The most common gene transfer vehicle used in gene therapy protocols are mammalian virus vectors. Specifically, retroviruses are one of the most common viral vectors used since they are able to permanently integrate their transgene into the host cell genome, providing, in principal, to a long-term cure. The potential applications of gene therapies are vast, ranging from monogenic disorders such as cystic fibrosis to complex gene disorders such as cancer. However, the application of such therapies in clinical settings has been limited partially because of inefficient gene delivery of the therapeutic gene to diseased cells. Furthermore, safety concerns of accidently altering the genetic expression in healthy bystander cells or nearby tissue has increased the interest in creating targeted viral vectors which infect only the diseased cells without infecting others. Thus, the success of gene therapy will depend on identifying and understanding the parameters critical for virus entry into cells, including factors that facilitate virus absorption onto the cell surface, virus binding, and fusion. The objective of this thesis was to understand the role of lipids in binding and infection, and to investigate the use of lipid-based conjugates to alter the surface of virus particles.

Thesis (Ph.D)--Biomedical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Joseph Le Doux; Committee Member: Anthanassios Sambanis; Committee Member: David Archer; Committee Member: Michelle LaPlaca; Committee Member: Steve Stice; Committee Member: Todd McDevitt. Part of the SMARTech Electronic Thesis and Dissertation Collection.

The transfer and expression of genes in cells is an important technique for basic research and gene therapy of human disease. A model for gene therapy has been investigated making use of a transfection complex consisting of three components, the DNA i.e. the gene to be transferred and expressed; a gene delivery vehicle viz. a cationic liposome and a cell specific targeting ligand, asialoorosomucoid (AOM). Cationic liposomes are positively charged liposomes that have been prepared from synthetic lipids and have been shown to complex or bind to DNA via electrostatic attraction. They have shown potential as an efficient non-viral gene delivery vehicle in human gene therapy. In this investigation, a novel cationic liposome consisting of 3B [N -(N',N'-dimethylaminopropane)carbamoyl] cholesterol (Chol-T), dioleoylphosphatidylethanolamine (DOPE) and biotinylcholesteryl formylhydrazide was prepared and assessed as a mediator of DNA delivery in a mammalian cell culture system viz. the HepG2 cell line. The cationic liposome was synthesised and characterised by electron microscopy. Foreign DNA may be specifically delivered to target cells by a carrier system which makes use of the recognition of the asialoglycoprotein AOM by cognate receptors on the HepG2 cell plasma membrane. The positively charged AOM was biotinylated and due to this biotinylation, binds streptavidin which contains specific binding sites for biotin. The cationic liposome itself contains biotin residues in its bi-Iayer which in turn binds streptavidin resulting in a ternary complex. Further, due to the DNA binding capability of the cationic liposome, a transfection complex is produced consisting of the three components. The experiments were based on the following concepts: (i) Hepatocytes possess a unique receptor that binds to and internalises galactose-terminal asialoglycoproteins by receptor mediated endocytosis. (ii) Due to electrostatic attraction, DNA binds to cationic liposomes forming soluble complexes. (iii) Through the biotin-streptavidin reaction, the biotinylated AOM is attached to the cationic liposome containing biotin forming complexes enabling targeted delivery of the DNA. (iv) DNA containing the pGL3 gene for the luciferase enzyme was used and following transfection experiments, the luciferase assay was performed to ensure successful transfection. The complexes were tested on the hepatocellular carcinoma cell line, HepG2, which possess the asialoglycoprotein receptor. Transfection studies were conducted using a transient expression system, the luciferase assay system. Some degree of success in the transfection of HepG2 cells was observed. Results obtained in this study suggest that transfection using our targeted transfection complex consisting of cationic liposomes and cell specific targeting ligands does in fact transfect cells by receptor mediation. / Thesis (M.Med.Sc.)-University of KwaZulu-Natal, 2006.

