Abrogation of Chk1-mediated S/G2 checkpoint by UCN-01 enhances ara-C-induced cytotoxicity in human colon cancer cells

Acta Pharmacol Sin. 2004 Jun;25(6):756-62.


Aim: To investigate whether 7-hydroxystaurosporine (UCN-01) affects cell cycle progression in arabinosylcytosine (ara-C) treated human colon carcinoma HT-29 cells.

Methods: Cytotoxicity, DNA synthesis, cell cycle distribution, protein level, and kinase activity were determined by clonogenic assay, flow cytometry, DNA synthesis assay, immunoblotting, and kinase assays, respectively.

Results: UCN-01 abrogated an S/G2-phase checkpoint in HT-29 cells treated with ara-C. When UCN-01 was added after treatment with ara-C, the rate of recovery of DNA synthesis was enhanced and colony-forming ability diminished. Thus, premature recovery of DNA synthesis was associated with increased cytotoxicity. Measurements of cyclin A and B protein levels, Cdk2 and Cdc2 kinase activities, Cdc25C phosphorylation, and Chk1 kinase activity were consistent with UCN-01-induced abrogation of the S/G2-phase checkpoint in ara-C treated cells.

Conclusion: The abrogation of the S/G2 checkpoint may be due to inhibition of Chk1 kinase by UCN-01. The enhanced cytotoxicity produced when UCN-01 was combined with ara-C suggested a rationale for the use of this drug combination for tumors that might be susceptible to cell cycle checkpoint abrogation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antineoplastic Agents / pharmacology
  • CDC2-CDC28 Kinases / metabolism
  • Cell Cycle Proteins / metabolism
  • Checkpoint Kinase 1
  • Cyclin A / metabolism
  • Cyclin B / metabolism
  • Cyclin-Dependent Kinase 2
  • Cytarabine / pharmacology*
  • DNA, Neoplasm / biosynthesis
  • Drug Synergism
  • Enzyme Inhibitors / pharmacology
  • G2 Phase / drug effects*
  • HT29 Cells
  • Humans
  • Protein Kinases / metabolism*
  • S Phase / drug effects*
  • Staurosporine / analogs & derivatives*
  • Staurosporine / pharmacology*
  • cdc25 Phosphatases / metabolism


  • Antineoplastic Agents
  • Cell Cycle Proteins
  • Cyclin A
  • Cyclin B
  • DNA, Neoplasm
  • Enzyme Inhibitors
  • Cytarabine
  • 7-hydroxystaurosporine
  • Protein Kinases
  • CHEK1 protein, human
  • Checkpoint Kinase 1
  • CDC2-CDC28 Kinases
  • CDK2 protein, human
  • Cyclin-Dependent Kinase 2
  • CDC25C protein, human
  • cdc25 Phosphatases
  • Staurosporine