Intracellular putrescine and spermidine deprivation induces increased uptake of the natural polyamines and methylglyoxal bis(guanylhydrazone)

Antitumor effects of two polyamine antimetabolites combined with mitomycin C on human stomach cancer cells xenotransplanted into nude mice

The antitumor effects of alpha-difluoromethylornithine (DFMO), methylglyoxal-bis-guanylhydrazone (MGBG) and mitomycin C (MMC), administered separately or in various combinations, on human stomach cancer cells xenotransplanted into BALB/c nude mice were studied using the protocol of Battelle's Columbus Laboratories (Ovejera et al., 1978). DFMO (1,000 mg/kg in 2 divided doses) and MGBG (50 mg/kg) were given intraperitoneally (i.p.) for 7 consecutive days from the time when the tumor weighed about 100 mg. MMC (2 mg/kg) was given i.p. every other day from the same time. Animals treated with either DFMO or MGBG alone displayed tumor growth comparable to that seen in untreated controls. In mice treated with DFMO plus MGBG with or without MMC, or in mice treated only with MMC, tumor growth was significantly lower than in untreated mice. In the group which received only combined DFMO/MGBG there was a rapid regrowth of the tumor after termination of therapy. Tumor putrescine levels decreased within 4 days following the administration of DFMO; however, spermidine levels did not decline with either DFMO or MGBG treatment even after 7 days. When combined DFMO/MGBG was given, there was a significant decline in spermidine levels 7 days after the initiation of treatment. In contrast, when MMC alone was administered, putrescine and spermidine levels in the tumor did not differ from those in control mice. Spermine decreased markedly in tumor with the combined administration of DFMO/MGBG as well as with combined DFMO/MGBG/MMC, but decreased only slightly when MMC alone or MMC plus either DFMO or MGBG was administered. By the 7th treatment day, DNA biosynthesis in the tumor had dropped markedly in all groups except those receiving DFMO or MGBG alone.

Pulmonary accumulation of methylglyoxal-bis(guanylhydrazone) by the oligoamine uptake system

The accumulation of methylglyoxal-bis(guanylhydrazone) (MGBG) into rat lung slices and its relationship to the accumulation of oligoamines has been investigated. MGBG was accumulated by rat lung slices by a process which obeyed saturation kinetics (Km 6.6 microM; Vmax 75.3 nmoles/g wet wt lung/hr). The uptake process appeared to be identical to those described for the accumulation of oligoamines and paraquat, being both KCN-(1 mM) and temperature-sensitive but insensitive to ouabain (100 microM). Pulmonary MGBG accumulation was found to be sodium-independent, either being enhanced or unaffected by sodium chloride-deficient media, so distinguishing the process from that described for the monoamine, 5-hydroxytryptamine. The ability and nature of various rat tissue slices to accumulate MGBG generally followed that of the oligoamines. Slices of lung, brain cortex and seminal vesicles accumulated MGBG by a KCN-sensitive and temperature-dependent process. These observations, together with the ability of MGBG to inhibit pulmonary oligoamine accumulation, indicate that it is the uptake system for the oligoamines which is mainly responsible for the in vitro accumulation of MGBG.

Carrier-mediated uptake of methylglyoxal bis(guanylhydrazone) by rat lungs perfused in situ

