title: Exposure of human osteosarcoma and bone marrow cells to tumour-targeted alpha-particles and gamma-irradiation: analysis of cell survival and microdosimetry.
abstract: OBJECTIVE
  This study was designed to compare the cytotoxic effects of an alpha-emitting radioimmunoconjugate, which binds to osteosarcoma but not to bone marrow cells, with those of external gamma-irradiation.
  
  
  METHODS
  The human osteosarcoma cell line, OHS-s1, and mononuclear cells from bone marrow (BM) harvested from healthy donors, were used for these experiments. Cells in suspension were added to various activity concentrations of the anti-osteosarcoma monoclonal antibody TP-3 radiolabelled with 211At. Following incubation for 1 h, unbound radioactivity was washed off and cell survival was determined from clonogenic assays. Microdosimetry was calculated based on binding and retention kinetics of 211At to the cells, as well as cellular and nuclear diameters. For comparison, cell suspensions were irradiated with a single dose of 60Co gamma-rays.
  
  
  RESULTS
  211At-labelled TP-3 showed heterogeneous binding to OHS-s1 cells, with a considerable variation among experiments. About 78% of the initially bound 211At decayed while associated with the OHS-s1 cells. D0 values estimated by microdosimetry were 0.33 (0.22-0.48, range) Gy and 1.18 (0.89-1.89) Gy for OHS-s1 and BM cells, respectively, whereas D0 values after external beam irradiation were 0.86+/-0.07Gy and 1.71+/-0.22Gy. The relative biological effectiveness (RBE) of 211At-labelled TP-3 at 37% survival was 3.43 for OHS-s1 and 1.55 for BM.
  
  
  CONCLUSIONS
  High-LET targeted alpha-particle exposure killed osteosarcoma cells more effectively than bone marrow cells, although heterogeneous antigen expression among these tumour cells limited the magnitude of this effect.
authors.affiliation: Department of Oncology, The Norwegian Radium Hospital, Montebello, Oslo.
authors.forename: E
authors.initials: E
authors.lastname: Aurlien
authors.forename: R H
authors.initials: RH
authors.lastname: Larsen
authors.forename: G
authors.initials: G
authors.lastname: Akabani
authors.forename: D R
authors.initials: DR
authors.lastname: Olsen
authors.forename: M R
authors.initials: MR
authors.lastname: Zalutsky
authors.forename: O S
authors.initials: OS
authors.lastname: Bruland
mesh_terms: D000512:Alpha Particles; D001854:Bone Marrow Cells / Q000473:pathology* / Q000528:radiation effects*; D002470:Cell Survival / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D012516:Osteosarcoma / Q000473:pathology* / Q000532:radiotherapy*; D014407:Tumor Cells, Cultured; D014965:X-Rays