Cytostatic effect of DL-alpha-difluoromethylornithine against Plasmodium falciparum and its reversal by diamines and spermidine

DL-alpha-difluoromethylornithine (DFMO) inhibited ornithine decarboxylase (ODC) activity and arrested the growth of Plasmodium falciparum at the early trophozoite stage. The inhibition of ODC activity did not result in the formation of an alternative diamine such as cadaverine. When putrescine or spermidine were added to the parasites grown in culture, the arrest was reversed, and normal schizogony was completed even in the presence of DFMO. Some reversal of the inhibition was achieved with cadaverine at high concentrations, while 1,3-diaminopropane and spermine failed to restore the development. Resumption of growth could be detected when putrescine was added even after 67 h of DFMO treatment. Electron microscopy did not reveal any changes in the morphology of parasites treated for 47 h, while 73 h of treatment with DFMO induced massive accumulation of pigment. Death was observed a few hours later. These results suggest that DFMO acts as a cytostatic rather than as a cytocidal agent. The four carbon diamine restored cell growth while the shorter or the longer homologous compounds showed little activity.

Effect of dietary methionine, arginine and ornithine on the metabolism and accumulation of polyamines, S-adenosylmethionine and macromolecules in rat liver and skeletal muscle

The interrelationship and possible causality of polyamine synthesis and the transmethylation pathway in the growth-retarding effects of inadequate or excess dietary methionine was studied in young male rats. Feeding the rats for 2 weeks diets containing toxic concentrations of methionine had no effect on polyamine and S-adenosylmethionine metabolism in skeletal muscle, but resulted in markedly elevated concentrations of S-adenosylmethionine and S-adenosylhomocysteine and slightly decreased accumulation of spermine and RNA in the liver. These changes were accompanied by liver-specific stimulation of methionine adenosyltransferase and reduction of spermine synthase activities. Inadequate arginine feeding or supplementation of the diets with ornithine or excess arginine resulted in no apparent changes in tissue methionine or polyamine metabolism and did not alleviate the effects of varied dietary methionine supply. Inhibition of putrescine synthesis by supplementing the diets with 2-difluoromethylornithine did not modify the effects of toxic concentrations of dietary methionine. It is suggested that although hepatic spermine synthase is sensitive to excess methionine feeding, methionine toxicity is not mediated by defective polyamine metabolism.

Blood-brain barrier breakdown by cold injury. Polyamine signals mediate acute stimulation of endocytosis, vesicular transport, and microvillus formation in rat cerebral capillaries

Polyamines have been previously implicated in the mediation of blood-brain barrier breakdown induced by cryogenic injury (H Koenig, AD Goldstone, CY Lu, Biochem Biophys Res Commun 116:1039, 1983). We studied acute (less than 5 minute) changes in capillary ultrastructure, microvascular permeability, and the levels of polyamines and their rate regulating synthetic enzyme ornithine decarboxylase (ODC) in rat cerebral cortex after focal cold injury. Microvascular permeability was measured by relative transport of intravenously administered fluorescein. Capillary ultrastructure was studied by quantitative stereology and morphometry after intravenous administration of horseradish peroxidase. Focal cold injury induced a 2.5-, 3.8-, 1.7-, and 1.4-fold increase in the levels of ODC, putrescine, spermidine and spermine, and a 46-fold increase in fluorescein uptake in perilesional cortex. Few capillaries in control cortex contained endocytic pits or horseradish peroxidase-positive vesicles, whereas most capillaries near lesions showed these structures. Cryoinjury induced a 5-fold increase in the relative volume of microvilli and horseradish peroxidase vesicles, a 2.3-fold increase in area of luminal endocytic pits, and a 6.3-fold increase in area of abluminal exocytic pits. The ODC inhibitor alpha-difluoromethylornithine blocked the cryoinjury-induced changes in ODC, polyamines, fluorescein uptake, and capillary ultrastructure. Putrescine negated the effect of alpha-difluoromethylornithine or capillary ultrastructure, and was previously shown to nullify the alpha-difluoromethylornithine effects on polyamines and fluorescein permeability (cited above). These data link rapid changes in ODC and polyamines to blood-brain barrier breakdown, and suggest that the abnormal permeability is associated with an acute, polyamine-mediated stimulation of microvillus formation, endocytosis, and vesicular transport in capillary endothelium.

