tiazofurin and Leukemia--Promyelocytic--Acute

Resveratrol (RV), a naturally occurring stilbene derivative, is a potent free radical scavenger causing a number of biochemical and antineoplastic effects. It was shown to induce differentiation and apoptosis in leukemia cells and was also identified as an inhibitor of ribonucleotide reductase (RR), a key enzyme of DNA synthesis. In this study, we report about the biochemical effects of RV in HL-60 human promyelocytic leukemia cells. RV effectively inhibited in situ RR activity. Furthermore, incubation of HL-60 cells with RV significantly decreased intracellular dCTP, dTTP, dATP and dGTP concentrations. In growth inhibition and clonogenic assays, RV acted synergistically with both Ara-C and tiazofurin in HL-60 cells. We conclude that RV could become a viable candidate as one compound in the combination chemotherapy of leukemia and therefore deserves further in vitro and in vivo testing.

Topics: Antimetabolites, Antineoplastic; Antineoplastic Agents, Phytogenic; Apoptosis; Cell Proliferation; Cytarabine; Drug Screening Assays, Antitumor; Drug Synergism; Free Radical Scavengers; Free Radicals; HL-60 Cells; Humans; Leukemia, Promyelocytic, Acute; Resveratrol; Ribavirin; Stilbenes

Resveratrol, a naturally occurring stilbene derivative, is a potent free-radical scavenger causing a number of biochemical and antineoplastic effects. It was shown to induce differentiation and apoptosis in leukemia cells. Resveratrol was also identified as an inhibitor of ribonucleotide reductase (RR), a key enzyme of DNA synthesis. We report about the biochemical effects of resveratrol on the concentration of deoxyribonucleoside triphosphates (dNTPs), the products of RR, and on the incorporation of 14C-labeled cytidine into the DNA of HL-60 human promyelocytic leukemia cells.. Incorporation of 14C-labeled cytidine into the DNA of resveratrol-treated HL-60 cells was measured. Concentration of dNTPs was determined by a HPLC method. Cytotoxic effects of resveratrol, Ara-C, and tiazofurin were analyzed using growth inhibition and clonogenic assays. Induction of apoptosis was studied using a Hoechst/propidium iodide staining method.. We found that resveratrol effectively inhibited incorporation of 14C-labeled cytidine into DNA. Furthermore, incubation of HL-60 cells with resveratrol significantly decreased intracellular dCTP, dTTP, dATP, and dGTP concentrations. Based on these results, we investigated the combination effects of resveratrol with Ara-C or tiazofurin, both antimetabolites, which are known to exhibit synergistic effects in combination with other inhibitors of RR. In growth inhibition, apoptosis, and clonogenic assays, resveratrol acted synergistically with both Ara-C and tiazofurin in HL-60 cells.. We conclude that resveratrol could become a viable candidate as one compound in the combination chemotherapy of leukemia and therefore deserves further testing.

Topics: Antineoplastic Agents; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Cell Differentiation; Cytarabine; Deoxyribonucleotides; DNA; Drug Synergism; HL-60 Cells; Humans; Leukemia, Promyelocytic, Acute; Resveratrol; Ribavirin; Ribonucleotide Reductases; Stilbenes

Increased ribonucleotide reductase (RR) activity has been linked with malignant transformation and tumor cell growth. Therefore, this enzyme is considered to be an excellent target for cancer chemotherapy. We have examined the effects of a newly patented RR inhibitor, trimidox (3,4,5-trihydroxybenzohydroxamidoxime). Trimidox inhibited the growth of human promyelocytic leukemia HL-60 cells with an IC50 of 35 mumol/L. Incubation of HL-60 cells with 50 mumol/L trimidox for 24 hours decreased deoxyguanosine triphosphate (dGTP) and deoxycytidine triphosphate (dCTP) pools to 24% and 39% of control values, respectively. Incubation of HL-60 cells with 20 to 80 mumol/L trimidox even up to a period of 4 days did not alter the distribution of cells in different phases of cell cycle. Sequential incubation of HL-60 cells with trimidox (25 mumol/L) for 24 hours and then with 10 mumol/L tiazofurin (an inhibitor of inosine monophosphate dehydrogenase) for 4 days produced synergistic growth inhibitory activity, and the cell number decreased to 16% of untreated controls. When differentiation-linked cell surface marker expressions were determined in cells treated with trimidox and tiazofurin, a significantly increased fluorescence intensity was observed for the CD 11b (2.9-fold). CD 33 (1.9-fold), and HLA-D cell surface antigens. Expression of the transferrin receptor (CD71) increased 7.3-fold in cells treated with both agents, compared with untreated controls. Our results suggest that trimidox in combination with tiazofurin might be useful in the treatment of leukemia.

