Effect of inhibitors of polyamine biosynthesis on gibberellin-induced internode growth in light-grown dwarf peas

When gibberellic acid (GA3) is sprayed on 9-day-old light-brown dwarf Progress pea (Pisum sativum) seedlings, arginine decarboxylase (ADC; EC 4.1.1.9) activity increases within 3 h and peaks at about 9 h after GA3 application. This is followed by a second lower peak at about 30 h; both peaks were higher than the corresponding peaks in the controls. In contrast, no appreciable effect of GA3 on internode length was observed until about 12 h, after which time a dramatic increase in growth rate occurred and persisted for about 12 h. Specific (DL-alpha-difluoromethylarginine) and non-specific (D-arginine and L-canavanine) inhibitors of ADC strongly inhibited ADC activity and to a lesser extent internode growth. The inhibition was reversed only slightly by the addition of polyamines. Actinomycin D and cycloheximide inhibited the rise in ADC activity induced by GA3. The half-life of the enzyme was increased by GA3 treatment. The results suggest that part of the GA3-induced increase in internode growth may result from enhanced polyamine biosynthesis through the ADC pathway. Furthermore, the GA3 induced increase in ADC activity probably requires de novo synthesis of both RNA and protein.

Influence of K-ras activation on the survival responses of Caco-2 cells to the chemopreventive agents sulindac and difluoromethylornithine

The nonsteroidal anti-inflammatory drug sulindac and the ornithine decarboxylase inhibitor difluoromethylornithine (DFMO) are both potent inhibitors of colon carcinogenesis in experimental models of this disease. The combination of these two agents is undergoing evaluation as a strategy for colon cancer chemoprevention in humans with resected colon polyps. We evaluated the effects of the major sulfide and sulfone metabolites of sulindac and DFMO alone, or in combinations, on the growth and survival of Caco-2 colon cancer-derived cells and in clones of these cells transfected with an activated K-ras oncogene. Both the sulfide and sulfone metabolites of sulindac reduced cell viability, measured by colony-forming assays, primarily by inducing apoptosis. Expression of an activated K-ras oncogene caused cells treated with either sulindac sulfide or sulfone to undergo apoptosis earlier than nontransfected controls. However, clonogenic survival, measured 2 weeks after drug treatment, was the same in both Caco-2 and ras-transfected Caco-2 cells treated with sulindac metabolites. A 24-h treatment with DFMO caused a dose-dependent decrease in the colony-forming ability of cells expressing an activated K-ras but had no effect on the viability of the parental Caco-2 cells. The DFMO-dependent decrease in colony formation in K-ras-activated cells occurred in the absence of apoptosis. Assessment of cell survival by colony-forming assays indicated that these two agents acted in an additive manner when combined. These data indicate that K-ras can influence the kinetics of apoptosis induction by sulindac metabolites and cell survival in response to DFMO. However, cytotoxicity induced by these agents occurs via unique mechanisms. These studies suggest that the combination of DFMO and sulindac may be useful in human cancer prevention strategies.

[Effect of alpha-difluoromethylornithine on growth characteristics and expression of ALT-04ag gene of human lung carcinoma cells]

OBJECTIVE

To study the effect of polyamine biosynthesis inhibition on growth characteristics of human lung carcinoma cells and its correlation with the expression of human lung carcinoma associated antigen ALT-04ag gene.

METHODS

The gene expression was detected by RT-PCR and immunocytochemical tests. The cell growth characteristics were studied by cell growth curves, morphological observation, FCM analysis and DNA electrophoresis.

RESULTS

Human lung squamous carcinoma cells L78 treated with 5 mmol/L alpha-difluoromethylornithine (DFMO) for 5 days showed significant growth inhibition and apoptosis induction. The mRNA and protein expressions of ALT-04ag gene in the cells were downregulated, while these changes resulted from DFMO treatment were prevented by provision of DFMO along with exogenous putrescine.

