Ethylglyoxal bis(guanylhydrazone) as an inhibitor of polyamine biosynthesis in L1210 leukemia cells

Ethylglyoxal bis(guanylhydrazone), a close derivative of the known anti-cancer drug methylglyoxal bis(guanylhydrazone), is also a powerful inhibitor of S-adenosylmethionine decarboxylase (EC 4.1.1.50), the enzyme needed for the synthesis of spermidine and spermine. There were, however, marked differences between the ethyl and methyl derivatives of glyoxal bis(guanylhydrazone) when tested in cultured L1210 cells. The cellular accumulation of ethylglyoxal bis(guanylhydrazone) represented only a fraction (20-25%) of that of the methyl derivative. Moreover, polyamine depletion, which is known to strikingly stimulate the uptake of methylglyoxal bis(guanylhydrazone), decreased, if anything, the uptake of ethylglyoxal bis(guanylhydrazone) by L1210 cells. The compound produced spermidine and spermine depletion fully comparable to that achieved with methylglyoxal bis(guanylhydrazone) at micromolar concentrations. Ethylglyoxal bis(guanylhydrazone) was growth-inhibitory to L1210 cells and produced an additive antiproliferative action when used together with 2-difluoromethylornithine. Ethylglyoxal bis(guanylhydrazone) was distinctly less effective than methylglyoxal bis(guanylhydrazone) in releasing bound polyamines from isolated cell organelles in vitro. Ethylglyoxal bis(guanylhydrazone) was also devoid of the early and profound mitochondrial toxicity typical to methylglyoxal bis(guanylhydrazone). These findings may indicate that this compound is a more specific inhibitor of polyamine biosynthesis with less intracellular polyamine 'receptor-site' activity than methylglyoxal bis(guanylhydrazone).     

Insensitivity of cardiac phosphofructokinase to adrenergic activation in Zucker rats. A post-receptor defect.

Glyoxal bis(guanylhydrazone), the parent compound of methylglyoxal bis(guanylhydrazone), was synthesized and tested for its ability to inhibit the biosynthesis of polyamines. It was found to be a powerful competitive inhibitor of adenosylmethionine decarboxylase (EC 4.1.1.50), yet the lack of the methyl group at the glyoxal portion increased the apparent Ki value for the enzyme by about 30-fold in comparison with methylglyoxal bis(guanylhydrazone). Glyoxal bis(guanylhydrazone) inhibited diamine oxidase (EC 1.4.3.6) activity as effectively as did methylglyoxal bis(guanylhydrazone). The cellular accumulation curves of glyoxal bis(guanylhydrazone) in L1210 cells were practically superimposable with those of methylglyoxal bis(guanylhydrazone), and the uptake of both compounds was distinctly stimulated by a prior treatment with 2-difluoromethylornithine. The drug decreased the concentration of spermidine in a dose-dependent manner and, in contrast with methylglyoxal bis(guanylhydrazone), without a concomitant accumulation of putrescine. The fact that putrescine concentrations were decreased in cells exposed to glyoxal bis(guanylhydrazone) was, at least in part, attributable to an inhibition of ornithine decarboxylase (EC 4.1.1.17) activity in cells treated with the compound. Under these experimental conditions equivalent concentrations of methylglyoxal bis(guanylhydrazone) [1,1'-[(methylethanediylidine)dinitrilo]diguanidine] elicited large increases in the enzyme activity. When combined with difluoromethylornithine, glyoxal bis(guanylhydrazone) potentiated the growth-inhibitory effect of that drug. Taking into consideration the proven anti-leukaemic activity of glyoxal bis(guanylhydrazone), its effectiveness to inhibit spermidine biosynthesis (without raising the concentration of putrescine) as well as its suitability for combined use with inhibitors of ornithine decarboxylase, this drug is apparently worthy of further testing in tumour-bearing animals, especially in combination with difluoromethylornithine or related inhibitors of ornithine decarboxylase.     

