Ornithine decarboxylase: essential in proliferation but not differentiation of human promyelocytic leukemia cells

Pharmacologic approaches to amino acid depletion for cancer therapy

Cancer cells undergo metabolic reprogramming to support increased demands in bioenergetics and biosynthesis and to maintain reactive oxygen species at optimum levels. As metabolic alterations are broadly observed across many cancer types, metabolic reprogramming is considered a hallmark of cancer. A metabolic alteration commonly seen in cancer cells is an increased demand for certain amino acids. Amino acids are involved in a wide range of cellular functions, including proliferation, redox balance, bioenergetic and biosynthesis support, and homeostatic functions. Thus, targeting amino acid dependency in cancer is an attractive strategy for a number of cancers. In particular, pharmacologically mediated amino acid depletion has been evaluated as a cancer treatment option for several cancers. Amino acids that have been investigated for the feasibility of drug-induced depletion in preclinical and clinical studies for cancer treatment include arginine, asparagine, cysteine, glutamine, lysine, and methionine. In this review, we will summarize the status of current research on pharmacologically mediated amino acid depletion as a strategy for cancer treatment and potential chemotherapeutic combinations that synergize with amino acid depletion to further inhibit tumor growth and progression.

Thymoquinone and Difluoromethylornithine (DFMO) Synergistically Induce Apoptosis of Human Acute T Lymphoblastic Leukemia Jurkat Cells Through the Modulation of Epigenetic Pathways

Thymoquinone (TQ), a natural anticancer agent exerts cytotoxic effects on several tumors by targeting multiple pathways, including apoptosis. Difluoromethylornithine (DFMO), an irreversible inhibitor of the ornithine decarboxylase (ODC) enzyme, has shown promising inhibitory activities in many cancers including leukemia by decreasing the biosynthesis of the intracellular polyamines. The present study aimed to investigate the combinatorial cytotoxic effects of TQ and DFMO on human acute T lymphoblastic leukemia Jurkat cells and to determine the underlying mechanisms. Here, we show that the combination of DFMO and TQ significantly reduced cell viability and resulted in significant synergistic effects on apoptosis when compared to either DFMO or TQ alone. RNA-sequencing showed that many key epigenetic players including Ubiquitin-like containing PHD and Ring finger 1 (UHRF1) and its 2 partners DNA methyltransferase 1 (DNMT1) and histone deacetylase 1 (HDAC1) were down-regulated in DFMO-treated Jurkat cells. The combination of DFMO and TQ dramatically decreased the expression of UHRF1, DNMT1 and HDAC1 genes compared to either DFMO or TQ alone. UHRF1 knockdown led to a decrease in Jurkat cell viability. In conclusion, these results suggest that the combination of DFMO and TQ could be a promising new strategy for the treatment of human acute T lymphoblastic leukemia by targeting the epigenetic code.

Methionine metabolism in health and cancer: a nexus of diet and precision medicine

Methionine uptake and metabolism is involved in a host of cellular functions including methylation reactions, redox maintenance, polyamine synthesis and coupling to folate metabolism, thus coordinating nucleotide and redox status. Each of these functions has been shown in many contexts to be relevant for cancer pathogenesis. Intriguingly, the levels of methionine obtained from the diet can have a large effect on cellular methionine metabolism. This establishes a link between nutrition and tumour cell metabolism that may allow for tumour-specific metabolic vulnerabilities that can be influenced by diet. Recently, a number of studies have begun to investigate the molecular and cellular mechanisms that underlie the interaction between nutrition, methionine metabolism and effects on health and cancer.

The Association between Salt and Potential Mediators of the Gastric Precancerous Process

Background: The process by which salt affects the gastric precancerous process has not been adequately studied in humans. Methods: We investigated the effects of salt on gastric inflammation, epithelial damage, the density of Helicobacter pylori infection, and gastric epithelial cell proliferation, all of which may be mediators between salt and gastric precancerous/cancerous lesions. These potential mediators were measured using gastric biopsies as: (a) the density of polymorphonuclear and mononuclear cells (gastric inflammation), (b) mucus depletion (gastric epithelial damage), and (c) the severity of H. pylori infection. Salt intake was measured with spot urine samples (using urinary sodium/creatinine ratios), self-reported frequency of adding salt to food, and as total added salt. Results: The average sodium/creatinine ratio (at baseline and post-treatment at five months) was associated with increased epithelial damage over the 12-year follow-up period among those with a greater severity of chronic inflammation and among those with continued H. pylori infection after treatment at five months. This association was stronger when both severe gastric inflammation and H. pylori infection were present at five months (ß: 1.112, 95% CI: 0.377, 1.848). Conclusion: In humans, salt was associated with an increase in epithelial damage in stomachs with more severe previous H. pylori-induced chronic inflammation.

Targeting polyamine metabolism for cancer therapy and prevention

The chemically simple, biologically complex eukaryotic polyamines, spermidine and spermine, are positively charged alkylamines involved in many crucial cellular processes. Along with their diamine precursor putrescine, their normally high intracellular concentrations require fine attenuation by multiple regulatory mechanisms to keep these essential molecules within strict physiologic ranges. Since the metabolism of and requirement for polyamines are frequently dysregulated in neoplastic disease, the metabolic pathway and functions of polyamines provide rational drug targets; however, these targets have been difficult to exploit for chemotherapy. It is the goal of this article to review the latest findings in the field that demonstrate the potential utility of targeting the metabolism and function of polyamines as strategies for both chemotherapy and, possibly more importantly, chemoprevention.

Arginine decarboxylase and polyamines required for embryogenesis in the wild carrot

Embryogenic cultures of Daucus carota treated with 1 millimolar alpha-difluoromethylarginine, a specific inhibitor of arginine decarboxylase, exhibited nearly a 50 percent reduction in embryo formation compared with controls. Putrescine and spermidine concentrations in the treated cells were greatly reduced. Addition of putrescine, spermidine, or spermine to the culture medium restored embryogenesis in the treated cultures. Embryogenesis was not significantly affected by alpha-difluoromethylornithine, an inhibitor of ornithine decarboxylase. These results suggest that polyamines have a major function in plant embryo development and that the wild carrot synthesizes polyamines through the biosynthetic pathway involving arginine decarboxylase rather than ornithine decarboxylase.

