Abstract
Phase-change Nanodroplets are an emerging sonoresponsive material that has attracted substantial attention in biomedical applications for both tumour imaging and therapeutic purposes due to their unique response to ultrasound. As ultrasound is applied at different frequencies and powers, nanodroplets have been shown to cavitate by the process of acoustic droplet vaporisation (ADV), causing the development of mechanical forces which promote sonoporation through cellular membranes. This allows drugs to be delivered efficiently into deeper tissues where tumours are located. Nanodroplets are smaller compared to microbubbles and may distribute better within tissues, e.g. in tumours. They are composed of a stabilising shell and a perfluorocarbon core. Nanodroplets can vaporise into echogenic microbubbles, forming cavitation nuclei when exposed to ultrasound. However, methods to quantify the perfluorocarbon core in nanodroplets are lacking. In this project, several characterisation methodology were developed to assess nanodroplets physiochemical properties, and the potential applications of NDs in multimodal imaging and immunotherapy were investigated.First, we fabricated nanodroplets with lipid shells and perfluorocarbons (perfluoropentane and/or perfluorohexane). To assess the amount of perfluorocarbon in the core, we used two methods, 19F NMR and FTIR. To assess the cavitation after vaporisation, we used an ultrasound transducer (1.1 MHz) and a high-speed camera. The 19F NMR based method showed that the fluorine signal correlated accurately with perfluorocarbon concentration. Using this correlation, we were able to quantify the perfluorocarbon core of nanodroplets. This method was used to assess the content of the perfluorocarbon of the nanodroplets in solutions over time. It was found that perfluoropentane nanodroplets lost their content faster and at a higher ratio compared to perfluorohexane nanodroplets. The high-speed imaging indicates that the nanodroplets generate cavitation comparable to that from commercial microbubble contrast agents. Nanodroplet characterisation should include perfluorocarbon concentration assessment as critical information for their further development.
Then, we modified nanodroplets with variable chemistry components, including polymer shell and magnetic resonance (MR) contrast lipid. The polymer coating can enhance the storage stability of nanodroplets and enable the loading of hydrophilic drugs. Nanodroplets incorporated with commercial MRI contrast lipid showed enhanced contrast in MRI phantom, which indicates they have potential to be used as MRI contrast agents and multimodal imaging agents.
Last, we developed cyclic GMP-AMP (cGAMP) loaded nanodroplets, which we hypothesised could be used to remodel the tumour microenvironment (TME). The stimulator of interferon genes (STING) signalling pathway can elicit an antitumour immune response and increase the response rate to immune checkpoint inhibitors in certain cancers. cGAMP is a natural STING agonist, but it has drawbacks like low bioavailability in target tissues, unwanted toxicities, susceptibility to enzyme degradation and narrow therapeutic windows. To overcome these challenges, we hypothesise that cavitation agents, which are nanodroplets in this study, combined with focused ultrasound (FUS) can be used. cGAMP loaded nanodroplets were developed with satisfactory encapsulate efficiency (90.87±4.57%), size (179.73±6.97 nm) and storage stability. After intratumoural administration of cGAMP nanodroplets, FUS was applied to the tumour tissue to activate the nanodroplets, which will efficiently deliver cGAMP intracellularly via sonoporation. Administration of a very small amount of cGAMP (0.1 mg/kg) has shown to significantly increase the percentages of plasmacytoid dendritic cells from 2.32±0.64% to 6.26±1.90% and inflammatory monocytes from 7.16±2.36% to 12.73±4.77% in 4T1 triple negative breast tumour, which indicates that this treatment strategy has remodelled the tumour microenvironment of ‘cold’ tumour in a positive way and has great potential to be used for cancer immunotherapy in the future.
| Date of Award | 1 Aug 2024 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Maya Thanou (Supervisor) & James Mason (Supervisor) |