Prognostic value of 5'nucleotidase in acute lymphoblastic leukemia with the common-ALL phenotype

NT5E is associated with unfavorable prognosis and regulates cell proliferation and motility in gastric cancer

Ecto-5′-nucleotidase (NT5E) is a glycosylphosphatidylinositol anchored cell surface protein, and has been suggested to be dysregulated in most types of human cancer including gastric cancer. The aim of the present study was to present more evidence about the clinical and prognostic value of Ecto-5′-nucleotidase in gastric cancer patients, and preliminarily explore the biological function of Ecto-5′-nucleotidase in gastric cancer cells. In our study, high Ecto-5′-nucleotidase expression was observed in gastric cancer tissues and cell lines, respectively, compared with normal gastric mucosa tissues cells. Meanwhile, TCGA database also indicated that Ecto-5′-nucleotidase expression levels were notably elevated in gastric cancer tissues compared with normal gastric mucosa tissues. Furthermore, high-expression of Ecto-5′-nucleotidase was obviously associated with advanced clinical stage, deep tumor invasion, lymph node metastasis and distant metastasis in gastric cancer patients. The survival analyses of TCGA database and our study consistent suggested high Ecto-5′-nucleotidase expression was negatively correlated with overall survival time in gastric cancer patients. The univariate and multivariate Cox proportional hazards regression model showed high Ecto-5′-nucleotidase expression was an independent poor prognostic factor for gastric cancer patients. Moreover, silencing of Ecto-5′-nucleotidase expression suppressed cell proliferation, migration and invasion in vitro in gastric cancer. In conclusion, Ecto-5′-nucleotidase is a credible prognostic biomarker, and serves as a potential therapeutic target in gastric cancer.

Cell-death-associated molecular patterns as determinants of cancer immunogenicity

SIGNIFICANCE

Accumulating evidence indicates that the success of some anticancer treatments (select chemotherapies or radiotherapy or trastuzumab) could be related to the stimulation of an anticancer immune response through the induction of an immunogenic tumor cell death (ICD).

RECENT ADVANCES

Preclinical data revealed that dying tumor cells can emit a series of danger signals (so-called "cell-death-associated molecular patterns" (CDAMP)) that will dictate the recruitment and activation of specific inflammatory phagocytes. Hence, tumor cells succumbing to ICD are characterized by specific metabolic and molecular changes that will trigger a hierarchy of polarizing cytokine-producing cells, culminating in the recruitment and reactivation of antitumor interferon-γ-producing effector T cells which contribute to the success of cytotoxic treatments.

CRITICAL ISSUES

In this review, we summarize the molecular and cellular bases of this ICD, underscoring the crucial role of high mobility group box 1 protein (HMGB1) and adenosine tri-phosphate, both of which are released from dying tumor cells during ICD and are implicated in the chemotherapy-elicited anticancer immune response.

FUTURE DIRECTIONS

We discuss here how such CDAMP could serve as predictive biomarkers that could discriminate immunogenic from nonimmunogenic anti-cancer compounds, and, in case of deficiency, could be compensated by surrogate products to ameliorate the success rate of conventional anticancer treatment modalities.

Pharmacogenetics influence treatment efficacy in childhood acute lymphoblastic leukemia

Pharmacogenetics covers the genetic variation affecting pharmacokinetics and pharmacodynamics, and their influence on drug-response phenotypes. The genetic variation includes an estimated 15 million single nucleotide polymorphisms (SNPs) and is a key determinator for the interindividual differences in treatment resistance and toxic side effects. As most childhood acute lymphoblastic leukemia treatment protocols include up to 13 different chemotherapeutic agents, the impact of individual SNPs has been difficult to evaluate. So far focus has mainly been on the widely used glucocorticosteroids, methotrexate, and thiopurines, or on metabolic pathways and transport mechanisms that are common to several drugs, such as the glutathione S-transferases. However, beyond the thiopurine methyltransferase polymorphisms, the candidate-gene approach has not established clear associations between polymorphisms and treatment response. In the future, high-throughput, low-cost, genetic platforms will allow screening of hundreds or thousands of targeted SNPs to give a combined gene-dosage effect (=individual SNP risk profile), which may allow pharmacogenetic-based individualization of treatment.