Ornithine decarboxylase interferes with macrophage-like differentiation and matrix metalloproteinase-9 expression by tumor necrosis factor alpha via NF-kappaB

Ornithine decarboxylase (ODC), a tumor promoter, provokes cell proliferation, and inhibits cell death; but the mechanism involved in cell differentiation remains unknown. Herein, we examine whether it functions during macrophage-like differentiation. Previous studies reveal that ODC, a rate-limiting enzyme of polyamine biosynthesis, and polyamines are involved in restraining immune response in activated macrophage. By using 12-O-tetradecanoylphorbol-13-acetate (TPA)-differentiated human promyelocytic HL-60 and promonocytic U-937 cells, we discover that polyamines block the expression, secretion and activation of MMP-9. Meanwhile conventional expression of ODC represses tumor necrosis factor-alpha (TNF-alpha) expression and nuclear factor-kappaB (NF-kappaB) activation as well as MMP-9 enzyme activity. Following stimulation by TNF-alpha, the secretion of MMP-9 is restored in ODC-overexpressed cells. In addition, the NF-kappaB inhibitors (pyrrolidinedithiocarbamate, BAY-11-7082 and lactacystin) suppress the TPA-induced MMP-9 enzyme activity. Concurrently, both the irreversible inhibitor of ODC, alpha-difluoromethylornithine, and TNF-alpha could not recover MMP-9 activation following NF-kappaB inhibitor treatment in parental cells. Furthermore, ODC could directly inhibit and attenuate NF-kappaB DNA binding and transcriptional activation. Therefore, we suggest that ODC inhibits the TNF-alpha-elevated MMP-9 activation via NF-kappaB as TPA-induced macrophage-like differentiation and this interrupting mechanism may provide a new conceivable resolution why leukemia is poorly differentiated besides atypical growth.

Targeting polyamine metabolism and function in cancer and other hyperproliferative diseases

The polyamines spermidine and spermine and their diamine precursor putrescine are naturally occurring, polycationic alkylamines that are essential for eukaryotic cell growth. The requirement for and the metabolism of polyamines are frequently dysregulated in cancer and other hyperproliferative diseases, thus making polyamine function and metabolism attractive targets for therapeutic intervention. Recent advances in our understanding of polyamine function, metabolic regulation, and differences between normal cells and tumour cells with respect to polyamine biology, have reinforced the interest in this target-rich pathway for drug development.

Induced focal adhesion kinase expression suppresses apoptosis by activating NF-kappaB signaling in intestinal epithelial cells

Focal adhesion kinase (FAK) integrates various extracellular and intracellular signals and is implicated in a variety of biological functions, but its exact role and downstream targeting signals in the regulation of apoptosis in intestinal epithelial cells (IECs) remains unclear. The current study tested the hypothesis that FAK has an antiapoptotic role in the IEC-6 cell line by altering NF-kappaB signaling. Induced FAK expression by stable transfection with the wild-type (WT)-FAK gene increased FAK phosphorylation, which was associated with an increase in NF-kappaB activity. These stable WT-FAK-transfected IECs also exhibited increased resistance to apoptosis when they were exposed to TNF-alpha plus cycloheximide (TNF-alpha/CHX). Specific inhibition of NF-kappaB by the recombinant adenoviral vector containing the IkappaBalpha superrepressor prevented increased resistance to apoptosis in WT-FAK-transfected cells. In contrast, inactivation of FAK by ectopic expression of dominant-negative mutant of FAK (DNM-FAK) inhibited NF-kappaB activity and increased the sensitivity to TNF-alpha/CHX-induced apoptosis. Furthermore, induced expression of endogenous FAK by depletion of cellular polyamines increased NF-kappaB activity and resulted in increased resistance to TNF-alpha/CHX-induced apoptosis, both of which were prevented by overexpression of DNM-FAK. These results indicate that increased expression of FAK suppresses TNF-alpha/CHX-induced apoptosis, at least partially, through the activation of NF-kappaB signaling in IECs.

Induction of polyamine oxidase 1 by Helicobacter pylori causes macrophage apoptosis by hydrogen peroxide release and mitochondrial membrane depolarization

Helicobacter pylori infects the human stomach by escaping the host immune response. One mechanism of bacterial survival and mucosal damage is induction of macrophage apoptosis, which we have reported to be dependent on polyamine synthesis by arginase and ornithine decarboxylase. During metabolic back-conversion, polyamines are oxidized and release H(2)O(2), which can cause apoptosis by mitochondrial membrane depolarization. We hypothesized that this mechanism is induced by H. pylori in macrophages. Polyamine oxidation can occur by acetylation of spermine or spermidine by spermidine/spermine N(1)-acetyltransferase prior to back-conversion by acetylpolyamine oxidase, but recently direct conversion of spermine to spermidine by the human polyamine oxidase h1, also called spermine oxidase, has been demonstrated. H. pylori induced expression and activity of the mouse homologue of this enzyme (polyamine oxidase 1 (PAO1)) by 6 h in parallel with ornithine decarboxylase, consistent with the onset of apoptosis, while spermidine/spermine N(1)-acetyltransferase activity was delayed until 18 h when late stage apoptosis had already peaked. Inhibition of PAO1 by MDL 72527 or by PAO1 small interfering RNA significantly attenuated H. pylori-induced apoptosis. Inhibition of PAO1 also significantly reduced H(2)O(2) generation, mitochondrial membrane depolarization, cytochrome c release, and caspase-3 activation. Overexpression of PAO1 by transient transfection induced macrophage apoptosis. The importance of H(2)O(2) was confirmed by inhibition of apoptosis with catalase. These studies demonstrate a new mechanism for pathogen-induced oxidative stress in macrophages in which activation of PAO1 leads to H(2)O(2) release and apoptosis by a mitochondrial-dependent cell death pathway, contributing to deficiencies in host defense in diseases such as H. pylori infection.

