Historical communication: Philadelphia-positive chronic myelogenous leukemia followed for 27 years

Different aneuploidies arise from the same bridge-induced chromosomal translocation event in Saccharomyces cerevisiae

Chromosome translocations are gross chromosomal rearrangements that have often been associated with cancer development in mammalian cells. The feasibility of drastically reshaping the genome with a single translocation event also gives this molecular event a powerful capacity to drive evolution. Despite these implications and their role in genome instability, very little is known about the molecular mechanisms that promote and accompany these events. Here, at the molecular level, we describe 10 morphologically and physiologically different translocants ensuing from the induction of the same bridge-induced translocation (BIT) event in the budding yeast Saccharomyces cerevisiae. We have demonstrated that, despite their common origin from the integration of the same linear DNA construct, all 10 translocation mutant strains have different phenotypes and the ability to sporulate and regulate gene expression and morphology. We also provide insights into how heterogeneous phenotypic variations originate from the same initial genomic event. Here we show eight different ways in which yeast cells have dealt with a single initial event inducing translocation. Our results are in agreement with the formation of complex rearrangements and abnormal karyotypes described in many leukemia patients, thus confirming the modellistic value of the yeast BIT system for mammalian cells.

BO-0742, a derivative of AHMA and N-mustard, has selective toxicity to drug sensitive and drug resistant leukemia cells and solid tumors

This is a preclinical study of BO-0742, a derivative of 3-(9-acridinylamino)-5-hydroxymethyl-aniline (AHMA) and N-mustard, as an anti-cancer agent. MTS assays revealed a broad spectrum of anti-cancer activities in vitro, with the greatest cytotoxicity against leukemia and neuroblastoma including those with drug resistant characteristics, and a good therapeutic index with leukemia being 10-40 times more sensitive to BO-0742 than hematopoietic progenitors. Administration of BO-0742 at an optimal dose schedule based on its pharmacokinetics significantly suppressed the growth of xenografts of human breast and ovarian cancers in mice. Thus, BO-0742 is a potent anti-cancer agent worthy of further clinical development.

Cellular and molecular effects of nonreciprocal chromosome translocations in Saccharomyces cerevisiae

Saccharomyces cerevisiae strains harboring a nonreciprocal, bridge-induced translocation (BIT) between chromosomes VIII and XV exhibited an abnormal phenotype comprising elongated buds and multibudded, unevenly nucleated pseudohyphae. In these cells, we found evidence of molecular effects elicited by the translocation event and specific for its particular genomic location. Expression of genes flanking both translocation breakpoints increased up to five times, correlating with an increased RNA polymerase II binding to their promoters and with their histone acetylation pattern. Microarray data, CHEF, and quantitative PCR confirmed the data on the dosage of genes present on the chromosomal regions involved in the translocation, indicating that telomeric fragments were either duplicated or integrated mostly on chromosome XI. FACS analysis revealed that the majority of translocant cells were blocked in G(1) phase and a few of them in G(2). Some cells showed a posttranslational decrease of cyclin B1, in agreement with elongated buds diagnostic of a G(2)/M phase arrest. The actin1 protein was in some cases modified, possibly explaining the abnormal morphology of the cells. Together with the decrease in Rad53p and the lack of its phosphorylation, these results indicate that these cells have undergone adaptation after checkpoint-mediated G(2)/M arrest after chromosome translocation. These BIT translocants could serve as model systems to understand further the cellular and molecular effects of chromosome translocation and provide fundamental information on its etiology of neoplastic transformation in mammals.

Chronic myelogenous leukemia in chronic phase for 16 years: ongoing hematological remission and late minor cytogenetic response under minimal interferon maintenance therapy

Philadelphia chromosome-positive chronic myelogenous leukemia was diagnosed in a now 37-year old woman 16 years ago. Induction therapy with hydroxyurea and busulphan led to hematological remission lasting for about 4 months without treatment. Then, intermittent busulphan over a 7 years' period, and subsequently, alpha-interferon was given, of which ever decreasing doses (currently 3.5 megaunits interferon-alpha-2c once every 14 days) have been required to keep leukocyte counts in the target range. Although no major cytogenetic response was achieved by maintenance therapy, the patient has now been in an ongoing chronic phase of disease for 16 years. This is a rare case of indolent chronic myelogenous leukemia, in which, for undefined reasons, the leukemic cells have not acquired the capacity to transform leading to disease acceleration, which usually is imminent after a few years.

