Polyamines in mammalian tumors. Part I

Polyamine pathway inhibition as a novel therapeutic approach to treating neuroblastoma

Polyamines are highly regulated essential cations that are elevated in rapidly proliferating tissues, including diverse cancers. Expression analyses in neuroblastomas suggest that up-regulation of polyamine pro-synthetic enzymes and down-regulation of catabolic enzymes is associated with poor prognosis. Polyamine sufficiency may be required for MYCN oncogenicity in MYCN amplified neuroblastoma, and targeting polyamine homeostasis may therefore provide an attractive therapeutic approach. ODC1, an oncogenic MYCN target, is rate-limiting for polyamine synthesis, and is overexpressed in many cancers including neuroblastoma. Inhibition of ODC1 by difluoromethylornithine (DFMO) decreased tumor penetrance in TH-MYCN mice treated pre-emptively, and extended survival and synergized with chemotherapy in treating established tumors in both TH-MYCN and xenograft models. Efforts to augment DFMO activity, or otherwise maximally reduce polyamine levels, are focused on antagonizing polyamine uptake or augmenting polyamine export or catabolism. Since polyamine inhibition appears to be clinically well tolerated, these approaches, particularly when combined with chemotherapy, have great potential for improving neuroblastoma outcome in both MYCN amplified and non-MYCN amplified neuroblastomas.

Lipophilic lysine-spermine conjugates are potent polyamine transport inhibitors for use in combination with a polyamine biosynthesis inhibitor

Cancer cells can overcome the ability of polyamine biosynthesis inhibitors to completely deplete their internal polyamines by the importation of polyamines from external sources. This paper discusses the development of a group of lipophilic polyamine analogues that potently inhibit the cellular polyamine uptake system and greatly increase the effectiveness of polyamine depletion when used in combination with DFMO, a well-studied polyamine biosynthesis inhibitor. The attachment of a length-optimized C(16) lipophilic substituent to the epsilon-nitrogen atom of an earlier lead compound, D-Lys-Spm (5), has produced an analogue, D-Lys(C(16)acyl)-Spm (11) with several orders of magnitude more potent cell growth inhibition on a variety of cultured cancer cell types including breast (MDA-MB-231), prostate (PC-3), melanoma (A375), and ovarian (SK-OV-3), among others. These results are discussed in the context of a possible membrane-catalyzed interaction with the extracellular polyamine transport apparatus. The resulting novel two-drug combination therapy targeting cellular polyamine metabolism has shown exceptional efficacy against cutaneous squamous cell carcinomas (SCC) in a transgenic ornithine decarboxylase (ODC) mouse model of skin cancer. A majority (88%) of large, aggressive SCCs exhibited complete or nearly complete remission to this combination therapy, whereas responses to each agent alone were poor. The availability of a potent polyamine transport inhibitor allows, for the first time, for a real test of the hypothesis that starving cells of polyamines will lead to objective clinical response.

Metabolic signature of breast cancer cell line MCF-7: profiling of modified nucleosides via LC-IT MS coupling

Background

Cancer, like other diseases accompanied by strong metabolic disorders, shows characteristic effects on cell turnover rate, activity of modifying enzymes and DNA/RNA modifications, resulting also in elevated amounts of excreted modified nucleosides. For a better understanding of the impaired RNA metabolism in breast cancer cells, we screened these metabolites in the cell culture supernatants of the breast cancer cell line MCF-7 and compared it to the human mammary epithelial cells MCF-10A. The nucleosides were isolated and analyzed via 2D-chromatographic techniques: In the first dimension by cis-diol specific boronate affinity extraction and subsequently by reversed phase chromatography coupled to an ion trap mass spectrometer.

Results

Besides the determination of ribonucleosides, additional compounds with cis-diol structure, deriving from cross-linked biochemical pathways, like purine-, histidine- and polyamine metabolism were detected. In total, 36 metabolites were identified by comparison of fragmentation patterns and retention time. Relation to the internal standard isoguanosine yielded normalized area ratios for each identified compound and enabled a semi-quantitative metabolic signature of both analyzed cell lines.

13 of the identified 26 modified ribonucleosides were elevated in the cell culture supernatants of MCF-7 cells, with 5-methyluridine, N²,N²,7-trimethylguanosine, N⁶-methyl-N⁶-threonylcarbamoyladenosine and 3-(3-aminocarboxypropyl)-uridine showing the most significant differences. 1-ribosylimidazole-4-acetic acid, a histamine metabolite, was solely found in the supernatants of MCF-10A cells, whereas 1-ribosyl-4-carboxamido-5-aminoimidazole and S-adenosylmethionine occurred only in supernatants of MCF-7 cells.

Conclusion

The obtained results are discussed against the background of pathological changes in cell metabolism, resulting in new perspectives for modified nucleosides and related metabolites as possible biomedical markers for breast carcinoma in vivo.

Molecular markers for predicting prognosis of renal cell carcinoma

Metastatic or recurrent renal cell carcinoma (RCC) carries a poor prognosis and long term survival is rare. However, many small RCCs that are incidentally discovered have an indolent course even without treatment. The variability in clinical outcome is a reflection of the underlying tumor biology. Currently, clinical variables such as tumor stage and histologic grade are widely accepted surrogates for tumor-specific cellular and molecular processes. Ongoing advances in genomic and proteomic technologies have produced an expanding list of molecular markers for predicting prognosis. We review expression array studies evaluating molecular signatures for predicting prognosis in patients with RCC and describe specific prognostic markers that have been validated in at least 50 cases of RCC.

The antiproliferative effects of agmatine correlate with the rate of cellular proliferation

Polyamines are small cationic molecules required for cellular proliferation. Agmatine is a biogenic amine unique in its capacity to arrest proliferation in cell lines by depleting intracellular polyamine levels. We previously demonstrated that agmatine enters mammalian cells via the polyamine transport system. As polyamine transport is positively correlated with the rate of cellular proliferation, the current study examines the antiproliferative effects of agmatine on cells with varying proliferative kinetics. Herein, we evaluate agmatine transport, intracellular accumulation, and its effects on antizyme expression and cellular proliferation in nontransformed cell lines and their transformed variants. H-ras- and Src-transformed murine NIH/3T3 cells (Ras/3T3 and Src/3T3, respectively) that were exposed to exogenous agmatine exhibit increased uptake and intracellular accumulation relative to the parental NIH/3T3 cell line. Similar increases were obtained for human primary foreskin fibroblasts relative to a human fibrosarcoma cell line, HT1080. Agmatine increases expression of antizyme, a protein that inhibits polyamine biosynthesis and transport. Ras/3T3 and Src/3T3 cells demonstrated augmented increases in antizyme protein expression relative to NIH/3T3 in response to agmatine. All transformed cell lines were significantly more sensitive to the antiproliferative effects of agmatine than nontransformed lines. These effects were attenuated in the presence of exogenous polyamines or inhibitors of polyamine transport. In conclusion, the antiproliferative effects of agmatine preferentially target transformed cell lines due to the increased agmatine uptake exhibited by cells with short cycling times.

Regulation of Polyamine and Cancer

This review describes my work in the field of polyamine research for the last 35 years. My research started with developing the improved synthesis of decarboxylated S-adenosylmethionine and then moved to the purification of spermidine synthase from rat prostate. I also took considerable efforts to find the synthetic procedure for various polyamines with high yield in order to prepare (15)N-labeled polyamines. On the basis of these methodological work, I searched for the inhibitor of spermidine synthase and found trans-4-methylcyclohexylamine (MCHA), the most effective one at the present time. I also developed a new analytical method for polyamines using stable isotope and ionspray ionization mass spectrometry (IS-MS). Based on these studies I examined the role of polyamines in liver regeneration and found that oral administration of MCHA effectively changed the concentration of polyamines and inhibited the hepatic growth. I also found the close relationship between the concentration ratio of spermidine to spermine and the extent of liver regeneration. These results may shed new light on the control of cell growth by polyamine in vivo.

Primary kidney growth and its consequences at the onset of diabetes mellitus

Diabetes mellitus is a primary contributor to progressive kidney dysfunction leading to end-stage renal disease (ESRD). In the early phase of diabetes, prior to the onset of further complications, both kidney size and glomerular filtration rate (GFR) increase. Glomerular hyperfiltration is considered a risk factor for downstream complications and progression to ESRD. Abnormalities in vascular control have been purported to account for the glomerular hyperfiltration in early diabetes. In this review we discuss a tubulo-centric concept in which tubular growth and subsequent hyper-reabsorption contribute to the onset of glomerular hyperfiltration that demarks the early stage of diabetes. Kidney growth, in this concept, is no longer relegated to a compensatory response to hyperfiltration, but rather plays a primary and active role in its genesis and progression. As such, components of kidney growth, such as the polyamines, may provide a means of early detection of diabetic kidney dysfunction and more effective therapeutic intervention.

Immunohistochemical analysis of tumor polyamines discriminates high-risk patients undergoing nephrectomy for renal cell carcinoma

Renal cell carcinoma (RCC) is known to display a wide variation in biological behavior and clinical outcome. Although usual bioclinical prognostic parameters (eg, nuclear grade, tumor stage) are to a certain extent useful in predicting the outcome of RCC after radical nephrectomy, they now appear to be insufficient. The polyamines (spermidine, spermine, and putrescine) are ubiquitous polycations that are essential for cell proliferation. To support their excessive proliferation, cancer cells have high rates of polyamine metabolism. Indeed, malignant cells typically have higher polyamine levels than their normal counterparts. Before this report, antipolyamine antibodies that are potentially valuable tools for the in situ observation of polyamines had not been exploited in clinical conditions. In the present study, tumor tissues obtained from radical nephrectomy performed for RCC (n = 73) were immunostained with the anti-spermine monoclonal antibody Spm8-2, and the immunoreactivity was evaluated as a prognostic tool. RCC cells displayed various reactivity to the antibody Spm8-2 that translated into a heterogeneous cytoplasmic staining. The prognostic value of the labeling index (LI) on clinical outcome was correlated with the usual clinicopathologic parameters, and the cell proliferation rate was evaluated using Ki-67 labeling. Multiple correspondence analysis and ascending hierarchical classification were performed to determine significant prognostic factors. Univariate statistical survival analysis demonstrated that tumor size (P < .001), nuclear grade (P < .01), necrosis (P < .007), tumor stage (P < .004), metastasis (P < .001), Ki-67 LI (P < .0003), and Spm8-2 immunoreactivity (P < .0001) were predictors of tumor-related death. A positive correlation was found between Ki-67 LI and Spm8-2 immunoreactivity (r' = .53). Multivariate analysis revealed that only Ki-67 LI and Spm8-2 immunoreactivity were significant independent factors in patients with metastases (P < .04 and <.001, respectively) and in patients without metastases (P < .006 and <.001, respectively). Moreover, 100% of the patients with Spm8-2 immunoreactivity <10% were alive at the end of the follow-up. In terms of predictive values, Spm8-2 immunoreactivity had the highest predictive values (sensitivity, 89; specificity, 75; risk ratio, 11) of all clinicopathologic parameters. This study demonstrates that the anti-spermine monoclonal antibody Spm8-2 may be used at the time of radical nephrectomy as a reliable prognostic marker for defining RCC patients at high risk for progression.

Comparative uptake of polyamines by prostate and non-prostate cancer cell lines

The Km and Vmax of [14C]-radiolabeled polyamines were determined for PC-3 and AT3B-1 cell lines. With PC-3 Km values are in the following order: ornithine> spermidine> spermine> putrescine, while with AT3B-1 it was spermidine> ornithine> spermine> putrescine. To determine which of these polyamines exhibit higher accumulation, the relative uptake of all the four amines was studied with prostate (PC-3, AT3B-1, LNCaP) and non-prostate (MCF-7, KLN-205, OVCAR) cell lines at 10 and 20 microM after 1 hour. Spermine and spermidine accumulated at higher levels in prostate (AT3B-1 and LNCaP) over non-prostate cell lines (p < 0.01). Putrescine accumulated more in PC-3 and LNCaP than the non-prostate cancer cells.

Genetic control of polyamine-dependent susceptibility to skin tumorigenesis

Overexpression of an ornithine decarboxylase (ODC) transgene greatly increases the susceptibility of mouse skin to carcinogen-induced tumor development. Like many phenotypes in transgenic models, this enhanced susceptibility phenotype is strongly influenced by genetic background. We have mapped tumor-modifier genes in intraspecific crosses between transgenic K6/ODC mice on a susceptible strain background (C57Bl/6J), a moderately resistant background (FVB), or a highly resistant background (C3H/HeJ). We identified several quantitative trait loci that influenced either tumor multiplicity or predisposition to the development of squamous cell carcinoma, but not both phenotypes. Because we did not use a tumor-promotion protocol to induce tumors, most of the quantitative trait loci mapped in this study are distinct from skin tumor-susceptibility loci identified previously. The use of a combined transgenic-standard strain approach to genetic analysis has resulted in detection of previously unknown genetic loci affecting skin tumor susceptibility.

Cloning and characterization of human agmatinase

Arginine decarboxylase (ADC) and agmatinase are part of an operon in Escherichia coli, which constitutes the primary pathway of polyamine synthesis from arginine. This pathway is also known to exist in plants, but until recently, neither agmatine nor ADC, the enzyme that synthesizes it, nor agmatinase the enzyme that is responsible for conversion of agmatine to putrescine, were known to exist in man or other mammals. We describe here the cloning of the agmatinase gene and the tissue distribution of its transcription product. Human agmatinase contains 352 amino acid residues and has a calculated molecular weight of 37,688 kDa. It has 56% similarity to E. coli agmatinase and 42% similarity to human arginases I and II and shares highly conserved substrate-binding domains with these well-characterized enzymes.

Significance of arginase and ornithine in malignant tumors of the human skin

During neoplastic development, several aspects of the regulation of polyamine synthesis undergo profound changes. In extrahepatic mammalian tissues in which the urea cycle is not functioning, arginase is believed to supply the cell with ornithine, a non-protein amino acid that is a precursor for biosynthesis of polyamines. Because the activity of ornithine decarboxylase and polyamine levels have been shown to be elevated during carcinogenesis, we decided to investigate the role of arginase in the development of malignant tumors of the human skin and to examine whether arginase activity and ornithine level can be used as biologic markers for distinguishing patients with squamous cell cancer from patients with basal cell cancer. For this purpose, we studied tissue arginase activity and ornithine level in tumor and adjacent normal tissues in 16 patients (55 +/- 10 years of age) with malignant skin tumors (8 of which were squamous cell cancers and 8 of which were basal cell cancers). The mean arginase activity and ornithine levels in tumor tissues (total) were 17.75 +/- 8.54 U/mg protein and 40.89 +/- 14.88 nmol/mg protein, respectively, versus 3.69 +/- 1.71 U/mg protein and 12.98 +/- 6.21 nmol/mg protein, respectively, for normal tissues. The mean specific arginase activity levels in squamous cell and basal cell cancers of the human skin were 18.49 +/- 10.47 U/mg protein and 16.63 +/- 6.00 U/mg protein, respectively. The mean ornithine levels in squamous cell and basal cell cancers of the human skin were 42.45 +/- 19.10 nmol/mg protein and 39.33 +/- 10.19 nmol/mg protein, respectively. Our results indicated that (1) arginase activity and ornithine levels are elevated in squamous cell and basal cell cancers of the human skin; (2) the increased activity of arginase and hence the elevated levels of ornithine may be important in the development of malignant tumors of the human skin; and (3) although arginase activity and ornithine level may be useful for distinguishing patients with malignant skin tumors from healthy subjects, they cannot be used as biologic markers for distinguishing patients with squamous cell cancer from patients with basal cell cancer.

An emerging role for agmatine

Polyamines, required components of proliferation, are autoregulated by the protein antizyme. To date, agmatine is the only molecule other than the polyamines that can induce antizyme, and thus influence cell homeostasis and growth. Agmatine has effectively suppressed proliferation in immortalized and transformed cell lines. An increased sensitivity to the anti-proliferative effects of agmatine observed in Ras transformed versus native cells paralleled an increase in agmatine uptake in the transformed cells. We hypothesize that agmatine may target transformed cells via selective transporters.

Polyamines. An overview

The polyamines spermine, spermidine, and putrescine are small organic molecules one or more of which are present in all living organisms. Many natural products contain polyamine residues. Polyamines are synthesized by a highly regulated pathway from arginine or ornithine and also can be transported in and out of cells. Polyamines are degraded to a variety of compounds the functions of which are largely unknown. Polyamines influence the transcriptional and translational stages of protein synthesis, stabilize membranes, and, in mammalian systems, modulate neurophysiological functions and may act as intracellular messengers. However, at the molecular level the mode of action of the polyamines is largely unknown.

Concomitant changes in polyamine pools and DNA methylation during growth inhibition of human colonic cancer cells

The effects of CGP 48664 and DFMO, selective inhibitors of the key enzymes of polyamine biosynthesis, namely, of S-adenosylmethionine decarboxylase (AdoMetDC) and ornithine decarboxylase (ODC), were investigated on growth, polyamine metabolism, and DNA methylation in the Caco-2 cell line. Both inhibitors caused growth inhibition and affected similarly the initial expression of the differentiation marker sucrase. In the presence of the AdoMetDC inhibitor, ODC activity and the intracellular pool of putrescine were enhanced, whereas the spermidine and spermine pools were decreased. In the presence of the ODC inhibitor, the AdoMetDC activity was enhanced and the intracellular pools of putrescine and spermidine were decreased. With both compounds, the degree of global DNA methylation was increased. Spermine and spermidine (but not putrescine) selectively inhibited cytosine-DNA methyltransferase activity. Our observations suggest that spermidine (and to a lesser extent spermine) controls DNA methylation and may represent a crucial step in the regulation of Caco-2 cell growth and differentiation.

Cooperativity between the polyamine pathway and HER-2neu in transformation of human mammary epithelial cells in culture: role of the MAPK pathway

Our experiments were designed to test the cooperativity between the polyamine pathway and HER-2neu in inducing transformation of human mammary epithelial cells in culture. Using the MCF-10A breast epithelial cell line, we observed that induction of overexpression of ornithine decarboxylase (ODC) (the first rate-limiting enzyme in polyamine biosynthesis) markedly potentiated the anchorage-independent growth stimulating effect of the beta2 isoform of neu differentiating factor (NDF) known to activate HER-2neu in MCF-10A cells. ODC overexpression, on the other hand, did not enhance growth in liquid culture, thus pointing to a specific effect on transformation rather than proliferation. ODC-overexpressing MCF-10A cells exhibited increased MAPK phosphorylation in response to administration of NDF and/or epidermal growth factor (EGF). In contrast, the phosphorylation of the members of the stress-activated protein kinase cascade p38 and SEK were not affected by ODC overexpression. Of note, in the absence of EGF and NDF, ODC overexpression failed to induce both clonogenicity and MAPK activation. These results suggest that increased polyamine biosynthetic activity critically interacts with HER-2neu in promoting human mammary cell transformation in culture and that the MAPK cascade is an important mediator of this interaction. If confirmed in future in vivo studies, our results may identify important new targets for the chemoprevention of human breast cancer.

Structure-activity relations of S-adenosylmethionine decarboxylase inhibitors on the growth of MCF-7 breast cancer cells

SAMDC is a key enzyme in the biosynthesis of spermidine and spermine, 2 polyamines that are essential for cell proliferation. Inhibition of polyamine biosynthesis is often targeted as a therapeutic strategy to suppress cancer cell growth as these cells contain elevated levels of polyamines. We examined the effect of a new group of SAMDC inhibitors, CGP33829, CGP35753, CGP36958, CGP39937, and CGP48664, (obtained from Ciba-Geigy, Basel, Switzerland), and their parent compound, MGBG, on the proliferation of MCF-7 breast cancer cells. MGBG had minimal effects on the proliferation of MCF-7 cells up to 6 microM concentration. In contrast, CGP48664 and CGP39937, containing 2 aromatic rings that delocalize the pi electron system of the backbone of MGBG, were potent inhibitors with 50% growth inhibition at 0.5 microM concentration. Other CGP compounds were less effective in inhibiting cell growth. The ability of CGP48664 to inhibit MCF-7 cell proliferation was related to its ability to inhibit SAMDC and to consequently deplete spermidine and spermine levels in the cell. Exogenous spermidine and spermine could reverse the growth inhibitory effects of this compound. CGP compounds also increased the activity of ODC, another enzyme involved in polyamine biosynthesis. Northern blot analysis of mRNA from MCF-7 cells progressing in cell cycle after G1 synchronization did not show an increase in ODC mRNA level by CGP48664. These data demonstrate structure-activity relationships of a series of MGBG derivatives on cell growth, enzyme activities, and polyamine biosynthesis in a hormone-responsive breast cancer cell line and suggest potential application of SAMDC inhibitors as therapeutic agents.

