Preclinical modeling of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) represent a heterogeneous group of hematological clonal disorders. Here, we have tested the bone marrow (BM) cells from 38 MDS patients covering all risk groups in two immunodeficient mouse models: NSG and NSG-S. Our data show comparable level of engraftment in both models. The level of engraftment was patient specific with no correlation to any specific MDS risk group. Furthermore, the co-injection of mesenchymal stromal cells (MSCs) did not improve the level of engraftment. Finally, we have developed an in vitro two-dimensional co-culture system as an alternative tool to in vivo. Using our in vitro system, we have been able to co-culture CD34+ cells from MDS patient BM on auto- and/or allogeneic MSCs over 4 weeks with a fold expansion of up to 600 times. More importantly, these expanded cells conserved their MDS clonal architecture as well as genomic integrity.

Rationale and efficacy of proteasome inhibitor combined with arsenic trioxide in the treatment of acute promyelocytic leukemia

Arsenic trioxide (ATO) mediates PML-RARA (promyelocytic leukemia-retinoic acid receptor-α) oncoprotein degradation via the proteasome pathway and this degradation appears to be critical for achieving cure in acute promyeloytic leukemia (APL). We have previously demonstrated significant micro-environment-mediated drug resistance (EMDR) to ATO in APL. Here we demonstrate that this EMDR could be effectively overcome by combining a proteasome inhibitor (bortezomib) with ATO. A synergistic effect on combining these two agents in vitro was noted in both ATO-sensitive and ATO-resistant APL cell lines. The mechanism of this synergy involved downregulation of the nuclear factor-κB pathway, increase in unfolded protein response (UPR) and an increase in reactive oxygen species generation in the malignant cell. We also noted that PML-RARA oncoprotein is effectively cleared with this combination in spite of proteasome inhibition by bortezomib, and that this clearance is mediated through a p62-dependent autophagy pathway. We further demonstrated that proteasome inhibition along with ATO had an additive effect in inducing autophagy. The beneficial effect of this combination was further validated in an animal model and in an on-going clinical trial. This study raises the potential of a non-myelotoxic proteasome inhibitor replacing anthracyclines in the management of high-risk and relapsed APL.

Self-renewal gene tracking to identify tumour-initiating cells associated with metastatic potential

Tumour-initiating cells (TICs) are rare cancer cells isolated from tumours of different origins including high-grade tumours that sustain neoplasic progression and development of metastatic disease. They harbour deregulated stem cells pathways and exhibit an unchecked ability to self-renew, a property essential for tumour progression. Among the essential factors maintaining embryonic stem (ES) cells properties, OCT-4 (also known as POU5F1) has been detected in tumours of different origins. Although ectopic expression results in dysplasic growth restricted to epithelial tissues, overexpression expands the proportion of immature cells in teratomas. However, OCT-4-expressing cells have not been purified from spontaneously occurring tumours, thus information concerning their properties is rather scant. Here, using p53-/- mice expressing green fluorescent protein and the puromycin resistance gene under the control of the Oct-4 promoter, we show that OCT-4 is expressed in 5% onwards of the undifferentiated tumour cell populations derived from different organs. OCT-4 expression was low as compared with ES cells, but was associated with a 'stemness' signature and expression of the chemokine receptor CXCR4. These cells displayed cancer stem cell features, including increased self-renewal and differentiation ability in vitro and in vivo. They not only formed allografts containing immature bone regions but also disseminated into different organs, including lung, liver and bone. Experiments based on RNA interference revealed that Oct-4 expression drives both their engraftment and metastasis formation. This work points out the crucial contribution of Oct-4-expressing TICs in the hierarchical organization of the malignant potential, leading to metastasis formation. Consequently, it provides an appropriate model to develop novel therapies aiming to strike down TICs by targeting self-renewal genes, therefore efficient to reduce tumour growth and metastatic disease.

New role for granulocyte colony-stimulating factor-induced extracellular signal-regulated kinase 1/2 in histone modification and retinoic acid receptor α recruitment to gene promoters: relevance to acute promyelocytic leukemia cell differentiation

The induction of the granulocytic differentiation of leukemic cells by all-trans retinoic acid (RA) has been a major breakthrough in terms of survival for acute promyelocytic leukemia (APL) patients. Here we highlight the synergism and the underlying novel mechanism between RA and the granulocyte colony-stimulating factor (G-CSF) to restore differentiation of RA-refractory APL blasts. First, we show that in RA-refractory APL cells (UF-1 cell line), PML-RA receptor alpha (RARα) is not released from target promoters in response to RA, resulting in the maintenance of chromatin repression. Consequently, RARα cannot be recruited, and the RA target genes are not activated. We then deciphered how the combination of G-CSF and RA successfully restored the activation of RA target genes to levels achieved in RA-sensitive APL cells. We demonstrate that G-CSF restores RARα recruitment to target gene promoters through the activation of the extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) pathway and the subsequent derepression of chromatin. Thus, combinatorial activation of cytokines and RARs potentiates transcriptional activity through epigenetic modifications induced by specific signaling pathways.

Germline mutations of the CBL gene define a new genetic syndrome with predisposition to juvenile myelomonocytic leukaemia

BACKGROUND

CBL missense mutations have recently been associated with juvenile myelomonocytic leukaemia (JMML), an aggressive myeloproliferative and myelodysplastic neoplasm of early childhood characterised by excessive macrophage/monocyte proliferation. CBL, an E3 ubiquitin ligase and a multi-adaptor protein, controls proliferative signalling networks by downregulating the growth factor receptor signalling cascades in various cell types.

