In acute myeloid leukemia, coexpression of at least two proteins, including P-glycoprotein, the multidrug resistance-related protein, bcl-2, mutant p53, and heat-shock protein 27, is predictive of the response to induction chemotherapy

To identify prognostic factors alternative or additional to P-glycoprotein (Pgp), we studied the impact of the multidrug resistance-related protein (MRP), bcl-2 (flow cytometry), mutant p53 (single-strand conformation polymorphism), and heat-shock protein 27 (HSP27, Western blotting) in myeloid blasts obtained at the time of diagnosis in patients with de novo acute myeloid leukemia (AML). We collected bone marrow samples from untreated AML patients, prepared the cells as well as the cellular protein, and froze all the material. We then analyzed 20 patients who responded with complete remission (CR) and 20 patients who had blast persistence (BP). The purpose of the study was to determine whether leukemic blasts from patients with BP were more resistant to chemotherapy than those from patients with CR. There was no significant correlation between the expression of any of these proteins alone and treatment outcome in both groups studied. In contrast, there was a significant correlation between the coexpression of at least two of these proteins and response (p = 0.0298), which turned out to be a significant independent prognostic factor for treatment failure (p = 0.0329, relative risk = 1.5) according to multivariate analysis. We conclude that drug resistance in AML is multifactorial. Thus, coexpression of different resistance mechanisms may be responsible for the primary drug resistance in de novo AML.

Induction of PPARgamma1 expression in human THP-1 monocytic leukemia cells by 9-cis-retinoic acid is associated with cellular growth suppression

9-cis-Retinoic acid (RA) and peroxisome proliferator activated receptor gamma (PPARgamma) regulates cellular growth and differentiation. In THP-1 cells, a human monocytic leukemia cell line, RA markedly induced PPARgamma1 RNA, nuclear PPARgamma1 protein and suppressed cell growth. The PPARgamma ligand, BRL49653 enhanced RA's growth suppression ability. With BRL49653 alone, THP-1 cell growth was only marginally suppressed. Cell cycle analysis revealed the G1 phase cell population was significantly increased when cells were treated with both ligands. RA induced growth suppression did not differentiate the THP-1 cells to macrophages. Phorbol ester (PMA) induced differentiation of cells to macrophage also induced PPARgamma1 expression, however when RA is given either simultaneously or sequentially to these cells, no further increase in expression of the nuclear receptor was observed. Overall, these data suggest RA induction of PPARgamma1 may block cell growth and may have application for the treatment of proliferative diseases.

Intestinal permeability in patients with acute myeloid leukemia

Intestinal permeability was studied in patients with acute myeloid leukemia (AML) before, during and after chemotherapy. Intestinal permeability was determined by the lactulose (La)/mannitol (Ma) absorption test in 16 adult patients with de novo AML. The hydrogen breath test was used to disclose bacterial fermentation of the test substances in the small intestine. The permeability was found significantly increased (p<0.02) in the patients before induction chemotherapy treatment. During induction treatment and throughout the cytopenic period the intestinal permeability was constantly and significantly increased, compared with controls. In patients with abnormally increased permeability, no increase in hydrogen breath test result was noted. From our results it can be concluded that increased intestinal permeability is present in AML patients before commencing chemotherapy. Factors other than chemotherapy would seem to be more important regarding the occurrence of intestinal disturbances in these patients.

Reconstitution of IL6-inducible differentiation of a myeloid leukemia cell line by activated Stat factors

Differentiation of the myeloid leukemia cell line M1 by treatment with IL6-type cytokines depends on activation of the Jak/Stat (Janus kinase/signal transducer and activator of transcription) pathway. Defects in this cascade are correlated with an impaired cytokine-inducible differentiation of various other myeloid cell lines. Although treatment with IL-6 increased the amount of activated transcription factor Stat3 in the myeloid leukemia line C, differentiation was not induced. However, after cotransfection with expression constructs for the tyrosine kinase Jak2 and Stat factors 3 or 5a, treatment of the cells with IL-6 caused a decrease in the number of viable cells. In parallel, an increase in the percentage of differentiated cells occurred. These findings are consistent with the hypothesis that the Jak/Stat signaling cascade plays an important role in cytokine-induced differentiation of myeloid leukemia cells.