In vivo, synergestic inhibition of MAT-LyLu rat prostatic adenocarcinoma growth by polyamine deprivation and low-dose cyclophosphamide

Polyamine deprivation in vivo produces significant tumor growth inhibition of the hormone-resistant, metastatic Dunning Mat-LyLu murine prostatic carcinoma. In order to produce a cytotoxic effect in addition to the cytostatic effect of polyamine deprivation, various chemotherapy regimens, combined with drug-containing polyamine-deficient chow (DC-PDC), were assessed. Triple chemotherapy combining methotrexate, cyclophosphamide and vindesine; and monochemotherapy with high-dose cyclophosphamide (90 mg. kg-1) and low-dose cyclophosphamide (20 mg.kg-1) were studied alone and in combination with DC-PDC. A variant of DC-PDC excluding the polyamine oxidase inhibitor MDL 72527 was also studied in combination with low-dose cyclophosphamide. The triple-chemotherapy regimen alone or in combination with polyamine deprivation was effective on tumor growth inhibition but was also toxic. High-dose cyclophosphamide alone produced significant tumor growth inhibition and an increase in life span. High-dose cyclophosphamide in combination with DC-PDC was also effective on tumor growth but was also toxic. Low-dose cyclophosphamide alone was moderately effective on tumor growth inhibition with a marginal increase in life span. When combined with polyamine deprivation, results with low-dose cyclophosphamide compared favourably with those of high-dose cyclophosphamide alone and prevented the formation of lung metastases. The polyamine oxidase inhibitor does not appear to be mandatory to achieve this effect if DC-PDC is combined with low-dose cyclophosphamide. Polyamine deprivation appears to be an important tool in anticancer therapy, allowing the use of reduced doses of cytotoxic agents with the same antitumoral efficacy.

Regulation of ornithine decarboxylase gene expression by the Wilms' tumor suppressor WT1

The importance of ornithine decarboxylase (ODC) to cell proliferation is underscored by the complex array of cell-specific mechanisms invoked to regulate its synthesis and activity. Misregulation of ODC has severe negative consequences on normal cell function, including the acquisition of tumorigenic growth properties by cells overexpressing ODC. We hypothesize that ODC gene expression is a candidate target for the anti-proliferative function of certain tumor suppressors. Here we show that the Wilms' tumor suppressor WT1 binds to multiple sites within the human ODC promoter, as determined by DNase I protection and methylation interference assays. The expression of WT1 in transfected HCT 116, NIH/3T3 and HepG2 cells represses activity of the ODC promoter controlling expression of a luciferase reporter gene. In contrast WT1 expression enhances ODC promoter activity in SV40-transfected HepG2 cells. Both the extent of modulation of ODC gene expression and the mediating WT1 binding elements are cell specific. Constructs expressing WT1 deletion mutants implicate two regions required for repressor function, as well as an intrinsic activation domain. Understanding the regulation of ODC gene expression by WT1 may provide valuable insights into the roles of both WT1 and ODC in development and tumorigenesis.

Direct identification of a polyamine binding domain on the regulatory subunit of the protein kinase casein kinase 2 by photoaffinity labeling

Phosphorylation of many protein substrates by the protein kinase casein kinase 2 (CK2) is stimulated severalfold in the presence of polyamines such as spermine. Previous experiments have shown that CK2 is a polyamine binding protein and that the regulatory beta subunit is required for this binding activity. To delineate the spermine binding site of CK2, we have applied a photoaffinity labeling method using a tritiated photoactivable analog of spermine, [3H]sperminediazonium. The photoaffinity labeled beta subunit was cleaved with cyanogen bromide, and two labeled peptides were separated by high performance liquid chromatography. The major one was the peptide T72EQAAEM78 and the minor one was a 22-amino acid peptide comprising residues Ile98 to Met119. Thr72 and His108 were identified as the labeled amino acids of the Thr72-Met78 and Ile98-Met119 peptides, respectively. In the same manner, we succeeded in determining the residue Leu220 as an alpha subunit residue covalently bound to the probe. The photoaffinity labeling method described here enabled the first elucidation, by direct microsequencing, of a polyamine binding site on CK2 for which we propose a provisional structural model. These observations suggest a possible mechanism for CK2 activation by polyamines at the molecular level.

Involvement of the polyamine pathway in breast cancer progression

These experiments were designed to test the role of the polyamine pathway in breast cancer progression utilizing an experimental system based on the development of ovary-independent rat mammary tumors and their sequential transplantation into syngeneic hosts. Three key enzymes involved in the PA biosynthetic/catabolic pathway (ornithine-decarboxylase (ODC), S-adenosylmethionine decarboxylase (SAMDC), and spermidine/spermine N'-acetyltransferase (SSAT)) were measured in tumors at different stages of progression. The most significant finding was the association between increased ODC activity and the acquisition of a hormone-independent, poorly differentiated phenotype. SSAT levels tended to be higher in hormone-independent tumors and, in this tumor category, they tended to be positively correlated with differentiation. However, significant interaction between hormone dependence and differentiation status on SSAT expression prevented reliable assessment of the possibly complex role of this enzyme in tumor progression. Neither hormone dependence nor differentiation status were correlated with SAMDC levels. We conclude that, among the three enzymes tested, ODC overexpression is the most significant alteration in the PA metabolic pathway associated with breast cancer progression in this experimental system.

Regulation of rat ornithine decarboxylase promoter activity by binding of transcription factor Sp1

Ornithine decarboxylase (ODC) is the rate-limiting enzyme of polyamine biosynthesis. We investigated the transcriptional regulation of the rat ODC gene using transient expression assays. The 5'-flanking region (-1156 to +13) of the ODC gene was sufficient to mediate strong basal expression of a luciferase reporter. Sequences between -345 and -93 contributed to basal promoter activity. This region, containing five potential Sp1 binding sites, was analyzed by electrophoretic mobility shift assays. Three specific DNA-protein complexes were identified using H35 nuclear extracts and the -345/-93 ODC probe. Binding to all three was eliminated by competition with an oligonucleotide containing an Sp1 binding site, but not by a mutant Sp1 oligonucleotide. Preincubation with an antibody against Sp1 supershifted complexes associated with one or more of Sp1 binding sites 1-4 as well as with site 5. DNase I footprinting revealed two protected regions: PR-I (-92 to -130) and PR-II (-304 to -332). PR-I contains a putative binding site for Sp1 that was protected by recombinant Sp1 protein. Transfection studies in Schneider SL2 cells demonstrated that the ODC promoter is transactivated up to 350-fold by Sp1 and that this transactivation is dependent on the presence of Sp1 binding sites 1-4. Thus, although the ODC promoter binds multiple nuclear proteins, Sp1 or a related protein appears to be a critical determinant of ODC transcription, possibly through cooperative interactions between Sp1 and additional transcription factors.