Effect of methylglyoxal bis(guanylhydrazone) on polyamine metabolism in normal and regenerating rat liver and rat thymus

1. Injections of sublethal doses of methylglyoxal bis(guanylhydrazone), a potent inhibitor of putrescine-activated S-adenosylmethionine decarboxylase in vitro, resulted after a few days in an immense increase in the activity of S-adenosylmethionine decarboxylase in normal and regenerating rat liver and in rat thymus. The increase in the activity of S-adenosylmethionine decarboxylase was at least partly due to a marked lengthening of the half-life of the enzyme. 2. In regenerating liver and thymus there was also a moderate stimulation of the activity of ornithine decarboxylase (EC 4.1.1.17) and a marked accumulation of tissue putrescine. 3. Injection of methylglyoxal bis(guanylhydrazone) into the rat also markedly decreased the activity of diamine oxidase (EC 1.4.3.6) in thymus. 4. In no cases where doses of methylglyoxal bis(guanylhydrazone) close to the LD(50) dose for the rat were used was it possible to lower tissue spermidine content to any significant extent. 5. Methylglyoxal bis(guanylhydrazone) seemed to act as a competitive inhibitor for the substrate S-adenosylmethionine and as an uncompetitive inhibitor for the activator putrescine in the decarboxylation of S-adenosylmethionine in vitro. 6. In the diamine oxidase reaction, with putrescine as the substrate, methylglyoxal bis(guanylhydrazone) was a non-competitive inhibitor for putrescine.     

Transfer of intestine-derived diamines into tumour cells during treatment of Ehrlich-ascites--carcinoma-bearing mice with polyamine anti-metabolites.

Treatment of Ehrlich-ascites-carcinoma-bearing mice with methylglyoxal bis(guanylhydrazone) alone or in combination with 2-difluoromethylornithine greatly enhanced the transfer of intragastrically administered radioactive putrescine and cadaverine into the carcinoma cells. Difluoromethylornithine alone did not have any effect on the accumulation of intestine-derived diamines in the tumour cells. The frequently reported restoration of difluoromethylornithine-induced polyamine depletion on administration of methylglyoxal bis(guanylhydrazone) is in all likelihood attributable to a profound inhibition of intestinal diamine oxidase (EC 1.4.3.6), resulting in an enhanced entry of intestinal (bacterial) diamines into general circulation and finally into tumour cells.     

Effects of phenylated compounds of methylglyoxal bis(guanylhydrazone) on diamine oxidase activity from rat small intestine

Two phenylated compounds of methylglyoxal bis(guanylhydrazone), potentially inhibitors of diamine oxidase activity, have been synthesized: phenylglyoxal bis(guanylhydrazone) and diphenylglyoxal bis(guanylhydrazone). Their inhibitory capacity was tested: while PGBG was able to reduce the enzyme activity by 50% at 1.3 microM, DPGBG was only able to reduce diamine oxidase activity by less than 2% at a concentration 1000-fold higher. The inhibition of PGBG was non-competitive and the Ki calculated by a Dixon plot was estimated as 1.7 microM.     

Characterization of the ATP-G-actin aggregates formed at low potassium chloride concentration.

Three bis(guanylhydrazones) (those of methylglyoxal, glyoxal and ethylglyoxal) were compared for their affinity for the putative polyamine carrier and for their cellular retention in L1210 mouse leukaemia cells. All the bis(guanylhydrazones) inhibited equally effectively the uptake of spermidine by the tumour cells, indicating that the compounds had roughly equal affinity for the polyamine carrier. The fact that methylglyoxal bis(guanylhydrazone) and glyoxal bis(guanylhydrazone) were much more effectively concentrated in the animal cells than was ethylglyoxal bis(guanylhydrazone) was obviously attributable to the finding that the efflux rate of ethylglyoxal bis(guanylhydrazone) greatly exceeded that of the other bis(guanylhydrazones). The rate of efflux of the drugs was slowed down if the tumour cells were treated with 2-difluoromethylornithine before exposure to the bis(guanylhydrazones). These results suggest that intracellular binding of the bis(guanylhydrazones) determines their cellular accumulation.     

Role of diamine oxidase during the treatment of tumour-bearing mice with combinations of polyamine anti-metabolites.

Treatment of mice bearing L1210 leukaemia with 2-difluoromethylornithine, a specific inhibitor of ornithine decarboxylase (EC 4.1.1.17), produced a profound depletion of putrescine and spermidine in the tumour cells. Sequential combination of methylglyoxal bis(guanylhydrazone), an inhibitor of adenosylmethionine decarboxylase (EC 4.1.1.50), with difluoromethylornithine largely reversed the polyamine depletion and led to a marked accumulation of cadaverine in the tumour cells. Experiments carried out with the combination of difluoromethylornithine and aminoguanidine, a potent inhibitor of diamine oxidase (EC 1.4.3.6), indicated that the methylglyoxal bis(guanylhydrazone)-induced reversal of polyamine depletion was mediated by the known inhibition of diamine oxidase by the diguanidine. In spite of the normalization of the tumour cell polyamine pattern upon administration of methylglyoxal bis(guanylhydrazone) to difluoromethylornithine-treated animals, the combination of these two drugs produced a growth-inhibitory effect not achievable with either of the compounds alone.     

