Targeting proteasome inhibition in hematologic malignancies

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.     

FISH panels for hematologic malignancies

Cytogenetic analysis of hematological malignancies has played a crucial role in the diagnosis and clinical management of patients, as well as in providing fundamental insights into the genetic basis of the pathogenesis of these diseases. Leukemias and lymphomas have lent themselves readily to karyotypic analysis and undoubtedly represent the greatest successes of cytogenetics in human cancer. Several cytogenetic changes have been shown to have considerable prognostic significance also and are being used as measurable targets for response to therapy. Molecular characterization of the recurrent cytogenetic abnormalities has identified genes involved in leukemogenesis and formed a basis for specific treatment strategies. Fluorescence in situ hybridization (FISH) analysis, since its introduction, has revolutionized the field and enabled a more precise determination of the presence and frequency of genetic abnormalities. It is particularly indispensable where metaphase cytogenetics may be difficult in the largely quiescent cells of some hematological malignancies, particularly the lymphoid disorders. FISH probes have been used extensively to detect nonrandom abnormalities in interphase nuclei and the true incidence of chromosome abnormalities has been proven to be much higher than that detected by conventional chromosomal analysis. The avail- ability of a comprehensive line of commercial probes for rapid identification of critical genetic aberrations has contributed to the widespread use of this technique. It has also led to the current practice in most laboratories to test for genetic aberrations by using FISH panels that have been designed to detect genetic changes important not only in the diagnosis of leukemias and lymphomas, but also because of their association with prognosis, to identify high-risk populations in specific hematological cancers, so they can be targeted for aggressive therapy.     

Proteomics in hematologic malignancies

Basic science research in hematology has been determining the functions of gene products using classical approaches that typically involve studying one or a few genes at a time. Proteomics, defined as the study of protein properties on a large scale, provides tools to globally analyze malignant hematologic cells. A major challenge in cancer therapy is the identification of drugs that kill tumor cells while preserving normal cells. Differential display via proteomics enables analysis of direct as well as side-effects of drugs at a molecular level. Proteomics also allows a better understanding of cell signaling pathways involved during apoptosis in hematologic cells. Storing the information in a 2D electrophoresis database enhances the efficiency of proteome research on malignant cells. Finally, the work needed to be carried out on proteomic analysis prior to routine clinical adoption is discussed, and the necessity for multi-institutional collaborations is emphasized.     

Proteomics in hematologic malignancies

Basic science research in hematology has been determining the functions of gene products using classical approaches that typically involve studying one or a few genes at a time. Proteomics, defined as the study of protein properties on a large scale, provides tools to globally analyze malignant hematologic cells. A major challenge in cancer therapy is the identification of drugs that kill tumor cells while preserving normal cells. Differential display via proteomics enables analysis of direct as well as side-effects of drugs at a molecular level. Proteomics also allows a better understanding of cell signaling pathways involved during apoptosis in hematologic cells. Storing the information in a 2D electrophoresis database enhances the efficiency of proteome research on malignant cells. Finally, the work needed to be carried out on proteomic analysis prior to routine clinical adoption is discussed, and the necessity for multi-institutional collaborations is emphasized.     

Drug-related thrombosis in hematologic malignancies

Cancer patients are at increased risk for thrombosis. Among the predisposing factors for the hemostatic imbalance, drugs have a definite role. Induction of thrombosis by drugs involves a variety of mechanisms: Enhancement of procoagulant activity, reduction in anticoagulants synthesis, stimulation of platelet aggregation and endothelial damage. L-asparaginase is associated with thrombotic events, mainly in the venous system. Supportive therapy with fresh frozen plasma is probably insufficient and heparin needs further evaluation. Venous thromboembolism has recently emerged following thalidomide use particularly in combination chemotherapy. The hematopoietic growth factors granulocyte colony-stimulating factor, macrophage-granulocyte colony-stimulating factor and erythropoietin have also been implicated in venous as well as in arterial thrombotic events. Numerous drugs are associated with thrombotic microangiopathy i.e., cyclosporine A, tacrolimus, cisplatin, bleomycin, gemcitabine. The clinical presentation, pathological mechanisms and therapeutic modalities are discussed.     

