Summary This prospective Phase II study is the first to assess the feasibility and efficacy of maintenance 5‐azacytidine for older patients with high‐risk myelodysplastic syndrome (MDS), chronic myelomonocytic leukaemia and MDS‐acute myeloid leukaemia syndromes in complete remission (CR) after induction chemotherapy. Sixty patients were enrolled and treated by standard induction chemotherapy. Patients that reached CR started maintenance therapy with subcutaneous azacytidine, 5/28 d until relapse. Promoter‐methylation status of CDKN2B ( P15 ink4b ), CDH1 and HIC1 was examined pre‐induction, in CR and 6, 12 and 24 months post CR. Twenty‐four (40%) patients achieved CR after induction chemotherapy and 23 started maintenance treatment with azacytidine. Median CR duration was 13·5 months, >24 months in 17% of the patients, and 18–30·5 months in the four patients with trisomy 8. CR duration was not associated with CDKN2B methylation status or karyotype. Median overall survival was 20 months. Hypermethylation of CDH1 was significantly associated with low CR rate, early relapse, and short overall survival ( P = 0·003). 5‐azacytidine treatment, at a dose of 60 mg/m 2 was well tolerated. Grade III‐IV thrombocytopenia and neutropenia occurred after 9·5 and 30% of the cycles, respectively, while haemoglobin levels increased during treatment. 5‐azacytidine treatment is safe, feasible and may be of benefit in a subset of patients.

The haematopoietic growth factor receptor Flt3 has been implicated as major cause of transformation in acute myeloid leukaemia. Intracellular signals mediated by wild-type Flt3 are involved in cell differentiation and survival whereas signalling via the mutant Flt3 ITD (internal tandem duplication) promotes enhanced cell growth. In this study, we identified tyrosines 768, 955 and 969 of Flt3 as phosphorylation sites and mediators of growth factor receptor binding protein 2 (Grb2) interaction, leading to the association of Grb2 associated binder 2 (Gab2) and contributing to proliferation and survival. Ba/F3 cells were transfected with either the wild-type Flt3 or the ITD, with or without a triple mutation of the Grb2 binding sites, and characterised in terms of proliferation and viability. Interestingly, the Flt3 ITD promoted increased survival but after introducing the triple mutation, this phenotype was lost. When looking into different downstream pathways, this effect was mainly caused by decreased phosphoinositide 3-kinase and Stat5 signalling, and the Flt3 ITD carrying the Grb2 binding mutations showed less Akt and Stat5 activation compared to the regular Flt3 ITD receptor. These findings not only reveal novel phosphorylation sites in Flt3 but contribute to the understanding of the molecular mechanism by which Flt3 ITD functions in pathological conditions.

Objective. Fms-like tyrosine kinase-3 (Flt3), a growth factor receptor normally expressed in hematopoietic progenitor cells, has been shown to have an important role in development of acute myeloid leukemia (AML) due to activating mutations. Flt3 mutations are found in approximately one-third of AML patients and correlate with a poor prognosis, thus making the Flt3 receptor a potential therapeutic target. The aim of the investigation was to analyze the kinetics and specificity of Flt3 autophosphorylation in wild-type Flt3 as well as in oncogenic Flt3 mutants.Materials and methods. We have used Ba/F3 cells stably expressing either wild-type, internal tandem duplication, or D835Y mutants of Flt3 in order to compare the site selectivity of tyrosine phosphorylation sites. By the use of a panel of phosphospecific antibodies directed against potential tyrosine phosphorylation sites in Flt3, we identified several novel phosphorylation sites in Flt3 and studied the kinetics and specificity of ligand-induced phosphorylation in living cells.Results. Eight phosphorylated tyrosines (pY589, pY591, pY599, pY726, pY768, pY793, pY842, and pY955) were investigated and shown to be differentially phosphorylated in the wild-type versus the mutated receptors. Furthermore, we show that tyrosines 726, 793, and 842 are novel phosphorylation sites of Flt3 in intact cells.Conclusion. In this study, we have looked at the site-specific phosphorylation in the wild-type Flt3 in comparison to the mutants found in AML We observed not only quantitative changes but, more importantly, qualitative differences in the phosphorylation patterns of the wild-type and the mutated Flt3 receptors, which might enhance the understanding of the mechanisms by which Flt3 contributes to AML in patients with mutations in Flt3. (C) 2009 ISEH - Society for Hematology and Stem Cells. Published by Elsevier Inc.

