Enhancement of the differentiation-inducing properties of 6-thioguanine by hypoxanthine and its nucleosides in HL-60 promyelocytic leukemia cells (original) (raw)
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Journal of Cellular Physiology, 1984
HL-60 human acute promyelocytic leukemia cells that lack hypoxanthineguanine phosphoribosyltransferase (HGPRT) activity have been developed by mutagenization and selection. These cells exhibited markedly decreased sensitivity to the cytotoxic action of 6-thioguanine (TG) and, in contrast to parental HL-60 cells, had the capacity to undergo terminal granulocytic differentiation after treatment with this purine antimetabolite. Analysis of extracellular and intracellular metabolites of TG revealed negligible metabolism of TG in these HGPRT-HL-60 cells. These findings are consistent with the concept that inhibition of cellular replication requires generation of analog nucleotide and suggest that TG itself is capable of initiation of differentiation. 6-Thioguanosine (TGuo) had limited activity, while P-2'-deoxythioguanosine (dTGuo) was inactive, as an inducer of maturation of HGPRT-HL-60 cells. These cells converted relatively large amounts of the nucleosides to the free base TG; the simultaneous exposure of cells to 8-aminoguanosine (AGuo), an inhibitor of purine nucleoside phosphorylase activity, decreased the degradation of TGuo and dTGuo to TG and promoted the intracellular accumulation of TG nucleotides, presumably through the action of nucleoside kinase activities. In a double mutant deficient in both HGPRT and deoxycytidine kinase (DCK) activities, dTCuo was devoid of cytotoxicity and was a n effective inducer of maturation. The potency of dTCuo as an inducer in this system was not significantly affected by the presence of AGuo. These results suggested that dTGuo itself was also an active initiator of maturation. Thus, induction of differentiation appeared to be due to the free base, TG, as well as its deoxynucleoside form, dTGuo, whereas t h e formation of TG nucleotides appeared to antagonize maturation and produce cytotoxicity.
Modulation of the cytotoxic mechanism of 6-thioguanine by 4-amino-5-imidazolecarboxamide
Cancer Chemotherapy and Pharmacology, 1990
Previous evidence has indicated that either purine starvation or incorporation into DNA may be the dominant biochemical effect of the antileukemic agent 6-thioguanine (TG), depending on exposure conditions. Furthermore, it has been suggested that the paradoxical decrease in TG-induced cytotoxicity at high drug concentrations may be due to an antagonistic interaction between these two mechanisms, in which purine starvation inhibits DNA synthesis and, therefore, incorporation of TG into DNA. In this report we test the hypothesis that by concurrent treatment of L1210 cells with TG and the purine precursor 4-amino-5-imidazolecarboxamide (AIC) it is possible to alleviate DNA synthesis inhibition caused by high concentrations of TG, thus enhancing TG incorporation into DNA and TG-induced cell kill. Both the cytotoxic and cytokinetic results presented support this hypothesis. However, gross incorporation of TG into DNA was not increased by AIC under conditions in which a significant enhancement of cytotoxicity (i.e., 1 log) was observed. These findings suggest that the potentiating effect of AIC may be most prominent on the subpopulation of cells that are resistant to treatment with TG alone, and they demonstrate that the cytotoxic effects of TG treatments are more accurately reflected by observing specific cytokinetic changes (delayed late S/G2 arrest) than by measuring the average extent of TG incorporation into DNA within a given population. Finally, we propose that it may be possible to select conditions for administration of TG that favor one or the other cytotoxic mechanism, depending on whether the clinical objective is induction of remission (where rapid cell lysis due to purine starvation would be desired) or eradication of subclinical disease during remission (where proliferation-dependent cytotoxicity due to DNA incorporation should be more effective).
International Journal of Cancer, 1999
Cell populations resistant to high doses (30 M) of 6-thioguanine (6-TG, 6-TG r cells) were selected from a human colon carcinoma cell line, LoVo. This cell line, which lacks hMSH2, a component of the human mismatch binding heterodimer hMutS␣, is resistant to low doses of 6-TG. The level of activity of hypoxanthine-guanine phosphoribosyltransferase, the enzyme responsible for the phosphoribosylation of the thiopurine, was comparable to that expressed in the parental cells. No significant difference was found in the levels of enzyme activities involved in the conversion of 6-TG or its derivatives into non-toxic compounds. In contrast, a significant difference was found in the uptake kinetics of 6-TG in the 2 cell types. Net uptake of 6-TG ceased after 100-sec incubation in the 6-TG r cells, while it appeared to continue throughout the 10-min incubation in the wild-type cells. As a consequence, after 10-min incubation, the total amount of 6-TG taken up by the parental LoVo cells was approximately 3 times higher than that present in the 6-TG r cells. Int.
