p21 limits S phase DNA damage caused by the Wee1 inhibitor MK1775

Cell Cycle. 2019 Apr;18(8):834-847. doi: 10.1080/15384101.2019.1593649. Epub 2019 Apr 3.


The Wee1 inhibitor MK1775 (AZD1775) is currently being tested in clinical trials for cancer treatment. Here, we show that the p53 target and CDK inhibitor p21 protects against MK1775-induced DNA damage during S-phase. Cancer and normal cells deficient for p21 (HCT116 p21-/-, RPE p21-/-, and U2OS transfected with p21 siRNA) showed higher induction of the DNA damage marker γH2AX in S-phase in response to MK1775 compared to the respective parental cells. Furthermore, upon MK1775 treatment the levels of phospho-DNA PKcs S2056 and phospho-RPA S4/S8 were higher in the p21 deficient cells, consistent with increased DNA breakage. Cell cycle analysis revealed that these effects were due to an S-phase function of p21, but MK1775-induced S-phase CDK activity was not altered as measured by CDK-dependent phosphorylations. In the p21 deficient cancer cells MK1775-induced cell death was also increased. Moreover, p21 deficiency sensitized to combined treatment of MK1775 and the CHK1-inhibitor AZD6772, and to the combination of MK1775 with ionizing radiation. These results show that p21 protects cancer cells against Wee1 inhibition and suggest that S-phase functions of p21 contribute to mediate such protection. As p21 can be epigenetically downregulated in human cancer, we propose that p21 levels may be considered during future applications of Wee1 inhibitors.

Keywords: CDK activity; DNA damage; Wee1 kinase; cancer treatment; checkpoint kinase inhibition; p21 (Cip1/Waf1).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Antineoplastic Agents / therapeutic use
  • Cell Cycle Proteins / antagonists & inhibitors*
  • Cell Survival / drug effects
  • Cell Survival / genetics
  • Cell Survival / radiation effects
  • Checkpoint Kinase 1 / antagonists & inhibitors
  • Cyclin-Dependent Kinase Inhibitor p21 / genetics
  • Cyclin-Dependent Kinase Inhibitor p21 / metabolism*
  • Cyclin-Dependent Kinases / antagonists & inhibitors
  • Cyclin-Dependent Kinases / metabolism
  • DNA Damage / drug effects*
  • DNA Damage / genetics
  • HCT116 Cells
  • Humans
  • Neoplasms / drug therapy
  • Neoplasms / metabolism*
  • Phosphorylation / drug effects
  • Protein-Tyrosine Kinases / antagonists & inhibitors*
  • Pyrazoles / pharmacology*
  • Pyrazoles / therapeutic use
  • Pyrimidinones / pharmacology*
  • Pyrimidinones / therapeutic use
  • RNA, Small Interfering / genetics
  • S Phase Cell Cycle Checkpoints / drug effects*
  • Transfection


  • Antineoplastic Agents
  • CDKN1A protein, human
  • Cell Cycle Proteins
  • Cyclin-Dependent Kinase Inhibitor p21
  • Pyrazoles
  • Pyrimidinones
  • RNA, Small Interfering
  • Protein-Tyrosine Kinases
  • WEE1 protein, human
  • CHEK1 protein, human
  • Checkpoint Kinase 1
  • Cyclin-Dependent Kinases
  • adavosertib

Grant support

This research was supported by grants from The Norwegian Cancer Society (62320, 198018), South-Eastern Norway Regional Health Authority (2016114) and the EEA Czech-Norwegian Research Programme -Norwegian Financial Mechanism 2009-2014 (PHOSCAN, 7F14061). LM was supported by the Grant Agency of the Czech Republic (17-04742S).