Rat lungs perfused in situ were employed to begin investigations of the pathways by which the tissue takes up circulating polyamines (PA). Uptake kinetics were studied using [14C]methylglyoxal bis(guanylhydrazone) (MGBG), a nonmetabolized substrate analogue thought to enter cells via the PA carrier. Lungs concentrated MGBG from the perfusate at a linear rate for at least 60 min. Uptake was saturable with respect to perfusate MGBG concentration; it exhibited an apparent Km of 12.5 microM and Vmax of 0.6 nmol X g lung-1 X min-1. MGBG (1 microM) uptake was inhibited rapidly and to a similar extent (30-40%) by the naturally occurring PAs spermidine, spermine, or putrescine (50 microM); no additional inhibition of uptake was exerted when all three compounds were present simultaneously (total concentration, 150 microM). No inhibition by 5-hydroxytryptamine was evident. Spermidine produced a half-maximal inhibitory effect at a perfusate concentration of 1.9 microM (vs. 1 microM MGBG). The spermidine-insensitive component of MGBG uptake operated at a Vmax similar to that of the control (total), 1.2 nmol X g-1 X min-1, but the apparent Km was increased 3.5-fold to 44 microM. These observations indicate that MGBG is taken up from the pulmonary circulation by a high-affinity, carrier-mediated, concentrative uptake process that is inhibited, at least in part, by naturally occurring polyamines.

Effect of estrogen and androgen administration on alpha-difluoromethylornithine-enhanced putrescine uptake by the rat prostate

Radiolabeled putrescine is a potential imaging agent for carcinoma of the prostate. The intrinsically high uptake of putrescine into the rat prostate and prostatic carcinoma can be further stimulated by pretreatment of the animals with alpha-difluoromethylornithine (DFMO) uptake, a polyamine synthesis inhibitor. Pharmacological castration of the animals followed by androgen stimulation and DFMO pretreatment achieved a 30:1 prostate/muscle ratio of 14C-putrescine uptake in elderly rats.

S-adenosylmethionine decarboxylase as target of chemotherapy

Although ornithine decarboxylase under most conditions is the rate-controlling enzyme of polyamine biosynthesis and thus the most logical target for chemical intervention, the inhibition of the enzyme triggers a series of compensatory reactions all aimed to circumvent the inhibition. These include secondary induction of adenosylmethionine decarboxylase, enhanced accumulation of extracellular polyamines and an overproduction of ornithine decarboxylase resulting from enhanced expression and gene amplification. Thus chemotherapy based on an intervention of polyamine formation has also to be directed to reactions other than the decarboxylation of ornithine. Adenosylmethionine decarboxylase is the second natural target for chemotherapy. Virtually all effective inhibitors of this enzyme are members of the family of bis(guanylhydrazones). Small modifications, such as increased hydrophobicity at the glyoxal portion of the parent compound glyoxal bis(guanylhydrazone), greatly enhance the inhibition of adenosylmethionine decarboxylase and diminish the undesirable inhibition of diamine oxidase. However, although ethylglyoxal and propylglyoxal bis(guanylhydrazone) appear to utilize the putative polyamine carrier for their cellular entry, their cellular accumulation, in contrast to that of glyoxal and methylglyoxal bis(guanylhydrazone), is not stimulated by putrescine and spermidine deprivation produced by inhibitors of ornithine decarboxylase. It is obvious that the cellular accumulation of each of the bis(guanylhydrazones) is determined by their different efflux rates: GBG and MGBG are effectively retained whereas EGBG is rapidly excreted by the tumor cells. GBG and MGBG, but possibly not EGBG, behave as mitochondrial poisons and rapidly produce extensive morphological damage of the mitochondria. The bis(guanylhydrazones) likewise inhibit carnitine-dependent mitochondrial oxidation of long-chain fatty acids, competitively in respect to carnitine. It is possible that this inhibition has something to do with the mitochondrial damage, as carnitine protects tumor cells from the early mitochondrial damage produced by MGBG. Carnitine also protects experimental animals from MGBG-induced acute toxicity and death.

Polyamines in clinical disorders

An edited summary of an Interdepartmental Conference arranged by the Department of Medicine of the UCLA School of Medicine, Los Angeles. The Director of Conferences is William M. Pardridge, MD, Associate Professor of Medicine.Polyamines, necessary for cell growth, influence many cell functions. As small polyvalent cations they can change the configuration of large polyvalent anions, such as DNA, and alter their sensitivity to other molecules including chemotherapeutic agents. By altering polyamine content in a cell, we can change its growth, its susceptibility to drugs and change other cellular functions. Malignant conditions, other proliferative diseases and infections are the most apparent clinical conditions likely to improve by depleting polyamines and suppressing cell growth. Proliferative disorders of the skin respond to many agents that suppress polyamine metabolism. Hyperoxia may suppress cell growth in the lung by suppressing polyamine metabolism.

