title: Fab fragment labeled with ICG-derivative for detecting digestive tract cancer.
abstract: BACKGROUND
  In previous studies, we generated infrared ray fluorescence-labeled monoclonal antibodies and developed an infrared ray fluorescence endoscope capable of detecting the monoclonal antibodies to establish a novel diagnostic technique for gastrointestinal cancer. Although the whole IgG molecule has commonly been used for preparation of labeled antibodies, labeled IgG displays insufficient sensitivity and specificity, probably resulting from non-specific binding of the Fc fragment to target cells or interference between fluorochromes on the identical labeled antibody, which might be caused by molecular structure. In this in vitro study, we characterized an Fc-free fluorescence-labeled Fab fragment, which was expected to yield more specific binding to target cells than the whole IgG molecule.
  
  
  METHODS
  An anti-mucin antibody and ICG-ATT, an ICG derivative, were used as the labeled antibody and labeling compound, respectively. Paraffin sections of excised gastric cancer tissues were subjected to staining. The labeled whole IgG molecule (ICG-ATT-labeled IgG) and the labeled Fab fragment (ICG-ATT-labeled Fab) were prepared according to a previous report, and the fluorescence properties, antibody activities, and features of fluorescence microscope images obtained from paraffin sections were compared.
  
  
  RESULTS
  Both ICG-ATT-labeled Fab and ICG-ATT-labeled IgG were excited by a near infrared ray of 766nm, and maximum emission occurred at 804nm. Antibody activities of ICG-ATT-labeled Fab were shown to be similar to those of unlabeled anti-MUC1 antibody. The fluorescence intensity obtained from paraffin sections of excised gastric cancer tissues revealed a tendency to be greater with ICG-ATT-labeled Fab than with ICG-ATT-labeled IgG.
  
  
  CONCLUSIONS
  The infrared ray fluorescence-labeled Fab fragment was likely to be more specific than the conventionally labeled antibodies. Fragmentation of antibodies is considered to contribute to improved sensitivity and specificity of labeled antibodies for detection of micro gastrointestinal cancers.
authors: Department of Digestive and Cardiovascular Medicine, Institute of Health Biosciences, The University of Tokushima Graduate School, 3-18-15 Kuramoto-cho, Tokushima City 770-8503, Japan.
authors: Hiromi
authors: H
authors: Yano
authors: Department of Digestive and Cardiovascular Medicine, Institute of Health Biosciences, The University of Tokushima Graduate School, 3-18-15 Kuramoto-cho, Tokushima City 770-8503, Japan.
authors: Naoki
authors: N
authors: Muguruma
authors: Department of Digestive and Cardiovascular Medicine, Institute of Health Biosciences, The University of Tokushima Graduate School, 3-18-15 Kuramoto-cho, Tokushima City 770-8503, Japan.
authors: Susumu
authors: S
authors: Ito
authors: Department of Digestive and Cardiovascular Medicine, Institute of Health Biosciences, The University of Tokushima Graduate School, 3-18-15 Kuramoto-cho, Tokushima City 770-8503, Japan.
authors: Eriko
authors: E
authors: Aoyagi
authors: Department of Digestive and Cardiovascular Medicine, Institute of Health Biosciences, The University of Tokushima Graduate School, 3-18-15 Kuramoto-cho, Tokushima City 770-8503, Japan.
authors: Tetsuo
authors: T
authors: Kimura
authors: Department of Digestive and Cardiovascular Medicine, Institute of Health Biosciences, The University of Tokushima Graduate School, 3-18-15 Kuramoto-cho, Tokushima City 770-8503, Japan.
authors: Yoshitaka
authors: Y
authors: Imoto
authors: Department of Digestive and Cardiovascular Medicine, Institute of Health Biosciences, The University of Tokushima Graduate School, 3-18-15 Kuramoto-cho, Tokushima City 770-8503, Japan.
authors: Jianxin
authors: J
authors: Cao
authors: Division of Pharmaceutical Chemistry, Faculty of Pharmaceutical Sciences, Institute of Health Biosciences, Tokushima, Japan.
authors: Shohei
authors: S
authors: Inoue
authors: Division of Pharmaceutical Chemistry, Faculty of Pharmaceutical Sciences, Institute of Health Biosciences, Tokushima, Japan.
authors: Shigeki
authors: S
authors: Sano
authors: Division of Pharmaceutical Chemistry, Faculty of Pharmaceutical Sciences, Institute of Health Biosciences, Tokushima, Japan.
authors: Yoshimitsu
authors: Y
authors: Nagao
authors: Division of Enzyme Chemistry, The Institute for Enzyme Research, The University of Tokushima Graduate School, Tokushima, Japan.
authors: Hiroshi
authors: H
authors: Kido