Dual addressing of thymidine synthesis pathways for effective targeting of proliferating melanoma

Cancer Med. 2017 Jul;6(7):1639-1651. doi: 10.1002/cam4.1113. Epub 2017 Jun 13.


Here, we examined the potential of blocking the thymidine de novo synthesis pathways for sensitizing melanoma cells to the nucleoside salvage pathway targeting endogenous DNA irradiation. Expression of key nucleotide synthesis and proliferation enzymes thymidylate synthase (TS) and thymidine kinase 1 (TK1) was evaluated in differentiated (MITFhigh [microphthalmia-associated transcription factor] IGR1) and invasive (MITFmedium IGR37) melanoma cells. For inhibition of de novo pathways cells were incubated either with an irreversible TS inhibitor 5-fluoro-2'-deoxyuridine (FdUrd) or with a competitive dihydrofolate-reductase (DHFR) inhibitor methotrexate (MTX). Salvage pathway was addressed by irradiation-emitting thymidine analog [123/125 I]-5-iodo-4'-thio-2'-deoxyuridine (123/125 I-ITdU). The in vivo targeting efficiency was visualized by single-photon emission computed tomography. Pretreatment with FdUrd strongly increased the cellular uptake and the DNA incorporation of 125 I-ITdU into the mitotically active IGR37 cells. This effect was less pronounced in the differentiated IGR1 cells. In vivo, inhibition of TS led to a high and preferential accumulation of 123 I-ITdU in tumor tissue. This preclinical study presents profound rationale for development of therapeutic approach by highly efficient and selective radioactive targeting one of the crucial salvage pathways in melanomas.

Keywords: Auger electron emitter; endogenous radiation; malignant melanoma; nucleoside synthesis pathway; thymidylate synthase.

MeSH terms

  • Animals
  • Antineoplastic Agents / pharmacology*
  • Antineoplastic Agents / therapeutic use
  • Biomarkers
  • Biosynthetic Pathways / drug effects*
  • Biosynthetic Pathways / radiation effects
  • Cell Cycle Checkpoints / drug effects
  • Cell Cycle Checkpoints / radiation effects
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Glutathione / metabolism
  • Humans
  • Iodine Radioisotopes
  • Melanoma / diagnostic imaging
  • Melanoma / drug therapy
  • Melanoma / metabolism*
  • Melanoma / pathology
  • Mice
  • Mitosis / drug effects
  • Mitosis / genetics
  • Molecular Imaging
  • Molecular Targeted Therapy
  • Nucleosides / metabolism
  • Oxidation-Reduction
  • Radiation
  • Signal Transduction / drug effects
  • Signal Transduction / radiation effects
  • Thymidine / biosynthesis*


  • Antineoplastic Agents
  • Biomarkers
  • Iodine Radioisotopes
  • Nucleosides
  • Iodine-123
  • Glutathione
  • Thymidine