Digging deep into “dirty” drugs – modulation of the methylation machinery

“Keywords Acute myeloid leukemia, azacitidine, decitabine, DNA methylation, epigenetics, hypomethylating agents, myelodysplastic syndrome, transcriptional regulation History Received 12 October 2014 Revised 26 November 2014 Accepted 1 December 2014 Published online 8 January 2015”

“The natural compound curcumin is thought to inhibit melanoma cell proliferation via regulation of UHRF1 and DNMT1 (Abusnina et al., 2011), and is currently being tested in various clinical trials (Table 1).”

“Keywords Acute myeloid leukemia, azacitidine, decitabine, DNA methylation, epigenetics, hypomethylating agents, myelodysplastic syndrome, transcriptional regulation History Received 12 October 2014 Revised 26 November 2014 Accepted 1 December 2014 Published online 8 January 2015”

“UHRF1 is an oncogene that acts as a transcriptional repressor, drives DNA hypomethylation, and plays an essential role in cell proliferation and carcinogenesis/leukemogenesis (Guan et al., 2013; Unoki et al., 2009).”

“As such, both drugs inhibit DNA methyltransferases (DNMTs; dependently or independently of DNA replication) resulting in the re-expression of tumor-suppressor genes; however, AZA also has an impact on mRNA and protein metabolism via its inhibition of ribonucleotide reductase, resulting in apoptosis.”

“Although detailed studies of histone modifications in MDS and AML remain to be described, they are thought to be critically involved in hematologic diseases, including leukemias (Issa, 2010).”

“Eighty-seven different MLL rearrangements have been identified in addition to partial tandem duplications, all of which seem to confer worse prognosis with shorter survival (Basecke et al., 2006; Daser & Rabbitts, 2005).”

“Micro-RNAs may be downregulated by aberrant epigenetic silencing, or by impaired synthesis by MDS mesenchymal stromal cells due to lack of ribonucleases necessary for micro-RNA maturation (Santamaria et al., 2012).”

“However, survival data indirectly suggest clinical superiority of AZA (Fenaux et al., 2009; Gurion et al., 2010; Kantarjian et al., 2012; Kumar et al., 2010; Lee et al., 2013).”

“Other HMTs known to be involved in MDS and AML include the PR domain zinc finger (PRDM) proteins PRDM3 (EVI1), which maps to 3q26, and PRDM16 (MEL1), which maps to 1q36 (Duhoux et al., 2012; Mochizuki et al., 2000; Trubia et al., 2006).”

“, 2006), fludarabine (Molina-Arcas et al., 2003) and cytarabine (AraC; Hubeek et al.”

“Genome-wide studies of histone modifications are rare in MDS/AML, but distinct patterns have been described (Muller-Tidow et al., 2010).”

“Mutations in other PRC2 components are rare in myeloid malignancies, but have recently been reported for SUZ12 and EED in MDS (Puda et al., 2012; Score et al., 2012).”

“In contrast, hypermethylated genes that did not show increased H3 acetylation were only transiently re-expressed by DAC, before reverting to an inactive state (Mossman et al., 2010).”

“…entities (psoriasis, Crohn’s disease, ulcerative colitis for infliximab, as well as rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis for etanercept), and have also shown clinical activity in MDS (Deeg et al., 2002; Raza et al., 2004; Scott et al., 2010a, b; Stasi et al., 2005).”

“Moreover, the maintenance methylation cofactor UHFR1 (and most other MPBs that act as transcriptional repressors), is unable to interact with 5-hmC, with MeCP2 being the exception (Otani et al., 2013).”

“, 2003), only one report of EZH2 overexpression in MDS exists (Xu et al., 2011).”

“Nevertheless, certain micro-RNAs have been proposed as diagnostic and prognostic micro-RNAs (Erdogan et al., 2011; Lin et al., 2014; Sokol et al., 2011), as biomarkers (Li et al., 2014) and/or as therapeutic targets in MDS/AML (Gong et al., 2014; Su et al., 2014).”

“Almost 35 years later, both drugs have shown significant clinical benefits with high overall response rates and improved overall survival in patients with myeloid malignancies (Fenaux et al., 2009, 2010; Kantarjian et al., 2012; Pleyer et al., 2013, 2014a, b).”

