Reviews in clinical and experimental hematology最新文献

Important insights into the cellular and molecular biology of cancer in general and of hematologic malignancies in particular have been gained in the past two decades. The genes, and their protein products, involved in the transformation of cells from normal to neoplastic, as well as in the progression of neoplastic cells to a more aggressive, therapy-resistant phenotype, are being elucidated in great detail. However, most hematologic malignancies, particularly adult acute leukemias, remain associated with high mortality rates and new therapeutic approaches are urgently needed. The challenge is therefore to carefully and efficiently translate the information gained into effective therapeutic strategies. The clinical success achieved by tyrosine kinase inhibitors, such as ST1571 in chronic myelogenous leukemia, has stimulated interest for kinase-based signaling pathways as therapeutic targets in hematologic malignancies. The mitogen-activated protein kinase (MAPK) pathway is a common point of convergence of many different mitogenic and anti-apoptotic signal transduction pathways in hematopoietic, as well as epithelial, cancer cells and can now be clinically targeted by highly selective small molecule inhibitors. The mounting preclinical evidence of anti-leukemic activity of MAPK inhibitors, alone or in combination with pro-apoptotic small molecules or with conventional chemotherapeutic agents provides rationale that MAPK inhibition-based treatment strategies could soon enrich our therapeutic armamentarium against human leukemias.

Proteasome inhibitors represent potential novel anti-cancer therapy. These agents inhibit the degradation of multi-ubiquitinated target proteins mediating cell cycle progression, apoptosis, NF-kappa B activation, inflammation, cell cycle regulatory proteins such as cyclins and cyclin dependent kinase inhibitors, as well as immune surveillance; and regulate anti-apoptosis and cell cycle progression. Proteasome inhibitors also directly induce caspase-dependent apoptosis of tumor cells, despite the accumulation of p21 and p27 and irrespective of the p53 wild type or mutant status. Recent studies demonstrate that PS-341, peptide boronate, has remarkable anti-tumor activity in preclinical and clinical studies, not only in multiple myeloma but also in other malignancies.

Histone acetyltransferase (HAT) and histone deacetylase (HDAC) activities determine the acetylation status of histones, and have the ability to regulate gene expression through chromatin remodeling. Aberrant histone acetylation is known to play a key role in leukemogenesis. A common biologic feature, shared by genetically heterogeneous acute myeloid leukemias (AML), is a block of hematopoietic differentiation by the fusion proteins produced by chromosomal translocations. In many cases, a DNA binding fusion protein, which abnormally interacts with transcriptional co-regulators and increases local concentration of HDAC complexes, imposes a transcriptional repressive state on target gene promoters, which may become refractory to physiologic stimuli. To target this transcriptional repression, HDAC inhibitors (HDACI) have been developed, which are thought to derepress a set of genes whose transcriptional activation induces cell-cycle arrest, apoptosis and cellular differentiation and thus anti-tumoral activity. Therefore, HDACI might be utilized as effective antileukemic agents, and are currently under clinical trials.

Over the last decade, a great deal of attention has been directed at elucidating the role of apoptosis regulators in governing survival decisions in neoplastic cells, particularly those of hematopoietic origin. A major focus of this work has involved investigation of the function of pro- and anti-apoptotic members of the BCL-2 family, and the relationship between these proteins and mitochondrial integrity. Currently, these proteins can be classified into two broad categories: those that modulate mitochondrial function and those that regulate the activation of caspases responsible for activation and execution of the apoptotic cascade. Within the first category, certain proteins (e.g., BCL-2, BCL-xL) act to preserve mitochondrial integrity by preventing loss of mitochondrial membrane potential and/or release of pro-apoptotic proteins such as cytochrome C into the cytosol. Other proapoptotic proteins (e.g., BAX, BAK, BIM) promote release of cytochrome C. These proteins are therefore primarily involved in regulation of the intrinsic, mitochondrial apoptotic pathway. Within the second category, proteins such as the inhibitors of apoptosis proteins (e.g., XIAP) or FLIP block the activation of caspases, particularly those involved in engagement of the receptor-related, extrinsic apoptotic pathway. Cross-talk between the intrinsic and extrinsic pathways exists. For example, the BH3-domain only protein BID is cleaved by the activation of pro-caspase-8 through the extrinsic pathway, and translocates to the mitochondrion to promote cytochrome C release. Apoptosis is also regulated by various signal transduction pathways, possibly through post-translational modifications in BCL-2 family proteins. For example, phosphorylation of BCL-2 through a JNK-dependent mechanism has been postulated to contribute to apoptosis induced by the taxane class of cytotoxic agents. Finally, attempts to modulate apoptotic pathways with small molecules have recently received much attention. For example, small molecule inhibitors of BCL-2 or mimetics of SMAC/DIABLO, which opposes the actions of XIAP, have recently been shown to promote the antineoplastic activity of conventional cytotoxic agents. It is likely that an improved understanding of apoptosis regulation will lead to new insights into neoplastic transformation, and may also provide important leads for the development of novel antileukemic strategies.

