Ornithine decarboxylase from Neurospora crassa. Purification, characterization, and regulation by inactivation

Ornithine decarboxylase, a highly regulated enzyme of the polyamine pathway, was purified 670-fold from mycelia of Neurospora crassa that were highly augmented for enzyme activity. The enzyme is significantly different from those reported from three other lower eucaryotic organisms: Saccharomyces cerevisiae, Physarum polycephalum, and Tetrahymena pyriformis. Instead, the enzyme closely resembles the enzymes from mammals. The Mr = 110,000 enzyme is a dimer of 53,000 Da subunits, with a specific activity of 2,610 mumol per h per mg of protein. Antisera were raised to the purified enzyme and were rendered highly specific by cross-absorption with extracts of a mutant strain lacking ornithine decarboxylase protein. With the antisera, we show that the inactivation of the enzyme in response to polyamines is proportional to the loss of ornithine decarboxylase protein over almost 2 orders of magnitude. This is similar to the inactivation process in certain mammalian tissues, and different from the process in S. cerevisiae and P. polycephalum, in which enzyme modification, without proportional loss of antigen, accompanies enzyme inactivation. The N. crassa enzyme is therefore suitable as a microbial model for studies of the molecular regulation of the mammalian enzyme.

Multiple pathways for uptake of paraquat, methylglyoxal bis(guanylhydrazone), and polyamines

The uptake of polyamines, methylglyoxal bis(guanylhydrazone) (MGBG), and paraquat [N,N-dimethyl-4,4'-bipyridylium] into control Chinese hamster ovary (CHO) cells and a mutant CHO cell line selected for resistance to the toxicity of MGBG was examined. In contrast to control CHO cells, the mutant cells had no detectable uptake of MGBG or any of the polyamines. There was no difference between the two cell lines in the uptake of alpha-aminoisobutyric acid (AIB), which indicates that there was no general change in membrane transport processes. The mutant cells were also found to be resistant to the toxicity of paraquat and to have a reduced capability to take up the herbicide. This finding confirms that the uptake of paraquat is necessary for the toxicity of this compound and that the paraquat is taken up by a transport system that also transports MGBG. Competition experiments showed that an excess of unlabeled paraquat inhibited uptake of MGBG and, to a lesser extent, uptake of putrescine and spermidine, but no inhibitory action on spermine uptake could be detected. Studies with type II cells isolated from rat lung also demonstrated uptake of paraquat and spermidine, but paraquat was only a weak inhibitor of spermidine uptake in this system. These results suggest that there may be multiple systems for the uptake of MGBG and polyamines and that paraquat is taken up by at least one but not by all of these systems.

Modulation of murine erythroleukemic cell differentiation by inhibitors of polyamine biosynthesis

The differentiation of murine erythroleukemic cells induced by hexamethylene bisacetamide is shown to be differently affected by two inhibitors of polyamine biosynthesis. Methyl glyoxal bis(guanyl hydrazone) (inhibitor or S-adenosyl methionine decarboxylase) inhibited this differentiation process. By using a novel experiment protocol the inhibitory effect of this drug on the induced differentiation was dissociated from pleiotropic effects on cell growth. Methyl glyoxal bis(guanyl hydrazone) only inhibited the induced differentiation if present during the first 6 h of culture of the cells with the inducer. No effect on the induced differentiation was observed if the drug was added to the culture medium 6 h after the inducer. alpha-Difluoro methylornithine (inhibitor of ornithine decarboxylase) stimulated the differentiation of these cells. Polyamine analysis demonstrated that alpha-difluoro methylornithine increased the rapidity and the amplitude of the changes in intracellular polyamines associated with this induced differentiation. The presence of methyl glyoxal bis(guanyl hydrazone) during the first 3 h with the inducer was sufficient to produce opposing changes in the intracellular polyamines. These results suggest that changes in either intracellular polyamines or the activities of polyamine biosynthetic enzymes play a regulatory role in the differentiation process induced in murine erythroleukemic cells by hexamethylene bisacetamide.