“DNMT3A mutations have been associated with decreased catalytic activity and DNA binding affinity, and are generally thought to enhance hypomethylation (Gowher et al., 2006).”

“Although PKC mutations are very uncommon in AML (Redig & Platanias, 2008), the expression of various PKCs, including PKCd, is often altered in both solid tumors and hematologic malignancies (Parker et al., 2014).”

“Mutations in epigenetic modulators are common in MDS and AML, and have been implicated in the development of these diseases (Fathi & Abdel-Wahab, 2012; Shih et al., 2012).”

“Very recently, MDS patients expressing lower levels of UCK1 were shown to be resistant to AZA, and had lower response rates and shorter overall survival (Valencia et al., 2014).”

“Retroviral overexpression of CDA caused significant resistance to DAC in vitro (Eliopoulos et al., 1998), and increased CDA expression/activity in human males in vivo has been linked with a reduced half-life of AZA and DAC, and possibly worse outcomes in MDS patients (Mahfouz et al., 2013).”

“DCK deficiency has been reported as a major mechanism of resistance to the nucleoside analogues DAC, Ara-C and gemcitabine (Galmarini et al., 2003; Qin et al., 2011; Saiki et al., 2012; Veuger et al., 2003).”

“Initially, it was believed that DAC would be the more potent inhibitor of DNA hypomethylation (compared to AZA), as it can more readily be incorporated into DNA (100% DAC incorporation into DNA, as compared to 10–20% in the case of AZA) (Jones et al., 1983).”

“The first inhibitors of mutant IDH1 are being extensively characterized in vitro (Davis et al., 2014), and several clinical trials with IDH inhibitors are currently recruiting (Table 1).”

“AML patients have been associated with a pattern of global hypomethylation that specifically targets HOX genes, resulting in gene expression changes (Qu et al., 2014).”

“When taking a closer look, and differentiating between methylation of promoters, gene bodies, CgP-islands, CgP-island shores, as well as various repetitive sequence classes, very distinct patterns of hypomethylation in nonpromoter interspersed repeat DNA elements were associated with AML, and have…”

“Furthermore, the BRD4 inhibitor JQ1 was shown to be highly active in AML cells bearing both NPM1 and DNMT3A mutations, reported to be associated with poor prognosis (Stewart et al., 2013).”

“UHRF1 is an oncogene that acts as a transcriptional repressor, drives DNA hypomethylation, and plays an essential role in cell proliferation and carcinogenesis/leukemogenesis (Guan et al., 2013; Unoki et al., 2009).”

“Furthermore, mutations in, and/or altered expression levels of nucleoside metabolizing enzymes, have been correlated with resistance to Ara-C and have been proposed as potential prognostic markers of response (Galmarini et al., 2001; Rathe & Largaespada, 2010; Yin et al., 2007).”

“CpG-islands within gene bodies showed the same extent of DAC-induced hypomethylation as CpGs in promoter regions (Klco et al., 2013; Yan et al., 2012), but conflicting results exist (Wong et al., 2013).”

“LRES is a mechanism of gene inactivation that affects multiple adjoining CgPislands observed in several human malignancies (Dallosso et al., 2012).”

“1 can also act as a transcriptional repressor by binding directly to MeCP2 in the above mentioned complex (Hwang et al., 2004; Kihara-Negishi et al., 2001; Suzuki et al., 2003) (Figure 2A).”

“In particular, JHDM1B promoted the proliferation of leukemic progenitor cells in murine models of AML via suppression of p15INK4b, and depletion of JHDM1B resulted in reduced colony formation in vitro (Nakamura et al., 2013; Sroczynska et al., 2014).”

“It must further be considered that global methylation levels in blood DNA may vary in relation with age, gender, alcohol drinken, white blood cell count, as well as with the method used for methylation detection (Maegawa et al., 2014; Zhu et al., 2012).”

“Ribonucleotide reductase (RR) reduces 10–20% of the diphosphate forms of AZA into deoxy-(DAC)-diphosphates, which can be incorporated into DNA after further phosphorylation to triphosphates (Kim et al., 1986) (Figure 4).”