Polyamines in colorectal cancer

Polyamine levels (putrescine, spermidine and spermine) in colorectal cancers (n = 25) were measured in order to assess their importance as markers of cellular proliferation. Colonic mucosa from healthy resection margins of patients with diverticular disease (n = 5) was used as control material. Polyamine levels (expressed as nanomoles per 100 mg tumour) in cancers ranged from 0.8 to 7.9 for putrescine (mean: 2.3 +/- 0.7), from 6.5 to 22.8 for spermidine (mean: 13.9 +/- 0.9) and from 13.0 to 37.5 for spermine (mean: 22.1 +/- 1.3). Mean spermidine and spermine content of cancers was more than three times mean spermidine (3.92 +/- 0.8), and more than four times mean spermine (5.0 +/- 1.2), content of normal colonic mucosa (P less than 0.01). Polyamine content of colorectal cancers was independent of tumour site, Dukes' stage, histological grade and the presence of palpable liver metastases at laparotomy. Because colorectal cancers contain such high levels of spermidine and spermine, polyamines may play an essential role in the regulation of their growth.

Different efflux rates may determine the cellular accumulation of various bis(guanylhydrazones)

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.

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.

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).

Potentiation of methylglyoxal-bis-guanylhydrazone by alpha-difluoromethylornithine in rat prostate cancer

The polyamines, putrescine, spermidine, and spermine, are fundamentally related to both normal and neoplastic cell proliferation. The prostate gland and prostatic tumors in man and rodents contain large amounts of polyamines. This suggests that inhibition of polyamine biosynthetic enzymes, ornithine decarboxylase (ODC) and S-adenosyl-methionine decarboxylase (SAMDC) may retard the growth of prostatic cancer. Since alpha-difluoromethylornithine (DFMO) and methylglyoxal-bis-guanylhydrazone (MGBG) are irreversible and competitive inhibitors of ODC and SAMDC, respectively, they were tested as single agents and in combination on a transplantable rapidly growing and hormone-resistant G subline of the Dunning R-3327 rat prostatic adenocarcinoma. Groups of rats bearing tumors were treated with various regimens of DFMO, MGBG, and DFMO plus MGBG, daily for 21 days. Analysis of differences in tumor growth between treatment groups and controls showed DFMO had no antitumor effect but was well tolerated, MGBG retarded growth rate significantly but resulted in drug deaths in over 50% of the animals, and the combination of DFMO and MGBG resulted in rapid decline in tumor growth rates after 5 to 9 days of treatment with reduced toxicity. At 21 days, or death, 38 of 60 (63%) rats had no viable tumor on histologic study, whereas tumor was present in each of the animals in the other groups. Alpha-difluoromethylornithine increased the intracellular uptake of MGBG and potentiated the antigrowth activity of MGBG on a hormone refractory rat prostatic tumor with less toxicity than MGBG alone.

Inhibition of S-adenosylmethionine decarboxylase and diamine oxidase activities by analogues of methylglyoxal bis(guanylhydrazone) and their cellular uptake during lymphocyte activation

Several congeners of methylglyoxal bis(guanylhydrazone) were tested for their ability to inhibit eukaryotic putrescine-activated S-adenosylmethionine decarboxylase (EC 4.1.1.50) and intestinal diamine oxidase (EC 1.4.3.6). All the compounds tested, namely methylglyoxal bis(guanylhydrazone), ethylglyoxal bis(guanylhydrazone), dimethylglyoxal bis(guanylhydrazone) and the di-N"-methyl derivative of methylglyoxal bis(guanylhydrazone), were strong inhibitors of both yeast and mouse liver adenosylmethionine decarboxylase activity in vitro. The enzyme from both sources was most powerfully inhibited by ethylglyoxal bis(guanylhydrazone). All the diguanidines likewise inhibited diamine oxidase activity in vitro. The maximum intracellular concentrations of the ethyl and dimethylated analogues achieved in activated lymphocytes were only about one-fifth of that of the parent compound. However, both derivatives appeared to utilize the polyamine-carrier system, as indicated by competition experiments with spermidine.