Permissive role for ornithine decarboxylase and putrescine in the luteinising hormone surge

Anterior pituitary gland fragments removed from Wistar-derived rats at 10.00 h on pro-oestrus were perifused with Krebs-bicarbonate medium in a column and exposed to hourly volleys of 6 1-min pulses of 10 nM luteinising hormone (LH)-releasing hormone (LHRH). LH release showed a characteristic pattern of prolonged (over 5 h) sensitisation to the releasing hormone, with the response to each volley becoming progressively greater. The addition of 2 mM difluoromethylornithine (DFMO; an inhibitor of ornithine decarboxylase) to the perifusion medium completely inhibited the response to all volleys of LHRH. This effect of DFMO was reversed by the concurrent inclusion of 2 mM putrescine in the medium. Putrescine alone had a small but non-significant enhancing effect on LHRH-induced release, and no significant effect on basal LH release in this system. In a second series of experiments, tissues were loaded with 1-14C-ornithine and the radioactive carbon dioxide released into the medium during the perifusion monitored. Unstimulated pituitary tissues showed constant low levels of carbon dioxide release during 5 h of incubation, but those given hourly volleys of LHRH showed progressively increasing release of radioactivity, which was blocked by the addition of DFMO. No LHRH-stimulated increase in 14CO2 production from 1-14C-ornithine was seen from pituitary tissue removed at 10.00 h on dioestrus. Administration of DFMO (10-100 mg/rat) on the afternoon of pro-oestrus 4 h before the expected peak of the LH surge reduced the magnitude of the subsequent surge and the concentration of the hormone found in the anterior pituitary gland in a dose-related manner. In addition, the concentration of putrescine, but not of spermidine or spermine, was significantly reduced in treated animals (50 mg/rat) at the time of this attenuated surge.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo effects of difluoromethylornithine on trypanothione and polyamine levels in bloodstream forms of Trypanosoma brucei

The effect of D,L-alpha-difluoromethylornithine (DFMO) on thiol and polyamine levels in Trypanosoma brucei was investigated by isolating trypanosomes from infected rats treated with DFMO for 12-48 h. Concentrations of thiols, polyamines and other amino-compounds were measured by an automated high-performance liquid chromatography method. The levels of DFMO in rat plasma (0.02-1.34 mM) is similar to that found in the parasites (0.27-0.99 mM), concentrations which exceed the Ki of DFMO for T. brucei ornithine decarboxylase. Treatment with DFMO increases intracellular levels of ornithine, S-adenosylmethionine and decarboxylated S-adenosylmethionine and decreases putrescine and spermidine. Putrescine is undetectable after 12 h treatment with DFMO and after 48 h spermidine is decreased by 76%. By 48 h, the spermidine-glutathione conjugates glutathionylspermidine and dihydrotrypanothione (bis(glutathionyl)spermidine) are also decreased by 41 and 66%, respectively. In contrast, levels of glutathione show a slight increase. These changes in metabolite levels are consistent with the biosynthetic pathway proposed for Crithidia fasciculata, where trypanothione is synthesized from spermidine and glutathione via the intermediates N1- and N8-glutathionyl-spermidine. Trypanothione is thought to have two important roles in trypanosomatid metabolism: the maintenance of intracellular thiols in the correct redox state and in the removal of hydrogen peroxide and other hydroperoxides. Thus, it is proposed that depletion of this metabolite may be an important contributory factor to the selective toxic effect of DFMO, particularly in its synergistic effect with other trypanocidal drugs.