Potential mechanisms of resistance to cytarabine in AML patients

To determine whether the human equilibrative nucleoside transporter 1 (hENT1), deoxycytidine kinase (dCK), cytoplasmic 5'-nucleotidase (5NT), cytidine deaminase (CDD), topoisomerase I (TOPO I) and topoisomerase II alpha (TOPO II) are involved in clinical resistance to cytarabine (ara-C), we analyzed the level of expression of these parameters by reverse transcriptase polymerase chain reaction (rt-PCR), at diagnosis in the blast cells of 77 acute myeloid leukemia (AML) patients treated with ara-C, including 31 for whom samples were collected at first relapse. By univariate and/or multivariate analyses, patients with expression of 5NT or hENT1 deficiency at diagnosis had significantly shorter disease-free survival (DFS) and overall survival (OS). These results suggest that expression of 5NT and reduced hENT1 in leukemic blasts at diagnosis are correlated with clinical outcome and may play a role in resistance mechanisms to ara-C in patients with AML.

Expression of high Km 5'-nucleotidase in leukemic blasts is an independent prognostic factor in adults with acute myeloid leukemia

Cytarabine (ara-C) requires activation into its triphosphorylated form, ara-CTP, to exert cytotoxic activity. Cytoplasmic 5'-nucleotidase (5NT) dephosphorylates ara-CMP, a key intermediate, preventing accumulation of ara-CTP and may reduce cellular sensitivity to the cytotoxic activity of ara-C. To determine whether the level of expression of 5NT is correlated with clinical outcome in patients with acute myeloid leukemia (AML) treated with ara-C, this study analyzed the levels of messenger RNA expression of high Km 5NT by real-time polymerase chain reaction at diagnosis in blast cells of 108 patients with AML. High Km 5NT was expressed at diagnosis in the blast cells of 54% of patients. In univariate analysis, (1) patients whose blast cells contained high levels (values greater than the median value for total population) of high Km 5NT at diagnosis had significantly shorter disease-free survival (DFS) than patients with low levels of high Km 5NT (11 months versus 17.5 months, P =.02) and (2) high levels of high Km 5NT also predicted significantly shorter overall survival (15.7 months versus 39 months, P = .01) in young patients (< or = 57 years; median value for the entire population). In a multivariate analysis taking into account age, karyotype risk, and other factors found to have prognostic significance in univariate analysis, (1) high Km 5NT expression was an independent prognostic factor for DFS and (2) high levels of high Km 5NT also predicted significantly shorter overall survival in young patients. These results demonstrate that the expression of high levels of high Km 5NT in blast cells is correlated with outcome in patients with AML.

Ecto-enzyme and signaling functions of lymphocyte CD73

CD73 or ecto-5'-nucleotidase (5'-NT) is a widely expressed ecto-enzyme which catalyzes the dephosphorylation of AMP and other nucleoside monophosphates. CD73 participates in purine salvage through this enzymatic activity, supplying cells with precursors for energy metabolism and nucleic acid biosynthesis. As an enzyme that produces adenosine, CD73 can also regulate adenosine receptor engagement in many tissues. However, CD73 also has functions independent of its enzyme activity. Like many glycosyl phosphatidylinositol (GPI)-anchored molecules, it transmits potent activation signals in T cells when ligated by antibodies. Less compelling evidence suggests that CD73 may function as a cell adhesion molecule. In the human immune system, CD73 is expressed on subsets of T and B cells, on germinal center follicular dendritic cells, and on thymic medullary reticular fibroblasts and epithelial cells. Many challenging areas remain to be explored before the role of CD73 in the immune system will be fully understood. These include an evaluation of the role of adenosine receptors in lymphoid development, the identification of physiological CD73 ligands, a functional assessment of the GPI anchor, and an analysis of the intricate cell-type-specific and developmental regulation of CD73 expression.