Effects of polyamines and methylglyoxal bis(guanylhydrazone) on hepatic nuclear structure and deoxyribonucleic acid template activity.

1. The interaction of polyamines and methylglyoxal bis(guanythydrazone) (1, 1'-[(methylethanediylidene)-dinitrilo]diguanidine) with isolated rat liver nuclei was investigated by electron microscopy. 2. At 4mM, putrescine was without effect; however, spermidine, spermine or methylglyoxal bis(guanythydrazone) resulted in dispersed chromatin and alterations in nucleolar structure. In addition, spermidine or methylglyoxal bis(guanylhydrazone) caused marked aggregation of interchromatin granules. 3. The DNA template property of calf thymus DNA was examined by using DNA polymerases from Escherichia coli, Micrococcus lysodeikticus and calf thymus in the presence of 0-5 mM-amine. 4. In the presence of DNA polymerase, spermine or methylglyoxal bis(guanylhydrazone) inhibited activity, whereas putrescine or spermidine had much less effect or in some cases stimulated [3H]dTMP incorporation. 5. Template activity which was inhibited by spermine or methylglyoxal bis(guanylhydrazone) could be partially restored by additional DNA or enzyme. 6. When mixed with calf thymus DNA, calf thymus histone inhibited template activity as measured with E. coli DNA polymerase. The template activity of such a 'histone-nucleate' could not be restored by putrescine, spermidine, spermine or methylglyoxal bis(guanylhydrazone). 7. DNA template activity of isolated rat liver nuclei was tested by using E. coli DNA polymerase. None of the amines was able to increase the template activity of the nuclear DNA in vitro.     

Induction of spermidine/spermine N1-acetyltransferase by methylglyoxal bis(guanylhydrazone)

The anti-tumor agent methylglyoxal bis(guanylhydrazone) was found to be a competitive inhibitor of spermidine/spermine N1-acetyltransferase with a Ki of about 8 microM. Treatment of rats with this drug lead to a very large increase in the total amount of spermidine/spermine N1-acetyltransferase in liver, kidney and spleen. The total increase as measured using a specific antiserum amounted to 700-fold in liver and 100-fold in kidney within 18 h of treatment with 80 mg/kg doses. At least part of this induction was due to a pronounced increase in the half-life of the acetyltransferase which increased from 15 min to more than 12 h. The very large increase in the amount of the enzyme is likely to overwhelm the direct inhibition, and a net increase in the acetylation of polyamines by this enzyme would be expected to occur after treatment with methylglyoxal bis(guanylhydrazone). The acetylated polyamines are known to be rapidly degraded by polyamine oxidase producing putrescine. Direct evidence that a substantial part of the increase in the content of putrescine in the liver of rats treated with methylglyoxal bis(guanylhydrazone) occurs via the induction of this acetylase/oxidase pathway was obtained. These results indicate that methylglyoxal bis(guanylhydrazone) affects cellular polyamine levels not only by means of its inhibitory effect on S-adenosylmethionine decarboxylase and diamine oxidase but also by the induction of spermidine/spermine N1-acetyltransferase. They also raise the possibility that the enormous increase in this enzyme which occurs with higher doses may contribute to the very severe toxicity of methylglyoxal bis(guanylhydrazone).     

Differential effects of 2-difluoromethylornithine and methylglyoxal bis(guanylhydrazone) on the testosterone-induced growth of ventral prostate and seminal vesicles of castrated rats