CONCLUSION

The effect of polyamine biosynthesis inhibition induced by DFMO restrains the growth characteristics and promotes apoptosis of human lung carcinoma L78 cells, which is associated with down regulation of ALT-04ag gene expression.

The gastrointestinal polyamine source depletion enhances DFMO induced polyamine depletion in MCF-7 human breast cancer cells in vivo

Due to the polyamine requirement for cell growth, blockade of polyamine biosynthesis is considered a potential anticancer target. The lack of efficacy of DFMO in vivo, has been attributed to other sources of polyamines, mainly from the gastrointestinal tract (alimentary and bacterial). An experiment was designed to test the role of intestinal polyamine deletion in addition to DFMO (a specific inhibitor of ODC) in established MCF-7 tumors in nude mice. Using DFMO and polyamine-free diet, the tumor putrescine concentrations were more profoundly decreased in comparison to DFMO alone and cellular spermine was also depleted, as has never been observed with DFMO alone. The blockade of the gastrointestinal sources of polyamines enhances the intracellular polyamine depletion induced by DFMO on MCF-7 tumor in nude mice.

Role of polyamines in gastroprotection induced by epidermal growth factor

Polyamines have been shown to stimulate cellular growth and differentiation, though their role in the prevention of acute gastric lesion induced by various noxious agents has been little studied. Epidermal growth factor (EGF) exhibits gastroprotective and ulcer healing properties due to its potent mitogenic and growth promoting action. This study was designed to compare the gastroprotective effects of spermine and EGF against gastric damage induced by absolute ethanol, acidified aspirin and stress and to determine the role of endogenous polyamines in EGF-induced gastroprotection. Spermine and EGF significantly reduced the lesions induced by all three ulcerogens. Oral administration of spermine or subcutaneous infusion of EGF in 24 h fasted rats with chronic gastric fistula resulted in similar inhibition of gastric acid and pepsin secretion. Pretreatment with difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (ODC), a key enzyme in the biosynthesis of polyamines, did not affect ethanol lesions, but reversed the protective effect EGF but not spermine against ethanol. This finding indicates that polyamines mediate, at least in part, EGF-induced gastroprotection. In tests with oral administration of aminoguanidine that is known to suppress the activity of diamino-oxidase (DAO) and to inhibit the degradation of polyamines, EGF showed a markedly enhanced gastroprotective activity against ethanol damage. Since indomethacin failed to affect the gastroprotective effects of spermine and EGF and neither of these agents influenced the mucosal generation of PGE2 in intact or injured gastric mucosa, we conclude that prostaglandins are not the major factors in spermine- and EGF-induced gastroprotection. This study demonstrates that polyamines are highly effective against gastric lesions induced by various ulcerogens and that they act as primary mediators of EGF-induced gastroprotection.

alpha-Difluoromethylornithine alters calcium signaling in platelet-derived growth factor-stimulated A172 brain tumor cells in culture

alpha-Difluoromethylornithine (DFMO), an irreversible inhibitor of the polyamine biosynthetic enzyme ornithine decarboxylase, inhibits the growth of brain tumor cell lines and is undergoing clinical trials as a treatment for brain tumors. Platelet-derived growth factor (PDGF) is thought to regulate the growth and development of precursors of both normal and neoplastic astrocytic cells; calcium signaling is thought to play a role in the transduction of PDGF signals. Using laser fluorescence image cytometry, flow cytometry, and spectrofluorometry, we studied the effect of DFMO on the calcium signals induced by PDGF in A172 human glioblastoma cells. Four days of treatment with 5 mM DFMO substantially shortened PDGF-induced calcium signals. The effect was reversed more than 10 h but less than 24 h after putrescine treatment, even though polyamines were repleted 4 h after putrescine and spermidine were added. DFMO did not substantially affect intracellular calcium release or the timing of the opening and closing of plasma membrane calcium channels. These findings support the notion that calcium signaling may be a target for inhibitors of polyamine metabolism.