Dopaminergic regulation of polyamine synthesis in the rat pituitary gland

The biosynthesis of polyamines, a group of growth-related amines, varied in the rat pituitary gland with the different stages of the estrous cycle. The activity of ornithine decarboxylase (ODC), which catalyzes the rate-limiting step in the biosynthesis of polyamines, was greatly increased in the pituitary gland during the evening of proestrus. Ovariectomy resulted in a disappearance of this cyclic change in polyamine synthesis, whereas estrogen treatment of the ovariectomized rats gave rise to daily afternoon peaks in pituitary ODC activity. Like the prolactin cells, pituitary polyamine biosynthesis appeared to be regulated by dopamine. The induction of ODC activity in the pituitary gland during proestrus or after estrogen treatment was almost completely repressed by bromocriptine, a dopaminergic compound. The dopamine antagonist haloperidol, on the other hand, was a potent inducer of pituitary ODC activity. Neither pituitary DNA synthesis nor prolactin secretion, which both are induced by estrogen, were affected by inhibition of polyamine synthesis, suggesting a biological function of the pituitary polyamines unrelated to these events.

Altered expression of beta-globin, transferrin receptor, and ornithine decarboxylase in Friend murine erythroleukemia cells inhibited by alpha-difluoromethylornithine

alpha-Difluoromethylornithine (DFMO) is an irreversible inhibitor of ornithine decarboxylase (ODC) and restricts the proliferation and differentiation of Friend murine erythroleukemia cells. We have studied the effect of this compound on the expression of ODC, transferrin receptor (TFR), and beta-globin during normal cellular proliferation and dimethylsulfoxide-induced terminal differentiation. Elevated RNA levels for ODC were observed during both normal Friend murine erythroleukemia cell division and replication associated with terminal differentiation, but these transcripts decreased as the cells ceased proliferating. However, in the presence of DFMO the levels of ODC remained elevated even when the cells had stopped dividing; this appears to be a feedback mechanism to overcome the effects of the inhibitor. TFR expression paralleled regular cell division and was curtailed when replication was reduced by DFMO. However, the inhibitor was unable to prevent the differentiation associated maintenance of TFR levels, well after proliferation terminated. While DFMO was able to restrict differentiation and hemoglobin synthesis, it did not inhibit the dimethylsulfoxide-induced expression of beta-globin RNA. We concluded that the block in differentiation caused by DFMO occurs along some pathway(s) other than the activation of beta-globin or TFR.

Modulation of arterial smooth muscle cells from contractile to synthetic phenotype requires induction of ornithine decarboxylase activity and polyamine synthesis

The role of polyamines in modulating cultivated arterial smooth muscle cells from contractile to synthetic phenotype was studied by biochemical and electron microscopic methods. Ornithine decarboxylase (ODC), the first and overall rate-limiting enzyme in polyamine biosynthesis, showed no detectable activity in freshly isolated contractile cells, rose to a peak of activity after 2 days of culture, simultaneously with the most rapid phase of phenotypic modulation, and thereafter returned to a lower level of activity. The increase in ODC activity was accompanied by a gradual rise in the cellular concentrations of the polyamines putrescine, spermidine and spermine. The polyamine synthesis inhibitors alpha-difluoromethylornithine and methylglyoxal-bis(guanylhydrazone) prevented transition into synthetic phenotype as well as initiation of cell growth. The results indicate that polyamines play an important role in the control of smooth muscle phenotype and growth.

Importance of the duration of inhibition on intestinal carcinogenesis by difluoromethylornithine in rats

The effect of the duration and sequence of inhibition of intestinal tumor formation in rats was studied to determine whether part time inhibition has any value. Four groups of male Sprague-Dawley rats were given 8 weekly s.c. injections of azoxymethane (AOM) 8 mg/rat. Three groups were given the inhibitor, difluoromethylornithine (DFMO) in the drinking water; one for the entire 26 weeks of the study, one for the first 13 weeks only, and one for the last 13 weeks. A control group was not given the inhibitor. While the continuous treatment group developed the least number of tumors per rat (1.5 vs. 5 for controls), still both groups given the inhibitor for just 13 weeks also developed fewer tumors than controls 5 vs. 3.2 (early treatment) and 5 vs. 2.8 (late treatment). These results show that part time inhibition, including its late application, does reduce intestinal tumor formation in rats.

