Fig. 7

In vivo FEN1/DNA-PKcs Synthetic Lethality. a Schematic representation of sc-13 or/NU-7441 therapy experiment in mice bearing established Luciferase-U87 xenografts. Mice were then randomized to treatment cohorts of either sc-13 (5 mg/kg, every other day by i.v injection) or/and NU-7441 (10 mg/kg, every other day by i.v injection) or vehicle treatments. n = 10 mice in each cohort. Mice were treated for a subsequent 28 days. Tumor volume was detected by bioluminescence imaging weekly. b Representative bioluminescence imaging of each cohort at different time point. c ROI levels indicating reduced tumor size of sc-13 or/and NU-7441 treated mice. d Surviving fraction of each group was shown. e Tumor structure shown by H&E staining and Ki67 labeling. Expression of TUNEL, RAD51, BRCA1 and PARP1 staining determined by IHC assay in mice tumor tissue. f-j Quantitation of indicated protein in mice samples. k Model for Tumor evolution process indicating DNA-PKcs deficient glioma cells relied on FEN1-upregulated signaling pathway and survived from DNA replication stress and drug stress selection. l In response to replication stress, remodeling of stalled forks generate a regressed arm that form a “chicken foot” structure containing. FEN1, through stabilize and promoting BRCA1 and RAD51 assembling to the nascent strand resulting in limited nucleolytic processing of the regressed arm by MRE11. Meanwhile, by associating with WRN, FEN1-WRN complex restored the stalled forks and prevent MRE11 mediated unlimited fork degradation, ensuring stalled forks restart. DNA-PKcs, another required factor for stalled forks protection and restart, associates with PARP1 and assembled to none MRE11 resected forks promoting stalled forks degradation. Loss of FEN1 and DNA-PKcs, nascent strands at reversed forks are subjected to over-resection by MRE11, resulting in fork degradation, breakage, genomic instability and ultimately causing synthetic lethal. A two-sided unpaired t test was used to calculate P-values. NS: not significant: P > 0.05