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Polysialylated NCAM (polySia-NCAM) is re-expressed in a number of tumours, including small cell lung carcinoma and neuroblastoma and is strongly associated with aggressive, invasive and metastatic tumours in the clinic. SiRNA knockdown of the polysialyltransferases (polySTs), the enzymes responsible for polysialylation of neural cell adhesion molecule (NCAM), has been shown to abolish cell migration. PolySia-NCAM is thus a highly attractive novel therapeutic target. A library of potential polyST inhibitors has been synthesised, using substrate-based design and computational chemistry. Compounds synthesised include N-acylmannosamine analogues, thio-linked CMP-sialic acid analogues, N-acyl modified sialic acids and compounds incorporating elements of both approaches. Novel methodology development in the synthesis of many of the compounds is described, notably a novel route to N-acyl sialosides. In addition, compounds identified from in silico screening were considered. Routes to synthesis and isolation of analogues of biologically active compounds are described. Using an enzyme assay, compounds were evaluated for their ability to reduce polySia synthesis through polyST inhibition. Effects of agents on polySia expression in cells, and the ability of compounds to reduce cell migration in vitro was studied using a wound healing ‘scratch assay’. The data from these experiments revealed a number of potent modulators of polySia assembly and their efficacy in reducing cell migration, as well as the limits of the biosynthetic pathway to accept unnatural sialic acid precursors. This is the first example of polyST inhibition modulating tumour cell migration, and points to the potential of the polysialyltransferases as a therapeutic target in metastatic tumours.

Polysialylated NCAM (polySia-NCAM) is re-expressed in a number of tumours, including small cell lung carcinoma and neuroblastoma and is strongly associated with aggressive, invasive and metastatic tumours in the clinic. SiRNA knockdown of the polysialyltransferases (polySTs), the enzymes responsible for polysialylation of neural cell adhesion molecule (NCAM), has been shown to abolish cell migration. PolySia-NCAM is thus a highly attractive novel therapeutic target. A library of potential polyST inhibitors has been synthesised, using substrate-based design and computational chemistry. Compounds synthesised include N-acylmannosamine analogues, thio-linked CMP-sialic acid analogues, N-acyl modified sialic acids and compounds incorporating elements of both approaches. Novel methodology development in the synthesis of many of the compounds is described, notably a novel route to N-acyl sialosides. In addition, compounds identified from in silico screening were considered. Routes to synthesis and isolation of analogues of biologically active compounds are described. Using an enzyme assay, compounds were evaluated for their ability to reduce polySia synthesis through polyST inhibition. Effects of agents on polySia expression in cells, and the ability of compounds to reduce cell migration in vitro was studied using a wound healing ‘scratch assay’. The data from these experiments revealed a number of potent modulators of polySia assembly and their efficacy in reducing cell migration, as well as the limits of the biosynthetic pathway to accept unnatural sialic acid precursors. This is the first example of polyST inhibition modulating tumour cell migration, and points to the potential of the polysialyltransferases as a therapeutic target in metastatic tumours. / EPSRC and BACR / The full text will be available at the end of the extended embargo: 5th March 2027

Neuroblastoma is a highly metastatic and invasive tumour with poor prognosis. Despite recent advances in the treatment of neuroblastoma, mortality is still high due to uncontrolled metastatic disease, and novel therapeutic approaches for the treatment of neuroblastoma are therefore desperately needed. A potential novel approach for therapy of neuroblastoma relates to the polysialic acid decoration of the neural cell adhesion molecule (PSANCAM). PSA-NCAM is selectively re-expressed in a number of tumours including neuroblastoma, where it is thought to modulate tumour dissemination. Expression is strongly associated with poor clinical prognosis and an aggressive tumour phenotype. Inhibition of the enzymes responsible for synthesis of PSA, the polysialyltransferases (polySTs) presents a novel and selective therapeutic opportunity. The aims of the studies described in this thesis are to evaluate PSANCAM expression and function in neuroblastoma, and to develop and utilise cell-based models to pharmacologically investigate novel polyST inhibitors. PSA-NCAM was seen to be highly expressed in neuroblastoma clinical specimens and associated with phenotypes of tumour aggressiveness. A screening panel consisting of cell lines with a range of PSA-NCAM expression types was established and utilised to develop assays for pharmacologically assessing novel polyST inhibitors. Using cytidine monophosphate (CMP), a naturally-occurring inhibitor of polySTs, the robustness of the assays was confirmed before progression to evaluate novel molecules. From 16 compounds identified in an in vitro screen of polyST inhibition, three promising polyST inhibitors were identified. These promising polyST inhibitors modulated PSA-NCAM expression on the tumour cell surface and led to a significant reduction in cell migration. Therefore the work presented in this thesis suggests that targeting polySTs is a promising novel therapeutic strategy for neuroblastoma and further research in this area is warranted. / Mu'tah University and Jordan Armed Forces, Hashemite Kingdom of Jordan. / The full text will be available at the end of the extended embargo period: 5th March 2027