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Updated: Feb 10, 2026
Genome-Wide CRISPR Screen for Unveiling Radiosensitive and Radioresistant Genes
Published on: May 23, 2025
Genome-wide and high-density CRISPR-Cas9 screens identify point mutations in PARP1 causing PARP inhibitor resistance
Stephen J Pettitt1,2, Dragomir B Krastev1,2, Inger Brandsma1,2
1The CRUK Gene Function Laboratory, The Institute of Cancer Research, London, SW3 6JB, UK.
Abstract:
Although PARP inhibitors (PARPi) target homologous recombination defective tumours, drug resistance frequently emerges, often via poorly understood mechanisms. Here, using genome-wide and high-density CRISPR-Cas9 "tag-mutate-enrich" mutagenesis screens, we identify close to full-length mutant forms of PARP1 that cause in vitro and in vivo PARPi resistance. Mutations both within and outside of the PARP1 DNA-binding zinc-finger domains cause PARPi resistance and alter PARP1 trapping, as does a PARP1 mutation found in a clinical case of PARPi resistance. This reinforces the importance of trapped PARP1 as a cytotoxic DNA lesion and suggests that PARP1 intramolecular interactions might influence PARPi-mediated cytotoxicity. PARP1 mutations are also tolerated in cells with a pathogenic BRCA1 mutation where they result in distinct sensitivities to chemotherapeutic drugs compared to other mechanisms of PARPi resistance (BRCA1 reversion, 53BP1, REV7 (MAD2L2) mutation), suggesting that the underlying mechanism of PARPi resistance that emerges could influence the success of subsequent therapies.
Insights
New research identifies full-length mutant forms of PARP1 that cause resistance to PARP inhibitors (PARPi) in tumors. These PARP1 mutations alter drug trapping and impact subsequent cancer therapy choices.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Poly (ADP-ribose) polymerase inhibitors (PARPi) are crucial in treating homologous recombination deficient tumors.
- Drug resistance to PARPi is a significant clinical challenge, often driven by complex and poorly understood mechanisms.
Purpose of the Study:
- To identify novel mechanisms of PARPi resistance.
- To investigate the role of PARP1 mutations in acquired resistance to PARP inhibitors.
Main Methods:
- Genome-wide and high-density CRISPR-Cas9 "tag-mutate-enrich" mutagenesis screens were employed.
- Functional assays were used to assess PARPi resistance and PARP1 trapping in vitro and in vivo.
Main Results:
- Close to full-length mutant forms of PARP1 were identified as a cause of PARPi resistance.
- Mutations in PARP1, including those in DNA-binding domains and a clinically observed mutation, confer resistance by altering PARP1 trapping.
- PARP1 mutations in BRCA1-mutant cells lead to distinct drug sensitivities compared to other resistance mechanisms.
Conclusions:
- Trapped PARP1 is a critical cytotoxic DNA lesion, and its modulation by PARP1 mutations influences PARPi efficacy.
- PARP1 intramolecular interactions may play a role in PARPi-mediated cytotoxicity.
- The specific mechanism of PARPi resistance can guide the selection of subsequent therapeutic strategies.
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