title: Imaging of CAIX-expressing xenografts in vivo using 99mTc-HEHEHE-ZCAIX:1 affibody molecule.
abstract: Carbonic anhydrase IX (CAIX) is a transmembrane enzyme involved in regulation of tissue pH balance. In cancer, CAIX expression is associated with tumor hypoxia. CAIX is also overexpressed in renal cell carcinoma and is a molecular target for the therapeutic antibody cG250 (girentuximab). Radionuclide imaging of CAIX expression might be used for identification of patients who may benefit from cG250 therapy and from treatment strategies for hypoxic tumors. Affibody molecules are small (7 kDa) scaffold proteins having a high potential as probes for radionuclide molecular imaging. The aim of the present study was to evaluate feasibility of in vivo imaging of CAIX-expression using radiolabeled Affibody molecules. A histidine-glutamate-histidine-glutamate-histidine-glutamate (HE)3-tag-containing CAIX-binding Affibody molecule (HE)3-ZCAIX:1 was labeled with [(99m)Tc(CO)3](+). Its binding properties were evaluated in vitro using CAIX-expressing SK-RC-52 renal carcinoma cells. (99m)Tc-(HE)3-ZCAIX:1 was evaluated in NMRI nu/nu mice bearing SK-RC-52 xenografts. The in vivo specificity test confirmed CAIX-mediated tumor targeting. (99m)Tc-(HE)3-ZCAIX:1 cleared rapidly from blood and normal tissues except for kidneys. At optimal time-point (4 h p.i.), the tumor uptake was 9.7 ± 0.7% ID/g, and tumor-to-blood ratio was 53 ± 10. Experimental imaging of CAIX-expressing SK-RC-52 xenografts at 4 h p.i. provided high contrast images. The use of radioiodine label for ZCAIX:1 enabled the reduction of renal uptake, but resulted in significantly lower tumor uptake and tumor-to-blood ratio. Results of the present study suggest that radiolabeled Affibody molecules are promising probes for imaging of CAIX-expression in vivo.
authors.affiliation: Unit of Biomedical Radiation Sciences, Rudbeck Laboratory, Uppsala University, SE-75185 Uppsala, Sweden.
authors.forename: Hadis
authors.initials: H
authors.lastname: Honarvar
authors.affiliation: Unit of Biomedical Radiation Sciences, Rudbeck Laboratory, Uppsala University, SE-75185 Uppsala, Sweden.
authors.forename: Javad
authors.initials: J
authors.lastname: Garousi
authors.affiliation: Affibody AB, SE-17163 Solna, Sweden.
authors.forename: Elin
authors.initials: E
authors.lastname: Gunneriusson
authors.affiliation: Affibody AB, SE-17163 Solna, Sweden.
authors.forename: Ingmarie
authors.initials: I
authors.lastname: Höidén-Guthenberg
authors.affiliation: Unit of Biomedical Radiation Sciences, Rudbeck Laboratory, Uppsala University, SE-75185 Uppsala, Sweden.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Altai
authors.affiliation: Department of Hospital Physics, Uppsala University Hospital, SE-75185 Uppsala, Sweden.
authors.forename: Charles
authors.initials: C
authors.lastname: Widström
authors.affiliation: Unit of Biomedical Radiation Sciences, Rudbeck Laboratory, Uppsala University, SE-75185 Uppsala, Sweden.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Tolmachev
authors.affiliation: Unit of Biomedical Radiation Sciences, Rudbeck Laboratory, Uppsala University, SE-75185 Uppsala, Sweden.
authors.forename: Fredrik Y
authors.initials: FY
authors.lastname: Frejd
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry; D000951:Antigens, Neoplasm / Q000096:biosynthesis* / Q000737:chemistry; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases / Q000096:biosynthesis* / Q000737:chemistry; D002292:Carcinoma, Renal Cell / Q000000981:diagnostic imaging* / Q000235:genetics / Q000473:pathology; D045744:Cell Line, Tumor; D003952:Diagnostic Imaging; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D051379:Mice; D011859:Radiography; D013667:Technetium / Q000737:chemistry; D014018:Tissue Distribution; D023041:Xenograft Model Antitumor Assays
chemical_list: D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; C106533:G250 monoclonal antibody; D013667:Technetium; C089226:CA9 protein, human; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases