Modulation of cell proliferation and polyamine metabolism in rat liver cell cultures by the iron chelator O-trensox

The antiproliferative effects of the iron chelator O-trensox and the ornithine-decarboxylase (ODC) inhibitor alpha-difluoromethylornithine (DFMO) were characterized in the rat hepatoma cell line FAO, the rat liver epithelial cell line (RLEC) and the primary rat hepatocyte cultures stimulated by EGF. We observed that O-trensox and DFMO decreased cell viabilty and DNA replication in the three culture models. The cytostatic effect of O-trensox was correlated to a cytotoxicity, higher than for DFMO, and to a cell cycle arrest in G0/G1 or S phases. Moreover, O-trensox and DFMO decreased the intracellular concentration of spermidine in the three models without changing significantly the spermine level. We concluded that iron, but also polyamine depletion, decrease cell growth. However, the drop in cell proliferation obtained with O-trensox was stronger compared to DFMO effect. Altogether, our data provide insights that, in the three rat liver cell culture models, the cytostatic effect of the iron chelator O-trensox may be the addition of two mechanisms: iron and polyamine depletion.

Integrin beta3-mediated Src activation regulates apoptosis in IEC-6 cells via Akt and STAT3

Intestinal epithelial (IEC-6) cells are resistant to apoptosis following the inhibition of ODC (ornithine decarboxylase) and subsequent polyamine depletion. The depletion of polyamines rapidly activates NF-kappaB (nuclear factor kappaB) and STAT3 (signal transducer and activator of transcription 3), which is responsible for the observed decrease in apoptosis. Since both NF-kappaB and STAT3 signalling pathways can be activated by Src kinase, we examined its role in the antiapoptotic response. Inhibition of ODC by DFMO (alpha-difluoromethylornithine) increased the activity of Src and ERK1/2 (extracellular-signal-regulated kinase 1/2) within 30 min, which was prevented by exogenous polyamines added to the DFMO-containing medium. Conversely, epidermal growth factor-mediated Src and ERK1/2 activation was not prevented by the addition of polyamines. Inhibition of Src with PP2 {4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine} and a DN-Src (dominant-negative Src) construct prevented the activation of Akt, JAK (Janus kinase) and STAT3. Spontaneous apoptosis was increased in DN-Src-expressing cells and the protective effect of polyamine depletion was lost. Polyamine depletion by DFMO increased integrin beta3 Tyr785 phosphorylation. Cells plated on fibronectin had significantly higher beta3 phosphorylation and Src activation compared with plastic. Exogenous polyamines added to the fibronectin matrix prevented Src activation. Arg-Gly-Asp-Ser inhibited beta3, Src and Akt phosphorylation and sensitized polyamine-depleted cells to tumour necrosis factor alpha/cycloheximide-mediated apoptosis. Fibronectin activated Src and subsequently protected cells from apoptosis. Together, these results suggest that the inhibition of ODC rapidly removes a small pool of available polyamines triggering the activation of beta3 integrin, which in turn activates Src. The subsequent Akt and JAK activation is accompanied by translocation of NF-kappaB and STAT3 to the nucleus and the synthesis of antiapoptotic proteins.

The methionine salvage pathway compound 4-methylthio-2-oxobutanate causes apoptosis independent of down-regulation of ornithine decarboxylase

4-Methylthio-2-oxobutanoic acid (MTOB) is the final compound of the methionine salvage pathway that converts the polyamine byproduct methylthioadenosine to adenine and methionine. Here we find that MTOB inhibits growth of several human cell lines in a dose-dependent manner. Growth inhibition was specific for MTOB as we did not observe any inhibition with other chemically related compounds. MTOB treatment causes apoptosis and reduction of ornithine decarboxylase (ODC) activity but not ODC mRNA. To determine if MTOB exerts its effects primarily via ODC inhibition, we compared the effects of MTOB with the ODC-specific inhibitor difluoromethylornithine (DFMO). We found that MTOB was a more potent inducer of apoptosis than DFMO, lacked activation of caspase 3/7, and was able to induce apoptosis in cells lacking p53. Our results show that MTOB-induced growth inhibition and apoptosis is not simply secondary due to ODC inhibition and implies that MTOB activates apoptosis via other mechanisms.

A comprehensive strategy to combat colon cancer targeting the adenomatous polyposis coli tumor suppressor gene

Somatic cells in the majority of colorectal polyps and cancers contain mutations/deletions in the adenomatous polyposis coli (APC) tumor suppressor gene. APC is involved in normal intestinal development and acts to influence a variety of cellular processes. Loss of APC function leads to intestinal neoplasia in both mice and humans. APC influences expression of specific genes, including the c-Myc oncogene, which functions as a transcriptional activator. Loss of APC function leads to alterations in c-Myc-regulated genes including ornithine decarboxylase (ODC), the first enzyme in polyamine synthesis. A single nucleotide polymorphism (SNP) in the ODC promoter affecting c-Myc-dependent expression has been associated with risk of colorectal and other cancers. Pharmaceuticals that target structural features of the c-Myc promoter, and suppress expression of c-Myc and other genes regulated by similar promoter elements, are being developed as potential colorectal cancer chemotherapies. Difluoromethylornithine (DFMO), a selective inhibitor of ODC, is under clinical evaluation as a colorectal cancer chemopreventive agent. APC and APC-dependent genes, such as c-Myc and ODC, may be useful as genetic markers of risk and as targets for chemoprevention and therapy for colorectal cancer.

In vivo enhancement of herpes simplex virus thymidine kinase/ganciclovir cancer gene therapy with polyamine biosynthesis inhibition

We have earlier demonstrated that inhibition of polyamine biosynthesis with difluoromethylornithine (DFMO) can be used to enhance the cytotoxicity of herpes simplex virus thymidine kinase/ganciclovir (HSV-TK/GCV) gene therapy in different tumor cell lines. Here, the utility of this treatment combination was tested in vivo in a nude mouse tumor model. First, the effect of DFMO was verified by treating mice bearing subcutaneous 9L rat glioma tumors with 2% DFMO in drinking water. The drug treatment induced almost complete suppression of ornithine decarboxylase activity, and as a result, a strong decrease in intratumoral putrescine and spermidine concentrations, which were normalized 4 days after drug removal. Consequently, the tumors displayed a significant reduction in the proliferation activity that was increased to 20% higher than the normal level at day 4 and returned to normal level 7 days after DFMO removal. Next, 9L tumors with 30% of TK-GFP fusion gene positive cells were induced and the animals were given DFMO and GCV in 2 treatment schemes, with the drug administration periods overlapping either 5 or 2 days. The analysis of tumor size at the end of the treatment revealed that DFMO can enhance HSV-TK/GCV cytotoxicity when the overlap between DFMO and GCV was 5 days, but the result was not significant. However, the 2-day overlap scheme yielded a significantly (p < 0.05, ANOVA) enhanced antitumor effect. In conclusion, the data here confirms that a novel combination of 2 clinically relevant treatment modalities, polyamine deprivation and HSV-TK/GCV suicide gene therapy, can be used synergistically in vivo.

Combination therapy with 2-difluoromethylornithine and a polyamine transport inhibitor against murine squamous cell carcinoma

Using a recently developed autochthonous mouse model of squamous cell carcinoma (SCC), a combination therapy targeting polyamine metabolism was evaluated. The therapy combined 2-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase (ODC), and MQT 1426, a polyamine transport inhibitor. In 1 trial lasting 4 weeks, combination therapy with 0.5% DFMO (orally, in the drinking water) and MQT 1426 (50 mg/kg i.p., bid) was significantly more effective than with either single agent alone when complete tumor response was the endpoint. In the combination group, 72% of SCCs responded completely vs. 21 and 0% for DFMO and MQT 1426, respectively. A second trial involved a 4-week treatment period followed by 6 weeks off-treatment. With apparent cures as an endpoint, combination therapy was again more effective than either agent alone: a 50% apparent cure rate was observed in the combination group vs. 7.7% in the DFMO group. MQT 1426 had no inhibitory effect on SCC ODC activity nor did it enhance the inhibition by DFMO, but SCC polyamine levels declined more rapidly when treated with combination therapy vs. DFMO alone. The apoptotic index in SCCs was transiently increased by combination therapy but not by DFMO alone. Thus, targeting both polyamine biosynthesis and polyamine transport from the tumor microenvironment enhances the efficacy of polyamine-based therapy in this mouse model of SCC.

Analysis of the interactions of Nrf-2, PMF-1, and CSN-7 with the 5'-flanking sequence of the mouse 4E-BP1 gene

Nuclear factor erythroid 2-related factor 2 (Nrf-2) binds to a specific polyamine responsive element (PRE) in the promoter region of the spermidine-spermine acetyltransferase (SSAT) gene, a key component of the polyamine catabolic pathway. Regulation of SSAT gene transcription requires the additional interaction of Nrf-2 with polyamine modulated factor 1 (PMF-1). Likewise, transcription of the eukaryotic initiation factor 4E binding protein 1 (4E-BP1) gene is regulated in a polyamine-dependent manner, but the actual mechanism has not previously been determined. Analysis of the 5'-flanking sequence of the murine 4E-BP1 gene indicated the presence of several potential PRE sites, which might be involved in regulating its transcription. Our goal in this research was to determine potential interactions between Nrf-2, PMF-1, the human homologue of the Arabidopsis signalosome complex (CSN-7), and these potential PRE sites. Four PCR fragments containing regions with considerable homology (78%) to the human PRE were generated from the 5'-flanking sequence of the mouse 4E-BP1 gene and the fragments were used in electrophoretic gel mobility shift and supershift assays. Purified Nrf-2 interacted with all four of these fragments, and similar gel shifts were observed with both cytoplasmic and nuclear fractions of NIH-3T3 cells. However, polyamine depletion with difluoromethylornithine (DFMO) eliminated the gel shift. Supershift assays indicated that the shift was due to the binding of Nrf-2, and the binding was competitive with a known Nrf-2 binding sequence. Purified PMF-1 did not bind any of the PCR fragments alone, but when added with Nrf-2, decreased the magnitude of the gel shift for one of the fragments (PRE located at -2060 relative to the transcription start site). CSN-7 did not interact with the sequences, nor did it inhibit protein/DNA interaction. These data indicate a possible mechanism by which polyamines enhance the binding of a Nrf-2/PMF-1 complex to the 5'-flanking region of the 4E-BP1 gene. Since polyamines increase expression of the 4E-BP1 gene, it seems likely that formation of this complex is involved in its transcriptional regulation.

B23 is a downstream target of polyamine-modulated CK2

Our previous studies have shown that the overexpression of ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis, increases the enzymatic activity of the polyamine-responsive enzyme casein kinase 2 (CK2). Because CK2 is known to preferentially associate with the nuclear matrix in response to other trophic stimuli, we investigated the effects of ODC overexpression on CK2 localisation and on the CK2-mediated phosphorylation of a known CK2 substrate, the nucleolar phosphoprotein B23. Immunofluorescence analysis of CK2 and B23 in primary keratinocytes revealed that ODC overexpression resulted in the colocalisation of CK2 with B23 at the nucleolar borders. ODC overexpression also increased CK2 kinase activity 2-fold at the nuclear matrix, a response which could be abrogated by treatment of K6/ODC transgenic keratinocytes with the ODC inhibitor alpha-difluoromethylornithine (DFMO). Levels of B23 protein were also elevated in ODC-overexpressing cells compared to normal cells or transgenic cells treated with DFMO. This increase in protein level was neither due to an increase in steady-state mRNA levels, nor was it due to increased stability of B23 protein. Phosphorylation of B23 was also increased in ODC-overexpressing cells, and this increased phosphorylation could be blocked by treatment of the cells with the CK2 kinase inhibitors apigenin or 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB). These data suggest that B23 may be a downstream effector of polyamines via phosphorylation by the protein kinase CK2.

EFFECTS OF POLYAMINES ON TWO STRAINS OF TRYPANOSOMA BRUCEI IN INFECTED RATS AND IN VITRO CULTURE

We studied the effects of polyamines, which are necessary for proliferation and antioxidation in Trypanosoma brucei gambiense Wellcome strain (WS) and Trypanosoma brucei brucei ILtat 1.4 strain (IL). No difference was found in activity of ornithine decarboxylase (ODC), a key enzyme in polyamine synthesis in trypanosomes, in both strains maintained in vitro; higher (P < 0.05) ODC values were found in IL in vivo. However, WS in vivo exhibited higher proliferation rates with higher spermidine content and decreased host survival times than IL. The in vitro proliferation and polyamine contents of WS increased with the addition of polyamine to the 1-difluoromethylornithine culture medium, but not IL. These results suggested that WS uses extracellular polyamine for proliferation. In the in vitro culture, WS was less tolerant of hydrogen peroxide (oxidative stress) than IL, and malondialdehyde levels in WS were higher than in IL. The expression of trypanothione synthetase mRNA in WS in vitro was higher than in IL. These results suggest that IL is dependent on the synthesis of polyamines for proliferation and reduction of oxidative stress, whereas WS is dependent on the uptake of extracellular polyamines. A thorough understanding of the differences in the metabolic capabilities of various trypanosomes is important for the design of more effective medical treatments.

Nitric oxide and polyamine pathway-dependent modulation of neutrophil free amino- and α-keto acid profiles or host defense capability

We have examined the effects of N(omega)-nitro-L-arginine-methylester-hydrochloride [L-NAME; inhibitor of nitric oxide synthase], S-nitroso-N-acetyl-penicillamine [SNAP; nitric oxide donor], alpha-difluoro-methyl-ornithine [DFMO; inhibitor of ornithine decarboxylase] arginine or ornithine as well as the combination of arginine or ornithine with L-NAME, SNAP or DFMO on intracellular free amino- and alpha-keto acid profiles and the immune function markers superoxide anion and hydrogen peroxide generation as well as released myeloperoxidase activity in neutrophils (PMN). Although the underlying mechanisms still remain unclear, we believe from our results that nitric oxide as well as polyamine-dependent pathways are involved in the signal transmission of free radical molecule, beneficial nutritional therapy or maleficient pharmacological stress-induced alterations in PMN nutrient composition. Relevant changes in intragranulocyte free amino- and alpha-keto acid homeostasis and metabolism, especially, may be one of the determinants in PMN nutrition that positively or negatively influences and modulate neutrophil host defence capability and immunocompetence.

Polyamine depletion inhibits apoptosis following blocking of survival pathways in human chondrocytes stimulated by tumor necrosis factor-alpha

Chondrocyte apoptosis can be an important contributor to cartilage degeneration, thereby making it a potential therapeutic target in articular diseases. To search for new approaches to limit chondrocytic cell death, we investigated the requirement of polyamines for apoptosis favored by tumor necrosis factor-alpha (TNF), using specific polyamine biosynthesis inhibitors in human chondrocytes. The combined treatment of C-28/I2 chondrocytes with TNF and cycloheximide (CHX) resulted in a prompt effector caspase activation and internucleosomal DNA fragmentation. Pre-treatment of chondrocytes with alpha-difluoromethylornithine (DFMO), an ornithine decarboxylase (ODC) inhibitor, markedly reduced putrescine and spermidine content as well as the caspase-3 activation and DNA fragmentation induced by TNF and CHX. DFMO treatment also inhibited the increase in effector caspase activity provoked by TNF plus MG132, a proteasome inhibitor. DFMO decreased caspase-8 activity and procaspase-8 content, an apical caspase essential for TNF-induced apoptosis. Although DFMO increased the amount of active, phosphorylated Akt, inhibitors of the Akt pathway failed to restore the TNF-induced increase in caspase activity blunted by DFMO. DFMO also reduced the increase in caspase activity induced by staurosporine, but in this case Akt inhibition prevented the DFMO effect. Pre-treatment with CGP 48664, an S-adenosylmethionine decarboxylase (SAMDC) inhibitor markedly reduced spermidine and spermine levels, and provoked effects similar to those caused by DFMO. Finally DFMO was effective even in primary osteoarthritis (OA) chondrocyte cultures. These results suggest that the intracellular depletion of polyamines in chondrocytes can inhibit both the death receptor pathway by reducing the level of procaspase-8, and the apoptotic mitochondrial pathway by activating Akt.

Role of polyamines derived from arginine in differentiation and proliferation of human blood cells

L-Arginine is a precursor of polyamine, nitric oxide (NO), creatine, and agmatine and is essential for the differentiation and proliferation of blood cells, although the precise biological role of L-arginine is unclear. We have recently reported that the depletion of L-arginine in cultured medium prevented both proliferation and differentiation of blood cells (Shima et al., Blood First Edition Paper, October 6, 2005; DOI 10.1182). Since one of metabolic products of L-arginine in the cells is polyamine that associates with cell differentiation and proliferation, the effects of L-arginine on the human K562 cell line and human cord blood-derived CD34 positive cells were investigated by focusing on polyamines such as putrescine, spermidine, and spermine in the present study. When polyamines were added to the culture medium in the absence of L-arginine, the cells did not grow or differentiate well. However, when intracellular polyamines were depleted using ornithine decarboxylase inhibitor, alpha-difluoromethylornithine (DFMO), the proliferation and differentiation of K562 cells to erythrocytes were reduced even in the presence of L-arginine. Moreover, in the presence of DFMO, cell differentiation and proliferation were recovered by the addition of putrescine or spermidine in the presence of L-arginine. Accordingly, it was demonstrated that polyamines are essential for the proliferation and differentiation of the blood cells as the metabolites of L-arginine and the externally added polyamines are also effective by being taken up through polyamine transporter.

STAT3-mediated transcription of Bcl-2, Mcl-1 and c-IAP2 prevents apoptosis in polyamine-depleted cells

Activation of STAT3 (signal transducer and activator of transcription 3) plays a crucial role in cell survival and proliferation. The aim of the present study was to clarify the role of STAT3 signalling in the protection of polyamine-depleted intestinal epithelial cells against TNF-alpha (tumour necrosis factor-alpha)-induced apoptosis. Polyamine depletion by DFMO (alpha-difluoromethylornithine) caused phosphorylation of STAT3 at Tyr-705 and Ser-727. Phospho-Tyr-705 STAT3 was immunolocalized at the cell periphery and nucleus, whereas phospho-Ser-727 STAT3 was predominantly detected in the nucleus of polyamine-depleted cells. Sustained phosphorylation of STAT3 at tyrosine residues was observed in polyamine-depleted cells after exposure to TNF-alpha. Inhibition of STAT3 activation by AG490 or cell-membrane-permeant inhibitory peptide (PpYLKTK; where pY represents phospho-Tyr) increased the sensitivity of polyamine-depleted cells to apoptosis. Expression of DN-STAT3 (dominant negative-STAT3) completely eliminated the protective effect of DFMO against TNF-alpha-induced apoptosis. Polyamine depletion increased mRNA and protein levels for Bcl-2, Mcl-1 (myeloid cell leukaemia-1) and c-IAP2 (inhibitor of apoptosis protein-2). Significantly higher levels of Bcl-2 and c-IAP2 proteins were observed in polyamine-depleted cells before and after 9 h of TNF-alpha treatment. Inhibition of STAT3 by AG490 and DN-STAT3 decreased Bcl-2 promoter activity. DN-STAT3 decreased mRNA and protein levels for Bcl-2, Mcl-1 and c-IAP2 in polyamine-depleted cells. siRNA (small interfering RNA)-mediated inhibition of Bcl-2, Mcl-1 and c-IAP2 protein levels increased TNF-alpha-induced apoptosis. DN-STAT3 induced the activation of caspase-3 and PARP [poly(ADP-ribose) polymerase] cleavage in polyamine-depleted cells. These results suggest that activation of STAT3 in response to polyamine depletion increases the transcription and subsequent expression of anti-apoptotic Bcl-2 and IAP family proteins and thereby promotes survival of cells against TNF-alpha-induced apoptosis.

Perillyl alcohol induces c-Myc-dependent apoptosis in Bcr/Abl-transformed leukemia cells

Bcr/Abl-transformed cells strongly resist apoptosis induced by most chemotherapy agents. However, in Bcr/Abl-transformed cells the monocyclic monoterpene, perillyl alcohol (POH), induces G0/G1 arrest and apoptosis without affecting Bcr/Abl expression or activity. The primary effect of POH is to cause growth arrest while apoptosis is a consequence of this arrest. Since Bcr/Abl induces constitutive expression of c-Myc, which is necessary for cell cycle transit from G1 into the S phase, we tested whether POH causes growth arrest by inhibiting expression of c-Myc. However, in POH-arrested Bcr/Abl-transformed cells, expression of c-Myc RNA and protein was not affected. Because expression of c-Myc during growth arrest can lead to apoptosis, we examined the role of c-Myc in POH-induced apoptosis. c-Myc induces expression of the ornithine decarboxylase (ODC) gene, which synthesizes polyamines that are necessary for cell growth. Myc-induced apoptosis operates through ODC and can be prevented with the ODC inhibitor, alpha-difluoromethylornithine (DFMO). We report that DFMO strongly protects cells from POH-induced apoptosis. These results show that in Bcr/Abl-transformed cells, POH activates a Myc-ODC apoptotic pathway that is not protected by the Bcr/Abl antiapoptotic mechanism.

Interaction between Polyamines and the Mitogen-Activated Protein Kinase Pathway in the Regulation of Cell Cycle Variables in Breast Cancer Cells

Inhibition of polyamine biosynthesis with alpha-difluoromethylornithine (DFMO) has been shown to inhibit proliferation of breast cancer cells although its mechanism of action has not been fully elucidated. To address this issue, we tested the effects of DFMO on cell cycle variables of MDA-MB-435 human breast cancer cells in culture. We also focused on the possible mediatory role of the mitogen-activated protein kinase (MAPK) pathway on the cell cycle effects of DFMO because this compound has been shown to activate MAPK signaling. We found that DFMO caused a p53-independent increase in p21 and its association with cyclin-dependent kinase (cdk)-2 and decreased cdk-2 protein as well as its phosphorylation on Thr160. In addition, DFMO markedly suppressed the expression of the full-length and low molecular weight forms of cyclin E. These effects of DFMO were reversible with exogenous putrescine, thus indicating that they are specifically mediated through polyamine depletion. Cdk-2 activity was drastically reduced in DFMO-treated breast cancer cells which exhibited a reduction in retinoblastoma (Rb) phosphorylation and protein. As a predictable consequence of these effects, DFMO caused a G1-S block. In addition, DFMO inhibited G2-M transition, most likely as a result of its induction of p21 expression. Inhibition of the MAPK pathway with PD98059 or U0126 blocked the DFMO-induced induction of p21 and the reduction of cdk-2 protein. PD98059 reversed the G2-M block induced by DFMO (probably as a result of suppression of p21) but not the G1-S arrest. MDA-MB-435 cells treated with PD98059 or U0126 in the presence and absence of DFMO exhibited a marked increase in the expression of p27 and its association with cdk-2, a decrease in phosphorylation of cdk-2 on Thr160, and a decrease in cyclin E expression. As predicted, PD98059 treatment reduced cdk-2 activity and Rb phosphorylation while reversing the decrease in Rb protein induced by DFMO. Neither DFMO nor PD98059, either alone or in combination, reduced cdk-4 activity despite a marked induction in p15 expression caused by DFMO. Our results indicate that activation of the MAPK pathway accounts for some of the effects of DFMO on cell cycle events of breast cancer cells. Inhibition of the MAPK pathway, however, does not reverse the cell cycle arrest induced by DFMO because of activation of alternative mechanisms leading to suppression of cdk-2 activity.

Effects of polyamine synthesis inhibitors on primary tumor features and metastatic capacity of human breast cancer cells

We have previously reported that inhibition of polyamine biosynthesis with alpha-difluoromethylornithine (DFMO) reduces pulmonary metastasis from MDA-MB-435 human breast cancer xenografts without affecting the volume of the primary tumors (Manni et al. Clin Exp Mets 20:321, 2003). In these experiments, we show that DFMO treatment (2% in drinking H(2)O) reduced the growth fraction of the primary tumors by 60%. However, this effect was counter-balanced by a similar reduction in non-apoptotic necrosis, thus accounting for the preservation of tumor volume in DFMO-treated mice. DFMO treatment caused a 4-fold increase in cytoplasmic staining for cleaved caspase-3 (as opposed to the nuclear staining observed in control tonsil tissue) in the absence of histologic evidence of apoptosis. DFMO treatment reduced the number of mice with pulmonary metastasis by approximately 80% and the number of metastasis per mouse by >90% in association with a reduction in invasiveness of the primary tumor in the surrounding dermis and muscle by approximately 30%. DFMO treatment increased ERK phosphorylation in the tumors, an effect that has been found by us in vitro to be causally linked to the anti-invasive effect of the drug (Manni et al. Clin Exp Metast 2004; 21: 461]. DFMO also increased tyrosine phosphorylation of STAT-3 and expression of STAT-1 and JNK proteins. Administration of SAM486A (1 mg/kg/i.p. daily), an inhibitor of S-adenosylmethionine decarboxylase, either individually or in combination with DFMO, was not found to exert any biological or biochemical effects, most likely as a result of its failure to suppress tissue polyamine levels under these experimental conditions.

Effect of Polyamine Homologation on the Transport and Biological Properties of Heterocyclic Amidines

Five sets of heterocyclic derivatives of various sizes and complexities coupled by an amidine function to putrescine, spermidine, or spermine were prepared. They were essentially tested to determine the influence of the polyamine chain on their cellular transport. To comment on affinity and on selective transport via the polyamine transport system (PTS), K(i) values for polyamine uptake were determined in L1210 cells, and the cytotoxicity and accumulation of the conjugates were determined in CHO and polyamine transport-deficient mutant CHO-MG cells, as well as in L1210 and alpha-difluoromethylornithine- (DFMO-) treated L1210 cells. Unlike spermine, putrescine and spermidine were clearly identified as selective motifs that enable cellular entry via the PTS. However, this property was clearly limited by the size of substituents: these polyamines were able to ferry a dihydroquinoline system via the PTS but did not impart any selectivity to bulkier substituents.

[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).

Induction of apoptotic cell death by putrescine

The polyamines are essential for cellular growth and differentiation. Ornithine decarboxylase (ODC), which catalyses the first step in the biosynthesis of the polyamines, has a very fast turnover and is subject to a strong feedback control by the polyamines. In the present study, we show that overexpression of a metabolically stable ODC in CHO cells induced a massive cell death unless the cells were grown in the presence of the ODC inhibitor alpha-difluoromethylornithine (DFMO). Cells overexpressing wild-type (unstable) ODC, on the other hand, were not dependent on the presence of DFMO for their growth. The induction of cell death was correlated with a dramatic increase in cellular putrescine levels. Analysis using flow cytometry revealed perturbed cell cycle kinetics, with a large accumulation of cells with sub-G1 amounts of DNA, which is a typical sign of apoptosis. Another strong indication of apoptosis was the finding that one of the key enzymes in the apoptotic process, caspase-3, was induced when DFMO was omitted from the growth medium. Furthermore, inhibition of the caspase activity significantly reduced the recruitment of cells to the sub-G1 fraction. In conclusion, deregulation of polyamine homeostasis may negatively affect cell proliferation and eventually lead to cell death by apoptosis if putrescine levels become too high.

Polyamines are involved in murine kidney development controlling expression of c-ret, E-cadherin, and Pax2/8 genes

Polyamines play an important role in cell growth and differentiation. We studied changes in morphogenesis and the expression of the developmental control genes in the embryonic mouse kidney in response to polyamine depletion, using a kidney organ culture approach and reducing the polyamine pools with alpha-difluoromethylornithine (DFMO), an irreversible suicide inhibitor of ornithine decarboxylase (ODC). We found that inhibition of ODC results in a systematic kidney organogenesis phenotype, in that the DFMO-treated kidney specimens were of smaller size, had less epithelial ureteric bud branches, and their mesenchymal-derived tubule formation was retarded. These dysmorphologies were shown to be associated with changes in cell proliferation. Whole-mount in situ experiments revealed that inhibition of ODC causes increases in epithelial c-ret and E-cadherin and a decrease in mesenchymal Pax-8 expression, whereas levels of epithelial Wnt-11, mesenchymal GDNF, FoxD1, and Pax-2 transcripts remain unchanged. We studied regulation of the Pax-2 gene by analyzing a mouse line in which lacZ was driven by an 8.5 kb Pax-2 enhancer in the epithelial ureteric bud, and found that Pax-2 expression, as indicated by lacZ expression, increased after DFMO treatment. Transient transfection experiments in HEK 293 cells with the minimal Pax-2 promoter showed enhanced transcription upon reduction of the polyamine pools. We propose that ODC and polyamines have an important role in kidney organogenesis, being involved in the regulation of the expression of genes implicated in epithelial-mesenchymal tissue interactions.

[Effect of alpha-difluoromethylornithine on the expression of ODC mRNA in the cortex and hippocampus in rats after cerebral ischemia reperfusion]

OBJECTIVE

To explore the mechanism of alpha-difluoromethylornithine (DFMO) inhibiting ODC activity in the cortex and hippocampus in rats.

METHODS

Forty male rats was randomly divided into ischemal control group and DFMO pretreatment group. DFMO was given intravenously half an hour before global cerebral ischemia, and expression of ODC mRNA was measured by comparative reverse transcription-polymerase chain reaction (RT-PCR) in the cortex and hippocampus in rats after 2, 4, 6 h and 8 h of reperfusion. The variations of the expression of ODC mRNA were studied in the DFMO pretreatment group and the ischemal control group respectively.

RESULTS

After 2, 4 and 6 h of reperfusion, the expression of ODC mRNA in the cortex and hippocampus in the pretreatment group was lower than that in the ischemia control group significantly (P <0.05, P <0.01), but not at 8 h reperfusion (P > 0.05).

CONCLUSION

DFMO suppressed the expression of ODC mRNA after different lengths of reperfusion following 10-minute global cerebral ischemia in rats and it may be one of the ways for DFMO to inhibit ODC activity.

Polyamine depletion inhibits irradiation-induced apoptosis in intestinal epithelia

Our group has previously shown that polyamine depletion delays apoptosis in rat intestinal epithelial (IEC-6) cells (Ray RM, Viar MJ, Yuan Q, and Johnson LR, Am J Physiol Cell Physiol 278: C480-C489, 2000). Here, we demonstrate that polyamine depletion inhibits gamma-irradiation-induced apoptosis in vitro and in vivo. Pretreatment of IEC-6 cells with 5 mM alpha-difluoromethylornithine (DFMO) for 4 days significantly reduced radiation-induced caspase-3 activity and DNA fragmentation. This protective effect was prevented by the addition of 10 muM exogenous putrescine. Radiation exposure to mice resulted in a high frequency of apoptosis over cells positioned fourth to seventh in crypt-villus units. Pretreatment of mice with 2% DFMO in drinking water significantly reduced apoptotic cells from approximately 2.75 to 1.61 per crypt-villus unit, accompanied by significant decreases in caspase-3 levels. Further examination showed that DFMO pretreatment inhibited the radiation-induced increase in the proapoptotic protein Bax. Moreover, DFMO pretreatment significantly enhanced the intestinal crypt survival rate by 2.1-fold subsequent to radiation and ameliorated mucosal structural damage. We conclude that polyamine depletion by DFMO inhibits gamma-irradiation-induced apoptosis of intestinal epithelial cells both in vitro and in vivo through inhibition of Bax and caspase-3 activity, which leads to attenuation of radiation-inflicted intestinal injury. These data indicate that DFMO may be therapeutically useful to counteract the gastrointestinal toxicity caused by chemoradiotherapy. This is the first demonstration that polyamines are required for apoptosis in vivo.

Arginase inhibition reduces endothelial dysfunction and blood pressure rising in spontaneously hypertensive rats

OBJECTIVE

A decrease in nitric oxide (NO) bioavailability has been proposed to contribute to endothelial dysfunction and increased peripheral resistances during essential arterial hypertension. Given that arginine is a substrate for both arginase and NO synthase, arginase activity may be a critical factor in NO bioavailability. To test this hypothesis, we evaluated the effects of the arginase inhibitor alpha-difluoromethylornithine (DFMO) in spontaneously hypertensive rats (SHR).

METHODS

Vascular reactivity experiments were performed on thoracic aortic rings from 10-week-old SHR and their normotensive counterparts, Wistar-Kyoto (WKY) rats. Blood pressure was measured by the tail-cuff method. DFMO treatment (30 mg/kg daily in drinking water) was started in 5-week-old SHR and maintained for 5 weeks. Aortic arginase I and arginase II expression as well as arginase activity were evaluated by western blotting and the spectrophotometric method, respectively.

