Novel therapies for myelodysplastic syndromes

MLL-AF6 fusion oncogene sequesters AF6 into the nucleus to trigger RAS activation in myeloid leukemia

A rare location, t(6;11)(q27;q23) (MLL-AF6), is associated with poor outcome in childhood acute myeloid leukemia (AML). The described mechanism by which MLL-AF6, through constitutive self-association and in cooperation with DOT-1L, activates aberrant gene expression does not explain the biological differences existing between t(6;11)-rearranged and other MLL-positive patients nor their different clinical outcome. Here, we show that AF6 is expressed in the cytoplasm of healthy bone marrow cells and controls rat sarcoma viral oncogene (RAS)-guanosine triphosphate (GTP) levels. By contrast, in MLL-AF6-rearranged cells, AF6 is found localized in the nucleus, leading to aberrant activation of RAS and of its downstream targets. Silencing MLL-AF6, we restored AF6 localization in the cytoplasm, thus mediating significant reduction of RAS-GTP levels and of cell clonogenic potential. The rescue of RAS-GTP levels after MLL-AF6 and AF6 co-silencing confirmed that MLL-AF6 oncoprotein potentiates the activity of the RAS pathway through retention of AF6 within the nucleus. Exposure of MLL-AF6-rearranged AML blasts to tipifarnib, a RAS inhibitor, leads to cell autophagy and apoptosis, thus supporting RAS targeting as a novel potential therapeutic strategy in patients carrying t(6;11). Altogether, these data point to a novel role of the MLL-AF6 chimera and show that its gene partner, AF6, is crucial in AML development.

Hypomethylating agents and chemotherapy in MDS

Until recently, the treatment of higher risk myelodysplastic syndrome was based on [1] Intensive chemotherapy using anthracycline-AraC combinations, leading to a lower complete remission rates and a shorter CR duration compared with de novo AML [2], low dose chemotherapy with limited CR rate mainly restricted to patients with normal karyotype. Azacitidine was the first drug to significantly improve survival in higher risk MDS, although it is not curative. Thus, the survival improvement obtained with azacitidine must be the starting point for combination studies, and for utilization of this drug in other situations (before allo SCT, or after chemotherapy or allo SCT as maintenance treatment).

Cost of the treatment of myelodisplastic syndrome in Brazil

INTRODUCTION

Myelodysplastic syndrome is an incurable and rare hematological disease that affects the production of blood cells. One aim of treatment is to maintain the blood-cell count to near-normal levels. This is mainly achieved with hematopoietic- growth factors and transfusions. Our objective was to determine the cost of supportive treatment/care for patients with low and intermediate I risk myelodysplastic syndrome in respect to private healthcare plans in Brazil.

METHOD

We adapted the National Comprehensive Cancer Network treatment guidelines for intermediate risk myelodysplastic syndrome patients to the Brazilian reality, adopting a decision tree to explore treatment combinations. Then, we calculated the costs for each branch of the tree, according to national prices. We also estimated total costs for a cohort of 100 patients, distributed across treatment combinations according to the expected epidemiology. We assumed a horizon of one year of treatment.

RESULTS

The mean cost of treatment for low and intermediate I risk myelodysplastic syndrome is US$ 42,758/patient/year. This cost can vary from US$ 24,282 to US$ 121,952, according to patient characteristics and the treatment used. Overall, patients that require immunotherapy with antithymocyte globulins are associated with the highest cost. Those that achieve disease stability solely with the use of erythropoietin were associated with the lowest cost.

CONCLUSION

In Brazil, treatment of low and intermediate I risk myelodysplastic syndrome is associated with a mean cost of the order of US$ 42,700/patient/year. New types of therapy have the potential to change this scenario if they can diminish the requirements for supportive care.

[Transformation of myelodysplastic syndrome to acute lymphoblastic leukemia: 2 new cases]

Myelodysplastic syndromes (MDS) are clonal disorders of hematopoietic stem cells, with a variable risk of transformation to acute myeloid leukemia. Progression into acute lymphoblastic leukemia (ALL) is an extremely rare event, with very few cases published in children. In this report, we describe two cases of myelodysplastic syndromes that progressed to ALL. Moreover, we review previously reported cases of MDS transformation to acute lymphoblastic leukemia in the pediatric population whose prognosis seems to be similar to that for adults.

Can hypomethylating agents provide a platform for curative therapy in myelodysplastic syndromes?

The hypomethylating agents (HMAs) azacitidine and decitabine have changed the treatment landscape of myelodysplastic syndromes (MDS) since their approval by the United States Food and Drug Administration (US FDA) in 2004 and 2006, respectively. However, neither agent is able to cure patients with MDS, and when patients fail to respond to treatment with these agents, their prognosis is poor. For this reason, investigators are currently testing combination regimens with an HMA as a backbone and altering the dose, schedule, and method of delivery of HMAs. Additionally, more than 30 new molecules are currently being tested in interventional studies for which patients with MDS are eligible to enroll. These efforts may further improve outcomes for patients with MDS. For the time being, allogeneic stem cell transplantation (ASCT) remains patients' only real opportunity for cure and should be performed whenever possible in patients with higher-risk disease.

Preclinical evaluation of Laromustine for use in combination with radiation therapy in the treatment of solid tumors

PURPOSE

These studies explored questions related to the potential use of Laromustine in the treatment of solid tumors and in combination with radiotherapy.

MATERIALS AND METHODS

The studies used mouse EMT6 cells (both parental and transfected with genes for O(6)-alkylguanine-DNA transferase [AGT]), repair-deficient human Fanconi Anemia C and Chinese hamster VC8 (BRCA2(-/-)) cells and corresponding control cells, and EMT6 tumors in mice assayed using cell survival and tumor growth assays.