Characterization of siglec-5, a novel glycoprotein expressed on myeloid cells related to CD33

We describe the characterization of siglec-5 (sialic acid-binding Ig-like lectin-5), a novel transmembrane member of the immunoglobulin superfamily, highly related to the myeloid antigen, CD33. A full-length cDNA encoding siglec-5 was isolated from a human activated monocyte cDNA library. Sequencing predicted that siglec-5 contains four extracellular immunoglobulin-like domains, the N-terminal two of which are 57% identical to the corresponding region of CD33. The cytoplasmic tail is also related to that of CD33, containing two tyrosine residues embodied in immunoreceptor tyrosine-based inhibitory motif-like motifs. The siglec-5 gene was shown to map to chromosome 19q13.41-43, closely linked to the CD33 gene. When siglec-5 was expressed on COS cells or as a recombinant protein fused to the Fc region of human IgG1, it was able to mediate sialic acid-dependent binding to human erythrocytes and soluble glycoconjugates, suggesting that it may be involved in cell-cell interactions. By using specific antibodies, siglec-5 was found to have an expression pattern distinct from that of CD33, being present at relatively high levels on neutrophils but absent from leukemic cell lines representing early stages of myelomonocytic differentiation. Western blot analysis of neutrophil lysates indicated that siglec-5 exists as a disulfide-linked dimer of approximately 140 kD.

Analysis of cell death in myeloid cells inducibly expressing the cell cycle protein p55Cdc

p55Cdc, a cell cycle protein is expressed in cycling mammalian cells and is required for normal cell division. Expression of this protein is regulated during the cell cycle, peaking in late G1 and S. We have previously shown that constitutive expression of p55Cdc results in inhibition of granulocyte differentiation. Degradation of p55Cdc is also required for apoptosis in growth factor and serum starved cells. In the present study we prepared stably transfected cells conditionally expressing p55Cdc in response to zinc stimulation to investigate the role of inducible p55Cdc expression in apoptosis of myeloid cells. We report that inducible expression of p55Cdc in the myeloid leukemic cell line 32Dc13 resulted in increased cell death. p55Cdc overexpression led to a statistically significant decrease in the viability of 32Dc13 cells compared with that of control cells. Furthermore, cell staining and flow cytometry analysis revealed that p55Cdc-overexpressing 32Dc13 cells progressed to apoptosis much earlier than uninduced cells. These results suggest that inducible expression of p55Cdc leads to earlier increases in cell death in the absence of growth factor and serum in myeloid leukemic cells.

Internal tandem duplication of the FLT3 gene is a novel modality of elongation mutation which causes constitutive activation of the product

An internal tandem duplication (ITD) of the FLT3 gene is found in nearly 20% of acute myeloid leukemia (AML) and 5% of myelodysplastic syndrome cases. Our serial studies on 51 samples with the FLT3 gene mutation indicated that the ITD was frequently (47/51) clustered in the tyrosine-rich stretch from codon 589 to 599 and rarely (3/51) in its downstream region, both of which are located within the juxtamembrane (JM) domain. One remaining sample had an insertion into the JM domain of nucleotides of unknown origin. To elucidate the biological relevance of the ITD or the insertion, we expressed various types of mutant FLT3 in Cos 7 cells. All mutant FLT3 studied were ligand-independently dimerized and their tyrosine residues were phosphorylated. The Y589 of FLT3 was essential for the phosphorylation in the wild FLT3, but a Y589F conversion did not affect the phosphorylation status of the mutant FLT3. These findings suggest that the elongation of the JM domain rather than increase of tyrosine residues causes gain-of-function of FLT3. Thus, ITD is a novel modality of somatic mutation which activates its product. Since the DNA corresponding to codon 593 to 602 potentially forms a palindromic intermediate, we propose that a DNA-replication error might be associated with generating the ITD of the FLT3 gene.

