Comparative evaluation of synthetic anti-HER2 Affibody molecules site-specifically labelled with 111In using N-terminal DOTA, NOTA and NODAGA chelators in mice bearing prostate cancer xenografts.
OBJECTIVE
In disseminated prostate cancer, expression of human epidermal growth factor receptor type 2 (HER2) is one of the pathways to androgen independence. Radionuclide molecular imaging of HER2 expression in disseminated prostate cancer might identify patients for HER2-targeted therapy. Affibody molecules are small (7 kDa) targeting proteins with high potential as tracers for radionuclide imaging. The goal of this study was to develop an optimal Affibody-based tracer for visualization of HER2 expression in prostate cancer.


METHODS
A synthetic variant of the anti-HER2 Z(HER2:342) Affibody molecule, Z(HER2:S1), was N-terminally conjugated with the chelators DOTA, NOTA and NODAGA. The conjugated proteins were biophysically characterized by electrospray ionization mass spectroscopy (ESI-MS), circular dichroism (CD) spectroscopy and surface plasmon resonance (SPR)-based biosensor analysis. After labelling with (111)In, the biodistribution was assessed in normal mice and the two most promising conjugates were further evaluated for tumour targeting in mice bearing DU-145 prostate cancer xenografts.


RESULTS
The HER2-binding equilibrium dissociation constants were 130, 140 and 90 pM for DOTA-Z(HER2:S1), NOTA-Z(HER2:S1) and NODAGA-Z(HER2:S1), respectively. A comparative study of (111)In-labelled DOTA-Z(HER2:S1), NOTA-Z(HER2:S1) and NODAGA-Z(HER2:S1) in normal mice demonstrated a substantial influence of the chelators on the biodistribution properties of the conjugates. (111)In-NODAGA-Z(HER2:S1) had the most rapid clearance from blood and healthy tissues. (111)In-NOTA-Z(HER2:S1) showed high hepatic uptake and was excluded from further evaluation. (111)In-DOTA-Z(HER2:S1) and (111)In-NODAGA-Z(HER2:S1) demonstrated specific uptake in DU-145 prostate cancer xenografts in nude mice. The tumour uptake of (111)In-NODAGA-Z(HER2:S1), 5.6 ± 0.4%ID/g, was significantly lower than the uptake of (111)In-DOTA-Z(HER2:S1), 7.4 ± 0.5%ID/g, presumably because of lower bioavailability due to more rapid clearance. (111)In-NODAGA-Z(HER2:S1) provided higher tumour-to-blood ratio, but somewhat lower tumour-to-liver, tumour-to-spleen and tumour-to-bone ratios.


CONCLUSIONS
Since distant prostate cancer metastases are situated in bone or bone marrow, the higher tumour-to-bone ratio is the most important. This renders (111)In-DOTA-Z(HER2:S1) a preferable agent for imaging of HER2 expression in disseminated prostate cancer.
Preclinical PET Platform, Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden.
Jennie
J
Malmberg
Anna
A
Perols
Zohreh
Z
Varasteh
Mohamed
M
Altai
Alexis
A
Braun
Mattias
M
Sandström
Ulrike
U
Garske
Vladimir
V
Tolmachev
Anna
A
Orlova
Amelie Eriksson
AE
Karlström
D000085:Acetates / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000276:immunology* / Q000493:pharmacokinetics; D001665:Binding Sites; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D002614:Chelating Agents / Q000737:chemistry*; D015972:Gene Expression Regulation, Neoplastic; D006571:Heterocyclic Compounds / Q000737:chemistry; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry; D006801:Humans; D007205:Indium Radioisotopes / Q000737:chemistry*; D007553:Isotope Labeling; D008297:Male; D051379:Mice; D057054:Molecular Imaging; D008969:Molecular Sequence Data; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000276:immunology*; D013379:Substrate Specificity
D000085:Acetates; D000911:Antibodies, Monoclonal; D002614:Chelating Agents; D006571:Heterocyclic Compounds; D006573:Heterocyclic Compounds, 1-Ring; D007205:Indium Radioisotopes; D018719:Erb-b2 Receptor Tyrosine Kinases; C572723:1-(1,3-carboxypropyl)-4,7-carboxymethyl-1,4,7-triazacyclononane; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid; C048993:1,4,7-triazacyclononane-N,N',N''-triacetic acid