Augmenting the Effect of Sonodynamic Therapy for the Treatment of Prostate Cancer

Sonodynamic therapy (SDT) uses low-intensity ultrasound to activate sensitisers and generate reactive oxygen species (ROS), inducing targeted cytotoxicity. Nanoparticle-based delivery improves hydrophobic drug solubility and enhances tumour accumulation via the enhanced permeability and retention (EPR) effect. This thesis investigates hematoporphyrin-containing poly(L-glutamic acid-L-tyrosine) [Poly(Glu, Tyr)] nanoparticles (HPNPs), designed to exploit tumour-specific features such as hypoxia, acidity, and abundant cathepsin B. HPNPs are selectively degraded by cathepsin B, particularly under acidic tumour conditions, producing smaller fragments with exposed hematoporphyrin and reduced negative charge. These changes enhance intratumoural diffusion and cellular uptake, facilitating targeted release and efficient ultrasound-triggered ablation. Upon ultrasound exposure, HPNPs generated ROS, particularly singlet oxygen, at levels comparable to free hematoporphyrin, the primary mediator of SDT-induced cytotoxicity. In addition to its therapeutic potential, HPNPs were shown to suppress cell invasion, potentially through effects of Poly(Glu, Tyr) on the post-translational polyglutamylation of tubulins, a hypothesis that requires further investigation. In vitro SDT across multiple prostate cancer cell lines demonstrated enhanced cytotoxicity under hypoxic and acidic conditions. Analysis of neuroendocrine markers and oxidative stress modulators identified chromogranin A-derived fragments, particularly serpinin and its active pyroglutamated form (pGlu-serpinin), as potential contributors to SDT resistance. Although direct detection of pGlu-serpinin remains challenging, its hypothesised role in attenuating ROS-mediated cytotoxicity may explain increased SDT resistance under hypoxia. To overcome resistance phenomena, certain inhibitors targeting cellular defence mechanisms were tested. Glutathione depletion offered minimal benefit, whereas inhibition of the ABCG2 efflux pump (Ko143) and mitoKATP channels (5-hydroxydecanoate, 5-HD) significantly enhanced SDT efficacy, especially under hypoxia. In vivo PC3 xenograft studies confirmed these findings: 5-HD co-treatment markedly improved tumour suppression in larger, hypoxic tumours, suggesting mitoKATP activity as a hypoxia-dependent therapeutic target. The combination of SDT and 5-HD induced sustained tumour volume reduction, highlighting its promise as a priming strategy for further combination therapies such as chemotherapy.