The expression of deoxyguanosine toxicity in T lymphocytes at different stages of maturation
The Journal of Immunology
Different human T cell populations were assayed for susceptibility of DNA synthesis to inhibition by deoxyguanosine. T lymphocytes from the thymus were most sensitive to inhibition of proliferation by deoxyguanosine (90% inhibition at 10 microM deoxyguanosine). This exquisite sensitivity of thymocytes appeared related to an enhanced ability of these cells for uptake and phosphorylation of deoxyguanosine to deoxyGTP and by their reduced ability to degrade accumulated deoxyGTP. Compared to more mature T lymphocytes and B cells, thymocytes contained the highest level of the salvage enzyme deoxynucleoside kinase and the lowest level of the nucleotide degrading enzyme, 5'-nucleotidase. The present study suggests that the levels of these 2 enzymes can serve as differentiation markers, identifying T cells at various stages of maturation, and that the loss of sensitivity to deoxyguanosine toxicity may be a stepwise process. Further, a deficiency in purine nucleoside phosphorylase may pr...
The Journal of Immunology
The effect of deoxyguanosine on mitogen- and antigen-induced proliferation of peripheral blood lymphocytes from healthy donors was studied. Deoxyguanosine was found to inhibit the proliferative response to mitogens and antigens. Concentrations of deoxyguanosine causing 50% inhibition of the proliferation proved to be dependent on the activity of catabolic enzymes, such as purine nucleoside phosphorylase (PNP), in sera used in the culture media. The inhibitory effect of deoxyguanosine on phytohemagglutinin (PHA)-induced cell proliferation was prevented by deoxycytidine as well as by hypoxanthine. These findings were analyzed further by determination of intracellular (deoxy)-nucleotide levels. Stimulation of lymphocytes by PHA in the presence of deoxyguanosine leads to intracellular accumulation of dGTP. The presence of hypoxanthine in addition to deoxyguanosine abolished the inhibitory effect but did not prevent dGTP accumulation. On the other hand, the addition of deoxycytidine in c...
Effects of uridine on the growth and differentiation of HL-60 leukemia cells
Leukemia Research, 1991
HL-60 leukemia cells, induced to differentiate, activate a Na÷-dependent nucleoside transport system, concomitant with a reduction in the nitrobenzylthioinosine (NBMPR)-sensitive facilitated transport of nucleosides. The consequence of these changes lead to the formation of intracellular pools of uridine. To examine the possible role of accumulated uridine in the commitment of HL-60 leukemia cells to undergo maturation, the effects of uridine on the growth and differentiation of HL-60 cells were monitored. Uridine at millimolar levels caused a concentration-dependent inhibition of cellular growth, resulting in the accumulation of cells in the G2/M phases of the cell cycle, phenomena that preceded the formation of differentiated cells. These effects of uridine were reduced by 10 p,M NBMPR, an inhibitor of the facilitated transport of nucleosides. The effects of 24 mM uridine on growth and differentiation of HL-60 cells were also prevented by 5 mM inosine, and partially prevented by either 2 mM hypoxanthine or 20 p.M adenosine. Pretreatment of HL-60 cells with 24 mM uridine for 6 days, followed by a 2 h exposure to TPA, resulted in the rapid attachment of cells to the tissue culture dish, and the extension of long processes. Although the concentrations of uridine required for the above effects are greater than those achieved during differentiation, these observations suggest that uridine may play a role in regulating the maturation process.
Leukemia Research, 1990
Co-incubation of human leukemia cell lines with naturally occurring nucleobases (hypoxanthine or adenine) significantly prevented the cytotoxic activity of 6-thiopurines. Extracellular hypoxanthine decreased the transport of 6-mercaptopurine into cells, but adenine had no significant effect. However, intracellular thioinosine monophosphate accumulation in the presence of 10 ~tM, 6mercaptopurine was reduced to below 1% or 10% of that of the controls when 50 ~tM hypoxanthine or adenine was added, respectively. Finally, in adenine phosphoribosyl transferase deficient mutants, adenine provided no protective effect against 6-thiopurines, whereas hypoxanthine retained its modulating activity. These data suggest that the nucleobases compete with 6-thiopurines for the ribose-phosphate donor, 5'-phosphoribosyl-l-pyrophosphate, thus preventing the formation of active metabolites Of 6-thiopurines.
Differentiation of neuroblastoma cells induced in culture by 6-thioguanine
International Journal of Cancer, 1973
In addition to cell death, 6-thioguanine ( T C ) and 6-mercaptopurine induced neurite formation in mouse neuroblastoma cell culture, whereas 2-aminopurine had no effect on growth or morphology. 6-TC was much more potent in causing morphological differentiation than any other agents used in this study. It increased the levels of catecholo-methyltransferase and choline acetyltransferase, but had no significant effect on the tyrosine hydroxylase ( T H ) activity. 5-bromodeoxyuridine increased the levels of all three enzymes. 6-TC produced cell death with very little neurite formation in human neuroblastoma cell culture.