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Shining light on drug discovery: optogenetic screening for TopBP1 biomolecular condensate inhibitors
Laura Morano1, Nadia Vie2, Adam Aissanou2
1IGH, Univ Montpellier, CNRS, Montpellier 3436, France.
Abstract:
Human topoisomerase IIβ binding protein 1 (TopBP1) is a scaffold protein involved in DNA replication initiation, DNA repair, transcription regulation, and checkpoint activation. TopBP1 forms nuclear condensates that act as a molecular switch to amplify ATR activity and promote the activation of the checkpoint effector kinase Chk1. In cancer cells, ATR activity is crucial to tolerate the intrinsically high level of DNA lesions and obstacles that block replication fork progression. Thus, ATR inhibitors are currently tested in clinical trials, often in combination with chemotherapy drugs. However, resistance and toxicity are still major issues. The weak interactions that hold TopBP1 condensates together are highly sensitive to changes in the cellular milieu, suggesting that small molecules may alter the formation of TopBP1 condensates. Here, we developed a high-throughput screening system to identify TopBP1 condensation modulators. This system allowed us to identify FDA-approved drugs, including thimerosal and quinacrine, that inhibit TopBP1 condensation and block the activation of ATR/Chk1 signaling. Mechanistically, quinacrine impaired TopBP1's ability to associate with chromatin, thereby interfering with its capacity to form condensates. Furthermore, quinacrine enhanced the therapeutic efficacy of 5-fluorouracil and irinotecan, components of the clinically used FOLFIRI regimen in a mouse model of peritoneal carcinomatosis from colorectal cancer.
Insights
FDA-approved drugs like quinacrine inhibit TopBP1 condensation, blocking ATR/Chk1 signaling. This approach enhances chemotherapy efficacy for colorectal cancer, addressing resistance and toxicity issues.
Area of Science:
- Molecular Biology
- Cancer Research
- Drug Discovery
Background:
- Topoisomerase IIβ binding protein 1 (TopBP1) is crucial for DNA replication, repair, and checkpoint activation.
- TopBP1 forms nuclear condensates that amplify ATR activity, activating Chk1 kinase, essential for cancer cell survival.
- ATR inhibitors show promise in cancer therapy but face resistance and toxicity challenges.
Purpose of the Study:
- To develop a high-throughput screening system to identify modulators of TopBP1 condensation.
- To identify FDA-approved drugs that can inhibit TopBP1 condensation and ATR/Chk1 signaling.
- To evaluate the therapeutic potential of identified TopBP1 condensation inhibitors in combination with chemotherapy.
Main Methods:
- Development of a high-throughput screening system for TopBP1 condensation modulators.
- Screening of FDA-approved drugs to identify compounds affecting TopBP1 condensation.
- Mechanistic studies on how identified drugs, like quinacrine, affect TopBP1 and ATR/Chk1 signaling.
- In vivo evaluation of drug efficacy in a preclinical colorectal cancer model.
Main Results:
- Identification of thimerosal and quinacrine as TopBP1 condensation inhibitors.
- Quinacrine was found to inhibit TopBP1 condensation by impairing chromatin association.
- Inhibition of TopBP1 condensation blocked ATR/Chk1 signaling.
- Quinacrine enhanced the efficacy of 5-fluorouracil and irinotecan in a colorectal cancer mouse model.
Conclusions:
- TopBP1 condensation is a druggable target for modulating ATR/Chk1 signaling.
- FDA-approved drugs like quinacrine can inhibit TopBP1 condensation and overcome therapeutic resistance.
- Quinacrine demonstrates potential as an adjuvant therapy to improve chemotherapy outcomes in colorectal cancer.
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