Localization of the c-ab1 oncogene adjacent to a translocation break point in chronic myelocytic leukaemia

Malignancy: Molecular Demonstration of BCR/ABL Fusion in a Patient with Chronic Myelogenous Leukemia with Basophilia Carrying a Variant t(16;22) (q24;q11) Philadelphia Chromosome

We report a patient with chronic myelogenous leukemia in chronic phase and basophilia which was found to carry a simple variant t(16;22) (q24;q11) Philadelphia (Ph) chromosome in unstimulated bone marrow mononuclear cells. Molecular analysis of peripheral blood and bone marrow mononuclear cells demonstrated the presence of a bcr-abl chimeric mRNA transcript of the b(3) -a(2) type. These findings confirm that band 9q34 participates in the formation of all Ph chromosomes, either standard or variant, even when this is not detectable by conventional cytogenetics. The available literature concerning variant Philadelphia translocations is also reviewed.

STI571: a gene product-targeted therapy for leukemia

Chronic myelogenous leukemia (CML) is a clonal hematopoietic stem-cell disorder characterized by the (9:22) translocation and resultant production of the constitutively activated bcr-abl tyrosine kinase. Characterized clinically by marked myeloid proliferation, it invariably terminates in an acute leukemia. Conventional therapeutic options include interferon-based regimens and stem-cell transplantation, with stem-cell transplantation being the only curative therapy. Through rational drug development, STI571, a bcr-abl tyrosine kinase inhibitor, has emerged as a paradigm for gene product-targeted therapy, offering new hope for expanded treatment options for patients with CML.

Comparison of effects of the tyrosine kinase inhibitors AG957, AG490, and STI571 on BCR-ABL--expressing cells, demonstrating synergy between AG490 and STI571

STI571 (formerly CGP57148) and AG957 are small molecule inhibitors of the protein tyrosine kinase (PTK) p145(abl) and its oncogenic derivative p210(bcr-abl). AG490 is an inhibitor of the PTK Janus kinase 2 (JAK2). No direct comparison of these inhibitors has previously been reported, so this study compared their effects on factor-dependent FDC-P1, 32D, and MO7e cells and their p210(bcr-abl)-expressing factor-independent derivatives. STI571 was a more potent inhibitor of (3)H-thymidine incorporation in p210(bcr-abl)-expressing cells than was AG957, and it showed superior discrimination between inhibitory effects on parental cell lines and effects on their p210(bcr-abl)-expressing derivatives. Assays performed with and without growth factor demonstrated that STI571 but not AG957 reversed the p210(bcr-abl)-driven factor independence of cell lines. p210(bcr-abl)-expressing cells were less sensitive to AG490 than to AG957 or STI571. However, for p210(bcr-abl)-expressing clones from all 3 cell lines, synergistic inhibition was demonstrated between STI571 and concentrations of AG490 with no independent inhibitory effect. Inhibition of nucleic acid synthesis with AG957 treatment was associated with reduced cell numbers, reduced viability, and small pyknotic apoptotic cells. At concentrations of STI571 that reversed the p210(bcr-abl) factor-independent phenotype, STI571 treatment and growth factor deprivation together were sufficient to induce apoptosis. This study concludes that, for the cell lines studied, (1) STI571 is a more potent and more selective inhibitor of a p210(bcr-abl)-dependent phenotype than AG957; (2) AG490 synergizes with STI571 to enhance its inhibitory effect on p210(bcr-abl)-driven proliferation; and (3) the combination of p210(bcr-abl)-tyrosine kinase inhibition and growth factor signal withdrawal can be sufficient to induce apoptotic death of transformed cells. (Blood. 2001;97:2008-2015)

Mechanisms of transformation by the BCR/ABL oncogene

The Philadelphia chromosome generates a chimeric oncogene in which the BCR and c-ABL genes are fused. The product of this oncogene, BCR/ABL, has elevated ABL tyrosine kinase activity, relocates to the cytoskeleton, and phosphorylates multiple cellular substrates. BCR/ABL transforms hematopoietic cells and exerts a wide variety of biological effects, including reduction in growth factor dependence, enhanced viability, and altered adhesion of chronic myelocytic leukemia (CML) cells. Elevated tyrosine kinase activity of BCR/ABL is critical for activating downstream signal transduction and for all aspects of transformation. This review will describe mechanisms of transformation by the BCR/ABL oncogene and opportunities for clinical intervention with specific signal transduction inhibitors such as STI-571 in CML.

Complete karyotype characterization of the K562 cell line by combined application of G-banding, multiplex-fluorescence in situ hybridization, fluorescence in situ hybridization, and comparative genomic hybridization

This study combines conventional cytogenetics, fluorescence in situ hybridization (FISH), multiplex-FISH and comparative genomic hybridization (CGH). In applying this multimodal approach on the human leukemia cell line K562, the chromosome composition was refined in detail and compared with data from the literature. A hypotriploid karyotype with a modal chromosome number of 67, and 21 unique marker chromosomes were identified. The classification of six markers was identical to published data and the composition of five further markers from the literature could be fully clarified for the first time. The composition of another five markers, which have been interpreted in divergent ways in different studies, were elucidated without doubt. Finally, five new markers of our study seem to have no equivalents in former studies, very likely due to limitations of conventional cytogenetics. The combinatory application of complementary techniques as shown in this study will be very useful to provide the basis of a refined genotype analysis on the chromosomal level.

Comparison of a multiplex reverse transcriptase-polymerase chain reaction for BCR-ABL to fluorescence in situ hybridization, Southern blotting, and conventional cytogenetics in the monitoring of patients with Ph1-positive leukemias

A multiplex reverse transcriptase-polymerase chain reaction (RT-PCR) assay for both major forms of BCR-ABL was compared with fluorescence in situ hybridization (FISH), karyotyping, and Southern blotting for disease monitoring in 37 follow-up bone marrow samples from 32 patients with Ph1-positive leukemia. Of these 37 samples, 33 were from patients with chronic myeloid leukemia (CML) (26 post allogeneic bone marrow transplantation [AlloBMT] and seven during interferon-alpha therapy) and 4 from Ph1-positive acute lymphoblastic leukemia (ALL) patients (1 post AlloBMT and 3 post high dose chemotherapy). For the 27 samples studied after AlloBMT (26 CML and 1 Ph1-positive ALL) the time after transplantation ranged from 1 to 107 months (median 47.5 months). In 8 (22%) of the 37 samples there were discrepant results among methods. The discrepancy rates relative to other techniques were: karyotyping 17% (5 of 29), Southern blotting 18% (6 of 33), multiplex RT-PCR 8% (3 of 37), and FISH 8% (3 of 37). Therefore, the relative accuracy of each method for disease monitoring in Ph1-positive leukemia was: 83% (24 of 29) for karyotyping, 82% (27 of 33) for Southern blotting, 92% (34 of 37) for FISH, and 92% (34 of 37) for multiplex RT-PCR. This multiplex RT-PCR assay appears equivalent to FISH in terms of accuracy, simplicity, and turnaround time and both are superior to Southern blot and conventional cytogenetics in the laboratory monitoring of Ph1-positive leukemias.

Chronic myelogenous leukaemia

In the last decade, improvements in both non-transplant and transplant therapy have extended the lives of patients with CML, particularly those in chronic phase. The future will probably bring a greater understanding of molecular leukaemogenesis and options for treating CML. Non-transplant therapies in development include novel agents and combination therapy. Transplant strategies seek to decrease regimen-related toxicity and directly manipulate the immune system to eradicate disease. Clinical and laboratory science seems poised to add novel therapies to the armamentarium against CML. It is exciting to contemplate what reviews of CML written 10 years from now will discuss.

Allosterically controllable maxizymes cleave mRNA with high efficiency and specificity

Ribozymes are small and versatile nucleic acids that can cleave RNA molecules at specific sites. However, because of the limited number of cleavable sequences on the target mRNA, in some cases conventional ribozymes do not have precise cleavage specificity. To overcome this problem, an allosteric version (a maxizyme) was developed that displayed activity and specificity in vivo. More than five custom-designed maxizymes have demonstrated sensor functions, which indicates that the technology might be broadly applicable in molecular biology and possibly in the clinic.