Inhibitory effects of phaseolotoxin on proliferation of leukemia cells HL-60, K-562 and L1210 and pancreatic cells RIN-m5F

Phaseolotoxin (PT) is a non-host specific phytotoxin produced by the plant pathogenic bacterium Pseudomonas syringae (P.s.) pv. phaseolicola. In the present study, the inhibitory effect of PT on the proliferation of leukemia cells was studied. After 4 days of treatment, PT decreased cell growth of leukemia cell lines HL-60, K-562 and L1210 in a dose-dependent manner. In addition, PT also reduced cell growth of the insulinoma pancreatic cell line RIN-m5F. IC50 values were 2.1 +/- 1.0 microM (HL-60), 13.3 +/- 3.7 microM (K-562), 2.5 +/- 0.4 microM (L1210) and 5.5 +/- 0.3 microM (RIN-m5F). Although the exact mechanism by which PT inhibits cell growth in these cells is currently not known, we present first evidence that PT may in part be active via inhibition of ornithine decarboxylase (ODC). Based on our findings, PT presents a lead compound with potential for further development into a new anti-cancer agent.

Helicobacter pylori induces macrophage apoptosis by activation of arginase II

Helicobacter pylori infection induces innate immune responses in macrophages, contributing to mucosal inflammation and damage. Macrophage apoptosis is important in the pathogenesis of mucosal infections but has not been studied with H. pylori. NO derived from inducible NO synthase (iNOS) can activate macrophage apoptosis. Arginase competes with iNOS by converting L-arginine to L-ornithine. Since we reported that H. pylori induces iNOS in macrophages, we now determined whether this bacterium induces arginase and the effect of this activation on apoptosis. NF-kappa B-dependent induction of arginase II, but not arginase I, was observed in RAW 264.7 macrophages cocultured with H. pylori. The time course of apoptosis matched those of both arginase and iNOS activities. Surprisingly, apoptosis was blocked by the arginase inhibitors N(omega)-hydroxy-L-arginine or N(omega)-hydroxy-nor-L-arginine, but not by the iNOS inhibitor N-iminoethyl-L-lysine. These findings were confirmed in peritoneal macrophages from iNOS-deficient mice and were not dependent on bacterial-macrophage contact. Ornithine decarboxylase (ODC), which metabolizes L-ornithine to polyamines, was also induced in H. pylori-stimulated macrophages. Apoptosis was abolished by inhibition of ODC and was restored by the polyamines spermidine and spermine. We also demonstrate that arginase II expression is up-regulated in both murine and human H. pylori gastritis tissues, indicating the likely in vivo relevance of our findings. Therefore, we describe arginase- and ODC-dependent macrophage apoptosis, which implicates polyamines in the pathophysiology of H. pylori infection.

Polyamines, and effects from reducing their synthesis during egg development in the yellow fever mosquito, Aedes aegypti

Development of eggs after a blood meal in the yellow fever mosquito Aedes aegypti involves hormonal changes, synthesis of nucleic acids, activation of the digestive enzyme trypsin, and production of the yolk protein vitellogenin. Polyamines have been implicated in growth processes and were here examined for possible involvement during egg development. The data suggest that polyamines are important for normal vitellogenesis in the mosquito. Polyamine levels and activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase, key enzymes in the polyamine pathway, were determined in the fat body for two days after a blood meal. During the time that the macromolecules required for vitellogenesis were being synthesized, polyamine levels increased as did the activities of their rate-limiting enzymes. Administration of suicide inhibitors of ornithine decarboxylase, alpha-difluoromethylornithine (DFMO) and alpha-monofluoromethyldehydroornithine methylester (MDME), limited increased polyamine levels and disrupted macromolecular syntheses, particularly during the first twenty-four hours after blood feeding. Specific metabolic processes reduced by DFMO included trypsin activity, and production of RNA, DNA and vitellogenin. MDME had differential effects on transcription of some mRNA species made after an oogenic meal. The level of actin mRNA was not affected by inhibiting polyamine synthesis, but the mRNA levels of vitellogenin, trypsin, and the vitelline membrane protein were decreased. Adding polyamines to a meal containing DFMO or MDME partially reversed the effects of these inhibitors. Increases in spermidine and spermine were associated with these reversals.

Structure of mammalian ornithine decarboxylase at 1.6 A resolution: stereochemical implications of PLP-dependent amino acid decarboxylases

BACKGROUND

Pyridoxal-5'-phosphate (PLP) dependent enzymes catalyze a broad range of reactions, resulting in bond cleavage at C alpha, C beta, or C gamma carbons of D and L amino acid substrates. Ornithine decarboxylase (ODC) is a PLP-dependent enzyme that controls a critical step in the biosynthesis of polyamines, small organic polycations whose controlled levels are essential for proper growth. ODC inhibition has applications for the treatment of certain cancers and parasitic ailments such as African sleeping sickness.

RESULTS

The structure of truncated mouse ODC (mODC') was determined by multiple isomorphous replacement methods and refined to 1.6 A resolution. This is the first structure of a Group IV decarboxylase. The monomer contains two domains: an alpha/beta barrel that binds the cofactor, and a second domain consisting mostly of beta structure. Only the dimer is catalytically active, as the active sites are constructed of residues from both monomers. The interactions stabilizing the dimer shed light on its regulation by antizyme. The overall structure and the environment of the cofactor are compared with those of alanine racemase.

CONCLUSIONS

The analysis of the mODC' structure and its comparison with alanine racemase, together with modeling studies of the external aldimine intermediate, provide insight into the stereochemical characteristics of PLP-dependent decarboxylation. The structure comparison reveals stereochemical differences with other PLP-dependent enzymes and the bacterial ODC. These characteristics may be exploited in the design of new inhibitors specific for eukaryotic and bacterial ODCs, and provide the basis for a detailed understanding of the mechanism by which these enzymes regulate reaction specificity.

Modulation of HSP70 and HSP27 gene expression by the differentiation inducer sodium butyrate in U-937 human promonocytic leukemia cells

The treatment of U-937 human promonocytic cells with the differentiation inducer sodium butyrate (0.75 mM) transiently increased heat-shock protein 70 (HSP70) mRNA levels between 3 and 6 h, and heat-shock protein 27 (HSP27) mRNA levels between 12 and 24 h, as indicated by northern blot assays. Gel retardation assays indicated that butyrate also stimulated heat-shock factor (HSF) binding activity between 3 and 6 h, suggesting that the activation of HSP70 gene expression was mediated by the heat-shock factor DNA response element (HSE). In addition, the treatment provoked a biphasic alteration of the c-fos mRNA level, consisting of a slight increase between 0.5 and 3 h followed by a greater increase between 12 and 48 h, while it caused a single increase between 12 and 48 h in c-jun mRNA level. The possible involvement of the heat-shock protein genes in the butyrate-induced differentiation of U-937 cells is discussed.

