 (L19-Hi20) at epsilon-Lys-NH2 residues of the molecule to allow for a direct chelator-based labeling with 99mTc. Tumor-targeting, pharmacokinetic, and scintigraphic imaging properties of the radiolabeled scFvs were evaluated in nude mice bearing murine F9 teratocarcinoma.
Results:
99mTc labeling of the L19 derivatives yielded radiochemically pure proteins maintaining high immunoreactivity to ED-B fibronectin, as measured by affinity chromatography. Size-exclusion high-performance liquid chromatographic analysis of labeled L19 derivatives demonstrated either dimeric species (L19-His) or a mixture of predominantly associative dimeric and monomeric species (AP39, L19-Hi20). 99mTc-AP39 showed the most favorable biodistribution and imaging properties with high and fast tumor uptake (8.3 percentage injected dose per gram at 3 h after injection), rapid blood clearance and renal excretion, leading to high signal-to-noise ratios (tumor-to-blood ratio of 6.4 at 3 h after injection), and excellent planar scintigraphy in vivo.
Conclusion:
ED-B fibronectin can be efficiently targeted by 99mTc-AP39 and scintigraphically visualized in tumor-bearing mice, providing a potentially useful clinical tool for imaging of angiogenesis-associated ED-B fibronectin-expressing human tumors.
Insights
This study developed 99mTc-AP39, a radiolabeled antibody fragment targeting ED-B fibronectin for molecular imaging. It demonstrated effective tumor visualization in mice, showing potential for clinical use in detecting angiogenesis-associated tumors.
Area of Science:
- Biomedical imaging
- Molecular oncology
- Radiopharmaceutical development
Background:
- Angiogenesis-associated extracellular matrix protein ED-B fibronectin is a target for solid tumor imaging.
- Single-chain antibody fragment (scFv) L19 targets ED-B fibronectin.
- Development of radiolabeled tracers is crucial for molecular imaging.
Purpose of the Study:
- To develop and evaluate 99mTc-labeled L19 derivatives for molecular imaging of ED-B fibronectin in solid tumors.
- To assess the in vivo imaging properties of these novel radiotracers.
Main Methods:
- Genetic modification of L19 scFv with AP39 or His6 tags.
- Chemical modification of L19 with Hi20 chelator.
- Radiolabeling with 99mTc and characterization of labeled compounds.
- In vivo evaluation in nude mice bearing F9 teratocarcinoma.
Main Results:
- 99mTc-labeled L19 derivatives maintained high immunoreactivity to ED-B fibronectin.
- 99mTc-AP39 exhibited favorable biodistribution, rapid tumor uptake (8.3% ID/g at 3h), and high tumor-to-blood ratios (6.4 at 3h).
- Excellent planar scintigraphy was achieved with 99mTc-AP39 in vivo.
Conclusions:
- 99mTc-AP39 efficiently targets ED-B fibronectin for scintigraphic visualization in tumor-bearing mice.
- This tracer shows potential as a clinical tool for imaging angiogenesis-associated ED-B fibronectin-expressing human tumors.
