Leukemic cells nucleotides

Giverhaug T, Loennechen T, Aarbakke J. Increased concentrations of methylated 6-mercaptopurine metabolites and 6-thioguanine nucleotides in human leukemic cells in vitro by methotrexate. Biochem Pharmacol 1998 55 1641-1646. 

SYNTHESIS OF PURINE NUCLEOTIDES IN HUMAN AND LEUKEMIC CELLS. INTERACTION OF 6-MERCAPTOPURINE AND ALLOPURINOL.1)... 

In a similar way the purine antimetabolite 6-mercapto-purine (6-MP)/ after conversion to the monophosphoribo-tide, acts as an inhibitor of this enzyme (9.10). There have been described other sites of action of 6-MP (4-7) which are marked by arrows in figure 1. We have previously demonstrated the inhibition of the enzymic formate activation (tetrahydrofolate formylase) in leukemic cells by 6-MP (12). inspite of a rather high inhibitory concentration of 6-MP between 10 and 10 M, this inhibition has some practical clinical implications for the treatment of acute leukemia/ as it is detected in sensitive leukemic cells only. In accordance with reports of several authors (8,9/10) we have postulated/ that 6-MP has to be converted into 6-thioinosinic acid for exerting its inhibitory effect on the de novo synthesis of purine-nucleotides. On the other hand DAVIDSON and WINTER have shown that both 6-MP sensitive and resistant cells con-... 

SYNTHESIS OF PURINE NUCLEOTIDES IN HUMAN AND LEUKEMIC CELLS... 

The tetrahydrofolate formylase was found in normal and leukemic leukocytes, the highest activities in immature blast cells of acute Leukemia (table 1). By determination of the 14C-formate incorporation a measurable netto de novo synthesis of purine nucleotides was only detected in immature leukemic cells. 

Activities of the formate activating enzyme and incorporation rates of 14C-formate into purine nucleotides in cell-free extracts of normal leukocytes and bone marrow cells and of leukemic cells. 

Interferon induction in normal and leukemic lymphocyte cultures with tilorone has been observed50. The interferon response observed in normal lymphocyte cultures appeared to be correlated with the toxic effect of tilorone. The effect observed in leukemic cultures required higher concentrations of tilorone, but, similarly, appeared to be related to cell viability. Tilorone has been reported to stimulate production of interferon by itself in mouse embryo fibroblasts and, in combination with poly rl poly rC/DEAE-dextran in mouse L929 cells51. Human foreskin fibroblasts were not stimulated. The degree of synergism between tilorone and the nucleotide-dextran complex was proportional to the concentrations of tilorone and poly rl/poly rC and was influenced by the times of addition of the compounds relative to each other. 

The carbon atoms 2 and 8 in the purine ring of inosinic acid are derived from C1 units. The latter are transferred as activated formate to GAR and AICR as specific formate acceptors. Therefore we have studied the tetra-hydrofolate dependent activation of formate in relation to the netto de novo synthesis of purine nucleotides in cell-free extracts of normal and leukemic leukocytes. In addition, the conversion of exogenous purines to corresponding monophosphoribonucleotides by the specific purine-phosphoribosyItransferases was determined. The aim of these investigations was to study the effect of 6-MP on the formate activating system, which is important for the de novo synthesis of purine nucleotides, on the utilization of preformed purine bases and, in addition, the interaction of allopurinol with 6-MP,... 

---