Inhibition of the polyamine synthesis enzyme ornithine decarboxylase sensitizes triple-negative breast cancer cells to cytotoxic chemotherapy.

Treatment of patients with triple-negative breast cancer (TNBC) is limited by a lack of effective molecular therapies targeting this disease. Recent studies have identified metabolic alterations in cancer cells that can be targeted to improve responses to standard-of-care chemotherapy regimens. Using MDA-MB-468 and SUM-159PT TNBC cells, along with LC-MS/MS and HPLC metabolomics profiling, we found here that exposure of TNBC cells to the cytotoxic chemotherapy drugs cisplatin and doxorubicin alter arginine and polyamine metabolites. This alteration was because of a reduction in the levels and activity of a rate-limiting polyamine biosynthetic enzyme, ornithine decarboxylase (ODC). Using gene silencing and inhibitor treatments, we determined that the reduction in ODC was mediated by its negative regulator antizyme, targeting ODC to the proteasome for degradation. Treatment with the ODC inhibitor difluoromethylornithine (DFMO) sensitized TNBC cells to chemotherapy, but this was not observed in receptor-positive breast cancer cells. Moreover, TNBC cell lines had greater sensitivity to single-agent DFMO, and ODC levels were elevated in TNBC patient samples. The alterations in polyamine metabolism in response to chemotherapy, as well as DFMO-induced preferential sensitization of TNBC cells to chemotherapy, reported here suggest that ODC may be a targetable metabolic vulnerability in TNBC.

Inhibition of the aryl hydrocarbon receptor/polyamine biosynthesis axis suppresses multiple myeloma.

Polyamine inhibition for cancer therapy is, conceptually, an attractive approach but has yet to meet success in the clinical setting. The aryl hydrocarbon receptor (AHR) is the central transcriptional regulator of the xenobiotic response. Our study revealed that AHR also positively regulates intracellular polyamine production via direct transcriptional activation of 2 genes, ODC1 and AZIN1, which are involved in polyamine biosynthesis and control, respectively. In patients with multiple myeloma (MM), AHR levels were inversely correlated with survival, suggesting that AHR inhibition may be beneficial for the treatment of this disease. We identified clofazimine (CLF), an FDA-approved anti-leprosy drug, as a potent AHR antagonist and a suppressor of polyamine biosynthesis. Experiments in a transgenic model of MM (Vk*Myc mice) and in immunocompromised mice bearing MM cell xenografts revealed high efficacy of CLF comparable to that of bortezomib, a first-in-class proteasome inhibitor used for the treatment of MM. This study identifies a previously unrecognized regulatory axis between AHR and polyamine metabolism and reveals CLF as an inhibitor of AHR and a potentially clinically relevant anti-MM agent.

MYC and tumor metabolism: chicken and egg.

Transcription factors of the MYC family are deregulated in the majority of all human cancers. Oncogenic levels of MYC reprogram cellular metabolism, a hallmark of cancer development, to sustain the high rate of proliferation of cancer cells. Conversely, cells need to modulate MYC function according to the availability of nutrients, in order to avoid a metabolic collapse. Here, we review recent evidence that the multiple interactions of MYC with cell metabolism are mutual and review mechanisms that control MYC levels and function in response to metabolic stress situations. The main hypothesis we put forward is that regulation of MYC levels is an integral part of the adaptation of cells to nutrient deprivation. Since such mechanisms would be particularly relevant in tumor cells, we propose that-in contrast to growth factor-dependent controls-they are not disrupted during tumorigenesis and that maintaining flexibility of expression is integral to MYC's oncogenic function.

Exogenous applications of Polyamines modulate drought responses in wheat through osmolytes accumulation, increasing free polyamine levels and regulation of polyamine biosynthetic genes.

Polyamines (PAs) can improve drought stress tolerance in plants; however, very limited information is available on the mechanism of action of exogenous application by different methods under drought stress in wheat. The present study investigates the mechanism through which seed priming and foliar spraying with PAs protect wheat plants from drought stress. 10 days old wheat seedlings were exposed to drought stress by withholding water alone or with 100 µM PAs solutions (putrescine, Put; spermine, Spm; and mixture of Put and Spm for 10 h seed-priming or three foliar sprays during withholding water. Drought stress impaired the wheat growth and altered the osmoprotectants, endogenous PAs levels, PAs biosynthetic genes expression and weight of 1000 grains compared to the corresponding control values. Exogenously applied PAs improved cell water status, accumulated osmoprotectants and PAs and up-regulated PAs biosynthetic genes, ADC, arginine decarboxylase; DHS, deoxyhypusine synthase; ODC, ornithine decarboxylase and SAMDC, S-adenosyl methionine decarboxylase. Put significantly regulate the endogenous PAs by both methods of application, however, Spm and mixture of Put and Spm could positively regulate the endogenous PAs and the biosynthetic gene expression by foliar spraying rather than seed priming. The data provide evidence that maintenance of water economy through stabilized cellular structure is an important strategy of drought tolerance by PAs in wheat.

