Leukaemic blasts differ from normal bone marrow mononuclear cells and CD34+ haemopoietic stem cells in their metabolism of cytosine arabinoside

Abstract

Different metabolites of cytosine arabinoside (AraC) contribute to its cytotoxicity including incorporation of AraCTP into DNA, the incorporation of AraUMP into RNA, inhibition of polymerase alpha and beta (AraCMP/CTP), an impairment of repair mechanisms (AraCTP), alterations of phospholipid metabolism (AraCDP-choline), a direct membrane interaction (AraC), the alteration of signal transduction pathways (AraCDP-choline, AraCTP) and the induction of apoptosis. Since little is known about the potential differences in AraC metabolism between leukaemic blasts and normal haemopoietic progenitor cells, the formation of all known AraC metabolites was determined in bone marrow samples from patients with acute myeloid leukaemia (AML), healthy volunteers and specimens of cellsorted CD34+ haemopoietic stem cells. Highly significant differences were found for phosphorylated AraC metabolites (AraCMP, -CDP, -CTP, AraUMP) between AML and normal mononuclear bone marrow (ng/107 cells respectively 1.30 v 2.66; 2.65 v 7.50; 33.68 v 99.0; 1.18 v 5.70). The highest differences were found for formation of AraCDP-choline (3.75 v 12.86) which might be relevant for the high efficacy of high-dose AraC regimens. In contrast, no differences were found in the deamination product AraU (2.01 v 2.91). Only minute amounts of phosphorylated AraU derivatives were detected, providing an explanation for the lacking contribution of AraU to cytosine arabinoside cytotoxicity. Results in normal CD34+ haemopoietic stem cells did not differ significantly from normal bone marrow mononuclear cells and therefore justify their use as a surrogate in determining AraC-induced haematotoxicity. These data suggest a metabolic basis for the relative selectivity of AraC cytotoxicity for AML blasts and provide a means to determine the role of different metabolites and their related mechanism of action for overall AraC cytotoxicity.

Circumvention of ara-C resistance by aphidicolin in blast cells from patients with AML

“…As only a small percentage of cells in the cord blood samples were stem cells, our results could be misleading. Yet, no difference in the metabolism of ara-C has been found between CD34 + stem cells isolated by FACS and normal bone marrow mononuclear cells (Braess et al, 1999). Because mononuclear cells isolated from cord blood closely resemble the morphology of those from normal bone marrow they can provide a good surrogate for investigations of haematological toxicity (Ghielmini et al, 1997), particularly as they are far easier to obtain.…”

Nonproliferating CML CD34+ progenitors are resistant to apoptosis induced by a wide range of proapoptotic stimuli

“…This may be attributed to imatinib-induced inhibition of proliferation since cytotoxicity of Ara-C may be affected by DNA repair capacity, proliferation rate, and cell cycle status. 39 Other studies 28,37 have reported that the combination of Ara-C and imatinib substantially decreased CML colony formation compared with imatinib or Ara-C alone but did not directly evaluate CD34 þ cell apoptosis. Inhibition of CFC growth may reflect effects on cell proliferation and differentiation in addition to apoptosis.…”

An Overview of the Vaccinia Virus Infectome: a Survey of the Proteins of the Poxvirus-Infected Cell

“…The inhibitor used was AraC, following its widespread use in vaccinia virus molecular biology. AraC and its metabolites have been documented to inhibit DNA and RNA polymerases, ribonucleotide reductase, and DNA damage repair mechanisms (6) and to damage RNA and DNA into which it or its metabolites are incorporated (33). It may also influence some signal transduction pathways (53).…”