Potential use of purine nucleosides and enzyme inhibitors for selective depletion of Thy-lymphoblasts from human bone marrow

8'-aminoguanosine inclusion results in enhanced efflux of taurine in preconditioned ischemic myocardium

Attenuated purine levels are characteristic findings of ischemic preconditioning (PC). Lower energy demand in PC myocardium leading to less nucleotide decay is a reasonable explanation. However, experimental data suggest that the activities of the enzymes involved in purine metabolism are increased in PC myocardium. Recently it was suggested that PC favored degradation of exogenous adenosine to inosine successively ending up in enhanced lactate production. This was probably because of the involvement of the hexose monophosphate pathway in the PC ischemic myocardium. This route may therefore be supplementary in energy metabolism as a metabolic flow can be started by adenosine ending up in lactate without initial adenosine 5'-triphosphate (ATP) investment. Purine nucleoside phosphorylase (PNP) is a key enzyme in the proposed metabolic route. In the current study the effect of PNP inhibition (with 8'-aminoguanosine) on myocardial energy metabolism during PC was studied in an open chest porcine heart model using the microdialysis technique. A dose-dependent inhibition of PNP by 8'-aminoguanosine was observed in PC myocardium. This inhibition resulted in an enhanced exodus of taurine reflecting a disturbed energy economy of the cardiomyocytes. Addition of inosine being a true substrate of PNP reversed these changes, which indicated that 8'-aminoguanosine was a competitive inhibitor of PNP. It is concluded that the ischemic PC phenomenon at least partly involves the activated enzyme PNP.

CREB antisense oligonucleotides induce non-apoptotic cell death in proliferating leukemia cells, but not normal hematopoietic cells, by a bizarre non-antisense mechanism

We report that antisense phosphorothioate oligodeoxyribonucleotides (PS-ODNs) against cyclic AMP response element-binding protein (CREB) induce the death of human leukemia cell lines including HL-60, Kasumi-1 and K562, OCI-AML1a and also primary leukemia cells isolated from patients with acute myelocytic leukemia and chronic myelocytic leukemia in blastic crisis. In contrast, normal human bone marrow CD34+ cells and normal peripheral blood lymphocytes were resistant to the antisense-mediated cell death. We found that antisense-treated HL-60 cells had prominent nuclear fragmentations but lacked apoptotic features including internucleosomal DNA cleavage and TUNEL positivity. Cell cycle analysis demonstrated a remarkable reduction in G1 phase population along with a mild accumulation of S phase and good preservation of G2/M phase, indicating cells died at G2/M without cycling into G1 phase. None of the sense-sequenced PS-ODNs induced cell death. Further, neither the expression nor the message of CREB protein was reduced by antisense treatment, indicating that cell death was mediated by a non-antisense mechanism. On the other hand, no consensus oligonucleotide sequence for cell death induction was detected. Rather, we found a good correlation between the melting temperatures and the anti-proliferative activities of the oligonucleotides. Thus, CREB antisense PS-ODNs selectively induce a non-apoptotic cell death in leukemic cells by an unknown hybridization-dependent mechanism.

In vitro and in vivo effects of 2'-deoxycoformycin (Pentostatin) on tumour cells from human gammadelta+ T-cell malignancies

Hepatosplenic gammadelta+ T-cell lymphoma represents a rare neoplasm of post-thymic phenotype, characterized by an aggressive clinical course and a poor response to conventional chemotherapy. In the present study, we have examined the cytotoxic effects of the purine analogue 2'-deoxycoformycin (dCF) on cultured mononuclear cells and purified gammadelta+ tumour cells from bone marrow or peripheral blood of four patients with hepatosplenic gammadelta+ T-cell lymphoma. At a concentration of 10 microM, dCF, in the presence of 2'-deoxyadenosine (dAdo), displayed an early and selective cytotoxic effect on gammadelta+ tumour T cells. After 48 h of in vitro exposure to dCF, the absolute number of viable CD3+/gammadelta+ tumour T cells was reduced by more than 90% in all samples with respect to control cultures, with absolute counts of viable CD3+/alphabeta+ lymphocytes being reduced only by 6-40% of the initial cell input. Analysis of cultures after 5 d of exposure to dCF plus dAdo revealed the persistence of normal CD3+/alphabeta+ T cells, which accounted, however, for only 20-25% of the initial cell input. Accordingly, the combination of dCF (10-100 microM) plus dAdo was able to induce a dose-dependent inhibition of clonogenic growth and [3H]-thymidine incorporation in purified CD3+/CD4-/CD8- gammadelta+ tumour cells. We also report that one patient with hepatosplenic gammadelta+ T-cell lymphoma in terminal leukaemic phase showed a striking haematological response to single-agent dCF given as fourth-line treatment. In particular, the selective clearance of gammadelta+ tumour T cells in peripheral blood and bone marrow was observed starting after the second course of treatment. Our results suggest that dCF may represent a potentially active drug for the management of this aggressive form of T-cell lymphoma.

Antisense therapeutics in chronic myeloid leukaemia: the promise, the progress and the problems

DNA sequences which are complementary or 'antisense' to a target mRNA can inhibit expression of that mRNA's protein product. Antisense therapeutics has therefore received attention for inhibiting oncogenes in haematological malignancy, in particular in chronic myeloid leukaemia. However, it is now becoming clear that antisense therapeutics is considerably more problematic than was naively initially assumed. In this article, some of these difficulties are discussed, together with the achievements in CML so far. Considerable further research is required in order to define an optimal antisense therapeutics strategy for clinical use.