Tamoxifen metabolite endoxifen interferes with the polyamine pathway in breast cancer.

Tamoxifen is the most widely used drug to treat women with estrogen receptor α (ERα)-positive breast cancer. Endoxifen is recognized as the active metabolite of tamoxifen in humans. We studied endoxifen effects on ERα-positive MCF-7 breast cancer cells. Estradiol increased the proliferation of MCF-7 cells by two- to threefold and endoxifen suppressed its effects. Endoxifen suppressed c-myc, c-fos and Tff1 oncogene expression, as revealed by RT-PCR. Estradiol increased the activity of ornithine decarboxylase (ODC) and adenosyl methioninedecarboxylase (AdoMetDC), whereas endoxifen suppressed these enzyme activities. Endoxifen increased activities of spermine oxidase (SMO) and acetyl polyamine oxidase (APAO) significantly, and reduced the levels of putrescine and spermidine. These data suggest a possible mechanism for the antiestrogenic effects of tamoxifen/endoxifen, involving the stimulation of polyamine oxidase enzymes. Therefore, SMO and APAO stimulation might be useful biomarkers for the efficacy of endoxifen treatment of breast cancer.

Targeting the polyamine-hypusine circuit for the prevention and treatment of cancer.

The unique amino acid hypusine is present in only two proteins in eukaryotic cells, eukaryotic translation initiation factor 5A-1 (eIF5A1), and eIF5A2, where it is covalently linked to the lysine-50 residue of these proteins via a post-translational modification coined hypusination. This unique modification is directed by two highly conserved and essential enzymes, deoxyhypusine synthase (DHPS), and deoxyhypusine hydroxylase (DOHH), which selectively use the polyamine spermidine as a substrate to generate hypusinated eIF5A. Notably, elevated levels of polyamines are a hallmark of most tumor types, and increased levels of polyamines can also be detected in the urine and blood of cancer patients. Further, in-clinic agents that block the function of key biosynthetic enzymes in the polyamine pathway markedly impair tumor progression and maintenance of the malignant state. Thus, the polyamine pathway is attractive as a prognostic, prevention and therapeutic target. As we review, recent advances in our understanding of the specific functions of hypusinated eIF5A and its role in tumorigenesis suggest that the polyamine-hypusine circuit is a high priority target for cancer therapeutics.

Spatial and temporal distribution of genes involved in polyamine metabolism during tomato fruit development.

Polyamines are organic compounds involved in various biological roles in plants, including cell growth and organ development. In the present study, the expression profile, the accumulation of free polyamines and the transcript localisation of the genes involved in Put metabolism, such as Ornithine decarboxylase (ODC), Arginine decarboxylase (ADC) and copper containing Amine oxidase (CuAO), were examined during Solanum lycopersicum cv. Chiou fruit development and maturation. Moreover, the expression of genes coding for enzymes involved in higher polyamine metabolism, including Spermidine synthase (SPDS), Spermine synthase (SPMS), S-adenosylmethionine decarboxylase (SAMDC) and Polyamine oxidase (PAO), were studied. Most genes participating in PAs biosynthesis and metabolism exhibited an increased accumulation of transcripts at the early stages of fruit development. In contrast, CuAO and SPMS were mostly expressed later, during the development stages of the fruits where a massive increase in fruit volume occurs, while the SPDS1 gene exhibited a rather constant expression with a peak at the red ripe stage. Although Put, Spd and Spm were all exhibited decreasing levels in developing immature fruits, Put levels maxed late during fruit ripening. In contrast to Put both Spd and Spm levels continue to decrease gradually until full ripening. It is worth noticing that in situ RNA-RNA hybridisation is reported for the first time in tomato fruits. The localisation of ADC2, ODC1 and CuAO gene transcripts at tissues such as the locular parenchyma and the vascular bundles fruits, supports the theory that all genes involved in Put biosynthesis and catabolism are mostly expressed in fast growing tissues. The relatively high expression levels of CuAO at the ImG4 stage of fruit development (fruits with a diameter of 3 cm), mature green and breaker stages could possibly be attributed to the implication of polyamines in physiological processes taking place during fruit ripening.

