Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / The in vitro relationship of sialic acids to the A, B, M, N, C, D, and E antigens of the human erythrocyte has been studied by means of the Landsteiner hapten inhibition test with the idea that substances that strongly inhibit anti-D might find practical application in the prevention and treatment of erythroblastosis fetalis. Our results suggest that N-acetyl neuraminic acid (NANA) is a major constituent of the D (Rh0), M, and N agglutinogens, a minor constituent of the A antigen, but is probably not a functional portion of the B, C, and E antigenic structures. [TRUNCATED] / 2031-01-01

Sialyltransferases, CMP-sialic acid synthetases and CMP-sialic acid transport proteins play a crucial role in the construction of cell surface glycoconjugates. These proteins also have a pivotal role to play in a number of diseases, including cancer. The sialyltransferase enzymes are responsible for transfering sialic acids from the donor substrate (CMP-sialic acid) to growing cell surface glycoconjugate chains within the Golgi apparatus. The CMP-sialic acid synthetase enzymes are responsible for the synthesis of the CMP-sialic acid, the donor substrate of the sialyltransferases in the nucleus, while the CMP-sialic acid transport proteins are responsible for transporting CMP-sialic acid from the Cytosol to the Golgi apparatus. When these proteins function in an abnormal way, hypersialylation results, leading to an increased level of sialylation on the cell surface. This increased level of sialylation aids in the detachment of primary tumour cells due to an increase in the level of overall negative charge, causing repulsion between the cancer cells. Therefore, the sialyltransferase enzymes, CMP-sialic acid synthetases and CMP-sialic acid transport proteins are intimately involved in the metastatic cascade associated with cancer. Chapter 1 provides a general introduction of cancer metastasis, discussing the roles of three target proteins (CMP-sialic acid synthetases, CMP-sialic acid transport proteins and sialyltransferases), as well as discussing their substrate specificities, with an emphasis on their involvements in cancer metastasis. The Chapter concludes with an overview of the types of compounds intended to be utilised as probes or inhibitors of these proteins. Chapter 2 describes the general approach towards the synthesis of CMP-Neu5Ac mimetics with a sulfur linkage in the presence of a phosphate group in the general structure 38. The precursor phosphoramidite derivative 45 was prepared and isolated in a good yield using Py.TFA. Unfortunately, the target compound 38 could not be prepared. Chapter 3 describes an alternative strategy wherein S-linked sialylnucleoside mimetics, of the general structure 39, with a sulfur linkage, but no phosphate group, between the sialylmimetic and the ribose moiety in the base is targeted. A series of these S-linked sialylnucleoside mimetics were successfully prepared. Cytidine, uridine, adenosine and 5-fluorouridine nucleosides were used to create a library of different nucleosides and with structural variability also present in the sialylmimetic portion. This small 'library' of 15 compounds was designed to shed light on the interaction of these compounds with the binding sites of the sialyltranferase, CMP-sialic acid synthetase and/or CM-sialic acid transport protein. Approaches towards the synthesis of O-linked sialylnucleoside mimetics of the general structure 40 are described in Chapter 4. Several methodologies are reported, as well as protecting group manipulations, for successful preparation of these sialylnucleoside mimetics. Cytidine and uridine were employed as the nucleosides, thus allowing a direct comparison between the O- and S-linked sialylnucleoside mimetics in biological evaluation. It appears from these synthetic investigations that gaining access into the O-linked series is not as straightforward as for the S-linked series, with alternative protecting group strategies required for the different nucleosides. The biological evaluation of some of the compounds reported in Chapters 3 and 4 is detailed in Chapter 5. The sialylnucleoside mimetics were evaluated, by 1H NMR spectroscopy, for their ability to inhibit CMP-KDN synthetase. In addition, an initial 1H NMR spectroscopic-based assay was investigated for inhibition studies of α(2,6)sialyltranferase in the absence of potential inhibitors. The final chapter (Chapter 6) brings together full experimental details in support of the compounds described in the preceding Chapters.

