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Selective inhibition of the DNA-dependent protein kinase (DNA-PK) by the radiosensitizing agent caffeine

Wesley D Block1, Dennis Merkle, Katheryn Meek

  • 1Department of Biological Sciences, Cancer Biology Research Group, University of Calgary, 3330 Hospital Drive N.W., Calgary AB, T2N 4N1, Canada.

Nucleic Acids Research
|April 3, 2004
PubMed

Insights

Caffeine inhibits DNA-PK activity, a key enzyme in DNA repair. However, it does not appear to be the primary target for caffeine

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Radiation Oncology

Background:

  • Caffeine is known to inhibit cell cycle checkpoints and sensitize cells to radiation.
  • It inhibits ATM and ATR kinases, crucial for DNA damage response.
  • Caffeine's effect on DNA-dependent protein kinase (DNA-PK), vital for DNA double-strand break repair, is less understood.

Purpose of the Study:

  • To investigate caffeine's effect on DNA-PK activity and its role in DNA repair.
  • To determine if DNA-PK is a target of caffeine-induced radiosensitization.

Main Methods:

  • Assessed caffeine's inhibition of DNA-PK phosphorylation of RPA32 in response to camptothecin.
  • Measured DNA-PK activity in immunoprecipitated, purified, and cell extracts using varying caffeine concentrations.
  • Determined the mechanism of inhibition and evaluated caffeine's effect on DNA-PK autophosphorylation and double-strand break repair in vivo.

Main Results:

  • Caffeine (2 mM) inhibited camptothecin-induced RPA32 phosphorylation on Thr21.
  • Caffeine inhibited DNA-PK activity with an IC50 of 0.2-0.6 mM via mixed non-competitive inhibition.
  • Higher caffeine concentrations were needed to inhibit DNA-PK autophosphorylation, and it did not inhibit DNA-PKcs-dependent repair in vivo.

Conclusions:

  • DNA-PK is inhibited by caffeine in vitro, suggesting it is not the primary target of caffeine-induced radiosensitization.
  • Caffeine's inhibitory effects on DNA-PK do not translate to impaired double-strand break repair in vivo.
  • Caffeine cannot be used to selectively differentiate between ATM, ATR, and DNA-PK-dependent substrate phosphorylation in cellular contexts.

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