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Neutrophils Alter DNA Repair Landscape to Impact Survival and Shape Distinct Therapeutic Phenotypes of Colorectal Cancer.

BACKGROUND & AIMS
Tumor-infiltrating neutrophils (PMNs) are a prominent feature of colorectal cancer (CRC), where they can promote cytotoxicity or exacerbate disease outcomes. We recently showed that in acute colon injury, PMNs can increase DNA double-strand breaks (DSB) burden and promote genomic instability via microRNA-dependent inhibition of homologous recombination (HR) repair. In this study, we aimed to establish whether in inflamed colon, neutrophils shape the DSB-repair responses to impact CRC progression and sensitivity/resistance to DNA-repair targeted therapy.


METHODS
Human sporadic CRC biopsies, TCGA gene expression analyses, tumor xenografts and murine CRC models, as well as small-molecule inhibition of key DSB-repair factors were leveraged to investigate changes in the DSB-repair landscape and identify unique CRC responses with/without tumor-infiltration by PMNs.


RESULTS
We reveal that neutrophils exert a functional dualism in cancer cells, driving temporal modulation of the DNA damage landscape and resolution of DSBs. PMNs were found to promote HR-deficiency in low-grade CRC by miR-155-dependent downregulation of RAD51, thus attenuating tumor growth. However, neutrophil-mediated genotoxicity due to accumulation of DSBs led to the induction of non-homologous end-joining (NHEJ), allowing for survival and growth of advanced CRC. Our findings identified a PMN-induced HR-deficient CRC phenotype, featuring low RAD51 and low Ku70 levels, rendering it susceptible to synthetic lethality induced by clinically approved PARP1 inhibitor Olaparib. We further identified a distinct PMN-induced HR-deficient CRC phenotype, featuring high Ku70 and heightened NHEJ, which can be therapeutically targeted by specific inhibition of NHEJ.


CONCLUSIONS
Our work delineates two mechanism-based translatable therapeutic interventions in sporadic CRC.