Multiplex in-cell reverse transcription-polymerase chain reaction for the simultaneous detection of p210 and p190 BCR-ABL mRNAs in chronic myeloid leukemia and Philadelphia-positive acute lymphoblastic leukemia cell lines

We designed a novel multiplex in-cell reverse transcription-polymerase chain reaction method for the simultaneous detection and differentiation of p190 and p210 BCR-ABL mRNAs within single cells from the human chronic myeloid leukemia and Philadelphia positive acute lymphoblastic leukemia. Human K562 chronic myeloid leukemia and SUP B-15 Ph+ acute lymphoblastic leukemia cell lines were used as positive controls for p210 and p190 BCR-ABL mRNAs, respectively. HL60 cell line was used as a negative control. After the leukemia cells were fixed and permeabilized, without extracting nucleic acids, the mRNAs were reverse transcribed to cDNAs, and the cDNAs were amplified by multiplex polymerase chain reaction with fluorescent primers specific for p190 and p210 BCR-ABL mRNAs. After transfer onto glass slides by cytospin, the amplified cells were detected by fluorescence microscopy. Fluorescence microscopy after propidium iodide or 4',6-diamidino-2-phenylindone counterstaining showed that the positive K562 cells exhibited a yellow-green fluorescent cytoplasm around a red nucleus, and that the positive SUP B-15 cells exhibited an orange cytoplasm around a blue nucleus. Only the red or blue nucleus was visible in respective negative HL60 cells. The specificity of amplification was confirmed by the absence of a signal when control experiments were performed either with RNase digestion of mRNA or without reverse transcriptase/Taq polymerase. We conclude that the multiplex in-cell reverse transcription-polymerase chain reaction method is capable of simultaneously detecting and differentiating the p210 and p190 BCR-ABL mRNAs of chronic myeloid leukemia and Philadelphia-positive acute lymphoblastic leukemia cells, and that it may be useful in quantitatively monitoring the minimal residual disease during therapy.

Alterations of P53 and RB genes and the evolution of the accelerated phase of chronic myeloid leukemia

Using the single-strand conformation polymorphism and heteroduplex analyses, the P53 and RB genes were analyzed in cell samples from twenty-eight patients with chronic myeloid leukemia (CML) both at diagnosis and at the onset of accelerated phase (AP) of the disease. No alterations of the P53 or RB genes were found in any of the chronic phase (CP) samples. Structural abnormalities of the P53 gene were observed in ten of twenty-eight AP samples within exons 4, 5, 7 and 9. Of the ten cases of AP disease with altered P53 genes, five patients also suffered from the deletion of the other allele. Alterations of the RB gene could be detected in six AP samples, and aberrant band patterns were found in the analysis of exons 2, 3, 4, 6, 7, 13, 14, 17, 21 and 26. Among the six AP samples with structural abnormalities of the RB gene, two showed the loss of the other allele. It is of note that alterations of both P53 and RB genes were observed in two AP samples. Our data strongly suggest that abnormalities of the P53 and RB genes and acceleration of CML are linked events in some cases of AP.

Advances in immunotherapy of hematologic malignancies: cellular and humoral approaches

Monoclonal antibodies have become an important modality for cancer therapy. Genetically engineered chimeric and humanized antibodies have demonstrated activity against overt lymphoma and leukemia, as well as minimal residual disease. Radioimmunotherapy in both nonmyeloablative and myeloablative regimens has produced significant responses and also minimized radiation exposure to normal tissues. Targeted alpha-particle therapy offers the possibility of selective tumor cell kill. Antibody-drug conjugates have produced remissions in acute leukemia. Many proteins potentially act as leukemia or lymphoma-specific antigens for major histocompatibility complex-restricted T cell cytotoxicity. These include the idiotype proteins, breakpoint cluster region (bcr)-abl and other fusion oncoproteins, myeloid-specific differentiation antigens and minor histocompatibility antigens. Clinical trials exploiting the new understanding of the T cell immunology are underway.

Masked antisense: a molecular configuration for discriminating similar RNA targets

Antisense technology has great potential for the control of RNA expression, but there remain few successful applications of the technology. Expressed antisense RNA can effectively down-regulate expression of a gene over long periods, but cannot differentiate partly identical sequences, such as the mRNA of fusion genes or those with point mutants. We have designed a structured form of expressed antisense, which can discriminate between highly similar mRNA molecules. These 'masked' antisense RNAs have most of the antisense sequence sequestered within duplex elements, leaving a short single-stranded region to initiate binding to target RNA. After contacting the correct target, the structured RNA can unravel, releasing the masked antisense region to form a stable duplex with the mRNA. We demonstrate that suitable masked antisense RNA can discriminate between the two forms of BCR-ABL mRNA that result from the Philadelphia chromosomal translocations, as well as discriminating the normal BCR and ABL mRNA.

Transformation of myeloid leukemia cells to cytokine independence by Bcr-Abl is suppressed by kinase-defective Hck

Bcr-Abl is the constitutively active protein-tyrosine kinase expressed as a result of the Philadelphia translocation in chronic myelogenous leukemia. Bcr-Abl is coupled to many of the same signaling pathways normally regulated by hematopoietic cytokines. Recent work shows that Hck, a member of the Src tyrosine kinase family with myeloid-restricted expression, associates with and is activated by Bcr-Abl. Here we investigated the mechanism of Hck interaction with Bcr-Abl and the requirement for Hck activation in Bcr-Abl transformation signaling. Binding studies demonstrated that the Hck SH3 and SH2 domains are sufficient for interaction with Bcr-Abl in vitro. Hck binding localizes to the Abl SH2, SH3, and kinase domains as well as the distal portion of the C-terminal tail. To address the requirement for endogenous Src family kinase activation in Bcr-Abl signaling, a kinase-defective mutant of Hck was stably expressed in the cytokine-dependent myeloid leukemia cell line DAGM. Kinase-defective Hck dramatically suppressed Bcr-Abl-induced outgrowth of these cells in the absence of cytokine compared with a control cell line expressing beta-galactosidase. In contrast, kinase-defective Hck did not affect cell proliferation in response to interleukin-3, suggesting that the effect is specific for Bcr-Abl. These data show that Hck interacts with Bcr-Abl through a complex mechanism involving kinase-dependent and -independent components and that interaction with Hck or other Src family members is essential for transformation signaling by Bcr-Abl.

CML vaccines as a paradigm of the specific immunotherapy of cancer

T cells are implicated in the effective control of chronic myeloid leukemia (CML). Recently, several clinical observations supported by laboratory data, indicate the presence of CML-specific T cells. Many proteins potentially act as leukemia-specific antigens for MHC-restricted cytotoxicity in CML. These include the bcr-abl fusion protein, myeloid-specific differentiation antigens and minor histocompatibility antigens. There is recent evidence to suggest that bcr-abl junctional peptides are capable of eliciting both CD4 and CD8 responses in normal healthy donors and in patients with CML. Moreover, T cell lines can be generated that react with autologous or HLA-matched fresh CML cells, suggesting that the bcr-abl fusion protein can be processed and expressed in the MHC cell surface molecules. Clinical trials exploiting the new understanding of the immunology of CML are underway.