2-Difluoromethylornithine totally prevented any increases in putrescine and spermidine concentrations in the ventral prostate of castrated rats during a 6-day testosterone treatment. Prostatic ornithine decarboxylase activity was inhibited by 80%, whereas S-adenosylmethionine decarboxylase was stimulated by more than 9-fold. In seminal vesicle, the inhibition of putrescine and spermidine accumulation, as well as of ornithine decarboxylase activity, was only minimal, and no stimulation of S-adenosylmethionine decarboxylase was observed. Administration of methylglyoxal bis(guanylhydrazone) to castrated androgen-treated rats resulted in a marked increase in concentrations of all prostatic polyamines. Prostatic ornithine decarboxylase activity was nearly 2 times and adenosylmethionine decarboxylase activity 9 times higher than that of the testosterone-treated animals. In contrast with ventral prostate, methylglyoxal bis(guanylhydrazone) treatment inhibited moderately the accumulation of spermidine and spermine in seminal vesicle, although both ornithine decarboxylase and S-adenosylmethionine decarboxylase activities were stimulated. Difluoromethylornithine inhibited significantly the weight gain of ventral prostate, but methylglyoxal bis(guanylhydrazone) produced a substantial increase in prostatic weight. These changes were largely due to the fact that the volume of prostatic secretion was greatly decreased by difluoromethylornithine, whereas methylglyoxal bis(guanylhydrazone) increased the amount of secretion. Treatment with difluoromethylornithine strikingly increased the methylglyoxal bis(guanylhydrazone) content of both ventral prostate and seminal vesicle, but even under these conditions the drug concentration remained low in comparison with other tissues. The results indicate that a combined use of these two polyamine anti-metabolites does not necessarily result in a synergistic growth inhibition of the androgen-induced growth of male accessory sexual glands.     

Polyamine metabolism in the kidneys of castrated and testosterone-treated mice after administration of methylglyoxal bis(guanylhydrazone)

The effects of methylglyoxal bis(guanylhydrazone) on $\text{S-}\text{adenosyl}\text{-}\text{l}\text{-}\text{methionine}$ decarboxylase (EC 4.1.1.50) activity were studied in the mouse kidney stimulated to growth by testosterone administration. The drug was found to be a potent inhibitor of the enzyme in vitro. Administration of methylglyoxal bis(guanylhydrazone) in vivo resulted in a transient inhibition followed by a strong enhancement of the enzyme activity. Dialysis of the kidney extract, to remove remaining methylglyoxal bis(guanylhydrazone), revealed a great and rapid increase in the activity of $\text{S-}\text{adenosyl}\text{-}\text{l}\text{-}\text{methionine}$ decarboxylase. Injections of testosterone to castrated mice resulted in a marked increase in kidney weight and an accumulation of renal putrescine, spermidine and spermine. These effects of testosterone could not be blocked by simultaneous injections of methylglyoxal bis(guanylhydrazone). It appears that due to secondary effects by which the inhibition of methylglyoxal bis(guanylhydrazone) on $\text{S-}\text{adenosyl}\text{-}\text{l}\text{-}\text{methionine}$ decarboxylase activity is circumvented the inhibitor seems to be of uncertain value in attempts to decrease selectively the in vivo levels of polyamines.     

Regulation of spermidine/spermine N1-acetyltransferase in L6 cells by polyamines and related compounds.

Exposure of rat L6 cells in culture to exogenous polyamines led to a very large increase in the activity of spermidine/spermine N1-acetyltransferase. Spermine was more potent than spermidine in bringing about this increase, but in both cases the elevated acetyltransferase activity increased the cellular conversion of spermidine into putrescine. The N1-acetyltransferase turned over very rapidly in the L6 cells, with a half-life of 9 min after spermidine and 18 min after spermine. A wide variety of synthetic polyamine analogues also brought about a substantial induction of spermidine/spermine N1-acetyltransferase activity. These included sym-norspermidine, sym-norspermine, sym-homospermidine, N4-substituted spermidine derivatives, 1,3,6-triaminohexane, 1,4,7-triaminoheptane and deoxyspergualin, which were comparable with spermidine in their potency, and N1N8-bis(ethyl)spermidine, N1N9-bis(ethyl)homospermidine, methylglyoxal bis(guanylhydrazone), ethylglyoxal bis(guanylhydrazone) and 1,1'-[(methylethanediylidene)dinitrilo]bis(3-amino-guanidine ), which were even more active than spermidine. It is suggested that these polyamine analogues may bring about a decrease in cellular polyamines not only by inhibiting biosynthesis but by stimulating the degradation of spermidine into putrescine.     

Putrescine-sensitive (artifactual) and insensitive (biosynthetic) S-adenosyl-L-methionine decarboxylase activities of Lathyrus sativus seedlings.

