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Unique functions of CHK1 and WEE1 underlie synergistic anti-tumor activity upon pharmacologic inhibition

Amy D Guertin1, Melissa M Martin2, Brian Roberts3, Melissa Hurd4, Xianlu Qu5, Nathan R Miselis5, Yaping Liu6, Jing Li6, Igor Feldman7, Yair Benita7, Andrew Bloecher1, Carlo Toniatti8 and Stuart D Shumway1*

Author Affiliations

1 Department of Oncology, Merck Research Laboratories, 33 Avenue Louis Pasteur, Boston, MA 02115, USA

2 Amgen, One Amgen Center Drive, Thousand Oaks, CA, 91320, USA

3 Hudson Alpha Institute, 2117 Shades Crest Road SE, Huntsville, AL, 35801, USA

4 Department of In Vivo Pharmacology, Merck Research Laboratories, 33 Avenue Louis Pasteur, Boston, MA, 02115, USA

5 Molecular Biomarkers, Merck Research Laboratories, 33 Avenue Louis Pasteur, Boston, MA, 02115, USA

6 Screening and Protein Sciences, Merck Research Laboratories, North Wales, 19454, USA

7 Informatics and Analysis, Merck Research Laboratories, 33 Avenue Louis Pasteur, Boston, MA, 02115, USA

8 Institute for Applied Cancer Science, 1901 East Rd., Unit 1956 Room 4SCR6.1009, Houston, TX, 77054, USA

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Cancer Cell International 2012, 12:45  doi:10.1186/1475-2867-12-45

Published: 13 November 2012



Inhibition of kinases involved in the DNA damage response sensitizes cells to genotoxic agents by abrogating checkpoint-induced cell cycle arrest. CHK1 and WEE1 act in a pathway upstream of CDK1 to inhibit cell cycle progression in response to damaged DNA. Therapeutic targeting of either CHK1 or WEE1, in combination with chemotherapy, is under clinical evaluation. These studies examine the overlap and potential for synergy when CHK1 and WEE1 are inhibited in cancer cell models.


Small molecules MK-8776 and MK-1775 were used to selectively and potently inhibit CHK1 and WEE1, respectively.


In vitro, the combination of MK-8776 and MK-1775 induces up to 50-fold more DNA damage than either MK-8776 or MK-1775 alone at a fixed concentration. This requires aberrant cyclin-dependent kinase activity but does not appear to be dependent on p53 status alone. Furthermore, DNA damage takes place primarily in S-phase cells, implying disrupted DNA replication. When dosed together, the combination of MK-8776 and MK-1775 induced more intense and more durable DNA damage as well as anti-tumor efficacy than either MK-8776 or MK-1775 dosed alone. DNA damage induced by the combination was detected in up to 40% of cells in a treated xenograft tumor model.


These results highlight the roles of WEE1 and CHK1 in maintaining genomic integrity. Importantly, the strong synergy observed upon inhibition of both kinases suggests unique yet complimentary anti-tumor effects of WEE1 and CHK1 inhibition. This demonstration of DNA double strand breaks in the absence of a DNA damaging chemotherapeutic provides preclinical rationale for combining WEE1 and CHK1 inhibitors as a cancer treatment regimen.