Polyamine transport in human promyelocytic leukemia cells and polymorphonuclear leukocytes

We examined the kinetics of polyamine uptake by human myeloid cells at different stages of maturity. The Km values of putrescine, spermidine and spermine transport by HL-60 cells were 52, 7.9 and 8.1 microM, respectively. These values decreased to 5.1, 1.7 and 0.77 microM, respectively, in HL-60 cells induced to mature past the promyelocyte stage by DMSO. In human PMNs, the respective Km values were 501, 479 and 381 microM. Transport by HL-60 cells was enhanced when intracellular polyamine levels were reduced with difluoromethylornithine. Thus, HL-60 cell maturation is accompanied by an increase in the affinity of their polyamine transport system. This system is much more efficient than that found in end-stage PMNs, suggesting that it plays a more important role in supporting the metabolic requirements of HL-60 cells. Alternatively, the low affinity of the PMN polyamine transport system could represent an adaptation to the high polyamine concentrations found at infection sites.

Phase I study of combined alpha interferon, alpha difluoromethylornithine (DFMO), and doxorubicin in advanced malignancy

Interferon (IFN) and conventional cytotoxic chemotherapeutic agents have been successfully combined in various studies. Alpha difluoromethylornithine (DFMO) is a novel antitumor agent which is an inhibitor of polyamine metabolism. A phase I study of IFN 24 x 10(6) U/m2/day IM (days 3-7), DFMO 9 gm/m2 p.o. daily (days 1-7), and a variable dose of doxorubicin starting at 20 mg/m2 (day 6), of each 28 day cycle was performed. The aim of the study was to determine the maximally tolerable dose of doxorubicin in this combination. Three patients were treated with doxorubicin at 20 mg/m2 and six patients at 40 mg/m2. The dose limiting toxicities were neutropenia, fatigue and fever. All other toxicities were mild and there was no grade IV toxicity. A doxorubicin dose of 40 mg/m2 produced tolerable toxicity and is recommended for phase II studies. No major antitumor effects were seen.

Sodium butyrate stimulates polyamine biosynthesis in colon cancer cells

Differentiation inducers act through polyamine-dependent and independent pathways. Sodium butyrate (NaB) inhibits proliferation and induces terminal differentiation in human and murine cancer cell lines. An effect of this agent on polyamine biosynthesis has not been demonstrated previously. In the present study, we examined the effects of NaB on polyamine biosynthesis in mouse colon cancer (MC-26) cells. All studies were performed on exponentially growing cells, and ODC and polyamine transport measurements were performed as described previously. NaB inhibited the growth of MC-26 cells in a dose-dependent manner. Cell shape was significantly altered by treatment with NaB (development of dendritic-like processes and flattening and spreading out of cells on culture dishes). NaB stimulated ODC activity in a dose-dependent manner. The activity was elevated by 8 h after treatment, and at 48 h there was a ten-fold increase in activity (compared with control activity). The increase in ODC activity led to an increase in polyamine biosynthesis; putrescine, spermidine, and spermine levels in MC-26 cells were significantly elevated by 24 h after treatment with NaB. Polyamine uptake was similar in control cells and cells treated with NaB alone. Our finding of significant stimulation of polyamine uptake by NaB after inhibition of endogenous synthesis (by an ODC-dependent pathway) in DFMO-treated cells suggests that cellular requirements are increased for polyamines in NaB-treated cells. We conclude that polyamine-dependent processes are important in the mechanism of action of NaB in colon cancer cells.

Role of putrescine in interleukin 1 beta production in human histiocytic lymphoma cell line U937

Treatment with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and incubation with lipopolysaccharide (LPS) induces interleukin 1 beta (IL-1 beta) production in the histiocytic lymphoma cell line U937. Here we investigated the effect of treatment with both TPA and 1 alpha, 25-dihydroxyvitamin D3 (1,25(OH)2D3) on LPS-induced IL-1 beta production in U937 cells. To clarify the mechanism of IL-1 beta production, the possible role of polyamines in this process was examined. Combined treatment with TPA and 1,25(OH)2D3 for 72 h followed by incubation with LPS for 24 h caused synergistic induction of both IL-1 beta release and mRNA expression. On the other hand, TPA increased the numbers of vitamin D3 receptors, which may be one mechanism of this synergistic induction. Ornithine decarboxylase (ODC), a rate-limiting enzyme for polyamine biosynthesis, was also induced by these compounds biphasically: the first peak of ODC activity was observed at 4 h of the incubation with the two compounds and the second peak was at 4 h after the addition of LPS. To find whether these peaks were related to IL-1 beta production, DL-alpha-difluoromethylornithine (DFMO), a specific irreversible inhibitor of ODC, was added together with TPA and 1,25(OH)2D3. DFMO decreased the cellular levels of putrescine and spermidine and suppressed IL-1 beta release and IL-1 beta mRNA expression by 65%. Exogenous putrescine, but not spermidine, abrogated these kinds of inhibition. Similar results were obtained with DFMO and the polyamines during the differentiation of the cells up to the monocyte or macrophage stage. These results thus suggest that changes in either of these intracellular polyamines, especially putrescine, help to regulate the differentiation of U937 cells, resulting in partial control of the regulation of IL-1 beta production.

Terminal differentiation of human erythroleukemia cell line K562 induced by aphidicolin

To analyze the relationship between differentiation and DNA replication, the effect of aphidicolin, a specific inhibitor for DNA polymerase alpha, was measured with respect to erythroid differentiation and activities of DNA polymerases alpha, beta, and gamma. Five micromolar aphidicolin completely blocked the growth of K562 cells and caused 80% of cells to become hemoglobin positive after 5 days exposure. The cessation of K562 cell growth induced by aphidicolin was irreversible, whereas the inhibition of HeLa cell growth was completely reversible. The enzyme activity of DNA polymerase alpha of K562 cells showed a 50-110% increase with aphidicolin treatment as compared to control K562 cells; activities of DNA polymerases beta and gamma were not affected. These features sharply contrasted with the erythroid induction of the same cells by hemin, where cell growth was not suppressed and DNA polymerase alpha was not increased but rather decreased. The enzyme activity of DNA polymerase alpha remained high even after removal of aphidicolin from the culture medium. These results suggest that treatment with aphidicolin might induce an accumulation of protein factors for replication and/or differentiation, causing rapid cell differentiation of cells without cell division.

