Imaging of EGFR expression in murine xenografts using site-specifically labelled anti-EGFR 111In-DOTA-Z EGFR:2377 Affibody molecule: aspect of the injected tracer amount.
BACKGROUND
Overexpression of epidermal growth factor receptor (EGFR) is a prognostic and predictive biomarker in a number of malignant tumours. Radionuclide molecular imaging of EGFR expression in cancer could influence patient management. However, EGFR expression in normal tissues might complicate in vivo imaging. The aim of this study was to evaluate if optimization of the injected protein dose might improve imaging of EGFR expression in tumours using a novel EGFR-targeting protein, the DOTA-Z(EGFR:2377) Affibody molecule.


METHODS
An anti-EGFR Affibody molecule, Z(EGFR:2377), was labelled with (111)In via the DOTA chelator site-specifically conjugated to a C-terminal cysteine. The affinity of DOTA-Z(EGFR:2377) for murine and human EGFR was measured by surface plasmon resonance. The cellular processing of (111)In-DOTA-Z(EGFR:2377) was evaluated in vitro. The biodistribution of radiolabelled Affibody molecules injected in a broad range of injected Affibody protein doses was evaluated in mice bearing EGFR-expressing A431 xenografts.


RESULTS
Site-specific coupling of DOTA provided a uniform conjugate possessing equal affinity for human and murine EGFR. The internalization of (111)In-DOTA-Z(EGFR:2377) by A431 cells was slow. In vivo, the conjugate accumulated specifically in xenografts and in EGFR-expressing tissues. The curve representing the dependence of tumour uptake on the injected Affibody protein dose was bell-shaped. The highest specific radioactivity (lowest injected protein dose) provided a suboptimal tumour-to-blood ratio. The results of the biodistribution study were confirmed by gamma-camera imaging.


CONCLUSIONS
The (111)In-DOTA-Z(EGFR:2377) Affibody molecule is a promising tracer for radionuclide molecular imaging of EGFR expression in malignant tumours. Careful optimization of protein dose is required for high-contrast imaging of EGFR expression in vivo.
Unit of Biomedical Radiation Sciences, Rudbeck Laboratory, Uppsala University, 751 81, Uppsala, Sweden. vladimir.tolmachev@bms.uu.se
Vladimir
V
Tolmachev
Daniel
D
Rosik
Helena
H
Wållberg
Anna
A
Sjöberg
Mattias
M
Sandström
Monika
M
Hansson
Anders
A
Wennborg
Anna
A
Orlova
D000818:Animals; D001665:Binding Sites; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D066246:ErbB Receptors / Q000378:metabolism*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry*; D006801:Humans; D007205:Indium Radioisotopes / Q000737:chemistry*; D007267:Injections; D051379:Mice; D057054:Molecular Imaging / Q000379:methods*; D009369:Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D011849:Radioactive Tracers; D011877:Radionuclide Imaging; D011993:Recombinant Fusion Proteins / Q000008:administration & dosage / Q000493:pharmacokinetics; D013379:Substrate Specificity; D014018:Tissue Distribution
D006573:Heterocyclic Compounds, 1-Ring; D007205:Indium Radioisotopes; D011849:Radioactive Tracers; D011993:Recombinant Fusion Proteins; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid; D066246:ErbB Receptors