The phosphatidylinositol polyphosphate 5-phosphatase SHIP1 associates with the dok1 phosphoprotein in bcr-Abl transformed cells

The initial phase of chronic myelogenous leukemia (CML) is triggered by constitutive protein tyrosine kinase activity of the chimeric kinase p210(bcr-abl) (Bcr-Abl). A major substrate of Bcr-Abl was recently identified as the RasGAP-associated 62 kDa docking protein Dok1. Here, we report complex formation between endogenous Dok1 and the SH2 domain-containing phosphatidylinositol polyphosphate 5-phosphatase SHIP1 in hematopoietic cells expressing Bcr-Abl. Expression of Bcr-Abl induced tyrosine phosphorylation of both Dok1 and SHIP1 and the formation of a Dok1/SHIP1 complex. Tyr(P) SHIP1 was also bound to Shc in Bcr-Abl expressing cells. A small amount of Shc/SHIP1/Dok1 trimolecular complex was detected and this was due to binding of Dok1 to SHIP1 that was bound to Shc. In contrast, association of Dok1 with SHIP1 or RasGAP was mutually exclusive. Both the SH2 domain of SHIP1 and the PTB domain of Dok1 were required for complex formation between the two proteins. Neither the specific activity of SHIP1 as an inositol phosphate 5-phosphatase nor the subcellular localization of SHIP1 appeared to be altered by tyrosine phosphorylation. However, the Dok1/SHIP1 complex was only detected in the cytosolic fraction of Bcr-Abl transformed hematopoietic cells. We propose that interaction between Dok1 and SHIP1 modulates the ability of these two proteins to interact with other cytosolic binding partners.

A FISH study of variant Philadelphia rearrangements

A total of 39 variant Philadelphia (Ph) translocations were studied by fluorescence in situ hybridization (FISH) using MBCR/ABL, mBCR/ABL, or DBCR/ABL probes. Seven cases did not have a BCR/ABL fusion signal. Of a total of 32 fusion-positive cases, 5 were simple variants involving chromosome 22 and another chromosome apart from chromosome 9; 23 were complex variants involving chromosomes 22, 9, and a third chromosome (18 cases), or 22, 9, and two other chromosomes (4 cases). Masked Ph rearrangements were detected in 4 cases. One case was a Ph chromosome mimic. Fluorescence in situ hybridization has become a widely used method for studying Ph rearrangements. The latest probe that is being used is the DBCR/ABL (double reciprocal BCR/ABL signals). The expected pattern for this probe is one green ABL signal (1G) on the normal 9, one red BCR signal (1R) on the normal 22, and two fusion signals, BCR/ABL and ABL/BCR (2F), on a derivative 22 and a derivative 9, respectively. Deviant patterns from 1G1R2F, and sometimes 1G1R2F, were indicative of a variant, as long as there was a fusion signal. However, in interphase analysis, it is not possible to visualize a variant rearrangement, and when a deviant pattern involving at least one fusion signal is observed, the following possibilities should be contemplated. The different patterns observed in fifteen Ph variants are described. The patterns observed in variants studied with the DBCR/ABL probe were 2G2R1F (40%), 1G1R2F (20%), 1G1R1F (20%), 1G2R1F (13.3%), and 2G1R1F (6.66%). A single mechanism is involved in the formation of each of these patterns. A 2G2R1F, FISH pattern in 6 cases appears to involve a single concerted event of simultaneous breaks on the participating chromosomes followed by mismatched joining. The three cases with 1G1R2F most probably arose by two sequential rearrangements. The 1G1R1F pattern suggests that either the BCR and ABL breakpoints are different, or there are deletions at the breakpoints, because residual signals are not observed. Two independent events appear to be involved in 1G2R1F with a reverse cryptic 9,22 rearrangement as the first event. In one case of 2G1R1F, the plausible explanation is an insertion of ABL next to BCR and either a simultaneous or a sequential translocation with another chromosome.

Vaccination of patients with chronic myelogenous leukemia with bcr-abl oncogene breakpoint fusion peptides generates specific immune responses

Chronic myelogenous leukemia (CML) presents a unique opportunity to develop therapeutic strategies using vaccination against a truly tumor-specific antigen that is also the oncogenic protein required for neoplasia. CML is characterized by the t(9;22) that results in the bcr-abl fusion oncogene and in the expression of a chimeric protein product p210. Previously we have shown that peptides derived from amino acid sequences crossing the b3a2 fusion breakpoint in p210 elicit class I restricted cytotoxic T lymphocytes and class II responses, respectively, in vitro. Such sequences may thus comprise absolutely tumor-specific antigens in a peptide-based vaccine. We evaluated the safety and immunogenicity of a multidose, bcr-abl breakpoint peptide vaccine in 12 adults with chronic-phase CML. Cohorts of 3 patients each received either 50 microg, 150 microg, 500 microg, or 1500 microg total peptide mixed with 100 microg QS-21 as an immunological adjuvant. Delayed-type hypersensitivity (DTH), humoral responses, and unprimed ex vivo autologous proliferation ((3)H-thymidine incorporation) and cytotoxicity (chromium-51 release) responses were measured. All 68 vaccinations were well tolerated without significant adverse effects. In 3 of the 6 patients treated at the 2 highest dose levels of vaccine, peptide-specific, T-cell proliferative responses (n = 3) and/or DTH responses (n = 2) were generated that lasted up to 5 months after vaccination. Cytotoxic T lymphocytes have not been identified. In conclusion, a tumor-specific, bcr-abl derived peptide vaccine can be safely administered to patients with chronic-phase CML and can elicit a bcr-abl peptide-specific immune response despite the presence of active disease in these patients and approximately 10(12) leukemia cells. (Blood. 2000;95:1781-1787)

Biologic and clinical aspects of autologous stem cell transplantation with mobilized peripheral blood cells in chronic myelogenous leukemia

Over the past 15 years, important developments in the cell and molecular biology of chronic myeloid leukemia (CML) have produced significant changes in understanding of the pathophysiology of the disease. In this article we deal essentially with cell biology as a basis for autografting. The most important achievements of the past years are summarized. There is an exodus of normal hematopoietic cells from bone marrow at the beginning of leukemic invasion. Normal early hematopoietic progenitors (LTC-IC) are preserved at diagnosis and are much more frequent than the Ph-positive counterpart; however, PH-negative LTC-IC rapidly decline with time without a parallel increase of PH-positive LTC-IC. Therefore, probably leukemic stem cells are much fewer than previously thought. Nevertheless, a frequency of Ph-positive KTC-IC of 1/5 10(6) mononuclear cells corresponds with a remarkable tumor burden. Interferon preserves Ph-progenitors in cytogenic remitters. From these studies a new strategy for autografting patients with CML has been developed and is described here. Questions raised by these new techniques are also addressed.

CrkL functions as a nuclear adaptor and transcriptional activator in Bcr-Abl-expressing cells

OBJECTIVE

To identify tyrosine phosphorylated proteins that interact with CrkL in Bcr-Abl-expressing cells and analyze the function of that association.

MATERIALS AND METHODS

Immunoprecipitation of CrkL was performed on lysates from parental cells (Rat-1, MO7e, or 32D) or Bcr-Abl-expressing cells (Rat-1p185, MO7p210, 32Dp210, K562) followed by immunoblotting for pTyr, Stat5, or CrkL. Interactions were confirmed in vitro using GST-CrkL fusion proteins. Electrophoretic mobility shift assays were performed on K562 nuclear extracts using a beta-casein promoter-derived probe. Supershift analysis was performed with CrkL, Stat5, Stat1, Grb2, and peptide-blocked CrkL and Stat5 antibodies. CrkL localization in Rat-1 and Rat-1p185 cells was detected with indirect immunofluorescence. Transcriptional activation was analyzed in COS7 cells transfected with a Stat-responsive luciferase reporter construct and Bcr-Abl, kinase-defective Bcr-Abl, CrkL, or Grb2.

RESULTS

We show that, in Bcr-Abl-expressing cells, CrkL+ interacts with tyrosine phosphorylated Stat5. Additionally, in the presence of Bcr-Abl, CrkL is found in the nucleus, can be detected in a Stat5/DNA complex, and increases transcriptional activation from a Stat-responsive reporter construct.

CONCLUSION

This suggests a novel role for CrkL, functioning as a nuclear adaptor protein that can associate with and activate Stat proteins in Bcr-Abl-expressing cells.