Implication of ornithine decarboxylase and polyamines in pancreatic growth of neonatal rats

The current study examines the effects of alpha-difluoromethylornithine (DFMO), an irreversible ornithine decarboxylase inhibitor, on pancreatic growth and development of rat neonates. Newborn rats were given daily subcutaneous injections of 300 or 500 mg kg-1 DFMO and killed after 7, 14, 21, and 28 days of treatment. Pancreatic weights and DNA, RNA, protein, amylase and chymotrypsin total contents (per pancreas) and concentrations were evaluated at the end of each period. Inhibition of body weight gain (30%) was maximal after 14 days of the 500 mg DFMO treatment. Pancreatic weight increase of 20% was significant after 7 days of the 300 mg DFMO treatment while deficits of 15, 20, and 14% were significant after 21 days of 300 mg DFMO and 14 and 21 days of 500 mg DFMO. Total DNA was already subnormal after one week of 500 mg DFMO with a maximal reduction of 30% after 28 days while a significant decrease of 15% was observed only after 3 weeks of 300 mg DFMO. Pancreatic hypertrophy was observed after 7 and 28 days of the 500 mg and after 14 days of the 300 mg DFMO treatment. Chymotrypsin total contents and concentrations were always preferentially affected over those of amylase. These data support the view that ornithine decarboxylase (ODC) and polyamines play an important role in cell replication and growth of the pancreatic tissue during the neonatal period.

Induction of ornithine decarboxylase activity and putrescine synthesis in arterial smooth muscle cells stimulated with platelet-derived growth factor

Cultivated arterial smooth muscle cells were used to study the effects of platelet-derived growth factor (PDGF) on polyamine synthesis and of polyamine synthesis inhibitors on initiation of DNA synthesis by PDGF. Quiescent (serum-starved) cells showed no detectable activity of ornithine decarboxylase (ODC), the first and overall rate-limiting enzyme in polyamine synthesis, and had low levels of the polyamines putrescine, spermidine and spermine. PDGF caused a marked increase in ODC activity, with a peak after 6 h followed by a rapid decline. The rise in enzyme activity was blocked by actinomycin D and cycloheximide, suggesting control at the transcriptional and translational levels, alpha-Difluoromethylornithine (DFMO), a catalytic and irreversible inhibitor of ODC, prevented the appearance of enzyme activity. The cellular content of putrescine increased distinctly in response to PDGF, with a peak after 8 h, abolished by simultaneous treatment with DFMO. In contrast, the concentrations of spermidine and spermine changed but little within the 20-h period examined here. DFMO inhibited the initiation of DNA synthesis without affecting the length of the prereplicative lag phase and was fully active if added within 4 h after PDGF. The effect of DFMO on DNA synthesis was counteracted by addition of polyamines to the culture medium and exogenous polyamines were also found to stimulate DNA synthesis in PDGF-free medium (spermine greater than spermidine greater than putrescine). It is concluded that induction of ODC and putrescine synthesis are integral parts in the mitogenic response of arterial smooth muscle cells to PDGF.

Intracellular polyamine biosynthesis is required for interleukin 2 responsiveness during lymphocyte mitogenesis

The objective of the present investigation was to define a more precise role for intracellular polyamine biosynthesis with respect to specific inducible events which regulate lymphocyte mitogenesis. In this regard, we have examined the effect of polyamine depletion on interleukin 2 (IL-2) production, receptor expression, and responsiveness in Con A stimulated mononuclear leukocytes (MNL). Polyamine depletion was achieved utilizing the specific irreversible inhibitor of ornithine decarboxylase (ODC), DL-alpha-difluoromethylornithine (DFMO). Polyamine depletion of MNL augmented detectable levels of Con A-induced IL-2 activity. In contrast, the ability of polyamine depleted MNL to respond to saturating levels of IL-2 (100 U/ml) following 72 or 96 hr of Con A stimulation was reduced 100 and 81%, respectively. Nonetheless, polyamine depletion did not impair the induction of IL-2 receptor expression. High-affinity IL-2 receptor density in the polyamine depleted population was greater than control cells late in culture (96 hr). The expression of high-affinity IL-2 receptors did not correlate with an ability to respond to IL-2 in the polyamine depleted population. The results of this study demonstrate for the first time that intracellular polyamine biosynthesis is required for IL-2 responsiveness during a primary mitogenic lymphocyte response.