The induction of vimentin gene expression by sodium butyrate in human promonocytic leukemia U937 cells

The administration of 1 mM sodium butyrate induced the phenotypic differentiation of human promonocytic leukemia U937 cells, as judged by the expression of cD11b and cD11c antigens, two differentiation-specific surface markers. At the same time, butyrate greatly induced the expression at the mRNA level of the vimentin gene. The increase in the level of this RNA started at 6 h of treatment and reached the maximum at Hour 24. Such an increase was caused at least in part by a stimulation in the rate of gene transcription, as suggested by transcription assays in isolated nuclei. Experiments in the presence of cycloheximide suggested that vimentin induction is probably a direct response to the action of butyrate, not mediated by the prior induction of other gene products. Unlike the case of vimentin, the levels of other RNAs, namely beta-actin, ornithine decarboxylase, and c-myc, were not enhanced, but they decreased at different times of treatment with butyrate. Finally, we observed that butyrate induced also the differentiation of HL60 cells, another human myeloid cell type. Nevertheless, the drug failed to stimulate the expression of vimentin in this cell line.

Metabolism and action of amino acid analog anti-cancer agents

The preclinical pharmacology, antitumor activity and toxicity of seven of the more important amino acid analogs, with antineoplastic activity, is discussed in this review. Three of these compounds are antagonists of L-glutamine: acivicin, DON and azaserine; and two are analogs of L-aspartic acid: PALA and L-alanosine. All five of these antimetabolites interrupt cellular nucleotide synthesis and thereby halt the formation of DNA and/or RNA in the tumor cell. The remaining two compounds, buthionine sulfoximine and difluoromethylornithine, are inhibitors of glutathione and polyamine synthesis, respectively, with limited intrinsic antitumor activity; however, because of their powerful biochemical actions and their low systemic toxicities, they are being evaluated as chemotherapeutic adjuncts to or modulators of other more toxic antineoplastic agents.

S-phase inhibitors induce vimentin expression in human promonocytic U-937 cells

The administration of hydroxyurea (3 x 10(-4) M) and cytosine arabinoside (10(-7) M) greatly induces the expression of the vimentin gene in human promonocytic leukemia U-937 cells. The induction takes place at both the mRNA and protein levels, as demonstrated by Northern blot, immunoblot and immunofluorescence assays. On the contrary, the drugs inhibit the expression of c-myc and ornithine decarboxylase, and do not modify significantly the expression of beta-actin. Since hydroxyurea and cytosine arabinoside trigger the phenotypic differentiation of U-937 cells, as demonstrated by the induction of the differentiation-specific CD11b and CD11c antigens, it is concluded that vimentin expression might be implicated in the maturation of these cells.

alpha-Difluoromethylornithine inhibits liver metastasis produced by intrasplenic injection of human tumor cells into nude mice

The purpose of these studies was to examine metastatic potentials of a human colon tumor xenograft (T6) and three different human tumor cell lines (LS174T, HT29 and A549) using the intrasplenic-nude mouse model system (ISMS model system). A further objective was to study the activity of alpha-difluoromethyl-ornithine (DFMO) against primary and metastatic growth of the xenograft and the three cell lines. DFMO is an irreversible inhibitor of ornithine decarboxylase, a rate-limiting step in polyamine biosynthesis. Tumor burdens in the liver of nude mice were observed 6 weeks after the intrasplenic injection with LS174T and 12-14 weeks after intrasplenic injections with T6, HT29 and A549. Most of the mice developed primary tumor growth in the spleens. DFMO showed significant activity against liver metastases but had little or no activity against primary tumor growth in the spleens of the ISMS model and against s.c. growth of the xenograft. The studies demonstrated that the ISMS model system is an excellent system for studying metastatic behavior of human tumors and for studying the antimetastatic activity of experimental drugs.

Modulation of ornithine decarboxylase gene transcript levels by differentiation inducers in human promyelocytic leukemia HL60 cells

We have analyzed the changes in the steady-state levels of ornithine decarboxylase (ODC) mRNA during differentiation of HL60 cells, a human promyelocytic leukemia cell line. Induction of differentiation with either retinoic acid, dimethylsulfoxide, dibutyryl cAMP or dihydroxy-vitamin D3 resulted in a decrease of the cellular content of ODC RNA. Such a decrease occurred late after induction and coincided with the slowing of cell growth activity and with the expression of a cell surface differentiation marker (CD11b antigen). In contrast, the inducers provoked a rapid reduction of c-myc RNA levels, which preceded both the slowing of cell growth and the expression of the differentiation marker. When the cells were treated with a phorbol ester (TPA), the down-regulation of ODC was preceded by a transient increase in the steady-state levels of this RNA. However, such an increase was not observed with other inducers. The possible significance of these results in relation to the control of HL60 cell differentiation is discussed.

Mononuclear cell polyamine content associated with myeloid maturation in patients with leukemia during administration of polyamine inhibitors

Fourteen patients with acute leukemia in relapse were treated with difluoromethylornithine (DFMO) alone or in combination with methylglyoxal-bis(guanylhydrazone) (MGBG) as part of Phase I studies. Five patients included in the trial exhibited morphologic evidence of cellular differentiation during the course of treatment. In one patient who exhibited no blasts and a normal white blood cell differential at the end of treatment the mononuclear cell content of all three polyamines declined after an initial increase in spermidine and spermine content. In the other patients in whom the cellular maturation was less pronounced the mononuclear cell polyamine levels remained stable or increased over the treatment time. No absolute difference was apparent between the cellular polyamine levels detected in patients at the times of the greatest increase in per cent circulating neutrophils as compared to the cellular levels present in patients whose circulating mononuclear cell number were increasing. Circulating mononuclear cell putrescine, spermidine, and spermine levels varied over two orders of magnitude from patient to patient and the range of values detected in each state completely overlapped those present in the other. It does not appear from the present study that there is a consistent human leukemic cell polyamine content at which cellular differentiation occurs.