Comparison and characterization of growth inhibition in L1210 cells by alpha-difluoromethylornithine, an inhibitor of ornithine decarboxylase, and N1,N8-bis(ethyl)spermidine, an apparent regulator of the enzyme

The cellular effects of alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase (ODC), and N1,N8-bis(ethyl)spermidine (BES), an apparent regulator of the enzyme were compared in cultured L1210 cells. Unlike DFMO, BES has no direct inhibitory effect on ODC activity. Rather the polyamine analogue is believed, from previous studies, to behave similarly to exogenous spermidine in its ability to suppress intracellular ODC activity but not in its ability to perform functions required for cell growth. The kinetics and extent of growth inhibition by 30 microM or 100 microM BES and 1 mM DFMO were nearly identical as were their effects on macromolecular precursor incorporation with leucine being the first and most significantly affected. By flow cytometry, neither BES nor DFMO induced obvious perturbations in the cell cycle. Both compounds effectively eliminated ODC activity in treated cells and depleted putrescine and spermidine pools with very similar kinetics of decline. These close similarities in drug effects between BES and DFMO, an established polyamine inhibitor, support previous indications that BES induces growth inhibition by depletion of cellular polyamines. BES differed distinctly from the ODC inhibitor by decreasing spermine pools, and by not increasing S-adenosyl-methionine decarboxylase activity, S-adenosylmethionine pools, or stimulating cellular uptake of polyamines. The data suggest that enzyme regulation by polyamine analogues such as BES represents a viable alternative to enzyme inhibition as an antiproliferative strategy directed at polyamine biosynthesis.

Effect of D,L-2-difluoromethylornithine and endocrine manipulation on the induction of mammary carcinogenesis by 1-methyl-1-nitrosourea

The purpose of this investigation was to establish an efficient route and dose regime for the long-term administration of tamoxifen in the study of mammary tumorigenesis in the rat. The second objective of this work was to determine whether treatment with D,L-2-difluoromethylornithine (DFMO), a synthetic inhibitor of the enzyme ornithine decarboxylase, would reduce the occurrence of mammary cancers in tamoxifen-treated or ovariectomized rats. A total of 265 female Sprague-Dawley rats were assigned to one of two experimental protocols. All animals were injected with 50 mg 1-methyl-1-nitrosourea (MNU) per kg body wt at 50 days of age. In experiment 1, beginning 7 days after the injection of the carcinogen, animals were assigned to one of six groups which received either 0, 1 or 5 mg tamoxifen citrate per kg AIN-76A purified diet in addition to either no DFMO or a 0.125% w/v solution of DFMO as the drinking water. The experiment was terminated 180 days following carcinogen treatment. Treatment with tamoxifen resulted in a dose-dependent reduction in cancer incidence, and the number of cancers induced and significantly prolonged the median cancer-free time. This effect was also accompanied by a decrease in the rate of body weight gain. Treatment with DFMO delayed latency and reduced tumor number. DFMO in addition to tamoxifen (1 mg/kg diet) further prolonged latency. In experiment 2 each animal was assigned to one or four treatment groups when its first palpable mammary tumor was detected. At that time each was either ovariectomized or sham-operated. In addition, the rats were either provided no DFMO or a 0.5% w/v solution of DFMO as the drinking water. The study was terminated 35 weeks following carcinogen injection. Ovariectomy significantly inhibited the occurrence of additional mammary tumors. Ovariectomy plus DFMO was more effective than ovariectomy alone in reducing tumor number. Collectively, these observations indicate that suppression of polyamine biosynthesis via the systemic administration of DFMO inhibits the development of ovarian hormone insensitive mammary tumors.