The expression of co-stimulatory molecules and their relationship to the prognosis of human acute myeloid leukaemia: poor prognosis of B7-2-positive leukaemia

We examined the expression of co-stimulatory molecules on leukaemic cells of 52 adult patients with acute myeloid leukaemia (AML) (34 men and 18 women) and analysed the relationship between these expressions and the patient's prognosis. B7-1 was not expressed in any of the 23 patients investigated, whereas B7-2 was expressed in 26/52 patients (50.0%). B7-2 was expressed in all AML patients with monocytic morphology (M4 or M5) and in 16/42 cases without monocytic morphology. CD54 was expressed in 28/ 37 patients examined (75.7%), and CD58 was expressed in all of the AML patients except one (M 7). The overall survival of the 26 B7-2-positive leukaemia patients (1-24 months, median survival 11.5 months) was significantly shorter than that of the 26 B7-2-negative leukaemia patients (1-71+ months, median 35.1 months) (P=0.0080). In addition, the B7-2-positive patients exhibited significantly shorter disease-free survival periods compared to the B7-2-negative patients (P=0.021). There was no significant difference in age, sex, haematological data and complete remission rate between the B7-2-positive and B7-2-negative patients. Our results indicated that B7-2 is one of the most crucial factors in the prognosis of adult acute leukaemia and can be expected to have an important role in tumour immunity.

Bcl-2 expression by myeloid precursors in myelodysplastic syndromes: relation to disease progression

RATIONALE AND METHODS

the bcl-2 oncogene blocks apoptosis in various cell types and is expressed by normal myeloid precursors, declining with maturation. To investigate whether bcl-2 plays a role in the increase of myeloblasts in myelodysplastic syndromes (MDS) and their progression to acute myeloid leukemia (AML), we studied bcl-2 expression in initial (pre-therapy) bone marrow biopsies from MDS at early (refractory anemia, RA, with or without ring sideroblasts) and advanced stages (RA with excess blasts, and in transformation). Sequential biopsies were also studied to evaluate the effect of time or disease progression, including evolution to AML, or therapy with granulocyte colony stimulating factor (G-CSF). Early myeloid precursors (EMPs), predominantly myeloblasts, were identified in paraffin sections after immunostaining; bcl-2-positive EMPs were enumerated as a percentage of all EMPs (Bcl-2%), and by their absolute frequency per x 900 microscopic field (Bcl-2 index).

FINDINGS

in initial biopsies, the Bcl-2% and Bcl-2 index in early MDS (9.9+/-2.6 and 1.4+/-0.6, respectively; mean+/-S.E.) were significantly lower than in advanced MDS (26.4+/-3.6, 4.6+/-1.4), but similar to controls (8.1+/-0.3 and 0.8+/-0.1). The Bcl-2% and Bcl-2 index in three patients with AML evolved from MDS (57.4+/-17.9 and 85.1+/-62.4) were similar to values for seven patients with de novo AML (63.0+/-10.0, 98.4+/-29.8) and significantly higher than values for other groups. Bcl-2% showed relative increments with time or disease progression (range, 21-273%; 11 of 18 sequential biopsies from six of ten MDS patients), which was not clearly altered by G-CSF therapy (four of six patients with, two of four patients without treatment).

CONCLUSIONS

bcl-2 expression by EMPs (in both proportion and absolute number) correlated with initial MDS stage, progressed over time independent of G-CSF therapy, and was associated with evolution to AML. These data provide support for the hypothesis that MDS progression is related to accumulation of immature myeloid cells with increased bcl-2 expression and decreased apoptosis.