“Both drugs are rapidly cleared from systemic circulation: plasma half-life 51.5 to 1.8 h, as compared to a half-life of 7–21 h at 37 C in neutral aqueous solutions in vitro (Liu et al., 2006; Yoo et al., 2007; Zhao et al., 2004).”

“, 2014), and DAC resulted in demethylation and significant upregulation of miR-124 and miR-125 in MDS patients responding to treatment (Ufkin et al., 2014; Vasilatou et al., 2013).”

“Furthermore, DOT1L inhibition has recently been reported to sensitize MLL- rearranged AML to chemotherapy (Liu et al., 2014).”

“In vitro data suggest synergism between the EZH2 inhibitor 3-deazaneplanocin-A (DZNep) and DAC and/or HDAC inhibitors in targeting AML cells (Fiskus et al., 2009; Momparler et al., 2012, 2014; Zhou et al., 2011).”

“Nevertheless, certain micro-RNAs have been proposed as diagnostic and prognostic micro-RNAs (Erdogan et al., 2011; Lin et al., 2014; Sokol et al., 2011), as biomarkers (Li et al.”

“This failure to discriminate clinical responders from non-responders based on baseline methylation levels and/or changes in methylation treatment, has been attributed to the limitations of current techniques available to measure ‘‘global’’ DNA methylation (Voso et al., 2014).”

“Both DAC and AZA are imported into cells by nucleoside transporters (Rius et al., 2009) (Figure 4).”

“Micro-RNAs may target key molecules of epigenetic reactions and their expression is another means of dynamically fine-tuning epigenetic regulation (Amiel et al., 2012).”

“The xanthin derivative pentoxifylline, approved for intermittent claudication from peripheral artery disease, also reduces the level of various cytokines, including TNFa; clinical activity in MDS and AML has been demonstrated (Erikci et al., 2008; Kim et al., 2006; Raza et al., 2000a, b).”

“CTCF is a transcription factor and candidate tumor suppressor involved in the control of erythroid and myeloid growth and differentiation, and knockdown results in differentiation blocks (Torrano et al., 2005).”

“On the other hand, another derivative, 5-fluoro-20deocycytidine (FdCyd) is the subject of ongoing clinical initiatives (Beumer et al., 2008; Guo et al., 2010; Zhao et al., 2012) (Table 1).”

“…common difference between ribonucleotide (incorporated into RNA) and deoxyribonucleotide (incorporated into DNA) concentrations; endogenous ribonucleotide concentrations are typically several orders of magnitude higher than the corresponding deoxyribonucleotide concentrations (Cohen et al., 2009).”

“PKCd agonists would, in theory, enhance HMA-mediated DNMT1-depletion and possibly result in enhanced blast cell apoptosis via other mechanisms, as has been observed in solid tumors (Datta et al., 2012; Easwaran et al., 2004; MochlyRosen et al., 2012; Reither et al., 2003).”

“1 can also act as a transcriptional repressor by binding directly to MeCP2 in the above mentioned complex (Hwang et al., 2004; Kihara-Negishi et al., 2001; Suzuki et al., 2003) (Figure 2A).”

“Almost 35 years later, both drugs have shown significant clinical benefits with high overall response rates and improved overall survival in patients with myeloid malignancies (Fenaux et al., 2009, 2010; Kantarjian et al., 2012; Pleyer et al., 2013, 2014a, b).”

“…various repetitive sequence classes, very distinct patterns of hypomethylation in nonpromoter interspersed repeat DNA elements were associated with AML, and have been proposed as discriminating biomarkers for use in AML diagnosis (Saied et al., 2012); prognostic relevance remains to be established.”

“…such as EZH2 and additional sex combs like transcription regulator 1 (ASXL1), have recently been detected in MDS and AML, and are described in more detail below in ‘‘HMTs in MDS/AML’’ (Boultwood et al., 2010; El-Sharkawi et al., 2014; Nikoloski et al., 2010; Thol et al., 2011b; Wang et al., 2013b).”