Dominant negative mutants of ornithine decarboxylase

Conserved lysines of mouse ornithine decarboxylase were individually mutated to arginines. The mutations at amino acid residues 69, 115, and 169 greatly reduced or abolished enzymatic activity. Lysine 69 is the site of Schiff base formation with the cofactor pyridoxal phosphate; the functional role of the other two lysines essential for activity is not known. Coexpression of wild type ornithine decarboxylase along with the lysine 115 to arginine mutant reduced the activity of the former without diminishing the amount of wild type protein. This form of negative complementation was seen when wild type and mutant protein were coexpressed either by in vitro translation or in bacteria. The data are consistent with the conclusion that a wild type and mutant subunit form a heterodimer that is enzymatically inactive.

[Effect of alpha-difluoromethylornithine and polyhexamethyleneguanidine (PMG), polyamine biosynthesis inhibitors on leucosis L1210 growth kinetics and life expectancy of animals with cancer]

The article deals with the study of polyamines content and y-glutamiltranspeptidase (gamma-GTP) activity in leucosis L1210 cells under the influence of inhibitors of polyamines synthesis such as alpha-difluoromethylornithine (alpha-DFMO) and polyhexamethylenguanidine (PMG). Injections of alpha-DFMO and PMG to animals essentially reduce putrescine and spermidine concentrations, and the levels of spermine and gamma-GTP activity increase under this influence. These modulation were associated with L1210 leucosis growth retardation. Antiblastic effect was dependent on inhibitors' doses and mode of injections' course. Under the optimum conditions the retardation index was 90-98%. The animals with retarded tumor growth had essentially longer survival time frame than blank tumor-bearing animals (index was 37.2 for a-DFMO and 67.5 for PMG).

Impact of Difluoromethylornithine and AMXT 1501 on Gene Expression and Capsule Regulation in Streptococcus pneumoniae

Streptococcus pneumoniae (Spn), a Gram-positive bacterium, poses a significant threat to human health, causing mild respiratory infections to severe invasive conditions. Despite the availability of vaccines, challenges persist due to serotype replacement and antibiotic resistance, emphasizing the need for alternative therapeutic strategies. This study explores the intriguing role of polyamines, ubiquitous, small organic cations, in modulating virulence factors, especially the capsule, a crucial determinant of Spn's pathogenicity. Using chemical inhibitors, difluoromethylornithine (DFMO) and AMXT 1501, this research unveils distinct regulatory effects on the gene expression of the Spn D39 serotype in response to altered polyamine homeostasis. DFMO inhibits polyamine biosynthesis, disrupting pathways associated with glucose import and the interconversion of sugars. In contrast, AMXT 1501, targeting polyamine transport, enhances the expression of polyamine and glucose biosynthesis genes, presenting a novel avenue for regulating the capsule independent of glucose availability. Despite ample glucose availability, AMXT 1501 treatment downregulates the glycolytic pathway, fatty acid synthesis, and ATP synthase, crucial for energy production, while upregulating two-component systems responsible for stress management. This suggests a potential shutdown of energy production and capsule biosynthesis, redirecting resources towards stress management. Following DFMO and AMXT 1501 treatments, countermeasures, such as upregulation of stress response genes and ribosomal protein, were observed but appear to be insufficient to overcome the deleterious effects on capsule production. This study highlights the complexity of polyamine-mediated regulation in S. pneumoniae, particularly capsule biosynthesis. Our findings offer valuable insights into potential therapeutic targets for modulating capsules in a polyamine-dependent manner, a promising avenue for intervention against S. pneumoniae infections.