Topics: Benzamidines; Cell Differentiation; Cell Division; Deoxyribonucleotides; DNA Replication; DNA, Neoplasm; Drug Synergism; Humans; IMP Dehydrogenase; Leukemia, Promyelocytic, Acute; Neoplasm Proteins; Ribavirin; Ribonucleotide Reductases; Ribonucleotides; Tumor Cells, Cultured

Cytokines, such as granulocyte macrophage colony stimulating factor (GM-CSF) or interleukin-3 (IL-3) recruit quiescent cells into the cell cycle and sensitize these cells towards cell cycle specific chemotherapeutic agents. We examined the in vitro effects of GM-CSF on HL-60 cells and tested its modulatory influence on biochemical and cytotoxic effects seen with tiazofurin, a potent and specific inhibitor of IMP dehydrogenase. Incubation of HL-60 cells with 500 U/ml GM-CSF for 4 d enhanced cell proliferation, which was accompanied by a significant increase in IMP dehydrogenase activity (from 2.22 in control cells to 3.70 nmol/mg/h in cells pretreated with GM-CSF). When HL-60 cells were incubated with 100 microM tiazofurin for 2 h, intracellular GTP decreased to 46% of untreated control cells. In HL-60 cells pretreated with GM-CSF, GTP pools decreased to 38% of control after incubation with tiazofurin which is 69% of the predicted value for additive effect. The MTT chemosensitivity assay yielded significantly decreased IC50 values for tiazofurin in HL-60 cells, preincubated with GM-CSF (IC50 decreased from 13 microM to 10 microM). Therefore our results suggest that combination therapy with GM-CSF and tiazofurin may be beneficial for the treatment of refractory leukaemia patients.

Topics: Antineoplastic Agents; Cell Division; Dose-Response Relationship, Drug; Drug Synergism; Granulocyte-Macrophage Colony-Stimulating Factor; Guanosine Triphosphate; Humans; IMP Dehydrogenase; In Vitro Techniques; Leukemia, Promyelocytic, Acute; Ribavirin; Tumor Cells, Cultured

Tiazofurin (TR), an inhibitor of IMP dehydrogenase, causes remissions and induced differentiation in human leukemia through lowering the concentrations of GTP and dGTP. A deoxycytidine analog, difluorodeoxycytidine (DFDC), is an anti-tumor agent phosphorylated by deoxycytidine kinase, resulting in decreased concentration of dCTP, leading to inhibition of DNA synthesis. In HL-60 cells DFDC induced differentiation and inhibited proliferation in a dose-dependent manner (IC50 = 4 nM); TR provided synergism with DFDC. DFDC inhibited proliferation in OVCAR-5 human ovarian carcinoma cells (IC50 = 25 nM) and colony formation in PANC-1 human pancreatic carcinoma cells (IC50 = 2 nM) and rat hepatoma 3924A cells (IC50 = 22 nM). TR and DFDC are synergistically cytotoxic in hepatoma cells and additive in PANC-1 cells. The two drugs together should be helpful in treating leukemias and solid tumors in humans.

