To determine the structure(s) of the spermidine conjugate excreted into urine, extensive pharmacokinetic studies on the turnover of [¹⁴C]spermidine were conducted in both rats and humans. These studies demonstrated that exogenously administered [¹⁴C]spermidine equilibrated with endogenous polyamine pools. Radiolabeled urine collected from the humans was subjected to a cleanup protocol and subsequent analysis by GC-MS, which demonstrated the presence of N-acetylspermidine. Further analysis of the radiolabeled urine by thin layer chromatography (TLC) demonstrated the presence of both N¹- and N⁸-acetylspermidine in an approximate 1 to 1 ratio. Using similar methodologies the monoacetyl derivatives of putrescine and cadaverine were found to be the primary conjugated products of these polyamines excreted into human urine. Radiolabeled rat tissue extracts, analyzed by TLC, demonstrated that all tissues studied contained [¹⁴C] N¹- and N⁸-acetylspermidine. N¹-acetylspermidine was the primary isomer detected in all tissues; although, N⁸-acetylspermidine was detected in all tissues studied. The N-acetylspermidine content of an isolated cell system was determined in Chinese hamster ovary cells. These cells contained both N¹- and N⁸-acetylspermidine in an approximate 2 to 1 ratio. To directly measure the N-acetylpolyamines excreted into urine, two high performance liquid chromatography (HPLC) methods were developed. Both HPLC methods utilize a cation exchange resin, one using high pH, low salt buffers and the other low pH and high salt buffers. The primary N-acetylpolyamine excreted into human urine is N-acetylputrescine with lesser amounts of N¹- and N⁸-acetylspermidine which exist in a 1 to 1 ratio. In contrast, cancer patients excreted elevated amounts of both N-acetylputrescine and N¹-acetylspermidine. Cystic fibrosis patients were also found to excrete elevated amounts of N¹-acetylspermidine resulting in a consistently elevated N¹- to N⁸-acetylspermidine ratio. Mice injected with P-388 leukemia tumor excreted elevated amounts of N-acetylputrescine, N¹-acetylspermidine and N⁸-acetylspermidine. In contrast, the excretion of the unconjugated polyamines putrescine and spermidine in these animals was decreased, suggesting that the altered polyamine excretion was not primarily due to the presence of the tumor. Administration of Adriamycin to the tumor bearing animals resulted in the elevation of N¹-acetylspermidine excretion which was proportional to the relative tumor burden. Similar results were obtained from 2 human leukemia patients studied following chemotherapy.

Prostate cancer is the second leading cancer in men. A large amount of polyamines are synthesised in the human prostate and are involved in prostate cell growth and its physiological functions. The content of intracellular polyamines is closely related to cell growth. An increase in cell growth is accompanied by a rise of intracellular polyamine content, and a depletion of intracellular polyamine pools can cause growth arrest or cell death. Therefore, maintaining polyamine concentrations is critical to the cell. Spermidine/spermine N1-acetyltransferase (SSAT) is the first and rate-limiting enzyme in the polyamine catabolic pathway. SSAT gene is highly inducible, with many stimuli including polyamine analogues and some anticancer drugs producing dramatic increases in activity. Many studies have focussed on polyamine analogues as inducers of SSAT activity as increases in SSAT are associated with a growth inhibition in many tumour cells. However, the mechanisms of this inhibition are not fully understood with respect to polyamine content. Additionally, in vivo results in SSAT transgenic mice studies are contradictory. For example, prostate carcinogenesis is reduced in TRAMP mice but Apcmin/+ mice show a promoted intestinal tumorigenesis. It is thus necessary to characterise the regulation of polyamine content and metabolism by SSAT in prostate cancer cells. The aim of the present study was to characterise the role of SSAT in both the growth of LNCaP prostate carcinoma cells and the response of these cells to anticancer drugs. Our hypothesis is that increased SSAT activity will inhibit cell growth and that this is associated with a decrease of intracellular polyamine pools. Furthermore, if SSAT induction is an essential part of the response of cancer cells to anticancer drugs, then altered SSAT activity should affect sensitivity of the cells to the drugs. The present study used a cell culture model of human prostate cancer: LNCaP wild type (WT) and SSAT cDNA transfected prostate carcinoma cell lines. The expression of SSAT in the transfected cell line (SSAT- & SSAT+) was controlled through the “Tet-off” system. This model system provided a background for comparison of effects under basal (WT), low (SSAT-), and high (SSAT+) SSAT activity. Due to our interest in acetylpolyamine derivatives and their low concentrations in cells, a new method for quantifying polyamine concentrations was developed using liquid chromatography-mass spectrometry (LC-MS). This method was highly sensitive and can detect polyamines about 250 fold lower than HPLC, as well as N-acetylpolyamines and N1,N12-diacetylspermine. In addition, a variety of methods were utilised to measure cell growth, enzyme activity, protein expression, polyamine efflux and apoptosis, which includes enzyme assays, western blot, radiochemical labelled assays, flow cytometry, spectrophotometry and fluorescent microscopy. A stable increase in SSAT activity was inhibitory to the cell growth. This inhibition was associated with significant changes in the activity of the polyamine pathway. The alterations included an increase in ODC, APAO, and SMO activity; an accumulation of intracellular N1-acetylspermidine and putrescine; a decrease in intracellular spermidine and spermine; an increased polyamine flux and efflux; and an increase in apoptosis. Combination treatment to the cells with DFMO and MDL72527 partially restored the growth of SSAT+ cells. The original contribution of this study to the field is that the cells with a higher SSAT activity are less sensitive to aspirin and 5-FU, and the sensitivity increased while the overexpressed SSAT activity decreased. The growth inhibition was associated with a depletion of total intracellular polyamine pools by the drug treatments. Moreover, to our knowledge, it is first time that the extracellular polyamine concentrations were quantified by LC-MS in human tumour cells. Overall, an increase in SSAT activity led to an inhibition of prostate cancer cell growth, and vice versa. Thereby, this study suggests that SSAT is a potential target for novel drug discovery for cancer chemotherapy or chemoprevention. For example, a combination treatment could be designed that acts as an inducer of SSAT activity in tumour cells, leading to an inhibition of the cell growth in the first place and increased sensitivity to cytotoxic agents. This would then be followed by an agent to decrease SSAT activity when the sensitivity of cancer cells to the cytotoxic treatment was optimal.