“Interestingly, blockade of tumor necrosis factor a (TNFa) and/or interleukin 12 (IL12) has been shown to significantly suppress AID expression (Takai et al., 2012).”

“…therapeutic approaches Genome-wide methylation studies have revealed that although HMAs induce global demethylation, only a limited number of genes are significantly reactivated, indicating the CpG demethylation is essential, but not sufficient to induce gene reactivation (Yang et al., 2012).”

“, 2005), as well as the DNMT inhibitors DAC and AZA, suggesting their potential role as predictive biomarkers for clinical response (Damaraju et al., 2012; Qin et al., 2009).”

“…on the involvement of the epigenetic machinery in the development of MDS/AML and their potential modulation by azanucleosides (if known); we also discuss which of these molecules may be additional therapeutic targets in MDS/AML, thus representing potential novel combination partners for HMAs.”

“Almost 35 years later, both drugs have shown significant clinical benefits with high overall response rates and improved overall survival in patients with myeloid malignancies (Fenaux et al., 2009, 2010; Kantarjian et al., 2012; Pleyer et al., 2013, 2014a, b).”

“Other HMTs known to be involved in MDS and AML include the PR domain zinc finger (PRDM) proteins PRDM3 (EVI1), which maps to 3q26, and PRDM16 (MEL1), which maps to 1q36 (Duhoux et al., 2012; Mochizuki et al., 2000; Trubia et al., 2006).”

“proteins are located at the loop bases (Tark-Dame et al., 2014; Xu et al., 2014).”

“In rhesus monkeys, co-administration of CDA inhibitors with DAC improved pharmacokinetic profile and boosted plasma levels (Ferraris et al., 2014).”

“Keywords Acute myeloid leukemia, azacitidine, decitabine, DNA methylation, epigenetics, hypomethylating agents, myelodysplastic syndrome, transcriptional regulation History Received 12 October 2014 Revised 26 November 2014 Accepted 1 December 2014 Published online 8 January 2015”

“toxic death in a patient exposed to the nucleoside analogue gemcitabine (Mercier et al., 2007).”

“in other entities (psoriasis, Crohn’s disease, ulcerative colitis for infliximab, as well as rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis for etanercept), and have also shown clinical activity in MDS (Deeg et al., 2002; Raza et al., 2004; Scott et al., 2010a, b; Stasi et al., 2005).”

“Keywords Acute myeloid leukemia, azacitidine, decitabine, DNA methylation, epigenetics, hypomethylating agents, myelodysplastic syndrome, transcriptional regulation History Received 12 October 2014 Revised 26 November 2014 Accepted 1 December 2014 Published online 8 January 2015”

“The first reports of AZA-mediated alteration in the processing of tRNA and rRNA, as well as inhibition of protein synthesis go as far back as 1973 (Cihak et al., 1974; Glover & LeylandJones, 1987; Lu & Randerath, 1980; Reichman & Penman, 1973).”

“…some authors have observed significant correlation of HMA-induced hypomethylation with response and overall survival (Shen et al., 2010; Yang et al., 2006), uncertainty remains regarding the prognostic value of hypomethylation induction (Khan et al., 2013; Shen et al., 2010; Voso et al., 2014).”

“…the prognostic relevance of these mutations in MDS, CMML and AML remains unclear, and may be disease-specific, as currently existing data are inconsistent (Abdel-Wahab et al., 2009; Kosmider et al., 2009a, b; Liu et al., 2013; Metzeler et al., 2011b; Pollyea et al., 2011; Wang et al., 2013a).”

“Cohesin is a multi-subunit protein complex, comprising four major subunits: structural maintenance of chromosomes 1A and 3 (SMC1A, SMC3), STAG1/2 and RAD21 (Leeke et al., 2014).”

“However, the presence of mutated TET2 has been associated with response to AZA and DAC in MDS and CMML by several (Braun et al., 2011; Itzykson et al., 2011; Traina et al., 2014; Voso et al., 2011), but not all groups (Pollyea et al., 2011).”

“Nucleosomes are mobile structures that can ‘‘slide’’ and reposition themselves along DNA without disruption of the histone octamer (Pennings et al., 1989).”