Topics: Animals; Antimetabolites, Antineoplastic; Cell Differentiation; Cell Line; Cell Survival; Deoxycytidine; Dose-Response Relationship, Drug; Drug Synergism; Female; Gemcitabine; Humans; IMP Dehydrogenase; Kinetics; Leukemia, Promyelocytic, Acute; Liver Neoplasms, Experimental; Models, Biological; Ovarian Neoplasms; Pancreatic Neoplasms; Rats; Ribavirin; Tetradecanoylphorbol Acetate; Tretinoin; Tumor Stem Cell Assay

In the regulation of GTP biosynthesis, complex interactions are observed. A major factor is the behavior of the activity of IMPDH, the rate-limiting enzyme of de novo GTP biosynthesis, and the activity of GPRT, the salvage enzyme of guanylate production. The activities of GMP synthase, GMP kinase and nucleoside-diphosphate kinase are also relevant. In neoplastic transformation, the activities and amounts of all these biosynthetic enzymes are elevated as shown by kinetic assays and by immunotitration for IMPDH. In cancer cells, the up-regulation of guanylate biosynthesis is amplified by the concurrent decrease in activities of the catabolic enzymes, nucleotidase, nucleoside phosphorylase, and the rate-limiting purine catabolic enzyme, xanthine oxidase. The up-regulation of the capacity for GTP biosynthesis is also manifested in the stepped-up capacity of the overall pathways of de novo and salvage guanylate production. The linking with neoplasia is also seen in the elevation of the activities of IMPDH and GMP synthase and de novo and salvage pathways as the proliferative program is expressed as cancer cells enter log phase in tissue culture. The activity of GMP reductase showed no linkage with neoplastic or normal cell proliferation; however, in induced differentiation in HL-60 cells the activity increased concurrently with the decline in the activity of IMPDH. This reciprocal regulation of the two enzymes is observed in differentiation induced by retinoic acid, DMSO or TPA in HL-60 cells. In support of enzyme-pattern-targeted chemotherapy, evidence was provided for synergistic chemotherapy with tiazofurin (inhibitor of IMPDH) and hypoxanthine (competitive inhibitor of GPRT and guanine salvage activity) in patients and in tissue culture cell lines. These investigations should contribute to the clarification of the controlling factors of GMP biosynthesis, the role of the various enzymes, the behavior of GMP reductase in mammalian cells and the application of the approaches of enzyme-pattern-targeted chemotherapy in patients.

Topics: Animals; Cell Differentiation; Cell Division; Colonic Neoplasms; Evaluation Studies as Topic; GMP Reductase; Guanosine Monophosphate; Guanosine Triphosphate; Humans; Hypoxanthine; Hypoxanthines; IMP Dehydrogenase; Inosine Monophosphate; Leukemia, Promyelocytic, Acute; Liver Neoplasms, Experimental; NADH, NADPH Oxidoreductases; Ribavirin; Tumor Cells, Cultured

The activity of IMP dehydrogenase (IMP DH), the rate-limiting enzyme of de novo GTP biosynthesis, was shown to be increased in cancer cells. Tiazofurin, an inhibitor of IMP dehydrogenase, proved to be an effective agent in the treatment of refractory granulocytic leukemia. To examine the cell cycle dependent alterations of GTP synthesis and sensitivities to tiazofurin, we measured IMP DH activities and GTP pools, as well as the effects of tiazofurin on cell cycle phase enriched HL-60 cells. We now show that IMP DH activities and GTP concentrations are increased in S-phase enriched fractions of HL-60 cells. Moreover, the depletion of GTP concentrations by tiazofurin is most effective in S-phase enriched HL-60 cells. These results may be utilized in cancer chemotherapy to combine tiazofurin with biologic response modifiers which recruit quiescent leukemic cells into the cell cycle.