Isolation and characterization of the promoter of the human 5'-nucleotidase (CD73)-encoding gene

Ecto-5'-nucleotidase (NT, CD73) is a purine salvage-pathway enzyme located on the surface of various cell types, including subsets of human lymphocytes and certain leukemias and lymphomas. In addition to purine salvage, NT has proposed roles in lymphocyte maturation and activation, and its expression has been associated with the resistance of some tumor cell lines to chemotherapeutic agents. To better understand the regulation of NT gene expression in normal lymphocyte development and the elevated expression seen in some drug-resistant tumor cell lines, we isolated NT genomic clones containing the promoter region. The genomic DNA upstream from the NT start codon is high in G+C content, with one cAMP-responsive element and five consensus Sp-1 binding sites, but no TATAA box. RNase protection assays identified a cluster of potential transcription start points (tsp). One tsp, at -63 bp relative to the start codon, was confirmed as authentic by 5'-RACE (rapid amplification of cDNA ends) cloning. Transient transfection experiments utilizing luc as a reporter gene have demonstrated that a 155-bp NT genomic DNA segment inclusive of the tsp functions as a promoter in both NT+ (WI-L2 and MG) and NT- (Jurkat, Hela and Raji) cell lines. The addition of 5'-flanking sequences extending as far as -1.9 kb did not confer cell-type-specific expression to the core promoter. However, nuclear run-on analysis of nascent NT transcripts suggested that differential transcription initiation is at least partially responsible for the regulation of NT expression. Thus, additional information is necessary, either at the chromatin level, or within elements outside of the promoter region, to direct tissue-specific expression of NT.

Clinical relevance of in vitro drug resistance testing in childhood acute lymphoblastic leukemia: the state of the art

Nowadays about two-thirds of children with acute lymphoblastic leukemia (ALL) can be cured with chemotherapy, but one-third die from the disease. The clinical response of leukemic cells to chemotherapy is roughly due to two factors: the effective drug levels reaching the cells and the resistance of these cells to the drugs. The clinical value of cellular drug resistance in children with ALL is not known. We developed an in vitro assay to study drug resistance in these children. In this article, the main results obtained with this MTT assay on samples from 137 children with ALL are summarized: (1) patients whose cells are resistant to several drugs at initial diagnosis have a poor prognosis; (2) relapsed leukemias show a considerable drug resistance which might partly explain the poor prognosis. Relapsed cases differ in their type and degree of resistance; (3) the poor outcome of high risk groups as defined by age and immunophenotype can partly be explained by specific patterns of drug resistance; (4) P-glycoprotein-mediated multidrug resistance is not an important cause of resistance in childhood ALL; and (5) no relation exists between the activities of the purine enzymes HGPRT, 5'NT, ADA, and PNP and drug resistance in childhood ALL. The conclusion is that in vitro drug resistance data have clinical relevance and can be used to develop more effective and less toxic treatment strategies in childhood ALL.

Possibilities and limitations of cytochemical methods in diagnosis of acute leukemia

Accurate identification and classification of leukemic blast cells is a very important prerequisite of the precise diagnosis of acute leukemia and has a great impact on therapy and prognosis. The purpose of this review is to consider, in the broad sense of the word, the present possibilities and limitations of enzyme cytochemistry and to emphasize how cytochemistry may contribute, on integration with the other methods of study, to the final classification and differential diagnosis of acute leukemia, a highly variable hematological disorder. In this review, the role of conventional enzyme cytochemistry, either dominant or subsidiary, in the discrimination of acute leukemia subtypes is discussed. The survey confirms the absolute necessity of immunologic marker analysis in the accurate diagnosis of acute lymphoblastic leukemia, undifferentiated or minimally differentiated leukemia and mixed-lineage leukemia because in these cases, the cytochemical evaluation provides insufficiently relevant information regarding blast cell origin, specificity of leukemia subtypes and the discrete stages of leukemic cell maturation. On the other hand, cytochemical investigation is appreciated to be dominant over immunophenotyping in characterizing acute myeloid leukemia, because of the lack of specificity of the majority of immunological markers against myeloid antigens and, because of the availability of standardized and sufficiently specific cytochemical reactions. The cytogenetic, molecular biological and electron microscopic studies mentioned in this review supplement the important information for correct differential diagnosis of acute leukemia. The prognostic impact of enzyme cytochemistry in correlation to other methods is evaluated.

