CpG methylation patterns and decitabine treatment response in acute myeloid leukemia cells and normal hematopoietic precursors

Department of Translational Hematology and Oncology Research, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH 44195, USA.
Leukemia: official journal of the Leukemia Society of America, Leukemia Research Fund, U.K (Impact Factor: 10.43). 08/2011; 26(2):244-54. DOI: 10.1038/leu.2011.207
Source: PubMed


The DNA hypomethylating drug decitabine maintains normal hematopoietic stem cell (HSC) self-renewal but induces terminal differentiation in acute myeloid leukemia (AML) cells. The basis for these contrasting cell fates, and for selective CpG hypomethylation by decitabine, is poorly understood. Promoter CpGs, with methylation measured by microarray, were classified by the direction of methylation change with normal myeloid maturation. In AML cells, the methylation pattern at maturation-responsive CpGs suggested at least partial maturation. Consistent with partial maturation, in gene expression analyses, AML cells expressed high levels of the key lineage-specifying factor CEBPA, but relatively low levels of the key late-differentiation driver CEBPE. In methylation analysis by mass spectrometry, CEBPE promoter CpGs that are usually hypomethylated during granulocyte maturation were significantly hypermethylated in AML cells. Decitabine-induced hypomethylation was greatest at these and other promoter CpGs that are usually hypomethylated with myeloid maturation, accompanied by cellular differentiation of AML cells. In contrast, decitabine-treated normal HSCs retained immature morphology, and methylation significantly decreased at CpGs that are less methylated in immature cells. High expression of lineage-specifying factor and aberrant epigenetic repression of some key late-differentiation driver genes distinguishes AML cells from normal HSCs, and could explain the contrasting differentiation and methylation responses to decitabine.

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    • "Following Cx25 knockdown, the proliferative capability of leukemia cells was interrogated but did not show a reduction compared with NT controls (Supplemental Figure 4B), indicating that the disruption of one connexin subunit was not sufficient to induce apoptosis. Interestingly, when Cx25 knockdown cells were incubated in the presence of the chemotherapeutic agent Ara-C at a concentration much lower than previously reported in the literature[24], the knockdown cells demonstrated a reduced capability to proliferate compared with their NT counterparts when incubated with 15 nM Ara-C (Figure 5A), suggesting that gap junction inhibition in combination with chemotherapy may be a potentially viable treatment strategy. These results indicate that Cx25 knockdown sensitizes leukemia cells to chemotherapeutics in vitro and may justify gap junction inhibition as an addition to current standard-of-care regimens. "
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    • "Increasing interest in targeting epigenetic pathways has led to multiple studies of DNA demethylating agents, including decitabine (DAC) administered in low dose regimens [3]–[5]. DAC is a nucleoside analog believed to have multiple distinct mechanisms of action, including; activation of methylation-silenced tumor-suppressor genes, up-regulation of microRNA and induction of DNA damage responses [6]–[10]. DAC achieved marketing authorisation for the treatment of MDS (approved in the US, based on randomised study versus best supportive care) and for AML in older patients (approved in the EU, following randomised controlled study versus cytarabine or best supportive care) [3], [11], [12]. "
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    • "The molecular actions of decitabine offer an important alternative to conventional apoptosis-based chemotherapy, since low, non-cytotoxic doses can induce cell cycle exit in cancer cells by p53-independent differentiation pathways[26, 34-35, 38]. However, this relatively low dosage could be particularly vulnerable to treatment failure caused by CDA-mediated degradation, exemplified by protection for cancer cells in CDA-rich organs. "
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