Light microscopic detection of BCR-ABL transcripts after in-cell RT-PCR: fusion gene expression might correlate with clinical evolution of chronic myeloid leukemia

A procedure for in-cell amplification of the hybrid BCR-ABL mRNA by reverse transcription and polymerase chain reaction (RT-PCR) without extraction of the nucleic acids was performed directly in fixed and permeabilized cells of leukemia patients (22 patients with Ph'-positive chronic myeloid leukaemia-CML and 1 with Ph'-positive acute leukaemia-AL, as well as 7 Ph'-negative cases) and Ph'-positive human leukaemia cell lines (K562, LAMA-84, BV173). The labelling of the amplified sequences was done employing biotinylated primers and a second PCR in a semi-nested fashion with a low number of cycles. An enzymatic system based on biotin-streptavidin-chromogen reaction was used for the detection of labeled PCR product, thus producing a coloured product, visible to the eye under a standard light microscope. All samples from patients with cytogenetic and molecular evidence of BCR-ABL rearrangement showed specific cytoplasmic staining at the site of the amplified hybrid transcripts. It allowed definite distinction between positive and negative cells. K562, LAMA-84, BV173 cells were characterized with strong diffuse staining while an interesting finding of the present study was the presence of variable quantities of colour product in patients' samples which might be due to different mRNA expression. Early and intermediate stages of myeloid maturation showed more intense reactivity. Cases with an aggressive course of accelerated or blast phase CML and AL were found to have a considerable subset of cells with strongly expressed signal while cases in chronic phase were characterised with uniform weak to moderate reaction. Our observations support the hypothesis that the amount of BCR-ABL transcript expression within neoplastic cells may play a role in dictating the eventual behaviour of the leukaemic clone. Future studies at a single cell level of larger series of consecutive cases with a follow up might be able to identify those patients who are prone to transformation and provide certain indications for further therapeutic decisions.

Molecular genetics, natural history and the demise of childhood leukaemia

The patterns of genetic change, clonal evolution, natural history and latency are very different in the paediatric leukaemias compared with adult epithelial cancers but are similar to those in other childhood cancers of mesenchymal stem cell origin. This distinction has a biological logic in the context of the selective pressures for clonal emergence in different developmental and cellular contexts and has a major impact on curability. Most childhood leukaemias and some other mesenchymal stem cell tumours are of fetal origin and can metastasize without corruption of restraints on cell proliferation or bypassing apoptosis. In marked contrast to most invasive or metastatic epithelial carcinomas in adults, these former cancers then retain sensitivity to therapeutic apoptosis. Moreover, their abbreviated and less complex evolutionary status is associated with less genetic diversity and instability, minimising opportunity for clonal selection for resistance. A minority of leukaemias in children and a higher fraction in adults do, however, have genetic alterations that bypass cell cycle controls and apoptosis imposition. These are the 'bad news' genotypes. The cellular and molecular diversity of acute leukaemia impacts also on aetiology. Paediatric acute leukaemias can be initiated prenatally by illegitimate recombination and fusion gene formation in fetal haemopoiesis. For acute lymphoblastic leukaemia (ALL) in children, twin studies suggest that a secondary postnatal molecular event is also required. This may be promoted by an abnormal or delayed response to common infections. Even for a classic case of a cancer that is intrinsically curable by systematic chemotherapy i.e. childhood ALL, prevention may turn out to be the preferred option.

Specificity of novel allosterically trans- and cis-activated connected maxizymes that are designed to suppress BCR-ABL expression

Chronic myelogenous leukemia (CML) is associated with the presence of the Philadelphia chromosome, which is generated by the reciprocal translocation of chromosomes 9 and 22. In the case of L6 (b2a2) mRNA, it is difficult to cleave the abnormal mRNA specifically because the mRNA includes no sequences that can be cleaved efficiently by conventional hammerhead ribozymes near the BCR-ABL junction. We recently succeeded in designing a novel maxizyme, which specifically cleaves BCR-ABL fusion mRNA, as a result of the formation of a dimeric structure. As an extension of our molecular engineering of maxizymes, as well as to improve their potential utility, we examined whether an analogous conformational change could be induced within a single molecule when two maxizymes were connected via a linker sequence. An active conformation was achieved by binding of the construct to the BCR-ABL junction in trans, with part of the linker sequence then acting as an antisense modulator in cis (within the complex) to adjust the overall structure. Results of studies in vitro in the presence of cetyltrimethylammonium bromide (CTAB) (but not in its absence) suggested that a certain kind of connected maxizyme (cMzB) might be able to undergo a desired conformational change and, indeed, studies in vivo confirmed this prediction. Therefore, we successfully created a fully functional, connected maxizyme and, moreover, we found that the activity and specificity of catalytic RNAs in vivo might be better estimated if their reactions are monitored in vitro in the presence of CTAB.

BCR/ABL directly inhibits expression of SHIP, an SH2-containing polyinositol-5-phosphatase involved in the regulation of hematopoiesis

The BCR/ABL oncogene causes chronic myelogenous leukemia (CML), a myeloproliferative disorder characterized by clonal expansion of hematopoietic progenitor cells and granulocyte lineage cells. The SH2-containing inositol-5-phosphatase SHIP is a 145-kDa protein which has been shown to regulate hematopoiesis in mice. Targeted disruption of the murine SHIP gene results in a myeloproliferative syndrome characterized by a dramatic increase in numbers of granulocyte-macrophage progenitor cells in the marrow and spleen. Also, hematopoietic progenitor cells from SHIP(-/-) mice are hyperresponsive to certain hematopoietic growth factors, a phenotype very similar to the effects of BCR/ABL in murine cells. In a series of BCR/ABL-transformed hematopoietic cell lines, Philadelphia chromosome (Ph)-positive cell lines, and primary cells from patients with CML, the expression of SHIP was found to be absent or substantially reduced compared to untransformed cell lines or leukemia cells lacking BCR/ABL. Ba/F3 cells in which expression of BCR/ABL was under the control of a tetracycline-inducible promoter showed rapid loss of p145 SHIP, coincident with induction of BCR/ABL expression. Also, an ABL-specific tyrosine kinase inhibitor, CGP57148B (STI571), rapidly caused reexpression of SHIP, indicating that BCR/ABL directly, but reversibly, regulates the expression of SHIP protein. The estimated half-life of SHIP protein was reduced from 18 h to less than 3 h. However, SHIP mRNA also decreased in response to BCR/ABL, suggesting that SHIP protein levels could be affected by more than one mechanism. Reexpression of SHIP in BCR/ABL-transformed Ba/F3 cells altered the biological behavior of cells in culture. The reduction of SHIP due to BCR/ABL is likely to directly contribute to the pathogenesis of CML.

Leukemia patient-derived lymphoblastoid cell lines exhibit increased induction of leukemia-associated transcripts following high-dose irradiation

Improvement in diagnostic cytogenetic techniques has led to the recognition of an increasing number of leukemia-associated chromosomal translocations and inversions. These genetic lesions frequently are associated with the disruption of putative transcription factors and the production of hybrid transcripts that are implicated in leukemogenesis. Epidemiologic evidence suggests that some, but not all, individuals with a history of gamma-irradiation exposure are at increased risk of developing chronic myeloid leukemia (CML). CML is characterized by the Philadelphia chromosome and transcription of the resulting hybrid BCR-ABL gene. Utilizing the leukemia-associated BCR-ABL p210 transcript as a marker, we sought differences in the induction of illegitimate genetic recombination following high-dose gamma-irradiation of karyotypically normal lymphoblastoid cell lines (LCL) derived from individuals with and without a history of myeloid leukemias. Six LCL [4 leukemia patient derived [2 acute myeloid leukemia and 2 CML] and 2 from normal individuals were analyzed with reverse transcriptase polymerase chain reaction for BCR-ABL under stringent conditions following exposure to 0, 50, or 100 Gy of LET gamma-irradiation delivered via a Varian linear accelerator at 4 MV. Transcripts identical to disease-associated b2a2 and b3a2 transcripts were detected both spontaneously (background illegitimate genetic recombination) and following gamma-irradiation. Background BCR-ABL positivity was demonstrable in 4 of the 6 LCL, with no significant difference in detection between leukemic- and nonleukemic-derived LCL. Overall, increasing gamma-irradiation dose resulted in an increased frequency of BCR-ABL transcript detection (0 Gy vs 50 Gy vs 100 Gy,p = 0.0023, Chi-square test). Within the leukemic- but not the nonleukemic-derived LCL there was significantly greater BCR-ABL positivity after gamma-irradiation compared to unirradiated equivalents. Furthermore, the BCR-ABL positivity of both the AML- and CML-derived LCL after gamma-irradiation was significantly greater than that of the nonleukemic-derived LCL after gamma-irradiation. We speculate that this difference in the detection of illegitimate after gamma-irradiation recombination may be due to aberrant DNA double strand break repair mechanisms in individuals predisposed to the development of myeloid leukemias.