Lung resistance protein (LRP) gene expression in adult acute myeloid leukemia: a critical evaluation by three techniques

The role of LRP in clinical drug resistance in acute myeloid leukemia (AML) is controversial. We therefore compared multiple assays, including RT-PCR, immunocytochemistry (ICC) and flow cytometry (FC), in 10 cell lines and in 47 fresh and thawed AML cells in order to validate and to quantitate measures for LRP phenotype detection. We also compared different ways of expressing the results. Lastly, in cell lines, we analyzed the 50% lethal concentration (LC50), by MTT assay, of cisplatin which could estimate the functionality of LRP. The reproducibility of LRP detection measured by RT-PCR, ICC and FC was good. In the same way, within the same technique, there was good correlation between the different methods of expressing the results of LRP level. Therefore, the discrepancies noted with the three techniques used were neither a problem of reproducibility nor a problem of results expression. On the other hand, there was only a correlation between ICC and FC, and no correlation between RT-PCR and LRP protein detection techniques. Therefore, RT-PCR is probably not the optimal technique for LRP detection. We have shown in 10 cell lines a higher correlation between FC and LC50 of cisplatin than between ICC and LC50 of cisplatin and no correlation between RT-PCR and LC50 of cisplatin. For five patients, there was a dissociation between ICC and FC. Four patients were positive by FC and negative by ICC and only one patient was negative by FC and positive by ICC. Therefore, if in vitro resistance to cisplatin represents the functionality of LRP, we recommend the use of FC rather than ICC to detect LRP expression. Besides the measurement of LRP as a diagnostic tool in the evaluation of resistance to chemotherapy in patients with AML, we urgently need to establish a functional test in order to assess LRP activity.

Stem cell factor enhances the adhesion of AML cells to fibronectin and augments fibronectin-mediated anti-apoptotic and proliferative signals

Acute myeloid leukaemia (AML) cells express the SCF receptor c-kit (CD117) on their cell surface and demonstrate enhanced adhesion to fibronectin (FN) following exposure to stem cell factor (SCF). Increased adhesion occurs within 5 min, is dose dependent, and persists beyond 2 h. Baseline and enhanced adhesion occur through the surface FN receptor very late antigen-5 (VLA-5, CD49e/CD29) which is expressed by AML cells. Unstimulated AML cells exposed to FN undergo less apoptosis than controls (inhibition 22.5 +/- 7.0%, P = 0.02, n = 8). Exposure to SCF alone without FN also inhibits AML cell apoptosis (by 19.0 +/- 7.7% compared to controls, P = 0.06, n = 8). Simultaneous exposure to SCF and FN increases the inhibition of AML cell apoptosis to 37.8 +/- 7.9% (P = 0.005 compared to control, P = 0.04 compared to FN alone, P = 0.06 compared to SCF alone) demonstrating that SCF not only enhances the propensity of AML cells to adhere to FN, but also results in an additive survival benefit following FN contact. Some but not all the reduction in apoptosis is mediated through VLA-5. The combination of SCF and FN also affects proliferation, resulting in a synergistic enhancement of AML cell proliferation in half the cases studied. When normal CD34+ human haemopoietic progenitors were studied, FN had little effect on their apoptosis and failed to enhance the anti-apoptotic effect of SCF. It did, however, synergise with SCF in promoting CD34+ cell proliferation. Exposure of AML cells to SCF and FN, both of which can be found in high concentration in the bone marrow stroma, inhibits apoptosis. Cytokines and extracellular matrix proteins augment each others' effects since SCF enhances adhesion to fibronectin, which in turn augments the survival signal delivered by the cytokine alone. Cytokine and adhesion receptors can combine to affect cell characteristics including proliferation and survival.