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.

Heterogeneous survival responses of human gastric cancer clones to alpha difluoromethylornithine in vitro

The effects of alpha Difluoromethylornithine (DFMO)2 on survival of human gastric cancer clones were studied in vitro. The responses were dose and time dependent. Treatments which lasted for less than 12 h were cytotoxic at only the highest doses used. The greatest effects on survival were observed only when cells were treated for 48 and 72 h. The effects on the clones produced by such prolonged treatment durations were heterogeneous, with survival values differing by as much as 460%. By contrast, the clonal survival responses to short DFMO treatments (12 h) were very uniform (dose differential of only 19%); however, this uniformity in response could be achieved only by using non-pharmacological doses of DFMO. The heterogeneity in survival responses in the clones might be slightly associated with their levels of intracellular spermidine. Clones with the smallest amounts of intracellular spermidine at the start of treatment were most sensitive to DFMO. However, this association may not hold up with further testing in other gastric cancer clones or when studied in other cancer lines in vitro.

Comparison of the effects of an ornithine decarboxylase inhibitor on the intestinal epithelium and on intestinal tumors

Ornithine decarboxylase (ODC) catalyzes the rate-limiting step in the synthesis of polyamines, it has a short half-life, and its synthesis is under hormonal control. Recently, insight into the role of ODC and thus into the physiology of polyamines has been gained by the use of an inhibitor of ODC, difluoromethylornithine (DFMO). In the present report cell proliferation was measured by a stathmokinetic method in the crypt epithelium of the jejunum and colon of normal rats and in dimethylhydrazine-induced colonic tumors. Growth of human colon tumor xenografts in immunosuppressed mice and mouse colon tumor isografts was also assessed. Cell proliferation in primary colonic tumors was substantially suppressed by a single dose of DFMO at 100 mg/kg whereas the normal crypt epithelium of the small and large intestine required two doses at 400 mg/kg to produce a similar magnitude of inhibition of cell proliferation. DFMO was also found to suppress cell proliferation in, and the growth of, the transplantable colon cancers. Because of the apparent selectivity of the antimitotic activity of DFMO towards tumors, ODC inhibitors may prove to be useful anticancer drugs.

Relationship between heat sensitivity and polyamine levels after treatment with alpha-difluoromethylornithine (DFMO)

Alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, was used to study the effect of polyamine depletion on delayed heat sensitization in Chinese hamster ovary cells (CHO). The cells were treated with 1 or 10 mM DFMO for 8 or 48 h and then given a single heat treatment (43 degrees C, 90 min) at intervals up to 150 h after DFMO addition. Cellular survival, DNA polymerase activity, and polyamine levels were measured. Delayed heat sensitization for cell lethality began 50-55 h (about two cell divisions) after addition of 10 or 1 mM of DFMO for 8 or 48 h, respectively; i.e., cell survival of heated control cells was about 10(-1), but decreased to 10(-4)-10(-5) in heated DFMO-treated cells by 100 h. During this same interval, delayed heat sensitization also was observed for loss of DNA polymerase beta activity (from 20% in cells heated without DFMO treatment to 7% in heated DFMO-treated cells), but none was observed for DNA polymerase alpha activity. Delayed heat sensitization disappeared at 120-130 h after DFMO addition, with survival of heated DFMO-treated cells returning to that for heated control cells. The onset of delayed heat sensitization occurred 30-40 h after intracellular levels of putrescine and spermidine were depleted by more than 95%; however, spermine levels were not lowered, and in some cases even increased. Levels of putrescine and spermidine increased 5-10 h before delayed heat sensitization disappeared. While putrescine reached 25% of control, spermidine exceeded control levels during this time. Furthermore, delayed heat sensitization could be reversed by adding 10(-3) M putrescine or 5 X 10(-5) M spermidine 85-95 h after DFMO addition; in both cases spermidine increased 5-10 h before the decrease in heat sensitization. Finally, neither delayed heat sensitization nor depletion of spermidine was observed in nondividing plateau-phase cells treated with DFMO, although putrescine was depleted. These results lead to the hypothesis that DFMO-induced heat sensitization which occurs after inhibition of the synthesis of putrescine is secondary to the depletion of spermidine in some critical compartment of the cell or to a biochemical alteration. This depletion or biochemical alteration apparently occurs as the cells divide about two times after the intracellular levels of soluble spermidine have been depleted.