Vitamin K1 exerts antiproliferative effects and induces apoptosis in three differently graded human colon cancer cell lines.

Vitamin K1 has been demonstrated as having anticancer potentiality mainly in liver cancer cells. Beyond the reported mechanisms of cancer inhibition (cell cycle arrest and induction of apoptosis), a possible control by vitamin K1 on molecules affecting cell growth could be hypothesized. In the literature, few (if any) data are available on its antitumor effects on colon cancer cells. Therefore, the aims of the study were to investigate in three differently graded human colon cancer cell lines (Caco-2, HT-29, and SW480) the effects of increasing concentrations of vitamin K1 (from 10 µM to 200 µM) administered up to 72 h on (1) cell proliferation, (2) apoptosis with the possible involvement of the MAPK pathway, and (3) polyamine biosynthesis. Vitamin K1 treatment caused a significant antiproliferative effect and induced apoptosis in all the cell lines, with the involvement of the MAPK pathway. A concomitant and significant decrease in the polyamine biosynthesis occurred. This is the first study demonstrating a significant polyamine decrease in addition to the antiproliferative and proapoptotic effects following vitamin K1 administration to colon cancer cell lines. Therapeutically, combinations of vitamin K1 with polyamine inhibitors and/or analogues may represent a suitable option for chemoprevention and/or treatment in future strategies for colorectal cancer management.

Novel protein-protein interaction between spermidine synthase and S-adenosylmethionine decarboxylase from Leishmania donovani.

Polyamine biosynthesis pathway has long been considered an essential drug target for trypanosomatids including Leishmania. S-adenosylmethionine decarboxylase (AdoMetDc) and spermidine synthase (SpdSyn) are enzymes of this pathway that catalyze successive steps, with the product of the former, decarboxylated S-adenosylmethionine (dcSAM), acting as an aminopropyl donor for the latter enzyme. Here we have explored the possibility of and identified the protein-protein interaction between SpdSyn and AdoMetDc. The protein-protein interaction has been identified using GST pull down assay. Isothermal titration calorimetry reveals that the interaction is thermodynamically favorable. Fluorescence spectroscopy studies also confirms the interaction, with SpdSyn exhibiting a change in tertiary structure with increasing concentrations of AdoMetDc. Size exclusion chromatography suggests the presence of the complex as a hetero-oligomer. Taken together, these results suggest that the enzymes indeed form a heteromer. Computational analyses suggest that this complex differs significantly from the corresponding human complex, implying that this complex could be a better therapeutic target than the individual enzymes.

Selective regulation of nicotine and polyamines biosynthesis in tobacco cells by enantiomers of ornithine.

L- and D-amino acids have diverse functions and effects on the metabolism, growth, and development of plants. Ornithine (Orn) plays a main role in the biosynthesis of many amino acids, nicotinic alkaloids, and polyamines in tobacco. This investigation describes the impact of Orn enantiomers on the production and distribution of free, conjugated, and bound polyamines, as well as nicotine in tobacco cells. It was recognized that the biosynthesis of metabolites was differently upregulated by each enantiomer. Putrescine was abundantly produced by exogenous L-ornithine (L-Orn), and both spermidine and spermine were significantly accumulated in D-ornithine (D-Orn)-supplied tobacco cells. Furthermore, nicotine production was highly upregulated by L-Orn, while the addition of D-Orn had no effect on the nicotine content of tobacco cells. It was observed that transcript expression of S-adenosylmethionine decarboxylase, as the key enzyme of spermidine/spermine biosynthesis, is coincident with their metabolic levels and is highly upregulated by D-Orn, as opposed to L-Orn. These results indicate that both enantiomers of Orn can trigger selected biosynthetic pathways in the cells, at the transcript level. Regarding these observations, it is proposed that L- and D-Orn function differently in the same biological pathways in which the latter, D-Orn specifically regulates important polyamines in the plant cells.

Repeated short-term stress synergizes the ROS signalling through up regulation of NFkB and iNOS expression induced due to combined exposure of trichloroethylene and UVB rays.

