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

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Triggering cancer cell death by inducing DNA damage is the primary aim of radiation therapy; however, normal cells are also damaged. Here, we showed that delivery of only four synthetic guide RNAs (sgRNAs) 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 poly ADP-ribose polymerase (PARP) inhibitors. When recombinant Cas9-nickase protein and multiple sgRNAs were delivered with PARP inhibitors 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 PARP inhibitors with verified safety and thus is a potentially powerful tool for personalized genome-based anti-cancer therapy.