OBJECTIVE:Although clinically approved for myelodysplastic syndromes (MDS), the mode of action of 5-azacytidine has not been well understood at the cellular level. The present study aimed at characterizing the mechanisms for 5-azacytidine-induced apoptosis, as well as the presence of a possible link between apoptosis and DNA hypomethylation. MATERIALS AND METHODS:We investigated the effects of 5-azacytidine on a spectrum of specific apoptotic pathways, as well as on global DNA methylation, assessed by luminometric methylation assay, in myeloid (P39, HL60) and T cells (Jurkat). RESULTS:5-Azacytidine induced dose-dependent apoptosis as well as non-dose-dependent global DNA hypomethylation at concentrations >or=0.5 microM. Hypomethylation was observed in the sorted apoptotic fraction (41% decrease with 1 microM after 24 hours), while nonapoptotic cells retained a methylation pattern similar to untreated cells (+/-6%). The induced apoptotic pattern involved several pathways: cleavage of Bcl-2 family proteins, activation of caspase-2 and -3-like, mitochondrial involvement characterized by loss of transmembrane potential (tetramethylrhodamine ethyl ester [TMRE]) and cytochrome release, and acidification of cytosol. Selective inhibition of caspase-3-like, -2, -8, -9, and pan-caspase activity, as well as stabilization of cytosolic pH by monensin completely failed to block apoptosis. Poly(ADP-ribose) polymerase (PARP) inhibitors only partially inhibited loss of TMRE (32% reduction) and caspase-2 activity (38% reduction); indicative of PARP operation (or action) upstream of caspase-2. Moreover, cytosine arabinoside induced a similar degree of apoptosis, while leaving methylation status mainly unaffected. CONCLUSIONS:5-Azacytidine acts via multiple and separately regulated pathways, including parallel induction of hypomethylation. The broad action of 5-azacytidine may explain its therapeutic effects in poor-prognostic MDS.

FMS-like tyrosine kinase-3 (Flt3) is a receptor tyrosine kinase, which is normally expressed in hematopoietic progenitor cells. It has been implicated as a major cause of transformation in acute myeloid leukemia (AML). There are two types of Flt3 gene mutations have been identified in AML: duplication of amino acids in the juxtamembrane region- Internal Tandem Duplication (ITD) and an activation loop point-mutation of D835 in kinase domain. These mutations cause constitutive activation or over expression of Flt3 receptor and therefore lead to alteration in signal transduction. These alterations occur in approximately 30% of AML patients. High occurrence of these mutations in the Flt3 receptor in AML patients makes it one of the most interesting therapeutic targets. In this study we have identified three novel in vivo phosphorylation sites of Flt3 receptor and further compared the activity of phosphorylation sites of Flt3 wild type, Flt3 ITD and D835Y mutations by using homemade phospho-specific antibodies directed against specific tyrosines. For this study murine hematopoietic Ba/F3 cells were stably transfected with wild-type Flt3, ITD and D835Y mutations. We have confirmed that the activation of the wild type Flt3 receptor is ligand dependent and response in a time dependent manner, but Flt3-ITD and D835Y are constitutive active and ligand independent. Phosphorylated tyrosines 589, 591, 599, 726, 768, 793, 842, and 955 of Flt3 receptor were investigated and shown to be differentially activated in wild-type versus the mutated receptor. Using this data we can further study the mechanisms of signaling pathways of the Flt3 receptor that are involved in many biological responses and understand the mechanism by which Flt3 ITD and D835Y functions in pathological conditions.

