Sophoridine is a quinolizidine natural product and the exploration of its derivatives has been carried out,and the potent anticancer compound IMB-HDC was acquired.Although previous studies have revealed that some sophoridine derivatives could induce DNA breakage,the underlying mechanisms of inhibition of DNA damage repair (ATR inactivation) and the apoptosis independent of p53,have not been elucidated.Our research reveals a novel DNA response mechanism different from general DNA-damaging agents,and that sophoridine derivate inhibits the phosphorylation of Tyr694 and Ser780 of STAT5a to induce the lessened shuttle from the cytoplasm to the nucleus,and leads to the decreased nuclear STAT5a and subsequently inhibits the expression of STAT5a target gene RAD51 that contributes to the checkpoint activation,thus inhibiting ATR activation.Meanwhile,IMB-HDC that induced the diminished expression of STAT5a target gene contributes to proliferation and leads to apoptosis.More importantly,we give the first evidence that promoting the effect of Tyr694 phosphonylation on nuclear location and subsequent STATSa target gene transcription depends on Ser780 increased or unchanged phosphorylation and was not correlated with Ser726 phosphorylation.