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Published on: August 12, 2015
A high-throughput approach to identify BRCA1-downregulating compounds to enhance PARP inhibitor sensitivity
Erin Sellars1,2, Margarita Savguira1, Jie Wu1
1Department of Pharmacology & Toxicology, University of Toronto, Toronto, ON M5S 1A8, Canada.
Abstract:
PARP inhibitors (PARPi) are efficacious in BRCA1-null tumors; however, their utility is limited in tumors with functional BRCA1. We hypothesized that pharmacologically reducing BRCA1 protein levels could enhance PARPi effectiveness in BRCA1 wild-type tumors. To identify BRCA1 downregulating agents, we generated reporter cell lines using CRISPR-mediated editing to tag endogenous BRCA1 protein with HiBiT. These reporter lines enable the sensitive measurement of BRCA1 protein levels by luminescence. Validated reporter cells were used in a pilot screen of epigenetic-modifying probes and a larger screen of more than 6,000 compounds. We identified 7 compounds that could downregulate BRCA1-HiBiT expression and synergize with olaparib. Three compounds, N-acetyl-N-acetoxy chlorobenzenesulfonamide (NANAC), A-443654, and CHIR-124, were validated to reduce BRCA1 protein levels and sensitize breast cancer cells to the toxic effects of olaparib. These results suggest that BRCA1-HiBiT reporter cells hold promise in developing agents to improve the clinical utility of PARPi.
Insights
Researchers developed a new method to identify drugs that can lower BRCA1 protein levels, potentially making PARP inhibitors more effective against BRCA1 wild-type cancers. This discovery could improve cancer treatment options.
Area of Science:
- Oncology
- Molecular Biology
- Drug Discovery
Background:
- PARP inhibitors (PARPi) show efficacy in BRCA1-null tumors but limited utility in BRCA1 wild-type tumors.
- Reducing BRCA1 protein levels is a potential strategy to enhance PARPi effectiveness in BRCA1 wild-type cancers.
Purpose of the Study:
- To identify novel agents capable of downregulating BRCA1 protein levels.
- To enhance the efficacy of PARP inhibitors in BRCA1 wild-type tumors.
Main Methods:
- CRISPR-mediated editing was used to create BRCA1-HiBiT reporter cell lines for sensitive protein level measurement.
- Reporter cells underwent screening of epigenetic modifiers and over 6,000 compounds.
- Validated compounds were tested for their ability to reduce BRCA1 protein and sensitize cells to olaparib.
Main Results:
- Seven compounds were identified that downregulated BRCA1-HiBiT expression and synergized with olaparib.
- N-acetyl-N-acetoxy chlorobenzenesulfonamide (NANAC), A-443654, and CHIR-124 were validated to reduce BRCA1 protein levels.
- These compounds sensitized breast cancer cells to olaparib's cytotoxic effects.
Conclusions:
- BRCA1-HiBiT reporter cells are a promising tool for developing agents to improve PARPi clinical utility.
- Pharmacological reduction of BRCA1 protein may overcome resistance to PARPi in BRCA1 wild-type cancers.
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