Selective regulation of Bcl-XL by a Jak kinase-dependent pathway is bypassed in murine hematopoietic malignancies

Bcl-2 family proteins are key regulators of apoptosis and function as cell death antagonists (e.g., Bcl-2, Bcl-XL, and Mcl-1) or agonists (e.g., Bax, Bad, and Bak). Here we report that among the Bcl-2 family of proteins tested (Bcl-2, Bcl-XL, Mcl-1, Bax, Bad, and Bak), Bcl-XL was unique in that its protein levels were tightly regulated by hemopoietins in both immortal and primary myeloid progenitors. Investigating signaling pathways utilized by cytokine receptors established that the regulation of Bcl-XL protein levels is mediated by the Jak kinase pathway and is independent of other signaling effectors including STATs, PI-3' kinase, and Ras. Moreover, we provide the first direct evidence that Bcl-X is altered in cancer, because bcl-X expression was activated selectively by retroviral insertions in murine myeloid and T-cell hemopoietic malignancies. Tumors harboring bcl-X insertions had altered bcl-X RNAs, expressed elevated levels of Bcl-XL protein, and lacked the requirements for cytokines normally essential for cell survival. Finally, overexpression of Bcl-XL effectively protected IL-3-dependent myeloid cells from apoptosis following removal of trophic factors. Therefore, Bcl-XL functions as a key cytokine regulated anti-apoptotic protein in myelopoiesis and contributes to leukemia cell survival.

Expression and function of the megakaryocyte growth and development factor receptor in acute myeloid leukemia blasts

The receptor for megakaryocyte growth and development factor (MGDF), also known as thrombopoietin, has recently been cloned. MGDF stimulates platelet production and maturation both in vitro and in vivo. MGDF may thus have a role in attenuating the thrombocytopenia associated with acute myeloid leukemia (AML) and its therapy. However, there is concern that MGDF might induce AML blast proliferation and thereby increase the risk of treatment failure. To address this concern, we studied the expression of c-mpl mRNA and c-Mpl protein by blasts from AML patients. In addition we examined the in vitro effect of MGDF as well as the combined effect of MGDF and granulocyte colony-stimulating factor (G-CSF) or stem cell factor (SCF) on leukemic blast proliferation, recruitment into S-phase, induction of programmed cell death and activation of signal transducers and activators of transcription (STAT) proteins. Our results demonstrate that blasts from a substantial proportion of cases of AML express the receptor at either the mRNA or protein level. Moreover, the function of the MGDF receptor was demonstrated by activation of STAT proteins following exposure to MGDF. Nevertheless, blast proliferation in response to MGDF was rare, and the proliferative effect of MGDF was less than that of G-CSF or SCF. Furthermore, MGDF did not prevent programmed cell death induced by cytarabine. Finally, there appeared to be no correlation between receptor expression by AML blasts and functional response to MGDF. Based on these data, it would appear that clinical trials of MGDF may be undertaken safely in patients with AML.

Myeloperoxidase detection by three-color flow cytometry and by enzyme cytochemistry in the classification of acute leukemia

In the classification of acute leukemia, the presence of myeloperoxidase (MPO) within the leukemic blasts indicates myeloid leukemia. Previous studies compared enzyme cytochemistry (EC) or flow cytometry (FC) with immunocytochemistry, in detecting MPO. Our study is the first direct comparison of EC with 3-color FC in a large group of acute leukemias. We studied 26 cases of acute myeloid leukemia (AML) and 4 cases of B-precursor acute lymphoblastic leukemia (B-ALL). Classification was according to the French-American-British criteria. The cells were analyzed for MPO expression by 3-color FC after cell permeabilization followed by staining with anti-MPO antibody. For FC, the blasts were defined by a combination of light scatter characteristics and dim CD45 expression. Concordance between EC and FC was seen in 27 of 30 cases (23/26 AML and all B-ALL), including all AML cases of M1, M2, M3, and M4 subtypes. In 1 of 4 AML-MO and 2 of 5 AML-M5a cases, FC demonstrated the presence of MPO in 8%, 86%, and 94% blasts; EC detected none. Three-color FC may be more sensitive than routine EC in demonstrating the presence of MPO in AML cases and may offer the advantage of multiparametric analysis.