Malaria affects the daily lives of more than 2 billion people worldwide and has been estimated to result in 300-500 million clinical cases annually leading to approximately 2 million deaths, mainly caused by the most virulent malaria species, Plasmodium falciparum. The lack of a vaccine and the rapid emergence and spread of drug resistant strains of P. falciparum, necessitate the development of new antimalarials and the identification and validation of new parasite-specific therapeutic targets. Numerous studies directed at interfering with the polyamine biosynthetic pathway in P. falciparum have shown its potential as a target for the development of a new class of antimalarials. The essential nature of P. falciparum spermidine synthase (PfSpdSyn), an enzyme in the polyamine pathway of the parasite warranted the further investigation to find novel lead compounds. The high cost and attrition rate of drug discovery has resulted in the implementation of smart drug discovery platforms in both academia and industry. The strategy implemented in this study involved the development of a dynamic receptor-based pharmacophore model (DPM) of PfSpdSyn complemented by a knowledge-based rational design strategy. The use of pharmacophore models to identify lead compounds has become increasingly popular over the last decade and has been shown to be a reliable method in the drug discovery process. The development of a DPM allows for the incorporation of protein exibility within the drug design process. This methodology results in a wealth of information of the chemical space of the active site and was incorporated in designing new inhibitors against PfSpdSyn using a knowledge-based rational design strategy. The active site of PfSpdSyn was subdivided into four binding regions (DPM1-DPM4) to allow for the identi cation of fragments binding within these speci c binding regions. DPMs representative of the chemical characteristics of each binding region were constructed and subsequently screened against the drug-like subset of the ZINC database. From the screens a total of nine compounds were selected for in vitro testing, complementing each other in exploring specific active site binding characteristics. From these compounds a new lead compound N-(3-aminopropyl)-cyclohexylamine (NAC; Ki 2.8 μM) was identified for PfSpdSyn. NAC was specifically designed to bind in both the putrescine and decarboxylated adenosylmethionine cavities by chemically bridging the catalytic center and was confirmed by kinetic studies. NAC shows great potential for lead optimization to increase its binding affinity. This study then paves the way for lead optimization and possibly the development of a novel antimalarial. The development of a DPM for PfSpdSyn has seen the establishment of this methodology in the Bioinformatics and Computational Biology Unit, Department of Biochemistry at the University of Pretoria. It can be concluded that the development of a DPM complemented by a knowledge-based rational design strategy is an effective approach for the identification of novel lead compounds in the presence of a 3D target structure. This paves the way for more studies on both malaria and other drug targets using DPMs. Copyright / Thesis (PhD)--University of Pretoria, 2009. / Biochemistry / unrestricted