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.

Biochemistry of the polyamines

The naturally-occurring polyamines exist in the free form, as N-acetyl derivatives and bound to protein. Their biosynthesis is subject to sensitive control, particularly of ornithine decarboxylase. This enzyme may be multifunctional and a key regulatory protein. Studies, principally with selective inhibitors, have elucidated the roles of polyamines in cell proliferation. Oxidized polyamines, in contrast, can be potent mitotic inhibitors. These effects are reviewed in terms of their chemistry and biochemistry. Their principal distinctions are that they can be made or degraded intracellularly, they can associate electrostatically with macromolecules by means of their spaced cationic groups, and these can be readily converted to covalent bonds.

Sequential inhibition of polyamine synthesis. A phase I trial of DFMO (alpha-difluoromethylornithine) and methyl-GAG [methylglyoxal-bis(guanylhydrazone)]

Both DFMO and methyl-GAG inhibit sequential enzymatic reactions in the pathway of polyamine biosynthesis. Since polyamines may be important factors in proliferation of cancer cells, we initiated a phase-I study of these agents in patients with advanced cancer. DFMO was given by mouth at a constant daily dose of 4 g/m2 starting on day 1 of the treatment protocol. The dose of methyl-GAG ranged from 200 to 700 mg/m2 administered IV every 2 weeks beginning on day 4. Twenty-two patients were entered into the protocol. Toxic reactions to this therapy were dose-related and included nausea, fatigue, diarrhea, and myelosuppression. One patient with colon cancer experienced a greater than 50% decrease in measurable disease but developed severe myelotoxicity. While DFMO was well tolerated, the combination of drugs appeared to cause substantially more hematologic and gastrointestinal toxicity than encountered during our recent experience with methyl-GAG used alone. We suggest that future studies of this drug combination carefully evaluate levels of polyamines and inhibition of enzymatic activity to minimize toxicity.

Inhibition of hormonal induction of tyrosine aminotransferase by polyamines in freshly isolated rat hepatocytes

We have analysed the effects of natural aliphatic polyamines on hormonal induction of tyrosine aminotransferase (TAT) in suspensions of hepatocytes isolated from adult fed rats. Glucagon or cyclic AMP derivatives (dibutyryl and 8-bromo) used alone caused a 4-5 fold increase in enzyme activity within 4h. This effect was independent of glucocorticoids, which also increased TAT activity (2.5-fold); when combined, the effects of the two inducers were additive. Spermine and putrescine totally inhibited the hormonally-mediated increase in enzyme activity when added at the onset of incubation with the inducers. Furthermore, polyamines could block the hormonal effect at any time during the course of TAT induction, with, however, a 30 min lag period, suggesting that they must enter the cells. Hepatocytes were indeed shown to take up spermine. At low external concentrations (less than 50 microM), an Na+-dependent, saturable and concentrative mechanism was predominant; at high concentrations (greater than 0.5 mM) transport occurred mainly through a non-saturable, Na+-independent mechanism, building up intracellular concentrations slightly lower than those in the medium. Dose-dependence analysis of the polyamine effect on enzyme induction indicated that half-maximal and maximal inhibition occurred with 0.75 mM- and 2.5 mM-spermine respectively, whereas 2.5mM- and 7.5 mM-putrescine were required respectively to obtain similar effects. Spermidine was much less effective and cadaverine had virtually no effect. None of the polyamines affected the rate of decay of TAT, nor did they directly or indirectly cause enzyme inactivation, indicating that a post-translational modification was unlikely to account for the polyamine effects. Similarly, these effects could not be ascribed to a non-specific inhibition of overall protein synthesis. We conclude that, in hepatocytes, polyamines (or their metabolites) directly interfere with one or several steps controlled by hormones in the synthesis of tyrosine aminotransferase.

