title: Evaluation of chemotherapy response in VX2 rabbit lung cancer with 18F-labeled C2A domain of synaptotagmin I.
abstract: The C2A domain of synaptotagmin I can target apoptotic cells by binding to exposed anionic phospholipids. The goal of this study was to synthesize and develop (18)F-labeled C2A-glutathione-S-transferase (GST) as a molecular imaging probe for the detection of apoptosis and to assess the response of paclitaxel chemotherapy in VX2 rabbit lung cancer.
  
  
  METHODS
  (18)F-C2A-GST was prepared by labeling C2A-GST with N-succinimidyl 4-(18)F-fluorobenzoate ((18)F-SFB). (18)F-C2A-GST was confirmed by high-performance liquid chromatography and sodium dodecyl sulfate polyacrylamide gel electrophoresis. The binding of (18)F-C2A-GST toward apoptosis was validated in vitro using camptothecin-induced Jurkat cells. Biodistribution of (18)F-C2A-GST was determined in mice by a dissection method and small-animal PET. Single-dose paclitaxel was used to induce apoptosis in rabbits bearing VX2 tumors (n = 6), and 2 VX2 rabbits without treatment served as control. (18)F-C2A-GST PET was performed before and at 72 h after therapy, and (18)F-FDG PET/CT was also performed before treatment. To confirm the presence of apoptosis, tumor tissue was analyzed and activated caspase-3 was measured.
  
  
  RESULTS
  (18)F-C2A-GST was obtained with more than 95% radiochemical purity and was stable for 4 h after formulation. (18)F-C2A-GST bound apoptotic cells specifically. Biodistribution in mice showed that (18)F-C2A-GST mainly excreted from the kidneys and rapidly cleared from blood and nonspecific organs. High focal uptake of (18)F-C2A-GST in the tumor area was determined after therapy, whereas no significant uptake before therapy was found in the tumor with (18)F-FDG-avid foci. The maximum standardized uptake value after therapy was 0.47 ± 0.28, significantly higher than that in the control (0.009 ± 0.001; P < 0.001). The apoptotic index was 79.81% ± 8.73% in the therapy group, significantly higher than that in the control (5.03% ± 0.81%; P < 0.001). Activated caspase-3 after paclitaxel treatment increased to 69.55% ± 16.27% and was significantly higher than that in the control (12.26% ± 5.39%; P < 0.001).
  
  
  CONCLUSIONS
  (18)F-C2A-GST was easily synthesized by conjugation with (18)F-SFB and manifested a favorable biodistribution. Our results demonstrated the feasibility of (18)F-C2A-GST for the early detection of apoptosis after chemotherapy in a VX2 lung cancer model that could imitate the human lung cancer initiation, development, and progress.
authors.affiliation: Nanjing First Hospital, Nanjing Medical University, Nanjing, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Wang
authors.forename: Wei
authors.initials: W
authors.lastname: Fang
authors.forename: Ming-Rong
authors.initials: MR
authors.lastname: Zhang
authors.forename: Ming
authors.initials: M
authors.lastname: Zhao
authors.forename: Biao
authors.initials: B
authors.lastname: Liu
authors.forename: Zizheng
authors.initials: Z
authors.lastname: Wang
authors.forename: Zichun
authors.initials: Z
authors.lastname: Hua
authors.forename: Min
authors.initials: M
authors.lastname: Yang
authors.forename: Katsushi
authors.initials: K
authors.lastname: Kumata
authors.forename: Akiko
authors.initials: A
authors.lastname: Hatori
authors.forename: Tomoteru
authors.initials: T
authors.lastname: Yamasaki
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Yanamoto
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Suzuki
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3 / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D005240:Feasibility Studies; D005462:Fluorine Radioisotopes; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007202:Indicators and Reagents; D007553:Isotope Labeling / Q000379:methods; D019169:Jurkat Cells; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000188:drug therapy*; D008297:Male; D051379:Mice; D057054:Molecular Imaging; D017239:Paclitaxel / Q000627:therapeutic use; D049268:Positron-Emission Tomography; D011817:Rabbits; D019275:Radiopharmaceuticals / Q000737:chemistry / Q000493:pharmacokinetics; D050863:Synaptotagmin I / Q000737:chemistry / Q000493:pharmacokinetics; D014018:Tissue Distribution
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D005462:Fluorine Radioisotopes; D007202:Indicators and Reagents; D019275:Radiopharmaceuticals; D050863:Synaptotagmin I; D053148:Caspase 3; D017239:Paclitaxel