Nucleoside incorporation into DNA and RNA in acute leukaemia: differences between the various leukaemia sub-types

Metabolism in Hematopoiesis and Its Malignancy

Hematopoietic stem cells (HSCs) are multipotent stem cells that can self-renew and generate all blood cells of different lineages. The system is under tight control in order to maintain a precise equilibrium of the HSC pool and the effective production of mature blood cells to support various biological activities. Cell metabolism can regulate different molecular activities, such as epigenetic modification and cell cycle regulation, and subsequently affects the function and maintenance of HSC. Upon malignant transformation, oncogenic drivers in malignant hematopoietic cells can remodel the metabolic pathways for supporting the oncogenic growth. The dysregulation of metabolism results in oncogene addiction, implying the development of malignancy-specific metabolism-targeted therapy. In this chapter, we will discuss the significance of different metabolic pathways in hematopoiesis, specifically, the distinctive metabolic dependency in hematopoietic malignancies and potential metabolic therapy.

A genome-wide approach identifies that the aspartate metabolism pathway contributes to asparaginase sensitivity

Asparaginase is an important component for treatment of childhood acute lymphoblastic leukemia (ALL). The basis for interindividual differences in asparaginase sensitivity remains unclear. To comprehensively identify genetic variants important in the cytotoxicity of asparaginase, we used a genome-wide association approach using the HapMap lymphoblastoid cell lines (87 CEU trio members) and 54 primary ALL leukemic blast samples at diagnosis. Asparaginase sensitivity was assessed as the drug concentration necessary to inhibit 50% of growth (inhibitory concentration (IC)(50)). In CEU lines, we tested 2,390,203 single-nucleotide polymorphism (SNP) genotypes at the individual SNP (P<0.001) and gene level (P<0.05), and identified 329 SNPs representing 94 genes that were associated with asparaginase IC(50). The aspartate metabolism pathway was the most overrepresented among 199 pathways evaluated (P=8.1 × 10(-3)), with primary involvement of adenylosuccinate lyase and aspartyl-tRNA synthetase genes. We validated that SNPs in the aspartate metabolism pathway were also associated with asparaginase sensitivity in primary ALL leukemic blast samples (P=5.5 × 10(-5)). Our genome-wide interrogation of CEU cell lines and primary ALL blasts revealed that inherited genomic interindividual variation in a plausible candidate pathway can contribute to asparaginase sensitivity.

Acute lymphoblastic leukemia with TEL-AML1 fusion has lower expression of genes involved in purine metabolism and lower de novo purine synthesis

Because de novo purine synthesis (DNPS) is a target of widely used antileukemic agents (eg, methotrexate, mercaptopurine), we determined the rate of DNPS and the expression of genes involved in purine metabolism in different subtypes of acute lymphoblastic leukemia (ALL). Among 113 children with newly diagnosed ALL, lymphoblasts with the TEL-AML1 translocation had significantly lower DNPS than all other genetic subtypes of B-lineage ALL or T-lineage ALL (352 ± 57 versus 1001 ± 31 or versus 1315 ± 76 fmol/nmol/h, P &lt; .0001). By assessing the expression of 82 genes involved in purine metabolism (KEGG pathway database) in ALL blasts from 38 patients with B-lineage ALL (14 with TEL-AML1, 24 without), we identified 16 genes that were differentially expressed in TEL-AML1–positive and TEL-AML1–negative ALL (P &lt; .001, false discovery rate [FDR] = 5%). The pattern of expression of these 16 genes discriminated TEL-AML1–positive ALL with a true accuracy of 84% in an independent test set (n = 17, confidence interval 70% to 94%, P &lt; .001). Western blots of selected genes documented corresponding levels of the proteins encoded. Differentially expressed genes included HPRT, IMPDH, PAICS, and GART, all of which were expressed at a significantly lower level in TEL-AML1 ALL. These findings have established that TEL-AML1 ALL has significantly lower de novo purine synthesis and differential expression of genes involved in purine metabolism.