Comparative testing of peripheral blood and bone marrow for BCR-ABL transcripts in patients post allogeneic bone marrow transplantation and during interferon treatment for chronic myeloid leukemia

Patients with CML post allogeneic BMT or during treatment with Interferon were monitored in bone marrow and peripheral blood for BCR-ABL transcripts by RT-PCR and in the majority of cases also by Southern blotting. Bone marrow and peripheral blood samples were obtained simultaneously and tested by RT-PCR with the objective to determine the usefulness to follow CML patients by testing peripheral blood rather than bone marrow samples. For the purpose of this study we have considered the test results obtained from bone marrow samples as the standard. A total of 111 CML patients were examined who underwent either an allogeneic BMT (n=91) or were treated with Interferon (n=20) amounting to a total of 163 assessments for BCR-ABL. Concordance of results was observed in 153 samples (93.9%). 10 samples showed discordance. Seven of these were subjected to repeat testing by RT-PCR. The previously obtained discordant results were confirmed. The sensitivity of peripheral blood assays was calculated to be 96.2% with a specificity of 89.5%. RT-PCR results restricted to Southern blot negative patients showed concordance of bone marrow and peripheral blood in 91.1% of tested samples with a sensitivity of 92.7% and a specificity of 88.6%. The subset of patients in which Southern blot testing was not available showed concordance at a similar level. Complete concordance was seen in all patients that were found to be positive by Southern blotting. We conclude from this study that peripheral blood testing for BCR-ABL transcripts by RT-PCR is a test with high sensitivity and specificity and may potentially replace bone marrow testing. This approach will probably result in a high level of acceptance by patients and may permit more frequent monitoring.

Tyrosine phosphorylation enhances the SH2 domain-binding activity of Bcr and inhibits Bcr interaction with 14-3-3 proteins

The cellular Bcr protein consists of an N-terminal serine/threonine kinase domain, a central guanine nucleotide exchange factor homology region and a C-terminal GTPase-activating protein domain. Previous work in our laboratory established that Bcr is a major transformation-related substrate for the v-Fps tyrosine kinase, and tyrosine phosphorylation of Bcr induces Bcr-Grb-2/SOS association in vivo through the Src homology 2 (SH2) domain of Grb-2. In the present study, we mapped the region of Bcr tyrosine phosphorylation by c-Fes, the human homologue of v-Fps, to Bcr N-terminal amino acids 162-413 by using a baculovirus/Sf-9 cell co-expression system. Tyrosine phosphorylation of Bcr by Fes greatly enhanced the binding of Bcr to the SH2 domains of multiple signalling molecules in vitro, including Grb-2, Ras GTPase activating protein, phospholipase C-gamma, the 85,000 M(r) subunit of phosphatidylinositol 3'-kinase, and the Abl tyrosine kinase. In contrast with SH2 binding, tyrosine phosphorylation of Bcr reduced its ability to associate with the 14-3-3 protein Bap-1 (Bcr-associated protein-1), a Bcr substrate and member of a family of phosphoserine-binding adaptor proteins. These experiments provide in vitro evidence that tyrosine phosphorylation may modulate the interaction of Bcr with multiple growth-regulatory signalling pathways.

Effects of the Tyrosine Kinase Inhibitor AG957 and an Anti-Fas Receptor Antibody on CD34+ Chronic Myelogenous Leukemia Progenitor Cells

The hallmark of chronic myelogenous leukemia (CML) is the Philadelphia (Ph) chromosome that fuses genetic sequences of the BCR gene on chromosome 22 with c-ABL sequences translocated from chromosome 9. BCR/ABL fusion proteins have a dysregulated protein tyrosine kinase (PTK) activity exerting a key role in malignant transformation. Targeting the tyrosine kinase activity of BCR/ABL or using agents capable of triggering apoptosis might represent attractive therapeutic approaches for ex vivo purging. AG957, a member of the tyrphostin compounds, exerts a selective inhibition of p210BCR/ABLtyrosine phosphorylation. We report here that preincubation of CML or normal CD34+ cells with graded concentration of AG957 (1 to 100 μmol/L) resulted in a statistically significant, dose-dependent suppression of colony growth from multipotent, erythroid, and granulocyte-macrophage progenitors as well as the more primitive long-term culture-initiating cells (LTC-IC). However, AG957 doses causing 50% inhibition (ID50) of CML and normal progenitors were significantly different for multilineage colony-forming units (CFU-Mix; 12 v 64 μmol/L; P = .008), burst-forming unit-erythroid (BFU-E; 29 v 89 μmol/L;P = .004), colony-forming unit–granulocyte-macrophage (CFU-GM; 34 v 85 μmol/L; P = .004), and LTC-IC (43 v 181 μmol/L; P = .004). In 5 of 10 patients, analysis of BCR/ABL mRNA on single progenitors by reverse transcription-polymerase chain reaction showed that AG957 at 50 μmol/L significantly reduced the mean (±SD) percentage of BCR/ABL-positive progenitors (92% ± 10% v 33 ± 5%;P = .001). Because AG957 treatment resulted in significantly higher percentages of apoptotic cells (30% v9%) in the BCR/ABL-transfected 32DLG7 cells as compared with 32D-T2/93 cells (BCR/ABL-negative), we investigated the combined effects of AG957 with the anti-Fas receptor (Fas-R) monoclonal antibody CH11 that triggers apoptosis. As compared with AG957 alone, the sequential treatment of CML CD34+ cells with AG957 (1 μmol/L) and CH11 (1 μg/mL) increased CFU-Mix, BFU-E, and CFU-GM growth inhibition by 1.6-fold, 3-fold, and 4-fold, respectively. In contrast, the treatment of normal CD34+ cells with AG957 and CH11 failed to enhance AG957-induced colony growth inhibition. We conclude that (1) AG957 inhibits in a dose-dependent manner CML CD34-derived colony formation by both primitive LTC-IC as well as committed CFU-Mix, BFU-E, and CFU-GM; (2) this growth inhibition is associated with the selection of a substantial amount of BCR/ABL-negative progenitors; and (3) the antiproliferative effect of AG957 is dramatically increased by combining this compound with the anti–Fas-R antibody CH11. These data may have significant therapeutic applications.