Polyamine Metabolism for Drug Intervention in Trypanosomatids

Neglected tropical diseases transmitted by trypanosomatids include three major human scourges that globally affect the world's poorest people: African trypanosomiasis or sleeping sickness, American trypanosomiasis or Chagas disease and different types of leishmaniasis. Different metabolic pathways have been targeted to find antitrypanosomatid drugs, including polyamine metabolism. Since their discovery, the naturally occurring polyamines, putrescine, spermidine and spermine, have been considered important metabolites involved in cell growth. With a complex metabolism involving biosynthesis, catabolism and interconversion, the synthesis of putrescine and spermidine was targeted by thousands of compounds in an effort to produce cell growth blockade in tumor and infectious processes with limited success. However, the discovery of eflornithine (DFMO) as a curative drug against sleeping sickness encouraged researchers to develop new molecules against these diseases. Polyamine synthesis inhibitors have also provided insight into the peculiarities of this pathway between the host and the parasite, and also among different trypanosomatid species, thus allowing the search for new specific chemical entities aimed to treat these diseases and leading to the investigation of target-based scaffolds. The main molecular targets include the enzymes involved in polyamine biosynthesis (ornithine decarboxylase, S-adenosylmethionine decarboxylase and spermidine synthase), enzymes participating in their uptake from the environment, and the enzymes involved in the redox balance of the parasite. In this review, we summarize the research behind polyamine-based treatments, the current trends, and the main challenges in this field.

Antitumor activity of norspermidine, a structural homologue of the natural polyamine spermidine

The structural specificities of the natural polyamines putrescine (Put), spermidine (Spd) and spermine (Spm) for cell growth are rather stringent, suggesting that appropriate structural analogues of these polycations could serve as potential antineoplastic agents via polyamine antagonism. Norspermidine (Nspd), a homologue of spermidine, had significant antitumor activity against L1210 leukemia, 3LL carcinoma and EL4 lymphoma in mice. The observed antitumor activity of the compound was potentiated by administration of a - difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase. DFMO treatment alone, or in combination with Nspd reduced tumoral Put and Spd levels by greater than 50% in all three tumor models. In animals receiving both Nspd and DFMO, Nspd accumulation in the tumor cells was increased by 50% or more compared to cells from animals receiving Nspd only. Co-administration of Spd, but not Put, abolished the antitumor activity of L1210 observed with DFMO and Nspd treatment, and also reduced the tumoral accumulation of Nspd. These results indicate that appropriate structural analogues of the natural polyamines may be useful as antineoplastic agents.

Inhibition of ionizing radiation recovery processes in polyamine-depleted Chinese hamster cells

Polyamines are involved in many cellular processes, including DNA structure and function. Since DNA, or some DNA-containing structure, is known to be the target for cell killing induced by ionizing radiation and a number of chemotherapeutic agents, we investigated the effects of polyamine depletion on cytotoxic responses of Chinese hamster cells to X-irradiation. Colony forming ability after single, acute radiation exposures of cells growing under oxic conditions was minimally affected by endogenous putrescine and spermidine depletion, achieved after treatment with alpha-difluoromethylornithine. Survival of cells rendered hypoxic and then irradiated was unaffected by alpha-difluoromethylornithine treatment. However, cellular recovery processes were nearly completely suppressed in polyamine-depleted cells, including sublethal damage recovery, as evidenced by split-dose irradiations in log phase cultures, and potentially lethal damage recovery, observed when growth-inhibited cultures were allowed time to repair radiation damage prior to being plated for colony formation. Both these recovery processes were restored by exogenous putrescine treatment. Reaccumulation of intracellular spermidine content closely correlated with restoration of potentially lethal damage recovery. Depletion of putrescine and spermidine pools had little effect on either single or double strand DNA break production or rejoining. These data demonstrate that both sublethal and potentially lethal damage recovery are polyamine-dependent processes in Chinese hamster cells, and imply that the mechanisms by which hamster cells recovery from these types of radiation damage are unrelated to their ability to rejoin DNA strand breaks, at least during the first hour after irradiation. Finally, these results suggest that the depletion of tumor polyamine content may be an effective method of enhancing the sensitivity of human tumors to fractionated radiotherapy.