Accuracy of immunohistochemistry and flow cytometry in estimating the proportion of leukemic cells in S phase in chronic myeloid leukemia patients

We compared the proportion of S phase cells in bone marrow and peripheral blood samples obtained from 17 patients with chronic myeloid leukemia (CML). Before sampling all patients received a one hour i.v. infusion of iododeoxyuridine (IdUrd). The proportion of S phase cells was studied by immunohistochemistry (IHC) in bone marrow biopsies, and by flow cytometry (FCM) in bone marrow aspirates and peripheral blood samples. The IdUrd labelling index (LI) in bone marrow biopsy sections (27.5 +/- 1.8%) was significantly higher than the proportion of IdUrd labelled cells in bone marrow aspirate (15.1 +/- 2.0%). The percentage of S phase cells in peripheral blood was approximately the same as that in the aspirate (12.4 +/- 1.3%) and was correlated with that of bone marrow aspirate indicating a high degree of the aspirate dilution by peripheral blood. It is likely that the differences in % S phase cells in the aspirate and the biopsy result from this dilution. Estimates of the % S phase cells in the peripheral blood study by IHC and FCM were essentially the same. Samples labelled for one hour in vitro resulted in 1.5 fold higher LI than the same samples labelled in vivo. We conclude that estimates of the 8% S phase cells in the bone marrow of patients with CML should be made by infusing patients with IdUrd or BrdUrd with immunohistochemical evaluation of a marrow biopsy. Additionally in vitro labelling is not reflective of the percent S phase cells in vivo in patients.

The role of blood platelets in nucleoside metabolism: regulation of megakaryocyte development and platelet production

In higher vertebrates, different types of blood cells develop from common precursors. Mammals are unique in possessing two types of blood cells--erythrocytes and platelets--which lack nuclei. Although platelets display consistent and easily-recognisable morphological and ultrastructural characteristics and show extreme metabolic and functional versatility, they are not true cells, being produced by fragmentation of giant polyploid precursors called megakaryocytes. At present, the physiological mechanisms which regulate megakaryocyte development and platelet production are not well understood. Platelets are actively involved in metabolism of purine derivatives and a significant platelet role in pyrimidine metabolism has also been demonstrated (see previous papers). Here an attempt is made to integrate information about platelet involvement in nucleic acid precursor metabolism with current concepts of haematopoiesis, particularly megakaryocyte development and platelet production. It is concluded (i) that megakaryocytic cells are immediate descendents of haematopoietic stem cells which have become polyploid as a result of genetic damage or metabolic imbalances, (ii) megakaryocytes and platelets are the ultimate regulators of stem cell development because they control the availability of thymidine and (iii) that the production of megakaryocytes and platelets is a physiological safety mechanism which prevents fixation of genetic damage and protects other cells from potentially cytotoxic and genotoxic stimuli.

Effects of cytapheresis on cell cycle distribution of peripheral blood and bone marrow cells in some hematological malignancies

Feulgen-DNA cytophotometry and 3H-thymidine autoradiography were used to evaluate therapeutic cytapheresis effects on cell cycle distributions of peripheral blood leukemic cells in 15 acute leukemia, 5 CML and 8 CLL patients and of bone marrow erythroblasts in 18 PV patients. Both individual cytapheresis procedures and a long-term program of cytapheresis altered cell cycle distributions and biochemistry which may be summarized as follows: An increase in percentage of cells in S-phase (acute leukemia, CML); a decrease in the differences between values of S-cell number obtained by cytophotometry and autoradiography (acute leukemia, CML, PV); a decrease in some cases in enlarged fraction of cells in G2 (blast crisis of CML, PV); an activation of G0----G1 transition and an increase in the PAS-positive lymphocyte fraction in CLL patients. An apparent increase of blasts in S-phase was found after a pheresis in acute leukemia patients who responded to subsequent chemotherapy. In "nonresponders", a pheresis had no effect on cell cycle distributions. The results of the study demonstrate that despite the wide variability of individual responses, cytapheresis activates cell proliferation and metabolic processes in patients with hematological malignancies.

Deoxythymidine and deoxycytidine incorporation into DNA in B leukemic cells

Measurements of radioactive DNA after incubation of normal and B leukemic peripheral mononuclear cells, from c-ALL and CLL with labeled deoxythymidine (dTh) and deoxycytidine (dCt) showed that for dTh, incorporation into DNA was similar for normal and c-ALL cells but lower in B-CLL cells and that for dCt, incorporation was highest in c-ALL and lowest in CLL cells. These results contrast with those of dTh and dCt kinase activities; the former has been previously found elevated in c-ALL cells, and the latter is found, in the present study, similar in the three groups tested.