Topics: Antimetabolites, Antineoplastic; Cell Cycle; Guanosine Triphosphate; Humans; IMP Dehydrogenase; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Leukemia, Promyelocytic, Acute; Ribavirin; Tumor Cells, Cultured

Among inducers of myeloid differentiation for leukemic cells, tiazofurin is of special interest because its mechanism of action is known; it inhibits inosine monophosphate dehydrogenase and thus decreases the guanine nucleotide pool. Reported here are three aspects of tiazofurin induction of myeloid differentiation in HL60 human acute promyelocytic leukemia cells. First, inductive efficacy was evaluated for analogues ara-tiazofurin, xylo-tiazofurin, and selenazofurin, for dinucleotide anabolites thiazole-4-carboxamide adenine dinucleotide (TAD) and selenazole-4-carboxamide adenine dinucleotide (SAD), and for a phosphodiesterase-resistant TAD analogue, beta-methylene TAD. The results showed that the parent compounds are more effective inducers than the dinucleotide derivatives and that the selenazole analogues are more effective inducers than the thiazole compounds. Second, HL60 cell induction by tiazofurin was shown to be synergistic with that produced by the antiviral agent ribavirin. Finally, tiazofurin was found to induce expression of a phosphatidylinositol-specific phospholipase C-sensitive Fc gamma-receptor III (FcRIII) on HL60 cells, a feature consistent with neutrophilic, but not monocytic, differentiation.

Topics: Cell Differentiation; Cell Line; Flow Cytometry; Humans; Kinetics; Leukemia, Promyelocytic, Acute; Phosphatidylinositol Diacylglycerol-Lyase; Phosphoinositide Phospholipase C; Phosphoric Diester Hydrolases; Ribavirin; Structure-Activity Relationship

Tiazofurin, a potent inhibitor of inosine 5'-phosphate dehydrogenase, depletes guanine nucleotide pools and induces granulocytic maturation of HL-60 leukemia cells. These effects are reversed when cells exposed to this agent for 24 h are washed and placed in tiazofurin-free medium. HL-60 cells treated with tiazofurin for a 24 h period, retain a precommitment memory that lessens the time interval necessary for cells to express the mature phenotype upon re-exposure. That protein synthesis was required for maintaining the expression of memory was demonstrated by the finding that memory was blocked when primed cells were exposed to cycloheximide during the intervening inducer-free interval, but not during the priming or subsequent drug exposure periods. The findings have significance with respect to the sequence of events required for commitment to a differentiation pathway.

Topics: Antimetabolites, Antineoplastic; Cell Cycle; Cell Differentiation; Cell Line; Cycloheximide; DNA Replication; DNA, Neoplasm; Guanosine; Humans; Kinetics; Leukemia, Promyelocytic, Acute; Ribavirin; Ribonucleotides; Thymidine; Tretinoin

Tiazofurin and retinoic acid synergistically induced differentiation and inhibited colony formation in HL-60 human promyelocytic leukemia cells in cell culture. The synergism was the result of different mechanisms of action, since the effect of tiazofurin, unlike that of retinoic acid, was prevented by addition of guanosine. Since it has been shown that tiazofurin down-regulated the expression of c-Ki-ras oncogene, and retinoic acid that of the myc oncogene, the joint impact of these drugs is of clinical interest particularly in end-stage leukemia where the therapeutic usefulness of tiazofurin has recently been demonstrated.

Topics: Antineoplastic Agents; Cell Differentiation; Cell Division; Cell Transformation, Neoplastic; Clone Cells; Dose-Response Relationship, Drug; Drug Synergism; Guanosine; Humans; IMP Dehydrogenase; Leukemia, Promyelocytic, Acute; Molecular Structure; Phenotype; Ribavirin; Ribonucleosides; Time Factors; Tretinoin; Tumor Cells, Cultured

The impact of tiazofurin on inhibition of IMP dehydrogenase was discussed at the clinical and molecular levels. 1. Evidence was provided for the role of IMP dehydrogenase and guanylates in the expression of the neoplastic program in cancer cells with particular relevance to human leukemic cells. 2. The argument for expecting an impact of tiazofurin in human myelocytic cells was provided. 3. Similarity of the kinetics of human leukemic cell IMP dehydrogenase to the rat hepatoma enzyme was documented. 4. New evidence was provided for the role of salvage in chemotherapy and the function of hypoxanthine in inhibiting guanine salvage. 5. The action of tiazofurin and retinoic acid was reported in HL-60 leukemic cells. 6. The effect of tiazofurin and retinoic acid on proliferation and cytotoxicity was outlined for hepatoma 3924A cells. 7. The effect of guanine on induced differentiation by tiazofurin and retinoic acid was examined. 8. Biochemical basis was provided for the lack of development of resistance in patients treated with tiazofurin. 9. Presumptive evidence was provided that tiazofurin treatment induced differentiation of leukemic cells in the patients. 10. The molecular biology of tiazofurin-induced differentiation in K-562 cells was reviewed with the possible relevance to clinical treatment that tiazofurin might also act through down-regulation of ras oncogene.

