The rapid increase of multi-drug resistant bacteria and associated deaths has stimulated research into the development of novel therapeutic options. Antimicrobial peptides (AMPs) display a high therapeutic potential in solving this problem. Research focuses on new ways to enhance the antibacterial activity of AMPs and this includes the amidation of the C-terminus. Once the structure of an AMP is altered it is altered it is necessary to revaluate the properties of this AMP compared to the unaltered peptide. In this study, a peptide fragment Os(3-12), based on a defensin from the tick Ornithodoros savignyi, was amidated at the C-terminus. The effect of C-terminal amidation on the structural, antibacterial, cytotoxic and antioxidant activities of Os(3-12)NH2 was investigated and compared to Os(3-12) as well as the parent peptide Os. Mode of action related to membrane permeabilization was evaluated. The effect of serum and on the antibacterial activity of Os(3-12)NH2 was also determined. Circular dichroism experiments indicated Os(3-12) and Os(3-12)NH2 to be unstructured in sodium dodecyl sulphate micelles and 50% trifluoroethanol, unlike Os which was predominantly α-helical. Although still less potent than Os, the determined minimum bactericidal concentration (MBC) for each peptide indicated that amidation increases the bactericidal activity of Os(3-12) by 16-fold against Escherichia coli and by 8-fold against both Pseudomonas aeruginosa and Bacillus subtilis. In comparison amidation enhanced the activity of the peptide towards Staphylococus aureus by only 2-fold. The kinetics of bactericidal activity revealed that Os(3-12)NH2 killed E. coli within 10 minutes and B subtilis within 60 minutes. SYTOX green was applied to evaluate the effects of the peptides on the membrane integrity of the bacterial cells. LL-37, a peptide known to disrupt microbial membranes, induced membrane permeabilization of both E. coli and S. aureus membranes. Both Os and Os(3-12)NH2 were found to also cause membrane permeabilization of these bacteria, albeit not to the same extent as LL-37, thus suggesting possible internal targets subsequent to membrane permeabilization. In the presence of 30% human serum and a physiological salt mixture comprising of 145 mM NaCl, 2.5 mM CaCl2 and 1 mM MgCl2 the bactericidal activity of Os(3-12)NH2 was lost. The amidated peptide was found to be non-toxic towards human erythrocytes and Caco-2 cells. Os(3-12)NH2 showed strong antioxidant activity and was found to be 15-fold more active than glutathione (GSH), a known antioxidant. In conclusion Os(3-12)NH2 has been identified as a multifunctional AMP that is nontoxic to mammalian cells. However the therapeutic potential of Os(3-12)NH2 may be restricted to topical applications due to the peptide’s inactivity under physiological conditions. Although Os(3-12)NH2 causes membrane permeabilization, indications are that there are additional intracellular targets that need to be identified. / Dissertation (MSc)--University of Pretoria, 2016. / Biochemistry / Unrestricted

Despite significant advances in cancer treatment, clinical response remains suboptimal and there is a continued requirement for improved chemotherapeutics. The attrition rate for new therapies is high, due principally to lack of in vivo efficacy and poor pharmacodynamics. Consequently better systems are required to determine in vivo preclinical efficiency and drug-target interactions. Engineering of cancer cells to express fluorescent or bioluminescent proteins, either endogenously or under the control of specific gene promoters, and their detection by noninvasive optical imaging has the potential to improve preclinical drug development. In this study, a panel of colorectal cancer cell lines were engineered to express fluorescent and luminescent proteins either constitutively or under control of gene-promoters for the DNA damage response gene p53 or the cell cycle regulator p21, both important pharmacodynamic sensors. These cell lines were characterised for their potential as in vivo models of primary and metastatic tumour therapy response, several showing significant potential. In addition to the development of these models, this study also addressed the pharmacokinetics of different luciferase substrates and identified optimal temporal and dose characteristics for each. Furthermore, a new application for bioluminescent imaging was developed and validated for use in preclinical evaluation of vascular disrupting agents, a new generation of cancer therapeutic. This study demonstrates that despite the dynamic and variable nature of fluorescent and bioluminescent imaging, reproducible results can be obtained if appropriate precautions are taken. The models developed herein will expedite cancer drug development whilst reducing and refining the use of animals in research.

