Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 95-104). Also available in print.

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 95-104). Also available online.

published_or_final_version / Chemistry / Master / Master of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

In most neoplasms malignant change occurs in a single cell which then proliferates. My purpose was to explore methods to study the cell that gives rise to hemopoietic cancer and to investigate the abnormalities at a molecular level. Cytogenetic analysis of cells from individual hemopoietic colonies revealed that monosomy 7 syndrome, a hematologic disorder of childhood, arises in a primitive cell capable of differentiating down both myeloid and erythroid pathways. Long-term bone marrow cultures (LTC) from patients with chronic myelogenous leukemia (CML) favor the growth of Philadelphia chromosome (Ph) negative progenitors which, although cytogenetically normal, could have been part of the malignant clone at a stage prior to the development of the Ph. LTC's were initiated with cells from 2 women with CML who were heterozygous for 2 electrophoretically distinct glucose-6-phosphate dehydrogenase (G6PD) enzyme variants. In one patient, 2/11 progenitors were Ph-negative after 4 to 6 weeks in LTC and 4/30 were nonclonal by G6PD enzyme analysis, i.e. the colonies expressed the enzyme not found in the malignant clone. In this case, karyotypically normal cells were truly normal. Next, gene transfer to human hemopoietic cells was demonstrated using recombinant retrovirus carrying the selectable marker gene, neor. With the K562 human leukemic cell line as targets up to 60% of infected cells became G418 resistant (G418r). Cloned populations of G418r cells showed unique patterns of retroviral integration in K562 DNA. When the target cells were progenitors from normal marrow, CML blood or fetal liver, the highest frequencies of G418r granulocyte-macrophage or large erythroid colonies was 16% and 5% respectively. Experiments infecting bone marrow cells in LTC with neor virus produced up to 2% G418r colonies after as long as 3 weeks in culture. Using v-src virus to infect LTC failed to perturb hemopoiesis, although infection of bone marrow-derived cells in these cultures was documented. In summary: 1. Unique populations of hemopoietic progenitors can be identified in culture using several genetic markers including chromosomes, G6PD analysis or gene transfer. 2. The feasibility of retroviral-mediated gene transfer for use on human hemopoietic cells has been demonstrated. / Medicine, Faculty of / Pathology and Laboratory Medicine, Department of / Graduate

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In the biopharmaceutical industry, essentially, there are three components that play the main role in producing biopharmaceutical products, the host cell, the expression vector and the bioreactor and/or production environment. To produce the highly valued and desired products, the choice of a suitable host is one of the most important aspects. The host required is not only required to produce the desired product, but also needs to demonstrate robustness in a bioreactor system. Constantly facing challenges in a bioreactor, cells often undergo apoptosis, a well-known limiting factor in biopharmaceutical production, which ultimately leads to low yield of valuable protein(s). We have genetically engineered a CHO-K1 cell line to constitutively express human insulin-like growth factor-1 (IGF-1) and murine polyoma large T-antigen (PyLT-Ag) to generate Super-CHO and CHO-T respectively, two cell lines that can potentially serve different niches in the biopharmaceutical industry. In the first part of the project, we hypothesised that suspension-adapted Super-CHO and CHO-T cells are both resilient cell lines relative to the suspension-adapted CHO-K1 (designated as CHO-XL-99) when facing nutrient depletion, one of the most common problems in a bioreactor. Furthermore, in the second part of this project, the suspension-adapted CHO cell lines were also tested against a cytotoxic heavy metal, cadmium. Without the protection of the metal-resistance element, metallothionein, both Super-CHO and CHO-T cells were also challenged with cadmium to demonstrate their robustness over the parental cell line, CHO-XL-99. In the subsequent study, this project also focussed on the transfection efficiency of each parental and engineered CHO cell lines. Different strategies have been employed in the past in an attempt to improve productivity in the biopharmaceutical industry, from alterations in vector construction, improved culture condition, down to enhanced product recovery. However, the transfer and expression of the gene-of-interest (GOI) has still proven to be the limiting factor for achieving increased specific productivity. In an effort to improve transfection efficiency, strategies including cell cycle synchronisation and various transfection methods to deliver the GOI into the cells have been employed. Thus, the third part of this project has used synchronising agents in conjunction with commercially available lipid- and polymer-based reagents as delivery vehicle for the model protein, EGFP. The combination of cell synchronisation and transfection vehicle on transfection efficiency is studied here, in addition to their individual or collective effect on cell growth, apoptosis and viability. In summary, this project demonstrates the incidence of apoptosis in the cell culture induced by nutrient depletion and heavy metal, and that the use of transfection reagents solely, or in combination with synchronising agents also correlates with the increase of apoptotic indices in the cell culture. The use of the robust cell lines for transfection is an important aspect, and the balance between cell viability and the effort for augmenting transfection efficiency has to be met in order to achieve the maximum biopharmaceutical yields.

The interest in using gene therapy to target a variety of both inherited and acquired diseases has intensified over the last two decades. Because free DNA is easily degraded by serum nucleases in the bloodstream, the need for developing carrier systems that can compact and protect the DNA was quickly realized. Viral vector systems were some of the earliest carriers used, primarily because of the ease with which such systems can infect host cells. However, difficulties experienced when using viral vectors, including immunogenicity and the potential for genetic recombinations, forced researchers to design alternative delivery strategies. Non-viral vectors offer one alternative to overcome this dilemma. In addition to avoiding the biological problems experienced using viral carriers, non-viral vectors also offer the potential for large-scale production. Dendrimers are one non-viral carrier that has shown appreciable ability to deliver DNA into cells, a process called transfection. In the past, triazine dendrimers have shown biocompatibility, and the ability to synthesize these structures to contain cationic charges on the surface makes these structures potentially suitable for transfection studies. In this study, a small library of triazine dendrimers was synthesized in an attempt to understand how variations to both the periphery and core of triazine dendrimers affect the transfection efficiency of these dendriplexes. In the first subset of structures, a common core was used and various peripheral groups were appended to the dendrimer surface. The physicochemical and biological data, obtained in collaboration with Thomas Kissel at Philipps-Universitat Marburg, showed that the surface groups have a notable affect on transfection efficiency. Dendrimers with a higher amine number and neutral surface groups show high DNA binding affinity and higher transfection efficiency. In the second subset of dendrimers, variations to the core showed that transfection efficiency is improved both by increasing generation number and dendrimer flexibility. With this data in hand, triazine dendrimers with both higher generation number and higher flexibility have been synthesized. Two different triazine linker groups, trimethylene-dipiperidine and polyglycoldiamine, have been used. These structures will be evaluated to determine if increasing both flexibility and generation number together can further improve transfection efficiency.