Possible Mechanism Of Decitabine Enhancing Cytotoxic Drugs To Treat Acute Myeloid Leukemia

Background and Aim:Acute myeloid leukemia is a type of abnormal clonal proliferation of bone marrow cells derived from hematopoietic stem cell genetic and epigenetic changes. The proliferation, differentiation and self-renewal of bone marrow cells appear disordered and the proportion of original cells is increased leading to the formation of hematopoietic dysfunction. Epigenetic mechanism can influence the chromatin structure by regulating gene expression and ensuring genetic information, which is the key regulation of normal gene expression of healthy cells, tissues and organs. Epigenetic changes may result in changes in gene expression and DNA methylation is the most common one. At present, the standard treatment of AML is anthracycline combined with cytarabine. Actually the up-regulation of DNA methyltransferase-1 is a feature of AML. 5-aza-2 deoxycytidine is one of demethylation agents, which has a dual mechanism of action: firstly,it can activate the silence of anti-oncogenes and promote cell differentiation by low concentration;secondly, it can suppress DNA synthesis and play a role of cytotoxicity by high concentration.The issue of DAC is so much concerned that it has aroused a wide discussion,especially DAC comibined with other chemotherapy regimens in relapsed and refractory or elderly myeloid leukemia patients, like homoharringtonine comibined with cytarabine or homoharringtonine comibined with cytarabine and granulocyte colony-stimulating factor, and achieved a high remission rate. This study was designed to compare the efficacy and adverse effects of reduced idarubicin or reduced homoharringtonine combined with cytarabine(IA regimen vs HA regimen) for the treatment of de novo acute myeloid leukemia and investigate the possible mechanism of decitabin enhancing cytotoxic drugs to resist myeloid leukemia.Methods:(1)We collected from 1st,January, 2013 to 30 th,June, 2015 of de novo AML patients treated with reduced dose of idarubicin or homoharringtonine combined with cytarabine as initial induction in Xijing hospital to compare their the efficacies and adverse reactions, except for the acute promyelocytic leukemia patients;(2)We performed MTT assay to assess the proliferation of myeloid HL-60 cell line after the decitabine and/or homoharringtonine treatment;(3)The rate of ?-catenin expression in cytoplasm and cell cycle distribution were analyzed by flow cytometry;(4) We utilized the Western Blot to probe the protein expressions of ?-catenin in cytoplasm and nucleus;(5) The localization of ?-catenin in cytoplasm and nucleus treatment was measured by immunofluorescence;(6)The expression of Wnt pathway-related m RNA were detected by q RT-PCR.Results:(1)The results showed that 46 of 67 patients in the low-dose IA therapy reached complete remission meanwhile there were 8 of 20 patients in the low-dose HA therapy after two courses of induction treatment. The CR rate of IA regimen was 68.7%, which was significantly higher than that of HA regimen(40%)(P=0.02).The overall response rates of IA group and HA group were 77.6% and 60% respectively, and there was no significant difference between the two groups(P>0.05). Both the hematological and non-hematological adverse effects were observed and no difference was found in the two regimen groups, neither in myelosuppression(P>0.05),the major hematological adverse effects, nor in non-hematological adverse effects(P>0.05),except for the median duration of absolute neutrophil count<1×109/L(P=0.003);(2) Decitabine and homoharringtonine can suppress the proliferation of HL-60 cells;(3) Decitabine prevented ?-catenin from the cytoplasm into the nucleus, and the expression levels of ?-catenin in cytoplasm and nucleus after united with HHT were significantly decreased;(4) HL-60 cells was arrested in S phase by decitabine and homoharringtonine;(5) the down-regulation of DAC transcription of Wnt pathway genes and expression, enhance the role of the United HHT.Conclusions:IA therapy was more effective than HA therapy, but the degree of adverse reactions of IA therapy was higher than that of HA therapy. Decitabine could prevent ?-catenin from the cytoplasm into the nucleus. It is possible for decitabine to enhance the cytotoxicity of homoharringtonine by inhibiting the Wnt pathway.