| BackgroudAcute myeloid leukemia (AML) is a heterogeneous group of malignant clonal diseases characterized by the differentiation inhibition, uncontrolled proliferation and apoptosis resistance of neoplastic hematopoietic cells, presenting with impaired hematopoiesis and its attendant complications, such as bleeding, infection, and organ infiltration. The annual morbidity of AML is about 3-4 per 100000, causing 1.6% of cancer deaths, which is the highest in leukemia. In patients younger than 65 years old, the morbidity of AML is 2-3 per 100000, which rises to 13-15 per 100,000 in patients above the age of 65. AML can occur in people of all ages, but is most common in old patients above the age of 65. The occurrence of AML is related to infection, radiation, chemical preparation, lifestyle and heredity.A great progress has been occurred in the AML therapy over 30 years, such as the emergence of new chemotherapy drugs and immunosuppressive drugs, the constant improvement of allogeneic hematopoietic stem cell transplantation(allo-HSCT) and the new combinations of different chemotherapy drugs. Although the CR rate of AML rise from 50% to 80% by the combination of potent chemotherapy drugs, the DFS and OS is still dismal, and the 5-year survival rate is only 30%. Most of these patient’s diseases course progressed into relapsed or refractory acute myeloid leukemias (RR-AML), and some patients evens died of the poor therapeutic effects. It’s a challenge to improve therapeutic effects and prognosis of the patients with RR-AML.With the understanding of AML pathogenesis deep, it is more and more clear that the chromosome aberrations and molecular abnormalities play an important role in the occurrence and development of AML. It has been used to stratify the risk of AML and evaluate the prognosis. Otherwise, the discovery of mechanism to induce AML by these molecular abnormalities provides a new therapy, a target therapy based on abnormal gene mutations. The most important mechanism of AML occurrence is the persistent activation of the signaling pathways, which would induce of uncontrolled proliferation. While the persistent activation of the signaling pathways is a result of abnormal gene mutations. Therefore, the key of AML therapy is abnormal gene mutations.FMS-like tyrosine kinase 3(FLT3) FLT3 is a member of the class Ⅲ receptor tyrosine kinase (RTK) family. In normal human hematopoiesis, FLT3 expression is restricted to CD34+hematopoietic stem cells, immature hematopoietic progenitors and dendritic cells. The structure consists of three regions including of an extracellular domain, a transmembrane domain and an intracellular domain. The N-terminal extracellular domain consists of five immunoglobulin-like domains. The transmembrane domain is made up of some inconsecutive kinase sites. The intracellular domain contains an intracellular juxtamembrane domain (JMD) and two kinase domains located in C-terminal interrupted by a kinase insert region.FLT3 regulates proliferation, differentiation and apoptosis of cells by binding of FLT3-ligand. When mutations occurres in FLT3 gene,the protein encoded by FLT3 gene with mutations would lead to constitutive activation of the receptor-tyrosine kinase (RTK) and its downstream signaling effectors, and confer a substantial advantage of proliferation and survival to leukemic cells.FLT3 is over expressed in various acute myeloid leukemias (AML), precursor-B acute lymphoblastic leukemia (pre-B ALL), T-acute lymphoblastic leukemia(T-ALL)and chronic myelocytic leukemia(CML) in accelerated phase or blastic phase.FLT3-internal tandem duplication (ITD) mutation concentrates in exon14 and exon15 of chromosome 13 and occurs in approximately25-35% of patients with cytogenetically normal acute myeloid leukemia(CN-AML), which is the most frequent type in FLT3 mutations. The presence of ITD mutation leads to weak auto-inhibitory activity of the receptor tyrosine kinase(RTK) by changing JM domain conformation, resulting in a ligand-independent dimerization, the tyrosine kinase domain autophosphorylation and constitutive activation of the downstream signaling pathways which regulate differentiation, proliferation and apoptosis of cells, such as mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK), signal transducer and activator of transcription 5 (STAT5) and phosphatidylinositol 3-kinase (PI3K)/AKT, thus inducing inhibition of differentiation, uncontrolled proliferation and apoptosis resistance of leukemia cells.FLT3-ITD mutated AML is characterized by increased white blood cell counts, high percentages of peripheral blood (PB) and bone marrow(BM) blast cells in clinic. The most significant impact of an ITD mutation is its association with a shorter CR time after chemotherapy, increased relapse risk, decreasing disease-free survival (DFS) and decreasing overall survival (OS). Even if AML can be treat by allo-HSCT, AML would relapse in a short time, and the second CR would hardly be induced. FLAG (fludarabine, cytarabine, G-CSF) is one of the most common salvage chemotherapies. The CR rate of refractory AML treated by FLAG is 48%-55%,while the treatment related mortality (TRM) of which is only 10%-11%. And adverse reactions including of the inhibition of BM was severe during therapy. Currently, there is still no standard therapy regimen