Abstract
5-Azacytidine (5AC), a hypomethylating agent, is clinically used for the treatment of patients with myelodysplastic syndromes (MDS). Cytidine deaminase (CDA) is a key enzyme in the detoxification of 5AC. We investigated whether the CDA expression could predict response to 5AC in MDS. Among leukemia-derived cell lines, MDS-L, an MDS-derived cell line with a relatively low CDA expression level, was found to be the most sensitive to 5AC. Combination with tetrahydrouridine, an inhibitor of CDA, synergistically potentiated the cytotoxic effect of 5AC. Treatment with 5AC markedly enhanced the expression level of CDA mRNA and showed demethylation at CpG sites in the 5′-flanking region of the CDA gene. We further compared the protein expression levels of CDA in matched clinical samples before and after treatment with 5AC in bone marrow cells from 8 MDS patients by an immunohistochemical analysis. The CDA expression level showed an approximately 2- to 3-fold increase after 5AC treatment in 3 of these cases, and these three patients with relatively higher CDA expression levels after 5AC treatment all showed better clinical responses to 5AC. In contrast, the 5 remaining patients, whose CDA expression showed no augmentation, observed no clinical benefit. Taken together, the optimized determination of the CDA expression levels before and after 5AC treatment, and the methylation status at CpG sites of 5′-flanking region of the CDA gene, may contribute to the development of precise 5AC therapy for MDS.
Highlights
Myelodysplastic syndromes (MDS) is a group of heterogenous hematopoietic stem cell disorders, resulting in cytopenia and an increased risk of progression into acute myeloid leukemia
Of the four cell lines, the expression levels of Cytidine deaminase (CDA) mRNA were higher in THP-1 and AMO-1 when there was low expression in myelodysplastic syndromes (MDS)-L and U266 (Figure 1B)
Western blot analysis showed the lowest expression of CDA protein in MDS-L (Figure 1F), consistent with its mRNA levels (Figure 1B)
Summary
Myelodysplastic syndromes (MDS) is a group of heterogenous hematopoietic stem cell disorders, resulting in cytopenia and an increased risk of progression into acute myeloid leukemia. The gene mutation of epigenetic regulators, including ten-eleven translocation 2, isocitrate dehydrogenase 1/2, DNA methyltransferase 3A, additional sex combs like 1 and enhancer of zeste homolog 2, have been implicated in the pathogenesis of MDS [1,2,3]. The DNA methylation profiles of MDS patients are distinct from healthy individuals [4]. Epigenetic deregulation, such as gene hypermethylation and histone deacetylation, plays a key role in the progression of MDS [5, 6]. Treatment with hypomethylating agents has been expected to improve the efficacy of treatments targeting MDS
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