Urinary polyamine levels in cancer patients treated with D,L-alpha-difluoromethylornithine, an inhibitor of polyamine biosynthesis

The polyamine biosynthesis inhibitor D,L-alpha-Difluoromethylornithine hydrochloride monohydrate (DFMO) has cytostatic and cytotoxic effects against various human tumor cell lines in vitro. We measured levels of the polyamines putrescine and spermidine in the urine of cancer patients undergoing "conventional" chemotherapy in a two-arm randomized phase I-II study with and without additional DFMO administered orally at a dose of 1.7 g/sq.m. t.i.d. The study group included 38 patients with carcinoma of the breast, stomach, prostate, or female genital organs or metastatic carcinoma of unknown origin. A control group of 32 patients with similar malignancies received "conventional" chemotherapy without DFMO. Polyamine levels were determined periodically in the urine of all patients. In DFMO-treated patients, a significant decrease in putrescine and spermidine levels was observed after 3 weeks of DFMO therapy (the first time point evaluated) that usually persisted throughout the course of treatment. Significant differences in polyamine levels between DFMO-treated and control patients were observed for patients in remission. Less significant differences were noted, however, for patients with static or progressive disease between DFMO-treated and control groups. DFMO activity appears to be reflected by a long-term decrease in urinary polyamine levels.

Effect of retinoic acid on the proliferation and tumorigenicity of mouse mastocytoma cells : Effect of retinoic acid on mastocytoma cells

Retinoic acid (RA) inhibited the in vitro growth of the mouse mast cell tumor line P(815) in a dose- and time-dependent manner. The inhibition was accompanied by an increase in the amount of neutral intracellular mucopolysaccharides. Study of cell cycle kinetics showed that exposure to retinoic acid led to a slowing-down of the cell-cycle progression possibly related to a more differentiated cell population disclosed by microscopy with a lower proliferative capacity. In vivo, delays in both tumor appearance and mouse mortality were observed after injecting RA into mice bearing mastocytomas. These results suggest that RA could be of interest in the treatment of human malignant systemic mastocytosis with proliferation of immature mast cells.

The changing profiles of L-ornithine decarboxylase and S-adenosyl-L-methionine decarboxylase activities in testicular cell types during sexual maturation of male rats

To understand the involvement of polyamines in testicular maturation and spermatogenesis, the activity of two enzymes involved in the polyamine synthetic pathway, L-ornithine decarboxylase (ODC) and S-adenosyl-L-methionine decarboxylase (AdoMetDC) were determined in whole testis and isolated testicular cell types during the sexual maturation of male rats. ODC activities per mg protein in whole testis and cultured Sertoli cells from 12- to 14-day-old rats were very high but declined as the age of the animals increased. ODC activities in both germ cells and interstitial cells increased as the age of the rats increased, reached a maximum at 22 days and then declined rapidly. On the other hand, AdoMetDC activity in whole testis, Sertoli cells, germ cells and interstitial cells was highest from 27 to 35 days, 18 to 22 days, 22 to 27 or 35 days, and 27 days of age, respectively, then decreased and remained at a constant lower level after 45 days. After 35 or 45 days of age, cellular AdoMetDC activities were relatively higher than ODC activities in the whole testis and germ cells, while the activity of both enzymes was comparable in the Sertoli cells. Correlation of these data with the development of germ cells during rat testicular maturation suggests that the high ODC activity in both Sertoli and germ cells is associated mainly with cell proliferation while the increase in AdoMetDC activity is most likely associated with the maturation of Sertoli cells and the meiosis of germ cells, particularly the formation of pachytene spermatocytes and the meiotic cell division of spermatocytes into spermatids.

Polyamine profiles in rat testis, germ cells and Sertoli cells during testicular maturation

Polyamine cellular concentrations (putrescine, spermidine and spermine) in the rat testis and testicular cell types were determined by fluorescence spectroscopy of their dansyl derivatives. A method is described to separate dansylated polyamines by high performance liquid chromatography in less than 12 minutes. In rat Sertoli cells, polyamine concentrations (per mg DNA) were greater than those in germ cells and the testis. The concentrations of all three polyamines increased with age. Concentrations of spermidine and spermine in germ cells also increased with age and leveled off after 27 to 35 days. On the other hand, higher putrescine levels were found in the testis of young rats (13 to 22 days) while the greatest spermidine and spermine contents were observed in the testis from rats of 31 to 35 days old. Of great interest, Sertoli cells from all age groups studied released a relatively large quantity of putrescine and a smaller amount of spermidine, but no spermine, into culture media. The amount of polyamine released by Sertoli cells varied with the age of the animal. Sertoli cells from 27-day-old rats released the greatest quantity of putrescine on a per mg DNA basis. The release of putrescine increased after hypotonic treatment that removed contaminating germ cells from the remaining Sertoli cells. It is concluded that cellular polyamine levels in the rat testis, germ cells and cultured Sertoli cells and the amount of polyamines released by Sertoli cells were age-dependent during the first wave of spermatogenesis.

Effect of retinoic acid on the phosphorylation of endogenous proteins in HL-60 cells

HL-60 cells were incubated with [32P]-Pi in order to label endogenous phosphoproteins in situ. These were then resolved via two-dimensional electrophoresis and autoradiograms were made from the gels. A comparison of autoradiograms made from retinoic-acid-differentiated cells with those made from control cells revealed a small number of phosphoproteins whose labeling was enhanced in differentiated cells. Incubating HL-60 cells with [35S]-methionine revealed that RA induced the synthesis of one of these proteins, (53 kDa, pl 4.8) although not to a degree sufficient to account for the increased phosphate labeling observed in differentiated cells. Difluoromethylornithine (DFMO), which arrests HL-60 cell proliferation without inducing differentiation, had no effect on endogenous protein phosphorylation. Treatment of DFMO-arrested cells with retinoic acid, however, increased the phosphorylation of the proteins and resulted in differentiation of the cells. Densitometric analysis of autoradiograms made from two-dimensional gels revealed that the phosphorylation of the 53-kDa, pl 4.8 protein was significantly elevated in cells exposed to RA for as little as 12 hours, i.e., before the cells were committed to differentiate and before a significant increase in the number of phenotypically mature cells was observed. It therefore appears that this protein may be an intermediate in the retinoic-acid-induced differentiation process.