for promoting the curative effect of FLT3-ITD mutated AML.Over the 15 years, various tyrosine kinase inhibitors (TKI) have been discovered and tested preclinically, and many have shown to selectively induce cell death in FLT3 mutated AML blasts by inhibiting FLT3 autophosphorylation and downstream signaling pathways. These FLT3 inhibitors provide a new target-therapy for FLT3 mutated AML patients.Sorafenib is a multiple RTK inhibitor of FLT3,RAF kinase, the vascular endothelial growth factor receptors (VEGFR), the platelet-derived growth factor receptor (PDGFR), c-KIT and RET. It was approved for the treatment of solid tumors, especially for advanced renal cell cancer (RCC). It was also discovered that the drug was effective to hepatocellular carcinom(HCC) and melanoma.Sorafenib shows its antileukemia activity via two mechanisms. On one hand, sorafenib inhibits the activity of Raf-1 and B-Raf from aberrantly activating the downstream signaling pathways, inducing of proliferation inhibition in AML cells. On the other hand, sorafenib results in upregulation of proapoptotic Bim, Bad and Bax protein levels and decreasing Mcl-1, X-linked inhibitor of apoptosis and surviving levels, which mainly lead to the activation of the intrinsic apoptotic pathway, inducing apoptosis of leukemia cells. Sorafenib has shown the efficacy of proliferation inhibition and inducing apoptosis of leukemia cells in preclinical and phase I/II clinical trials by domestic and international scientists in patients with AML. Furthermore, sorafenib is more potent in inducing apoptosis in cells withFLT3-ITD than those with wtFLT3.Cytosine arabinoside (ara-C), a deoxycytidine analogue, is an S-phase specific anti-metabolite pyrimidine drug, which could entry into a cell via specific membrane transport proteins. Intracellularly, ara-C is sequentially phosphorylated by deoxycytidine kinase (DCK) to ara-C triphosphate (ara-CTP). Ara-CTP, the active metabolite of ara-C, can result in cell death by inhibiting DNA synthesis by competitively inhibiting DNA polymerase.It was clear that sorafenib has synergy with cytarabine. On a study in 2011, Hu.S observed that sorafenib increased the cellular accumulation of ara-CTP in AML cell lines which were treated with sorafenib and cytarabine, by enhanceing formation of ara-C to its phosphorylated metabolites or reducing cellular efflux. Compared with cells treated with cytarabine alone, the cellular accumulation of ara-CTP rose up to 3 to 5 fold in those AML cells. Beacuse the drug concentration was lower than the cytarabine-resistent RR-AML cells, it was safe and effective to use the combination therapy regimen for RR-AML. Otherwise, the study of Zhang and Ricci demonstrated that sorafenib resulted in upregulation of proapoptotic Bim, Bad and Bax protein levels and decreased Mcl-1, X-linked inhibitor of apoptosis and surviving levels, which mainly led to the activation of the intrinsic apoptotic pathway, promoting the sensitivity of cytarabine to AML cell lines and therapy effect. It is a clinical basis for treating AML by sorafenib and cytarabine.There has been abundant studies of sorafenib for FLT3-ITD and wtFLT3 mutated AML in preclinical and phase Ⅰ/Ⅱ clinical trials on abroad, while there are less studies in our country. In our study, six patients with FLT3-ITD mutated RR-AML and one patient with wtFLT3 mutated RR-AML were treated by sorafenib and low dose cytarabine to make a primary exploration on the efficacy and safety of the therapy regimen in RR-AML. It may provide a reference for the treatment of AML by sorafenib in clinic.ObjectiveTo make a primary study on the efficacy and safety of sorafenib combined with low dose cytarabine in RR-AML.Methods1. In June 2013 to April 2015, fresh bone marrow samples were obtain from patients with RR-AML at the time of hospitalization in hematology department of southern medical university zhujiang hospital. Mononuclear cells were isolated from the bone marrow samples by method of lymphocyte apart fluid and were used to extract DNA. Because FLT3-ITD mutation concentrated in exon14 and exonl5 domain, we amplified the domain by PCR. ITD mutation was analyzed by agarose gel electrophoresis(AGE).2. The clinical data, such as sex, age, blood routine examination, bone marrow cellular morpholcg, chromosome karyotype, immunophenotyping and chemotherapy regimens before sorafenib, were reviewed and used to make a statistical analysis.3. Six patients with FLT3-ITD mutated RR-AML and one patient with wtFLT3 mutated RR-AML were treated by sorafenib and low dose cytarabine. The percentages of bone marrow blast cells, blood routine, liver function, kidney function were monitored dynamically, and the clinical curative effect and adverse reactions were observed during therapy.ResultsOf seven RR-AML patients, five achieved complete remission(CR), two achieved partial remission(PR), the overall responsive rate was 100% after one course of therapy. No severe bleeding, nausea and vomiting and other side effects were found.ConclutionsSorafenib combined with low dose cytarabine efficiently induce remission of FLT3 mutated RR-AML patients with mild adverse reactions. It is well tolerated by these patients and worth of further clinical trails to verify its safty and efficiency. |
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