The crude extracts of 3-day-old etiolated seedlings of Lathyrus sativus contained two S-adenosyl-L-methionine decarboxylase activities. The artifactual putrescine-dependent activity was due to the H2O2 generated by diamine oxidase (EC 1.4.3.6) of this plant system and was inhibited by catalase. This observation was confirmed by using an electrophoretically and immunologically homogeneous preparation of L. sativus diamine oxidase. In the presence of putrescine, diamine oxidase, in addition to S-adenosylmethionine, decarboxylated L-lysine, L-arginine, L-ornithine, L-methionine and L-glutamic acid to varying degrees. The decarboxylation was not metal-ion dependent. The biosynthetic S-adenosylmethionine decarboxylase (EC 4.1.1.21) was detected after removing diamine oxidase specifically from the crude extracts by employing an immunoaffinity column. This Mg2+-dependent decarboxylase was not stimulated by putrescine or inhibited by catalase. The enzyme activity was inhibited by semicarbazide, 4-bromo-3-hydroxybenzoylamine dihydrogen phosphate and methylglyoxal-bis (guanylhydrazone). It was largely localized in the shoots of the etiolated seedlings and was purified 40-fold by employing a p-hydroxymercuribenzoate/AH-Sepharose affinity column, which also separated the decarboxylase activity from spermidine synthase.     

Characterization of lipid-protein interactions in acetylcholinesterase lipoprotein extracted from bovine erythrocytes.

1. The activation of human peripheral blood lymphocytes by phytohaemagglutinin in vitro was accompanied by striking increases in the concentrations of the natural polyamines putrescine, spermidine and spermine. 2. The enhanced accumulation of polyamines could be almost totally abolished by dl-alpha-difluoromethylornithine, a newly discovered irreversible inhibitor of l-ornithine decarboxylase (EC 4.1.1.17), or by methylglyoxal bis(guanylhydrazone) {1,1'-[(methylethanediylidene)dinitrilo]diguanidine}, an inhibitor of S-adenosyl-l-methionine decarboxylase (EC 4.1.1.50). The inhibition of polyamine accumulation was associated with a marked suppression of DNA synthesis, which was partially or totally reversed by low concentrations of exogenous putrescine, spermidine, spermine and cadaverine and by higher concentrations of 1,3-diaminopropane. 3. In contrast with some earlier studies, we found that methylglyoxal bis(guanylhydrazone), at concentrations that were sufficient to prevent polyamine accumulation, also caused a clear inhibition of protein synthesis in the activated lymphocytes. Similar results were obtained with difluoromethylornithine. The decrease in protein synthesis caused by both compounds preceded the impairment of DNA synthesis. The inhibition of protein synthesis by difluoromethylornithine was fully reversed by exogenous putrescine, spermidine and spermine, and that caused by methylglyoxal bis(guanylhydrazone) by spermidine and spermine. In further support of the idea that the inhibition of protein synthesis by these compounds was related to the polyamine depletion, we found that difluoromethylornithine caused a dose-dependent decrease in the incorporation of [(14)C]leucine into lymphocyte proteins which closely correlated with the decreased concentrations of cellular spermidine. 4. Difluoromethylornithine and methylglyoxal bis(guanylhydrazone) also elicited a variable depression in the incorporation of [(3)H]uridine and [(14)C]adenine into total RNA. The apparent turnover of lymphocyte RNA remained essentially unchanged in spite of severe polyamine depletion brought about by difluoromethylornithine. 5. The present results, as well as confirming the anti-proliferative action of the inhibitors of polyamine biosynthesis, suggest that polyamine depletion may interfere with reactions at different levels of gene expression.     

Comparison of inhibitors of S-adenosylmethionine decarboxylase from different species.

S-Adenosyl-L-methionine decarboxylases were purified from rat ventral prostate, yeast (Saccharomyces cerevisiae), slime mould (Physarum polycephalum) and bacteria (Escherichia coli) and tested for inhibition by a variety of nucleosides related to S-adenosylmethionine and by methyl- and ethyl-glyoxal bis(guanylhydrazone). Although the enzymes from these different sources are markedly different with respect to activation by cations, the inhibition by nucleosides was quite similar. Very little inhibition was seen when analogues of S-adenosylmethionine with a different base were tested or when the ribose ring was opened or the positive charge on the sulphur atom was not present. Some derivatives in which the amino acid portion of the molecule was altered were more potent inhibitors, but again there was little difference between the enzymes from different sources. 5'-(Dimethylsulphonio)-5'-deoxyadenosine and S-adenosyl-3-methylthiopropylamine were the most inhibitory substances and had similar Ki values, suggesting that the aminopropyl group does not contribute significantly to the binding. All of the S-adenosylmethionine decarboxylases were strongly competitively inhibited by methylglyoxal bis(guanylhydrazone) and even more powerfully by its ethyl analogue, although the putrescine-activated enzymes from prostate and yeast were more sensitive than the bacterial and slime-mould enzymes. All of the S-adenosylmethionine decarboxylases tested bound to a column of methylglyoxal bis(guanylhydrazone) linked to Sepharose and were not eluted by 0.5 M-NaCl, but could be released by 1 mM concentrations of the drug, providing a rapid and efficient method for their purification.     