Topics: Animals; Antimetabolites, Antineoplastic; Cell Differentiation; Cell Division; Cell Line; Guanosine; Humans; IMP Dehydrogenase; Ketone Oxidoreductases; Leukemia, Promyelocytic, Acute; Liver Neoplasms, Experimental; Rats; Ribavirin; Ribonucleosides; Tretinoin; Tumor Cells, Cultured

Tiazofurin is an effective inducer of the maturation of HL-60 promyelocytic leukemia cells, as monitored by increased phagocytic ability and the capacity to reduce nitroblue tetrazolium (NBT). The antimetabolite acts as a potent inhibitor of IMP dehydrogenase, which results in a profound depression in the cellular levels of guanine nucleotides. Flow cytometric analysis of DNA histograms indicated that the commitment of HL-60 cells to differentiate when exposed to tiazofurin was preceded by a transient delay in the G1 phase of the cell cycle. HL-60 leukemia cells enriched in the various phases of the cell cycle by centrifugal elutriation were utilized to further characterize the relationship between the phase of the cell cycle and the commitment to enter a pathway of differentiation. Fractions composed mainly of G1 cells demonstrated an increased capacity to mature when exposed to tiazofurin, whereas fractions containing cells from the S and G2 + M phases of the cell cycle had a lower ability to enter a differentiation pathway. The findings suggest that the commitment of HL-60 cells to mature when exposed to tiazofurin is mediated during the G1 phase of the cell cycle.

Topics: Cell Cycle; Cell Differentiation; Cell Separation; Centrifugation; Humans; Leukemia, Promyelocytic, Acute; Ribavirin; Ribonucleosides; Tumor Cells, Cultured

The synthetic nucleoside analogue, tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide, NSC 286193) is an inhibitor of the enzyme inosine monophosphate (IMP) dehydrogenase and depletes guanine nucleotide pools. In the present study, we have monitored the effects of tiazofurin on human HL-60 promyelocytic cell differentiation and protooncogene expression. Tiazofurin (10 microM) induced a more differentiated HL-60 cell phenotype as determined by histochemical staining and decreased myeloperoxidase gene expression. This induction of differentiation was associated with a loss of proliferative capacity and decreases in clonogenic survival. The results also demonstrate that tiazofurin induces a down-regulation of c-myc mRNA levels. In contrast, there was no detectable change in the level of 3.8-kilobase c-myb transcripts. Furthermore, treatment of HL-60 cells with tiazofurin resulted in the appearance of an additional c-myb mRNA with an apparent size of 3.3 kilobases. The addition of guanosine to tiazofurin-treated HL-60 cells prevented the down-regulation of c-myc transcripts and also inhibited induction of the 3.3-kilobase c-myb transcript. Moreover, this additional transcript was not detected during induction of HL-60 cells by dimethyl sulfoxide, tumor necrosis factor, and retinal, but was induced by another IMP dehydrogenase inhibitor, mycophenolic acid. These results suggest a role for guanosine ribonucleotides in the regulation of c-myc and c-myb gene expression during HL-60 cell differentiation. The results also suggest that changes in c-myb expression can be dissociated from that of c-myc and induction of myeloid differentiation.

Topics: Cell Differentiation; Humans; IMP Dehydrogenase; Ketone Oxidoreductases; Leukemia, Promyelocytic, Acute; Proto-Oncogenes; Ribavirin; Ribonucleosides; Transcription, Genetic; Tumor Cells, Cultured