ATR and Ewing sarcoma: Furthermore, recent work from Nieto-Soler et al. showed, using DNA fiber analysis, that Ewing sarcoma cells exhibit elevated levels of endogenous DNA replication stress and are sensitive in vitro and in vivo to inhibitors of Ataxia Telangiectasia and Rad3-Related Protein (ATR), a kinase activated by DNA damage and impaired DNA replication [25].