METHODS AND RESULTS

CBL mutations were screened in 65 patients with JMML. A homozygous mutation of CBL was found in leukaemic cells of 4/65 (6%) patients. In all cases, copy neutral loss of heterozygosity of the 11q23 chromosomal region, encompassing the CBL locus, was demonstrated. Three of these four patients displayed additional features suggestive of an underlying developmental condition. A heterozygous germline CBL p.Y371H substitution was found in each of them and was inherited from the father in one patient. The germline mutation represents the first hit, with somatic loss of heterozygosity being the second hit positively selected in JMML cells. The three patients display a variable combination of dysmorphic features, hyperpigmented skin lesions and microcephaly that enable a 'CBL syndrome' to be tentatively delineated. Learning difficulties and postnatal growth retardation may be part of the phenotype.

CONCLUSION

A report of germline mutations of CBL in three patients with JMML is presented here, confirming the existence of an unreported inheritable condition associated with a predisposition to JMML.

Epigenetic patterns of the retinoic acid receptor β2 promoter in retinoic acid-resistant thyroid cancer cells

Treatment with retinoic acid (RA) is effective to restore radioactive iodine uptake in metastases of a small fraction of thyroid cancer patients. In order to find predictive markers of response, we took advantage of two thyroid cancer cell lines, FTC133 and FTC238, with low RA-receptor (RAR)beta expression but differing in their response to RA. We report that in both cell lines, RA signalling pathways are functional, as transactivation of an exogenous RARbeta2 promoter is effective in the presence of pharmacological concentrations of all-trans RA, and enhanced in RA-resistant FTC238 cells after ectopical expression of RARbeta, suggesting a defective endogenous RARbeta2 promoter in these cells. Further analyses show that whereas the RARbeta2 promoter is in an unmethylated permissive status in both FTC133 and FTC238 cells, it failed to be associated with acetylated forms of histones H3 or H4 in FTC238 cells upon RA treatment. Incubation with a histone deacetylase inhibitor, alone or in combination with RA, restored histone acetylation levels and reactivated RARbeta and differentiation marker Na+/I- symporter gene expression. Thus, histone modification patterns may explain RA-refractoriness in differentiated thyroid cancer patients and suggest a potential benefit of combined transcriptional and differentiation therapies.

Phenotypic and functional characterization of bone marrow mesenchymal stem cells derived from patients with multiple myeloma

Multiple myeloma (MM) is a B-cell neoplasia caused by the proliferation of clonal plasma cells, primarily in the bone marrow (BM). The role of the BM microenvironment in the pathogenesis of the disease has been demonstrated, especially for the survival and growth of the myeloma plasma cells. Functional characterization of the major component of the BM microenvironment, namely the recently characterized mesenchymal stem cells (MSCs), was never performed in MM. Based on a series of 61 consecutive patients, we evaluated the ability of MSCs derived from myeloma patients to differentiate into adipocytes and osteocytes, inhibit T-cell functions, and support normal hematopoiesis. MSCs phenotypic characterization and quantification of interleukin-6 (IL-6) secretion were also performed. As compared to normal MSCs, MSCs from MM patients exhibited normal phenotype, differentiation capacity and long-term hematopoietic support, but showed reduced efficiency to inhibit T-cell proliferation and produced abnormally high amounts of IL-6. Importantly, these characteristics were observed in the absence of any detectable tumor plasma cell. Chromosomal analysis revealed that MM patients MSCs were devoid of chromosomal clonal markers identified in plasma cells. MM MSCs present abnormal features that may participate in the pathogenesis of MM.

Extramedullary relapse in acute promyelocytic leukemia treated with all-trans retinoic acid and chemotherapy

We analyzed the incidence, presenting features, risk factors of extramedullary (EM) relapse occurring in acute promyelocytic leukemia (APL) treated with all-trans retinoic acid (ATRA) and chemotherapy by using a competing-risk method. In total, 740/ 806 (92%) patients included in three multicenter trials (APL91, APL93 trials and PETHEMA 96) achieved CR, of whom 169 (23%) relapsed, including 10 EM relapses. Nine relapses involved the central nervous system (CNS) and one the skin, of which two were isolated EM relapse. In patients with EM disease, median WBC count was 26950/mm3 (7700-162000). The 3-year cumulative incidence of EM disease at first relapse was 5.0%. Univariate analysis identified age <45 years (P=0.05), bcr3 PML-RARalpha isoform (P= 0.0003) and high WBC counts (> or = 10,000/ mm3) (P<0.0001) as risk factors for EM relapse. In multivariate analysis, only high WBC count remained significant (P= 0.001). Patients with EM relapse had a poorer outcome since median survival from EM relapse was 6.7 months as compared to 26.3 months for isolated BM relapse (P=0.04). In conclusion, EM relapse in APL occurs more frequently in patients with increased WBC counts (> or = 10,000/mm3) and carries a poor prognosis. Whether CNS prophylaxis should be systematically performed in patients with WBC > or = 10,000/mm3 at diagnosis remains to be established.

Telomerase targeting by retinoids in cells from patients with myeloid leukemias of various subtypes, not only APL

Numerous strategies have been proposed to specifically inhibit telomerase (human telomerase reverse transcriptase (hTERT)) but to date only a few are clinically relevant in anticancer therapy. Recently, we have shown that long-term treatment with all-trans retinoic acid (ATRA), a compound clinically approved for differentiation therapy of acute promyelocytic leukemia (APL), represses hTERT in differentiation-resistant APL cell lines leading to telomere shortening and death. This signaling requires the co-activation of the retinoic acid receptor alpha (RARalpha) and the retinoic X receptor (RXR). In contrast to differentiation-therapy, which is only successful in this subtype of leukemia, the telomerase-targeted pathway could also be of use in non-APL. Here, we demonstrate that repression of hTERT occurs in fresh blasts cells from patients with myeloid leukemias of various subtypes exposed ex vivo to ATRA or synthetic retinoids. These results support the idea that, by hTERT targeting, retinoids can induce telomere shortening and cell death and their integration in therapy protocols for myeloid leukemias refractory to maturation should be considered.

