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DNA Replication Dynamics and Cellular Responses to ATP Competitive CDC7 Kinase Inhibitors
Michael D Rainey1, Huong Quachthithu1, David Gaboriau1
1Centre for Chromosome Biology, School of Natural Sciences, National University of Ireland Galway H91 TK33, Ireland.
Abstract:
The CDC7 kinase, by phosphorylating the MCM DNA helicase, is a key switch for DNA replication initiation. ATP competitive CDC7 inhibitors are being developed as potential anticancer agents; however how human cells respond to the selective pharmacological inhibition of this kinase is controversial and not understood. Here we have characterized the mode of action of the two widely used CDC7 inhibitors, PHA-767491 and XL-413, which have become important tool compounds to explore the kinase's cellular functions. We have used a chemical genetics approach to further characterize pharmacological CDC7 inhibition and CRISPR/CAS9 technology to assess the requirement for kinase activity for cell proliferation. We show that, in human breast cells, CDC7 is essential and that CDC7 kinase activity is formally required for proliferation. However, full and sustained inhibition of the kinase, which is required to block the cell-cycle progression with ATP competitor compounds, is problematic to achieve. We establish that MCM2 phosphorylation is highly sensitive to CDC7 inhibition and, as a biomarker, it lacks in dynamic range since it is easily lost at concentrations of inhibitors that only mildly affect DNA synthesis. Furthermore, we find that the cellular effects of selective CDC7 inhibitors can be altered by the concomitant inhibition of cell-cycle and transcriptional CDKs. This work shows that DNA replication and cell proliferation can occur with reduced CDC7 activity for at least 5 days and that the bulk of DNA synthesis is not tightly coupled to MCM2 phosphorylation and provides guidance for the development of next generation CDC7 inhibitors.
Insights
CDC7 kinase is essential for cell proliferation, but achieving sustained inhibition is challenging. MCM2 phosphorylation is not a reliable biomarker for DNA replication inhibition by CDC7 inhibitors.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- CDC7 kinase regulates DNA replication initiation by phosphorylating the MCM helicase.
- CDC7 inhibitors are investigated as anticancer agents, but their precise cellular effects are unclear.
- Understanding the response of human cells to CDC7 inhibition is crucial for therapeutic development.
Purpose of the Study:
- To characterize the mode of action of CDC7 inhibitors PHA-767491 and XL-413.
- To investigate the cellular response to pharmacological CDC7 inhibition using chemical genetics and CRISPR/Cas9.
- To evaluate MCM2 phosphorylation as a biomarker for CDC7 inhibition and DNA replication.
Main Methods:
- Chemical genetics approach to study CDC7 inhibition.
- CRISPR/Cas9 technology to assess kinase activity requirement for proliferation.
- Analysis of MCM2 phosphorylation as a biomarker.
- Assessment of combined inhibition with cell-cycle and transcriptional CDKs.
Main Results:
- CDC7 kinase activity is essential for human breast cell proliferation.
- Sustained and complete inhibition of CDC7 is difficult to achieve with ATP-competitive inhibitors.
- MCM2 phosphorylation is a sensitive but low-dynamic-range biomarker, easily lost at low inhibitor concentrations.
- Cellular effects of CDC7 inhibitors can be modulated by co-inhibition of other CDKs.
- DNA replication and proliferation can persist for days with reduced CDC7 activity.
Conclusions:
- CDC7 is essential for proliferation, but its inhibition presents challenges for drug development.
- MCM2 phosphorylation is not a reliable indicator of DNA synthesis inhibition by CDC7 inhibitors.
- Next-generation CDC7 inhibitors require careful design considering off-target effects and biomarker validation.
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