Deletions of the derivative chromosome 9 occur at the time of the Philadelphia translocation and provide a powerful and independent prognostic indicator in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is characterized by formation of the BCR-ABL fusion gene, usually as a consequence of the Philadelphia (Ph) translocation between chromosomes 9 and 22. Large deletions on the derivative chromosome 9 have recently been reported, but it was unclear whether deletions arose during disease progression or at the time of the Ph translocation. Fluorescence in situ hybridization (FISH) analysis was used to assess the deletion status of 253 patients with CML. The strength of deletion status as a prognostic indicator was then compared to the Sokal and Hasford scoring systems. The frequency of deletions was similar at diagnosis and after disease progression but was significantly increased in patients with variant Ph translocations. In patients with a deletion, all Ph+ metaphases carried the deletion. The median survival of patients with and without deletions was 38 months and 88 months, respectively (P = .0001). By contrast the survival difference between Sokal or Hasford high-risk and non-high-risk patients was of only borderline significance (P = .057 and P = .034). The results indicate that deletions occur at the time of the Ph translocation. An apparently simple reciprocal translocation may therefore result in considerable genetic heterogeneity ab initio, a concept that is likely to apply to other malignancies associated with translocations. Deletion status is also a powerful and independent prognostic factor for patients with CML. The prognostic significance of deletion status should now be studied prospectively and, if confirmed, should be incorporated into management decisions and the analysis of clinical trials. (C) 2001 by The American Society of Hematology

Targeting self-renewal pathways in myeloid malignancies

A fundamental property of hematopoietic stem cells (HSCs) is the ability to self-renew. This is a complex process involving multiple signal transduction cascades which control the fine balance between self-renewal and differentiation through transcriptional networks. Key activators/regulators of self-renewal include chemokines, cytokines and morphogens which are expressed in the bone marrow niche, either in a paracrine or autocrine fashion, and modulate stem cell behaviour. Increasing evidence suggests that the downstream signaling pathways induced by these ligands converge at multiple levels providing a degree of redundancy in steady state hematopoiesis. Here we will focus on how these pathways cross-talk to regulate HSC self-renewal highlighting potential therapeutic windows which could be targeted to prevent leukemic stem cell self-renewal in myeloid malignancies

The detection pf p53 and cyclin D1 in chronic myelogenous leukaemia patients using fluorescence in situ hybridisation

ThesisChronic myelogenous leukaemia (CML) is a myeloproliferative disorder that results from the neoplastic transformation of haematopoietic progenitor cells. It accounts for 15-20% of leukaemias in adults and occurs with an incidence of 1-2 cases per 100 000 population, and the patients have a median survival period of 3-4 years from diagnosis. Knowledge of normal haematopoiesis has increased the understanding of how specific perturbations may lead to the development of a transformed or malignant phenotype that is now clinically recognized as leukaemia. The discovery of oncogenes initiated a laboratory effort where the focus was to elucidate as yet undescribed oncogenes and to understand how single allele mutations could act dominantly in the "gain of function" ability to transform cells and cause tumours. These investigations obscured the existence of another set of genes which also appeared to be permissive of tumour formation. In contrast to the oncogenes, these genes behaved in a recessive manner so that "loss of function" as opposed to "gain of function", resulted in tumour formation. These genes therefore appeared to behave as tumour suppressor genes. The role of tumour suppressor genes is to prevent tissue overgrowth, nullify cells with damaged genomes, and metastasis. The structure and expression of the p53 gene is altered in about 25% of myeloid blast crisis of CML, whereas chronic phase CML rarely has detectable p53 alterations, suggesting that mutations in the p53 gene might be involved in the evolution of some cases of blast crisis. Oncogenes are genes that have the ability to transform normal cells into cancer cells. Not all O-type cyclins are expressed in each tissue, suggesting that their function may be linked to the specific tissues in which they are expressed. Increased expression of cyclin 01 can playa critical role in tumour development and in maintenance of the malignant phenotype, thus over-expression of cyclin 01 can produce complex effects on various cellular functions involved in growth control and cell cycle progression. Fluorescence in situ hybridization (FISH) allows the detection of numerical aberrations in interphase cell nuclei and provides a simple, fast and reliable means to assess genetic instability in cancer ce lls. Significant p53 loss of allele was detected in 6 out of 25 samples, indicating that the p53 tumour suppressor gene can be involved in the progression of CML from chronic phase to blastic phase. Cyclin 01 amplification was not detected in any of the samples investigated by FISH, indicating that cyclin 01 is not expressed in cells of the lymphoid and myeloid lineages