Inhibition of DNA and protein synthesis in UV-irradiated mouse skin by 2-difluoromethylornithine, methylglyoxal bis(guanylhydrazone), and their combination

Exposure of mouse skin to UVB irradiation greatly enhanced the biosynthesis and accumulation of putrescine and spermidine before or concomitantly with stimulation of epidermal macromolecular (DNA and protein) synthesis. Topical treatment of UV-exposed skin with 2 inhibitors of polyamine biosynthesis, 2-difluoromethylornithine (DFMO) and methylglyoxal bis(guanylhydrazone) (MGBG) prevented the enhanced epidermal accumulation of polyamines, especially spermidine, and also inhibited the incorporation of radioactive precursors into DNA and protein. When applied in combination, these 2 antimetabolites of polyamines produced an inhibition of macromolecular synthesis that was at least additive: [3H]thymidine incorporation decreased by 80% and [14C]leucine incorporation by 44% as compared with the UVB-irradiated control mice. A slight decrease in the ratio of [3H]histidine/[14C]leucine incorporation indicated that protein synthesis of the differentiating cell layers was also affected by the inhibitors. The effects of the combined DFMO and MGBG treatment were partially reversed by concomitant topical application of spermidine.

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.

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 alpha-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.

Tumor selective enhancement of radioactivity uptake in mice treated with alpha-difluoromethylornithine prior to administration of 14C-putrescine

A group of EMT6 tumor bearing male BALB/c mice which had been treated with alpha-difluoromethylornithine (DFMO, a specific, irreversible inhibitor of ornithine decarboxylase, the enzyme which catalyzes the biosynthesis of putrescine), 8 mg/mouse, ip, 20 and 5 hrs before the 14C-putrescine dose, and a group of control animals were administered 14C-putrescine (0.5 muCi, 0.1 mCi/mmol, iv) 60 min prior to sacrifice. Radioactivity uptake data was obtained for the tumor and 13 major normal organs. In the control animals the tumor exhibited one of the highest uptakes of radioactivity. For DFMO-pretreated mice the radioactivity distribution among most of the normal tissues was not very different from that obtained for the control animals. However, the uptake into the tumor was enhanced by a factor of approximately 4. So, high tumor-to-tissue ratios (3.8, lung to 38, brain) were attained as a result of DFMO treatment.

In vivo effects of alpha-DL-difluoromethylornithine on the metabolism and morphology of Trypanosoma brucei brucei

The EATRO 110 isolate of Trypanosoma brucei brucei was grown in rats for 60 h and the animals treated with the ornithine decarboxylase inhibitor alpha-DL-difluoromethylornithine 12 h or 36 h prior to sacrifice. Control untreated animals died 72-80 h after infection. Treated parasites were shorter and broader than the predominantly long slender forms found in untreated controls and many had two or more nuclei and kinetoplasts. Trypanosomes were purified from blood and examined for disruption of polyamine metabolism. ODC activity decreased by more than 99% after 12 h treatment and putrescine and spermidine levels also decreased dramatically. Spermine, not normally present in control cells, increased to detectable, low levels (less than 1 nmol mg-1 protein) after 36 h treatment. alpha-DL-Difluoromethylornithine-treated cells were unable to synthesize putrescine from [3H]ornithine but were able to convert [3H]putrescine + methionine to spermidine. 12-h treated parasites responded to polyamine depletion by assimilating radiolabeled polyamines in vitro at 2- to 4-times the rate of untreated cells. The metabolism of S-adenosylmethionine was also altered in treated parasites: decarboxylated S-adenosylmethionine increased more than 1000-fold over untreated cells while S-adenosylmethionine decarboxylase activity, associated with the formation of spermidine and spermine in other eukaryotes, paradoxically declined in treated cells. Synthesis of macromolecules was perturbed in treated parasites: rates of DNA and RNA synthesis declined 50-100%, while protein synthesis increased up to 4-fold in 36-h treated cells. alpha-DL-Difluoromethylornithine treatment progressively limits the parasites' ability to synthesize nucleic acids and blocks cytokinesis while inducing morphological changes resembling long slender leads to short stumpy transformation.