“…on the involvement of the epigenetic machinery in the development of MDS/AML and their potential modulation by azanucleosides (if known); we also discuss which of these molecules may be additional therapeutic targets in MDS/AML, thus representing potential novel combination partners for HMAs.”

“We summarize current knowledge on the involvement of the epigenetic machinery in the development of MDS/AML and their potential modulation by azanucleosides (if known); we also discuss which of these molecules may be additional therapeutic targets in MDS/AML, thus representing potential novel combination partners for…”

“CTCF Hypermethylation (and thus downregulation) of CTCF has also been linked to the pathogenesis of acute promyelocytic leukemia (Manodoro et al., 2014).”

“Elevated PKCd expression has been described in several hematologic malignancies, including 45% of AML patients (Pearn et al., 2007).”

“…entities (psoriasis, Crohn’s disease, ulcerative colitis for infliximab, as well as rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis for etanercept), and have also shown clinical activity in MDS (Deeg et al., 2002; Raza et al., 2004; Scott et al., 2010a, b; Stasi et al., 2005).”

“This shortrange ‘‘oozing’’ model involves recurrent rounds of deacetylation of H4K16 histone tails by silent information regulator (SIR) protein complexes, which propagate gene silencing along the chromosome (Oppikofer et al., 2013).”

“In contrast, thousands of genes changed their histone methylation (H3K4me3 and/or H3K27me3) status, with the most plasticity being observed in LSCs. Progressive loss of activating H3K4me3 status coincided with gene silencing during differentiation (Yamazaki et al., 2013).”

“8 h, as compared to a half-life of 7–21 h at 37 C in neutral aqueous solutions in vitro (Liu et al., 2006; Yoo et al., 2007; Zhao et al., 2004).”

“Strong up-regulation of DNMT1 and 3A has been demonstrated in the vast majority of MDS bone marrow biopsies (Langer et al., 2005).”

“Other HMTs known to be involved in MDS and AML include the PR domain zinc finger (PRDM) proteins PRDM3 (EVI1), which maps to 3q26, and PRDM16 (MEL1), which maps to 1q36 (Duhoux et al., 2012; Mochizuki et al., 2000; Trubia et al., 2006).”

“These authors developed an epigenetic score, and AML patients with ‘‘low stem cell commitment’’-associated epigenetic signature scores had significantly longer overall survival than patients with higher epigenetic scores (Bartholdy et al., 2014).”

“LRES was found to be correlated with the above mentioned CpG-island hypermethylator phenotype (CIMP) in colorectal cancer (Karpinski et al., 2008).”

“…entities (psoriasis, Crohn’s disease, ulcerative colitis for infliximab, as well as rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis for etanercept), and have also shown clinical activity in MDS (Deeg et al., 2002; Raza et al., 2004; Scott et al., 2010a, b; Stasi et al., 2005).”

“…CREBBP, MYST3 and MYST4) are commonly involved in chromosomal translocations, which are involved in leukemogenesis through aberrant acetylation of all core histones, as well as on various nonhistone proteins (Camos et al., 2006; Murati et al., 2004; Pattabiraman et al., 2014; Shigeno et al., 2004).”

“This causes DNA mutations and double strand breakage (Perez-Duran et al., 2007) (Figure 4).”

“…such as EZH2 and additional sex combs like transcription regulator 1 (ASXL1), have recently been detected in MDS and AML, and are described in more detail below in ‘‘HMTs in MDS/AML’’ (Boultwood et al., 2010; El-Sharkawi et al., 2014; Nikoloski et al., 2010; Thol et al., 2011b; Wang et al., 2013b).”

“proteins are located at the loop bases (Tark-Dame et al., 2014; Xu et al., 2014).”

“EZH2 is only active when it is associated with the other PRC2 core components: embryonic ectoderm development (EED), suppressor of zeste 12 homolog (SUZ12) and retinoblastoma binding protein 4 (RBBP4); (Kogure et al., 2013; Margueron & Reinberg, 2011) (Figure 2C).”

“This block was linked to cell cycle arrest in S-phase, thus inhibiting DNA-replication-dependent mechanisms of both drugs (Choi et al., 2007).”