Sialic acids are involved in many biological processes. In glycoproteins and glycolipids they are essential for signalling and mediate molecular interactions as well as being targets for many pathogens such as influenza virus. The synthesis of sialylated glycoconjugates is of great importance. The incorporation of sialic acid through chemical synthesis carries several difficulties, enzymatic strategies using glycosyltransferases are very attractive alternative strategy, and have been used on a broad range of substrates forming glycosidic linkages with regio-and stereo-specificity. The work presented herein shows the study and application of two enzymes, Photobacteriumdamselae alpha2,6-sialyltransferase (Pd2,6ST) and Trypanosoma cruzi trans-sialidase (TcTS) which are used in the synthesis of sialyloligosaccharides. Both enzymes were expressed in E.coli and purified for biotransformations. In the first application new sialylated chromogenic compounds were generated through this enzymatically by using TcTS and a Pd2,6ST. These compounds were used for the detection of neuraminidase activity in a number of biological samples and led to the discovery of neuraminidase activity from Bacillus pumilus and Arthrobacter aurescens, two different bacteria in which the presence of neuraminidases had never been described. Secondly, TcTS was used to study lipid glycosylations. Glycans in biological systems can be associated to complex lipidic microdomains and the presence of these microdomains can affect the activity of some enzymes. In case of Trypanosoma cruzi trans-sialidase, a decreased activity was detected when the acceptor substrate was part of the aggregated lipid rafts compared to activity observed when the reaction was performed using fully dispersed substrate. Thirdly, the sialylation of glycoarrays using Pd2,6ST was studied. For the first time, sialylated glycans with alpha2,6- glycosidic linkages were successfully incorporated into a gold glycoarray platform, which had been previously developed for the label-free detection of carbohydrate-protein interactions. Successful enzymatic incorporation of sialic acids onto the arrays was confirmed with commercial available lectins. Finally, by using the gold glycoarray platform containing both 2,3 and 2,6 linked sialic acids as well as other common glycans, the carbohydrate-binding properties of the surface proteins of the bacterium Lactobacillus reuteri was studied using MALDI-ToF MS techniques. For first time, strong interactions were observed between a mucus binding protein and Neu5Ac alpha2,6-linked glycans, with much weaker binding to 2,3-linked analogues. Such glycan structures have been identified in abundant manner in colon mucins and this study contributes to the understanding of complex interactions between mucins and probiotic organisms as well as pathogenic bacteria. These studies show that glycan arrays can contribute both to the understanding of probiotics as well as to the identification of glycan binding proteins as targets for new drugs.

The production of recombinant glycoproteins from mammalian cell cultures requires robust processes that can achieve high protein yield while ensuring the efficacy of these proteins as human therapeutics. We describe two approaches currently being developed in our group to genetically engineer cell lines with desirable characteristics for recombinant protein production. To enhance the degree of sialylation in the glycoprotein product, we propose to increase intracellular sialic acid availability by overexpressing the CMP-sialic acid transporters. We are also interested in engineering mammalian cells that can proliferate at reduced cultivation temperatures. Low temperature cultivation of mammalian cells has been shown to enhance glycoprotein production but reduces cell growth. It is hypothesized that a mutant cell line that can proliferate at low temperatures may be coupled with low temperature cultivation to improve recombinant protein production. / Singapore-MIT Alliance (SMA)

Viruses are common causative agents of ocular infection among humans. Epidemic keratoconjuntivitis (EKC) is a severe and contagious ocular disease with reported outbreaks worldwide. It is estimated that this disease affects 20-40 million individuals every year, which leads to huge socioeconomic costs for the affected countries. EKC is characterized by keratitis and conjunctivitis but is also associated with pain, edema, lacrimation, and decreased vision that can prolong for months after the infection and in rare cases years. This disease is caused by human adenoviruses (HAdVs), which belong to the family of Adenoviridae. Currently, there is no available treatment against EKC. EKC is mainly caused by HAdV-8, HAdV-19, HAdV-37, HAdV-53, HAdV-54, and HAdV-56, which belong to species D HAdVs. HAdV-8, HAdV-19 and HAdV-37 have previously been shown to use sialic acid (SA)-containing glycans as cellular receptors to bind to and infect human corneal epithelial (HCE) cells. To characterize the receptor in more detail, we performed a glycan array, which included SA-containing glycans. A branched hexasaccharide terminating with SA in each arm was identified as a candidate receptor. This glycan corresponds to the glycan motif found on a ganglioside, GD1a. By performing a series of biological and biochemical experiments we confirmed the function of the GD1a glycan as a cellular receptor for EKC-causing HAdVs. However, the glycan used as a receptor was linked to plasma membrane protein(s) through O-glycosidic bonds, rather than to a lipid (as in the ganglioside). X-ray crystallography analysis showed that the two terminal SA:s interacted with two of the three previously identified SA-binding sites on the knob domain of the HAdV-37 capsid protein known as the fiber. Based on the structural features of the GD1a:HAdV-37 knob interaction, we assumed that a three-armed molecule with each arm terminating with SA would be an efficient inhibitor. Such molecules were designed, synthesized and found to efficiently prevent HAdV-37 binding to and infection of corneal cells. These results indicate that trisialic acids-containing compounds may be used for treatment of EKC. After binding to its primary receptor, most HAdVs have been shown to interact with αVβ3 and αVβ5 integrins to enter human cells. This interaction occurs through the RGD (arginine-alanine-aspartic acid) motif in the capsid protein known as the penton base. However, it was not clear if corneal epithelial cells express αVβ3 and αVβ5 integrins. Thus, to better understand additional early steps of infection by EKC-causing HAdVs, we performed binding and infection competition experiments using human corneal epithelial cells and siRNA, integrin specific antibodies, peptides and RGD-containing ligands indicating that α3, αV, β1 affected HAdV-37 infection of but not binding to HCE cells. We could also see that HAdV-37 co-localize with α3 and αV at after entry into HCE cells. In situ histochemistry confirmed that the expression of α3 and αV in human corneal tissue. Overall, our results suggest that αV and α3 integrins are important for HAdV-37 infection of corneal cells. Altogether, these results provide further insight into the biology of HAdVs and open up for development of novel antiviral drugs.

