Simultaneous CRISPR/Cas9-induced double-strand breaks are lethal in models of pancreatic cancer

While radiation is an effective oncologic therapy, killing cancer by inducing DNA double-strand breaks (DSBs), it lacks specificity for neoplastic cells. We have previously adapted the CRISPR/Cas9 gene-editing technology as a cancer-specific treatment modality targeting somatic mutations in pancreatic cancer (PC). However, its tumoricidal potential remains unclear, especially in comparison with therapeutic doses of radiation. Here, we demonstrate that CRISPR/Cas9-induced DSBs are more cytotoxic in PCs than a comparable number of radiation-induced DSBs. We observed more than 90% tumor growth inhibition by targeting 9 sites with cancer-specific sgRNAs. Through both bioinformatics and cytogenetics analyses, we found that CRISPR/Cas9-induced DSBs triggered ongoing chromosomal rearrangements, with 87% of structural variants not directly produced from the initial CRISPR/Cas9-induced DSBs, and chromosomal instability peaking before cell death. By comparing the cytotoxicity of CRISPR/Cas9- and radiation-induced DSBs, we demonstrated that the number of DSBs required to achieve equitoxic effects was approximately 3 times higher for radiation than CRISPR/Cas9. Finally, we showed that PC cells that had survived CRISPR/Cas9 targeting retained susceptibility to subsequent CRISPR/Cas9-induced DSBs at different genomic sites with more than 87% growth inhibition. Together, our data support the therapeutic potential of CRISPR/Cas9 as an anticancer strategy.