NR2E3 and leukemia: This result might be on account of that: (1) fludarabine and cladribine both play roles in inducing cells apoptosis through inhibiting RNR and DNA stands which leading to a suppression of leukemia blasts [10, 13]; (2) Ara-C forms Ara-CTP which possesses cytotoxic effect and the produce and accumulation of Ara-CTP is greatly elevated by purine analogs including fludarabine and cladribine [4].