title: Toward in vivo imaging of heart disease using a radiolabeled single-chain Fv fragment targeting tenascin-C.
abstract: Antibodies specific to a particular target molecule can be used as analytical reagents, not only for in vitro immunoassays but also for noninvasive in vivo imaging, e.g., immunoscintigraphies. In the latter case, it is important to reduce the size of antibody molecules in order to achieve suitable in vivo "diagnostic kinetics" and generate higher-resolution images. For these purposes, single-chain Fv fragments (scFvs; M(r) < 30 kDa) have greater potential than intact immunoglobulins (~150 kDa) or Fab (or Fab') fragments (~50 kDa). Our recent observation of enhanced tenascin-C (Tnc) expression at sites of cardiac repair after myocardial infarction prompted us to develop a radiolabeled scFv against Tnc for in vivo imaging of heart disease. We cloned the genes encoding the heavy and light chain variable domains of the mouse anti-Tnc monoclonal antibody 4F10, and combined them to create a single gene. The resulting scFv-4F10 gene was expressed in E. coli cells to produce soluble scFv proteins. scFv-4F10 has an affinity for Tnc (K(a) = 3.5 × 10(7) M(-1)), similar to the Fab fragment of antibody 4F10 (K(a) = 1.3 × 10(7) M(-1)) and high enough to be of practical use. A cysteine residue was then added to the C-terminus to achieve site-specific (111)In labeling via a chelating group. The resulting (111)In-labeled scFv was administered to a rat model of acute myocardial infarction. Biodistribution and quantitative autoradiographic studies indicated higher uptake of the radioactivity at the infarcted myocardium than the noninfarcted one. Single photon emission computed tomography (SPECT) provided in vivo cardiac images that coincided with the ex vivo observations. Our results will promote advances in diagnostic strategies for heart disease.
authors.affiliation: Kobe Pharmaceutical University, 4-19-1, Motoyama-Kitamachi, Higashinada-ku, Kobe 658-8558, Japan. no-kobay@kobepharma-u.ac.jp
authors.forename: Norihiro
authors.initials: N
authors.lastname: Kobayashi
authors.forename: Kenichi
authors.initials: K
authors.lastname: Odaka
authors.forename: Tomoya
authors.initials: T
authors.lastname: Uehara
authors.forename: Kyoko
authors.initials: K
authors.lastname: Imanaka-Yoshida
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kato
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Oyama
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tadokoro
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Akizawa
authors.forename: Shuji
authors.initials: S
authors.lastname: Tanada
authors.forename: Michiaki
authors.initials: M
authors.lastname: Hiroe
authors.forename: Toshimitsu
authors.initials: T
authors.lastname: Fukumura
authors.forename: Issei
authors.initials: I
authors.lastname: Komuro
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Arano
authors.forename: Toshimichi
authors.initials: T
authors.lastname: Yoshida
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Irie
mesh_terms: D000818:Animals; D007205:Indium Radioisotopes / Q000737:chemistry; D051379:Mice; D009203:Myocardial Infarction / Q000000981:diagnostic imaging*; D011485:Protein Binding; D019275:Radiopharmaceuticals / Q000737:chemistry / Q000493:pharmacokinetics; D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D057127:Single-Chain Antibodies / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D019063:Tenascin / Q000276:immunology / Q000378:metabolism*; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D007205:Indium Radioisotopes; D019275:Radiopharmaceuticals; D011994:Recombinant Proteins; D057127:Single-Chain Antibodies; D019063:Tenascin