RRM2 and acute myeloid leukemia: Several RNR inhibitors are also used in anti-leukaemia therapies, such as hydroxyurea (HU) that targets RRM2 to treat chronic myeloid leukaemia (CML) and AML and the ribonucleoside analogues cytarabine and clofarabine that target RRM1 to treat acute leukaemia [23,24,25].