title: Transfectant mosaic spheroids: a new model for evaluation of tumour cell killing in targeted radiotherapy and experimental gene therapy.
abstract: BACKGROUND
  We describe an in vitro tumour model for targeted radiotherapy and gene therapy that incorporates cell population heterogeneity.
  
  
  METHODS
  Transfectant mosaic spheroids (TMS) and transfected mosaic monolayers (TMM) are composed of two cell populations derived from a single cell line. The cells of one population were transfected with the noradrenaline transporter gene (NAT), allowing active uptake of a radiolabelled targeting agent meta-[131I]iodobenzylguanidine ([131I]MIBG); the other population of cells was derived from the same parent line and transfected with a marker gene - green fluorescent protein (GFP). After treatment with [131I]MIBG, cell kill was determined in TMM by clonogenic assay and in TMS by clonogenic assay and spheroid growth delay.
  
  
  RESULTS
  We have used the TMS model to assess the 'radiological bystander effect' (radiation cross-fire) conferred by the beta-emitting radiopharmaceutical [131I] MIBG whose cellular uptake is facilitated by the transfected gene encoding NAT. We show that cell killing by [131I]MIBG in both TMS and TMM cultures increased in direct proportion to the fraction of NAT-transfected cells and that the degree of cell killing against fraction transfected was greater in TMS, suggestive of a greater bystander effect in the three-dimensional culture system.
  
  
  CONCLUSIONS
  TMS provide a useful model for assessment of the effectiveness of targeted radiotherapy in combination with gene therapy when less than 100% of the target cell population is expressing the NAT transgene. Further, this novel model offers the unique opportunity to investigate radiation-induced bystander effects and their contribution to cell cytotoxicity in radiotherapy and other gene therapy applications.
authors.affiliation: Department of Radiation Oncology, Glasgow University, CRC Beatson Laboratories, Glasgow, Scotland. gpma55@udcf.gla.ac.uk
authors.forename: M
authors.initials: M
authors.lastname: Boyd
authors.forename: S C
authors.initials: SC
authors.lastname: Mairs
authors.forename: K
authors.initials: K
authors.lastname: Stevenson
authors.forename: A
authors.initials: A
authors.lastname: Livingstone
authors.forename: A M
authors.initials: AM
authors.lastname: Clark
authors.forename: S C
authors.initials: SC
authors.lastname: Ross
authors.forename: R J
authors.initials: RJ
authors.lastname: Mairs
mesh_terms: D019797:3-Iodobenzylguanidine / Q000378:metabolism; D016923:Cell Death / Q000235:genetics / Q000528:radiation effects; D005434:Flow Cytometry; D015316:Genetic Therapy; D005910:Glioma / Q000235:genetics* / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D007457:Iodine Radioisotopes / Q000378:metabolism / Q000633:toxicity; D009030:Mosaicism / Q000235:genetics*; D018874:Spheroids, Cellular
chemical_list: D007457:Iodine Radioisotopes; D019797:3-Iodobenzylguanidine