All trans retinoic acid abrogates spontaneous monocytic growth in juvenile chronic myelomonocytic leukaemia

INTRODUCTION

All trans retinoic acid, the active metabolite of vitamin A, exerts profound effects on cell differentiation. On normal myeloid progenitors, retinoids switch the differentiation program of granulo-macrophagic progenitors towards the granulocytic lineage and consequently reduce CFU-M colony formation. Bone marrow and peripheral blood mononuclear cells from children with Juvenile Chronic Myelomonocytic Leukaemia show typical spontaneous monocytic growth. We questioned whether in this disease, retinoids could switch myelomonocytic growth and inhibit the abnormal CFU-M colony proliferation.

METHODS

Ten JCML samples were studied in the presence of ATRA in methyl cellulose colony assay, before (CFU-C) or after (pre-CFU) liquid suspension culture.

RESULTS

In vitro characteristics of JCML such as spontaneous monocytic growth in the absence of growth factor was noted in all patients. In the presence of leucocyte-conditioned medium, nine samples showed only CFU-M growth and one sample CFU-GM growth. Incubation with ATRA inhibited CFU-M colony formation in nine cases. Enhancement of granulocytic differentiation (CFU-G) was noted in nine cases. ATRA also inhibited CD34+ JCML monocytic growth and GM-CSF hypersensitivity.

CONCLUSION

These data suggest that, in JCML progenitors, retinoid pathways are functional and inhibition of immature monocytic progenitors cells may be achieved with retinoids, without impeding granulocytic cell growth.

Prognostic implication of FLT3 and Ras gene mutations in patients with acute promyelocytic leukemia (APL): a retrospective study from the European APL Group

Internal tandem duplications (ITDs) of the FLT3 gene have been observed in about 35% of APL cases. If FLT3-ITD is associated with a worse outcome in patients with acute myeloid leukemia (AML) in general, its prognostic value in acute promyelocytic leukemia (APL) is still a matter of debate. We investigated incidence, associated clinical features, and prognostic implication of FLT3-ITD, but also FLT3-D835 point mutation and N-Ras or K-Ras mutations in 119 APL patients, all prospectively enrolled in the two consecutive APL-93 and APL-2000 trials. Mutation incidences were 38, 20, and 4%, for FLT3-ITD, FLT3-D835, and Ras, respectively. The presence of FLT3-ITD was associated with high white blood cell count, high Sanz index, M3-variant subtype, and V/S PML-RAR alpha isoforms. Complete remission (CR), induction death, and death in CR rates were not affected by FLT3 or Ras mutations, as well as cumulative incidence of relapse. However, a trend for a shorter overall survival (P=0.09) was observed in FLT3-ITD patients, because of a very poor postrelapse survival (P=0.02). This feature, which has been also reported in patients with AML in general, is suggestive of an underlying genetic instability in FLT3-ITD patients, leading to the acquisition of additional unknown bad-prognosis gene mutations at relapse.

Outcome of acute promyelocytic leukemia treated with all trans retinoic acid and chemotherapy in elderly patients: the European group experience

We analyzed the outcome of patients aged more than 60 included in a multicenter trial in newly diagnosed acute promyelocytic leukemia (APL93 trial), which tested the role of early addition of chemotherapy to all trans retinoic acid (ATRA) and of maintenance with ATRA and/or low-dose chemotherapy. In total, 129/533 (24.2%) patients included in this trial were older than 60. The CR rate was 86% in patients older than 60 as compared to 94.5% in younger patients (P=0.0014), due to a higher incidence of early deaths in elderly patients. The 4-year incidence of relapse was 15.6% in adults older than 60 and 23.2% in younger adults although most elderly patients received less intensive consolidation chemotherapy. However, 18.6% of the patients older than 60 years who achieved CR died in CR, mainly from sepsis during consolidation course or maintenance treatment, as compared to 5.7% of younger adults (P<0.001). Thus, overall 4-year survival of elderly patients was 57.8% as compared to 78% in younger adults (P<0.0001). APL in elderly patients appears as sensitive to ATRA-Chemotherapy based regimen as in younger adults. Less favorable outcome is mainly due to an increase of early deaths and to toxicity of consolidation treatment, strongly suggesting a beneficial role for less intensive consolidation chemotherapy and possibly introduction of arsenic derivates in the treatment of APL in the elderly.

Autologous and allogeneic stem-cell transplantation as salvage treatment of acute promyelocytic leukemia initially treated with all-trans-retinoic acid: a retrospective analysis of the European acute promyelocytic leukemia group

PURPOSE

To retrospectively determine the outcome of acute promyelocytic leukemia (APL) patients who underwent autologous or allogeneic stem-cell transplantation (SCT) during second complete remission.

PATIENTS AND METHODS

Of 122 relapsing patients included in two successive multicenter APL trials who achieved hematological second complete remission (generally after a salvage regimen of all-trans-retinoic acid [ATRA] combined with chemotherapy), 73 (60%) received allogeneic (n = 23) or autologous (n = 50) SCT.

RESULTS

Seven-year relapse-free survival (RFS), event-free survival (EFS), and overall survival (OS) in the autologous SCT group were 79.4%, 60.6%, and 59.8%, respectively, with a transplant-related mortality (TRM) of 6%. Of the 28 and two patients autografted with negative and positive, respectively, reverse transcriptase-polymerase chain reaction before auto SCT, three (11%) and one relapsed, respectively. In the allogeneic SCT group, 7-year RFS, EFS, and OS were 92.3%, 52.2%, and 51.8%, respectively, with 39% TRM. OS was significantly better in the autologous SCT group than in the allogeneic SCT group (P = .04), whereas RFS and EFS did not differ significantly (P = .19 and P = .11, respectively). In patients not receiving transplantation, 7-year RFS, EFS, and OS were 38%, 30.4%, and 39.5%, respectively.