Effects of the Tyrosine Kinase Inhibitor AG957 and an Anti-Fas Receptor Antibody on CD34+ Chronic Myelogenous Leukemia Progenitor Cells

The hallmark of chronic myelogenous leukemia (CML) is the Philadelphia (Ph) chromosome that fuses genetic sequences of the BCR gene on chromosome 22 with c-ABL sequences translocated from chromosome 9. BCR/ABL fusion proteins have a dysregulated protein tyrosine kinase (PTK) activity exerting a key role in malignant transformation. Targeting the tyrosine kinase activity of BCR/ABL or using agents capable of triggering apoptosis might represent attractive therapeutic approaches for ex vivo purging. AG957, a member of the tyrphostin compounds, exerts a selective inhibition of p210BCR/ABLtyrosine phosphorylation. We report here that preincubation of CML or normal CD34+ cells with graded concentration of AG957 (1 to 100 μmol/L) resulted in a statistically significant, dose-dependent suppression of colony growth from multipotent, erythroid, and granulocyte-macrophage progenitors as well as the more primitive long-term culture-initiating cells (LTC-IC). However, AG957 doses causing 50% inhibition (ID50) of CML and normal progenitors were significantly different for multilineage colony-forming units (CFU-Mix; 12 v 64 μmol/L; P = .008), burst-forming unit-erythroid (BFU-E; 29 v 89 μmol/L;P = .004), colony-forming unit–granulocyte-macrophage (CFU-GM; 34 v 85 μmol/L; P = .004), and LTC-IC (43 v 181 μmol/L; P = .004). In 5 of 10 patients, analysis of BCR/ABL mRNA on single progenitors by reverse transcription-polymerase chain reaction showed that AG957 at 50 μmol/L significantly reduced the mean (±SD) percentage of BCR/ABL-positive progenitors (92% ± 10% v 33 ± 5%;P = .001). Because AG957 treatment resulted in significantly higher percentages of apoptotic cells (30% v9%) in the BCR/ABL-transfected 32DLG7 cells as compared with 32D-T2/93 cells (BCR/ABL-negative), we investigated the combined effects of AG957 with the anti-Fas receptor (Fas-R) monoclonal antibody CH11 that triggers apoptosis. As compared with AG957 alone, the sequential treatment of CML CD34+ cells with AG957 (1 μmol/L) and CH11 (1 μg/mL) increased CFU-Mix, BFU-E, and CFU-GM growth inhibition by 1.6-fold, 3-fold, and 4-fold, respectively. In contrast, the treatment of normal CD34+ cells with AG957 and CH11 failed to enhance AG957-induced colony growth inhibition. We conclude that (1) AG957 inhibits in a dose-dependent manner CML CD34-derived colony formation by both primitive LTC-IC as well as committed CFU-Mix, BFU-E, and CFU-GM; (2) this growth inhibition is associated with the selection of a substantial amount of BCR/ABL-negative progenitors; and (3) the antiproliferative effect of AG957 is dramatically increased by combining this compound with the anti–Fas-R antibody CH11. These data may have significant therapeutic applications.

ALL- and CML-type BCR/ABL mRNA transcripts in chronic myelogenous leukemia and related disorders

Using the reverse transcription polymerase chain reaction, we investigated acute lymphoid leukemia (ALL)-type, and chronic myelogenous leukemia (CML)-type BCR/ABL mRNA expression in a total of 66 patients with chronic myeloproliferative disorder (CMPD). Thirty-six of 37 patients with CML were positive for CML-type mRNA. Thirteen of the 25 CML had ALL-type mRNA expression. The patients with ET, PV, MF, and CMML did not have any detectable BCR/ABL expression. The most remarkable finding was that two patients, a Ph1-positive CML patient and a patient with a presumptive diagnosis of essential thrombocythemia (ET), showed only ALL-type chimeric mRNA expression.

A Novel SH2-Containing Phosphatidylinositol 3,4,5-Trisphosphate 5-Phosphatase (SHIP2) Is Constitutively Tyrosine Phosphorylated and Associated With src Homologous and Collagen Gene (SHC) in Chronic Myelogenous Leukemia Progenitor Cells

Because of the probable causal relationship between constitutive p210bcr/abl protein tyrosine kinase activity and manifestations of chronic-phase chronic myelogenous leukemia (CML; myeloid expansion), a key goal is to identify relevant p210 substrates in primary chronic-phase CML hematopoietic progenitor cells. We describe here the purification and mass spectrometric identification of a 155-kD tyrosine phosphorylated protein associated with src homologous and collagen gene (SHC) from p210bcr/abl-expressing hematopoietic cells as SHIP2, a recently reported, unique SH2-domain–containing protein closely related to phosphatidylinositol polyphosphate 5-phosphatase SHIP. In addition to an N-terminal SH2 domain and a central catalytic region, SHIP2 (like SHIP1) possesses both potential PTB(NPXY) and SH3 domain (PXXP) binding motifs. Thus, two unique 5-ptases with striking structural homology are coexpressed in hematopoietic progenitor cells. Stimulation of human hematopoietic growth factor responsive cell lines with stem cell factor (SCF), interleukin-3 (IL-3), and granulocyte-macrophage colony-stimulating factor (GM-CSF) demonstrate the rapid tyrosine phosphorylation of SHIP2 and its resulting association with SHC. This finding suggests that SHIP2, like that reported for SHIP1 previously, is linked to downstream signaling events after activation of hematopoietic growth factor receptors. However, using antibodies specific to these two proteins, we demonstrate that, whereas SHIP1 and SHIP2 selectively hydrolyze PtdIns(3,4,5)P3 in vitro, only SHIP1 hydrolyzes soluble Ins(1,3,4,5)P4. Such an enzymatic difference raises the possibility that SHIP1 and SHIP2 may serve different functions. Preliminary binding studies using lysates from p210bcr/abl-expressing cells indicate that both Ptyr SHIP2 and Ptyr SHIP1 bind to the PTB domain of SHC but not to its SH2 domain. Interestingly, SHIP2 was found to selectively bind to the SH3 domain of ABL, whereas SHIP1 selectively binds to the SH3 domain of Src. Furthermore, in contrast to SHIP1, SHIP2 did not bind to either the N-terminal or C-terminal SH3 domains of GRB2. These observations suggest (1) that SHIP1 and SHIP2 may have a different hierarchy of binding SH3 containing proteins and therefore may modulate different signaling pathways and/or localize to different cellular compartments and (2) that they may be substrates for tyrosine phosphorylation by different tyrosine kinases. Because recent evidence has clearly implicated both PI(3,4,5)P3 and PI(3,4)P2 in growth factor-mediated signaling, our finding that both SHIP1 and SHIP2 are constitutively tyrosine phosphorylated in CML primary hematopoietic progenitor cells may thus have important implications in p210bcr/abl-mediated myeloid expansion.

A Novel SH2-Containing Phosphatidylinositol 3,4,5-Trisphosphate 5-Phosphatase (SHIP2) Is Constitutively Tyrosine Phosphorylated and Associated With src Homologous and Collagen Gene (SHC) in Chronic Myelogenous Leukemia Progenitor Cells

Because of the probable causal relationship between constitutive p210bcr/abl protein tyrosine kinase activity and manifestations of chronic-phase chronic myelogenous leukemia (CML; myeloid expansion), a key goal is to identify relevant p210 substrates in primary chronic-phase CML hematopoietic progenitor cells. We describe here the purification and mass spectrometric identification of a 155-kD tyrosine phosphorylated protein associated with src homologous and collagen gene (SHC) from p210bcr/abl-expressing hematopoietic cells as SHIP2, a recently reported, unique SH2-domain–containing protein closely related to phosphatidylinositol polyphosphate 5-phosphatase SHIP. In addition to an N-terminal SH2 domain and a central catalytic region, SHIP2 (like SHIP1) possesses both potential PTB(NPXY) and SH3 domain (PXXP) binding motifs. Thus, two unique 5-ptases with striking structural homology are coexpressed in hematopoietic progenitor cells. Stimulation of human hematopoietic growth factor responsive cell lines with stem cell factor (SCF), interleukin-3 (IL-3), and granulocyte-macrophage colony-stimulating factor (GM-CSF) demonstrate the rapid tyrosine phosphorylation of SHIP2 and its resulting association with SHC. This finding suggests that SHIP2, like that reported for SHIP1 previously, is linked to downstream signaling events after activation of hematopoietic growth factor receptors. However, using antibodies specific to these two proteins, we demonstrate that, whereas SHIP1 and SHIP2 selectively hydrolyze PtdIns(3,4,5)P3 in vitro, only SHIP1 hydrolyzes soluble Ins(1,3,4,5)P4. Such an enzymatic difference raises the possibility that SHIP1 and SHIP2 may serve different functions. Preliminary binding studies using lysates from p210bcr/abl-expressing cells indicate that both Ptyr SHIP2 and Ptyr SHIP1 bind to the PTB domain of SHC but not to its SH2 domain. Interestingly, SHIP2 was found to selectively bind to the SH3 domain of ABL, whereas SHIP1 selectively binds to the SH3 domain of Src. Furthermore, in contrast to SHIP1, SHIP2 did not bind to either the N-terminal or C-terminal SH3 domains of GRB2. These observations suggest (1) that SHIP1 and SHIP2 may have a different hierarchy of binding SH3 containing proteins and therefore may modulate different signaling pathways and/or localize to different cellular compartments and (2) that they may be substrates for tyrosine phosphorylation by different tyrosine kinases. Because recent evidence has clearly implicated both PI(3,4,5)P3 and PI(3,4)P2 in growth factor-mediated signaling, our finding that both SHIP1 and SHIP2 are constitutively tyrosine phosphorylated in CML primary hematopoietic progenitor cells may thus have important implications in p210bcr/abl-mediated myeloid expansion.

