Targeted nanoparticle platforms for selective photodynamic therapy of cancer
Numerous studies have demonstrated the substantial improvement in the photodynamic therapy (PDT) of cancer using multifunctional nanoparticles. The tumour-selectivity of nanoparticles carrying PDT agents can be achieved through conjugation to cancer-specific biomolecules that provide the particles with an improved tumour localisation and a marked enhancement in the therapeutic outcome. The primary aim of this thesis was to establish the therapeutic potential of lectin, a carbohydrate binding protein, targeted PDT treatment of cancer cells using zinc phthalocyanine (C11Pc)-PEG gold nanoparticles (ca. 4 nm). Using a number of colorimetric techniques the interactions of Concanavalin A and succinyl-Concanavalin A with MCF-7 and SK-BR-3 human breast cancer cells expressing α-mannose was explored. The targeted PDT treatment of the breast cancer cells was attempted using C11Pc-PEG gold nanoparticles conjugated to Concanavalin A. However, Concanavalin A conjugation provided no enhancement in photodynamic breast cancer cell kill, as compared to the non-conjugated C11Pc-PEG gold nanoparticles. The lectin jacalin was also conjugated to C11Pc-PEG gold nanoparticles to target HT-29 human colon cancer cells expressing the oncofoetal Thomsen-Friedenreich (T) antigen. Using laser scanning confocal microscopy a substantial improvement in the cellular internalisation was observed with the jacalin nanoparticle conjugates, as compared to the non-conjugated particles. Similarly, the phototoxicity of the HT-29 cells incubated with the jacalin conjugates was dramatically improved following irradiation at 633 nm, as compared to treatment using the non-conjugated particles. The PDT efficacy of the lectin-photosensitising nanoparticle conjugates was competitively inhibited by methyl-α-galactopyranoside and the T antigen-expressing glycoprotein, asialofetuin. The ApoTox-GloTM triplex assay confirmed that the jacalin targeted phototoxicity of the HT-29 cells was through necrosis, with no evidence of apoptotic induction. Overall, it was found that jacalin conjugated nanoparticles achieved a ca. 95-98% photodynamic cancer cell kill, whereas the non-conjugated particles were minimally phototoxic. The targeting efficiency of jacalin was compared to that of a monoclonal anti-HER-2 antibody. C11Pc-PEG gold nanoparticles functionalised with either the lectin or the antibody were used to target SK-BR-3 breast cancer cells and HT-29 colon cancer cells. Both nanoparticle conjugates exerted a similar level of targeted phototoxicity in both the breast cancer and colon cancer cell lines. The predominant mechanism of lectin or antibody targeted phototoxicity was found to be necrosis in both the SK-BR-3 cells and the HT-29 cells. Using confocal microscopy, both conjugates were shown to partially localise in the acidic organelles, suggesting that the conjugates were uptaken by the SK-BR-3 cells and the HT-29 cells through receptor mediated endocytosis. Finally, in an exploratory study, titanium dioxide nanoparticles coated in polyacrylic acid were investigated as potential agents for sonodynamic cancer therapy. The findings suggested that exposure of the particles to ultrasound (1 MHz, 0.5 W.cm-2) lead to a sonocatalytic enhancement in singlet oxygen production. Preliminary in vitro studies using HT-29 colon cancer cells show that preincubation with the nanoparticles had no effect on sonodynamic cell death. However, extracellular sonodynamic activation of the nanoparticles may prove more effective than intracellular activation at delivering the ultrasound-induced reactive oxygen species to the cancer cells.
Networked Digital Library of Theses and Dissertations