title: Novel Carcinoembryonic-Antigen-(CEA)-Specific Pretargeting System to Assess Tumor Cell Viability after Irradiation of Colorectal Cancer Cells.
abstract: OBJECTIVE
  To date, no valid imaging modality exists for early response prediction to neoadjuvant radiochemotherapy in carcinoembryonic-antigen-(CEA)-expressing rectal cancers (UICC stages II and III). It is hypothesized that the uptake of an anti-CEA antibody is directly related to the number of viable tumor cells and may be quantified by immuno-positron emission tomography (immuno-PET). Therefore, we evaluated a novel pretargeting system using TF2, a humanized bispecific trivalent monoclonal antibody (mAb), directed against CEA and the IMP-288-peptide, a hapten for binding radiometals for imaging. Uptake and kinetics of the pretargeting system were investigated in vitro prior to and after irradiation.
  
  
  METHODS
  TF2 was labeled with ¹³¹I and IMP-288 with ¹¹¹InCl₃. The colorectal cancer cell lines HT29, SW480, and T84 with known varying CEA expression were incubated (≤ 72 hours) with ¹³¹I-TF2 or the TF2-¹¹¹In-IMP-288 pretargeting system. Parallel cultures were irradiated with 2-10 Gy high-energy photons. Tracer uptake, proliferation, apoptosis, and CEA-RNA expression of cancer cells were investigated.
  
  
  RESULTS
  The uptake of tracers was dependent on CEA expression and cell count of the cell lines (uptake/10⁶ cells: 0.3% in HT29, 1.5% in SW480, and 14% in T84, p < 0.001). The TF2-¹¹¹In-IMP-288 pretargeting system showed a higher uptake after 4 and 72 hours compared to (131)I-TF2 in parallel cultures. Only in one cell line (SW480) an increased apoptosis after irradiation could be detected. Irradiation increased dose dependently both the specific uptake of ¹³¹I-TF2 and of the TF2-¹¹¹In-IMP-288 system (4-fold in HT29 and T84 after 10 Gy (72 hours), p < 0.001). These results were CEA-mRNA independent.
  
  
  CONCLUSIONS
  This novel pretargeting system allows the quantitative analysis of CEA-expressing colorectal cancer cells and represents a promising tool for evaluation of tumor cell viability after irradiation.
authors.affiliation: Department of Nuclear Medicine, University Medical Center, Georg-August-University Göttingen, Göttingen, Germany. meller.birgit@googlemail.com
authors.forename: Birgit
authors.initials: B
authors.lastname: Meller
authors.forename: Margarete
authors.initials: M
authors.lastname: Rave-Fränck
authors.forename: Christian
authors.initials: C
authors.lastname: Breunig
authors.forename: Markus
authors.initials: M
authors.lastname: Schirmer
authors.forename: Manfred
authors.initials: M
authors.lastname: Baehre
authors.forename: Roger
authors.initials: R
authors.lastname: Nadrowitz
authors.forename: Torsten
authors.initials: T
authors.lastname: Liersch
authors.forename: Johannes
authors.initials: J
authors.lastname: Meller
mesh_terms: D018033:Antibodies, Bispecific; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D014408:Biomarkers, Tumor / Q000097:blood* / Q000235:genetics / Q000276:immunology; D002272:Carcinoembryonic Antigen / Q000097:blood* / Q000235:genetics / Q000276:immunology; D002455:Cell Division / Q000187:drug effects / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects* / Q000528:radiation effects*; D015179:Colorectal Neoplasms / Q000097:blood / Q000188:drug therapy* / Q000473:pathology / Q000532:radiotherapy*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000528:radiation effects; D006573:Heterocyclic Compounds, 1-Ring; D006801:Humans; D066298:In Vitro Techniques; D020360:Neoadjuvant Therapy; D009367:Neoplasm Staging; D009842:Oligopeptides; D049268:Positron-Emission Tomography / Q000379:methods; D012334:RNA, Neoplasm / Q000235:genetics; D011882:Radiotherapy, High-Energy
chemical_list: D018033:Antibodies, Bispecific; D014408:Biomarkers, Tumor; D002272:Carcinoembryonic Antigen; C515662:DOTA-tyrosyl-lysyl(histaminyl-succinyl-glycyl)-glutamyl-lysyl(histaminyl-succinyl-glycyl)amide; D006573:Heterocyclic Compounds, 1-Ring; D009842:Oligopeptides; D012334:RNA, Neoplasm