Phase I-II clinical trial with alpha-difluoromethylornithine--an inhibitor of polyamine biosynthesis

Alpha-difluoromethylornithine (DFMO) is an enzyme-activated, irreversible inhibitor of ornithine decarboxylase, the first enzyme in the synthesis of the polyamines putrescine, spermidine and spermine. DFMO has been shown to have a cytostatic and cytotoxic effect against various human tumor cell lines. The present study was designed to evaluate the toxicity and efficacy of this compound when administered orally at a dose of 1.7 g/m sq. t.i.d. added to conventional chemotherapy to 38 patients with carcinoma of the breast, stomach, prostate, female genital organs or metastatic carcinoma of unknown origin. A control group of 32 patients with similar malignancies received conventional chemotherapy only. Gastrointestinal, hematologic and biochemical abnormalities caused by DFMO were negligible. Reasonable ototoxicity was the major toxic effect caused by DFMO and resulted in discontinuation of therapy in 6 of 38 patients (15.8%). No differences in disease progression were seen between those patients receiving DFMO plus conventional chemotherapy and those receiving only conventional chemotherapy.

Inhibition of polyamine synthesis reduces the growth rate and delays the expression of differentiated phenotypes in primary cultures of embryonic mesoderm from chick

Inhibition of polyamine synthesis in early chick embryos blocks their development at gastrulation. Analyses of arrested embryos show that mesodermal outgrowth and differentiation are drastically impaired. To study these effects in greater detail, we have used primary cultures of embryonic mesoderm from chick. The cultures were treated with alpha-difluoromethylornithine (DFMO), an enzyme-activated irreversible inhibitor of ornithine decarboxylase, the first and rate-limiting enzyme in polyamine synthesis. In control culture medium, mesodermal cells retained their in ovo outgrowth behavior and differentiation pattern. Addition of 10 mM DFMO to the culture medium, however, retarded attachment and outgrowth, and reduced the rate of proliferation of the mesodermal cells. Furthermore, the expression of differentiated phenotypes, such as beating heart tissue, erythroid cells, and adipocyte-like cells, was delayed. Simultaneous addition of 100 microM putrescine prevented or reduced the effects of DFMO, showing that these were indeed caused by polyamine deficiency. In the DFMO-treated mesoderm, DNA synthesis was markedly suppressed by the first day. Similar effects on RNA and protein synthesis developed at a later time. Our data suggest that a reduction in the concentrations of the polyamines decreases the rate of mesodermal cell proliferation, and as a consequence delays the expression of differentiated phenotypes.

A randomized trial of 13-cis retinoic acid with or without cytosine arabinoside in patients with the myelodysplastic syndrome

Ninety-eight consecutive patients with myelodysplastic syndrome were randomized to a treated or a control group, both receiving conventional supportive therapy. The treated group were given 13-cis-retinoic acid 20 mg/d if marrow blasts were less than or equal to 5% or cytosine arabinoside 10 mg/d subcutaneously on 6 d/week if marrow blasts were 6-30%, to which retinoic acid was added after 12 weeks. Serum levels of the drugs in the treated group were similar to those that would produce inhibition of CFU-GM growth in vitro. In patients in the low blast group receiving retinoic acid, myeloid surface antigens reverted from an abnormal to a normal pattern. Log rank analysis carried out after 25 months showed no significant difference in survival between the treated and control group, either in the total patient population or in the high and low blast groups considered separately. However, analysis of 39 non-sideroblastic patients with less than or equal to 5% blasts showed an increase in survival in the treated group.

Effect of 13-cis-retinoic acid on survival of patients with myelodysplastic syndrome

A randomised therapeutic trial of 13-cis-retinoic acid was carried out in 70 patients with myelodysplastic syndrome having 5% or fewer marrow blast cells. Among non-sideroblastic patients the 1-year survival in the treated group was 77%, compared with 36% in the control group. There were too few deaths among patients with sideroblastic anaemia to allow any effect of therapy on survival to be evaluated.

Leukaemogenesis: a postulated mechanism involving tyrosine protein kinase and DNA topoisomerase

The weight of available evidence suggests that leukaemogenesis is a multi-step, complex process. Since there are different types of leukaemia, it seems likely that a variety of distinct molecular mechanisms are involved, arising from different combinations of genetic defects. It is not therefore surprising that studies at genetic, karyotypic, biochemical, cellular and clinical levels all reveal considerable heterogeneity of abnormalities. An attempt to define associations between abnormalities at these different levels in the myeloid leukaemias, led to a new hypothesis which provides a link between activation of the tyrosine kinase group of oncogenes and two components of multi-step leukaemogenesis: reduced differentiation and the tendency for acquisition of further genetic changes.

Effects of DL-alpha-difluoromethylornithine on the growth and metastasis of B16 melanoma in vivo

The effects of DL-alpha-difluoromethylornithine (DFMO), a specific irreversible inhibitor of ornithine decarboxylase, on the growth of experimental mouse B16-F10 melanoma cells were investigated. DFMO (3%) in drinking water was administered to B16-F10 melanoma-bearing mice. At 24 days, B16-F10 melanomas in DFMO-fed mice weighed 75% less than those in control mice (p less than 0.001). DFMO reduced putrescine and spermidine levels in B16-F10 melanoma by 98% and 84%, respectively, and prolonged the mean survival time from 25.9 +/- 1.2 to 35.7 +/- 2.2 days (p less than 0.001). The effects of DFMO on experimental metastasis were also investigated. DFMO treatment resulted in a significant decrease in pulmonary metastasis induced by i.v. injection of B16-F10 melanoma cells.

Leukaemogenesis: a postulated mechanism involving tyrosine protein kinase and DNA topoisomerase

The weight of available evidence suggests that leukaemogenesis is a multi-step, complex process. Since there are different types of leukaemia, it seems likely that a variety of distinct molecular mechanisms are involved, arising from different combinations of genetic defects. It is not therefore surprising that studies at genetic, karyotypic, biochemical, cellular and clinical levels all reveal considerable heterogeneity of abnormalities. An attempt to define associations between abnormalities at these different levels in the myeloid leukaemias, led to a new hypothesis which provides a link between activation of the tyrosine kinase group of oncogenes and two components of multi-step leukaemogenesis: reduced differentiation and the tendency for acquisition of further genetic changes.