Despite significant advances in cancer treatment, clinical response remains suboptimal and there is a continued requirement for improved chemotherapeutics. The attrition rate for new therapies is high, due principally to lack of in vivo efficacy and poor pharmacodynamics. Consequently better systems are required to determine in vivo preclinical efficiency and drug-target interactions. Engineering of cancer cells to express fluorescent or bioluminescent proteins, either endogenously or under the control of specific gene promoters, and their detection by noninvasive optical imaging has the potential to improve preclinical drug development. In this study, a panel of colorectal cancer cell lines were engineered to express fluorescent and luminescent proteins either constitutively or under control of gene-promoters for the DNA damage response gene p53 or the cell cycle regulator p21, both important pharmacodynamic sensors. These cell lines were characterised for their potential as in vivo models of primary and metastatic tumour therapy response, several showing significant potential. In addition to the development of these models, this study also addressed the pharmacokinetics of different luciferase substrates and identified optimal temporal and dose characteristics for each. Furthermore, a new application for bioluminescent imaging was developed and validated for use in preclinical evaluation of vascular disrupting agents, a new generation of cancer therapeutic. This study demonstrates that despite the dynamic and variable nature of fluorescent and bioluminescent imaging, reproducible results can be obtained if appropriate precautions are taken. The models developed herein will expedite cancer drug development whilst reducing and refining the use of animals in research.

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Orientador: Maria Palmira Daflon Gremião / Resumo: Glioblastomas (GBM) representam 77% dos tumores malignos do sistema nervoso central (SNC) e ainda hoje, apesar de todos os avanços na terapia, continua com prognóstico limitado. A existência de barreiras fisiológicas como a barreira hematoencefálica (BHE) representa o principal obstáculo que impede que concentrações adequadas do fármaco atinjam o local de ação. Por suas vantagens anatômicas, uma estratégia proposta para a administração de fármacos destinados ao SNC consiste no uso da via nasal. Além disso, o uso de terapias combinadas utilizando fármacos capazes de agir em diferentes alvos moleculares deve ser considerada para o tratamento de doenças complexas como GBM. O candidato a fármaco ácido alfa-ciano-4-hidroxicinâmico (CHC) e o anticorpo monoclonal cetuximab (CTX) já são explorados devido à capacidade de agir em diferentes alvos moleculares nas células tumorais e aplicados em conjunto, como uma nova abordagem combinada, podem melhorar os resultados terapêuticos. De forma complementar, a utilização de sistemas de liberação baseados em nanotecnologia trará inevitavelmente ganhos terapêuticos à combinação proposta, permitindo que atributos específicos sejam agregados ao sistema e possibilite não somente a administração nasal, como também a associação de diferentes fármacos em um único carreador. Assim, o presente estudo propõe o desenvolvimento de diferentes plataformas poliméricas baseadas em poli(ácido láctico-co-glicólico) (PLGA) e quitosana trimetilada (TMC) ou quito... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Glioblastomas (GBM) account for 77% of malignant tumors in the central nervous system (SNC), and today, despite all advances in therapy, remains with a limited prognosis. The existence of physiological barriers as the blood brain barrier (BBB) represents the main obstacle that limits appropriate concentrations of drugs designed to therapy. Due to their anatomical advantages, a strategy proposed for direct delivery to SNC involves the use of the nose-to-brain route. Besides, combination therapy that uses multiple drugs against different molecular targets should be considered for complex diseases such as GBM. Drugs like alpha-cyano-4-hydroxycinnamic acid (CHC) and the monoclonal antibody cetuximab (CTX) are already explored for their capacity to act against different hallmarks of cancer and applied together, as a novel combining approach, might improve therapeutic outcomes. Therefore, advances in nanotechnology-based delivery systems will inevitably bring therapeutic gains to the proposed combination since they enable acquisition of important characteristics desired and also the association of different drugs into a single carrier. Thus, the current study proposes the development of different polymeric platforms based on poly(lactic-co-glycolic acid) (PLGA) and trimethyl chitosan (TMC) /chitosan oligosaccharide (OCS) for CHC encapsulation. Both CHC-loaded developed systems (PLGA/TMC and PLGA/OCS) exhibited nanostructure organization of about 300 to 400 nm, containing chitosan o... (Complete abstract click electronic access below) / Doutor