The influence of Bz-DOTA and CHX-A''-DTPA on the biodistribution of ABD-fused anti-HER2 Affibody molecules: implications for (114m)In-mediated targeting therapy.
OBJECTIVE
Affibody molecules represent a novel class of high-affinity agents for radionuclide tumour targeting. Fusion of the Affibody molecules with an albumin-binding domain (ABD) enables modification of the blood kinetics of the Affibody molecules and reduction of the renal dose. (177)Lu-CHX-A''-DTPA-ABD-(Z(HER2:342))(2), an anti-HER2 Affibody molecule-ABD fusion protein has earlier demonstrated promising results in treatment of HER2-expressing micro-xenografts in mice. The use of the in vivo generator (114m)In/(114)In as a label for ABD-fused Affibody molecules would create preconditions for efficient treatment of both micrometastases (due to conversion and Auger electrons of (114m)In) and bulky tumours (due to high-energy beta particles from the daughter nuclide (114)In). The goal of this study was to investigate if different chelators influence the biodistribution of ABD-(Z(HER2:342))(2) and to find an optimal chelator for attachment of (114m)In to the Affibody molecule-ABD fusion protein.


METHODS
Isothiocyanate derivatives of Bz-DOTA and CHX-A''-DTPA were coupled to ABD-(Z(HER2:342))(2). The cellular processing of both conjugates was studied in vitro. The influence of chelators on the biodistribution was investigated in mice using double isotope ((114m)In and (111)In) labelling.


RESULTS
The apparent affinity of CHX-A''-DTPA-ABD-(Z(HER2:342))(2) and Bz-DOTA-ABD-(Z(HER2:342))(2) to the extracellular domain of HER2 was similar, 13.5 and 15.0 pM, respectively. It was found that both conjugates were internalized by SKOV-3 cells. The use of CHX-A''-DTPA provided better cellular retention of the radioactivity, better tumour accumulation of radioactivity and better tumour to organ dose ratios than Bz-DOTA-ABD-(Z(HER2:342))(2).


CONCLUSIONS
CHX-A''-DTPA is more suitable for (114m)In labelling of Affibody molecule-ABD fusion proteins for radionuclide therapy.
Affibody AB, Bromma, Sweden. Vladimir.tolmachev@bms.uu.se
Vladimir
V
Tolmachev
Helena
H
Wållberg
Karl
K
Andersson
Anders
A
Wennborg
Hans
H
Lundqvist
Anna
A
Orlova
D000418:Albumins / Q000378:metabolism; D000818:Animals; D045744:Cell Line, Tumor; D006801:Humans; D007205:Indium Radioisotopes; D051379:Mice; D008807:Mice, Inbred BALB C; D009368:Neoplasm Transplantation; D009942:Organometallic Compounds / Q000493:pharmacokinetics* / Q000627:therapeutic use; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics* / Q000627:therapeutic use; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000493:pharmacokinetics* / Q000627:therapeutic use; D014018:Tissue Distribution
D000418:Albumins; D007205:Indium Radioisotopes; D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; D018719:Erb-b2 Receptor Tyrosine Kinases; D011993:Recombinant Fusion Proteins; C546786:177Lu-CHX-A''-DTPA-ABD-(Z(HER2-342))2; C546787:Bz-DOTA-ABD-(Z(HER2-342))2