Design, synthesis and biological evaluation of a multifunctional HER2-specific Affibody molecule for molecular imaging.
OBJECTIVE
The purpose of this study was to design and evaluate a novel platform for labelling of Affibody molecules, enabling both recombinant and synthetic production and site-specific labelling with (99m)Tc or trivalent radiometals.


METHODS
The HER2-specific Affibody molecule PEP05352 was made by peptide synthesis. The chelator sequence SECG (serine-glutamic acid-cysteine-glycine) was anchored on the C-terminal to allow (99m)Tc labelling. The cysteine can alternatively serve as a conjugation site of the chelator DOTA for indium labelling. The resulting (99m)Tc- and (111)In-labelled Affibody molecules were evaluated both in vitro and in vivo.


RESULTS
Both conjugates retained their capacity to bind to HER2 receptors in vitro and in vivo. The tumour to blood ratio in LS174T xenografts was 30 at 4 h post-injection for both conjugates. Biodistribution data showed that the (99m)Tc-labelled Affibody molecule had a fourfold lower kidney accumulation compared with the (111)In-labelled Affibody molecule while the accumulation in other organs was similar. Gamma camera imaging of the conjugates could clearly visualise the tumours 4 h after injection.


CONCLUSIONS
Incorporation of the C-terminal SECG sequence in Affibody molecules provides a general multifunctional platform for site-specific labelling with different nuclides (technetium, indium, gallium, cobalt or yttrium) and for a flexible production (chemical synthesis or recombinant).
Tran
Thuy A
TA
Department of Radiology, Rudbeck Laboratory, Uppsala University, Uppsala, Sweden. thuy.tran@bms.uu.se
Rosik
Daniel
D
Abrahmsén
Lars
L
Sandström
Mattias
M
Sjöberg
Anna
A
Wållberg
Helena
H
Ahlgren
Sara
S
Orlova
Anna
A
Tolmachev
Vladimir
V
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D045744:Cell Line, Tumor; D015195:Drug Design; D005260:Female; D006801:Humans; D007553:Isotope Labeling; D007700:Kinetics; D051379:Mice; D057054:Molecular Imaging; D008969:Molecular Sequence Data; D009369:Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism; D011849:Radioactive Tracers; D011877:Radionuclide Imaging; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics; D013379:Substrate Specificity; D014018:Tissue Distribution
D011849:Radioactive Tracers; D018719:Erb-b2 Receptor Tyrosine Kinases; D011993:Recombinant Fusion Proteins