Aberrant TSG101 transcripts in acute myeloid leukaemia

Recently, a tumour susceptibility gene, TSG101, has been identified at chromosome 11p15. A large intragenic deletion of this gene has been demonstrated in primary breast tumours. To evaluate the role of the TSG101 gene in leukaemia, bone marrow and/or peripheral blood from 68 acute myeloid leukaemia patients, five haemopoietic cell lines (HL60, U937. Raji, KG-1, K562) and 30 normal controls were analysed by reverse transcription of the TSG101 mRNA, followed by PCR amplification and sequencing of the products. The results showed aberrant TSG101 transcripts in 24/68 (35%) acute myeloid leukaemia (AML) patients, all of the cell lines (100%) and 3/30 (10%) normal controls. Our study indicated that the abnormal transcripts may have resulted from aberrant RNA splicing as evidenced by these aberrant transcripts. Also, normal full-length transcripts were present in all specimens examined. The aberrant transcript occurred more frequently in the AML and cell lines. However, because aberrant transcripts of TSG101 were also found in the normal controls, the role of TSG101 as a tumour suppressor gene should be evaluated carefully.

Hepatocyte growth factor/scatter factor (HGF/SF) affects proliferation and migration of myeloid leukemic cells

Hepatocyte growth factor (HGF), also known as scatter factor (SF), is produced by mesenchymal cells, including bone marrow (BM) stromal cells, and has mitogenic and motogenic effects on a variety of cell types. Recently, a role has been assigned to HGF/SF and its receptor, c-MET, in both normal and malignant hemopoiesis. We investigated the function of HGF/SF on hemopoietic mononuclear cells (MNC) from patients with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) with circulating blasts. In contrast to results with normal MNC, HGF/SF alone stimulated the proliferation and colony formation of MNC from these patients. MNC from some (4/13) of the AML patients also produced HGF/SF (0.1-0.2 ng/ml/day), while we could not detect HGF/SF in cultures from normal MNC. Furthermore, it appeared that HGF/SF induced migration of leukemic cells in Boyden using KG1a cells as a model for leukemic blasts. The membranes dividing the two compartments of the Boyden chambers were coated with fibronectin. HGF/SF significantly promoted migration in 3/5 samples of MDS patients and in 5/7 samples of AML patients. Supernatant of human BM stromal cells, which is chemoattractive for normal human hemopoietic progenitor cells, also promoted migration of MNC from 4/5 MDS patients and 6/7 AML patients. Since HGF/SF is one of the growth factors produced by BM stromal cells, a neutralizing antibody directed against HGF/SF was added to the BM stroma supernatant, which reduced migration significantly in 2/3 MDS and in 3/6 AML responders to BM stroma supernatant. In conclusion, HGF/SF promotes proliferation and migration of hemopoietic cells from AML and MDS patients in vitro and may therefore contribute to the malignant potential of these cells.

Expression of the leptin receptor in human leukaemic blast cells

The leptin receptor is a member of the cytokine receptor superfamily, and is expressed in CD34 haemopoietic stem cells. We examined expression of the leptin receptor in fresh human leukaemia cells. Northern blot analysis showed the leptin receptor was expressed in leukaemic cells from patients with acute myeloblastic leukaemia, acute lymphoblastic leukaemia and chronic myeloid leukaemia (CML). In CML, higher expression was observed in blast crisis than in chronic phase. The expression of leptin receptor decreased during in vitro differentiation of leukaemic blast cells. It appeared that expression of the leptin receptor was associated with immature leukaemic blast cells. Our findings may indicate the possibility that leptin has some role in leukaemia.

Desferioxamine increases iron depletion and apoptosis induced by ara-C of human myeloid leukaemic cells

We investigated whether changes in iron metabolism and the transferrin receptor (TRF-R) expression were involved in the antileukaemic effects of arabinoside cytosine (ara-C). Treatment with 100 nM ara-C for 48h reduced thymidine uptake and increased the surface expression of the TRF-R on leukaemic blasts derived from 13/16 (81%) patients and on the HL-60 and U-937 cell lines. Whereas intracellular non-haem iron was strongly depleted 24 h after ara-C addition, TRF-R up-regulation and recovery of intracellular non-haem iron concentration occurred together after a longer exposure of the cultured cells to the drug. Since iron is an essential regulator of cell proliferation we have evaluated the effects of the combination between ara-C and the iron chelator desferioxamine (DSF) on the growth of HL-60 and U-937 cells. We found that desferioxamine strongly potentiated the effects of ara-C on leukaemic cell growth inhibition and apoptosis. This is the first report of a positive interaction between ara-C and an iron chelator in terms of antileukaemic effects.