Restraint stress is known to catalyse the pathogenesis of the variety of chronic inflammatory disorders. The present study was designed to evaluate the effect of repeated short-term stress (RRS) on cellular transduction apart from oxidative burden and early tumour promotional biomarkers induced due to combined exposure of trichloroethylene (TCE) and Ultra-violet radiation (UVB). RRS leads to the increase in the expression of the stress responsive cellular transduction elements NFkB-p65 and activity of iNOS in the epidermal tissues of mice after toxicant exposure. RRS augments the steep depletion of the cellular antioxidant machinery which was evidenced by the marked depletion in GSH (Glutathione and GSH dependant enzymes), superoxide dismutase and catalase activity that were observed at significance level of P < 0.001 with increase in lipid peroxidation, H(2)O(2) and xanthine oxidase activity (P < 0.001) in the stressed animals and down regulation of DT-diaphorase activity (P < 0.001). Since, the induction of NFkB-p65 and inducible nitric oxide synthase expression mediated can lead to the hyperproliferation, we estimated a significant increment (P < 0.001) in the synthesis of polyamines in mice skin evidenced here by the ornithine decarboxylase which is the early marker of tumour promotion and further evaluated PCNA expression. All these findings cues towards the synergising ability of repeated short-term stress in the toxic response of TCE and UVB radiation.

Arginine and polyamines in Helicobacter pylori-induced immune dysregulation and gastric carcinogenesis.

L-arginine (L-Arg) is metabolized by nitric oxide synthase and arginase enzymes. The gastric pathogen Helicobacter pylori causes peptic ulcer disease and gastric cancer. We have shown that alterations in L-Arg availability and metabolism into polyamines contribute significantly to the dysregulation of the host immune response to this infection. Nitric oxide (NO) derived from inducible NO synthase (iNOS) can kill H. pylori. There are multiple mechanisms leading to failure of this process, including competition for L-Arg substrate by H. pylori arginase, and induction of host macrophage arginase II (Arg2) and ornithine decarboxylase (ODC). Generation of spermine by ODC inhibits iNOS translation and NO-mediated H. pylori killing. Expression of ODC is dependent on formation of a unique AP-1 complex, leading to upregulation of c-Myc as a transcriptional enhancer. Macrophage apoptosis is mediated by oxidation of spermine via the enzyme spermine oxidase (SMO) that generates hydrogen peroxide (H(2)O(2)), and thus oxidative stress-induced mitochondrial membrane polarization. Our studies have demonstrated that apoptosis occurs through a pERK → pc-Fos/c-Jun → c-Myc → ODC → SMO pathway. In gastric epithelial cells, activation of oxidative stress by H. pylori is dependent on SMO induction and results in both apoptosis and DNA damage, such that inhibition or knockdown of SMO markedly attenuates these events. In summary, L-Arg metabolism by the arginase-ODC pathway and the activation of SMO leads to H. pylori-induced DNA damage and immune dysregulation through polyamine-mediated oxidative stress and impairment of antimicrobial NO synthesis. Our studies indicate novel targets for therapeutic intervention in H. pylori-associated diseases, including gastritis, ulcer disease, and gastric cancer.

Quercetin inhibits human DLD-1 colon cancer cell growth and polyamine biosynthesis.

BACKGROUND/AIM: Polyamines and ornithine decarboxylase are involved in cell growth and differentiation. The polyphenol quercetin may exert anti-tumour properties by influencing proliferation, differentiation, and apoptosis. The aim of the study was to investigate the effects of increasing concentrations of quercetin (from 0.1 to 100 µM) on polyamine biosynthesis, cell proliferation, and apoptosis in the DLD-1 cells. MATERIALS AND METHODS: Polyamine levels and ornithine decarboxylase activity were evaluated by HPLC and radiometric technique, respectively. The proliferative response was estimated by 3-(4,5 dimethylthiazol-2yl)-2,5-diphenyl-tetrazolium bromide (MTT) test and [(3)H]-thymidine incorporation in cell DNA. Apoptosis was investigated by DNA fragmentation. RESULTS: At concentrations ≥50 µM, quercetin significantly reduced ornithine decarboxylase activity, putrescine and spermidine levels compared to controls and cells treated with 0.1 µM concentration. Quercetin concentrations ≥70 µM caused a significant reduction in the conversion of MTT tetrazolium salt and [(3)H]-thymidine incorporation. The same concentrations were needed to induce the apoptosis. CONCLUSION: The present study demonstrates that quercetin can affect growth of DLD-1 cells by both decreasing polyamine biosynthesis and inducing apoptosis. Due to the extensive dietary consumption of polyphenols, such as quercetin, the biological activity of these compounds deserves further investigation.

Activated polyamine catabolism leads to low cholesterol levels by enhancing bile acid synthesis.

