Mechanism of delayed cell death following simultaneous CRISPR-Cas9 targeting in pancreatic cancers

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 to 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 >90% tumor growth inhibition by targeting 9 sites with cancer-specific single-guide RNAs (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 (CIN) peaking before cell death. By comparing the cytotoxicity of CRISPR-Cas9- to radiation-induced DSBs, we demonstrate that the number of DSBs required to achieve equitoxic effects was [~]3 times higher for radiation than CRISPR-Cas9. Finally, we show that PC cells that had survived CRISPR-Cas9 targeting retained susceptibility to subsequent CRISPR-Cas9-induced DSBs at different genomic sites with >87% growth inhibition. Together, our data support the therapeutic potential of CRISPR-Cas9 as an anti-cancer strategy.