CONCLUSION

These retrospective data suggest that autologous SCT is very effective in APL relapsing after treatment with ATRA if performed in molecular remission. Allogeneic SCT yields few relapses, but it is associated with high TRM when performed after salvage with very intensive chemotherapy. Salvage with arsenic trioxyde, which has lower toxicity, should further improve the outcome of relapsing APL, especially before allogeneic SCT.

Cyclooxygenase-1, but not -2, is upregulated in NB4 leukemic cells and human primary promyelocytic blasts during differentiation

Cyclooxygenase (COX)-1 or -2 and specific prostaglandin (PG) synthases catalyze the formation of various PGs. We investigated the expression and activity of COX-1 and -2 during granulocyte-oriented maturation induced by all-trans-retinoic acid (ATRA) of NB4 cells, originated from a human acute promyelocytic leukemia (APL), and in blasts from APL patients. The expression of COX isoenzymes or prostaglandin synthases was also investigated in circulating granulocytes and human bone marrow. COX-1 was expressed and enzymatically active in NB4 cells and primary blasts. COX-1 mRNA and protein were induced by ATRA. COX-1 protein increased approximately 2-3.5-fold by culture day 3 in NB4 cells and primary blasts, while basal COX-2 expression was very low and unaffected by ATRA. COX-1-dependent PGE(2) biosynthesis increased during differentiation approx. 5-fold. Indomethacin and the selective COX-1 inhibitor SC-560, but not selective COX-2 inhibition, impaired NB4 differentiation, reducing NADPH-oxidase activity, CD11b and CD11c expression. The immunohistochemistry of granulocytes and myeloid precursors in the bone marrow showed a large prevalence of COX-1 as compared to COX-2. In conclusion, COX-1 is induced during ATRA-dependent maturation and appears to contribute to myeloid differentiation both in vitro and ex vivo, and COX-1 activity may potentiate the differentiation of human APL.Leukemia (2004) 18, 1373-1379. doi:10.1038/sj.leu.2403407 Published online 10 June 2004

Outcome of Childhood Acute Promyelocytic Leukemia With All-Trans-Retinoic Acid and Chemotherapy

Purpose

To determine the results of treatment combining all-trans-retinoic acid (ATRA) and chemotherapy (CT) in childhood acute promyelocytic leukemia (APL).

Patients and Methods

Children (< 18 years) with newly diagnosed APL were included in the APL93 trial, treated by ATRA followed or combined with daunorubicin-cytarabine, and then randomly assigned between no maintenance, intermittent ATRA, continuous CT, or both.

Results

Of the 576 patients included in APL93 trial, 31 (5%) were children, including 22 girls (71%) and nine boys (29%). Thirty of the children (97%) obtained complete remission (CR). ATRA syndrome occurred in four children (13%), who all achieved CR, and headaches occurred in 12 children (39%), with signs of pseudotumor cerebri in five children (16%). Seven patients (23%) relapsed. None of the eight patients who received both ATRA and CT for maintenance relapsed. All relapsing patients achieved a second CR. Twenty-two patients remained in first CR after 43+ to 96+ months, six remained in second CR after 17+ to 66+ months, and three patients had died. The 5-year event-free survival (EFS), relapse, and overall survival rates were 71%, 27%, and 90%, respectively. No difference between adults and children included in the APL93 trial was seen for CR rate, 5-year relapse rate, EFS, and overall survival, but significantly better survival was seen in children after adjustment on WBC counts (P = .02) and incidence of microgranular M3 variant (P = .04).

Conclusion

ATRA combined with CT for induction and also probably for maintenance provides as favorable results in children with APL as in adults and currently constitutes the reference first-line treatment in both age groups.

Myelodysplastic syndrome after acute promyelocytic leukemia: the European APL group experience

With improved treatment of acute promyelocytic leukemia (APL) by all trans retinoic acid (ATRA) combined to anthracycline-aracytin chemotherapy (CT), a larger number of those patients may be at risk of late complications. Recently, the Rome group reported five cases of myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML, non-APL) occurring during the course of 77 APL patients (6.5%) in complete remission (CR). From 1991 to 1998, we treated 677 newly diagnosed cases of APL, and 617 of them achieved CR with ATRA combined to CT (n=579) or CT alone (n=38); 246 of them received subsequent maintenance CT with 6 mercaptopurine and methotrexate. With a median follow-up of 51 months, 6 patients (0.97%) developed MDS, 13-74 months after the diagnosis of APL. In all six cases, t(15;17) and PML-RARalpha rearrangement were absent at the time of MDS diagnosis, and karyotype mainly showed complex cytogenetic abnormalities involving chromosomes 5 and/or 7, typical of MDS observed after treatment with alkylating agents, although none of the six patients had received such agents for the treatment of APL. Our findings suggest that MDS can indeed be a long-term complication in APL, although probably at lower incidence than that previously reported.

Early onset of chemotherapy can reduce the incidence of ATRA syndrome in newly diagnosed acute promyelocytic leukemia (APL) with low white blood cell counts: results from APL 93 trial

Treatment combining ATRA and chemotherapy (CT) has improved the outcome of APL patients, by comparison with CT alone. ATRA syndrome is a life-threatening complication of ATRA treatment whose prophylaxis remains somewhat controversial. In APL93 trial, newly diagnosed APL patients </=65 years and with initial WBC counts below 5000/mm(3) were randomized between ATRA until CR achievement followed by CT (ATRA --> CT) and ATRA with early addition of CT, on day 3 of ATRA treatment (ATRA + CT). The incidence of ATRA syndrome in the ATRA --> CT arm was 18% (22/122) as compared to 9.2% (17/184) in the ATRA + CT arm (P = 0.035). In the ATRA --> CT arm, three (2.5%) patients died from ATRA syndrome, as compared to one (0.5%) in the ATRA + CT group. Early addition of chemotherapy to ATRA in newly diagnosed APL with low WBC counts significantly reduced the incidence of ATRA syndrome.