The phosphatidilinositol 3-kinase/protein kinase B (PI3K-AKT) pathway presents an exciting new target for molecular therapeutics. While exhibiting great promise, additional preclinical and clinical studies will be required to determine how best to target this pathway to improve patient outcome. A number of questions need to be answered prior to the implementation into patient care practices. As described below, the PI3K-AKT pathway regulates a broad spectrum of cellular processes, some of which are necessary to maintain normal physiological functions, which potentially contribute to the toxicity of the drugs targeting the pathway. Elucidation of the precise function of the PI3K-AKT isoforms, could promote the development of isoform specific approaches to provide a selective action on tumor cells. However, whether this will be possible due to conservation of structural domains is not yet clear. Inhibition of the PI3K-AKT pathway at multiple sites or a combination with inhibitors of different signaling pathways may allow the development of an acceptable therapeutic index for cancer management. Further, inhibition of the PI3K-AKT pathway combined with conventional chemotherapy or radiation therapy may provide a more effective strategy to improve patient outcome. As molecular therapeutics target the underlying defects in patient tumors, molecular diagnostics are required to identify patients with particular genetic aberrations in the pathway. It will be critical to provide adequate therapeutic strategies tailored to each patient. In addition, patients with different genetic backgrounds or in different health conditions could respond adversely to particular therapeutics. Therefore, identification of patients for particular drugs based on the underlying genetic defects in the tumor as well as the characteristics of the host would be of benefit for improving patient outcome. Linking the targeted therapeutics to molecular imaging approaches will determine appropriate biologically relevant dose for patients. It will also define expected tumor responsiveness and eventually will improve efficacy and decrease toxicity. In this regard, personalized molecular medicine is likely to soon provide effective cancer treatment.

In the last decades, treatment of patients with beta-thalassemia has changed considerably, with advances in red cell transfusion and the introduction of iron chelation therapy. This progress has greatly increased the probability for a thalassemic child to reach adult age with a good quality of life. At present, the prognosis for thalassemia major patients is "open-ended". Compliance with the conventional treatment and psychological support are critical to obtain good results. The expectancy of a long survival of good quality encourages the patients to plan their future life, having a job, a family and often children. Optimal treatment of thalassemia major is expensive and for this reason, unfortunately, available only for a minority of patients in the world. Despite the significant advances, other progresses are expected to further improve survival and quality of life. The major aim is the cure of the disease, increasing the possibility of bone marrow transplantation using HLA-matched unrelated donors, and hopefully, in the future, gene therapy. However, even the conventional treatment and in particular iron chelation is expected to improve. Efforts should be made by the Western countries, and by the international health and economic organizations to provide continuous and concrete support for achieving a high standard of management for thalassemia in all places of the world.