Extremely high and specific activity of DNA enzymes in cells with a Philadelphia chromosome

BACKGROUND

Chronic myelogenous leukemia (CML) results from chromosome 22 translocations (the Philadelphia chromosome) that creates BCR-ABL fusion genes, which encode two abnormal mRNAs (b3a2 and b2a2). Various attempts to design antisense oligonucleotides that specifically cleave abnormal L6 BCR-ABL fusion mRNA have not been successful. Because b2a2 mRNA cannot be effectively cleaved by hammerhead ribozymes near the BCR-ABL junction, it has proved very difficult to engineer specific cleavage of this chimeric mRNA. Nonspecific effects associated with using antisense molecules make the use of such antisense molecules questionable.

RESULTS

The usefulness of DNA enzymes in specifically suppressing expression of L6 BCR-ABL mRNA in mammalian cells is demonstrated. Although the efficacy of DNA enzymes with natural linkages decreased 12 hours after transfection, partially modified DNA enzymes, with either phosphorothioate or 2'-O-methyl groups at both their 5' and 3' ends, remained active for much longer times in mammalian cells. Moreover, the DNA enzyme with only 2'-O-methyl modifications was also highly specific for abnormal mRNA.

CONCLUSIONS

DNA enzymes with 2'-O-methyl modifications are potentially useful as gene-inactivating agents in the treatment of diseases such as CML. In contrast to conventional antisense DNAs, some of the DNA enzymes used in this study were highly specific and cleaved only abnormal BCR-ABL mRNA.

The critical role of chromosome translocations in human leukemias

Many chromosome abnormalities, especially translocations of inversions, are closely associated with a particular morphologic or phenotypic subtype of leukemia, lymphoma, or sarcoma. Cloning the genes at the breakpoints of these rearrangements has had a major impact on our understanding of the molecular biology of cancer. One such gene is MLL (myeloid-lymphoid or mixed lineage leukemia) located at chromosome band 11q23. The target gene(s) of MLL is unknown at present, but because of its homology to the trithorax gene in Drosophila as well as experimental data from mice, it appears to be involved in maintaining the function of some of the homeobox genes. Most genes involved in translocations have homologs in other organisms. Comparison of the functions of these genes in human cells with their function in other systems has enriched our understanding of their role in cell biology.

Molecular genetics, natural history and the demise of childhood leukaemia

The patterns of genetic change, clonal evolution, natural history and latency are very different in the paediatric leukaemias compared with adult epithelial cancers but are similar to those in other childhood cancers of mesenchymal stem cell origin. This distinction has a biological logic in the context of the selective pressures for clonal emergence in different developmental and cellular contexts and has a major impact on curability. Most childhood leukaemias and some other mesenchymal stem cell tumours are of fetal origin and can metastasize without corruption of restraints on cell proliferation or bypassing apoptosis. In marked contrast to most invasive or metastatic epithelial carcinomas in adults, these former cancers then retain sensitivity to therapeutic apoptosis. Moreover, their abbreviated and less complex evolutionary status is associated with less genetic diversity and instability, minimising opportunity for clonal selection for resistance. A minority of leukaemias in children and a higher fraction in adults do, however, have genetic alterations that bypass cell cycle controls and apoptosis imposition. These are the 'bad news' genotypes. The cellular and molecular diversity of acute leukaemia impacts also on aetiology. Paediatric acute leukaemias can be initiated prenatally by illegitimate recombination and fusion gene formation in fetal haemopoiesis. For acute lymphoblastic leukaemia (ALL) in children, twin studies suggest that a secondary postnatal molecular event is also required. This may be promoted by an abnormal or delayed response to common infections. Even for a classic case of a cancer that is intrinsically curable by systematic chemotherapy i.e. childhood ALL, prevention may turn out to be the preferred option.

Nucleophosmin-anaplastic lymphoma kinase of large-cell anaplastic lymphoma is a constitutively active tyrosine kinase that utilizes phospholipase C-gamma to mediate its mitogenicity

Large-cell anaplastic lymphoma is a subtype of non-Hodgkin's lymphoma characterized by the expression of CD30. More than half of these lymphomas have a chromosomal translocation, t(2;5), that leads to the expression of a hybrid protein comprised of the nucleolar phosphoprotein nucleophosmin (NPM) and the anaplastic lymphoma kinase (ALK). Here we show that transfection of the constitutively active tyrosine kinase NPM-ALK into Ba/F3 and Rat-1 cells leads to a transformed phenotype. Oncogenic tyrosine kinases transform cells by activating the mitogenic signal transduction pathways, e.g., by binding and activating SH2-containing signaling molecules. We found that NPM-ALK binds most specifically to the SH2 domains of phospholipase C-gamma (PLC-gamma) in vitro. Furthermore, we showed complex formation of NPM-ALK and PLC-gamma in vivo by coimmunoprecipitation experiments in large-cell anaplastic lymphoma cells. This complex formation leads to the tyrosine phosphorylation and activation of PLC-gamma, which can be corroborated by enhanced production of inositol phosphates (IPs) in NPM-ALK-expressing cells. By phosphopeptide competition experiments, we were able to identify the tyrosine residue on NPM-ALK responsible for interaction with PLC-gamma as Y664. Using site-directed mutagenesis, we constructed a comprehensive panel of tyrosine-to-phenylalanine NPM-ALK mutants, including NPM-ALK(Y664F). NPM-ALK(Y664F), when transfected into Ba/F3 cells, no longer forms complexes with PLC-gamma or leads to PLC-gamma phosphorylation and activation, as confirmed by low IP levels in these cells. Most interestingly, Ba/F3 and Rat-1 cells expressing NPM-ALK(Y664F) also show a biological phenotype in that they are not stably transformed. Overexpression of PLC-gamma can partially rescue the proliferative response of Ba/F3 cells to the NPM-ALK(Y664F) mutant. Thus, PLC-gamma is an important downstream target of NPM-ALK that contributes to its mitogenic activity and is likely to be important in the molecular pathogenesis of large-cell anaplastic lymphomas.

c-myc locus amplification and the acquisition of trisomy 8 in the evolution of chronic myeloid leukaemia

The biological progression of chronic myeloid leukaemia is often associated with secondary cytogenetic abnormalities but the molecular mechanisms underlying this progression are poorly understood. This study explores the association of c-myc gene amplification with the progression of chronic myeloid leukaemia in fourteen individuals. Three of these cases showed amplification of c-myc during the course of their disease. Cytogenetic and molecular analysis of serial samples from some patients suggested the successive expansion of distinct clones of malignant cells. Our findings also suggest that trisomy 8 and locus amplification could represent alternative mechanisms for increasing c-myc gene dosage.

Molecular genetic characterization of the Philadelphia chromosome detected in reactor personnel highly exposed to radiation from the Chernobyl accident

Clonal del(22q) chromosome aberrations were coincidentally observed in highly exposed reactor personnel of the Chernobyl power plant accident in the course of retrospective biological dosimetry. These aberrant chromosomes were detected in PHA-stimulated cultures from peripheral blood after FPG staining and revealed a morphology similar to a Philadelphia chromosome. A rearrangement of the BCR gene on 22q11 could be confirmed in unstimulated peripheral blood by RFLP analysis from three of four del(22q) carrying cases. FISH analysis of the del(22q) carrying cases with BCR- and ABL-specific DNA probes additionally exhibited a BCR-ABL fusion in 5.2 to 9% of cells in unstimulated blood. Breakpoints within the BCR gene could be located either in the M-bcr or the m-bcr region and thus, a specific breakpoint region could not be detected in these four patients. Since typical clinical leukemic symptoms associated with the translocation (9;22)(q24;q11) could not be observed in these highly irradiated subjects (1.1 to 5.8 Gy), the role of this particular aberration in the development of a radiation-induced leukemia remains obscure.