Chromatin remodeling agents for cancer therapy

Alterations in chromatin structure profoundly influence gene expression during normal cellular homeostasis and malignant transformation. Methylation of cytosines within CpG islands located in promoter and proximal coding regions facilitates recruitment of chromatin-remodeling proteins, which inhibits gene expression. Posttranslational modifications, such as acetylation, methylation, and phosphorylation, of core histone proteins \u27\u27mark\u27\u27 regions of chromatin for recognition by multiprotein complexes, which promote either chromatin relaxation and gene expression or chromatin compaction and repression of gene expression. Many genes become transcriptionally silenced during the development of cancer. Covalent epigenetic modifications such as DNA hypermethylation and histone post-translational modifications are an important early event during carcinogenesis and tumor development. Genes involved in key DNA damage responses pathways, apoptosis signaling and DNA repair, can frequently become methylated and epigenetically silenced in tumors. This may lead to differences in intrinsic sensitivity of tumors to chemotherapy, depending on the specific function of the gene inactivated. The fact that cancer can have an epigenetic etiology has encouraged the development of a new therapeutic option that might be termed "epigenetic therapy". The DNA methylation paradox, manifested as derepression of cancer-testis antigens and silencing of tumor suppressors during malignant transformation, provides rationale for the utilization of chromatin remodeling agents for cancer therapy. In this review, the recent advances in the understanding and clinical development of DNA methyltransferase and Histone deacetylase inhibitors, as well as their current role in cancer therapy, will be discussed

Constitutive cytoplasmic localization of p21Waf1/Cip1 affects the apoptotic process in monocytic leukaemia

In the present study, we analysed the expression and localization of p21Waf1/Cip1 in normal and malignant haematopoietic cells. We demonstrate that in normal monocytic cells, protein kinase C (PKC)-induced p21 gene activation, which is nuclear factor-κB (NF-κB) independent, results in predominantly cytoplasmic localized p21 protein. In acute monocytic leukaemia (M4, M5), monocytic blasts (N=12) show constitutive cytoplasmic p21 expression in 75% of the cases, while in myeloid leukaemic blasts (N=10), low nuclear and cytoplasmic localization of p21 could be detected, which is also PKC dependent. Constitutive p21 expression in monocytic leukaemia might have important antiapoptotic functions. This is supported by the finding that in U937 cells overexpressing p21, VP16-induced apoptosis is significantly reduced (20.0±0.9 vs 55.8±3.8%, P<0.01, N=5), reflected by a reduced phosphorylation of p38 and JNK. Similarly, AML blasts with high cytoplasmic p21 were less sensitive to VP16-induced apoptosis as compared to AML cases with low or undetectable p21 expression (42.25 vs 12.3%, P<0.01). Moreover, complex formation between p21 and ASK1 could be demonstrated in AML cells, by means of coimmunoprecipitation. In summary, these results indicate that p21 has an antiapoptotic role in monocytic leukaemia, and that p21 expression is regulated in a PKC-dependent and NF-κB independent manner.

The detection pf p53 and cyclin D1 in chronic myelogenous leukaemia patients using fluorescence in situ hybridisation

ThesisChronic myelogenous leukaemia (CML) is a myeloproliferative disorder that results from the neoplastic transformation of haematopoietic progenitor cells. It accounts for 15-20% of leukaemias in adults and occurs with an incidence of 1-2 cases per 100 000 population, and the patients have a median survival period of 3-4 years from diagnosis. Knowledge of normal haematopoiesis has increased the understanding of how specific perturbations may lead to the development of a transformed or malignant phenotype that is now clinically recognized as leukaemia. The discovery of oncogenes initiated a laboratory effort where the focus was to elucidate as yet undescribed oncogenes and to understand how single allele mutations could act dominantly in the "gain of function" ability to transform cells and cause tumours. These investigations obscured the existence of another set of genes which also appeared to be permissive of tumour formation. In contrast to the oncogenes, these genes behaved in a recessive manner so that "loss of function" as opposed to "gain of function", resulted in tumour formation. These genes therefore appeared to behave as tumour suppressor genes. The role of tumour suppressor genes is to prevent tissue overgrowth, nullify cells with damaged genomes, and metastasis. The structure and expression of the p53 gene is altered in about 25% of myeloid blast crisis of CML, whereas chronic phase CML rarely has detectable p53 alterations, suggesting that mutations in the p53 gene might be involved in the evolution of some cases of blast crisis. Oncogenes are genes that have the ability to transform normal cells into cancer cells. Not all O-type cyclins are expressed in each tissue, suggesting that their function may be linked to the specific tissues in which they are expressed. Increased expression of cyclin 01 can playa critical role in tumour development and in maintenance of the malignant phenotype, thus over-expression of cyclin 01 can produce complex effects on various cellular functions involved in growth control and cell cycle progression. Fluorescence in situ hybridization (FISH) allows the detection of numerical aberrations in interphase cell nuclei and provides a simple, fast and reliable means to assess genetic instability in cancer ce lls. Significant p53 loss of allele was detected in 6 out of 25 samples, indicating that the p53 tumour suppressor gene can be involved in the progression of CML from chronic phase to blastic phase. Cyclin 01 amplification was not detected in any of the samples investigated by FISH, indicating that cyclin 01 is not expressed in cells of the lymphoid and myeloid lineages. Keywords: chronic myelogenous leukaemia, p53, cyclin 01, fluorescence in situ hybridizatio

