Surprisingly, thioparib strongly, and in a concentration‐dependent manner, inhibited HR activity in U2OS‐DR‐GFP human osteosarcoma cell lines, as measured by the direct repeat (DR)‐GFP reporter assay, in which the ATR inhibitor VE‐821 was used as a positive control (Fig 5A). This evidence concerns the gene ATR and osteosarcoma.