No description available.

Although great progress has been made, cancer still remains one of the most prevalent maladies plaguing mankind. New treatment methodologies using nanoparticles have come to the forefront by allowing for enhanced delivery of therapeutics to the tumor site. The design of the nanoparticle should allow for long circulation times, tumor-specific targeting and efficient release at the site of action. This requires that both the external shell and internal core of the nanoparticle be carefully selected to meet the maximal criteria of each of these steps. Poly(sialic acid) (PSA), a naturally occurring polysaccharide, meets all of the benchmarks of an effective exterior coating yet remains relatively unexplored in the field of drug delivery. Due to stealth properties, natural tumor targeting ability, and inherent pH-responsive elements, PSA has frequently been viewed as a “next-generation” surface coating. Just as important, the internal composition of the carrier should aid in effective drug loading but also rapid release. The selection of the core containing groups as well as therapeutic should be maximized in order to customize the carrier to drug. Here, we have developed PSA micelles composed of various internal groups selected to maximize drug loading and facilitate release. Loading of the chemotherapeutic doxorubicin was optimized through variations in non-covalent bonding forces between drug and carrier. Furthermore, PSA micelles composed of internal pH-responsive groups of varying hydrophobicity were also developed to tailor micelle swelling points at conditions analogous towards those found upon cellular uptake. Both of these were effective delivery platforms towards MCF-7 human breast adenocarcinoma cells. / Bioengineering

No / Application of the Lewis acid BF3·Et2O to the selective synthesis of 5-acetamido-2,6-anhydro-3,5-dideoxy-d-glycero-d-galacto-non-2-enonic acid (Neu5Ac2en) and the related oxazoline, methyl 7,8,9-tri-O-acetyl-2,3,4,5-tetradeoxy-2,3-didehydro-2,3-trideoxy-4',5'-dihydro-2'-methyloxazolo[5,4-d]- d-glycero-d-talo-non-2-enonate is described.

Yes / α2,8-Linked polysialic acid (polySia) is an oncofoetal antigen with high abundance during embryonic development. It reappears in malignant tumours of neuroendocrine origin. Two polysialyltransferases (polySTs) ST8SiaII and IV are responsible for polySia biosynthesis. During development, both enzymes are essential to control polySia expression. However, in tumours ST8SiaII is the prevalent enzyme. Consequently, ST8SiaII is an attractive target for novel cancer therapeutics. A major challenge is the high structural and functional conservation of ST8SiaII and -IV. An assay system that enables differential testing of ST8SiaII and -IV would be of high value to search for specific inhibitors. Here we exploited the different modes of acceptor recognition and elongation for this purpose. With DMB-DP3 and DMB-DP12 (fluorescently labelled sialic acid oligomers with a degree of polymerisation of 3 and 12, respectively) we identified stark differences between the two enzymes. The new acceptors enabled the simple comparative testing of the polyST initial transfer rate for a series of CMP-activated and N-substituted sialic acid derivatives. Of these derivatives, the non-transferable CMP-Neu5Cyclo was found to be a new, competitive ST8SiaII inhibitor.

This research focused on the study of the amino sugar recycling and sialic acid degradation pathway as a possible entry point for N-acyl glucosamines for the production of sialic acid analogs. Meeting this objective would allow the development of a bacterial strain capable of producing non-natural nonulosonic acids that could be used in the development of medicines, vaccines or useful compounds for the study of interactions between pathogenic organisms and their host. The first step was to understand how N-acetyl-D-glucosamine-6-phosphate deacetylase reacts to different types of substrates in order to determine its tolerance to the size of acyl groups in acyl amino sugars. This was achieved by studying the enzymatic activity in an in vitro system. We determine that the enzyme has a preference for small and slightly bulky acyl groups. Then, an in silico docking modeling and an in vivo system experiment were carried out. These experiments allowed to confirm the previous results. The second project was carried out due to the uncertainty of whether the kinase involved in the catabolic pathway would be able to phosphorylate the substrates. By quantifying residual ATP, the high specificity of N-acetyl-D-glucosamine kinase could be verified. This result led us to think about the design of an organic synthesis strategy that would allow the phosphorylation of glucosamine in carbon 6. A simple synthetic route was designed based on the protection of the two most reactive moieties of the amino sugars and the reactivity of the hydroxy group on carbon 6. However, we had problems with the purification step of the final product due to its high polarity. The next stage of this investigation was to confirm the transformation of GlcNAc into ManNAc. For this, an NMR analysis was designed that would detect the presence of both sugars in the reaction system. The epimerization of ManNAc to GlcNAc was detected successfully. Notwithstanding, the reverse reaction could not be detected. Based on the results obtained in the previous stage, we realized that an error was made in the epimerization reaction since we placed the wrong kinase because we did not take into account its substrate specificity. Finally, we tried to produce sialic acid analogs in a fermentative system using different genetic variants of Escherichia coli. Two of the expected analogs, Neu5Pr and Neu5nBu, were obtained. In addition, NagA activity towards substrates with small acyl groups was confirmed.