H RAS mutations in haematologically normal individuals

INTRODUCTION

Point mutations in N, K and H RAS have been found in adverse haematological malignancies. The background frequency of RAS mutations in the normal population has yet to be determined. Here we report the results of a screen for RAS mutations from normal individuals.

MATERIALS AND METHODS

DNA from peripheral blood or bone marrow from 115 haematologically normal individuals was screened for point mutations in N, K and H RAS, at amino acid positions 12, 13 and 61. The screening was done using polymerase chain reaction and oligonucleotide hybridisation and candidate mutations were subsequently confirmed by cloning and sequencing.

RESULTS AND CONCLUSION

Point mutations were identified in DNA from two of the 115 individuals. Both mutations resulted in an amino acid substitution at position 12 in H RAS. Both individuals with detectable H RAS mutations remain haematologically normal.

Functional G-CSF pathways in t(8;21) leukemic cells allow for differentiation induction and degradation of AML1-ETO

INTRODUCTION

Efficacy of differentiating agents requires that their specific cellular targets are still expressed and functional in the leukemic cells. One hypothesis to target sensitive cells is to select leukemic clones which harbor disrupted transcription factors. CBFalpha and CBFbeta are core-binding proteins which have been identified as transcription regulators of hematopoietic genes and shown to be altered in numerous leukemias. In M2 AML, the t(8;21) translocation, CBFalpha (AML1) is altered and produced as the AML1-ETO fusion protein. The fusion protein blocks transcription and differentiation mediated by G-CSF. Interestingly, AML1-ETO leukemic cell lines are sensitive to numerous cytokines in vitro and can be induced to differentiate in the presence of G-CSF and PMA.

MATERIALS AND METHODS

As in the APL differentiation model, primary culture provides a useful tool for therapeutic screening of differentiation inducers, we analysed the in vitro sensitivity of 10 fresh M2 AML t(8;21) leukemic samples to G-CSF and the functionality of G-CSF intracellular pathways. In vitro data were compared with in vivo data from four patients treated with rhG-CSF at the dosage of 5 microg/kg/day i.v. for two to three weeks before the initiation of AML induction chemotherapy and immunophenotypic analysis performed weekly to monitor in vivo differentiation.

RESULTS

In vitro, an increase in CD34+ cells expressing differentiation antigens (CD11b, CD13 or CD15) was noted along with a decrease of immature CD34+/differentiation antigen negative cells. After two weeks of a daily rhG-CSF administration in vivo, a significant, albeit transient, decrease of blast count was achieved, concomitant with an increase in differentiated leukemic cells suggesting that in vivo differentiation occurs. Fresh t(8;21) leukemic cells possess functional G-CSF signaling pathways as normal activity and kinetics of STAT1 and STAT3 binding was observed. Furthermore, differentiation induction leads to a subsequent degradation of the AML1-ETO oncoprotein.

CONCLUSION

The data presented here supports the claim that G-CSF can induce in vitro and in vivo differentiation of M2 AML t(8;21) cells.

Deregulated expression of promyelocytic leukemia zinc finger protein in B-cell chronic lymphocytic leukemias does not affect cyclin A expression

INTRODUCTION

The promyelocytic leukemia zinc finger (PLZF) gene encodes a transcription factor expressed in myeloid, lymphoid and CD34(+) progenitor cells. Structurally related to BCL-6, which is involved in human lymphoma, PLZF may have a role in proliferation, differentiation and survival of hematopoietic cells, that could be mediated by transcriptional repression of the cyclin A gene.

MATERIALS AND METHODS

Quantitative competitive reverse transcription-polymerase chain reaction was used to measure the levels of expression of PLZF and cyclin A in normal leukocyte subsets (including CD19(+) lymphocytes, n=21) and malignant B lymphocytes (including B-chronic lymphocytic leukemias [B-CLL], n=63). Results obtained with this method were confirmed by Western and Northern blot analysis. Transactivation assays were performed using an expression construct for PLZF and two cyclin A promoter luciferase reporters in an Epstein-Barr virus (EBV)-transformed B-cell line. Cyclin A expression, cell growth kinetics, and cell cycle were analysed in stable clones of the Burkitt lymphoma (BL) B-cell line DG75 with inducible expression of PLZF, generated using the tetracycline-regulated expression system.

RESULTS

Expression of PLZF was 100-fold downregulated in 90% B-CLL (56/63) compared to normal B lymphocytes (P<0.001). B-CLL patients with the highest levels of PLZF had a poorer survival (P<0.013). In transactivation assays, PLZF inhibited the activity of the cyclin A reporters by 50%, demonstrating that PLZF can repress cyclin A expression in non-malignant B lymphocytes. However, in B-CLL patients, the level of cyclin A expression was found to be within the normal range. Altered PLZF function in B lymphoid malignancies was further corroborated in the PLZF-regulatable DG75 clones, where induction of PLZF expression did not significantly alter the levels of cyclin A expression, the cell growth kinetics, or the cell cycle phase distribution.

CONCLUSION

The lower survival of patients with the highest levels of PLZF suggests that this protein may be a marker of progression in B-CLL. The absence of co-ordinated regulation of PLZF and cyclin A genes in B-CLL and in a malignant B-cell line may indicate a loss of cyclin A control by PLZF in B-CLL and other B-cell disorders. Deregulation of PLZF could thus play a role in B-cell malignancy.