Altered properties of human T-lymphoblast soluble low Km 5'-nucleotidase: comparison with B-lymphoblast enzyme

Soluble low Km 5'-nucleotidases have been purified from human cultured T- and B-lymphoblasts to compare their properties and to examine the mechanism of different rates of nucleotide dephosphorylation. The enzyme from B-lymphoblasts (MGL-8) was 4385-fold purified with a specific activity of 114 mumol/min/mg, while the enzyme from T-lymphoblasts (CEM, MOLT-4) was 4355-fold purified with a specific activity of 35 mumol/min/mg. The activity of both enzymes have an absolute requirement for Mg++. The B-cell enzyme has maximum activity with Mg2+ > Mn2+ > Co2+, while the T-cell enzyme had maximum activity with Co2+ > Mn2+ > Mg2+. The optimum activity was at pH 7.4-9.0 for the B-cell enzyme and pH 9.0 for the T-cell enzyme. Substrate specificity was the same for both enzymes with the following relative Vmax values: CMP > UMP > dUMP > dCMP > dAMP > IMP > GMP > dIMP > dGMP. The Km values for AMP and IMP were 12 and 25 microM for the B-cell enzyme, and 7.0 and 12 microM for the T-cell enzyme. ATP and ADP are competitive inhibitors of these enzymes with apparent Ki values of 100 and 20 microM for the B-cell enzyme, and 44 microM and 8 microM for the T-cell enzyme, respectively. The apparent molecular mass by gel filtration column chromatography is 145 kD for the B-cell enzyme and 72 kDa for the T-cell enzyme. The subunit molecular masses by Western blots are 69.2 kD for both enzymes. These properties suggest that the B-lymphoblast enzyme is identical or similar to the enzyme from human placenta. However, the T-cell enzyme has some different properties. We conclude that these differences plus a lower content of low Km 5'-nucleotidase in T-cells may account for the decreased ability of T-lymphoblasts to dephosphorylate nucleotides and may contribute to the selective cytotoxicity of deoxyribonucleosides for T-lymphoblasts as compared to B-lymphoblasts.

Relation of 5'-nucleotidase and phosphatase activities with immunophenotype, drug resistance and clinical prognosis in childhood leukemia

Ecto-5'-nucleotidase (ecto-5'NT) catalyzes the extracellular dephosphorylation of nucleotides like IMP. Cytoplasmic 5'NT (cyto-5'NT) and non-specific (e.g. acid- and alkaline) phosphatases (AP) regulate the intracellular degradation of nucleotides. High NT and AP activities might cause a resistance to the thiopurines 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG). We studied the relation between these enzymes and immunophenotype, drug resistance and prognosis in 77 children with acute lymphoblastic leukemia (ALL). Enzyme activities were assessed radiochemically; in vitro drug resistance was measured with the MTT assay. AP activities were higher in T-ALL and B-ALL than in precursor B-ALL. Cyto-5'NT activity was very low in all phenotypes and accounted for a significant proportion of total IMPase activity only in the very immature CD10- c mu- precursor B-ALL. CD10+ ALL cases with high ecto-5'NT activities showed a trend (p = 0.065) for a lower probability of continuous complete remission than those with a low activity. Ecto-5'NT activity was not related to in vitro drug resistance to 6-TG. A weak correlation was found between in vitro 6-TG resistance and cyto-5'NT and AP activities. We conclude that high ecto-5'NT activities do not cause a resistance to 6-thiopurines in childhood ALL. Some patients have high cyto-5'NT and AP activities associated with 6-thiopurine resistance.

Prognostic implication of ecto-5'-nucleotidase activity in acute lymphoblastic leukemia

Ecto-5'-nucleotidase (5'-N) activity was determined in 191 patients (71 children and 120 adults) with acute leukemia. Elevated values for 5'-N were registered in common acute lymphoblastic leukemia (ALL), but blast cells of T-cell ALL (T-ALL) and common ALL antigen-negative non-T-ALL had low enzyme activity comparable with the values of acute non-lymphocytic leukemia. Dependence of remission duration on 5'-N activity was analyzed in 74 adults with ALL, treated similarly in a prospective multicenter trial. The remission curves for ALL patients with 5'-N activity lower than 10 nmol/h x 10(6) cells were substantially and significantly better than those of patients with high activity (greater than 10 nmol/h x 10(6) cells). This difference was also evident in the immunologic subclass common ALL. Statistical evaluation showed that an interaction between immunologic subtype of the blast cells and their 5'-N activity had prognostic significance for remission duration. In addition to the independent factor, initial age, this interaction was also prognostic for survival.