DNA synthesis in pulmonary alveolar macrophages and type II cells: effects of ozone exposure and treatment with alpha-difluoromethylornithine

An increase in the number of pulmonary alveolar macrophages (AM) can be induced by a number of toxic insults to the lung, including ozone, an important photochemical oxidant air pollutant. This increase could arise from an influx of monocytes from the vascular or interstitial compartments, or from proliferation of AM in situ. While proliferation of alveolar type II cells after oxidant exposure has been well documented, it is not clear whether AM are also capable of this response. Rats were exposed to air or to 0.12, 0.25, or 0.50 ppm ozone for 1, 2, 3, 7, or 14 d, 20 h/d. The labeling index in both AM and type II cells increased about 10-fold after 2 d of exposure to 0.25 and 0.50 ppm of ozone, but returned to control levels by the end of 1 wk of exposure. These changes closely paralleled the temporal and dose-response characteristics of changes in total lung DNA synthesis. alpha-Difluoromethylornithine (DFMO) administered to rats during a 2-d exposure to 0.50 ppm ozone did not inhibit the ozone-induced increase in labeling index in AM or type II cells, although evidence of inhibition of lung ornithine decarboxylase activity was obtained, and the ozone-induced increase in total lung DNA synthesis was inhibited by 23%. These results suggest that, like type II cells, AM are capable of entering the cell cycle and synthesizing new DNA in situ in response to short-term exposure to environmentally relevant doses of ozone, and that the ozone-induced stimulation of DNA synthesis in these cell types was refractory to inhibition by DFMO.

Human myeloma cells acquire resistance to difluoromethylornithine without overproducing ornithine decarboxylase

An exposure of a human myeloma cell line to 2-difluoromethylornithine the mechanism-based inhibitor of ornithine decarboxylase (EC 4.1.1.17), resulted in a selection of tumor cells readily growing in the presence of 4 mM difluoromethylornithine, a concentration that swiftly halted the growth of the parental cells. Determination of the intracellular polyamines revealed that there were measurable amounts of putrescine and spermidine in the resistant cells. Restriction enzyme analyses of genomic DNA isolated from the resistant cells indicated that the gene dosage for ornithine decarboxylase was not increased to any appreciable extent. Similarly, the accumulation of mRNA was unaltered. The resistant myeloma cells, however, displayed arginase (EC 3.5.3.1) activity that was roughly ten times higher than that in the parental cells.

Evidence that hypoxic pulmonary vascular remodeling in rats is polyamine dependent

This study tested the hypothesis that the polyamines, a family of low-molecular-weight organic cations with documented regulatory roles in cell growth and differentiation, are mediators of chronic hypoxia-induced pulmonary vascular remodeling. Relative to room air controls, chronically hypoxic animals (inspired O2 fraction = 0.1; 21 days) exhibited higher pulmonary arterial pressures (measured in room air), thicker medial layers in pulmonary arteries of 50-100 microns diam, increased hematocrits, and right ventricular hypertrophy. In addition, lung contents of the polyamines, putrescine, spermidine, and spermine were greater in hypoxic animals than in controls. alpha-Difluoromethylornithine (DFMO), an inhibitor of polyamine synthesis, attenuated the hypoxia-induced elevations in lung putrescine and spermidine content and blunted the increases in pulmonary arterial pressure and medial thickness. Neither the increased hematocrit nor right ventricular hypertrophy associated with chronic hypoxia were abrogated by DFMO. In addition, DFMO failed to influence vasoconstrictor responses provoked by acute hypoxic ventilation in isolated, buffer-perfused rat lungs. These observations suggest that depression of polyamine biosynthesis with DFMO blunts the sustained increase in pulmonary arterial pressure by attenuating hypoxia-induced medial thickening.