We present an overview of the currently known molecular basis of red cell membrane disorders. A detailed discussion of the structure of the red cell membrane and the pathophysiology and clinical aspects of its disorders is reported. Generally speaking, hereditary spherocytosis (HS) results from a loss of erythrocyte surface area. The mutations of most cases of HS are located in the following genes: ANK1, SPTB, SLC4A1, EPB42 and SPTA1, which encode for ankyrin, spectrin beta-chain, the anion exchanger 1 (band 3), protein 4.2 and spectrin alpha-chain, respectively. Hereditary elliptocytosis (HE) reflects a diminished elasticity of the skeleton. Its aggravated form, hereditary pyropoikilocytosis (HPP), implies that the skeleton undergoes further destabilization. The mutations responsible for HE and HPP, lie in the SPTA1 and SPTB gene, and in the EPB41 gene encoding protein 4.1. Allele alpha LELY is a common polymorphic allele, which plays the role of an aggravating factor when it occurs in trans of an elliptocytogenic allele of the SPTA1 gene. Southeast Asian ovalocytosis derives from a change in band 3. The genetic disorders of membrane permeability to monovalent cations required a positional cloning approach. In this respect, channelopathies represent a new frontier in the field. Dehydrated hereditary stomatocytosis (DHS) was shown to belong to a pleiotropic syndrome: DHS + fetal edema + pseudohyperkalemia, which maps 16q23-24. Splenectomy is strictly contraindicated in DHS and another disease of the same class, overhydrated hereditary stomatocytosis, because it increases the risk of thromboembolic accidents.

Primary immune deficiencies (PID) represent inborn errors of immunity. Over the years, detailed analysis of the clinical and laboratory features associated with these unique and rare disorders have shed light on the complex array of signals and processes that govern development and activation of the immune system. While the first examples of PID pertained to severe defects in lymphoid development, more recently a variety of gene defects have been identified in humans that do not compromize the ability to generate lymphocytes, but rather result in profound immune dysregulation. In many cases, identification of the molecular and cellular bases of PID has preceeded development of animal models by gene targeting. Finally, since the very first cases reported in humans, PID have also represented a unique tool to investigate the efficacy of novel therapeutic approaches (from molecular therapy to hematopoietic stem cell transplantation to somatic cells gene therapy), that have been applied or may apply to a variety of more common human diseases.

The term congenital neutropenia (CN) has been used for a group of hematologic disorders characterized by severe neutropenia with absolute neutrophil counts (ANC) below 0.5 x 10(9)/L associated with increased susceptibility to bacterial infections. This group of diseases includes primary bone marrow failure syndromes with isolated neutropenias and neutropenias associated with metabolic or immunologic disorders or with a complex syndrome. To avoid confusion, we prefer using the term CN only for the most severe disorder among this group: severe neutropenia characterized by an early stage maturation arrest of myelopoiesis leading to bacterial infections from early infancy. This disease has originally been described as Kostmann syndrome with an autosomal recessive inheritance. Recent pathogenetic investigations have demonstrated that this clinical phenotype includes also autosomal dominant and sporadic cases with different point mutations in the neutrophil elastase gene in a subgroup of patients. Data on over 400 patients with CN collected by the Severe Chronic Neutropenia International Registry demonstrate that independent from the CN-subtype more than 90% of these patients respond to recombinant human granulocyte-colony stimulating factor (rHuG-CSF filgrastim, lenograstim) with ANC that can be maintained around 1.0 x 10(9)/L. Adverse events include mild splenomegaly, moderate thrombocytopenia, osteoporosis and malignant transformation into myelodysplastic syndrome/leukemia. Development of additional genetic aberrations, e.g., G-CSF-receptor gene mutations, monosomy 7 or ras mutations during the course of the disease indicate an underlying genetic instability leading to an increased risk of malignant transformation. If and how G-CSF treatment impacts on these adverse events remains unclear since there are no historical controls for comparison. Hematopoietic stem cell transplantation is still the only available treatment for patients refractory to G-CSF treatment.

Apoptosis, the cell's intrinsic death program, plays a critical role in the regulation of tissue homeostasis, especially in cell systems with a high turnover rate such as hematopoiesis. Imbalances between survival, proliferation and death of precursor cells or mature cells may result in accelerated loss or impaired output or uncontrolled polyclonal or monoclonal expansion and may pave the way to the development of leukemia. Congenital hematologic disorders are characterized by disturbed growth control of hematopoietic cells. In the previous years, it has become clear that deregulated apoptosis contributes or is even a key determinator of the pathophysiology of diseases such as lymphoproliferation, aplastic anemia or chronic neutropenia. Hematopoietic growth factors have been shown not only to stimulate proliferation of hematopoietic stem cells and committed precursor cells, but also to act as survival factors protecting developing precursor cells from apoptotic signals. The molecular delineation of pathways of apoptosis signaling or survival in hematopoietic cells is expected to provide tools for molecular understanding of the pathophysiology of congenital and acquired hematopoietic disorders and to identify targets for therapeutic intervention strategies.