Retinoic acid receptor alpha1 variants, RARalpha1DeltaB and RARalpha1DeltaBC, define a new class of nuclear receptor isoforms

Retinoic acid (RA) binds and activates retinoid X receptor (RXR)/retinoic acid receptor (RAR) heterodimers, which regulate the transcription of genes that have retinoic acid response elements (RARE). The RAR isotypes (alpha, beta and gamma) are comprised of six regions designated A-F. Two isoforms of RARalpha, 1 and 2, have been identified in humans, which have different A regions generated by differential promoter usage and alternative splicing. We have isolated two new splice variants of RARalpha1 from human B lymphocytes. In one of these variants, exon 2 is juxtaposed to exon 5, resulting in an altered reading frame and a stop codon. This variant, designated RARalpha1DeltaB, does not code for a functional receptor. In the second variant, exon 2 is juxtaposed to exon 6, maintaining the reading frame. This isoform, designated RARalpha1DeltaBC, retains most of the functional domains of RARalpha1, but omits the transactivation domain AF-1 and the DNA-binding domain. Consequently, it does not bind nor transactivate RARE on its own. Nevertheless, RARalpha1DeltaBC interacts with RXRalpha and, as an RXRalpha/RARalpha1DeltaBC heterodimer, transactivates the DR5 RARE upon all-trans-RA binding. The use of RAR- and RXR-specific ligands shows that, whereas transactivation of the DR5 RARE through the RXRalpha/RARalpha1 heterodimer is mediated only by RAR ligands, transactivation through the RXRalpha/RARalpha1DeltaBC heterodimer is mediated by RAR and RXR ligands. Whilst RARalpha1 has a broad tissue distribution, RARalpha1DeltaBC has a more heterogeneous distribution, but with significant expression in myeloid cells. RARalpha1DeltaBC is an infrequent example of a functional nuclear receptor which deletes the DNA-binding domain.

In vitro all-trans retinoic acid sensitivity of acute promyelocytic leukemia blasts: a novel indicator of poor patient outcome

Acute promyelocytic leukemia (APL) blasts possess a unique sensitivity to the differentiating effects of all-trans retinoic acid (ATRA). Multicenter trials confirm that the combination of differentiation and cytotoxic therapy prolongs survival in APL patients. However relapses still occur, and exquisite adaptation of therapy to prognostic factors is essential to aim at a possible cure of the disease. A heterogeneity was previously reported in the differentiation rate of patients' APL blasts, and it was postulated that this may reflect the in vivo heterogeneous outcome. In this study, it is demonstrated that patients of the APL93 trial whose leukemic cells achieved optimal differentiation with ATRA in vitro at diagnosis had a significantly improved event-free survival (P =.01) and lower relapse rate (P =.04). This analysis highlights the importance of the differentiation step in APL therapy and justifies ongoing studies aimed at identifying novel RA-differentiation enhancers.

Biological features of primary APL blasts: their relevance to the understanding of granulopoiesis, leukemogenesis and patient management

In recent years, discovery of the in vitro and in vivo differentiation of APL blasts by all-trans retinoic acid (ATRA) has modified the therapeutic approach of APL and lead to important advances in understanding the biology of APL. Since it became apparent that differentiation therapy of APL with ATRA was indeed a true model of targetted therapy, evidencing the molecular targets of retinoic acid efficacy became crucial. These molecular targets are closely related to the biological features of APL cells, some of which are well-known and have contributed to the morphological and cytogenetic definition of the leukemia, others have just been defined or re-discovered in the light of a better understanding of molecular controls of cell growth and differentiation. The aims of characterizing the biological features of APL cells should allow a better management of APL therapy and the identification of potential markers for differentiation therapies in other leukemias or solid tumors.

The novel co-activator CRABPII binds to RARalpha and RXRalpha via two nuclear receptor interacting domains and does not require the AF-2 'core'

We identify the RARalpha, RXRalpha and CRABPII domains required for the physical interaction of these proteins. On RARalpha and RXRalpha, the sequences correspond to the DEF and DE domains, respectively, but the interaction with CRABPII does not require the AF-2AD 'core'. On CRABPII, two interacting domains are identified (NRID1 and NRID2), one of which contains the only enhancement transactivation domain of CRABPII. The interaction is ligand-independent and does not require the ligand-binding domain of CRABPII. These results further stress that interaction of CRABPII with the nuclear receptors defines a novel level of transcriptional control.

Is the thrombopoietin assay useful for differential diagnosis of thrombocytopenia? Analysis of a cohort of 160 patients with thrombocytopenia and defined platelet life span

BACKGROUND

Thrombopoietin (TPO), the major hormone controlling platelet production, has been measured in thrombocytopenias with discordant results. The aim of our work was to assess the value of the TPO assay for differential diagnosis of thrombocytopenias in a large cohort of patients classified according to the results of their platelet isotopic study.

METHODS

We measured TPO (R&D Systems) in serum of 160 thrombocytopenic patients referred to our department for platelet life span isotopic studies. We classified patients as follows: (a) idiopathic or autoimmune thrombocytopenia group (ITP; patients with increased platelet destruction and shortened platelet life span; n = 67); (b) pure genetic thrombocytopenia group (patients with decreased platelet production, normal platelet life span, and without bone marrow aplasia; n = 55); (c) bone marrow aplasia group (BM; patients with decreased platelet production, normal platelet life span, and bone marrow aplasia; n = 13).

RESULTS

In patients with pure genetic thrombocytopenia, TPO (median, 55 ng/L) was not different from TPO in patients with ITP (median, 58 ng/L) or controls (n = 54; median, 51 ng/L). Only in patients with bone marrow aplasia was TPO significantly higher (median, 155 ng/L) and negatively correlated to the platelet count (r(2) = 0.5014).

CONCLUSIONS

Although the median serum TPO is increased in thrombocytopenia with decreased platelet production from bone marrow aplasia, it does not differentiate patients with pure genetic thrombocytopenia from those with ITP.