RESULTS

DFMO (1.2 x 10 mol/l) enhanced the vascular response to acetylcholine both in SHR (+24%, P < 0.01) and WKY rats (+12%, P < 0.01), and reversed the effects of the NO synthase inhibitor N-nitro-L-arginine-methyl-ester. The vasorelaxant response to sodium nitroprusside on endothelium-denuded rings was not affected by DFMO, neither in SHR nor in WKY rats. In SHR, DFMO prevented the increase in blood pressure and improved the response of aortic rings to acetylcholine. Finally, as compared with WKY rats, SHR exhibited increased expression of vascular arginase I (+72%, P < 0.05) and arginase II (+91%, P < 0.05) as well as increased arginase activity (+26%, P < 0.05).

CONCLUSIONS

Our results showed that arginase inhibition reduced endothelial dysfunction and blood pressure rising in SHR.

Depletion of polyamines and increase of transforming growth factor-beta1, c-myc, collagen-type I, matrix metalloproteinase-1, and metalloproteinase-2 mRNA in primary human gingival fibroblasts

BACKGROUND

The polyamines spermidine, spermine, and putrescine are known to be deeply linked with growth processes, gene expression, and extracellular matrix synthesis. Their cellular content depends primarily on the activity of the enzyme ornithine decarboxylase. High levels of ornithine decarboxylase and polyamines have been found in proliferative, inflammatory, and neoplastic pathologies of the oral cavity and in gingival fluid. Difluoromethylornithine (DFMO) selectively inhibits ornithine decarboxylase, thus depleting polyamine content and preventing cell proliferation and synthesis activity. The aim of this study was to investigate whether DFMO treatment could modify the genes involved in cell proliferation and extracellular matrix turnover.

METHODS

Fibroblasts derived from non-inflamed gingiva were maintained in Dulbecco's modified Eagle's medium (DMEM) plus alpha-difluoromethylornithine for 4 days. At 0, 24, 48, 72, and 96 hours cell number was assessed, polyamine levels were quantified with high performance liquid chromatography (HPLC) method, and transforming growth factor-beta1 (TGF-beta1), c-myc, matrix metalloproteinases (MMP)-1 and 2, collagen type I (COL-I) and tissue inhibitor of matrix metalloproteinases (TIMP)-1 were evaluated by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Fibroblasts treated with DFMO significantly decreased cell proliferation, ornithine decarboxylase activity, and putrescine levels at all treatment times, spermidine after 72 and 96 hours, and spermine after 96 hours of culture. Total polyamines decreased (P < or =0.01) at 96 hours after DFMO treatment, while c-myc, TGF-beta1, MMP-1 and 2, COL-I mRNA significantly increased. Conversely, TIMP-1 did not show any significant change. The polyamines trend was not correlated to c-myc, TGF-beta1, MMP-1 and -2, and TIMP-1 mRNA levels. Transforming growth factor-beta1 and c-myc mRNA expression were related and correlated to MMP-1 and 2, COL-I and TIMP-1 mRNA trend after DFMO treatment.

CONCLUSIONS

Our data show that as the polyamine content decreases, TGF-beta1, c-myc, MMP-1 and -2, and COL-I mRNA levels increase, therefore a negative regulatory role of the polyamines on the mRNA expression could be suggested.

Polyamine depletion reduces TNFalpha/MG132-induced apoptosis in bone marrow stromal cells

Polyamines are powerful modulators of both growth and survival in mammalian cells. In this study, we investigated the possibility of attenuating the process of apoptosis in bone marrow stromal cells (BMSCs), which comprise mesenchymal stem cells, by reducing the intracellular levels of polyamines. BMSCs were isolated from rat femurs and expanded for 12 days. At this time, BMSCs were CD34neg, CD45neg, and mostly CD90pos. BMSCs were grown for an additional 2 days in the presence of 1 mM alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, which reduced the content of both putrescine and spermidine by nearly 90%. DFMO treatment progressively slowed down BMSC proliferation, as determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assay, without arresting their growth completely. The effect of polyamine depletion on caspase-3 activity was evaluated in BMSCs after treatment with 500 U/ml tumor necrosis factor-alpha (TNFalpha) and 5 microM MG132, an inhibitor of proteasome. Caspase-3 activity increased linearly over a period of 24-hour stimulation (p<.01), but this augmentation was blunted by 50% after DFMO administration (p<.05). The effect of DFMO on TNFalpha/MG132-induced upregulation of caspase-3 activity was reversed by the addition of 100 microM putrescine, confirming that polyamines were really involved in the apoptotic process. Also, the number of apoptotic BMSCs after TNFalpha/MG132 treatment, as determined by terminal transferase-mediated dUTP nick end-labeling (TUNEL) assay, were threefold reduced after polyamine depletion (p<.05). On the contrary, DFMO did not affect the MG132-mediated increase in p53 abundance, nor its translocation to the nucleus. Thus, polyamine depletion can be considered a useful tool for counteracting programmed cell death in BMSCs without involving the p53 proapoptotic protein.