Pancreatic cancer has the lowest survival rate among the 21 most common forms of cancer with only 5 % of patients surviving five years after their initial diagnosis. Several studies have investigated the potential of neo-adjuvant chemo- and / or radiotherapy to downstage tumours and increase the number of patients eligible for resection. Unfortunately, such treatments are often associated with significant off-target effects due to the non-specific nature of the chemotherapy regimen. Therefore, the development of targeted treatments that reduce side-effects related to systemic chemotherapy have enormous potential as neoadjuvant and palliative pancreatic cancer treatments by reducing tumour burden to either enable surgery or to provide symptom relief. Photodynamic therapy (PDT) is a clinically approved anti-cancer treatment that involves the activation of an otherwise inactive sensitisier drug with light, which in the presence of molecular oxygen, generates cytotoxic reactive oxygen species (ROS). In contrast, Sonodynamic therapy (SDT) is an emerging anti-cancer treatment that involves the activation of an otherwise inactive sensitiser drug using low-intensity ultrasound (US). The combination of sensitiser and ultrasound, in the presence of molecular oxygen, generates cytotoxic levels of ROS causing cell death via oxidative stress. As oxygen is a key requirement for the generation of ROS in PDT or SDT and given the fact that hypoxia is a characteristic of most solid cancerous tumours, treating hypoxic tumours using PDT or SDT can be a challenge. Therefore, an area of interest in this thesis was to investigate new methods for enhancing PDT and SDT efficacy in hypoxic tumors. Chapter 1 provided a background to current cancer treatments, PDT, SDT, improvement of tumor oxygenation and drug delivery systems while Chapter 2 detailed the materials and methods utilised in subsequent results chapters. The first results chapter, Chapter 3 investigated whether combined SDT / gemcitabine treatment, using intravenously delivered oxygen carrying lipid stabilised microbubbles (MBs) as delivery vehicle, can provide a significant reduction in the volume of Mia-PaCa-2 tumours compared to SDT or gemcitabine treatment alone and evaluate potential toxic effects in healthy non-tumour bearing mice. It was observed that the combination of US with the Rose Bengal, Gemcitabine and oxygen loaded Microbubbles (O2MBs-RB/GEM) enhanced cytotoxicity when compared to either IV treatment alone in a panel of four pancreatic cancer cell lines. In addition, the treatment of ectopic Mia Paca-2 tumours with the combined SDT/antimetabolite therapy resulted in a statistically significant decrease in tumour volume compared to untreated tumours. The effects of multiple treatments on tumour growth was also investigated and it was observed that a second treatment 48h following the initial treatment also provided a significant delay in tumour re-growth. This work is under revision in the Journal of Controlled Release. The second results chapter (Chapter 4) evaluated whether external magnetic and lowintensity ultrasound fields can enhance the efficacy of combined antimetabolite / sonodynamic therapy, delivered using magnetically responsive microbubbles, in an orthotopic murine model of pancreatic cancer. When decorated with the sensitiser Rose Bengal (RB) and the antimetabolite 5-FU and subjected to ultrasound treatment, magnetic responsive microbubbles (MagO2MB) conjugates induced a significant reduction in pancreatic cancer cell viability, of more than 50%. The combined application of external magnetic and ultrasound fields during IV delivery of the MagO2MB conjugates resulted in a 48.3% reduction in orthotopic pancreatic tumour volumes 9 days after treatment, while the application of ultrasound alone resulted in a reduction of only 27.9%. In addition, a significant increase in apoptosis was observed in tumours that were treated with the MagO2MB conjugates and exposed to both magnetic and ultrasonic fields when compared to the ultrasound treatment alone or untreated groups. This work has been published in the Journal of Controlled Release. The third and final results chapter (Chapter 5) investigated the ability of calcium peroxide nanoparticles to improve oxygenation in a hypoxic environment and enhance PDT-mediated treatment of BxPc-3 pancreatic cancer cells in vitro and an ectopic Mia Paca-2 xenograft murine model in vivo. A significant elevation in tumour pO2 was observed 10 mins following IV administration of a suspension of the particles. This increase in tumour pO2 was also shown to have a dramatic effect on PDT efficacy with significant reductions in tumour growth observed in mice treated with the particles before PDT when compared to PDT alone. This work has also been published in the Journal of Controlled Release. V Chapter 6 summarised the conclusions of all the results chapters and provides an outlook for future work.
- pH-sensitive polymer
- CaO2 nanoparticles