Expression of signal transducers and activators of transcription proteins in acute myeloid leukemia blasts

Hematopoietic cytokine receptor signaling pathways involve activation of signal transducers and activators of transcription (STAT) proteins, which are postulated to be involved in cellular differentiation. Aberrant STAT isoforms (beta forms rather than the normal alpha forms) have been described and have been found to block the normal signaling pathway from the receptor. Bcr/Abl proteins have been suggested to directly activate STATs, without exposure to growth factors. We asked whether STATs play a role in leukemogenesis. We analyzed constitutive and induced patterns of STAT activity in pretreatment blasts from 36 newly diagnosed acute myeloid leukemia (AML) patients and studied protein tyrosine kinases (PTKs) that may be involved in STAT activity, using in vitro and in-gel kinase assays. The beta forms were expressed in 21 of 27 samples (78%). Constitutive STAT3 and STAT5 activity was found in samples from 28 and 22% of patients, respectively. Response to exogenous cytokines identified two groups. STAT activity in one group was modulated by exogenous cytokines: constitutive STAT activity increased in some patients but decreased or disappeared in response to cytokines in others. The second group was cytokine insensitive. Additionally, we found constitutive PTK activity in two patients whose blasts demonstrated constitutive STAT activity, suggesting that PTKs use cytokine receptor signal pathways to activate STATs in AML blasts without exposure to exogenous cytokines. Our data suggest that (a) constitutive expression of aberrant STATs may be involved in blocking differentiation of AML blasts, (b) exogenous cytokines may activate STAT-inhibitory pathways, and (c) STATs may be activated by PTKs in some AML blasts.

The reliability and specificity of c-kit for the diagnosis of acute myeloid leukemias and undifferentiated leukemias. The European Group for the Immunological Classification of Leukemias (EGIL)

We document findings on c-kit (CD117) expression in 1,937 pediatric and adult de novo acute leukemia cases, diagnosed in five single European centers. All cases were well characterized as to the morphologic, cytochemical, and immunologic features, according to the European Group for the Immunological Classification of Leukemias (EGIL). The cases included 1,103 acute myeloid leukemia (AML), 819 acute lymphoblastic leukemia (ALL), 11 biphenotypic acute leukemia (BAL), and 4 undifferentiated (AUL). c-kit was expressed in 741 (67%) AML cases, regardless of the French-American-British (FAB) subtype, one third of BAL, all four AUL, but only in 34 (4%) of ALL cases. The minority of c-kit+ ALL cases were classified as: T-cell lineage (two thirds), mainly pro-T-ALL or T-I, and B lineage (one third); cells from 62% of these ALL cases coexpressed other myeloid markers (CD13, CD33, or both). There were no differences in the frequency of c-kit+ AML or ALL cases according to age being similar in the adult and pediatric groups. Our findings demonstrate that c-kit is a reliable and specific marker to detect leukemia cells committed to the myeloid lineage, and therefore should be included in a routine basis for the diagnosis of acute leukemias to demonstrate myeloid commitment of the blasts. c-kit expression should score higher, at least one point, in the system currently applied to the diagnosis of BAL, as its myeloid specificity is greater than CD13 and CD33. Findings in ALL and AUL suggest that c-kit identifies a subgroup of cases, which may correspond to leukemias either arising from early prothymocytes and/or early hematopoietic cells, both able to differentiate to the lymphoid and myeloid pathways.