Thrombosis in children with hematologic malignancies

This review is based on pediatric reports (- January 2004) on the presence of symptomatic thrombosis in children with hematologic malignancies, mainly acute lymphoblastic leukemia, treated with different treatment protocols and associated with acquired and inherited prothrombotic risk factors (factor V G1691A, factor G20210A, MTHFR C677T genotypes, protein C, protein S, antithrombin, elevated levels of lipoprotein(a), and homocysteine). The interactions of treatment modalities, study designs, ethnical backgrounds and associated central lines are discussed. Based on the data presented here, we suggest the use of prednisone and E. coli asparaginase concomitantly administered in a leukemic patient suffering a prothrombotic risk factor to be responsible for the onset of venous thrombosis in the majority of cases. In addition, primary preventive anticoagulant/antithrombotic strategies are discussed.     

Characterization of hematologic malignancies by flow cytometry

The quantitative assessment of cellular DNA and RNA content by flow cytometry to provide useful information for both diagnosis and prognosis of patients with hematologic malignancies is reviewed. While the characterization of cell surface antigens seems to be more germane to questions of the normal cell counterpart (stage) of malignant transformation and the biology of regulation of proliferation and differentiation by cell-cell contact and humoral factors, DNA-derived and RNA-derived parameters were surprisingly sensitive in the distinction of major morphologic groups, drug sensitivity and long-term prognosis. Our findings to date in the study of leukemias, lymphomas and myelomas are summarized.     

Targeting cell cycle and apoptosis for the treatment of human malignancies

Oncogenic transformation leads to cell cycle aberration and apoptosis dysregulation. Targeting cell cycle and apoptosis pathways has emerged as an attractive approach for the treatment of cancer. The activity of cdks can be modulated by targeting these kinases with small molecules that bind to the ATP binding pocket of cdks, or by altering the composition of the cdk/endogenous cdk inhibitor complexes by different mechanisms. Apoptosis can be modulated by targeting pro-apoptotic or pro-survival pathways. Several proteins relevant to oncogenic and proliferative processes, such as p53, bcl-2, AKT, ras and epidermal growth factor receptor, are also important in blocking apoptosis. Several small molecules that modulate cell cycle control and apoptosis have been approved recently and many will be approved in the near future. Several challenges remain, including finding ways of targeting these agents specifically to tumors (sparing normal cells), and the development of rationales for combining these new agents with standard therapies and for prioritizing the development of an overwhelming number of novel small molecules targeting cell cycle and apoptosis. Novel technologies such as genomics and proteomics will be instrumental in designing combinatorial regimens tailored to patients on the basis of the genetic makeup of tumors. Irrespective of all shortcomings, the future of modulation of apoptosis and cell cycle machinery for oncology therapy is quite exciting.     

Kinases as drug discovery targets in hematologic malignancies

Protein kinases have emerged as one of the most promising targets for rational drug discovery. In a similar manner to imatinib mesylate (Gleevec), hematological malignancies offer multiple pharmacologic opportunities for manipulation of kinase-induced tumor cell proliferation. Certain kinases have been validated as targets for drug discovery in hematological malignancies (such as BCR-ABL and FLT3); other novel kinases hold considerable interest for targeted intervention: myeloid leukemias (KDR, KIT, CSF-1R, RAS and RAF), lymphoid leukemias (JAK2 fusion protein, TIE-1, CDK modulators), lymphoma (ALK, CDK modulators, mTOR), myeloproliferative disorders (PDGF-R or FGF-R fusion gene products, FGF-R1) and myeloma (FGF-R3, STAT3). Over the past five years, the number of kinase-targeted drug therapies undergoing clinical development has increased exponentially. This review will focus on novel kinase targets currently undergoing preclinical and clinical investigation.     

Microbiologic consequences of new approaches to managing hematologic malignancies