RESULTS

Hypoxia during Laromustine treatment did not protect EMT6 cells or human fibroblasts from this agent. Rapidly proliferating EMT6 cells were more sensitive than quiescent cultures. EMT6 cells expressing mouse or human AGT, which removes O(6)-alkyl groups from DNA guanine, thereby protecting against G-C crosslink formation, increased resistance to Laromustine. Crosslink-repair-deficient Fanconi Anemia C and VC8 cells were hypersensitive to Laromustine, confirming the importance of crosslinks as lethal lesions. In vitro, Laromustine and radiation produced additive toxicities to EMT6 cells. Studies using tumor cell survival and tumor growth assays showed effects of regimens combining Laromustine and radiation that were compatible with additive or subadditive interactions.

CONCLUSIONS

The effects of Laromustine on solid tumors and with radiation are complex and are influenced by microenvironmental and proliferative heterogeneity within these malignancies.

Thiazolide-induced apoptosis in colorectal cancer cells is mediated via the Jun kinase-Bim axis and reveals glutathione-S-transferase P1 as Achilles' heel

Glutathione-S-transferase of the Pi class (GSTP1) is frequently overexpressed in a variety of solid tumors and has been identified as a potential therapeutic target for cancer therapy. GSTP1 is a phase II detoxification enzyme and conjugates the tripeptide glutathione to endogenous metabolites and xenobiotics, thereby limiting the efficacy of antitumor chemotherapeutic treatments. In addition, GSTP1 regulates cellular stress responses and apoptosis by sequestering and inactivating c-Jun N-terminal kinase (JNK). Thiazolides are a novel class of antibiotics for the treatment of intestinal pathogens with no apparent side effects on the host cells and tissue. Here we show that thiazolides induce a GSTP1-dependent and glutathione-enhanced cell death in colorectal tumor cell lines. Downregulation of GSTP1 reduced the apoptotic activity of thiazolides, whereas overexpression enhanced it. Thiazolide treatment caused strong Jun kinase activation and Jun kinase-dependent apoptosis. As a critical downstream target of Jun kinase we identified the pro-apoptotic Bcl-2 homolog Bim. Thiazolides induced Bim expression and activation in a JNK-dependent manner. Downregulation of Bim in turn significantly blocked thiazolide-induced apoptosis. Whereas low concentrations of thiazolides failed to induce apoptosis directly, they potently sensitized colon cancer cells to TNF-related apoptosis-inducing ligand- and chemotherapeutic drug-induced cell death. Although GSTP1 overexpression generally limits chemotherapy and thus antitumor treatment, our study identifies GSTP1 as Achilles' heel and thiazolides as novel interesting apoptosis sensitizer for the treatment of colorectal tumors.

Molecular biology of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a group of clonal hematopoetic disorders marked by ineffective hematopoiesis, peripheral cytopenias, and an increased risk of transformation to acute myeloid leukemia. Multiple processes govern hematopoietic progenitor proliferation and natural differentiation into mature myeloid elements. Molecular events that disrupt any of these processes have the potential to lead to ineffective hematopoiesis and an MDS phenotype. Recent advances in genomic analysis have identified a number of new genes that may be involved. The molecular description of MDS will lead to better understanding, classification, and treatment of this disease.

NF-κB as a potential therapeutic target in myelodysplastic syndromes and acute myeloid leukemia

IMPORTANCE OF THE FIELD

The inactive NF-κB-inhibitor of NF-κB (IκB) complex is activated by stimuli including pro-inflammatory cytokines, mitogens, growth factors and stress-inducing agents. The release of NF-κB facilitates its translocation to the nucleus, where it promotes cell survival by initiating transcription of genes encoding stress-response enzymes, cell-adhesion molecules, pro-inflammatory cytokines and anti-apoptotic proteins. NF-κB and associated regulatory factors (IκB kinase subunits and bcl-3) are implicated in hematological and solid tumour malignancies. NF-κB appears to be involved in cell proliferation control, apoptosis control, angiogenesis promotion and possibly regulation of diffusion of metastases. There are several reports that inhibition of NF-κB as a therapeutic target may have a role in tumour cell death or growth inhibition.

AREA COVERED IN THIS REVIEW

We review data about inhibition of NF-κB in acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS). We describe the molecular mechanisms underlying NF-κB deregulation in these haematological malignancies.

WHAT THE READER WILL GAIN

Constitutive activation of NF-κB in the nucleus has been reported in some varieties of MDS/AML. The in vitro and in vivo results of NF-κB inhibition in myeloid malignancies are highlighted.

TAKE HOME MESSAGE

NF-κB selective inhibitory drugs may be useful, either as single agents or associated with conventional chemotherapy.

New treatments for myelodysplastic syndromes

In the last decade, significant advances have been made in the treatment of patients with Myelodysplastic Syndromes (MDS). Although best supportive care continues to have an important role in the management of MDS, to date the therapeutic approach is diversified according to the IPSS risk group, karyotype, patient's age, comorbidities, and compliance. Hematopoietic growth factors play a major role in lower risk MDS patients, and include high dose erithropoiesis stimulating agents and thrombopoietic receptor agonists. Standard supportive care should also include iron chelating therapy to reduce organ damage related to iron overload in transfusion-dependent patients. Biologic therapies have been introduced in MDS, as lenalidomide, which has been shown to induce transfusion independence in most lower risk MDS patients with del5q. Hypomethylating agents have shown efficacy in INT-2/high risk MDS patients, reducing the risk of leukemic transformation and increasing survival. Other agents under development for the treatment of MDS include histone deacetylase inhibitors, farnesyltransferase inhibitors, clofarabine and ezatiostat.