“As such, both drugs inhibit DNA methyltransferases (DNMTs; dependently or independently of DNA replication) resulting in the re-expression of tumor-suppressor genes; however, AZA also has an impact on mRNA and protein metabolism via its inhibition of ribonucleotide reductase, resulting in apoptosis.”

“deficiency is directly involved in the development of AML in mice (Basova et al., 2013), and humans (Bonadies et al.”

“However, the presence of mutated TET2 has been associated with response to AZA and DAC in MDS and CMML by several (Braun et al., 2011; Itzykson et al., 2011; Traina et al., 2014; Voso et al., 2011), but not all groups (Pollyea et al., 2011).”

“Keywords Acute myeloid leukemia, azacitidine, decitabine, DNA methylation, epigenetics, hypomethylating agents, myelodysplastic syndrome, transcriptional regulation History Received 12 October 2014 Revised 26 November 2014 Accepted 1 December 2014 Published online 8 January 2015”

“PU.1 deficiency is directly involved in the development of AML in mice (Basova et al., 2013), and humans (Bonadies et al., 2010).”

“Various somatic alterations in genes encoding proteins that regulate DNA methylation and post-transcriptional histone modifications, have been identified (Dolnik et al., 2012; Nikoloski et al., 2012).”

“The CDA inhibitor tetrahydrouridine (THU) was assessed in humans in the 1990s and is being revived in clinical trials, with or without second generation DNMT inhibitors (Ferraris et al., 2014; Marsh et al., 1993) (Table 1).”

“In MDS, global hypermethylation (rather than hypomethylation) has been reported (Romermann et al., 2008).”

“Several second generation DNMT inhibitors are currently being developed and include 5,6-dihydro-5-azacitidine (DHAC, NSC264880), which was found to be less toxic and more stable than DAC at doses that induce comparable DNA hypomethylation and gene reactivation (Matousova et al., 2011).”

“However, via the same mechanism AID can also cause chromosomal translocations or mutations in proto-oncogenes, thus promoting tumor formation and/or leukemic evolution in a variety of hematologic malignancies (Kinoshita & Nonaka, 2006).”

“Recent evidence suggests the former scenario (Santini et al., 2013).”

“Keywords Acute myeloid leukemia, azacitidine, decitabine, DNA methylation, epigenetics, hypomethylating agents, myelodysplastic syndrome, transcriptional regulation History Received 12 October 2014 Revised 26 November 2014 Accepted 1 December 2014 Published online 8 January 2015”

“…in primary AML patient samples and murine models of acute leukemia, partially through the down-regulation of the critical oncogenes, MYC and Bcl2 (Chen et al., 2014; Dawson et al., 2014; Delmore et al., 2011; Fiskus et al., 2014b; Mertz et al., 2011; Valent & Zuber, 2014; Zuber et al., 2011).”

“DNMT3A and 3B expression has been negatively correlated with MDS disease risk, being more pronounced in high-risk MDS (Hopfer et al., 2009).”

“Nevertheless, certain micro-RNAs have been proposed as diagnostic and prognostic micro-RNAs (Erdogan et al., 2011; Lin et al., 2014; Sokol et al., 2011), as biomarkers (Li et al., 2014) and/or as therapeutic targets in MDS/AML (Gong et al., 2014; Su et al., 2014).”

“Keywords Acute myeloid leukemia, azacitidine, decitabine, DNA methylation, epigenetics, hypomethylating agents, myelodysplastic syndrome, transcriptional regulation History Received 12 October 2014 Revised 26 November 2014 Accepted 1 December 2014 Published online 8 January 2015”

“However, survival data indirectly suggest clinical superiority of AZA (Fenaux et al., 2009; Gurion et al., 2010; Kantarjian et al., 2012; Kumar et al., 2010; Lee et al., 2013).”

“Many issues of HDAC inhibitors and their potential clinical utility in MDS remain only partially understood, and pose translational and clinical challenges (Stintzing et al., 2011).”

“…CREBBP, MYST3 and MYST4) are commonly involved in chromosomal translocations, which are involved in leukemogenesis through aberrant acetylation of all core histones, as well as on various nonhistone proteins (Camos et al., 2006; Murati et al., 2004; Pattabiraman et al., 2014; Shigeno et al., 2004).”