Effects of nonsteroidal antiinflammatory drugs on oxidative pathways in A/J mice

The tobacco-specific N-nitrosamine, NNK, is a potent carcinogen in laboratory animals. The authors have shown previously that NNK-induced lung tumorigenesis in A/J mice can be reduced significantly by certain nonsteroidal antiinflammatory drugs (NSAIDs), such as sulindac, ibuprofen, or piroxicam treatments. In this study, the authors investigated whether NSAIDs could reduce NNK-induced oxidative, DNA damage and/or inhibit endogenous lipid peroxidation, or prostaglandin E2 (PGE2) synthesis in A/J mice. In the first experiment, A/J mice were gavaged with NNK (112 mumol/kg b.w.) three times a week while being maintained on a diet to which either ibuprofen (263 mg/kg diet), naproxen (230 mg/kg), sulindac (123 mg/kg), piroxicam (25 mg/kg), indomethacin (5 mg/kg), or no NSAIDs had been added. Levels of 8-OH-dG in the DNA of lung and liver were measured by high-performance liquid chromatography with electron capture detector. Treatment with NSAIDs had no significant effects on the endogenous or NNK-induced formation of 8-OH-dG in the lung of the mice. In a second experiment, after treatment of A/J mice with NSAIDs for 2 weeks, lipid peroxidation was assayed by determining thiobarbituric acid-reactive substances (TBA-RS) in lung tissues, and prostaglandin E2 levels were measured in plasma by an enzyme immunoassay. Treatments with some NSAIDs lowered the levels of lipid peroxidation and plasma levels of PGE2 below basal levels. Taken together, these results suggest that the inhibition of NNK-induced lung tumorigenesis by NSAIDs is more likely related to an inhibition of prostaglandin synthesis than to a direct inhibition of lipid peroxidation or oxidative DNA damage induced by NNK.

Oral precancer: preventive and medical approaches to management

Leukoplakias are among the most common potentially malignant oral lesions. Some are idiopathic, others are related to habits such as tobacco and/or alcohol use. Medical management includes reducing or abandoning these habits, increasing the intake of fruit and vegetables in the diet, and possibly the use of active agents. Retinoids, carotenoids and topical cytotoxic agents show promise, and newer therapies are on the horizon.

Effects of polyamine biosynthesis inhibitors on the progesterone-initiated increase in intracellular free Ca2+ and acrosome reactions in human sperm

This laboratory has previously reported that progesterone can initiate a rapid transient increase in the concentration of intracellular free Ca2+ ([Ca2+]i) and an increase in a Ca(2+)-requiring exocytotic event, the acrosome reaction (AR) in human sperm. Rapid increases in Ca2+ fluxes of some mammalian cells caused by another steroid, testosterone, require polyamine biosynthesis. Herein, we tested two polyamine biosynthesis suicide inhibitors for their effects on the progesterone-initiated increase in [Ca2+]i and AR in capacitated human sperm in vitro: DL-alpha-(difluoromethyl)ornithine hydrochloride (DFMO), an inhibitor of putrescine synthesis by ornithine decarboxylase and (5'[[(Z)-4-amino-2-butenyl]methylamino]-5'-deoxyadenosine (MDL 73811), an inhibitor of S-adenosylmethionine decarboxylase (required for spermidine and spermine synthesis). Sperm were capacitated in vitro and preincubated 10 min with 4.9 mM DFMO or 9.8 microM MDL 73811 with or without various polyamines (245 microM). Progesterone (3.09 microM final concentration) or progesterone solvent (ethanol, 0.1% final concentration) was then added, sperm fixed 1 min after additions and AR assayed by indirect immunofluorescence or with fluorescein-labeled Con A lectin. DFMO strongly inhibited the AR, but putrescine (product of ornithine decarboxylase and precursor of spermidine and spermine) reversed that inhibition. Preincubation for 25 min with DMFO + spermidine also reversed DFMO inhibition. MDL 73811 inhibited the progesterone-initiated AR, and a 10 min preincubation with spermidine, but not putrescine or spermine, reversed that inhibition. Preincubations with putrescine alone or with spermidine alone followed by addition of the progesterone solvent did not initiate the AR, and such preincubations followed by progesterone addition did not increase the AR more than progesterone alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Persistent decrease in spermidine/spermine N1-acetyltransferase activity in 'post-regeneration' rat liver

The activity of cytosolic spermidine/spermine N1-acetyltransferase and polyamine levels were measured in livers of rats killed at different times after partial hepatectomy. The enzyme activity, which showed an early increase a few hours after the operation, had significantly and persistently decreased by the time the liver mass had been regained (10 days) compared to intact rats or sham-operated rats, and up to 30 days after partial hepatectomy, compared to intact rats of the same age. The early induction of spermidine/spermine N1-acetyltransferase activity was also confirmed by the high level of N1-acetylspermidine, which normally is undetectable, and by a dramatic increase in putrescine content. Spermidine levels were increased during the first 10 days after partial hepatectomy, i.e., when the liver had regained its mass, and progressively decreased after this time until 30 days after the operation. The changes in spermine content were similar but not as marked as the changes in spermidine content at the different observation times.

Polyamine plasma levels and liver regeneration following partial hepatic resection in man

Polyamines (putrescine, spermidine, and spermine) are widely distributed in animal and vegetal tissues, where their intracellular concentration strictly correlates with normal and pathological cell growth and protein synthesis. By means of a sensitive HPLC technique, the fasting plasma concentrations of polyamines were measured serially in 11 patients who underwent partial hepatic resection because of focal liver lesions. Samples were obtained before surgery and over the next 6 months, during hepatic regeneration. Liver volume was also measured by ultrasound on the basis of the 3 maximum diameters of the liver. From 2 to 4 weeks after surgery, plasma putrescine increased by a maximum of 78%, and spermidine by approximately 50%. No changes were observed in spermine levels. The spermidine/spermine ratio nearly doubled during liver regeneration. The volume of the liver decrease from 1505 [SD 236] ml to 743 [151] ml after resection, and returned to nearly normal values after 6 months (1231 [100] ml, p < 0.05 vs. basal values). The liver regeneration rate was highest 2-4 weeks after resection, and declined thereafter, when prevailing polyamine concentrations returned to normal. These data show that liver regeneration is accompanied by a significant increase in fasting putrescine and spermidine concentrations, which might be biochemical signals of active liver cell regeneration.