Inhibition of intestinal carcinogenesis in rats: effect of difluoromethylornithine with piroxicam or fish oil

An inhibitor of ornithine decarboxylase, difluoromethylornithine (DFMO), and two inhibitors of prostaglandin biosynthesis, piroxicam and menhaden fish oil, were examined for their effect on intestinal tumorigenesis in male Sprague-Dawley rats fed a 5% fat semisynthetic diet. Each agent was given individually in one of two doses as follows: DFMO, 0.05% and 0.1% in the drinking water; piroxicam, 65 mg/kg diet and 130 mg/kg diet; and menhaden fish oil, 1.25% and 2.50% of the diet. Additional animal groups were given combinations of the lower dose of DFMO and the lower dose of either piroxicam or fish oil. Intestinal tumors were induced by sc injections of azoxymethane (AOM; CAS: 25843-45-2) at 8 mg/kg (body wt) weekly for 8 weeks. Test diets were started 1 week prior to the first dose of AOM, and the rats were sacrificed 26 weeks later. Rats that received either dose of DFMO or the high dose of piroxicam developed significantly fewer intestinal tumors compared to controls. The low dose of piroxicam and the fish oil given at either dose level had no effect. The combination of the low dose of DFMO and the low dose of piroxicam reduced tumor formation more than either dose of DFMO alone, whereas the low dose of DFMO and fish oil together was no more effective than either dose of DFMO alone. These results show that a combination of a small amount of DFMO and piroxicam, each acting through a different mechanism, exerts an additive inhibitory effect on intestinal tumor formation in rats.

[Combined efficacy of polyamine antimetabolites and cis-diamminedichloroplatinum]

The combined antitumor effects of the polyamine antimetabolites, alpha-difluoro methylornithine (DFMO) and methylglyoxal-bis-guanylhydrazone (MGBG), with CDDP were studied using human gastric cancer cells xenotransplanted into nude mice. DFMO (1000 mg/kg in two divided doses) and MGBG (50 mg/kg) were given IP for six consecutive days from the time when the xenotransplanted tumor weighted about 100 mg, and CDDP (3.0 mg/kg) was given IP every other day from the same time. Animals treated with DFMO plus MGBG with or without CDDP as well as with CDDP only displayed suppressed tumor growth, compared to untreated mice. In mice treated with these three drugs, however, tumor growth was rather rapid compared to those treated with CDDP only, although tumoral CDDP levels in animals given DFMO, MGBG and CDDP were higher than those given CDDP only. When DFMO, MGBG and CDDP or DFMO and MGBG were administered, tumoral spermidine and spermine levels decreased markedly. On the other hand, tumor DNA biosynthesis in the CDDP only group dropped markedly 24 hours after the termination of therapy. These results suggest that an alteration in the DNA structure caused by polyamine deficiency may prevent cross-link formation in DNA by CDDP.

Effect of inhibitors of ornithine decarboxylase on retrovirus induced transformation of murine erythroid precursors in vitro

alpha-Difluoromethylornithine (DFMO) and methyl acetylene putrescine (MAP) are inhibitors of the rate limiting enzyme in polyamine synthesis, ornithine decarboxylase. We studied the effects of these compounds on the formation of retrovirus transformed erythroid colonies. DFMO was able to effectively reduce the number of transformed colonies at a concentration of 10(-3) M, whereas MAP achieved total inhibition at 10(-4) M. Putrescine, the product of ornithine decarboxylase, did not alter colony number by itself but it was able to overcome the inhibitory effects of both DFMO and MAP. Addition of DFMO at times after the initiation of culture decreased its effectiveness in reducing transformed colony numbers, while the converse was true for the erythroid stimulant, erythropoietin. We concluded from these data that DFMO and MAP probably diminished colony formation by inhibiting proliferation of the target cells for the retroviruses.

