title: Evaluation of ((4-hydroxyphenyl)ethyl)maleimide for site-specific radiobromination of anti-HER2 affibody.
abstract: Affibody molecules are a new class of small phage-display selected proteins using a scaffold domain of the bacterial receptor protein A. They can be selected for specific binding to a large variety of protein targets. An affibody molecule binding with high affinity to a tumor antigen HER2 was recently developed for radionuclide diagnostics and therapy in vivo. The use of the positron-emitting nuclide (76)Br (T(1/2) = 16.2 h) could improve the sensitivity of detection of HER2-expressing tumors. A site-specific radiobromination of a cysteine-containing variant of the anti-HER2 affibody, (Z(HER2:4))(2)-Cys, using ((4-hydroxyphenyl)ethyl)maleimide (HPEM), was evaluated in this study. It was found that HPEM can be radiobrominated with an efficiency of 83 +/- 0.4% and thereafter coupled to freshly reduced affibody with a yield of 65.3 +/- 3.9%. A "one-pot" labeling enabled the radiochemical purity of the conjugate to exceed 97%. The label was stable against challenge with large excess of nonlabeled bromide and in a high molar strength solution. In vitro cell tests demonstrated that radiobrominated affibody binds specifically to the HER2-expressing cell-line, SK-OV-3. Biodistribution studies in nude mice bearing SK-OV-3 xenografts have shown tumor accumulation of 4.8 +/- 2.2% IA/g and good tumor-to-normal tissue ratios.
authors.affiliation: Department of Chemistry, Organic Chemistry, Uppsala University, Uppsala, Sweden.
authors.forename: Eskender
authors.initials: E
authors.lastname: Mume
authors.forename: Anna
authors.initials: A
authors.lastname: Orlova
authors.forename: Barbro
authors.initials: B
authors.lastname: Larsson
authors.forename: Ann-Sofie
authors.initials: AS
authors.lastname: Nilsson
authors.forename: Fredrik Y
authors.initials: FY
authors.lastname: Nilsson
authors.forename: Stefan
authors.initials: S
authors.lastname: Sjöberg
authors.forename: Vladimir
authors.initials: V
authors.lastname: Tolmachev
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm / Q000032:analysis / Q000378:metabolism; D001665:Binding Sites; D001967:Bromine Radioisotopes / Q000737:chemistry*; D045744:Cell Line, Tumor; D006801:Humans; D008301:Maleimides / Q000737:chemistry; D051379:Mice; D008819:Mice, Nude; D009374:Neoplasms, Experimental / Q000473:pathology; D019151:Peptide Library; D010455:Peptides / Q000737:chemistry / Q000493:pharmacokinetics*; D025941:Protein Interaction Mapping; D019275:Radiopharmaceuticals / Q000138:chemical synthesis* / Q000493:pharmacokinetics*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000032:analysis / Q000378:metabolism*; D013205:Staphylococcal Protein A / Q000737:chemistry; D014018:Tissue Distribution; D014183:Transplantation, Heterologous
chemical_list: D000951:Antigens, Neoplasm; D001967:Bromine Radioisotopes; D008301:Maleimides; D019151:Peptide Library; D010455:Peptides; D019275:Radiopharmaceuticals; D018719:Erb-b2 Receptor Tyrosine Kinases; D013205:Staphylococcal Protein A