Cell proliferation and carcinogenesis may share a common basis of permeable plasma membrane clusters

Wound potentials increase the surface potential of exposed areas of nearby cells. In these cells, soluble cytoplasmic bases are assumed gradually to move nearer the exposed area. Acidic molecules on the cell surface migrate to points opposite the bases. The image-charged species are mutually attracted to form transmembrane clusters. At clusters, membrane permeability increases and the cell is stimulated to cycle. When the wound heals, its clusters disperse, leaving a small 'permanent' residuum. Permanent clusters initiate cells to malignancy. They have (or develop) lipophilic molecules on both surfaces that help fix them in the membrane. Exposed cells contaminated with polycyclic aromatic hydrocarbon carcinogens (PAH) readily form permanent clusters. At mitosis, clusters on parental plasma membrane pass with that membrane to a daughter cell. Promotion results from many short-term or a single long-term exposure of initiated membranes to abnormal surface charge. Permanent clusters increase on the membrane after repeated wounding, proximity of charged foreign bodies like plastic film or asbestos, or oxidation of surface molecules. Progression requires acceleration of cluster growth so the daughter cell membranes become as leaky at maturity as was the parent membrane. One mechanism suggested involves reversible phosphorylation by membrane-bound kinases; another involves attraction of a basic protein (p36) to the membrane.

Palladium(II) salt and complexes of spermidine with a six-member chelate ring. Synthesis, characterization, and initial DNA-binding and antitumor studies

By reaction of spermidine trihydrochloride with K2PdCl4 and PdCl2 at different pH's, we have synthesized the [sperH3]2[PdCl4]3 (I), [PdCl2(sperH)]2[PdCl4] (II), and [(PdCl2)3(sper)2] (III) compounds. The structure of these compounds was studied by IR and 1H NMR; complex II was analyzed by x-ray diffraction. In this complex the spermidine is attached to the PdCl2 group forming a six-member chelate ring with a protonated terminal amine group. The crystal of [PdCl2(sperH)]2[PdCl4] x 2H2O (II) is monoclinic, P2(1)/n, with a = 7.023(1) A, b = 12.662(1) A, c = 18.435(3) A, and beta = 99.95(1) degrees, Z = 4, R = 0.051, and Rw = 0.058 on the basis of 2690 independent reflections. We have compared the antitumor activity in vitro against the isolated human breast carcinoma MDA-MB 468 cell line of compounds I, II, and III with that of cis-diamminedichloroplatinum(II), cis-DDP. The results show that compounds III and III have values of ID50 similar (0.74 microgram/ml) or even lower (0.56 microgram/ml) than cis-DDP (0.80 microgram/ml). We also observed that compounds I, II, and III have the ability to induce conformational changes in covalently closed circular (ccc) form of the pUC8 plasmid DNA. Compounds II and III also induce conformational changes in the open circular (oc) form of this plasmid.

Multiple promoter elements govern expression of the human ornithine decarboxylase gene in colon carcinoma cells

Overexpression of the ornithine decarboxylase (ODC) gene may be important to the development and maintenance of colonic neoplasms, as well as tumors in general. In this study, we examined the promoter elements governing constitutive expression of the human ODC gene in HCT 116 human colon carcinoma cells and, for comparison, K562 human erythro-leukemia cells. It was determined by functional analysis that the promoter elements responsible reside within the 378 bp immediately upstream from the transcription start site. Within this sequence, there are at least three regions that modulate the efficiency of the ODC promoter cooperatively. Both DNA bandshift and footprint assays demonstrated all three regions to be rich in sites that bind to nuclear proteins isolated from HCT 116 and K562 cells; the protein binding pattern of non-transformed, diploid fibroblasts was found to be much less complex. Several of the protein binding sequences have little or no homology to common regulatory elements. We suggest that the constitutive activity of the ODC gene in HCT 116 colon carcinoma cells, and perhaps transformed cells in general, involves a complex interaction of multiple regulatory sequences and their associated nuclear proteins. Finally, the saturation of the promoter in these transformed cell lines suggests that high levels of protein binding in the ODC promoter may contribute to elevated constitutive expression of this gene.

Regulation of arginase production by glucocorticoid in three human gastric cancer cell lines

Gastric cancer tissues have high levels of glucocorticoid receptors (GR) and arginase. To investigate the interrelation of glucocorticoid, GR and arginase, three human gastric cancer cell lines (AZ-521, NUGC-3, KATO-III) were treated with hydrocortisone in the presence or absence of a glucocorticoid antagonist RU38486. GR were found to be present in all three lines, and hydrocortisone significantly increased the production of total arginase in all 3 lines. The induction of arginase production by hydrocortisone was inhibited by RU38486. These findings suggest that the regulation of arginase production by hydrocortisone in gastric cancer cells is mediated through GR.

The growth of MAT-LyLu rat prostatic adenocarcinoma can be prevented in vivo by polyamine deprivation

The combination of inhibitors of ornithine decarboxylase and polyamine oxidase, and of antibiotics suitable for the (partial) decontamination of the gastrointestinal tract, with a polyamine deficient diet, is responsible for the almost complete inhibition of the growth of MAT-LyLu prostatic adenocarcinoma. In the tumor-bearing animals, erythrocyte spermidine levels were reduced, but spermine concentrations were increased. As has been previously observed, the increase in erythrocyte spermine level was associated with an enhancement of malignant cell death. Adriamycin administration did neither diminish tumor growth, nor potentiate the antitumor effect of polyamine deprivation treatment. Interruption of the polyamine deprivation treatment was accompanied by a significant enhancement of tumor growth. Since polyamine deprivation causes only reversible growth inhibition, it seems not appropriate as a monotherapy.

Variations in amplification and expression of the ornithine decarboxylase gene in human breast cancer cells

The polyamine biosynthetic pathway plays a critical role in the growth of human breast cancer cells. Ornithine decarboxylase (ODC) is a key enzyme in polyamine biosynthesis. To understand the regulation of ODC activity and polyamine accumulation in breast cancer cells, we studied amplification and expression of the ODC gene in four breast cancer cell lines. ODC gene dosage was analyzed by Southern blot hybridization and was 4- to 12-fold higher in T-47D, MDA-MB-231, and BT-20 cell lines than in the MCF-7 cell line. ODC mRNA level was 2- to 3-fold higher in BT-20 and MDA-MB-231 cell lines than in the other two lines. We also measured ODC activity and polyamine concentration in these cell lines, and determined their sensitivity to an ODC inhibitor, difluoromethylornithine (DFMO). BT-20 cells showed significantly higher ODC activity and polyamine concentrations than the other three cell lines. BT-20 cells were resistant to the growth inhibitory effect of DFMO even at 4 mM concentration, whereas the proliferation of MCF-7, T47D, and MDA-MB-231 cells was inhibited by this drug. These results suggest that different transcriptional and post-transcriptional mechanisms control the regulation of ODC gene expression in breast cancer cell lines.