Role of polyamines in experience-dependent brain plasticity

Enriched experience increases brain growth, neuronal differentiation and learning abilities. Polyamines are modulators of growth and differentiation. We studied the effect of difluoromethylornithine (DFMO, an inhibitor of putrescine synthesis) on brain growth of rats exposed either to a complex or an impoverished environment. In both environmental conditions, DFMO decreased cortical putrescine by 50% and increased spermine by 13%; spermidine remained constant. Cortical RNA was not affected significantly by DFMO but DNA was decreased exclusively in rats exposed to the impoverished environment. Environmental complexity increased cortical weight, RNA and spermidine content. These differences were larger in DFMO-injected rats than in saline controls. Since stimulants such as amphetamines also enhance the environmental effects it was conceivable that DFMO might act as a stimulant. We have measured the effect of DFMO on rats' exploratory activity and found it decreased by the drug. Therefore the enhancing effect of DFMO cannot be explained by its behavioral activity. We propose that DFMO enhances the experience-dependent brain plasticity by facilitating differentiation of neurons.

Polyamines in normal and cancer cells

Based on available evidence, it appears that polyamines are critical for proliferation of both normal and transformed cells. Although the requirement of polyamines for DNA replication and cell proliferation is established, the molecular events in which the polyamines are essential are yet unknown. Furthermore, transformed and cancer cells, possibly because of their higher proliferative rate, appear to be more dependent on polyamine metabolism than their normal counterparts. This has been shown by the in vivo response of tumor models and human tumor xenografts in nude mice to polyamine depletion by DFMO. Although there has been associated toxicity to the host, the inhibition of cell proliferation has been higher in the implanted tumors than in the host. DFMO, a specific irreversible inhibitor of ODC, has been used extensively in studies which have shed light on the role of polyamines in cell proliferation and differentiation. DFMO has shown interesting anti-tumor effect in a number of experimental tumor models. Currently, DFMO clinical trials are being completed, and it will be of interest to see whether this polyamine inhibitor, or other newer polyamine analogs and inhibitors, will find a place in the treatment of neoplastic disorders.

Synthesis of N-chlorosulfonyl dicyclohexylamine as a potent inhibitor for spermidine synthase and its effects on human leukemia Molt4B cells

N-Chlorosulfonyl dicyclohexylamine (CSD) was synthesized as a potent inhibitor of spermidine synthase and analyzed for antiproliferative effects on leukemic cells. The compound specifically inhibited spermidine synthase in a competitive mode with the substrate putrescine (Ki, 1.8 X 10(-7) M). When human leukemia Molt4B cells were cultured in the presence of the inhibitor, the intracellular level of spermidine and the rate of cell proliferation were markedly depressed. In these polyamine depleted and growth retarded cells the synthesis of protein, but not of DNA or RNA, was found to be significantly diminished.

Cell cycle kinetics responses of human stomach cancer cells to reduction in polyamine levels by treatment with alpha difluoromethylornithine in vitro

Treatment of human gastric cancer clones in vitro with low doses of DFMO (5 mM) produced elongation of the cell population doubling times and lowering of the saturation densities. By contrast, DFMO treatment of normal human skin fibroblasts altered only the saturation density. The lack of an effect of 5 mM DFMO on the doubling time of normal fibroblasts may be directly related to baseline intracellular putrescine levels, which were about 2.5 times higher than in the cancer cells. The same dose of DFMO caused a rapid decrease in intracellular polyamine levels in the tumor clones. The effects on the doubling time and saturation density were almost totally abolished by the addition of 50 microM putrescine to the growth medium during the first 24 h of treatment with DFMO. Exposure to 5 mM DFMO for 24 h caused the human gastric cancer cells to become blocked in G1 phase only, and this led to a reduction in the fraction of cells in S phase. The G1 block was reversible and this cohort of cells eventually passed through S phase and then through G2 and M. A higher 100 mM dose of DFMO and longer exposure times for both doses produced cell cycle changes and death of more than 90% of the cell population. These data suggest that cell kinetics changes observed under these experimental conditions may reflect polyamine-related alterations in the biochemical events of cell cycle progression kinetics; but may also be the result of DFMO-induced loss of cell viability.

Human lung tumor sensitivity to difluoromethylornithine as related to ornithine decarboxylase messenger RNA levels

The differential response to polyamine depletion has been studied in two types of human lung tumor cells. Small cell lung carcinoma cells die following polyamine depletion by difluoromethylornithine treatment while non-small cell lines demonstrate a typical cytostatic response. We now report that a small cell line, NCI H82, has a lower apparent capacity for polyamine biosynthesis than does a representative non-small cell, NCI H157. In subconfluent cultures, the ornithine decarboxylase activity is 25 times lower in the small cell than the non-small cell and by comparison, the polyamines in the small cell line are markedly reduced. Most significantly, levels of mRNA coding for ornithine decarboxylase are approximately 100-fold lower in the small cell than the non-small cell line, and this difference does not appear to be a result of gene rearrangement. These results suggest that differential sensitivity to polyamine depletion is related to different steady-state levels of ornithine decarboxylase mRNA.

Relationship between ornithine decarboxylase activity and hexamethylene bisacetamide-induced differentiation of murine erythroleukemia cells

A transitory increase in ornithine decarboxylase (ODC) activity is shown not to be a prerequisite for the differentiation induced by hexamethylene bisacetamide (HMBA) in murine erythroleukemic (MEL) cells. On the contrary, conditions are described, where inhibition of the ODC activity with alpha-difluoromethyl ornithine (DFMO) stimulated the induced differentiation. Polyamine analysis demonstrated that a reduction in intracellular putrescine and spermidine occurred in MEL cells before commitment to erythrodifferentiation. The presence of DFMO increased the rapidity and the amplitude of these changes. No effect of dexamethasone on these changes in ODC activity or intracellular polyamines was observed.

Differential release of polyamines by cultured rat Sertoli cells

Cellular and media concentrations of polyamines in Sertoli cell cultures were determined by fluorescent spectroscopy of dansylated compounds after separation by high-performance liquid chromatography. In spite of low cellular levels of putrescine, the Sertoli cells released relatively large amounts of putrescine and spermidine even after several media changes. The inclusion in the culture media of cortisol, insulin, and thyroxine significantly elevated cellular polyamine levels, altered the spermidine to spermine ratio, and enhanced putrescine release by 3- to 4-fold. No spermine, however, was detected in the media under any of the conditions studied. The polyamine concentrations in cultured Sertoli cells from 13-day-old rats and the pattern of polyamine release by these cells differed significantly from those in the Sertoli cells from 46-day-old rats. These data demonstrate the differential release of polyamines by cultured rat Sertoli cells. The profiles of polyamine secretion appear to be age-dependent, and the significance of this phenomenon is discussed.