ALBERT

Description: In childhood acute lymphoblastic leukemia (ALL), early response to therapy is of crucial prognostic significance. In the frontline ALL-BFM (Berlin-Frankfurt-Münster) trial, treatment stratification is based on blast count estimation in peripheral blood at day 8 of induction prephase with prednisone and one dose of intrathecal methotrexate at day 1. To approach yet unknown mechanisms of therapy resistance and to characterize cells persisting under therapy on molecular level, we investigated gene expression profiles of leukemic blasts at day 8 of therapy (“day 8” cells) and their changes as compared with blast cells at initial diagnosis (“day 0” cells). To this end, an experimental procedure has been established including flow sorting of leukemic cells by their leukemia-associated immunophenotype and preparation of cRNA, starting from a small number of cells and using an additional amplification step. Experiments have shown that flow sorting procedure does not affect RNA quality, and this experimental approach facilitates investigation of patient samples with blast cell counts as low as 50 blast cells/μl. Blast cells from ten patients with B-cell precursor ALL were investigated using Affymetrix HG U133A microarrays, and gene expression data were processed by normalization procedure on probe level by variance stabilization. Genes commonly up- or downregulated in blast cells under therapy were identified in matched pairs of day 8 and day 0 samples using Significance Analysis of Microarrays (SAM) and a filtering criterion of at least two-fold mean change. By this procedure a group of 84 genes with a false discovery rate of less than 10 % was identified. In this group, 24 genes, reportedly involved at different levels of the cell cycle regulation, including cell cycle progression (CDC2, cyclin B2), DNA replication (e.g. thymidylate synthetase TYMS, ribonucleotide reductase RRM2, proteins MCM 4 and 6) and execution of mitosis (e.g. cell cycle checkpoint kinases CHEK1 and BUB1B, kinesin-like proteins 1 and 7, and MAD2L1), were found to be downregulated in the day 8 cells. In contrast, genes (n=7) encoding for proteins involved in survival signaling (e.g. IL-4/IL-13 common receptor chain, membrane-spanning 4-domains MS4A1 and CD20) showed increased expression in day 8 blasts. Taken together, the described experimental approach enabled gene expression analysis of ALL cells persisting under therapy and pointed to increased survival signaling in day 8 blasts and their preferential positioning in the G1 cell cycle phase.

Description: In the multicentric ALL-BFM (Berlin-Frankfurt-Munster) study, all patients are uniformly treated during the first week of induction therapy which uses glucocorticoids (GC) as the principal therapeutic agent. The GC response assessed at day 8 of therapy provides one of the basic parameters for further risk stratification. In spite of the clinical significance, molecular mechanisms of GC action in vivo are largely unknown. Our recent genome-wide analysis of gene expression in blasts persisting during induction therapy identified a common set of genes differentially expressed in blasts at day 8 (d8) and at diagnosis (d0) (n=457, false discovery rate

Description: Although the genetic mechanisms underlying the induction of ALL are similar, the molecular events leading to diverse clinical presentation and course are not well characterized. High PB white blood cell (WBC) counts reflect tumor burden in PB and have been used in the past as a clinical risk factor in ALL. We hypothesized that, given differential microenvironment signaling provided by BM and PB, ALLs with high or low WBC counts (WBChigh and WBClow) might differ with regard to their dependence on the microenvironment. To approach this issue, we investigated gene expression changes in PB blasts as compared to their BM counterparts in patients with precursor B-cell ALL (n=15). Blasts were isolated from BM and PB samples by flow sorting and investigated for mRNA levels using Affymetrix HG U133A microarrays. Gene expression data, normalized by variance stabilization on probe level, were analysed in matched PB-BM pairs using a SAM-like analysis of log ratios in a balanced permutation test. By these procedures, a limited number of 38 genes consistently changed in PB vs BM blasts was identified (false discovery rate 〈 0.01). Leukemic PB cells were characterized by upregulation of genes encoding for cell adhesion- and trafficking-related proteins (CD11b, CD73, S100A4, EMP3). Furthermore, downregulation of the cell cycle- and proliferation-associated genes (thymidylate synthetase TYMS, kinesin KIF11, topoisomerase TOP2A, ribonucleotide reductase RRM2, kinetochore protein ZWINT) indicated decreased proliferative activity of leukemic cells in PB microenvironment. Finally, the gene encoding for Bcl-2 protein, known to be a powerful downstream mediator of survival signaling from microenvironment in various experimental settings, was consistently downregulated in PB as compared to BM blasts. Within the group of WBClow patients (n=8, mean WBC=17x103/μl), most of these genes retained their statistical significance. By contrast, no consistent expression changes in PB vs BM blasts were found in WBChigh patients (n=7, mean WBC=201x103/μl). In summary, investigation of differential gene expression in leukemic cells from PB and BM indicated decreased levels of proliferative and survival signaling in the PB microenvironment and a higher dependence on this signaling of leukemic cells from WBClow as compared to WBChigh patients.