Combined use of 2-difluoromethylornithine and methylglyoxal bis(guanylhydrazone) in normal and leukemia-bearing mice

Mice were treated with daily injections of methylglyoxal bis(guanyl-hydrazone) (MGBG) without or with concurrent administration of 2-difluoromethylornithine (DFMO) in drinking water for 15 days. Analysis of 10 different tissues for their MGBG content during the treatment revealed little evidence for a tissue specific cumulative accumulation of the drug given either alone or in combination with DFMO. On the contrary, tissue MGBG levels tended to increase until the 4th to 7th day of the treatment, whereafter a gradual decline or a plateau was obvious in most tissues. The concomitant DFMO treatment produced a consistent elevation of tissue MGBG concentrations in bone marrow cells and possibly also in intestinal tissue. In L1210 leukemia-bearing DBA mice, MGBG was most actively taken up by the ascitic leukemia cells. A priming of the tumor-bearing mice with DFMO for a few days before the start of MGBG injections resulted in a strikingly enhanced accumulation of the latter drug in the leukemia cells and also in the spleen, which was apparently heavily infiltrated by tumor cells. In liver, small intestine and in bone marrow cells of tumor-bearing animals the concentration of MGBG was not influenced by the DFMO treatment. In DBA mice without the L1210 tumor, DFMO only insignificantly increased the level of MGBG in bone marrow cells whereas no increase was seen in the spleen, in contrast to the same organ obtained from tumor-bearing mice. This combined treatment, in comparison with DFMO or MGBG alone, also produced the best therapeutic response as revealed by marked reduction of the tumor mass.

Effect of epidermal polyamine depletion on the accumulation of methylglyoxal bis(guanylhydrazone) in mouse skin

A systemic or topical treatment of mice with alpha-difluoromethylornithine, and irreversible inhibitor of mammalian ornithine decarboxylase, produced a rapid depletion of epidermal putrescine and spermidine. When methylglyoxal bis(guanylhydrazone), another inhibitor of polyamine biosynthesis and a potent antiproliferative agent, was subsequently administered the epidermal concentration of the latter drug rose distinctly higher than without a prior difluoromethyl ornithine treatment. The combined use of these 2 antimetabolites of polyamines also profoundly depressed epidermal DNA synthesis, especially in UV-irradiated skin. A "priming" with difluoromethyl ornithine may therefore offer a means to enhance the epidermal accumulation of otherwise poorly absorbed methylglyoxal bis(guanylhydrazone).

Polyamines in mycoplasmas and in mycoplasma-infected tumour cells

Three out of four different mycoplasma strains analysed for the polyamine contents contained relatively high concentrations of putrescine, cadaverine, spermidine and spermine. In addition to ornithine decarboxylase (EC 4.1.1.17) activity, the mycoplasmas also exhibited comparable or higher lysine decarboxylase (EC 4.1.1.18) activity fully resistant to the action of 2-difluoromethylornithine, an irreversible inhibitor of eukaryotic ornithine decarboxylase. 2-Difluoromethylornithine did not modify the polyamine pattern of actively growing mycoplasmas. Ehrlich ascites carcinoma cells and L1210 mouse leukemia cells infected with any of the four mycoplasma strains contained, in addition to putrescine, spermidine and spermine, and also easily measurable concentrations of cadaverine; the latter diamine was absent in uninfected cultures. When the infected cells were exposed to difluoromethylornithine, the accumulation of cadaverine was markedly enhanced. The modification of cellular polyamine pattern by mycoplasmas, especially in the presence of inhibitors of eukaryotic ornithine decarboxylase, could conceivably be used as an indicator of mycoplasma infection in cultured animal cells.