Effect of polyamine depletion in vivo by DL-alpha-difluoromethylornithine on functionally distinct populations of tumoricidal effector cells in normal and tumor-bearing mice

The objective of the present investigation was to examine the effect of in vivo polyamine depletion by DL-alpha-difluoromethylornithine (DFMO), a specific irreversible inhibitor of ornithine decarboxylase, on cell-mediated tumoricidal activity in normal and tumor-bearing (B16 melanoma) mice. DFMO treatment in vivo for 6 days reduced splenic leukocyte polyamine levels and the induction of cytotoxic T-lymphocytes (greater than 50%) in both normal and tumor-bearing mice. However, substantially less inhibition was observed in the ability to generate cytotoxic T-lymphocytes following 18 days of DFMO treatment. In contrast, DFMO treatment for 6 or 18 days did not impair splenic natural cell-mediated cytotoxicity, assessed against natural killer sensitive YAC-1 target cells and natural cytotoxic sensitive WEHI-164 target cells, in normal or tumor-bearing mice. Natural cell-mediated cytotoxicity was not observed against fresh B16 melanoma cells. However, macrophage-mediated tumoricidal activity directed against B16 melanoma cells was augmented 79% following 6 but not 18 days of DFMO treatment. These results demonstrate that DFMO can exert very selective effects on functionally distinct populations of antitumor effector cells in vivo depending upon the schedule of DFMO administration.

Role of ornithine decarboxylase and polyamines in early postnatal lung growth

We assessed the importance of ornithine decarboxylase (ODC) and polyamines in early postnatal lung growth. Lung-ODC activity in newborn rats rose rapidly after birth and was highest at 4-6 days of age. Lung putrescine and spermidine specific contents also peaked during this period, but spermine specific content remained relatively unchanged. The temporal pattern of these changes differed markedly from that in the heart, brain, and kidney where ODC activity is highest at birth then rapidly declines. The period of peak lung-ODC activity and polyamine specific content correlated with rapid increases in lung DNA content, protein content, and weight. The specific irreversible ODC inhibitor, alpha-difluoromethylornithine, significantly reduced lung-ODC activity and putrescine and spermidine specific content; it also caused significant early reductions in lung DNA and protein content without simultaneously affecting body weight and appearance. Morphometrically, the lungs of alpha-difluoromethylornithine-treated rats had significantly fewer type 2 epithelial cells, interstitial cells, and capillary endothelial cells than the lungs of controls. We conclude that ODC and polyamines play an important role in postnatal lung growth and that alpha-difluoromethylornithine can be used as a probe to disrupt lung growth.

Effects of DL-alpha-difluoromethylornithine on Leishmania donovani promastigotes

Alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, has been demonstrated to be an effective agent against a variety of parasitic protozoa but not against Leishmania spp. In this report, we show that Leishmania donovani promastigotes in continuous culture are sensitive to the growth inhibitory and cytotoxic effects of DFMO. Incubation of the promastigotes with DFMO obliterates intracellular putrescine pools and depletes spermidine concentrations, which correlates with the onset of growth inhibition. The effects of DFMO on the growth and the intracellular polyamine pools can be reversed completely by the addition of 10 microM putrescine to the culture medium. These results suggest that the treatment of leishmaniasis may be amenable to chemotherapeutic manipulation by DFMO.