Around 50% of patients with high-risk MDS or MDS-AML may enter CR after induction chemotherapy, but CR duration, as well as overall survival is usually short. To address this clinical problem the Nordic MDS Group designed a prospective multicenter phase II study, which assessed the clinical feasibility and utility of long-term maintenance treatment with azaciditine. Sixty patients with high-risk MDS (IPSS intermediate-2 or high) (n=23) or AML following a previous known MDS (n=37) were enrolled between 2004 and 2006. The mean age was 68 (54–83) and patients should not be eligible for stem cell transplantation. Induction treatment consisted of standard doses of daunorubicin and ara-C. Patients in CR received low dose azacitidine subcutaneously 5/28 days until relapse, unless unacceptable toxicity developed. Methylation status of the P15ink4b (P15), E-cadherine (CDH) and Hypermethylated in Cancer 1 (HIC) gene was analysed at study start, in CR and in some patients during follow up. Last follow up was on August 1 2008, 24 months after the last CR was reported. Twenty-four patients (40%) reached CR and 23 of these started maintenance treatment with azacitidine. The initial dose of azacitidine was 75 mg/m2 but as four of the first five enrolled patients developed grade 4 cytopenia, the starting dose was lowered to 60 mg/m2, and was allowed to be reduced to 45 or 30 mg/m2 to avoid severe cytopenias. The mean dose of azacitidine was 54.3 mg/m2. Azacitidine was well tolerated. In 52% of the cases no side effects at all were reported. The most commonly reported side effect was mild rashes at the injection site (35%). Twenty-two percent developed fever or some kind of infection, mostly mild. Myelosuppression (grade 1–3) was seen in 22% of the cases. As previously reported, the probability of reaching CR was negatively correlated to promoter hypermethylation of CDH (p=0.008) and none of the 6 patients hypermethylated on all 3 genes reached CR (p=0.03) and hence only four patients hypermethylated on other genes than P15 received demethylating therapy. The median CR duration for the azacididine treated group was 13.5 months (2–49+) and median survival time from time of inclusion in the study for the same group was 20 months (4–52+). Four of 23 patients (17%) had a CR exceeding 24 months (32–52+). The two patients hypermethylated on CDH pre-induction had CR durations of only 2 and 5 months respectively. By last follow up 3 patients were still in CR. Of 10 patients without any methylation pre-treatment, all but one maintained this pattern in CR. Of the nine patients with pre treatment methylation of at least one gene, only one remained hypermethylated in CR. This patient had a CR duration of only 5 months. One patient showed development of P15 hypermethylation in the bone marrow sampled at 12 months and relapsed at 15 months. These findings support previous reports on P15 hypermethylation as a marker for minimal residual disease (MRD) and threatening relapse. In the whole group, survival was significantly shorter in patients with CDH methylation (3 vs 9 months, p=0.005), while pre-treatment p15 methylation status did not affect CR duration or overall survival. In conclusion, we show for the first time that maintenance treatment with azacytidine is feasible and associated with a median CR duration of 13.5 months, and very mild side effects. However azacytidine does not seem to prevent relapse in the majority of patients, including those with hypermethylation pre-treatment and/or in CR. Hypermethylation of multiple genes is a strong negative factor for survival, probability of CR, and CR duration. We observe a subset of patients, 17%, with a CR duration of >24 months; but no persistent pattern regarding cytogenetics, methylation or morphology could be identified in this group. The strong negative impact of E-Cadherin methylation, a gene involved in adhesion, warrants further investigation.

PURPOSE:Promoter hypermethylation of, for example, tumor-suppressor genes, is considered to be an important step in cancerogenesis and a negative risk factor for survival in patients with myelodysplastic syndromes (MDS); however, its role for response to therapy has not been determined. This study was designed to assess the effect of methylation status on the outcome of conventional induction chemotherapy. EXPERIMENTAL DESIGN:Sixty patients with high-risk MDS or acute myeloid leukemia following MDS were treated with standard doses of daunorubicin and 1-beta-d-arabinofuranosylcytosine. Standard prognostic variables and methylation status of the P15(ink4b) (P15), E-cadherin (CDH), and hypermethylated in cancer 1 (HIC) genes were analyzed before treatment. RESULTS:Forty percent of the patients achieved complete remission (CR). CR rate was lower in patients with high WBC counts (P = 0.03) and high CD34 expression on bone marrow cells (P = 0.02). Whereas P15 status alone was not significantly associated with CR rate (P = 0.25), no patient with hypermethylation of all three genes achieved CR (P = 0.03). Moreover, patients with CDH methylation showed a significantly lower CR rate (P = 0.008), and CDH methylation retained its prognostic value also in the multivariate analysis. Hypermethylation was associated with increased CD34 expression, but not with other known predictive factors for response, such as cytogenetic profile. CONCLUSIONS:We show for the first time a significant effect of methylation status on the outcome of conventional chemotherapy in high-risk MDS and acute myelogenous leukemia following MDS. Provided confirmed in an independent study, our results should be used as a basis for therapeutic decision-making in this patient group.