[A new molecule in antiparasitic therapy: alpha-difluoromethylornithine]

Alpha-difluoromethylornithine (DFMO) is a specific irreversible inhibitor of ornithine-decarboxylase (ODC), key enzyme in the biosynthesis of polyamines, physiological compounds involved in cell multiplication. Pharmacokinetic studies of the drug revealed good oral absorption, low metabolisation and mainly urinary excretion. Short half-life (3 hrs to 3 hrs 30) implicates daily repeated administrations. DFMO is well tolerated, side effects being reversible on discontinuing drug therapy. They chiefly include diarrheas, hematological perturbations (thrombocytopenia) and hear losses (high dosages). Experimental studies show best results on trypanosomes: curative action in mice infected with Trypanosoma brucei brucei. DFMO is effective too against infection with sporozoïtes of Plasmodium berghei. Early clinical observations in African patients with Trypanosoma brucei gambiense sleeping sickness show favorable results: efficacy in both stages of the disease, without significant toxicity. Further trials are required to define optimal therapeutic applications. By the way, DFMO already seems to be a promising alternative to conventional therapy of African trypanosomiasis, expecting other indications in the field of antiparasitic chemotherapy.

Synergistic inhibition of polyamine synthesis and growth by difluoromethylornithine plus methylthioadenosine in methylthioadenosine phosphorylase-deficient murine lymphoma cells

The antiproliferative effects of the ornithine decarboxylase inhibitor alpha-difluoromethylornithine (DFMO) are limited by the inability of the compound to deplete completely cellular polyamine pools. 5'-Deoxy-5'-methylthioadenosine (MeSAdo), the purine end product of the polyamine biosynthetic pathway, is an inhibitor of spermine and spermidine synthesis. Furthermore, a substantial number of human tumors are deficient in MeSAdo phosphorylase, and cannot degrade MeSAdo. It therefore seemed possible that DFMO and MeSAdo could interact synergistically to inhibit polyamine synthesis in MeSAdo phosphorylase-deficient malignant cells. To test this hypothesis, we have analyzed the effects of DFMO, in combination with MeSAdo, on polyamine synthesis and growth in a MeSAdo phosphorylase-deficient murine lymphoma cell line (R1.1-H), and a MeSAdo resistant mutant (R1.1-H3). Cultivation of the R1.1-H3 cells in medium containing 250 microM DFMO and 500 microM MeSAdo caused profound depletion of putrescine, spermidine, and spermine, and the accumulation of both decarboxylated S-adenosylmethionine and its acetylated derivative to levels that exceeded by nearly 3-fold the total cellular content of S-adenosylmethionine. Similarly, DFMO sensitized the lymphoma cells to the growth inhibitory effects of MeSAdo. Supplementation of the medium with putrescine, spermidine, or spermine partially protected R1.1-H3 cells from the DFMO-MeSAdo drug combination. It is conceivable that MeSAdo, or related nucleosides, may potentiate the cytostatic effects of DFMO toward MeSAdo phosphorylase-deficient tumors.

Growth inhibition of pathogenic yeast isolates by alpha-difluoromethylornithine: an inhibition of ornithine decarboxylase

A large body of evidence exists suggesting that polyamines can play essential roles in cellular growth and differentiation. We examined the ability of alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, the major rate-limiting enzyme in polyamine biosynthesis, to inhibit the growth of Candida albicans, C. tropicalis, and C. parapsilosis. Substantial growth-inhibition was observed for all three species at DFMO concentrations ranging from 1 to 100 mM. C. tropicalis was significantly more susceptible to DFMO than C. albicans or C. parapsilosis. Depletion of cellular polyamine pools was seen in all 3 species following exposure to DFMO and polyamine depletion enhanced the susceptibility of the organisms to DFMO. The action of DFMO was specifically antagonized by exogenous polyamines. These data suggest that polyamines are important in the growth of Candida spp. and that inhibitors of polyamine biosynthesis may be useful as antifungal agents.