An inhibitor of ornithine decarboxylase antagonizes superoxide generation by primed human polymorphonuclear leukocytes

Tumor necrosis factor-alpha (TNF-alpha) induces a rapid increase in polymorphonuclear leukocyte (PMN) polyamine content which appears to be required for optimal priming of the respiratory burst. The objective of the present study was to determine whether inhibition of polyamine biosynthesis modifies PMN responses to lipopolysaccharide (LPS), granulocyte-macrophage colony-stimulating factor (GM-CSF), or granulocyte colony-stimulating factor (G-CSF). Treatment with alpha-difluoromethylornithine (DFMO), a selective inhibitor of the rate-limiting biosynthetic enzyme ornithine decarboxylase, produced dose-dependent inhibition of the respiratory burst in PMNs that were primed by these agents and subsequently activated by formyl-Met-Leu-Phe (fMLP). However, DFMO did not significantly inhibit fMLP-stimulated superoxide generation or alter the induction of PMN adhesion and interleukin-1 beta (IL-1 beta) mRNA expression by LPS or GM-CSF. Antagonism of priming by DFMO correlated with a dose-dependent attenuation of fMLP-induced intracellular Ca2+ mobilization (r > or = 0.96). Since Ca2+ plays an important role in modulating the respiratory burst in primed PMNs, this could, in part, account for the selective effects of DFMO.

[Cloning and expression of a gene associated with HL60 cell apoptosis induced by inhibition of polyamine biosynthesis]

OBJECTIVE

To clone the gene associated with apoptosis induced by an inhibitor of polyamine biosynthesis, alpha-difluoromethylomithine (DFMO).

METHODS

The differential substraction screening was used for gene cloning. The gene expression and apoptosis of transfected HL60 cells were detected by Northern blot, morphological assay, FCM and ladder map of DNA electrophoresis, respectively.

RESULTS

An apoptosis-associated gene named dF4 was cloned from HL60 cells treated with polyamine biosynthesis inhibitor. The programmed cell death was demonstrated in the HL60 cells transfected by dF4 gene.

CONCLUSION

dF4 gene cloned in this study could be a gene regulating apoptosis of HL60 cells.

Cytoskeletal organization and cell motility correlates with metastatic potential and state of differentiation in prostate cancer

The actin cytoskeleton is the key cellular machinery responsible for cellular movement. Changes in the organization and distribution of actin and actin binding protein are necessary for several cellular processes such as focal adhesion formation, cell motility and cell invasion. Here we examined differences in cytoskeletal protein distribution, cell morphometry and cell motility of metastatic and non-metastatic cells. Correlations were found between metastatic potential phenotypic properties such as cell motility, cell spreading and cytoskeletal organization in prostate cancer. As a cell progresses from a normal state to a malignant state, it loses its ability to function normally and also become poorly differentiated. Differentiation therapy is concerned with the redirection of malignant cells toward a terminal, non-dividing state using non-cytotoxic agents. Two well acknowledged differentiation agents, retinoic acid (RA) and diflouromethylomithine (DFMO) were examined for their ability to alter cellular phenotypes associated with metastatic potential in rat prostate cancer cell lines. The results of these studies indicate that there are sub-cellular differences between non-metastatic and highly metastatic cells relative to cytoskeletal organization. We also show that treatment of highly metastatic cells with either RA or DFMO significantly alters cell morphology, cell morphometry and motility to states similar to non-metastatic cells.

alpha-difluoromethylornithine induces apoptosis as well as anti-angiogenesis in the inhibition of tumor growth and metastasis in a human gastric cancer model