The naturally occurring polyamines play an essential role in cell growth and proliferation. The enzyme spermidine N8- acetyltransferase catalyzes the acetylation of spermidine utilizing acetyl-CoA as the acetyl donor. In this study, an in vitro acetyltransferase assay was used to determine the types of compounds which can inhibit this reaction. The enzyme was partially purified from rat liver nuclei and solubilized in 0.4 M KCl. The Km for spermidine was 0.47 mM. Studies on the nature of the active site indicated that: (i) a sulfhydryl group is essential for optimal activity as shown by inhibition with parahydroxymercuribenzoate and N -ethylmaleimide, (ii) a metal ion does not appear to be necessary for catalytic activity of this enzyme since EDTA, 2,2-dipryridil, and 1,10 phenanthroline were poor inhibitors of this enzyme, (iii) a lysine or another primary amine is likely to play a crucial role in this reaction since succinate anhydride and 2,4,6-trinitrobenzene sulfonic acid were effective inhibitors of this reaction and (iv) tyrosine is not likely present at the catalytic site since N -acetylimidazole produced no inhibition.

No description available.

Trypanosomiasis and Leishmaniasis are tropical diseases caused by the parasites Trypanosoma and Leishmania, that cause severe medical and economical problems for millions of people in the developing world. Trypanosomiasis can be divided into African and American trypanosomiasis, which are caused by Trypanosoma brucei and Trypanosoma cruzi respectively. There are more than 20 different species of Leishmania worldwide that cause Leishmaniasis, but the most severe infection, visceral leishmaniasis, is caused by Leishmania donovani. Both diseases are transmitted by blood sucking insects like the tsetse fly and the sand fly. The majority of existing drugs for trypanosomiasis and leishmaniasis are either too toxic or have low efficacy, and in some cases parasites have also developed resistance. There is therefore a pressing need to develop new chemotherapeutic agents, and in this context, the enzyme trypanothione reductase (TryR) has emerged as an attractive validated target for drug design. The natural product cadabicine, extracted from the plant Cadaba farinosa, is a diphenyl ether-containing macrocyclic spermidine alkaloid which has been identified as a potential inhibitor of TryR by virtual screening. In order to investigate the potential of cadabicine as a TryR inhibitor, an efficient synthetic route to the natural product was delivered. This work was focused on the preparation and combination of three key synthetic units, namely an orthogonally protected spermidine derivative and two functionalised cinnamic acid units. This approach lead to the formation of the macrocycle by an intramolecular nucleophilic aromatic substitution followed by a convenient conversion to the natural product. In the same manner cyclic and noncyclic analogues of cadabicine were prepared, in order to examine the structure-activity relationship of these alkaloids to TryR.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