Polyamines: from molecular biology to clinical applications

The polyamines putrescine, spermidine and spermine represent a group of naturally occurring compounds exerting a bewildering number of biological effects, yet despite several decades of intensive research work, their exact physiological function remains obscure. Chemically these compounds are organic aliphatic cations with two (putrescine), three (spermidine) or four (spermine) amino or amino groups that are fully protonated at physiological pH values. Early studies showed that the polyamines are closely connected to the proliferation of animal cells. Their biosynthesis is accomplished by a concerted action of four different enzymes: ornithine decarboxylase, adenosylmethionine decarboxylase, spermidine synthase and spermine synthase. Out of these four enzyme, the two decarboxylases represent unique mammalian enzymes with an extremely short half life and dramatic inducibility in response to growth promoting stimuli. The regulation of ornithine decarboxylase, and to some extent also that of adenosylmethionine decarboxylase, is complex, showing features that do not always fit into the generally accepted rules of molecular biology. The development and introduction of specific inhibitors to the biosynthetic enzymes of the polyamines have revealed that an undisturbed synthesis of the polyamines is a prerequisite for animal cell proliferation to occur. The biosynthesis of the polyamines thus offers a meaningful target for the treatment of certain hyperproliferative diseases, most notably cancer. Although most experimental cancer models responds strikingly to treatment with polyamine antimetabolites--namely, inhibitors of various polyamine synthesizing enzymes--a real breakthrough in the treatment of human cancer has not yet occurred. It is, however, highly likely that the concept is viable. An especially interesting approach is the chemoprevention of cancer with polyamine antimetabolites, a process that appears to work in many experimental animal models. Meanwhile, the inhibition of polyamine accumulation has shown great promise in the treatment of human parasitic diseases, such as African trypanosomiasis.

Increase in spermine content coordinated with siderophore production in Paracoccus denitrificans

Spermine is present in relatively low amounts in Paracoccus denitrificans cultured aerobically in an ammonium succinate minimal salts medium supplemented with 50 microM iron(III). However, in iron-deprived cultures [minimal salts medium containing 0.5 microM iron(III)], spermine content increases by an order of magnitude in coordination with the well-known responses to iron derivation, e.g., derepression of siderophore synthesis and siderophore excretion. When iron-deprived cultures exhibiting both high spermine content and strong siderophore production are reseeded into fresh minimal salts medium containing 50 microM iron[III], both siderophore production and spermine content fall rapidly. Five hours after iron supplementation, spermine is below limits of detection. These results suggest a specific role for spermine in the response of P. denitrificans to low-iron stress.

Erythrocyte polyamine levels in human prostatic carcinoma

Abnormally high red blood cell polyamine levels were found in benign prostatic hyperplasia and in prostatic adenocarcinoma patients. In prostatic adenocarcinoma patients a relationship was noted between the importance of red blood cell spermidine and spermine concentrations, and the clinical stage of the disease (Whitmore classification). Considering prostatic adenocarcinoma patient populations, patients with metastases (groups 3 and 4) statistically differed from those without metastases (group 2). Furthermore, red blood cell polyamine level determination discriminated patients in the hormonal escape group (group 4) from those usually considered as hormone responsive (groups 2 and 3). No statistically significant correlation was observed between red blood cell polyamine levels and usual tumor markers (prostatic acid phosphatase and prostate specific antigen). These results confirmed that red blood cell polyamine levels must be considered as a circulating index of cell proliferation that might be of clinical importance during the long-term followup and treatment of prostatic adenocarcinoma patients.

Regulation of polyamine biosynthesis by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

We have examined the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on tissue polyamine concentrations in CD1 mice. Two days after a low dose treatment with TCDD, polyamine content of the liver and thymus of treated mice showed a 49-82% decrease, but that of spleen was not affected. Based on this finding, we examined the role of alterations in polyamine levels in the toxicity of TCDD. We administered the polyamine biosynthetic inhibitor difluoromethylornithine (DFMO) to animals treated with a toxic dose of TCDD. DFMO dramatically increased the toxicity of TCDD as measured by mortality, ascites and changes in organ weights. In addition, administration of the polyamine putrescine was able to reduce the toxicity of TCDD. These results suggest that a decrease in polyamine concentrations in critical organs may play an important role in the toxic effects of TCDD.

Metabolism and action of amino acid analog anti-cancer agents

The preclinical pharmacology, antitumor activity and toxicity of seven of the more important amino acid analogs, with antineoplastic activity, is discussed in this review. Three of these compounds are antagonists of L-glutamine: acivicin, DON and azaserine; and two are analogs of L-aspartic acid: PALA and L-alanosine. All five of these antimetabolites interrupt cellular nucleotide synthesis and thereby halt the formation of DNA and/or RNA in the tumor cell. The remaining two compounds, buthionine sulfoximine and difluoromethylornithine, are inhibitors of glutathione and polyamine synthesis, respectively, with limited intrinsic antitumor activity; however, because of their powerful biochemical actions and their low systemic toxicities, they are being evaluated as chemotherapeutic adjuncts to or modulators of other more toxic antineoplastic agents.

Structure-function relationships of icosahedral plant viruses

X-ray diffraction studies on single crystals of a few viruses have led to the elucidation of their three dimensional structure at near atomic resolution. Both the tertiary structure of the coat protein subunit and the quaternary organization of the icosahedral capsid in these viruses are remarkably similar. These studies have led to a critical re-examination of the structural principles in the architecture of isometric viruses and suggestions of alternative mechanisms of assembly. Apart from their role in the assembly of the virus particle, the coat proteins of certian viruses have been shown to inhibit the replication of the cognate RNA leading to cross-protection. The coat protein amino acid sequence and the genomic sequence of several spherical plant RNA viruses have been determined in the last decade. Experimental data on the mechanisms of uncoating, gene expression and replication of several classes of viruses have also become available. The function of the non-structural proteins of some viruses have been determined. This rapid progress has provided a wealth of information on several key steps in the life cycle of RNA viruses. The function of the viral coat protein, capsid architecture, assembly and disassembly and replication of isometric RNA plant viruses are discussed in the light of this accumulated knowledge.

