Occupational and environmental risk factors of the myelodysplastic syndromes in the North of France

Emerging drugs for the treatment of myelodysplastic syndrome

Myelodysplastic syndromes (MDS) are a heterogeneous group of clonal haematopoietic stem cell disorders characterised by ineffective haematopoiesis and an increased risk of developing acute myeloid leukaemia. At present, the only curative option is allogeneic stem cell transplantation. However, the majority of patients are not eligible for this therapy, due to excessive treatment-related morbidity and mortality or lack of a suitable donor. As a result, the need for alternative therapies is great. Our improved understanding of the molecular pathogenesis of MDS has resulted in several new promising therapeutic agents. This review will consider the rational development of new agents based on the molecular biology of MDS.

Bone marrow progenitor cells from chemically exposed workers display an intrinsic ability for autonomous proliferation

In this study, the autonomous proliferation of bone marrow progenitor cells (CFU-C), a pathological phenomenon observed in many hematological abnormalities, was investigated in 31 individuals who had been diagnosed as having neutropenia. Of these subjects, 18 had been chronically exposed (range of exposure 5-30 years) to a variety of petroleum distillates. We observed that the group of exposed individuals presented higher numbers of autonomous CFU-C when compared with those unexposed subjects. In addition, follow-up data demonstrated that 20% of the exposed population (4 of the 18) developed malignant hematological diseases. The autonomous CFU-C obtained from all individuals studied was composed predominantly of macrophages. This suggests an involvement of these cells in the development of hematological abnormalities, probably as a result of increased production of chemical myelotoxic metabolites.

Complex cytogenetics in a case of probably work related MDS/AML

In the majority of cases of overt acute myeloid leukemia (AML), there is no knowledge about a preleukemic phase of myelodysplastic syndrome (MDS). A few recent case-control studies suggest an association between MDS and several occupations. We report a unique case of MDS/AML related to the patient's work condition with numerous cytostatic agents. The karyotype revealed a spectrum of genetic rearrangements identified by conventional cytogenetics, fluorescence in situ hybridization (FISH) and spectral karyotyping (SKY). We suggest that amplification of chromosomal material may play a greater role in leukemogenesis than has been recognized previously.

Low frequency of NRAS and KRAS2 gene mutations in childhood myelodysplastic syndromes

In children, myelodysplastic syndromes (MDS) represent less then 10% of all hematological malignancies; consequently, molecular genetic studies dealing with this group of patients are scarce. We have analyzed 35 archival bone marrow samples of children with MDS for the presence of mutations in the first and second exons of the NRAS and KRAS2 genes. Mutations were detected with single-strand conformation polymorphism analysis in three patients. One patient harbored a mutation in the second exon of NRAS and two patients in the second exon of KRAS2. Sequencing was performed in two samples and novel mutations were found in both. One patient had a missense mutation in codon 45 of NRAS; the other had a silent mutation in codon 53 and a missense mutation in codon 55 of KRAS2.

Novel therapies for myelodysplastic syndromes

BACKGROUND

The assessment of patients with myelodysplastic syndromes (MDS) and the choice of therapies remain challenging. New therapies are now emerging after the identification of molecular targets that result in improvement of hematologic parameters and may hold promise for the prevention of disease progression.

METHODS

A review of the English literature was performed that included original articles and related reviews from MEDLINE (PubMed) and abstracts based on published meeting material.

RESULTS

MDS is a heterogeneous group of disorders. Although current classification and prognostic schemes have proven valid to define subgroups, they are insufficient to take into consideration the significant biologic diversity of MDS. New molecular targets are identified as the mosaic of pathophysiologic pathways in MDS is being unraveled. Novel and targeted therapeutic agents, such as the inhibition of farnesyl transferases and receptor tyrosine kinases, more potent thalidomide analogs, and arsenic trioxide, have shown encouraging results and may offer durable benefit to patients with MDS.

CONCLUSIONS

Although progress has been made in the understanding of clinical manifestations and some of the molecular pathways underlying ineffective hematopoiesis and leukemic transformation in MDS, intensive clinical and laboratory research continues to 1) identify further relevant pathophysiologic pathways, 2) better define MDS subgroups, and 3) develop new drugs based on a clearer understanding of disease biology.

Oxidative stress and the myelodysplastic syndromes

The evolution of higher organisms from anaerobic to aerobic living has promoted an elaborate mechanism of defense against potentially toxic oxidants. Many environmental toxicants implicated in the pathogenesis of myelodysplastic syndromes (MDS), including benzene and ionizing radiation, exert toxicity via pro-oxidant mechanisms. The emerging data suggest a probable genetic susceptibility to environmental carcinogenesis through functional polymorphic variants in enzymes that metabolize toxicants and/or protect against oxidative stress. The most studied enzyme is NAD(P)H:quinone oxidoreductase (NQO1). CD34+ cells from individuals homozygous for the NQO1 C609T nonfunctional allelic variant are incapable of enzyme induction following exposure to benzene, thus potentially increasing the hematotoxicity of benzene metabolites. Serologic and molecular markers of oxidative stress are present in many patients with MDS and include an increased concentration of the lipid peroxidation product malondialdehyde and the presence of oxidized bases in CD34+ cells. Potential mechanisms of oxidative stress include mitochondrial dysfunction via iron overload and mitochondrial DNA mutation, systemic inflammation, and bone marrow stromal defects. The biological activity of the antioxidant aminothiol amifostine in vivo suggests that these pathways may be meaningful targets for future therapy in MDS patients.

The myelodysplastic syndrome(s): a perspective and review highlighting current controversies

The myelodysplastic syndrome (MDS) includes a diverse group of clonal and potentially malignant bone marrow disorders characterized by ineffective and inadequate hematopoiesis. The presumed source of MDS is a genetically injured early marrow progenitor cell or pluripotential hematopoietic stem cell. The blood dyscrasias that fall under the broad diagnostic rubric of MDS appear to be quite heterogeneous, which has made it very difficult to construct a coherent, universally applicable MDS classification scheme. A recent re-classification proposal sponsored by the World Health Organization (WHO) has engendered considerable controversy. Although the precise incidence of MDS is uncertain, it has become clear that MDS is at least as common as acute myelogenous leukemia (AML). There is considerable overlap between these two conditions, and the former often segues into the latter; indeed, the distinction between AML and MDS can be murky, and some have argued that the current definitions are arbitrary. Despite the discovery of several tantalizing pathophysiological clues, the basic biology of MDS is incompletely understood. Treatment at present is generally frustrating and ineffective, and except for the small subset of patients who exhibit mild marrow dysfunction and low-risk cytogenetic lesions, the overall prognosis remains rather grim. In this narrative review, we highlight recent developments and controversies within the context of current knowledge about this mysterious and fascinating cluster of bone marrow failure states.

Important features of myelodysplastic syndrome

Myelodysplastic syndromes (MDS) are characterized by peripheral cytopenias in combination with a hyperplastic bone marrow. During the last 15 years, important progress has been made in the understanding of the biology and prognosis of myelodysplastic syndromes. The classification according to the World Health Organization (WHO) includes mainly morphological criteria and is supplemented by the International Prognostic Scoring System (IPSS) which takes cytogenetical changes into consideration when determining the prognosis of MDS. Also MDS after radiotherapy, chemotherapy or chemical exposure must be distinguished from primary MDS. The underlying mechanisms in primary MDS have not yet been established but it is a multistep alteration to the hematopoietic stem cells that include genes involved in cell cycle control, mitotic checkpoints as well as growth factor receptors, secondary signal proteins and transcription factors which gives the cell a growth advantage over its normal counterpart.