Polyamines and autocrine control of tumor growth by prolactin in experimental breast cancer in culture

We have previously observed that both polyamines and an autocrine mechanism are involved in the stimulation by ovine PRL (oPRL) of growth of the N-nitrosomethylurea-induced rat mammary tumor cultured in vitro in the soft agar clonogenic assay. These experiments were designed to test the interaction between these two pathways of oPRL action in this system. In agreement with previous findings in our laboratory, conditioned medium obtained from oPRL-treated (oPRL-CM), but not untreated, tumors consistently stimulated colony formation when added to N-nitrosomethylurea mammary tumors plated in soft agar under serum-free medium conditions. Administration of alpha-difluoromethyl-ornithine (DFMO), an irreversible inhibitor of polyamine biosynthesis, abolished the colony-stimulating effect of oPRL-CM. The inhibitory effect of DFMO was reversed in a dose-dependent fashion by the addition of spermidine, which entirely restored the growth-promoting action of oPRL-CM. In addition, the administration of increasing amounts of spermidine potentiated the colony-stimulating effect of suboptimal concentrations of oPRL-CM. In contrast, manipulation of the polyamine environment with DFMO and/or spermidine administration did not affect the number of colonies formed when conditioned medium from untreated tumors was added instead of oPRL-CM. We conclude that the polyamine pathways plays an essential role in the expression of autocrine control of tumor growth by oPRL.

Inhibition of polyamine biosynthesis by alpha-difluoromethylornithine in African trypanosomes and Pneumocystis carinii as a basis of chemotherapy: biochemical and clinical aspects

The symposium provided dramatic evidence of the value of the use of polyamine inhibition via alpha-difluoromethylornithine (DFMO, eflornithine) for advances in chemotherapy of Trypanosoma brucei gambiense sleeping sickness and Pneumocystis carinii pneumonia in acquired immune deficiency syndrome (AIDS) and also for further understanding the metabolic importance of the ubiquitous polyamines in these organisms.

Increased content of mRNA for a precursor of S-adenosylmethionine decarboxylase in rat prostate after treatment with 2-difluoromethylornithine

Total poly(A)-containing mRNA was isolated from rat ventral prostate and translated in a reticulocyte lysate system. The proteins corresponding to S-adenosylmethionine decarboxylase were precipitated with a specific antiserum to this protein. Two proteins were found; one having an Mr of 32,000, which corresponded to the subunit of this enzyme, and a larger protein of Mr 37,000. Immunopurification of polysomes with the antiserum to S-adenosylmethionine decarboxylase followed by mRNA extraction yielded an mRNA preparation which was 10-30% pure mRNA for S-adenosylmethionine decarboxylase. The translation of this mRNA showed clearly that the protein of Mr 37,000 was a precursor of the Mr 32,000 S-adenosylmethionine decarboxylase subunit. Treatment with 2-difluoromethylornithine, which depletes cellular spermidine and is known to increase the content of S-adenosylmethionine decarboxylase protein, led to a 9-fold increase in the content of its mRNA, but treatment with methylglyoxal bis(guanylhydrazone) did not change the mRNA content.

Post-translational modification of the protein-synthesis initiation factor eIF-4D by spermidine in rat hepatoma cells

