Relationship of In Vitro Toxicity of Technetium-99m to Subcellular Localisation and Absorbed Dose

Int J Mol Sci. 2021 Dec 15;22(24):13466. doi: 10.3390/ijms222413466.


Auger electron-emitters increasingly attract attention as potential radionuclides for molecular radionuclide therapy in oncology. The radionuclide technetium-99m is widely used for imaging; however, its potential as a therapeutic radionuclide has not yet been fully assessed. We used MDA-MB-231 breast cancer cells engineered to express the human sodium iodide symporter-green fluorescent protein fusion reporter (hNIS-GFP; MDA-MB-231.hNIS-GFP) as a model for controlled cellular radionuclide uptake. Uptake, efflux, and subcellular location of the NIS radiotracer [99mTc]TcO4- were characterised to calculate the nuclear-absorbed dose using Medical Internal Radiation Dose formalism. Radiotoxicity was determined using clonogenic and γ-H2AX assays. The daughter radionuclide technetium-99 or external beam irradiation therapy (EBRT) served as controls. [99mTc]TcO4- in vivo biodistribution in MDA-MB-231.hNIS-GFP tumour-bearing mice was determined by imaging and complemented by ex vivo tissue radioactivity analysis. [99mTc]TcO4- resulted in substantial DNA damage and reduction in the survival fraction (SF) following 24 h incubation in hNIS-expressing cells only. We found that 24,430 decays/cell (30 mBq/cell) were required to achieve SF0.37 (95%-confidence interval = [SF0.31; SF0.43]). Different approaches for determining the subcellular localisation of [99mTc]TcO4- led to SF0.37 nuclear-absorbed doses ranging from 0.33 to 11.7 Gy. In comparison, EBRT of MDA-MB-231.hNIS-GFP cells resulted in an SF0.37 of 2.59 Gy. In vivo retention of [99mTc]TcO4- after 24 h remained high at 28.0% ± 4.5% of the administered activity/gram tissue in MDA-MB-231.hNIS-GFP tumours. [99mTc]TcO4- caused DNA damage and reduced clonogenicity in this model, but only when the radioisotope was taken up into the cells. This data guides the safe use of technetium-99m during imaging and potential future therapeutic applications.

Keywords: auger electron therapy; dosimetry; molecular radionuclide therapy; radiobiology; sodium iodide symporter; technetium; triple-negative breast cancer cells.

MeSH terms

  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism
  • Cell Line, Tumor
  • Dose-Response Relationship, Radiation
  • Humans
  • Iodine Radioisotopes / pharmacology
  • Radiopharmaceuticals / pharmacology
  • Symporters / genetics
  • Technetium / pharmacokinetics*
  • Technetium / pharmacology*
  • Tissue Distribution


  • Iodine Radioisotopes
  • Radiopharmaceuticals
  • Symporters
  • Technetium-99
  • sodium-iodide symporter
  • Technetium