Transgenic mice with activated polyamine catabolism due to overexpression of spermidine/spermine N(1)-acetyltransferase (SSAT) have significantly reduced plasma total cholesterol levels. In our study, we show that low cholesterol levels were attributable to enhanced bile acid synthesis in combination with reduced cholesterol absorption. Hepatic cholesterol 7alpha-hydroxylase (CYP7A1), the rate-limiting enzyme catalyzing the conversion of cholesterol to bile acids, plays an important role in the removal of excess cholesterol from the body. We suggest that by reducing activity of Akt activated polyamine catabolism increased the stability and activity of peroxisome proliferator-activated receptor gamma co-activator 1alpha, the critical activator of CYP7A1. This is supported by our finding that the treatment with SSAT activator, N (1) ,N(11)-diethylnorspermine, reduced significantly the amount of phosphorylated (active) Akt in HepG2 cells. In summary, activated-polyamine catabolism is a novel mechanism to regulate bile acid synthesis. Therefore, polyamine catabolism could be a potential therapeutic target to control hepatic CYP7A1 expression.

[Molecular functions of polyamines in neoplastic growth and their role in control of the NF-kappaB transcription factor in experimental tumors cells].

PA were found to promote creation of the NF-kappaB complex with the correspondent DNA sequences (NRE), p50 NF-kappaB-subunit affinity with NRE is essentially magnified in PA presence. This is one of important demonstrations of PA involvement in transcription control. NF-kappaB activity in experimental mammary tumors cells was shown to depend on PA metabolism. Retardation of experimental mammary tumors growth caused by the inhibitors of PA biosynthesis was accompanied with decreased expression of protein products of the NF-kappaB-dependent genes such as c-myc, bcl-xl. It was hypothesized that under PA depletion not classic NF-kappaB (p50/p65 heterodimer) but p50/p50 homodimer is mainly created, and this homodimer, because of PA deficiency, is not able to promote transcription of the gene have been tested.

Polyamine biosynthesis impacts cellular folate requirements necessary to maintain S-adenosylmethionine and nucleotide pools.

Folate (vitamin B9) is utilized for synthesis of both S-adenosylmethionine (AdoMet) and deoxythymidine monophosphate (dTMP), which are required for methylation reactions and DNA synthesis, respectively. Folate depletion leads to an imbalance in both AdoMet and nucleotide pools, causing epigenetic and genetic damage capable of initiating tumorigenesis. Polyamine biosynthesis also utilizes AdoMet, but polyamine pools are not reduced under a regimen of folate depletion. We hypothesized that high polyamine biosynthesis, due to the high demand on AdoMet pools, might be a factor in determining sensitivity to folate depletion. We found a significant correlation (P<0.001) between polyamine biosynthesis and the amount of folate required to sustain cell line proliferation. We manipulated polyamine biosynthesis by genetic and pharmacological intervention and mechanistically demonstrated that we could thereby alter AdoMet pools and increase or decrease demand on folate availability needed to sustain cellular proliferation. Furthermore, growing a panel of cell lines with 100 nM folate led to imbalanced nucleotide and AdoMet pools only in cells with endogenously high polyamine biosynthesis. These data demonstrate that polyamine biosynthesis is a critical factor in determining sensitivity to folate depletion and may be particularly important in the prostate, where biosynthesis of polyamines is characteristically high due to its secretory function.

Effects of Lactobacillus rhamnosus GG on proliferation and polyamine metabolism in HGC-27 human gastric and DLD-1 colonic cancer cell lines.

Previous in vitro and in vivo studies have suggested that lactobacilli can exert antiproliferative effects on the gastrointestinal epithelium. However, their role in affecting the cellular proliferative mechanisms is not completely clear. The aim of this study was to investigate the effects of increasing concentrations of Lactobacillus rhamnosus strain GG (L. GG) homogenate on cell growth and proliferation (by MTT, [3H]-thymidine incorporation and polyamine biosynthesis) in neoplasms originating from different gastrointestinal tracts. Thus, HGC-27 human gastric cancer cells and DLD-1 human colonic adenocarcinoma cells were evaluated. Besides, in order to verify which bacterial fraction was involved in the antiproliferative effects, the cytoplasm and cell wall extracts were tested separately. Gastric HGC-27 and colonic DLD-1 cells showed significant differences in their proliferative behavior, in particular in their polyamine profile and biosynthesis. Notwithstanding, one and the other proved to be sensitive to the growth inhibition by the highest concentrations of bacterial homogenate. Both HGC-27 and DLD-1 cells were resistant to the bacterial cell wall fractions, whereas increasing cytoplasm fraction concentrations induced an evident antiproliferative effect. These data suggest that cytoplasm extracts could be the responsible for L. GG action on proliferation in these two cell lines from gastric and colonic neoplasms.

