Novel payloads for immunotoxin-based treatment of neuroblastoma

Neuroblastoma is the most common form of extracranial solid tumour in childhood and the second biggest cause of cancer-related deaths in infants. Despite intensive, multi-modal treatment of advanced stage disease, prognosis is poor and relapse is common. This means that alternative forms of treatment are urgently needed. Targeted toxins are cytotoxic enzymes fused to a targeting ligand or antibody that bind to a receptor or antigen highly expressed on the cancer cell surface. Upon binding, the toxin is internalised and its cytotoxic activity leads to cell death. All currently used toxins function via the inhibition of protein synthesis, making them highly potent in both healthy and transformed cells. Low-level expression of target receptor, or non-specific uptake into healthy cells has caused dose-limiting side effects in all targeted toxins tested to date which has severely restricted their use in cancer treatment. In this thesis, novel protein delivery techniques were used to investigate the use of two enzymes, Burkholderia lethal factor 1 (BLF1) and botulinum neurotoxin type C (BoNT/C) protease, as possible alternative payloads for targeted toxin therapy in the treatment of neuroblastoma. BLF1 inhibits translation initiation by inactivation of eIF4A, and BoNT/C protease disrupts important membrane recycling events by cleavage of SNARE proteins. Both of these cytotoxic mechanisms show a degree of selectivity towards neuroblastoma cells. Future targeted toxins based on these enzymes may therefore have higher specificity towards neuroblastoma cells than conventional enzymes, leading to an increased therapeutic window and decreased side effects.