Characterizing the WRN DNA Helicase in Prostate Cancer and Implications for Microsatellite Unstable Metastatic Prostate Cancers

Abstract

Prostate cancer is the most common non-skin malignancy in men worldwide and the second most common cause of cancer mortality in men. Metastatic prostate cancer (mPC) is highly heterogenous and enriched for aberrations in genes involved in DNA repair, the loss of which generates further genetic alterations and genomic instability that ultimately promotes tumorigenesis. The DNA Helicase-Exonuclease RECQL2 protein, commonly referred to as WRN, plays an integral role in DNA repair by regulating the dynamics of the replication fork. WRN is lost along the 8p chromosomal arm in 10% of prostate cancers; however, the role of WRN in mPC remains unclear. WRN has also been established as a promising target for synthetic lethality in mismatch repair deficient (MMRd) cancer cells with microsatellite instability (MSI), an aggressive subtype of metastatic disease that promotes oncogenesis via genome hypermutability. We aimed to identify the prognostic value of WRN-specific copy loss in mPC patient tumors as well as investigate the sensitivity of MSI-mPC cell models to engineered WRN knockdown. We first showed that adverse outcomes are associated with WRN copy number status in mPC, and connect mutual exclusivity between loss of WRN and mismatch repair deficient tumors using large scale clinical datasets. Then, we tested the sensitivity to WRN inhibitor NSC 19630 in the LUCaP PDX xenograft lines, and found marked sensitivity in tumor lines with DNA Repair Deficiency (DRD). Further, we demonstrated that MSI prostate cancer cells are indeed sensitive to WRN loss over time. Finally, using quantified confocal imaging, we showed that tertiary DNA secondary structures at GC rich regions, known as G-Quadruplexes, are associated with replicative stress in MMRd-MSI cells and are themselves a promising target for chemotherapeutics. Together, this work expands the knowledge of DRD heterogeneity in mPC and provides novel insight into the molecular mechanisms of WRN sensitivity in MSI cells.