Variability in the levels of PML-RAR alpha fusion transcripts detected by the laboratories participating in an external quality control program using several reverse transcription polymerase chain reaction protocols

BACKGROUND AND OBJECTIVES

The detection of PML-RAR by reverse transcription (RT) polymerase chain reaction (PCR) in acute promyelocytic leukemia (APL) patients who are in hematologic remission influences therapeutic decision making in several trials. In the light of this, the Spanish group has recently designed an external quality assessment program (EQAP) of RT-PCR detection of PML-RAR, which includes a study of sensitivity of the participating laboratories.

DESIGN AND METHODS

Eighteen laboratories were involved in the program. Ten laboratories followed the method of Biondi et al., 5 employed that of Borrow et al. and the 3 remaining used other protocols. The sensitivity was studied in five rounds of quality control. The first two shipments consisted of dilutions of NB4 RNA into non-APL RNA. The third round consisted of serial dilutions of the NB4 cell line into HL60 cells. The fourth and five rounds consisted of plasmid dilutions containing the bcr1 and bcr3 PML-RAR isoforms.

RESULTS

The results showed that the distinct methods allow detection of the PML-RAR hybrid up to a dilution of 10(-4), and exceptionally, up to 10(-5). The laboratories following the method of Biondi et al. usually detected the 10(-3) dilution and less frequently the 10(-4) one, whereas those using other methods usually detected PML-RAR transcript in the 10(-4) dilution, and less commonly in the 10(-5) dilution. However, each of the PCR methods used by EQAP participating laboratories successfully detected at least 50 copies of PML-RAR alpha fusion transcript in plasmid dilution controls.

INTERPRETATION AND CONCLUSIONS

The results point to heterogeneous sensitivity amongst participating laboratories. This may reflect differences in methodology, although variations in sample quality may also account for discrepant findings.

Retinoic acid-induced apoptosis in leukemia cells is mediated by paracrine action of tumor-selective death ligand TRAIL

The therapeutic and preventive activities of retinoids in cancer are due to their ability to modulate the growth, differentiation, and survival or apoptosis of cancer cells. Here we show that in NB4 acute promyelocytic leukemia cells, retinoids selective for retinoic-acid receptor-alpha induced an autoregulatory circuitry of survival programs followed by expression of the membrane-bound tumor-selective death ligand, TRAIL (tumor necrosis factor-related apoptosis-inducing ligand, also called Apo-2L). In a paracrine mode of action, TRAIL killed NB4 as well as heterologous and retinoic-acid-resistant cells. In the leukemic blasts of freshly diagnosed acute promyelocytic leukemia patients, retinoic-acid-induced expression of TRAIL most likely caused blast apoptosis. Thus, induction of TRAIL-mediated death signaling appears to contribute to the therapeutic value of retinoids.

Treatment of acute promyelocytic leukaemia

We review improvements achieved in the treatment of acute promyelocytic leukaemia (APL) over the last ten years. The combination of all- trans retinoic acid (ATRA) and conventional anthracycline-ARA-C chemotherapy (CT) has clearly demonstrated its superiority over CT alone (in terms of relapse and survival) in newly diagnosed APL. Combination treatment probably also reduces the incidence of initial failures, and complete remission (CR) rates greater than 90% are now regularly reported in large multicentre trials. Some randomized studies strongly suggest than prolonged maintenance treatment (for 1 or 2 years) with ATRA and low dose CT, and possibly very early introduction of anthracycline CT during induction treatment (i.e. not after ATRA) may reduce the incidence of relapse. With those treatments, the risk of relapse appears to be only 10-15%, although it remains greater in patients who initially have white blood cell counts (often associated with variant M(3)morphology, short bcr(3)isoform etc.) and patients with residual disease detectable by RT-PCR at the end of consolidation courses.ATRA syndrome remains the major side effect of ATRA treatment. It occurs in 10-15% of patients and is currently fatal in at least 10% of them. Rapid onset of CT and/or high dose steroids should improve its outcome.A sizeable proportion of APL patients who relapse after ATRA and CT can be durably salvaged by the same treatment followed by allogeneic or autologous stem cell transplantation, provided the transplant (in the autologous setting) is RT-PCR negative. Arsenic trioxide can induce CR in most APL patients refractory to ATRA and CT. It acts mainly by inducing apoptosis of APL cells. A place for arsenic trioxide earlier in the treatment of APL must currently be more precisely defined. Another issue in the treatment of APL is reducing the toxicity of first line treatment without increasing the relapse risk. Preliminary findings suggest that this could be achieved by consolidation CT using an anthracycline alone, without cytarabine.

Future perspectives for acute promyelocytic leukemia therapy

Acute promyelocytic leukemia (APL) is the first leukemia where targeted therapy proved to be effective, as only patients with retinoic acid-sensitive APL leukemic-clones responded in vivo. The future perspectives of APL therapy should persist in targeting either the APL's cell-specific characteristics concerning differentiation, cell cycle, and survival potentials, or the molecular markers specific to the APL clone. Converging recent advances in cellular therapy and in scientific concepts of cell differentiation should aim toward a possible cure of APL.

All-trans retinoic acid and chemotherapy in the treatment of acute promyelocytic leukemia

All-trans retinoic acid (ATRA) can induce complete remission (CR) in most patients with acute promyelocytic leukemia (APL) through in vivo differentiation of APL-blasts. However, it cannot eliminate the leukemic clone and must be used in combination with anthracycline-based chemotherapy. Experience accumulated over the last 10 years has clearly shown that the combination of ATRA and chemotherapy gave better survival than chemotherapy alone in newly diagnosed APL because of fewer relapses and a slightly higher CR rate. It is also strongly suggested that maintenance treatment with ATRA, and possibly with low-dose chemotherapy, can further reduce the incidence of relapse. Overall, more than 90% of patients with newly diagnosed APL can achieved CR, and about 75% can be cured by the combination of ATRA and chemotherapy. ATRA syndrome remains the major side effect of ATRA treatment, which should be prevented by addition of chemotherapy and/or dexamethasone in case of increasing white blood cell (WBC) counts. Current issues in the treatment of newly diagnosed APL include the role of early addition of chemotherapy to ATRA, whether or not ara-C is useful in combination with anthracycline, and a possible interest of arsenic trioxide during consolidation in patients remaining at relatively high risk of relapse.