The rates of synthesis and turnover of the rare amino acid hypusine [N6-(4-amino-2-hydroxybutyl)-2,6-diaminohexanoic acid] in protein were studied in relationship to polyamine metabolism and growth rates in rat hepatoma tissue-culture (HTC) cells. Hypusine is selectively formed in the eukaryotic translation initiation factor eIF-4D, by a post-translational mechanism involving spermidine [Cooper, Park, Folk, Safer & Braverman (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 1854-1857]. The half-life of the hypusine-containing protein was longer than 24 h. In cells whose intracellular spermidine pools had been initially depleted, by using DL-alpha-difluoromethylornithine (DFMO), maximum synthesis rates of hypusine in protein were 5-10 times higher, on restoration of endogenous spermidine contents by exogenous addition, than those observed in untreated exponential-phase cultures. In cells pretreated with DFMO, the rate of hypusine synthesis was constant for up to 1 h after the addition of 5 microM-spermidine, whereas endogenous spermidine contents varied from less than 1 to more than 10 nmol/mg of protein. However, the overall amount of hypusine formed, during the first 1 h after the addition of various concentrations of spermidine (0.05-10 microM) to the culture medium, was markedly dependent on the final endogenous spermidine content achieved at the end of the 1 h measurement interval. Early in exponential-phase growth, protein-bound hypusine was synthesized at a rate of 1-2 pmol/h per mg of protein. This rate decreased to less than 0.5 pmol/h per mg of protein when cell growth rates decreased as cultures reached high cell densities. Analysis of the polyamine substrate specificity for hypusine formation showed that N1-acetylspermidine did not compete with spermidine in the reaction, nor did N1-(buta-2,3-dienyl)-N2-methylbutane-1,4-diamine, and irreversible inhibitor of polyamine oxidase, block the reaction. On the basis of comparative radiolabelling experiments, spermine was either a poor substrate, or not a substrate, for hypusine formation. These results confirm that spermidine is the likely precursor of the aminohydroxybutyl moiety of hypusine, and show that overall hypusine formation, but not necessarily the synthesis rate, is dependent on the endogenous spermidine concentration, especially under conditions where spermidine concentrations are initially low, as is the case after DFMO treatment, and then increase.

alpha-Difluoromethylornithine induces differentiation of a human embryonal carcinoma cell line in vitro

Human embryonal carcinoma cells could serve as a useful model system for analysis of early human development. A limited number of human embryonal carcinoma cell lines have been generated from in vivo tumors. We report here that alpha-difluoromethylornithine, a specific enzyme-activated inhibitor of ornithine decarboxylase activity, can induce differentiation in human embryonal carcinoma cells. The differentiated phenotype could be distinguished from undifferentiated cells by altered cellular morphology, biochemical and cell surface antigenic properties. These results suggest that alterations in the intracellular levels of polyamines may play a role in human embryonal carcinoma cell differentiation, and possibly human embryogenesis.

Hormonal regulation of postprandial induction of gastrointestinal ornithine decarboxylase activity

The growth of gastrointestinal mucosa can be related to ingestion and digestion of diet, with fasting producing mucosal hypoplasia and hyperphagia producing mucosal hyperplasia. Experiments were designed to determine whether induction of polyamine metabolism following ingestion of a meal was related to mucosal growth. Activity of the enzyme ornithine decarboxylase (ODC) in both jejunum and ileum but not in duodenum was dependent on the presence of food in the gut; ODC activity was more than 200-fold greater in mucosa of fed rats than in fasted rats. Inhibition of ODC with difluoromethylornithine lead to mucosal atrophy in ileum but not in duodenum. Refeeding of fasted rats resulted in significant induction of ODC in duodenal, ileal, and colonic, but not fundic, mucosa. In addition, two hormones, epidermal growth factor and glucagon, were effective inducers of ileal ODC activity. Direct evidence for hormonal involvement in the postprandial rise in mucosal ODC activity was provided by experiments in rats that had undergone ileal bypass surgery. After refeeding of fasted rats mucosal ODC activity was induced in both ileum left in continuity and in the bypassed segment. Refeeding of elemental diets demonstrated that ingestion of carbohydrate alone was sufficient for maximal enzyme induction. Mixed amino acids or glyceryl trioleate were no more effective inducers than nonnutritive solutions of cellulose or saccharin. These data demonstrate that hormones which are released during ingestion and digestion of a meal are the stimuli for induction of mucosal polyamine metabolism, suggesting that food-induced mucosal growth is hormonally mediated.