The role of 5'nucleotidase in therapy-resistance of childhood leukemia

Purine nucleotides become available for a cell by two routes, namely purine de novo synthesis and the purine salvage pathway. 5'Nucleotidase is a purine pathway enzyme and is present in two forms. Cytoplasmic 5'nucleotidase (cyto 5'NT) catalyzes the intracellular degradation of purine nucleotides into their corresponding nucleosides. The plasma membrane bound form (ecto 5'NT) has its active site facing the external medium. Its function is the extracellular dephosphorylation of nucleotides, to which cells are generally impermeable, into nucleosides and the transport of these nucleosides through the cell membrane. Lymphoblastic 5'NT activity varies between different children with common-ALL. 5'NT positive cases have a higher relapse rate and thus a poorer prognosis than 5'NT negative cases. This can be explained by two hypotheses which are not mutually exclusive: 1. Rescue hypothesis. When purine de novo synthesis is blocked by methotrexate (MTX) and/or 6-mercaptopurine (6-MP), the malignant cell has to rely on the purine salvage pathway. This pathway depends on the ecto-5'NT activity. So, leukemic cells might be resistant to MTX and/or 6-MP because of ecto-5'NT activity. 2. Breakdown hypothesis. Leukemic cells are resistant to 6-MP because of the breakdown of the toxic nucleotide form of 6-MP into the nucleoside form by cyto-5'NT.

Enzymes of purine metabolism in lymphoid neoplasms, clinical relevance for treatment with enzyme inhibitors

A few enzymes of the purine degradative pathway have proved valuable in diagnosis and treatment of lymphomas and lymphocytic leukemia. Of particular interest are the enzymes adenosine deaminase (ADA), purine nucleoside phosphorylase (PNP) and ecto-5'-nucleotidase (5NT). Intact activities of ADA and PNP have been shown to be vital for lymphoid cells. During development, lymphoid precursors go through remarkable changes in the concentrations of these enzymes and the neoplasms derived from them show a "frozen" biochemical profile similar to the corresponding normal cell of origin. Knowledge of the role of these enzymes has led to the pharmacological use of enzyme inhibitors for the specific treatment of lymphoid neoplasms. This review concerns the enzymatic make-up of normal and neoplastic lymphocytes and exploitation of this knowledge for the treatment of lymphomas. Special emphasis will be put on the clinical use of an ADA-inhibitor, deoxycoformycin.

Prognostic significance of acid alpha-naphthyl acetate esterase and acid phosphatase in childhood acute lymphoblastic leukemia

We studied the prognostic value of the enzymes acid alpha-naphthyl acetate esterase (ANAE) and acid phosphatase (AP) in 89 children with acute lymphoblastic leukemia (ALL). Follow-up data were available for 61 out of 67 cases of non T- non B-ALL, which were treated in different hospitals according to the same protocols. Sex, age, initial white blood cell count (WBC) and number of high risk patients (WBC above 25 X 10(9)/l) were comparable between enzyme-positive and -negative cases. The probabilities of complete continuous remission (CCR) were virtually identical in the AP+ and AP- group. For the ANAE+ group the probability of CCR was lower than for the ANAE- group, but this difference was not statistically significant (0.10 greater than p greater than 0.05). Within the common-ALL group (n = 32), no difference was found in probability of CCR between the AP+ and AP- group but ANAE+ cases had a significantly lower probability of CCR than ANAE- cases. This study is a contribution to the view that the cytochemical profile of ALL cells may have prognostic value.

Low cytidine deaminase levels in human hematopoietic cell lines

Purine and pyrimidine enzyme profiles of human cell lines have been investigated. A novel observation was the finding that most of the cell lines showed very low or undetectable levels of cytidine (deoxycytidine) deaminase, while they possessed pyrimidine 5'-nucleotidase, cytidine and deoxycytidine kinase activities. Most cell lines showed high levels of adenosine deaminase and purine nucleoside phosphorylase activities and low levels of purine 5'-nucleotidase. We propose that high adenosine deaminase and purine nucleoside phosphorylase activities and low cytidine deaminase activity may be of importance for immature hematopoietic cells in order to ensure a balanced synthesis of the DNA precursors.