Changing bone marrow micro-environment during development of acute myeloid leukaemia in rats

The Brown Norwegian rat transplanted with promyelocytic leukaemic cells (BNML) has been used as a model for human acute myeloid leukaemia. We have previously shown that both the blood supply to the bone marrow and the metabolic rate decrease in relation to the leukaemic development in these rats. Here we have investigated how the development and progression of this leukaemia affect oxygenation, pH and proliferation of normal and leukaemic cells in vivo. Bone marrow pH was measured by a needle electrode. Nitroimidazol-theophylline (NITP) was used to identify hypoxic cells, and we applied bromodeoxyuridine (BrdUrd) to identify DNA replicating cells. The leukaemia progressed slowly until day 27 after which a rapid deterioration could be observed leading to severe changes over the following 5 d. In whole blood there was evidence of progressing metabolic acidosis. In bone marrow the fraction of leukaemic cells increased to > 90% and the pH dropped to about 6.5. The fraction of NITP+ cells increased to > 80% in bone marrow and to about 40% in blood. The fraction of BrdUrd+ cells was unchanged in blood, but decreased in bone marrow both for normal cells (from about 20% to 5%), and for leukaemic cells (from about 45% to 25%), evidently as a result of the severely changed microenvironment. In this study we have demonstrated in vivo the development of an acidic and hypoxic bone marrow hampering normal haemopoiesis during leukaemic growth. Our data support the notion of BNML as a valuable tool for studying leukaemogenesis.

Proportion of blasts with a clear halo around nucleoli at the end of induction therapy of acute myeloid leukemia correlates with achievement of complete remission, remission duration and relapse

Bone marrow aspirates from 60 patients with acute myeloid leukemia (AML) were investigated using 95% ethanol fixation Papanicolaou stained preparations. The blasts were grouped into those with a clear halo around nucleoli (BCHN) and those without a clear halo. The patients were classified into three groups according to the degree of persistent BCHN at the end of induction therapy: group 1, no BCHN; group 2, less than 1% BCHN; and group 3, 1% or more BCHN. All patients in groups 1 (17 cases) and 2 (12 cases), and 12 of 31 cases in group 3 achieved complete remission (CR). Of 17 patients in group 1, two underwent bone marrow transplantation and two died from infection. Of the 37 patients who achieved CR, relapse was observed in two of 13 patients in group 1, and in all patients in groups 2 and 3. As to the patients treated with N4-behenoyl-1-beta-D-arabinofuranosyl-cytosine + daunorubicin + 6-mercaptopurine + prednisolone (BHAC-DMP) protocol, the percentages and number of BCHN at the diagnosis of AML in group 1 were significantly lower than those of groups 2 and 3. The percentage and number of BCHN at the diagnosis of AML were significant factors for the achievement of CR and for the prediction of long-term outcome. The reduction of BCHN to less than 1% at the end of induction therapy is a good indicator for the achievement of CR, and the disappearance of BCHN is a useful target for a long-lasting first CR; conversely, the persistence of BCHN is a major adverse factor for relapse.

[The modulation effect of granulocyte-colony stimulating factor on the mdr1/P-gp expression in acute myeloid leukemic cells]

OBJECTIVE

To investigate the correlation between cell differentiation and mdr1 gene expression in acute myeloid leukemic(AML) cells.

METHODS

The modulation effect of granulocyte-colony stimulating factor(G-CSF) on the mdr1 gene expression in AML cells was studied in vitro by using polymerase chain reaction(PCR), in vitro cell culture, immunocytochemical and MTT assays.

RESULTS

AML cells retained the ability to respond to the differentiation stimulus. Expressions of P-glycoprotein(P-gp) and mdr1 mRNA were downregulated in differentiated cells, meanwhile, a significant decrease of DNR IC50 in the AML cells with down-expression mdr1 gene was revealed and their sensitivity to anti-cancer drugs increased.

CONCLUSION

Leukemic cell differentiation was closely correlated with mdr1 expression. It might be an effective method to overcome drug resistance of leukemic patient by using differentiation inducing agents.