Inhibition of DNA synthesis by methylglyoxal bis(guanylhydrazone) during lymphocyte transformation

The phytohemagglutinin induced DNA synthesis in guinea pig lymph node cells was inhibited remarkably by methylglyoxal bis(guanylhydrazone). This inhibitory effect was dependent on the time of its addition to the lymph node cell culture after stimulation with phytohemagglutinin. If methylglyoxal bis(guanylhydrazone) was added 48 hr after the stimulation, no inhibition of DNA synthesis was observed. Exogenous spermidine added at an early time of cell culture reversed the inhibitory effect of methylglyoxal bis(guanylhydrazone). However, no reversion occurred when spermidine was added at a late time of the cell culture.     

Purification of S-adenosylmethionine decarboxylase from soybean.

S-Adenosylmethionine decarboxylase (EC 4.1.1.19) was purified to homogeneity from the cytosol of soybean (Glycine max) axes by ammonium sulfate fractionation, DEAE-Sepharose and methylglyoxalbis(guanylhydrazone)-Sepharose 6B chromatographies. The enzyme was free from diamine oxidase activity. The molecular weight of the enzyme estimated by gel filtration and sodium dodecyl sulfate polyacrylamide gel electrophoresis was 66,000. The Km value for S-adenosylmethionine was 0.26 mM. The optimum pH and temperature were 7.5 and 40 degrees C. Neither putrescine nor Mg2+ affected the enzyme activity, but the enzyme was inhibited by spermidine, spermine, methylglyoxalbis(guanylhydrazone), sodium borohydride and phenylhydrazine. Agmatine was a novel inhibitor which inhibited S-adenosylmethionine decarboxylase and arginine decarboxylase, preventing the accumulation of decarboxylated S-adenosylmethionine and putrescine, respectively.     

Stimulation of melanotic expression in murine melanoma cells exposed to polyamine antimetabolites

An exposure of cultured Cloudman S91 melanoma cells to inhibitors of polyamine biosynthesis, 2-difluoromethylornithine (DFMO) and methylglyoxal bis(guanylhydrazone) (MGBG), distinctly promoted the expression of differentiated biochemical functions of the tumor cells. Slight to moderate growth inhibition produced by the compounds was associated with a stimulation of melanogenesis, as reflected by a striking enhancement of tyrosinase (EC 1.10.3.1) activity and an increase in cellular melanin content. Both antimetabolites acted synergistically with α-melanotropin (MSH), as regards the stimulation of melanogenesis. Exposure of the melanoma cells to MSH resulted in most experiments in a marked decrease of the intracellular polyamine pools, usually involving all three polyamines (putrescine, spermidine and spermine). The DFMO-induced stimulation of melanogenesis was totally suppressed by the administration of putrescine, whereas the MSH-stimulated tyrosinase activity was not influenced by the diamine. Although many recent reports indicate that terminal differentiation is accompanied by a distinct stimulation of polyamine biosynthesis, our results suggest that in certain cells polyamine deprivation may lead to an enhanced expression of differentiated phenotype.     

Induction of ornithine decarboxylase activity in mouse tissues by phorbol ester is effectively blocked by methylglyoxal bis(butylamidinohydrazone)

Ornithine decarboxylase (ODC) was induced in the liver, lung and brain of the mouse injected intraperitoneally with 12-O-tetradecanoylphorbol 13-acetate (TPA), showing maximal enzyme activity four hours after the injection. The increase of ODC activity was due to the enhanced syntheses of mRNA and protein. The induction of ODC activity by TPA was specifically blocked by methylglyoxal bis(butylamidinohydrazone) (MGBB), a competitive inhibitor of ODC and S-adenosylmethionine decarboxylase, but not by the analog methylglyoxal bis(guanylhydrazone) (MGBG).