TOPORS and osteosarcoma: Using previously established chromatin fractionation–based and quantitative imaging–based assays to monitor DNMT1 DPC repair kinetics15, we found that TOPORS-knockout (KO) in independent HAP1 clones or siRNA-mediated knockdown in U2OS osteosarcoma cells strongly delayed DNMT1 DPC resolution after 5-AzadC treatment (Fig. 1c–e and Extended Data Fig. 1c–e).