1,2-Dimethylhydrazine-induced alterations in N1-acetylspermidine levels in rat distal colonic mucosa: effects of 2-difluoromethylornithine

Recently, our laboratory has demonstrated that N1-acetylspermidine levels were increased in the distal colonic mucosa of rats administered 1,2-dimethylhydrazine for 15 and 26 weeks. In order to further explore the possible role of this acetylated polyamine in the malignant transformation process induced by this carcinogen, groups of rats were subcutaneously injected weekly with dimethylhydrazine (20 mg/kg body wt.) or diluent for 5, 10, 15 and 26 weeks +/- 1% 2-difluoromethylornithine in the drinking water. The latter agent, an irreversible inhibitor of ornithine decarboxylase, has previously been shown to inhibit colonic tumor formation in this experimental model. At each of these time periods, rats from each group were killed, their proximal and distal colonic mucosa harvested and examined, and compared with respect to polyamine levels, including N1-acetylspermidine, as well as the activities of ornithine decarboxylase, S-adenosylmethionine decarboxylase, spermidine N1-acetyltransferase and polyamine oxidase. The results of these experiments demonstrated that: (1) N1-acetylspermidine levels in the proximal colonic segment of all animals were similar at each time point; (2) N1-acetylspermidine levels were also similar in the distal colons of all animals at 5 and 10 weeks. At 15 weeks, however, the level of N1-acetylspermidine was increased in the dimethylhydrazine-treated distal colonic segment secondary to increases in the activity of spermidine N1-acetyltransferase; and (3) at 26 weeks, the level of this acetylated polyamine remained higher in dimethylhydrazine-treated distal 'uninvolved' colonic mucosa and was markedly elevated in colonic tumors; (4) co-administration of difluoromethylornithine decreased the elevated levels of N1-acetylspermidine to control values in the distal colons of animals treated with carcinogen for 15 and 26 weeks; and (5) difluoromethylornithine markedly reduced the number of tumors induced by dimethylhydrazine in the distal but not proximal colonic mucosa at 26 weeks.

2-Deoxy-D-glucose inhibits the antitumor effects of alpha-difluoromethylornithine on the growth of colon cancer in vivo

The glycolytic inhibitor, 2-deoxy-D-glucose (2-DG), has been shown to inhibit the growth of certain cancers. alpha-Difluoromethylornithine (DFMO) is an irreversible inhibitor of ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis. DFMO has been shown to inhibit cancer growth in a number of models. The present study was designed to investigate the effects of 2-DG alone and combined with DFMO on MC-26 mouse colon adenocarcinoma tumors growing in vivo. Twenty-eight male Balb/c mice were inoculated with 250,000 MC-26 cells, and then randomized into four groups of 7 each: group I served as control; group II received DFMO (3% in drinking water); group III received 2-DG (500 mg/kg/d IP); group IV received combination of 2-DG and DFMO. Treatment began 5 days after tumor cell inoculation. MC-26 tumor area was reduced 73% by DFMO compared to a 24% reduction caused by 2-DG. The tumor weight was reduced 80% by DFMO and 52% by 2-DG. The tumor contents of DNA, RNA, and protein were significantly reduced by DFMO but not 2-DG. The tumor concentration of the polyamines putrescine and spermidine were reduced by DFMO alone or combined with 2-DG while spermine levels remained unchanged. 2-DG alone did not alter polyamine levels. These results indicate that both 2-DG and DFMO, when added as single agents, inhibit tumor growth. However, the addition of 2-DG to the DFMO regimen inhibited the antitumor effects of DFMO. Survival studies performed on MC-26 cells in vitro corroborated the antagonisms between DFMO and 2-DG that were shown in vivo.

A phase I study of hepatic arterial infusion using difluoromethylornithine

Ten patients with metastatic disease to the liver were treated with difluoromethylornithine (DFMO) administered by continuous hepatic arterial infusion. Two of nine evaluable patients had an objective partial response. Stable disease was recorded in three patients. Ototoxicity was encountered in all patients who received a daily dose of DFMO equal to or greater than 1.0 g/m2.

Polyamine biosynthetic decarboxylases in muscles of rats with different experimental myopathies

The activities of the two polyamine biosynthetic decarboxylases (PBD), L-ornithine decarboxylase (ODC) and S-adenosyl-L-methionine decarboxylase (SAMD), have been measured in quadriceps femoris of rats killed at different times after the induction of calciphylaxis- or serotonin(5-HT)-induced myopathy. Decreases in both PBD levels were observed at early times after both myotoxic treatments. Subsequent progressive increases in both enzyme levels were observed to nearly control values by 4 days after 5-HT administration. In the 5-HT-treated rats, the effects on the myocardial PBD activities were different from those in skeletal muscle, with no effect on ODC but much on SAMD, when rats were killed shortly after 5-HT injection. These results demonstrate that the time-course of the changes in PBD activities in quadriceps femoris mirrors quite well the successive occurrence of degenerative and regenerative processes during the calciphylaxis-induced myopathy and the 5-HT-induced myopathy; it is 5-HT that is mainly responsible for the decreases in PBD levels observed in both experimental myopathies, since dihydrotachysterol alone was without any effect on PBD activity levels and 5-HT alone was effective; myocardial ODC reacts more slowly to 5-HT than quadriceps femoris ODC.

"In vivo" (35S)-methionine interaction with rat-liver DNA and the effect of chemical carcinogens

1. After intraperitoneal administration of (35S)methionine (25 mg, 1.6 mCi/kg), detectable amount of radioactivity resulted associated to rat-liver DNA: the interaction reached the maximum value (about 18 pmol/mumol DNA P) by 2 h after administration of radioactive aminoacid. 2. The (35S)-binding was inhibited by the hepatocarcinogenic ethionine and dimethylnitrosamine, and was stimulated by the non-hepatocarcinogenic methylnitrosourea. 3. Hplc analysis of (35S)DNA enzymic digest evidenced two radioactive compounds, the UV behaviour of which is reported.

Polyamine levels and gastrin receptors in colon cancers

Polyamines and gastrin receptors (GR) were studied in samples of colon cancer and mucosa from 40 patients and in control mucosa from 11 patients without cancer. Polyamines (i.e., putrescine, spermidine, spermine) are essential for growth and differentiation. The concentration of polyamines is elevated in rapidly proliferating normal tissues and in some cancers. The presence of GR in human colon cancers has been previously reported. The purpose of the present study was twofold: (1) to determine whether polyamine levels are elevated in colon cancers and in adjacent normal colon mucosa compared to colon mucosa from patients without cancer; and (2) to examine the relationship between polyamine levels and GR in colon cancers. Polyamine levels in colon cancers were significantly higher than in the normal colon mucosa from the same patients. The polyamines, spermidine and spermine, were significantly higher in colon mucosa from patients with cancer compared to patients without cancer. Spermidine and the spermidine:spermine ratio, an index of cell proliferation, were increased in colon cancers with GR compared to cancers without GR. There were no significant correlations between polyamine levels and the following: patient age, CEA level, site of cancer, stage, or differentiation. Because polyamine levels are increased in colon mucosa from patients with cancer, measurement of polyamines may detect patients at risk for subsequent development of colon cancer. Increased levels of polyamines in colon cancers with GR is evidence that gastrin may play a trophic role in human colon cancers.