Copenhagen rat prostatic tumor ornithine decarboxylase activity (ODC) and the effect of the ODC inhibitor alpha-difluoromethylornithine

The R3327MAT-Lu tumor is a rapidly growing anaplastic derivative of the Dunning R3327 prostatic adenocarcinoma. We have found the ornithine decarboxylase (ODC) activity of this tumor to be as sensitive to inhibition by alpha-difluoromethylornithine (DFMO) as normal rat prostate. The same was true for all the other R3327 tumor derivatives we studied. The in vivo inhibition of ODC by DFMO allowed increased uptake of exogenously administered putrescine by the R3327AT tumor. Further, DFMO was inhibitory to the growth of the R3327MAT-Lu both in vitro and in vivo.

Synergistic action of two polyamine antimetabolites leads to a rapid therapeutic response in childhood leukemia

Sequential administration of alpha-difluoromethyl ornithine and methylglyoxal bis(guanylhydrazone), two differently acting inhibitors of the biosynthesis of natural polyamines, produced a rapid and distinct therapeutic response in four children with advanced lymphoblastic and in one with myeloblastic leukemia. The synergism between the action of the two compounds was based upon a unique drug interaction; a preceding treatment with difluoromethyl ornithine greatly increased the uptake of subsequently administered methylglyoxal bis(guanylhydrazone) as verified by the actual determinations of the latter drug in the circulating leukemia cells. The side-effects associated with the combined drug regiment were either absent or mild.

Uptake and excretion of polyamines from baby hamster kidney cells (BHK-21/C13). The effect of serum on confluent cell cultures

In confluent cultures of BHK-21/C13 cells there was little uptake of exogenous polyamines and only a low level of polyamine biosynthesis. These cultures continuously excreted polyamines into the extracellular medium. Spermidine, in both the free and bound form, was the predominant excretion product, whereas the major intracellular polyamine was spermine implying that excretion of polyamines was specific. Reinitiation of growth by the addition of fresh serum immediately increased the uptake of exogenous putrescine, increased the biosynthesis of polyamines and decreased the excretion of polyamines. Thus, polyamine transport into and out of the cell appears to be regulated by the growth status of that cell.

Polyamine deprivation-induced enhanced uptake of methylglyoxal bis(guanylhydrazone) by tumor cells

1. Putrescine and spermidine depletion produced by alpha-difluoromethylornithine, an irreversible inhibitor or ornithine decarboxylase (EC 4.1.1.17), resulted in a strikingly enhanced cellular uptake of methylglyoxal bis(guanylhydrazone) in cultured Ehrlich ascites carcinoma cells and human lymphocytic leukemia cells. 2. A prior priming of the cells with difluoromethylornithine followed by a short exposure of the cells to methylglyoxal bis(guanylhydrazone) rapidly established intracellular concentrations of the latter drug approaching 10 mM. 3. The enhanced transport of methylglyoxal bis(guanylhydrazone) into the tumor cells apparently required metabolic energy as the uptake of extracellular drug rapidly ceased and intracellular methylglyoxal bis(guanylhydrazone) was excreted into the medium when the glycolysis of the tumor cells was inhibited by iodoacetate. 4. A sequential treatment of cultured tumor cells with difluoromethylornithine until established polyamine depletion followed by an addition of low concentrations of methylglyoxal bis(guanylhydrazone) produced an antiproliferative action not achieved with either of the drugs alone. 5. A similar treatment schedule, i.e a priming of mice inoculated with Ehrlich ascites cells with difluoromethylornithine for a few days, likewise enhanced the uptake of methylglyoxal bis(guanylhydrazone) by the carcinoma cells, but only marginally increased the drug concentration in the liver and small intestine of the animals.