Influence of gender and sex hormones on 5alpha-dihydrotestosterone elicited effect in isolated left atria of rats: Role of beta-adrenoceptors and ornithine decarboxylase activity.

Androgens elicit an acute cardiotonic effect in cardiac preparations of rats. This effect is produced via an extracellular interaction that may be coupled to pertussis-sensitive G-proteins and is associated with an increase in cAMP, polyamine synthesis and intracellular calcium. The nature of the targets and the existence of a dimorphic effect in this nongenomic effect of androgens are unknown. The purpose of this study was to characterize a possible gender and sex hormone influence on the 5alpha-dihydrotestosterone-elicited cardiotonic effect, taking into account the possible role of the beta-adrenoceptors and ornithine decarboxylase activity on this response. [Float1]Regarding this, the effect of 5alpha-dihydrotestosterone on isolated left atria from male, estrogenized female and gonadectomized male and female rats was studied. The results showed that 5alpha-dihydrotestosterone-elicited cardiotonic effect was preserved independent of gender and sex hormones, being higher in control males than in the rest of the groups. This correlated with the testosterone plasma levels, except in estrogenized females, suggesting that the androgens positively and the estrogens negatively regulated the response. In all groups, 5alpha-dihydrotestosterone produced an increase in cAMP levels, but only in control males did it produce an increase in ornithine decarboxylase activity. In the other groups, the absence of an effect on ornithine decarboxylase might limit the capability of the response to the androgen. Altogether, androgens may help to control cardiac performance by a direct interaction on the heart in both sexes. Gender and sex differences in the magnitude of inotropism being due mainly to changes in beta-adrenoceptors and cAMP production and in intracellular polyamine synthesis.

ODC1 is a critical determinant of MYCN oncogenesis and a therapeutic target in neuroblastoma.

Neuroblastoma is a frequently lethal childhood tumor in which MYC gene deregulation, commonly as MYCN amplification, portends poor outcome. Identifying the requisite biopathways downstream of MYC may provide therapeutic opportunities. We used transcriptome analyses to show that MYCN-amplified neuroblastomas have coordinately deregulated myriad polyamine enzymes (including ODC1, SRM, SMS, AMD1, OAZ2, and SMOX) to enhance polyamine biosynthesis. High-risk tumors without MYCN amplification also overexpress ODC1, the rate-limiting enzyme in polyamine biosynthesis, when compared with lower-risk tumors, suggesting that this pathway may be pivotal. Indeed, elevated ODC1 (independent of MYCN amplification) was associated with reduced survival in a large independent neuroblastoma cohort. As polyamines are essential for cell survival and linked to cancer progression, we studied polyamine antagonism to test for metabolic dependence on this pathway in neuroblastoma. The Odc inhibitor alpha-difluoromethylornithine (DFMO) inhibited neuroblast proliferation in vitro and suppressed oncogenesis in vivo. DFMO treatment of neuroblastoma-prone genetically engineered mice (TH-MYCN) extended tumor latency and survival in homozygous mice and prevented oncogenesis in hemizygous mice. In the latter, transient Odc ablation permanently prevented tumor onset consistent with a time-limited window for embryonal tumor initiation. Importantly, we show that DFMO augments antitumor efficacy of conventional cytotoxics in vivo. This work implicates polyamine biosynthesis as an arbiter of MYCN oncogenesis and shows initial efficacy for polyamine depletion strategies in neuroblastoma, a strategy that may have utility for this and other MYC-driven embryonal tumors.

Investigations about N-aminopropyl transferases probably involved in biomineralization.

Polyamines are widespread distributed all over in living organisms. In Thalassiosira pseudonana 10 N-aminopropyl transferase like nucleotide sequences exists. It is assumed that these sequences are involved in the biomineralization of the diatom shell. The cDNA of the sequences were cloned, recombinant overexpressed and assayed with decarboxylated S-adenosylmethionine and several radioactive labelled polyamines. However, only a spermidine synthase and a thermospermine synthase were found to be enzymatically active in an in vitro assay. Both enzyme activities could be recognized in the crude extracts of Thalassiosira pseudonana and Cyclotella meneghiana. In further investigations the kinetics of the thermospermine synthase was determined and a site-specific mutagenesis of the bindig cavity of decarboxylated S-adenosylmethionine was carried out.