Role of ornithine decarboxylase in functional development of rat gastric mucosa

The effects of inhibiting polyamine synthesis on the functional development of the gastric mucosa were studied in rats from 5 to 40 days old. They were treated from day 14 after birth with alpha-difluoromethylornithine (DFMO) at a concentration of 2% in the drinking water of mothers and pups. The rats were weaned on day 18. Basal acid and pepsin secretion, oxyntic gland mucosal pepsinogen content, and antral gastrin content followed similar developmental patterns in control animals. Levels of these parameters remained measurable but low until around the time of weaning, when dramatic log linear rises were observed. DFMO failed to delay the onset of the rises in any of these maturational indices. Ornithine decarboxylase (ODC) activity in the oxyntic gland mucosa was low but discernible in rats of every age studied. DFMO significantly reduced ODC activity at every age except 40 days, where there was no difference from control values. Our results suggest that ODC activity in the rat gastric mucosa does not change appreciably during neonatal development and that inhibiting putrescine synthesis from its precursor ornithine by DFMO treatment does not prevent or delay gastric mucosal maturation.

The effect of alpha-difluoromethylornithine, an inhibitor of polyamine biosynthesis, on mitogen-induced interleukin 2 production

The objective of the present investigation was to examine the effect of DL-alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, on mitogen-induced interleukin 2 production. Treatment with DFMO reduced nylon wool T cell polyamine levels. In contrast, DFMO treatment enhanced, greater than two-fold, detectable levels of concanavalin A-induced interleukin 2 activity. This observed augmentation was not limited to in vitro DFMO treatment, since oral administration of DFMO to C57BL/6 mice also enhanced concanavalin A-induced interleukin 2 levels in vitro. Treatment with exogenous putrescine reversed the effect of DFMO on interleukin 2 levels. These results suggest that the effect of DFMO on interleukin 2 levels is mediated through polyamines. Therefore, polyamine biosynthesis may play a role in the intracellular regulation of interleukin 2 production.

Effect of intravenous alpha-difluoromethylornithine on the polyamine levels of normal tissue and a transplantable fibrosarcoma

The effect of a continuous i.v. infusion of alpha-difluoromethylornithine (DFMO) on the polyamine metabolism of tumor and normal host tissue was determined. Non-tumor-bearing Fischer 344 rats or rats bearing a transplantable fibrosarcoma received continuous infusions of DFMO through a central venous catheter at three dose levels. Treatment with DFMO resulted in a time- and dose-dependent, cytostatic effect on the growth of the tumor. In fibrosarcoma-bearing rats the tumor putrescine levels were reduced after 6 and 12 days of DFMO treatment. Tumor spermidine levels were consistently reduced after 6 and 12 days of treatment with the reduction being dose dependent. The decrease in tumor ornithine decarboxylase activity was dose dependent. Erythrocyte putrescine levels were decreased in tumor- and non-tumor-bearing rats, suggesting that DFMO reduces the tumor contribution to the erythrocyte pool. Erythrocyte spermidine levels of fibrosarcoma- and non-tumor-bearing rats were elevated at the lower DFMO doses administered for 12 days but returned to normal as the dose was increased. Erythrocyte spermine levels were elevated in both groups of rats at all DFMO doses. Although normal host tissue weights were not affected by treatment with DFMO, the putrescine and spermidine levels of liver, spleen, and kidney and ornithine decarboxylase activity of the liver and kidney were decreased. These data demonstrate that i.v. DFMO has a cytostatic effect toward a rapidly growing fibrosarcoma associated with the depletion of both tumor putrescine and spermidine levels.

Diamine oxidase is important in assessment of polyamine effects on hemopoietic cell proliferation in vitro

A difference was observed in the effect of difluoromethlyornithine (DFMO), a specific inhibitor of ornithine decarboxylase, on human and murine granulocyte-macrophage precursor cell (CFU-C) proliferation in vitro, in the presence of fetal bovine serum (FBS) and horse serum (HS). A dose of DFMO which almost totally abolished CFU-C colonies in cultures containing FBS had no effect or very little effect on CFU-C in cultures supplemented with HS. This effect could be reversed by aminoguanidine reacting with diamine oxidase (DAO), which is present in FBS but not in HS. The importance of DAO in the assessment of polyamine effects is also suggested by decreased colony formation in cultures containing HS and DFMO only after the addition of this enzyme. Additionally, Mo T cell line cultures containing DFMO demonstrated a substantially lower intracellular concentration of putrescine in the presence of FBS rather than HS.

