Single-Stranded DNA Gap Accumulation Is a Functional Biomarker for USP1 Inhibitor Sensitivity

Area of Science:

• Genetics
• Molecular Biology
• Oncology

Background:

• BRCA1 deficiency in tumors creates synthetic lethality vulnerabilities.
• PARP and POLQ inhibitors exploit these vulnerabilities by inducing DNA damage.
• USP1 inhibitors are emerging as a therapeutic strategy for BRCA1-deficient cancers.

Purpose of the Study:

• To investigate the mechanism of USP1 inhibitors in BRCA1-deficient cells.
• To determine if USP1 inhibition induces single-stranded DNA (ssDNA) gaps.
• To evaluate USP1 inhibitors as a predictive biomarker for treatment response.

Main Methods:

• Treatment of BRCA1-deficient cells and xenograft models with USP1 inhibitors.
• Assessment of ssDNA gap accumulation and proliferating cell nuclear antigen (PCNA) ubiquitination.
• Evaluation of drug resistance and synergistic effects with PARP and POLQ inhibitors.
• Analysis of patient-derived ovarian tumor organoids for sensitivity and ssDNA gap correlation.

Main Results:

• USP1 inhibition induced ssDNA gaps in BRCA1-deficient cells, correlating with drug sensitivity.
• USP1 inhibition increased monoubiquitinated PCNA, mediated by RAD18.
• RAD18 knockdown conferred resistance to USP1 inhibitors and reduced ssDNA gaps.
• USP1 inhibition overcame PARP inhibitor resistance and showed synergy with PARP and POLQ inhibitors.
• Sensitivity in ovarian tumor organoids correlated with ssDNA gap accumulation.

Conclusions:

• USP1 inhibitors induce synthetic lethality in BRCA1-deficient cells via ssDNA gap accumulation.
• USP1 inhibition is a promising therapeutic strategy, potentially overcoming resistance to other inhibitors.
• ssDNA gap assessment serves as a predictive biomarker for USP1 inhibitor efficacy in clinical trials.