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Updated: Jan 20, 2026
Genome-Wide CRISPR Screen for Unveiling Radiosensitive and Radioresistant Genes
Published on: May 23, 2025
A Genome-wide CRISPR Screen Identifies CDC25A as a Determinant of Sensitivity to ATR Inhibitors
Sergio Ruiz1, Cristina Mayor-Ruiz1, Vanesa Lafarga1
1Genomic Instability Group, Spanish National Cancer Research Centre (CNIO), Madrid 28029, Spain.
Abstract:
One recurring theme in drug development is to exploit synthetic lethal properties as means to preferentially damage the DNA of cancer cells. We and others have previously developed inhibitors of the ATR kinase, shown to be particularly genotoxic for cells expressing certain oncogenes. In contrast, the mechanisms of resistance to ATR inhibitors remain unexplored. We report here on a genome-wide CRISPR-Cas9 screen that identified CDC25A as a major determinant of sensitivity to ATR inhibition. CDC25A-deficient cells resist high doses of ATR inhibitors, which we show is due to their failure to prematurely enter mitosis in response to the drugs. Forcing mitotic entry with WEE1 inhibitors restores the toxicity of ATR inhibitors in CDC25A-deficient cells. With ATR inhibitors now entering the clinic, our work provides a better understanding of the mechanisms by which these compounds kill cells and reveals genetic interactions that could be used for their rational use.
Insights
Cancer cells with CDC25A deficiency resist ATR inhibitors by avoiding mitosis. Combining ATR and WEE1 inhibitors forces mitotic entry, restoring cancer cell toxicity and offering new therapeutic strategies.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Synthetic lethality is a key strategy in cancer drug development, targeting cancer cells by exploiting their DNA damage vulnerabilities.
- ATR kinase inhibitors are genotoxic to cancer cells with specific oncogenes, but resistance mechanisms are poorly understood.
Purpose of the Study:
- To identify mechanisms of resistance to ATR inhibitors.
- To explore genetic interactions that can overcome this resistance for improved cancer therapy.
Main Methods:
- A genome-wide CRISPR-Cas9 screen was employed to identify genes determining sensitivity to ATR inhibition.
- Cellular assays were used to assess the impact of CDC25A deficiency on ATR inhibitor efficacy and mitotic entry.
- Combination therapy studies with ATR and WEE1 inhibitors were conducted.
Main Results:
- CDC25A was identified as a major determinant of sensitivity to ATR inhibitors.
- CDC25A-deficient cells exhibit resistance to ATR inhibitors due to impaired premature mitotic entry.
- Forcing mitotic entry using WEE1 inhibitors re-sensitized CDC25A-deficient cells to ATR inhibitors.
Conclusions:
- CDC25A loss confers resistance to ATR inhibitors by preventing drug-induced mitotic catastrophe.
- Targeting WEE1 in combination with ATR inhibitors can overcome resistance in CDC25A-deficient cancers.
- These findings provide insights into rational therapeutic strategies for ATR inhibitor clinical use.
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