“…of all analyzed genes) are frequently hypermethylated in MDS, and that hypermethylation across the genome correlates with poor prognosis and transformation to AML, as well as AML relapse (Figueroa et al., 2009; Jiang et al., 2009; Kroeger et al., 2008; Maegawa et al., 2014; Zhao et al., 2014).”

“…direct T-cell stimulatory effects, upregulation of T-cell co-stimulatory molecules CD80 and CD86 on dendritic cells, and induction of anticancer humoral immune responses with enhanced antibody dependent cellular cytotoxicity (Ersvaer et al., 2007, 2010; Hampson et al., 2005; Olsnes et al., 2009).”

“Keywords Acute myeloid leukemia, azacitidine, decitabine, DNA methylation, epigenetics, hypomethylating agents, myelodysplastic syndrome, transcriptional regulation History Received 12 October 2014 Revised 26 November 2014 Accepted 1 December 2014 Published online 8 January 2015”

“Total genomic 5-mC levels decreased on average by 14% in AML patients treated with DAC (Klco et al., 2013; Yang et al., 2006), and global reductions in methylation were also observed in isolated AML blasts (Claus et al., 2013).”

“…entities (psoriasis, Crohn’s disease, ulcerative colitis for infliximab, as well as rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis for etanercept), and have also shown clinical activity in MDS (Deeg et al., 2002; Raza et al., 2004; Scott et al., 2010a, b; Stasi et al., 2005).”

“Therapeutic targeting of IDH1 seems promising (Levis, 2013).”

“Changes in micro-RNA expression levels were observed at response to therapy (Merkerova et al., 2014), and DAC resulted in demethylation and significant upregulation of miR-124 and miR-125 in MDS patients responding to treatment (Ufkin et al., 2014; Vasilatou et al., 2013).”

“%) and only rarely in AML (AbdelWahab et al., 2011; Grossmann et al., 2011; Xu & Li, 2012).”

“Although sample number was very limited, AZA-triphosphate levels were 2.5–55 times higher than DAC-triphosphate concentrations previously published by the same group (Derissen et al., 2014; Jansen et al., 2012).”

“Mutations within all individual protein components of the cohesin-complex have been described, are mutually exclusive, and occur in 4–21% of MDS and AML patients (Leeke et al., 2014; Malcovati et al., 2014; Thol et al., 2014).”

“Selective small molecule JHDM inhibitors are currently being developed (Luo et al., 2011; Xu et al., 2013), but have not yet reached clinical trials.”

“Although PKC mutations are very uncommon in AML (Redig & Platanias, 2008), the expression of various PKCs, including PKCd, is often altered in both solid tumors and hematologic malignancies (Parker et al., 2014).”

“As DNMT1 mRNA levels are not significantly affected, DNMT1 degradation is thought to be purely post-transcriptional (Tsai et al., 2014).”

“Recently, JHDM1B was reported to be highly expressed in primary AML samples and is possibly required for leukemia maintenance (Nakamura et al., 2013).”

“Furthermore, mutations in, and/or altered expression levels of nucleoside metabolizing enzymes, have been correlated with resistance to Ara-C and have been proposed as potential prognostic markers of response (Galmarini et al., 2001; Rathe & Largaespada, 2010; Yin et al., 2007).”

“Several months ago, the first assay for quantitative detection of AZA-triphosphate in peripheral blood mononuclear cells was published (Derissen et al., 2014).”

“Keywords Acute myeloid leukemia, azacitidine, decitabine, DNA methylation, epigenetics, hypomethylating agents, myelodysplastic syndrome, transcriptional regulation History Received 12 October 2014 Revised 26 November 2014 Accepted 1 December 2014 Published online 8 January 2015”

“It is thought that this may be precisely due to, and not despite, the fact that AZA is mainly incorporated into RNA (and not DNA) (Santini, 2009).”

“CpG-islands within gene bodies showed the same extent of DAC-induced hypomethylation as CpGs in promoter regions (Klco et al., 2013; Yan et al., 2012), but conflicting results exist (Wong et al., 2013).”