Polyamines are essential in various biological systems such as cellular proliferation including tumor growth, differentiation and neoplastic transformation including carcinogenesis. alpha-Difluoromethylornithine (DFMO) is a specific irreversible inhibitor of ornithine decarboxylase, a key enzyme in polyamine biosynthesis, and has been used for clinical chemotherapy and chemoprevention trials against several tumors with various effects. The cellular mechanisms of DFMO action are unclear. Because our hypothesis with regard to polyamine-directed chemoprevention includes anti-angiogenesis and apoptosis as essential parts of the cellular mechanism of action of DFMO, we examined these effects in our human gastric cancer model. In our initial experiments, DFMO inhibited the growth of both human umbilical vein endothelial cells (HUVEC), angio-endothelial cells in vitro, and KKLS, a gastric cancer cell line, in culture, and also the growth of KKLS cells transplanted into nude mice. DFMO also inhibited liver metastasis of KKLS orthotransplanted in the stomach of nude mice. The vessel density of DFMO-treated tumors was significantly lower than that of non-treated tumors. The apoptotic index was significantly greater in DFMO-treated tumors than in non-treated tumors. These results suggest that anti-angiogenesis and apoptosis play significant roles in the DFMO inhibition of the growth and metastasis in this human gastric cancer model and provide evidence that DFMO induces apoptosis.

Nuclear ornithine decarboxylase. Electron microscope autoradiographic identification of the active enzyme using alpha-[5-3H]difluoromethylornithine

alpha-Difluoromethylornithine (DFMO) is an enzyme-activated irreversible inhibitor of ornithine decarboxylase, that forms a covalent bond with the active enzyme. The highly selective binding of tritium-labeled DFMO to ornithine decarboxylase in vivo, as identified by electron microscope autoradiography, was used to determine the intracellular distribution of the enzyme in the germ cells of a polychaete (Ophryotrocha labronica). In mid-oogenesis ornithine decarboxylase was predominantly located in the nurse cells, which are actively supporting growth of the oocytes. On the basis of biochemical analyses ornithine decarboxylase has been considered mainly cytoplasmic in its distribution. However, in metabolically active polychaete cells (oocytes, nurse cells, intestinal and body wall cells), binding sites for tritiated DMFO, indicating the presence of active ornithine decarboxylase, were as abundant in the nucleus. The nucleolus was the most densely labeled organelle in nurse cells and oocytes.

Effect of tumour size on the in vivo growth inhibition of human colon carcinoma cells (HT-29) by colon mitosis inhibitor

We have previously shown that the colon mitosis inhibitor (CMI) suppresses the growth of transplanted HT-29 human colon carcinoma cells by approximately 40%. However, this effect declined along the time-course, as the inoculums progressively grew larger. In the present work we designed a test to assess the effectiveness of CMI as a function of tumour size. After ranking the terminal tumours by ascending size in the control group and the CMI group the growth inhibition was calculated at each rank position. The observed negative correlation between control tumour size and CMI inhibition (r = -0.94, p < 0.001) clearly demonstrated decreased growth inhibition with increased tumour size. Consequently, a retrospective analysis of the smallest and slowest growing tumours showed a profound growth inhibition (72-81%, p < 0.008), whereas a similar analysis of the large and fast growing tumours revealed no significant CMI effect. The increased CMI effect among slow growing tumours was apparently not associated with increased susceptibility to CMI in a subset of slow growing cells because the slow growing subclone HT-29A4 did not show increased CMI effect. Furthermore, HT-29A4 displayed a similar tendency of decreased CMI effect with increased tumour size (r = -0.70, p < 0.001). Interestingly, the same tendency of increased growth inhibitory effect on smaller tumours was also seen with retinoic acid and difluoromethylornithine (r = -0.96, p < 0.001). The apparent enhanced responsiveness among small tumours underlines the importance of early chemoprevention and chemotherapy.

Beneficial effects of a polyamine biosynthesis inhibitor on lupus in MRL-lpr/lpr mice

Difluoromethylornithine (DFMO), an experimental drug that inactivates ornithine decarboxylase and thus reduces the production of polyamines has a beneficial effect on the mean survival time and the clinical and laboratory manifestations of murine lupus in female MRL-lpr/lpr mice. DFMO-treated mice showed a 29% increase in the mean survival time compared with age- and sex-matched control mice of the same strain. Lymphadenopathy was evident in untreated mice at 14 weeks of age, but was delayed until 19 weeks of age in DFMO-treated mice. In addition, the sera of DFMO-treated mice contained a significantly lower concentration of anti-DNA antibodies compared with untreated mice. These results open the possibility of development of a new class of therapeutic agents based on polyamine biosynthesis inhibitors for the treatment of human autoimmune disease. Possible mechanisms for the action of DFMO include its inhibitory action on cell proliferation as well as its ability to prevent DNA from assuming an immunogenic left-handed Z-DNA conformation.

