Inhibition of DNA and Histone Methylation by 5-Aza-2′-Deoxycytidine (Decitabine) and 3-Deazaneplanocin-A on Antineoplastic Action and Gene Expression in Myeloid Leukemic Cells

Abstract

Epigenetic alterations play an important role in the development of acute myeloid leukemia (AML) by silencing of genes that suppress leukemogenesis and differentiation. One of the key epigenetic changes in AML is gene silencing by DNA methylation. The importance of this alteration is illustrated by the induction of remissions in AML by 5-aza-2′-deoxycytidine (5-AZA-CdR, decitabine), a potent inhibitor of DNA methylation. However, most patients induced into remission by 5-AZA-CdR will relapse, suggesting that a second agent should be sought to increase the efficacy of this epigenetic therapy. An interesting candidate for this purpose is 3-deazaneplanocin A (DZNep). This analog inhibits EZH2, a histone methyltransferase that trimethylates lysine 27 histone H3 (H3K27me3), a marker for gene silencing. This second epigenetic silencing mechanism also plays an important role in leukemogenesis as shown in preclinical studies where DZNep exhibits potent inhibition of colony formation by AML cells. We reported previously that 5-AZA-CdR in combination with DZNep exhibits a synergistic antineoplastic action against human HL-60 AML cells and the synergistic activation of several tumor suppressor genes. In this report, we showed that this combination also induced a synergistic activation of apoptosis in HL-60 cells. The synergistic antineoplastic action of 5-AZA-CdR plus DZNep was also observed on a second human myeloid leukemia cell line, AML-3. In addition, 5-AZA-CdR in combination with the specific inhibitors of EZH2, GSK-126, or GSK-343, also exhibited a synergistic antineoplastic action on both HL-60 and AML-3. The combined action of 5-AZA-CdR and DZNep on global gene expression in HL-60 cells was investigated in greater depth using RNA sequencing analysis. We observed that this combination of epigenetic agents exhibited a synergistic activation of hundreds of genes. The synergistic activation of so many genes that suppress malignancy by 5-AZA-CdR plus DZNep suggests that epigenetic gene silencing by DNA and histone methylation plays a major role in leukemogenesis. Targeting DNA and histone methylation is a promising approach that merits clinical investigation for the treatment of AML.

Epigenetic therapy combinations in acute myeloid leukemia: what are the options?

“…Dysfunction of EZH1/2 has been associated with unregulated self-renewal of leukemic stem cells and a poor prognosis of AML and MDS patients harboring these mutations. 82,83 Recent preclinical studies showed synergistic effects of EZH2 inhibition with the HMA decitabine and the HDAC inhibitor panobinostat. 83–85 The underlying mechanism is the enhanced effect on gene silencing by simultaneously preventing DNA methylation by HMAs or histone acetylation with HDAC inhibitors in combination with increasing the pro-transcriptional effect of histone methylation by EZH2 inhibition.…”

“…82,83 Recent preclinical studies showed synergistic effects of EZH2 inhibition with the HMA decitabine and the HDAC inhibitor panobinostat. 83–85 The underlying mechanism is the enhanced effect on gene silencing by simultaneously preventing DNA methylation by HMAs or histone acetylation with HDAC inhibitors in combination with increasing the pro-transcriptional effect of histone methylation by EZH2 inhibition. 83 Additionally, trimethylation of histone H3K27 by EZH2 has been shown to mark genes for silencing by DNA methylation and is one of the mechanisms that has been linked with decitabine resistance.…”

Targeting Metalloenzymes for Therapeutic Intervention

“…194–198 Drugs, such as azacitidine and decitabine, which inhibit DNA methyltransferase, are currently used for the treatment of myelodysplastic syndrome, a disorder which develops prior to acute myeloid leukaemia. 199,200…”

Clinical efficacy of cytarabine + aclarubicin + recombinant human granulocyte colony-stimulating factor regimen combined with decitabine for adult acute myeloid leukemia

“…Therefore, treatment with CGA regimen alone cannot achieve satisfactory results. Decitabine is a type of DNA methyltransferase inhibitor, which can induce demethylation as well as differentiation and formation of hematopoietic cells at low doses, but it results in obvious cytotoxic effect at high doses (Momparler et al 2017).…”