L'îlot génomique pks code une machinerie de biosynthèse complexe synthétisant la colibactine, une génotoxine produite par certaines souches de Escherichia coli. Cette génotoxine induit des cassures double-brin de l'ADN sur les cellules eucaryotes in vitro et in vivo. La colibactine n'est pas une protéine, mais un métabolite secondaire de type polycétide/peptide non-ribosomal (PK/NRP). Des résultats préliminaires de l'équipe semblaient indiquer que certains gènes du core genome de E. coli seraient également impliqués dans la production de la colibactine. L'objectif de cette thèse était d'identifier les gènes non-essentiels de E. coli situés hors de l'îlot génomique pks impliqués dans la synthèse de colibactine, en construisant une banque de mutants par insertion de transposons. Ce criblage a permis d'identifier 29 gènes candidats, mais deux groupes de gènes ont été particulièrement étudiés dans la suite du projet : trois gènes codants des protéines chaperons, et trois gènes codant des enzymes impliquées dans le métabolisme des polyamines. Le premier projet a permis de montrer que la protéine chaperon HtpG (ou Hsp90Ec), homologue bactérien de la protéine de choc thermique eucaryote Hsp90, est requise pour la production de colibactine, mais aussi de yersiniabactine, un sidérophore (ou système bactérien de captation du fer) appartenant à la même famille chimique que la colibactine. De plus, la protéase ClpQ intervient de concert avec Hsp90Ec dans la production de colibactine et de yersiniabactine. Ces résultats confirment ainsi l'interconnexion entre la synthèse des deux facteurs de virulence de E. coli, la colibactine et la yersiniabactine. Enfin, l'analyse des effets de la mutation du gène htpG au cours d'une infection systémique chez l'animal, dans des modèles de sepsis et de méningite néonatale chez les rongeurs, démontre le rôle de la protéine de réponse au stress Hsp90Ec dans la virulence de E. coli. Le second projet a révélé que les polyamines sont impliquées dans la production de colibactine. L'étude du métabolisme des polyamines par une approche de microbiologie moléculaire a démontré que la spermidine est la polyamine nécessaire à la production de colibactine. Les résultats préliminaires de ce projet indiquent que la spermidine participerait à la régulation de l'expression de certains gènes de l'îlot génomique pks, et de fait modulerait la biosynthèse de colibactine. Des études complémentaires sont en cours pour élucider les mécanismes impliqués. Les résultats de cette thèse sont une illustration parfaite de l'intégration symbiotique d'un élément génétique mobile acquis au cours de l'évolution au sein du chromosome bactérien, grâce à plusieurs connexions bilatérales permettant la production de facteurs de virulence par E. coli. / The pks genomic island codes a complex biosynthetic assembly line that synthetizes the colibactin, a genotoxin produced by some strains of Escherichia coli. This genotoxin generates DNA double-strand breaks in eukaryotic cells both in vitro and in vivo. Colibactin is not a protein, but a secondary metabolite belonging to the chemical family of hybrid polyketide/nonribosomal peptide compounds. Preliminary results from our research team suggested that certain genes of the E. coli core genome (i.e. genes present in all strains of the species) could also be involved in the colibactin production. The main goal of this thesis was to identify non-essential E. coli genes located outside the pks island that are required for colibactin biosynthesis, with the screening of a transposon mutant library. This revealed 29 potential candidate genes, but the project focused specifically on two groups of genes: three genes encoding chaperone proteins, and three genes encoding enzymes involved in polyamines metabolism. The first project highlighted the role of the molecular chaperone HtpG (or Hsp90Ec), the bacterial homolog of eukaryotic heat shock protein 90, in the production of colibactin, but also yersiniabactin, a siderophore (i.e. a bacterial iron uptake system) that belongs to the same chemical family as colibactin. Furthermore, the ClpQ protease was involved in colibactin and yersiniabactin production in combination with Hsp90Ec. These results confirmed the interplay between the biosynthesis of two E. coli virulence factors, colibactin and yersiniabactin. Finally, analysis of the effects of htpG disruption during systemic infection in animals, using rodent models of sepsis and neonatal meningitis, demonstrated the role of the stress-responsive molecular chaperone Hsp90Ec in E. coli virulence. The second project revealed the involvement of polyamines in the biosynthesis of colibactin. A molecular microbiology approach demonstrated that spermidine was the polyamine required for colibactin production. Preliminary results suggested that spermidine could regulate the expression of some pks island genes, and therefore could modulate colibactin production. Further experiments are in progress to elucidate the molecular mechanisms involved in this regulation. Together, the results of this thesis perfectly illustrate the symbiotic integration of a mobile genetic element acquired during evolution into the bacterial chromosome, through several crosstalks allowing the production of virulence factors in E. coli.

Amantadine is a cationic aliphatic primary amine eliminated by the kidneys, excreted predominantly unchanged into the urine, and undergoes limited metabolism. Renal tubule secretion has an important role in its elimination. We studied two aspects of amantadine disposition, firstly acetylation, by developing a model to induce the enzyme spermidine/spermine N1-acetyltransferase (SSAT1) with N1, N11-diethylnorspermine (DENSPM) and alcohol (Alc) as representative agents reported to induce its activity, and secondly renal secretion, by studying the effect of intravenous bicarbonate infusion on its renal elimination. We drew two conclusions, firstly, longer exposure to Alc combined with DENSPM administration provided the greatest potentiation of SSAT1 enzyme activity than each agent alone, which indicates a high likelihood of synergy between Alc and DENSPM; and secondly, bicarbonate load administered to healthy male volunteers impairs amantadine renal secretion in the absence of a clinically important change in blood pH, serum creatinine concentration or urinary creatinine clearance.

Amantadine is a cationic aliphatic primary amine eliminated by the kidneys, excreted predominantly unchanged into the urine, and undergoes limited metabolism. Renal tubule secretion has an important role in its elimination. We studied two aspects of amantadine disposition, firstly acetylation, by developing a model to induce the enzyme spermidine/spermine N1-acetyltransferase (SSAT1) with N1, N11-diethylnorspermine (DENSPM) and alcohol (Alc) as representative agents reported to induce its activity, and secondly renal secretion, by studying the effect of intravenous bicarbonate infusion on its renal elimination. We drew two conclusions, firstly, longer exposure to Alc combined with DENSPM administration provided the greatest potentiation of SSAT1 enzyme activity than each agent alone, which indicates a high likelihood of synergy between Alc and DENSPM; and secondly, bicarbonate load administered to healthy male volunteers impairs amantadine renal secretion in the absence of a clinically important change in blood pH, serum creatinine concentration or urinary creatinine clearance.