Correlation between the effects of polyamine analogues on DNA conformation and cell growth

Effects of a number of synthetic analogues of the natural polyamines on the B-Z transition of poly(dG-me5dC) and on the aggregation of calf thymus DNA in solution were studied using circular dichroic and UV spectroscopy. The efficiency of induction of the B-Z transition decreased with a decrease in the length of the central alkyl chain of the analogues, and the ability of analogues to aggregate DNA was markedly reduced for compounds ethylated at the terminal amines. Both structural variations appear to have important effects on the biological functions of polyamines. Most analogues studied depleted intracellular levels of natural polyamines, but only those that did not readily induce the B-Z transition and/or aggregate DNA were good inhibitors of cell growth. All but one of the analogues studied were able to rescue cells--at least in part--from the growth-inhibitory effects of alpha-difluoromethylornithine. The single analogue that was unable to effect rescue also failed to induce both the B-Z transition and the aggregation of DNA.

Alpha-difluoromethylornithine, an inhibitor of polyamine biosynthesis, augments cyclosporin A inhibition of cytolytic T lymphocyte induction

The objective of the present investigation was to examine the effect of alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, in combination with the immunosuppressant cyclosporin A (CsA) on cytolytic T lymphocytes (CTL) induction in vitro and in vivo. Treatment with DFMO (0.2 mg/ml) or CsA (10 ng/ml) alone in vitro inhibited mitogen-induced CTL generation by 56% and 51%, respectively. Similarly, DFMO or CsA treatment alone inhibited alloantigen-induced CTL generation by 50% and 62%, respectively. Combination treatment with DFMO and CsA reduced mitogen- and alloantigen-mediated CTL induction by 79% and 90%, respectively. In vivo, DFMO treatment alone did not inhibit alloantigen induced CTL generation. However, DFMO potentiated the immunosuppressive effects of CsA in vivo on CTL induction. DFMO treatment reduced activated lymphocyte putrescine and spermidine levels by 81% and 91%, respectively. Combination treatment with DFMO and CsA, at concentrations that effectively inhibited CTL induction, did not further deplete polyamine levels beyond those levels observed with DFMO alone. CsA treatment with or without DFMO did reduce detectable levels of interleukin 2 (IL-2) activity. DFMO treatment alone did not impair IL-2 production. These results indicate that CsA and DFMO may inhibit different processes required for CTL induction, IL-2 production and polyamine biosynthesis. Therefore, inhibitors of polyamine biosynthesis may be useful in lowering the doses of CsA required to inhibit CTL induction.

Polyamines are involved in retinoic acid-mediated induction of tissue transglutaminase in human peripheral blood monocytes

The differentiation of human peripheral blood monocytes (HPBM) into macrophages, when cultured in vitro, has been associated with an increase in the expression of tissue transglutaminase (TGc). Retinoic acid (RA) addition to 5-day-old cultured monocytes, 36 h later induced about 5-folds increase of TGc content. The preliminary exposure of cultured monocytes to alpha-difluoromethylornithine (DFMO) significantly reduced TGc induction caused by RA. DFMO alone does not induce significant changes in the time-course of TGc activity. In cultured monocytes exposed to DFMO, putrescine and spermidine, but not spermine were significantly depleted. The supplementation of putrescine (1 mM) or spermidine (0.5 mM) to culture medium reversed the inhibiting effect of DFMO on RA-mediated induction of TGc. However, the addition of polyamines in the absence of RA or DFMO did not mimic the induction of TGc by RA. We conclude that TGc induction by RA during in vitro maturation of monocytes to macrophages may be modulated by polyamine availability.