Hypermethylierung von E-Cadherin und HIC-1 bei zwei prognostisch verschiedenen AML-Subgruppen

In der vorliegenden Arbeit wurde der Methylierungsstatus von zwei zytogenetisch definierten Formen der akuten myeloischen Leukämie verglichen. Es wurde DNA von sieben Patienten mit t(8;21), die der Niedrigrisikogruppe zugeteilt werden und acht Patienten mit Monosomie 5 bzw.7 oder del(5q) bzw. del(7q), die eine schlechtere Prognose besitzen und der Hochrisikogruppe angehören sowie die DNA von acht nicht an einer malignen Erkrankung leidenden Kontrollpersonen untersucht. Es sollte festgestellt werden, ob sich bestimmte prognostisch divergente AML-Subgruppen bezüglich der Methylierungsfrequenzen oder des Methylierungsphänotyps unterscheiden. Eine semiquantitative Abschätzung des Methylierungsstatus durch PCR-Produkt-Sequenzierung analog Melki et al. war für diesen Zweck jedoch nicht geeignet, so dass eine erheblich arbeits- und kostenintensivere Methode (Klonierung und automatische Sequenzierung) durchgeführt werden musste. Es konnte bei allen AML-Patienten eine signifikant höhere Methylierungsfrequenz als bei den Kontrollpersonen nachgewiesen werden, was bedeutet, dass Methylierung im Sinne einer epigenetischen Alteration offenbar eine Relevanz bei der Entstehung der AML besitzt. Im Unterschied zur vorangehenden Aussage lässt eine Analyse der zytogenetischen Subgruppe jedoch keinen Unterschied in Bezug auf Topographie und Häufigkeit methylierter CpG-Dinukleotide erkennen. Anhand der untersuchten zwei Promotorregionen (E-Cadherin und HIC-1) kann also festgestellt werden, dass aberrante Methylierung bei AML eine häufige Begleiterscheinung ist, aber nach vorläufiger Erkenntnis keine Präferenz zu bestimmten zytogenetischen Risikokonstellationen aufweist. Weitere Untersuchungen zu dieser Frage wären erforderlich, um die pathogenetische Bedeutung von Promotormethylierung bei der AML einzuschätzen und darauf basierend mögliche therapeutische Substanzen, wie z.B. Demethylierungsagenzien für die Behandlung fortgeschrittener Leukämien zu entwickeln

Cause and Consequences of Genetic and Epigenetic Alterations in Human Cancer

Both genetic and epigenetic changes contribute to development of human cancer. Oncogenomics has primarily focused on understanding the genetic basis of neoplasia, with less emphasis being placed on the role of epigenetics in tumourigenesis. Genomic alterations in cancer vary between the different types and stages, tissues and individuals. Moreover, genomic change ranges from single nucleotide mutations to gross chromosomal aneuploidy; which may or may not be associated with underlying genomic instability. Collectively, genomic alterations result in widespread deregulation of gene expression profiles and the disruption of signalling networks that control proliferation and cellular functions. In addition to changes in DNA and chromosomes, it has become evident that oncogenomic processes can be profoundly influenced by epigenetic mechanisms. DNA methylation is one of the key epigenetic factors involved in regulation of gene expression and genomic stability, and is biologically necessary for the maintenance of many cellular functions. While there has been considerable progress in understanding the impact of genetic and epigenetic mechanisms in tumourigenesis, there has been little consideration of the importance of the interplay between these two processes. In this review we summarize current understanding of the role of genetic and epigenetic alterations in human cancer. In addition we consider the associated interactions of genetic and epigenetic processes in tumour onset and progression. Furthermore, we provide a model of tumourigenesis that addresses the combined impact of both epigenetic and genetic alterations in cancer cells