Critical development periods for inhibition of ornithine decarboxylase by alpha-difluoromethylornithine: effects on ontogeny of sensorimotor behavior

The roles of ornithine decarboxylase and the polyamines in behavioral development were examined through the use of alpha-difluoromethylornithine, a specific irreversible inhibitor of ornithine decarboxylase. alpha-Difluoromethylornithine was administered either prenatally during gestation (days 15-17) or postnatally (days 1-20) to examine critical periods of sensitivity. Prenatal alpha-difluoromethylornithine administration resulted in a deficit in early sensorimotor ontogeny: latencies in surface righting reflex (postnatal days 1-5) and negative geotaxis (postnatal days 5-8) were prolonged, and time spent pivoting (postnatal days 7, 9, and 11) was reduced. In contrast, postnatal alpha-difluoromethylornithine primarily influenced later maturing, complex integrative behaviors such as swimming and open field activity. Thus, the behavioral effects of alpha-difluoromethylornithine exposure are highly dependent upon the age at which the drug is administered, a finding in keeping with the participation of the ornithine decarboxylase/polyamine system in cell replication and differentiation during discrete periods of neural development. The behavioral consequences of ornithine decarboxylase inhibition during these critical periods are thus related primarily both to the timetable for cellular maturation in each brain region.

Effects of human interferon and alpha-difluoromethylornithine on T47D cells

The effect of human interferon (IFN) and alpha-difluoromethylornithine (DFMO), an enzyme-activated irreversible inhibitor of eukaryotic ornithine decarboxylase, on the rate of DNA synthesis and the increase of ornithine decarboxylase activity of T47D cells was examined. It was found that IFN or DFMO alone causes little or appreciable inhibition of the [3H]thymidine incorporation, respectively. Each of the drugs alone has a significant inhibitory effect on ornithine decarboxylase activity. Combination of the two drugs has a synergistic effect and eliminates completely the [3H]thymidine incorporation and the activity of ornithine decarboxylase. The biological implication of IFN and DFMO is discussed with regard to the regulation of ornithine decarboxylase activity and the antiproliferative effects of the two drugs.

A novel mechanism of resistance to alpha-difluoromethylornithine induced by cycloheximide. Growth with abnormally low levels of putrescine and spermidine

Treatment of the chemically transformed fibroblasts BP-A31 and other cell lines with low concentrations of cycloheximide (CHM) for 72 h followed by the removal of the protein synthesis inhibitor leads to the proliferation of alpha-difluoromethylornithine (DFMO)-resistant phenotypes. These drug-resistant cells contain almost no ornithine decarboxylase (ODC) activity and concomitantly very low levels of putrescine and spermidine. Southern blot analysis and measurements of ODC activity and intracellular polyamine levels showed that the described mechanism of inducing resistance to DFMO triggered by CHM does not involve ODC gene amplification, altered transport of the drug or reduced affinity of the enzyme for DFMO.

Haematological cell proliferation and differentiation responses to perturbations of polyamine biosynthesis

Combined administration of methylglyoxal-bis-guanylhydrazone (MGBG) (25 mg/kg) with difluoromethylornithine (DFMO), or MGBG alone at a higher dose (50 mg/kg), to mice resulted in a decreased white cell count (WBC) in the peripheral blood while DFMO or MGBG alone at a lower dose (25 mg/kg) had no effect. As expected, DFMO alone increased the number of colony forming units spleen (CFU-s), colony forming units diffusion chamber granulocyte (CFU-dg) and colony forming units culture (CFU-c) in the bone marrow. MGBG treatment led to an increase in CFU-dg alone. Combined treatment seemingly had no effect on marrow stem cells. Total tibial and differential counts were not affected by any of the treatments. Cell proliferation in diffusion chamber cultures, as judged by CFU-dg colony formation, was impaired by MGBG alone or in combination with DFMO, at dose levels which had no effect or increased the precursor cell number in the bone marrow. This effect was partially reversed with either putrescine or spermidine. Determination of intracellular polyamine concentrations, demonstrated decreased putrescine and spermidine levels after DFMO administration. As expected, MGBG treatment resulted in decreased spermidine and spermine levels, concomitant with an increase in putrescine. In mice which received both agents, rather than only MGBG, after 3 days higher intracellular polyamine concentrations were observed. After 11 days, however, there was no significant difference between the two groups.