Transforming potential of Dbl family proteins correlates with transcription from the cyclin D1 promoter but not with activation of Jun NH2-terminal kinase, p38/Mpk2, serum response factor, or c-Jun

The dbl family of oncogenes encodes a large, structurally related, family of growth-regulatory molecules that possess guanine nucleotide exchange factor activity for specific members of the Rho family of Ras-related GTPases. We have evaluated matched sets of weakly and strongly transforming versions of five Dbl family proteins (Lfc, Lsc, Ect2, Dbl, and Dbs) to determine their ability to stimulate signaling pathways that are activated by Rho family proteins. We found that the transforming potential of this panel did not correlate directly with their ability to activate Jun NH2-terminal kinase, p38/Mpk2, serum response factor, or c-Jun. In contrast, transient stimulation of transcription from the cyclin D1 promoter provided a strong correlation with transforming potential, and we found constitutive up-regulation of cyclin D1 protein in Dbl family protein-transformed cells. In addition, we observed that at least two Dbl family members (Lfc and Ect2) induced changes in the actin cytoskeleton and exhibited nuclear signaling profiles that are consistent with a broader range of in vivo substrate utilization than is predicted from their in vitro exchange specificities. In summary, although Dbl family proteins exhibit signaling profiles that are consistent with their in vivo activation of Rho proteins, stimulation of cyclin D1 transcription is the only activity that correlates with transforming potential, thus suggesting that deregulated cell cycle progression may be important for Dbl family protein transformation.

Changes in oncogene expression implicated in evolution of chronic granulocytic leukemia from its chronic phase to acceleration

Expression of nine oncogenes was investigated in cell samples from fifteen patients with Philadelphia chromosome (Ph)-positive chronic granulocytic leukemia (CGL) both at diagnosis and at the onset of accelerated phase (AP) of the disease. The bcr-abl fusion gene, the H-ras gene and the c-myb gene were universally expressed. In comparison with the chronic phase (CP) of the disease, an increase in the levels of bcr-abl-, c-myb- and H-ras-related transcripts was found in three, two and three AP samples, respectively. Elevation of the bcr-abl-related message was associated with duplication of the Ph chromosome and amplification of the bcr-abl fusion gene in one AP sample. No CP samples were positive for c-myc or c-sis expression. On the contrary, c-myc and c-sis were expressed in three and four AP samples, respectively. The presence of c-myc-related transcript was associated with trisomy 8 with or without amplification of the c-myc oncogene in leukemia cells of two patients with CGL in AP. No changes of oncogene expression were found in four AP samples. However, we observed deletions of chromosome 13 and 17 or i(17q) in three of them, suggesting that tumor suppressor gene alterations may also be responsible for the development of AP of CGL. Our data indicate that heterogeneous alterations in oncogenes and tumor suppressor genes accompany the evolution of CGL-CP to the AP of the disease.

High Level Engraftment of NOD/SCID Mice by Primitive Normal and Leukemic Hematopoietic Cells From Patients With Chronic Myeloid Leukemia in Chronic Phase

We have previously shown that intravenously injected peripheral blood (PB) or bone marrow (BM) cells from newly diagnosed chronic myeloid leukemia (CML) patients can engraft the BM of sublethally irradiated severe combined immunodeficient (SCID) mice. We now report engraftment results for chronic phase CML cells in nonobese diabetic (NOD)/SCID recipients which show the superiority of this latter model. Transplantation of NOD/SCID mice with 7 to 10 × 107 patient PB or BM cells resulted in the continuing presence of human cells in the BM of the mice for up to 7 months, and primitive human CD34+ cells, including those detectable as colony-forming cells (CFC), as long-term culture-initiating cells, or by their coexpression of Thy-1, were found in a higher proportion of the NOD/SCID recipients analyzed, and at higher levels than were seen previously in SCID recipients. The human CFC and total human cells present in the BM of the NOD/SCID mice transplanted with CML cells also contained higher proportions of leukemic cells than were obtained in the SCID model, and NOD/SCID mice could be repopulated with transplants of enriched CD34+ cells from patients with CML. These results suggest that the NOD/SCID mouse may allow greater engraftment and amplification of both normal and leukemic (Ph+) cells sufficient for the quantitation and characterization of the normal and leukemic stem cells present in patients with CML. In addition, this model should make practical the investigation of mechanisms underlying progression of the disease and the development of more effective in vivo therapies.

High Level Engraftment of NOD/SCID Mice by Primitive Normal and Leukemic Hematopoietic Cells From Patients With Chronic Myeloid Leukemia in Chronic Phase

We have previously shown that intravenously injected peripheral blood (PB) or bone marrow (BM) cells from newly diagnosed chronic myeloid leukemia (CML) patients can engraft the BM of sublethally irradiated severe combined immunodeficient (SCID) mice. We now report engraftment results for chronic phase CML cells in nonobese diabetic (NOD)/SCID recipients which show the superiority of this latter model. Transplantation of NOD/SCID mice with 7 to 10 × 107 patient PB or BM cells resulted in the continuing presence of human cells in the BM of the mice for up to 7 months, and primitive human CD34+ cells, including those detectable as colony-forming cells (CFC), as long-term culture-initiating cells, or by their coexpression of Thy-1, were found in a higher proportion of the NOD/SCID recipients analyzed, and at higher levels than were seen previously in SCID recipients. The human CFC and total human cells present in the BM of the NOD/SCID mice transplanted with CML cells also contained higher proportions of leukemic cells than were obtained in the SCID model, and NOD/SCID mice could be repopulated with transplants of enriched CD34+ cells from patients with CML. These results suggest that the NOD/SCID mouse may allow greater engraftment and amplification of both normal and leukemic (Ph+) cells sufficient for the quantitation and characterization of the normal and leukemic stem cells present in patients with CML. In addition, this model should make practical the investigation of mechanisms underlying progression of the disease and the development of more effective in vivo therapies.

Chronic myeloid leukemia with minor-bcr breakpoint developed hybrid type of blast crisis

Although a breakpoint in the minor breakpoint cluster region (m-bcr) of the BCR gene is observed in about two-thirds of patients with Philadelphia chromosome-positive acute lymphoblastic leukemia, this type of genomic rearrangement occurs very rarely in chronic myeloid leukemia (CML). We describe here the eighth case of m-bcr CML, and delineate unique clinical characteristics found in common to the 7 cases reported previously. Monocytosis with a low neutrophil/monocyte ratio resembling chronic myelomonocytic leukemia was the most striking feature of m-bcr CML. Splenomegaly and basophilia were not conspicuous in chronic phase. A high percentage of immature granulocytes and low neutrophil alkaline phosphatase score were the findings in common with classical CML. Lymphoid and myeloid blast changes have been observed at and shortly after presentation so far. We found a hybrid type of blast crisis in the course of m-bcr CML.Thus, m-bcr CML may be a definite subtype of CML, exhibiting distinct clinical characteristics. The presence of fusion product of m-bcr mRNA in an earlier myeloid cell may involve monocytic lineage in addition to myeloproliferative defects.

The Philadelphia chromosome as a secondary change in leukemia: three case reports and an overview of the literature

Three cases of acute nonlymphocytic leukemia with a Philadelphia chromosome (Ph) as a secondary abnormality are reported. The Ph was late-appearing in one patient and appeared as an additional anomaly in the other two patients. Fluorescence in situ hybridization studies of the first patient identified the presence of a minor BCR/ABL rearrangement. The findings of these cases support the conclusion that the Ph plays a role not only in leukemogenesis, but also in disease progression. An overview of the literature dealing with similar cases is also presented.