Therapeutic Effects of Targeted Intervention of SETDB1 in Acute Myeloid Leukemia

OBJECTIVE Acute myeloid leukemia(AML) is an aggressive hematological malignancy. Despite remarkable insights into the molecular pathogenesis and albeit modest advances in treatment, the 5-year survival rate of AML patients is only 25%-30%. A characteristic feature of AML is failure to terminally differentiate into functional mature myeloid cells. A notable exception in AML therapy has been use of all-trans retinoic acid(ATRA) in individuals with acute promyelocytic leukemia (APL). ATRA can induce APL cell differentiation, highlighting that differentiation-based therapy holds great promise for AML treatment. Unfortunately, ATRA only reverses the survival curve of patients with APL, which only accounts for 10% of the total AML. Therefore, there is an unmet need to reveal new druggable targets for broad differentiation-based therapies. SET domain, bifurcated 1(SETDB1) is a histone 3 lysine 9(H3K9)-specific methyltransferase and is essential for the gene expression via regulating histone methylation. Aberrant expression of epigenetic regulators often leads to myeloid malignancies, such as histone demethylase LSD1, METTL3, indicated targeting epigenetic regulators in AML leukemia treatment holds great promise. SETDB1 is involved in regulating cancer development, such as abnormally high expression in hepatocellular carcinoma(HCC) and knocking down SETDB1 expression inhibits the motility and metastatic ability of HCC. However, it is still unclear about the role of SETDB1 in AML leukemogenesis and malignant progression, and whether targeted intervention of SETDB1 can be used for leukemia differentiation therapy. Therefore, this study is aim to explore the role of histone methyltransferase SETDB1 in the malignant progression of AML and the therapeutic effect of SETDB1 suppression in AML. METHODS Based on TCGA(The Cancer Genome Atlas) and GTEx(Genotype-Tissue Expression) databases, an analysis of the expression of SETDB1 in different cancer species and a comparison of the expression of SETDB1 in bone marrow cells of AML patients and normal bone marrow cells was conducted. Additionally, the correlation between the expression of SETDB1 and different risk stratification, micro residual disease(MRD) as well as different FAB(French-American-British) subtypes in AML patients were analyzed based on information obtained from the TCGA and TARGET databases. GSEA(Gene set enrichment analysis) for patients with high and low SETDB1 expression were performed to analysis the relationship between SETDB1 expression and differentiation. During the research, the silencing efficiency of SETDB1 was examined by RT-qRCR in AML cells. Furthermore, the effect of SETDB1 knockdown on the proliferation and viability of AML cells was evaluated using Trypan blue staining assay. CD11b, CD14 expression level alongside cell nuclear morphologic changes and nitrotetrazolium blue chloride(NBT) reduction ability were used to determine the therapeutic effect of shSETDB1 in AML cell differentiation. RESULTS SETDB1 was significantly highly expressed in AML patients compared to other cancer types, and was also significantly higher expressed than that in normal bone marrow cells. SETDB1 was obviously highly expressed in high-risk AML patients as well as patients with residual MRD. SETDB1 silencing significantly inhibited AML cell proliferation without any obvious cell death. Besides, genes typically upregulated in hematopoietic stem cells(HSCs) and downregulated in myeloid cell development were highly enriched in patients with high SETDB1 expression and SETDB1 was also found to be relatively highly expressed in undifferentiated or partially differentiated M0-M2 FAB subtypes. More importantly, flow cytometry analysis showed that shSETDB1 significantly increased the expression of CD11b and CD14 in AML cells and the upregulation ratio of CD11b and CD14 corresponded to the silencing effect of SETDB1. Moreover, SETDB1-declined cells had a more mature nuclear morphology and enhanced NBT-reducing ability in AML cells, suggesting the depletion of SETDB1 may drive myeloid differentiation and maturation in AML cells. CONCLUSION Histone methyltransferase SETDB1 is specifically highly expressed in AML and closely associates with the malignant progression of leukemia. Targeting SETDB1 is expected to be a promising strategy for differentiation therapy in AML, which provides new opportunities for AML treatment.