Evaluation of ((4-Hydroxyphenyl)ethyl)maleimide for Site-Specific Radiobromination of Anti-HER2 Affibody

• Published in: Bioconjugate chemistry 2005-11, Vol.16 (6), p.1547-1555
• Main Authors: Mume, Eskender, Orlova, Anna, Larsson, Barbro, Nilsson, Ann-Sofie, Nilsson, Fredrik Y, Sjöberg, Stefan, Tolmachev, Vladimir
• Format: Article
• Language: English
• Subjects: Animals; Antigens, Neoplasm - analysis; Antigens, Neoplasm - metabolism; Binding Sites; Biochemistry; Bromine Radioisotopes - chemistry; Cell Line, Tumor; Chemistry; Gene expression; Humans; Kemi; Maleimides - chemistry; Mice; Mice, Nude; NATURAL SCIENCES; NATURVETENSKAP; Neoplasms, Experimental - pathology; Organic chemistry; Organisk kemi; Peptide Library; Peptides - chemistry; Peptides - pharmacokinetics; Peptides/chemistry/pharmacokinetics; Protein Interaction Mapping; Proteins; Radiopharmaceuticals - chemical synthesis; Radiopharmaceuticals - pharmacokinetics; Radiopharmaceuticals/chemical synthesis/pharmacokinetics; Receptor, ErbB-2 - analysis; Receptor, ErbB-2 - metabolism; Staphylococcal Protein A - chemistry; Tissue Distribution; Transplantation, Heterologous; Tumors
• ISSN: 1043-1802; 1520-4812; 1520-4812
• DOI: 10.1021/bc050056o

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 76Br (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, (ZHER2:4)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.