The uptake of 3'-deoxy-3'-[18F]fluorothymidine into L5178Y tumours in vivo is dependent on thymidine kinase 1 protein levels

Eur J Nucl Med Mol Imaging. 2005 Mar;32(3):257-63. doi: 10.1007/s00259-004-1611-0. Epub 2004 Sep 4.


Purpose: The aim of this study was to investigate the role of thymidine kinase 1 (TK1) protein in 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT) positron emission tomography (PET) studies.

Methods: We investigated the in vivo kinetics of [18F]FLT in TK1+/- and TK1-/- L5178Y mouse lymphoma tumours that express different levels of TK1 protein.

Results: [18F]FLT-derived radioactivity, measured by a dedicated small animal PET scanner, increased within the tumours over 60 min. The area under the normalised tumour time-activity curve were significantly higher for the TK1+/- compared with the -/- variant (0.89+/-0.02 vs 0.79+/-0.03 MBq ml(-1) min, P=0.043; n=5 for each tumour type). Ex vivo gamma counting of tissues excised at 60 min p.i. (n=8) also revealed significantly higher tumour [18F]FLT uptake for the TK1+/- variant (6.2+/-0.6 vs 4.6+/-0.4%ID g(-1), P=0.018). The observed differences between the cell lines with respect to [18F]FLT uptake were in keeping with a 48% higher TK1 protein in the TK1+/- tumours versus the -/- variant (P=0.043). On average, there were no differences in ATP levels between the two tumour variants (P=1.00). A positive correlation between [18F]FLT accumulation and TK1 protein levels (r=0.68, P=0.046) was seen. Normalisation of the data for ATP content further improved the correlation (r=0.86, P=0.003).

Conclusion: This study shows that in vivo [18F]FLT kinetics depend on TK1 protein expression. ATP may be important in realising this effect. Thus, [18F]FLT-PET has the potential to yield specific information on tumour proliferation in diagnostic imaging and therapy monitoring.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biomarkers, Tumor / metabolism*
  • Dideoxynucleosides / pharmacokinetics*
  • Lymphoma / diagnostic imaging*
  • Lymphoma / metabolism*
  • Male
  • Metabolic Clearance Rate
  • Mice
  • Organ Specificity
  • Radionuclide Imaging
  • Radiopharmaceuticals / pharmacokinetics
  • Thymidine Kinase / metabolism*
  • Tissue Distribution


  • Biomarkers, Tumor
  • Dideoxynucleosides
  • Radiopharmaceuticals
  • Thymidine Kinase
  • thymidine kinase 1
  • alovudine