Simultaneous Inhibition Of Mcl-1 And Induction Of DNA Damage By Chidamide Potentiates The Cytotoxicity Of ABT-199 In AML

Acute myeloid leukemia(AML)is a hematologic malignancy originated from clonal disorder of myeloid hematopoietic stem cells.It is characterized by the uncontrolled rapid proliferation of myeloid primitive cells.In spite of the advancement of therapeutic strategies,which led to a 65%?75%complete remission rate in adult AML patients,five-year survival rate in patients with AML is only 27.4%.According to the European database,the relapse rate of AML patients younger than 60 years old is up to 35%(low-risk stratification)?80%(high-risk stratification),while that of patients older than 60 years old is up to 60%?85%.Most patients will experience relapse and thus results in poor clinical outcomes.Meanwhile,side effects of severe infection and bleeding caused by conventional chemotherapy(i.e.,Cytarabine and Daunorubicin)also significantly affect the survival duration of patients with AML.Many patients die from the complications of chemotherapy rather than disease itself.Therefore,agents used in clinic that targeting different targets and different signal pathways should be combined with each other in order to find the most reasonable,precise,eutherapeutic therapeutic strategies,and thus maximize the therapeutic benefit of patients with AML.It is no doubt that elimination of leukemia cells effectively while spare normal hematopoietic cells has very important significance and broad application prospect.Recently,the development of Bcl-2 selective inhibitor(e.g.,ABT-199)attracts increasing attentions in the treatment of hematologic malignancy.Previous works have demonstrated that ABT-199 could selectively target Bcl-2 family and thus effectively and safely induces apoptosis in leukemia cells.However,acquired resistance after ABT-199's exposure via compensatory elevated other anti-apoptotic proteins tremendously enlarges the defect of no affinity for Mcl-1 of ABT-199,which become the Achilles's heel of ABT-199 in clinical use.Previous studies have shown that epigenetic regulation plays an important role in the occurrence and development of AML.In our previous findings,we found that histone deacetylase inhibitors(HDACi)Chidamide selectively killed AML stem/progenitor cells via disturbance of DNA damage repair response caused by chromatin modification.Meanwhile,it was reported that Chidamide activated the p53 pathway and thus down-regulated the expression of Mcl-1,suggesting that Chidamide in combination with ABT-199 might present the synergistic potential to target AML cells.First,we confirm that low-cytotoxicity dose of Chidamide combined with ABT-199 exerts significant anti-AML property in AML cells,reflected by apoptosis induction,cell cycle arrest,proliferation inhibition,in a time-and dose-dependent manner.With the prolongation of treatment,viable leukemia cells gradually died out within 72 hrs.Meanwhile,the clonogenicity ability of AML cells would be remarkably impaired after drug withdrawal.Second,the in vivo anti-leukemia property of Chidamide/ABT-199 is further confirmed by a AML cell line mouse model and a PDX model generated from a refractory/relapse AML patient carrying FLT3-ITD mutation.Third,our results also imply that Chidamide/ABT-199 effectively kills primary AML myeloblasts,especially those with hyperleukocytosis,as well as the CD34+CD38-AML stem/progenitor cells,while sparing normal hematopoietic progenitor cells.Last,we also demonstrate that the anti-AML ability of low-cytotoxicity dose of Chidamide in combination with ABT-199 is mechanistically associated with inactivation of Mcl-1 and simultaneous induction of DNA damage accumulation,as well as the exacerbation of ABT-199-induced loss of mitochondrial membrane potential.Taken together,our study sheds light on a novel and potent drug combination of Chidamide combined with ABT-199.which exhibits a robust and broad anti-AML activity both in vitro and in vivo against AML cell lines and primary cells.Mechanistically,in addition to inactivation of Mcl-1,induction of DNA damage accumulation and intrinsic apoptotic pathway might also contribute to the anti-leukemia activity of Chidamide/ABT-199.Therefore,the present study provides a theoretical and solid basis for the clinical translation and future clinical trial of Chidamide combined with ABT-199 in the treatment of patients with AML.