Hepatocyte-directed liposomal gene delivery systems have received much attention in view of the present lack of suitable treatment alternatives for several liver-associated disorders. While targeting of liposomes to the asialoglycoprotein receptor (ASGP-R), nearly-exclusive to hepatocytes, is a well-documented means of achieving cell-specificity, several intra- and extracellular barriers reduce the efficacy of liposomal gene transfer. These include the aggregation and opsonisation of lipoplexes by serum components; and endo/lysosomal degradation of internalised DNA. This study has attempted to address the individual concerns by modifying hepatotropic liposomes with a steric stabilising, polyethylene glycol (PEG) shroud, and an endosomal escape-inducing proton sponge moiety. Novel galactosylated (SH02) and imidazolylated (SH04) cholesterol derivatives were successfully synthesised with the aim of conferring the respective functions of ASGP-R-specificity and proton sponge capability upon cationic liposome formulations. The individual derivatives afforded stable, unilamellar vesicles (< 200 nm, Z-average diameter) when incorporated at 10 % on a molar basis with the cytofectin, 3β[N-(N',N'-dimethylaminopropane)-carbamoyl] cholesterol (Chol-T) and co-lipid, dioleoylphosphatidylethanolamine (DOPE). Modification of these formulations with 1,2-distearoyl-sn-glycero-phosphoethanolamine-N-[carboxy(polyethylene glycol)2000] (DSPEPEG₂₀₀₀), at 5 mol %, gave smaller vesicles (< 110 nm, Z-average diameter) and moderately reduced the instability associated with the combination of both SH02 and SH04 in a single formulation. Individual preparations formed electrostatic complexes with pCMV-luc plasmid DNA, as demonstrated by gel retardation assays and electron microscopy. Furthermore, the liposomes afforded some protection to the DNA cargo against serum nuclease attack during a 4 hour-long exposure to foetal calf serum at 37 °C. However, the DNA-binding and protecting capabilities of the liposomes were reduced upon addition of the PEG coating. Growth inhibition assays showed that lipoplexes derived from individual formulations were well tolerated by human hepatocyte-derived, HepG2, and embryonic kidney, HEK293, cell lines. Expression of the luciferase transgene mediated by non-pegylated formulations containing SH02 was significantly higher in hepatocytes than in the ASGP-R-negative, kidney cells. Furthermore, receptor-mediated internalisation of non-pegylated, galactosylated carriers by hepatocytes was demonstrated by the gross inhibition of transfection in the presence of excess asialofetuin, a natural ligand to the ASGP-R. Liposome acid titration profiles highlighted the endosomal pH-buffering capacity afforded by SH04. However, the imidazolylated lipid enhanced the transfection activity of the non-sterically stabilised Chol-T/DOPE system, but not that of its targeted counterpart, and only with respect to HEK293 cells. Finally, pegylation reduced the transfection capability of liposomes by at least three orders of magnitude in both cell lines. The results suggest that further optimisation of liposome composition is necessary in order to achieve a liposomal system that simultaneously embodies hepatocyte-targeting, proton sponge and long-circulating properties. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2012.

Allium white rot (AWR) is a soilborne disease that seriously damages commercial cultivation of onion (Allium cepa) and garlic (Allium sativum) crops. The disease has been found everywhere onions are cultivated and at present no system of control has been found that fully prevents the occurrence of the disease. The fungus responsible for the disease, Sclerotium cepivorum, uses oxalic acid to kill Allium bulb and root tissue in growing onion and garlic plants. Research suggests recombinant oxalate oxidase and oxalate decarboxylase enzymes may be able to degrade this acid and confer resistance against pathogens that rely on it, such as Sm. cepivorum or Sclerotinia sclerotiorum. To test the efficacy of these enzymes against white rot pathogens, three transgenes for wheat oxalate oxidase, barley oxalate oxidase and Flammulina oxalate decarboxylase were transformed into onions and garlic by Agrobacterium-mediated transformation. Allium species are highly recalcitrant to transformation, so these three transgenes were also transformed into tobacco to provide fast-recovering, easy to test transformants to assess the efficacy of the transgenes. Transformed garlic and tobacco lines were analysed to assess the integration and expression of the transgenes, then challenged with Sm. cepivorum or Sa. sclerotiorum, respectively, to assess the bioactivity of recombinant wheat oxalate oxidase, barley oxalate oxidase, and Flammulina oxalate decarboxylase against oxalic acid-dependent pathogens. Results show that one line of tobacco expressing the Flammulina oxalate decarboxylase enzyme was found to be consistently resistant to Sclerotinia sclerotiorum. Garlic lines transformed with this transgene failed to display stable transgene expression or disease resistance, possibly due to silencing of the transgene in recovered transformant tissue.

Allium white rot (AWR) is a soilborne disease that seriously damages commercial cultivation of onion (Allium cepa) and garlic (Allium sativum) crops. The disease has been found everywhere onions are cultivated and at present no system of control has been found that fully prevents the occurrence of the disease. The fungus responsible for the disease, Sclerotium cepivorum, uses oxalic acid to kill Allium bulb and root tissue in growing onion and garlic plants. Research suggests recombinant oxalate oxidase and oxalate decarboxylase enzymes may be able to degrade this acid and confer resistance against pathogens that rely on it, such as Sm. cepivorum or Sclerotinia sclerotiorum. To test the efficacy of these enzymes against white rot pathogens, three transgenes for wheat oxalate oxidase, barley oxalate oxidase and Flammulina oxalate decarboxylase were transformed into onions and garlic by Agrobacterium-mediated transformation. Allium species are highly recalcitrant to transformation, so these three transgenes were also transformed into tobacco to provide fast-recovering, easy to test transformants to assess the efficacy of the transgenes. Transformed garlic and tobacco lines were analysed to assess the integration and expression of the transgenes, then challenged with Sm. cepivorum or Sa. sclerotiorum, respectively, to assess the bioactivity of recombinant wheat oxalate oxidase, barley oxalate oxidase, and Flammulina oxalate decarboxylase against oxalic acid-dependent pathogens. Results show that one line of tobacco expressing the Flammulina oxalate decarboxylase enzyme was found to be consistently resistant to Sclerotinia sclerotiorum. Garlic lines transformed with this transgene failed to display stable transgene expression or disease resistance, possibly due to silencing of the transgene in recovered transformant tissue.

Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniversitet, 2004. / Härtill 4 uppsatser.

Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniversitet, 2004. / Härtill 5 uppsatser.

Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniv. / Härtill 4 uppsatser.

Thesis (Ph. D.)--Illinois State University, 1995. / Title from title page screen, viewed May 2, 2006. Dissertation Committee: Anthony J. Otsuka (chair), Herman E. Brockman, David W. Borst, H. Tak Cheung, Radheshyam K. Jayaswal. Includes bibliographical references (leaves 170-187) and abstract. Also available in print.