Description: A consistently increased mRNA expression of the adhesion receptor CD11b is a hallmark of the reported genomewide gene expression changes in precursor B-cell acute lymphoblastic leukemia (PBC-ALL) after 1 week of induction therapy. To investigate its clinical relevance, CD11b protein expression in leukemic blasts has been prospectively measured at diagnosis (159 patients) and during therapy (53 patients). The initially heterogeneous expression of CD11b inversely correlated with cytoreduction rates measured at clinically significant time points of induction therapy in the ALL–Berlin-Frankfurt-Münster 2000 protocol. CD11b positivity conferred a 5-fold increased risk of minimal residual disease (MRD) after induction therapy (day 33) and of high-risk group assignment after consolidation therapy (day 78). In the multivariate analysis CD11b expression was an independent prognostic factor compared with other clinically relevant parameters at diagnosis. During therapy, CD11b expression increased early in most ALL cases and remained consistently increased during induction/consolidation therapy. In more than 30% of MRD-positive cases, the CD11b expression on blast cells exceeded that of mature memory B cells and improved the discrimination of residual leukemic cells from regenerating bone marrow. Taken together, CD11b expression has considerable implications for prognosis, treatment response monitoring, and MRD detection in childhood PBC-ALL.

Description: Abstract 752 Risk stratification in the childhood ALL-BFM clinical trial has been based on molecular/cytogenetic markers and the in vivo response to treatment (blast reduction in peripheral blood after prednisone prephase, bone marrow clearance after induction treatment and minimal residual disease (MRD) after induction and induction consolidation). These criteria classify about 50% of ALL cases into standard-risk (SR) and high-risk (HR) groups. The intermediate-risk (IR) ALL group, showing moderate levels of MRD, provides the majority of relapses, but still lacks specific prognostic markers which could distinguish between those patients subsequently relapse and those remaining relapse-free (IR+r and IR-r). We established a bank of NOD/SCID ALL xenografts representing IR+r and IR-r subgroups (12 vs 13 patients) and characterized the samples in a broad series of functional assays. There was no difference in the sensitivity to drugs (dexamethasone, daunorubicin, L-asparaginase and vincristine) between the IR+r and IR-r groups, however, the rate of spontaneous apoptosis in vitro was significantly higher in the IR+r group than in the IR-r group (69 +/− 7% vs 39 +/− 6%, p=0.02). Given that in the presence of stromal cells the cell death level has been similar in both IR groups (9 +/− 5% vs 7 +/− 7%, p=0.8), these observations suggest that the IR+r ALL is more dependent on survival signals from microenvironment than IR-r ALL. In the NOD/SCID engraftment model, leukemic cells from IR+r patients engrafted more rapidly than cells from IR-r patients (93 +/− 12 days vs 170 +/− 24 days, p=0.006), pointing to a better in vivo cooperation between leukemia cells and microenvironment in the IR+r cases. In order to identify the underlying molecular pathways, gene expression changes induced in the presence and absence of stroma have been investigated at genome-wide level (Human Gene 1.0 ST Affymetrix array). Of the apoptosis-regulating genes, a caspase inhibitior from the IAP family, BIRC3, was found to be up-regulated significantly higher in the IR-r than in the IR+r group (3.7 +/− 1.1 vs 1.7 +/− 0.1-fold up-regulation, p=0.016). The adhesion molecule VCAM1 has been generally up-regulated by the co-incubation with stroma, with a tendency to a higher up-regulation in the IR-r (4.4 +/− 0.7-fold) than in the IR+r (2.7 +/− 1.0-fold) group. We further speculated that interaction with microenvironment is a mutual process which also implicates gene expression changes of the stroma. To this end, mouse stromal cells (MS5 cell line) were incubated with a series of ALL samples (n=3), purified by MACS sorting and investigated using Mouse Gene 1.0 ST Affymetrix arrays. The list of genes whose expression increased by at least 2-fold in all 3 cases (n=10), included the macrophage inflammatory peptide-1alpha (MIP1A/CCL3), a chemokine known to regulate chemotaxis of lymphocytes. Our data suggest that the cooperation of ALL with microenvironment may provide a promising approach to molecularly discriminate ALL cases with relapse and to identify potential relapse-associated targets within the IR-ALL group. Disclosures: No relevant conflicts of interest to declare.