Experimental parameters and a biological standard for acridine orange detection of drug-induced alterations in chromatin condensation

We investigated a number of sample-preparative parameters for use of flow cytometry to detect chromatin condensation in cells stained with acridine orange after DNA in situ is partially denatured by acid treatment. Stability and data reproducibility for both control and drug-treated ME-180 and HT-29 cells were assessed over: a range of cell concentrations in 2.56 X 10(-5) M acridine orange; 15 days of storage in fixative; various times between RNase digestion and staining; and increasing times between staining and analysis. Listmode data for red and green fluorescence were collected and mean fluorescence intensities of G1, S, and G2 subpopulations of HT-29 and ME-180 cells were computed. These were normalized to data from HeLa-S3 cells and fluorescent microspheres to control for inter-experiment variations in staining and instrumental parameters, respectively. The normalized red and green fluorescence data were used to calculate alpha 1 for G1 cells [alpha t = red fluorescence/(total fluorescence)]. Exponentially growing HeLa-S3 cells were a very consistent and reproducible biological standard to control for fixation and staining variability. Mean fluorescence intensities of control and difluoromethylornithine-treated (i.e., polyamine depleted) cells remained stable and reproducible across all tested ranges for cell concentration, storage in fixative, and time after RNase digestion. This technique can thus be used to evaluate difluoromethylornithine-induced changes in chromatin condensation of samples stored for as long as 2 weeks and analyzed all on 1 day.

Increased ornithine decarboxylase activity and polyamine biosynthesis are required for optimal cytolytic T lymphocyte induction

The objective of the present investigation was to evaluate the requirement for increased ornithine decarboxylase (ODC) activity and polyamine biosynthesis in the induction of cytolytic T lymphocytes (CTL). In this regard, we have utilized alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC. DFMO treatment completely abrogated Con A-induced NW T-cell ODC activity. Similarly, DFMO treatment reduced putrescine and spermidine biosynthesis 100 and 87% respectively by the end of a 48-hr incubation period. Polyamine depletion reduced the Con A-mediated polyclonal induction of CTL by 52 and 81% at 24 and 48 hr of culture, respectively. The effect of DFMO on CTL induction could be reversed by the addition of exogenous putrescine. These data indicate that the observed effects of DFMO on CTL induction were mediated through inhibition of polyamine biosynthesis. Therefore, increased ODC activity and polyamine biosynthesis are required for optimal CTL induction. Furthermore, polyamine depletion did not impair IL-2 production; however, IL-2-dependent proliferation was reduced. These data are the first to discriminate between the requirement for polyamines with regard to IL-2 responsiveness, rather than IL-2 production, during a primary T-cell mitogenic response.

Effect of combinations of difluoromethylornithine (DFMO) and 9[(1,3-dihydroxy-2-propoxy) methyl]guanine (DHPG) on human cytomegalovirus

Both the nucleoside analog 9[(1,3-dihydroxy-2-propoxy)methyl]guanine (ganciclovir; DHPG) and the polyamine synthesis inhibitor difluoromethylornithine (DFMO) have been reported to inhibit replication of cytomegalovirus (CMV) in vitro. In these studies, DHPG inhibited human CMV replication at concentrations of 0.1 microM or greater, while DFMO was active (and then only inconsistently) at 5 mM or greater. (DFMO was added to cells 3 days before virus to maximize polyamine depletion.) However, DHPG combined with DFMO synergistically inhibited the replication of CMV strain AD169 and one wild-type CMV strain in human foreskin fibroblasts; the effect was evident on both virus yield and plaque formation. The synergistic effect of these two drugs on CMV replication could potentially be exploited clinically to limit drug toxicity or increase efficacy.