Patients with high-risk myelodysplastic syndromes (MDS) or acute myeloid leukaemia (AML) secondary to MDS may reach complete remission (CR) following intensive chemotherapy but the CR-duration is usually very short. Promoter hypermethylation of e.g. tumour suppressor genes is considered to be important in cancerogenesis and a negative risk factor for survival in patients with MDS. We designed a prospective clinical trial to assess the impact of methylation status on the outcome of induction chemotherapy and to evaluate the effect of maintenance treatment with 5-azacytidine (aza) on CR duration. Sixty patients with a median age of 68 years (54–83) with high risk MDS (n=23) or AML (n=37) following MDS were treated with standard doses of daunorubicin and ara-C. Standard prognostic variables, and methylation status of the P15 ink4b (P15) , E-cadherin (CDH) and Hypermethylated in Cancer 1 (HIC) genes were analyzed before treatment. Patients in CR were given low dose aza subcutaneously for 5 days/4 weeks until relapse. The CR rate was 40%; significantly lower in patients with high white blood cell counts (P=0.03) and high CD34 expression on bone marrow cells (P=0.02). While P15 status alone was not associated with CR rate (P=0.25) patients with CDH methylation showed a lower CR rate (P=0.008). Moreover, no patient with hypermethylation of all three genes achieved CR (P=0.03). CDH methylation retained its prognostic value in the multivariate analysis. Hypermethylation was associated with increased CD34 expression but not with blast count or cytogenetic risk group. Median duration of CR was 13 months (2 to +37) and 7/ 23 patients (30%) had a CR duration >20 months. Three of four patients with trisomy 8 had CR >20 months. The overall survival of patients reaching CR was 17 months (6 to +40). Methylation status before treatment did not correlate with CR duration. We demonstrate for the first time a significant impact of methylation status on the outcome of conventional chemotherapy in high-risk MDS and MDS-AML and propose that this variable should be further evaluated in prospective studies. CR duration is promising, with a substantial portion of patients showing durable responses.

Objective. 5-azacytidine (azacytidine), a DNA hypomethylating agent, was recently approved as the first therapeutic agent for the treatment of myelodysplastic syndromes. The present subcutaneous dosing schedule, 75 mg/m(2) for 7/28 days, is based on early clinical studies and may constitute a practical problem for patients. The present in vitro study aimed at evaluating the pharmacodynamics of azacytidine, thereby providing a rationale for clinical dose-finding studies.Methods. P39 cells were incubated with 0.1, 0.5, and 1 mu M azacytidine daily for 24, 48, and 72 hours, followed by 48 hours in drug-free medium. The effects of azacytidine on cell growth, proliferation, apoptosis, cell cycle status, and promoter methylation of E-cadherin, ER, and HIC genes were studied.Results. Azacytidine decreased cell growth and proliferation, increased apoptosis, and affected cell cycle status in a dose-dependent manner. However, the exposure time, 24 to 72 hours, at doses between 0.5 and 1 mu M, did not significantly affect any of these variables. Using first-order exponential pharmacokinetic model, we found that the effect of 1, 2, or 3 PM over 24 hours did not differ from that of 0.5 to 1 mu M given over 48 to 72 hours. Induction of promoter hypomethylation was observed already after 24 hours of exposure with >= 0.5 mu M azacytidine with no clear dose-effect relationship.Conclusion. Our results indicate that optimal cellular effects of azacytidine might be achieved by shorter exposure times. The model provides information about the relation between azacytidine dose intensity and exposure time on malignant myeloid cells, which could serve as a rationale for further clinical development of practical, safe, and cost-effective dosing schedules. (c) 2006 International Society for Experimental Hematology.