Description: Effective therapy of high-risk leukemia with established cytotoxic drugs may be limited by poor antitumor efficacy, systemic toxicity, and the induction of drug resistance. Here, we provide the first evidence that hydrolytically activated prodrugs may overcome these problems. For this purpose, VP16 was functionally blocked by hydrolytically cleavable carbonate linkers with unique characteristics to generate 2 novel prodrugs of VP16. First, we established a more than 3-log higher efficacy of the 2 prodrugs compared with VP16 on a panel of naturally drug-resistant tumor cell lines. Second, the prodrugs did overcome VP16-induced multidrug resistance-1 gene (MDR-1)—mediated multidrug resistance in vitro in a newly established VP16-resistant T-cell leukemia cell line MOVP-3 by functionally blocking MDR-1—mediated efflux. Third, in vivo studies showed a maximum tolerated dose of ProVP16-II (〉 45mg/kg), which was at least 3-fold higher than that of VP16 (15 mg/kg). Finally, tests of ProVP16-II in a multidrug-resistant xenograft model of T-cell leukemia expressing MDR-1 indicated that only the mice treated with this prodrug revealed a complete and long-lasting regression of established, drug-resistant leukemia. In summary, the hydrolytically activated etoposide prodrugs proved effective against multidrug-resistant T-cell leukemia in vitro and in vivo and provide proof of concept for a highly promising new strategy for the treatment of MDR-1 drug-resistant malignancies. (Blood. 2003;102:246-253)

Description: In childhood acute lymphoblastic leukemia (ALL), persistence of leukemic blasts during therapy is of crucial prognostic significance. To approach the mechanisms of therapy resistance, we addressed genome-wide gene expression in blasts persisting after one week of induction therapy (day 8 blasts) and their molecular signatures as compared with blast cells at initial diagnosis (day 0 blasts). In order to approach this issue experimentally, a procedure has been established including flow sorting of leukemic blasts by their leukemia-associated immunophenotype and preparation of cRNA, starting from a small number of cells. Blast cells from 12 patients with precursor B-cell ALL were investigated using Affymetrix HG U133A microarrays, and genes commonly up- or down-regulated in blast cells under therapy were identified in matched pairs of day 8 and day 0 samples. In spite of the heterogeneous clinical features of the patients (mean rate of cytoreduction after 7 days of initial therapy = 82%, range between 33% and 99%), we were able to determine a set of 310 genes whose expression was commonly changed between day 8 and day 0 with an estimated false discovery rate of 0.05. The identified set of genes indicated inhibited cell cycling, reduced metabolism, and expression changes of multiple factors related to B-cell differentiation. These changes collectively suggested that gene expression in day 8 blasts is shifted towards resting mature B cells. To test this hypothesis, we isolated normal B cells from peripheral blood samples of leukemic patients and compared their gene expression to that of leukemic blasts using Principal Component Analysis (PCA). PCA revealed that day 8 samples are positioned between day 0 samples and normal B-cell samples, and statistical significance of this observation could be established using the Jonckheere-Terpstra test. Changes of B-cell differentiation markers on protein level supported this finding. In addition, we analyzed all genes with regard to the correlation of their expression changes with the rates of cytoreduction in peripheral blood. We observed differential impairment of the key components of the translational machinery including ribosome, eukaryotic 43S preinitiation complex and eukaryotic 48S initiation complex. Overall, expression levels of these factors decreased in therapy-sensitive patients but did not change in therapy-resistant patients. Taken together, investigation of leukemia cells persisting during therapy identifies common and individual expression changes which may potentially affect sensitivity towards anti-leukemic agents and offers new insights into the mechanisms of therapy resistance in ALL.