“…DNA due to mutation at the DNMT1 catalytic site, which participates in covalent bond formation between DNMT1 and C-G or DAC-G dinucleotides in the DNA Datta et al. (2012), Reither et al. (2003) 7 RR knockout blocks the conversion of AZA-MP to DAC-MP, and thus abrogates AZA incorporation into DNA.”

“The xanthin derivative pentoxifylline, approved for intermittent claudication from peripheral artery disease, also reduces the level of various cytokines, including TNFa; clinical activity in MDS and AML has been demonstrated (Erikci et al., 2008; Kim et al., 2006; Raza et al., 2000a, b).”

“DCK deficiency has been reported as a major mechanism of resistance to the nucleoside analogues DAC, Ara-C and gemcitabine (Galmarini et al., 2003; Qin et al., 2011; Saiki et al., 2012; Veuger et al., 2003).”

“In murine cancer models, molecular features involved in LRES include (i) DNA hypermethylation of specific CgP islands, and (ii) acquisition of inactive histone marks, both of which result in downregulation of gene expression (Forn et al., 2013).”

“In line with the above, TET2-mutant AML has recently been shown to have the expected hypermethylation phenotype (Madzo et al., 2013).”

“Recently, DAC was shown to reverse PU.1 mediated transcriptional repression (Aoyama et al., 2012).”

“Hypomethylation induced by HMAs results in significant variation in nuclear texture patterns, higher-order chromatin organization, distribution of heterochromatin regions, and ultimately in chromatin decondensation (Poplineau et al., 2013).”

“However, clinically relevant results are yet to be demonstrated (Garcia-Manero, 2012; Quintas-Cardama et al., 2011; Stintzing et al., 2011).”

“On the other hand, another derivative, 5-fluoro-20deocycytidine (FdCyd) is the subject of ongoing clinical initiatives (Beumer et al., 2008; Guo et al., 2010; Zhao et al., 2012) (Table 1).”

“1, as well as of its downstream genes, resulting in differentiation induction (Cheng et al., 2013).”

“DHAC has been evaluated in clinical trials as early as 1985 (Curt et al., 1985; Kratzke et al., 2008).”

“These histone modifications clearly define solid tumor cell lines with alternate responsiveness to HMA treatment (Mayor et al., 2011; Mossman et al., 2010).”

“The xanthin derivative pentoxifylline, approved for intermittent claudication from peripheral artery disease, also reduces the level of various cytokines, including TNFa; clinical activity in MDS and AML has been demonstrated (Erikci et al., 2008; Kim et al., 2006; Raza et al., 2000a, b).”

“In the latter, remethylation started without time-delay at a significantly slower rate, and continued at a constant low level (Wodarz et al., 2013).”

“As such, both drugs inhibit DNA methyltransferases (DNMTs; dependently or independently of DNA replication) resulting in the re-expression of tumor-suppressor genes; however, AZA also has an impact on mRNA and protein metabolism via its inhibition of ribonucleotide reductase, resulting in apoptosis.”

“Keywords Acute myeloid leukemia, azacitidine, decitabine, DNA methylation, epigenetics, hypomethylating agents, myelodysplastic syndrome, transcriptional regulation History Received 12 October 2014 Revised 26 November 2014 Accepted 1 December 2014 Published online 8 January 2015”

“HMTs have been identified as promising new targets in leukemia treatment (Flemming, 2012).”

“The xanthin derivative pentoxifylline, approved for intermittent claudication from peripheral artery disease, also reduces the level of various cytokines, including TNFa; clinical activity in MDS and AML has been demonstrated (Erikci et al., 2008; Kim et al., 2006; Raza et al., 2000a, b).”

“Keywords Acute myeloid leukemia, azacitidine, decitabine, DNA methylation, epigenetics, hypomethylating agents, myelodysplastic syndrome, transcriptional regulation History Received 12 October 2014 Revised 26 November 2014 Accepted 1 December 2014 Published online 8 January 2015”

“(DAC/5-AZA) inhibit DNA methyltransferases (mainly DMNT1 and DMNT3) resulting in the re-expression of tumor-suppressor genes [419, 420].”