BCR-ABL gene variants

The BCR-ABL hybrid gene, the main product of the t(9;22)(q34;q11) translocation, is found in the leukaemic clone of at least 95% of CML patients. The fusion protein encoded by BCR-ABL varies in size, depending on the breakpoint in the BCR gene. Three breakpoint cluster regions have been characterized to date: major (M-bcr), minor (m-bcr) and micro (mu-bcr). The overwhelming majority of CML patients have a p210 BCR-ABL gene (M-bcr), whose mRNA transcripts have a b3a2 and/or a b2a2 junction. There is apparently no significant difference between patients with a 5' or a 3' M-bcr breakpoint, except maybe for a slight predominance of b3a2-expressing cases among those with increased platelet counts (ET-like syndrome). The smallest of the fusion proteins, p190BCR-ABL, (m-bcr breakpoint) is principally associated with Ph-positive ALL. Rare cases of CML are due to a p190-type of BCR-ABL gene and, in these, the disease tends to have a prominent monocytic component, resembling CMML. CML resulting from a p230 BCR-ABL gene (mu-bcr breakpoint) is also rare, and has been associated with the CNL variant and/or with marked thrombocytosis. Exceptional CML cases have been described with BCR breakpoints outside the three defined cluster regions, or with unusual breakpoints in ABL resulting in BCR-ABL transcripts with b2a3 or b3a3 junctions, or with aberrant fusion transcripts containing variable lengths of intronic sequence inserts. The reciprocal ABL-BCR gene found in the derivative 9q+ chromosome of the t(9;22) is transcriptionally active in nearly two-thirds of CML patients but has not been shown so far to have a functional role in CML. 'Ph-negative CML' comprises cases of typical CML in whom the BCR-ABL gene can be detected by molecular methods and others who are genuinely BCR-ABL negative and usually have an atypical disease phenotype.

Molecular analysis of an asymptomatic Ph-positive CML patient with 27 years of prolonged remission

We describe the results of clinical, cytogenetic, and molecular biological studies of a patient who, after two courses of treatment with Busulphan, has remained free of symptoms of Philadelphia chromosome-positive chronic myeloid leukemia for 27 years, except for the persistence of a Ph1 chromosome and the presence of its transcribed chimeric mRNA.

The relationship between the location of the breakpoint within the M-bcr and clinical parameters

The Philadelphia chromosome (t9;22)(q34;q11) is a characteristic abnormality in chronic myeloid leukemia. In greater than 95% of the cases, the breakpoint occurs with the M-bcr region of the BCR gene on chromosome 22. Several studies have attempted to correlate the location of the breakpoint within the M-bcr with a clinical parameter. The majority of studies have examined the relationship between the site of breakpoint and the median chronic phase duration (CPD). Some studies have reported a correlation, with 5' breakpoint patients who have a longer median CPD than patients with a 3' breakpoint. However, other groups have reported that no correlation exists. Furthermore, data from some of the latter groups have suggested that a correlation may exist with the lineage of blast crisis which developed and 3' breakpoint patients had a higher than expected number of lymphoid blast crisis. A correlation between high platelet counts at diagnosis and patients with a 3' breakpoint or those who expressed a b3-a2 BCR-ABL mRNA has also been described. No consistent conclusion from any of these studies can be drawn. This may due, in part, to some degree of patient and sample selection, although environmental, genetic or life-style factors may also contribute.

Cell biology of CML--a model linking the chronic and terminal phases

A model for the pathogenesis of chronic myeloid leukaemia (CML) is proposed. It relies on a comparison between normal steady-state and regenerating haemopoiesis and suggests that chronic phase CML stem cells have a finite capacity for self-renewal. According to the model, metamorphosis of the disease occurs once the potential for chronic phase cell production has been exhausted. The model considers also the generation of leukocytosis in the chronic phase and the origin of the terminal phase. Comparison with normal regenerating haemopoiesis allows discrimination between features of CML that are fundamentally abnormal and those which are normally associated with regeneration.

Ph-negative T cells in a patient with chronic myelogenous leukemia for twenty-eight years

The frequency of metaphases without a Philadelphia chromosome was determined in mitogen-stimulated cultures of peripheral blood mononuclear cells (PBMC) and purified T lymphocytes (93% CD2-positive) from a patient with chronic myelogenous leukemia (CML) for 28 years. The PBMC cultures contained few Ph-negative cells (8%), but they constituted 92% of the metaphases in T cell cultures, indicating few if any Ph-positive T cells in the patient's circulation. The results demonstrate that T cells derived from the leukemic clone may fail to replace the non-neoplastic population even when CML arises in childhood and the patient survives for many years. This raises questions concerning the normal role of the bone marrow as a source of T cells after infancy, and also whether Ph-positive lymphocytes may be at a disadvantage for growth.