Additional chromosomal abnormalities in patients with acute promyelocytic leukaemia (APL) do not confer poor prognosis: results of APL 93 trial

In spite of the recent improvement in the outcome of acute promyelocytic leukaemia (APL) with treatment combining all trans retinoic acid (ATRA) and chemotherapy (CT), some patients with this disease still have a poor outcome. The prognostic significance of chromosomal abnormalities in addition to t(15;17) in APL is uncertain. We examined the prognostic significance of secondary chromosomal changes in 292 patients included in a European trial who were treated with ATRA and CT. The incidence of chromosomal abnormalities in addition to t(15;17) was 26% and trisomy 8 was the most frequent secondary change (46% of the cases with secondary changes). No significant differences were seen with regard to age, sex, initial white blood cell count, % of circulating blasts, platelet count, fibrinogen level and incidence of microgranular variants between patients with or without additional rearrangements. Outcome was also similar between patients with t(15;17) alone and patients with t(15;17) and other clonal abnormalities for complete remission (92% vs. 93% respectively), event-free survival at 2 years (76.1% vs. 78.1% respectively), relapse at 2 years (16.7% vs. 11.6% respectively) and overall survival at 2 years (79.9% vs. 79.5% respectively). Analysis according to the type of induction treatment (ATRA followed by CT or ATRA plus CT) or the type of maintenance treatment (with ATRA, low-dose CT or both) also failed to show any difference between the two groups. Thus, in a large cohort of APL patients treated with ATRA and CT, additional chromosomal abnormalities had no impact on prognosis.

Retinoic acid receptor alpha (RAralpha) Mutations in Human Leukemia

The retinoic acid receptor alpha (RARalpha) plays a central role in the biology of the myeloid cellular compartment. Chromosomal translocations involving the RARalpha locus probably represent the malignant initiating events in acute promyelocytic leukemia (APL). Recent studies that identify novel interactions between RARalpha and the nuclear receptor co-activators and co-repressors, new functions of the oncogenic RARalpha fusion proteins and their catabolism in retinoic acid-induced differentiation, and the availability of new transgenic mice models have provided important insights into our understanding of the mechanisms by which mutant forms of RARalpha can be implicated in the development of leukemia. Novel alterations of the RARalpha gene identified in hematopoietic malignant disorders other than APL, such as myelodysplastic syndromes, non-APL acute myeloid leukemias and B-chronic lymphocytic leukemias, suggest that disruption of the RARalpha gene might predispose to myeloid and lymphoid disorders.

Oral 9-cis retinoic acid (Alitretinoin) in the treatment of myelodysplastic syndromes: results from a pilot study

A multicenter phase II study was initiated to investigate the efficacy, toxicity and tolerability of an oral regimen of 9-cis retinoic acid (9CRA) as a differentiation-inducing agent stimulating both retinoic acid receptor (RAR) and retinoic X receptor (RXR). Thirty patients with myelodysplastic syndromes (MDS) were enrolled into the study. The MDS subtypes were distributed as follows: 14 refractory anaemia (RA), four refractory anaemia with ringed sideroblasts (RARS), and 12 refractory anaemia with excess blasts (RAEB). The age ranged from 40 to 81 years (median 70). None of these had previously received treatment for MDS other than supportive therapy. 9CRA (Alitretinoin capsules, kindly provided by Allergan-Ligand Retinoid Therapeutics) was given daily at 60 mg/m2 p.o. for 1 week, followed by an intra-patient escalation to 100 mg/m2 during the second week, up to a maximum of 140 mg/m2. The planned treatment duration was 48 weeks. Twenty-five were available for assessment. One patient (4%) with RA achieved complete hematological remission. Four (16%), two with RA, two with RAEB, had minor responses resulting in decreased transfusion requirements or increased neutrophils. Thus, the overall response rate was 20% in evaluable patients with MDS and 17% in the study group on an intention-to-treat basis. The most frequent side-effects included headache (77%), dry skin (57%), arthralgias (30%), and rash (23%). In conclusion, although modest responses were noted in this study, the treatment tolerability was suboptimal. It is conceivable that a lower dosage schedule may be efficacious and better tolerated so enabling prolonged exposure which may be required to induce a differentiation effect.

Submicroscopic insertion of RARalpha gene into chromosome 15 in two cases of acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is characterized by a specific translocation (15;17)(q22;q21), resulting in the formation of PML/RARalpha chimeric transcripts. We report two female patients with PML/RARalpha-positive classical APL, whose leukemic cells expressed a variant translocation, t(5;15)(q13;q22) and t(15;17)(q22;p13), respectively. Both translocations were confirmed by whole chromosome painting which revealed no apparent involvement of 17q. A two-color fluorescence in situ hybridization with a 5' PML and a 3' RARalpha probe showed, in both cases, the presence of a PML-RARalpha fusion gene, on the der(15)t(5;15) long arm, and on the der(17)t(15;17) short arm, respectively. These two complex rearrangements resulted most probably from a two-step mechanism: (1) a submicroscopic insertion into 15q of a 17q segment including the 3' part of the RARalpha gene; (2) a reciprocal translocation between der(15) and a variable chromosome arm, with a breakpoint distal and proximal to RARalpha insertion in the case of t(5;15) and t(15;17), respectively. Molecular and prognosis significance of these variant translocations are discussed.