title: Decreased radioiodine uptake of FRTL-5 cells after (131)I incubation in vitro: molecular biological investigations indicate a cell cycle-dependent pathway.
abstract: OBJECTIVE
  In radioiodine therapy the "stunning phenomenon" is defined as a reduction of radioiodine uptake after diagnostic application of (131)I. In the current study, we established an in vitro model based on the "Fisher rat thyrocyte cell line no. 5" (FRTL-5) to investigate the stunning.
  
  
  METHODS
  TSH-stimulated FRTL-5 cells were incubated with (131)I. Time-dependent (131)I uptake and the viability of FRTL-5 cells were evaluated at 4-144 h after radioiodine application. All data was corrected for number of viable cells, half life and (131)I concentration. Sodium iodide symporter (NIS) and the housekeeping gene (beta-actin, GAPDH) levels were quantified by quantitative polymerase chain reaction (qPCR). Additionally, immunohistochemical staining (IHC) of NIS on the cell membrane was carried out.
  
  
  RESULTS
  FRTL-5 monolayer cell cultures showed a specific maximum uptake of (131)I 24-48 h after application. Significantly decreased (131)I uptake values were observed after 72-144 h. The decrease in radioiodine uptake was correlated with decreasing mRNA levels of NIS and housekeeping genes. In parallel, unlike in controls, IHC staining of NIS on FRTL-5 cells declined significantly after (131)I long-term incubation.
  
  
  CONCLUSIONS
  It could be demonstrated that during (131)I incubation of FRTL-5 cells, radioiodine uptake decreased significantly. Simultaneously decreasing levels of NIS mRNA and protein expression suggest a NIS-associated mechanism. Since mRNA levels of housekeeping genes decreased, too, the reduced NIS expression might be provoked by a cell cycle arrest. Our investigations recommend the FRTL-5 model as a valuable tool for further molecular biological investigations of the stunning phenomenon.
authors.affiliation: Clinic of Radiology and Nuclear Medicine, University of Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany. Birgit.Meller@uk-sh.de
authors.forename: Birgit
authors.initials: B
authors.lastname: Meller
authors.forename: Erzsébet
authors.initials: E
authors.lastname: Gaspar
authors.forename: Wibke
authors.initials: W
authors.lastname: Deisting
authors.forename: Barbara
authors.initials: B
authors.lastname: Czarnocka
authors.forename: Manfred
authors.initials: M
authors.lastname: Baehre
authors.forename: Björn E
authors.initials: BE
authors.lastname: Wenzel
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000528:radiation effects*; D002460:Cell Line; D007457:Iodine Radioisotopes / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D051381:Rats; D011916:Rats, Inbred F344; D015398:Signal Transduction / Q000528:radiation effects*; D013961:Thyroid Gland / Q000378:metabolism* / Q000528:radiation effects*
chemical_list: D007457:Iodine Radioisotopes