Antisense Oligodeoxyribonucleotides Suppress Hematologic Cell Growth Through Stepwise Release of Deoxyribonucleotides

Antisense oligodeoxyribonucleotides (ODNs) are now being extensively investigated in an attempt to achieve cell growth suppression through specific targeting of genes related to cell proliferation, despite increasing evidence of non-antisense cytotoxic effects. In the context of anti-BCR/ABL antisense strategies in chronic myeloid leukemia, we have re-examined the antiproliferative effect of phosphodiester and phosphorothioate ODNs on the leukemic cell line BV173 and on CD34+ bone marrow cells in liquid culture. The 3′ sequences of the ODNs determine their effect. At concentrations of 10 μmol/L (for phosphorothioate ODNs) or 25 μmol/L (for phosphodiester ODNs), all the tested ODNs exert an antiproliferative activity, except those that contain a cytosine residue at either their two most terminal 3′ positions. We show that this antiproliferative effect is due to the toxicity of the d-NMPs (5′ monophosphate deoxyribonucleosides), the enzymatic hydrolysis products of the ODNs in culture medium. The toxicity of the d-NMPs on hematologic cells depends on their nature (d-CMP [2′deoxycytidine 5′-monophosphate] is not cytotoxic), on their concentration (d-GMP [2′-deoxyguanosine 5′-monophosphate], TMP [thymidine 5′-monophosphate], and d-AMP [2′-deoxyadenosine 5′-monophosphate] are cytotoxic at concentrations between 5 and 10 μmol/L), and on the coincident presence of other d-NMPs in the culture medium (d-CMP neutralizes the toxicity of d-AMP, d-GMP, or TMP). The antiproliferative activity of ODNs is thus restricted to conditions where the 3′ hydrolysis process by exonucleases generates significant amounts of d-NMPs with a low proportion of d-CMP. Our results reveal a novel example of a nonantisense effect of ODNs, which should be taken into account when performing any experiment using assumed antisense ODNs.

Antisense Oligodeoxyribonucleotides Suppress Hematologic Cell Growth Through Stepwise Release of Deoxyribonucleotides

Antisense oligodeoxyribonucleotides (ODNs) are now being extensively investigated in an attempt to achieve cell growth suppression through specific targeting of genes related to cell proliferation, despite increasing evidence of non-antisense cytotoxic effects. In the context of anti-BCR/ABL antisense strategies in chronic myeloid leukemia, we have re-examined the antiproliferative effect of phosphodiester and phosphorothioate ODNs on the leukemic cell line BV173 and on CD34+ bone marrow cells in liquid culture. The 3′ sequences of the ODNs determine their effect. At concentrations of 10 μmol/L (for phosphorothioate ODNs) or 25 μmol/L (for phosphodiester ODNs), all the tested ODNs exert an antiproliferative activity, except those that contain a cytosine residue at either their two most terminal 3′ positions. We show that this antiproliferative effect is due to the toxicity of the d-NMPs (5′ monophosphate deoxyribonucleosides), the enzymatic hydrolysis products of the ODNs in culture medium. The toxicity of the d-NMPs on hematologic cells depends on their nature (d-CMP [2′deoxycytidine 5′-monophosphate] is not cytotoxic), on their concentration (d-GMP [2′-deoxyguanosine 5′-monophosphate], TMP [thymidine 5′-monophosphate], and d-AMP [2′-deoxyadenosine 5′-monophosphate] are cytotoxic at concentrations between 5 and 10 μmol/L), and on the coincident presence of other d-NMPs in the culture medium (d-CMP neutralizes the toxicity of d-AMP, d-GMP, or TMP). The antiproliferative activity of ODNs is thus restricted to conditions where the 3′ hydrolysis process by exonucleases generates significant amounts of d-NMPs with a low proportion of d-CMP. Our results reveal a novel example of a nonantisense effect of ODNs, which should be taken into account when performing any experiment using assumed antisense ODNs.

Selective toxicity of purine nucleosides to human leukaemic cells

The in vitro cytotoxicity of various purine nucleosides and purine enzyme inhibitors, alone or in combination, and of the alkylating agent mafosfamide (Asta Z7557), incubated for 4 and 24 h have been studied in 17 leukaemic cell lines and normal bone marrow (BM). The purine nucleosides and their analogues included: 2'chlorodeoxyadenosine (CdA), 2'deoxyadenosine (AdR), 3'deoxyadenosine (3'AdR) (cordycepin), adenosine (AR), adenine arabinoside (Ara-A), deoxyguanosine (GdR) and guanine arabinoside (Ara-G). Purine enzyme inhibitors included 2-deoxycoformycin (dCF) and 8-aminoguanosine (8-AG). Cytotoxicity was based on inhibition of (i) incorporation of 3H-leucine into cell proteins and (ii) colony forming units--granulocytic/monocytic (CFU-GM) and for mixed cell colonies (CFU-GEMM). Marked and selective inhibition of T-cell growth was shown by the combinations dCF with either AdR or Ara-A, 8-AG and GdR and by CdA or Ara-G alone; these compounds even at high concentrations produced only partial inhibition of the growth of normal bone marrow CFU-GM and CFU-GEMM except for CdA which completely inhibited the formation of CFU-GEMM colonies. The combination dCF + cordycepin and alkylating agent mafosfamide were, however, toxic to all the cell lines at the concentrations employed, as well as to CFU-GM and CFU-GEMM. The high therapeutic index of some of the purine nucleosides with a relatively short exposure time makes them candidates for selective in vitro removal of residual neoplastic cells in autologous bone marrow transplantation (ABMT) for T-ALL.

Acute lymphoblastic leukemia in childhood

This article reviews the current biologic understanding of acute lymphoblastic leukemia and describes current approaches to treatment. It discusses the areas likely to be the focus of future research for this disease, including therapy for high-risk patients, understanding the reasons for treatment failure, and identification of new antileukemic agents.

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.