Combining Multiplexed CRISPR/Cas9-Nickase and PARP Inhibitors Efficiently and Precisely Targets Cancer Cells.

Triggering cancer cell death by inducing DNA damage is the primary aim of radiotherapy; however, normal cells are also damaged. In this study, we showed that delivery of only four synthetic guide RNAs with Cas9 endonuclease efficiently induced simultaneous DNA double-strand breaks, resulting in efficient cell death in a cell type-specific manner. Off-target effects of Cas9 endonuclease were prevented by using Cas9-nickase to induce DNA single-strand breaks and blocking their repair with PARP inhibitors (PARPi). When recombinant Cas9-nickase protein and multiple synthetic guide RNAs were delivered with PARPis into cultured cells, in vivo xenografts, and patient-derived cancer organoids via lipid nanoparticles, cancer cells were unable to tolerate the induced DNA damage even in the presence of a functional BRCA2 gene. This approach has the potential to expand the use of PARPis with verified safety and thus is a potentially powerful tool for personalized genome-based anticancer therapy. SIGNIFICANCE: Targeting cancer-specific variants with CRISPR/Cas9-nickase induces cancer-specific cell death in combination with DNA repair pathway inhibitors, demonstrating the potential of CRISPR cancer therapy for treating a broad range of cancers.