Exploring New Strategy And Mechanism Of Anti-Acute Myeloid Leukemia By Inducing Leukemia Cells Complete Senescence Mediated By Triptonide,A Monomer Derived From The Traditional Chinese Medicinal Herbs

Leukemia is a malignant disease in hematopoietic system with poor prognosis.During the past ten yeas,the incidence and death toll of leukemia in China was continuesly increased year by year,the leukemia patients increase approximate 10% annually in average,leukemia has become an important disease to endanger the lives and health of our people.In China,acute leukemia is more common than chronic leukemia(5.5:1).The acute myeloid leukemia(AML)is prevalent,the disease gets rapid progression,and the patients are shortly lived if the patients are not effectively treated.AML is a heterogeneous disease with multiple genes aberrant.More than 150 oncogenes have been reported to be responsible for the genesis of AML.The pathology of AML is characterized by excessive cell proliferation,differentiation blockage,apoptosis dysfunction,and senescence defect.For a long time,chemotherapy is a main approach to treat leukemia.Currectly used leukemia therapeutics mainly inhibit leukemia cell proliferation,induce cell apoptosis or differentiation;whereas,the approach to induce cell senescence for leukemia treatment has not been well explored.The most anti-AML drugs used in the clinics are low specificity,high toxicity,easy to get drug resistance,resulting in low treatment efficacy and recurrence frequently.Thus,leukemia is still a challenge to human beings,and effective anti-leukemia drugs are highly desired.In a normal person,after the bone marrow hematopoietic stem cells differentiate into different blood cell lineages and the cells carry on their duty,the differentiated cells undergo a complete senescence process,characterized by irreversible cell growth arrest,programmed cell death;eventually,the cells are iliminated by the immune system in the body.Whereas,leukemia cells usually defect in senescence,so the cells can not erter a complete senescent program,and become immortalized.Meanwhile,a part of leukemia cells become immature senescent,temporary cell cycle arrest and dormancy.Unfortunately,the dormant cells can be reactivated by various carcinogenes,cause cell uncontrolled proliferation,resulting in leukemia recurrence.At present,the drugs effectively to induce leukemia cell senescence remains lack.Facing the severe situation,we asked a scientific question,whether induction of leukemia cell senescence could effectively inhibit leukemia? Accordingly,we raise a scientific hypothesis that inducing a complete senescence of leukemia cells can effectively inhibit leukemia,and designed a series of studies to explore novel anti-leukemia agents through persuading leukemic cell complete senescence.In recent years,we used modern science and technology to explore new anti-leukemia agents from the treasure house of the traditional Chinese medicinal herbals.Using AML cell models,we found that triptonide could induce acute myeloid leukemia cell HL60 and acute monocytic leukemia cell U937 complete senescence,resulting in effective inhibition of leukemia cell growth,tumorigenicity,and exert potent anti-leukemia with very low toxicity as follows:(1)Triptonide potently inhibited growth and colony formation of HL-60 and U937 cells with IC50 values of 11.8 and 7.5 nM,respectively.In a mouse xenograft model,triptonide nearly completely suppressed human leukemia cell HL60 tumorigenicity(>99%)with very low toxicity.(2)Triptonide enlarged HL60 and U937 cell size,let the nucleus difficult to split,increased the particles in the nucleus,resulting in a typical cell senescent morphological change.In addition,triptonide boosted high activity of senescent biomarkers ?-galactosidase and formation of senescence-associated heterochromatin clusters(SAHF)in HL60 and U937 cells.(3)Mechanuistic studies revealed that triptonide reduced the expression of senescent master gene telomerase reverse transcriptase(TERT)through inhibiting TERT gene promoter activity and the amount of c-Myc,a ranscription factor responsible to promote TERT gene transcription in leukemia cells;in addition,triptonide upregulated another two senescence important genes p16 and p21 to cause cell cycle arrest and to enhace leukemia cell senescence.Furthermore,triptonide increased expression of pro-apoptotic gene DNA damage-induced transcription factor 3(DDIT3)in leukemia cells to escalate leukemia cell apoptosis by selective activation of mitogen-activated protein kinase kinase-3(MKK3)/p38 signaling pathway,leading to leukemia cell complete senescence.Collectively,triptonide induces leukemia cell complete senescence by inhibiting expression of senescence key gene TERT,increasing expression of important senescent p16 and p21 genes,and activating the MKK3-p38-DDIT3 signaling pathway in leukemia cells,resulting in an effective anti-leukemia effect.Our study provide the solid data to support our scientific hypothesis that inducing a complete senescence of leukemia cells can effectively inhibit leukemia,providing new strategy and drug candidates for novel anti-leukemia therapy.