Opportunistic infections have always been pitfalls on the road of progress in the treatment of diseases that are accompanied by compromised host defences. Because of the severe morbidity and mortality associated with these infections, they have become substantial challenges for the clinicians who offer such patients care. With medical progress, the number of immunocompromised patients is still steadily climbing and it has become evident that deficiencies in host defences mechanisms are multiple as well as changing in harmony with alterations in treatment modalities for underlying diseases. Under normal circumstances, the intact epithelial surfaces of the gastrointestinal tract will prohibit invasion by micro-organisms and the mucociliary barrier of the respiratory tract prevents aspiration of fungal cells and spores, while, in contrast, dead or damaged tissue creates a nidus for infection. It is, however, questionable whether transmigration of organisms inevitably leads to infection. With the growing use of potent immunosuppressive purine analogues, fludarabine, pentostatin and cladibrine, and anti-T and anti-B cell antibodies, such as rituximab and campath, in the management of lymphoreticular malignancies, in combination with increasing emphasis on dose intensity, the number of patients at risk has almost reached levels encountered in recipients of allogenic stem cell grafts as a consequence of long-lasting deficiencies in the cellular immunity. The spectrum of opportunistic pathogens are shifting as anti-leukemic and anti-lymphoma therapy become more intensive and bone marrow transplant practices evolve. Recent studies demonstrate, that patients treated with nonmyeloablative allogeneic transplantation (or "minitransplants") to reduce transplant-related toxicity, are at high risk of contracting a serious infections. Initially bacterial infections were most problematic. However, as strategies to control bacterial infections improved, viruses demanded more attention from the clinicians but the associated morbidity declined due to advances in rapid diagnostics and the introduction of effective antivirals such as acyclovir and ganciclovir. Next to viruses, resistant bacteria, particularly Gram-positive organisms like enterococci and methicillin-resistant staphylococci urged to vigilance. It was obvious that enhanced use of antibacterials inevitably will be accompanied by selection and induction of resistant organisms. Today, opportunistic fungi have become the most frequent and dangerous pathogens. Since the 1980's the rate of nosocomial invasive fungal diseases has doubled without any sign of slowing at the turn of the millenium. During the past decades we have even observed an increased incidence of invasive fungal infections in patients who are not in an end stage of their underlying disease. Yeasts and moulds rank amongst the most frequently isolated pathogens. The relative incidence of the various fungal infections depends on geography as well as on medical practices and local conditions. Candida Aspergillus species remain the prominent fungal pathogens but more rare species are increasingly cultured.     

Translocation of nucleoside analogs across the plasma membrane in hematologic malignancies

Nucleoside analogs are currently used in the treatment of various hematologic malignancies due to their ability to induce apoptosis of lymphoid cells. For nucleoside-derived drugs to exert their action, they must enter cells via nucleoside transporters from two gene families, SLC28 and SLC29 (CNT and ENT, respectively). Once inside the cell, these drugs must be phosphorylated to their active forms. In contrast, some members of the ATP-binding cassette (ABC) protein family have been identified as responsible for the efflux of the phosphorylated forms of these nucleoside-derived drugs. Here, we review the main nucleoside analogs used in hematologic malignancies and focus especially on those that are currently used in chronic lymphocytic leukemia (CLL). Moreover, we discuss the pharmacological profile of the nucleoside transporters, which determines the bioavailability of and cell sensitivity to these nucleoside-derived drugs. We also discuss the expression of nucleoside transporters and their activities in CLL as well as the possibility of modulating these transporter activities as a means of modulating intracellular drug availability and, consequently, responsiveness to therapy.     

Targeting aneuploidy for cancer therapy

Tumor cells frequently display an abnormal number of chromosomes, a phenomenon known as aneuploidy. Tang et al. (2011) now show that aneuploid cells are particularly sensitive to compounds that induce proteotoxic and energy stress. Could this vulnerability lead to new cancer therapies?     

Apoptosis: Molecular regulation of cell death and hematologic malignancies

We describe the molecular mechanisms of apoptosis and its relationships with hematologic malignancies, stressing the concept that, both positive and negative deregulation of apoptosis, may be involved in hematologic human diseases. So, this fundamental process must be balanced by so far unknown mechanisms, involving caspases (cysteine proteases, cleaving the protein substrate after an aspartate residue). These, so far known, ten proteases, are interconnected in a molecular cascade, initiated by the release of cytochrome C from mitochondrial membranes and its interaction with APAF-1 (the homolog of the Caenorhabditis e. CED-4) and with caspase 9, that initiates the proteolitic cascade (1,2). The conclusion is that apoptosis is a very important process, but yet poorly known in molecular details, in spite of the efforts of many scientists. Even the role of bcl-2, the main gene protecting from apoptosis, is still unknown. We close this chapter with a list of ten different technical approaches that can be useful tools to study apoptosis, and tracing the molecular principles on which they are based.