Synthesis and characterization of active targeted gold nanoparticles and polymeric nanoparticles for photoacoustic and photothermal therapy

Abstract

Theranostics is a prominent medicine field involving nanoscience and nanotechnology in a single multifunctional formulation for efficient therapeutic effect and diagnosis. Moreover, the advances in nanomedicine have manifested the development of imaging-guided drug delivery, a promising methodology to improve the therapeutic efficiency of nanomedicine. This work aims to address the obstacle of the "false positive" PA signal, practically an "always on" situation, by developing some novel theranostic nanoplatforms through a smart design and good application of nanomaterials with specific properties. Chapter three presents the work on engineering novel gold nanoprobe with aggregation behaviour induced by pH sensing in the tumor microenvironment (TME) for PAI. The design details for targeted nanoprobe in chapter three are listed as follow. The gold nanoparticle surface was decorated with two thiol conjugate ligands for stabilization in circulation and normal tissues. The ligands respond to the tumor's acidic extracellular pH by aggregation. The pH-responsive active tumor-targeting c(RGDyk)- MHDA/LSC@AuNPs nanoprobe was easily fabricated and demonstrated an enhanced contrast effect to achieve in vitro and in vivo PAI. One of the advantages of PAI is its capability to differentiate different kinds of contrast agents according to their unique absorbance profiles simultaneously in a single mixture. Chapter four is devoted to developing the pH-sensitive near-infrared (NIR) Croc dyes-loaded copolymeric polyethylene glycol (PEG) - PLGA NPs for in vivo multiplexed PAI and pH-responsive photothermal therapy (PTT) in a triple-negative breast model. Based on the in vitro and in vivo data, the class of PLGA nanoparticles, such as iRGD-PLGA/Croc815 (PPC815) and Cys-PLGA/Croc770 (CPC770), could become a new generation of nanoplatforms capable of assisting multi-spectra unmixing of PAI. In the field of PAI-based diagnosis, PLGA NPs have various advantages, such as excellent biocompatibility in biological media and water solubility in the physiological environment with no noticeable morphology change over one week. The PLGA nanoparticle could also trigger real-time diagnosis by monitoring PTT responsiveness for pre-clinical translation. Chapter five discusses the development of an "all-in-one" system of iRGD-PLGA-encapsulated gold nanocages (AuNCs) / Epigallocatechin-3-gallate (EGCG) nanoprobe for syngeneic inhibition of hypoxia-inducible factor-alpha (HIF-1α) assisted multispectral optoacoustic tomography imaging (MSOT) guided PTT combined chemotherapy. The integration of EGCG and AuNCs into the targeted polymeric system can kill cancer cells by inhibiting the HIF-1α pathway with induction of apoptosis combined PTT and chemotherapy. These results demonstrated the feasibility of iRGD-PLGA/AuNCs/EGCG (PAuE) NPs as nano-theranostics agents in MSOT guided PTT/chemotherapy combination therapy for theranostics. Scope of work: Despite the establishment of contrast agents for theranostics, they are still limited by some drawbacks, such as low stability and complicated procedures in designing it to be "all-in-one", and low sensitivity to generate responsive signal for accurate diagnostics. As a result, these limitations paved the way for the development of responsive strategy, which are beneficial to the biomedical field by providing an alternative for stable, simple and sensitive image platform. Referring to the aforementioned problems, this project aims to develop a new generation of gold-based and PLGA nano platforms for theranostics using PAI and PTT. Those nano-platforms are able to provide high sensitivity, low cost and real-time imaging of the tumor site accurately. The inherent merits of gold nanoparticles are combined with the targeted ligand and pH responsive ligands as novel design to maximize the performance of the pH activated systems by increasing the stability and specificity of the PAI systems. Moreover, the developed polymeric nano-system is loaded with different small molecules, such as organic dyes or chemo-drug to evaluate its feasibility as future therapeutic agents for clinical applications. Chapter one introduces the fundamental working principles and knowledge of PAI, MSOT and PTT and introduces state-of-art nanotechnology regarding different contrast agents and PTAs. Also, comprehensive reviews on the status of multimodal bioimaging, bio-detection, PTT and drug delivery in the field of nanomaterial are given, and current challenges and future developments are discussed. Finally, the gold-based and PLGA polymeric nanoparticles project is briefly introduced. In chapter two, the synthetic route for gold nanoparticle-based contrast agents and PLGA based polymeric nanoparticles is introduced. The fundamentals and mechanisms of the one-step and ligand exchange in synthesis are presented. Moreover, the chapter depicts the principles of different characterization techniques and instruments. After that, chapter three presents the work on optimizing and evaluating the c(RGDyk)-MHDA/LSC@AuNPs nanoprobe system, which provides new insight into the targeted gold-based photoacoustic detection. The work aims to address two important concerns, particularly in addressing "false positive" PA signal long-term stability of gold nanoparticles. The designed AuNPs exhibit absorption at the UV region at around 680 nm via aggregation by NIR laser and generated PA signal in vivo and in vitro via a noninvasive pathway. The preparation of PLGA nano-system described in chapter four fosters the new PLGA core-shell detection scheme for both contrast agents and photothermal transducers. Croc dye's high pH sensitivity overcome the drawback of background signal from blood via a clear distinguishing signal for the TME for multispectral unmixing in one animals via different surface modification nanoparticles. Furthermore, this project would provide a new insights in vivo spectral unmixing techniques that can utilize the distinct maximum absorptions peaks to study biology on a molecular imaging level via two types of pH-activated probes, CPC770 and PPC815. The developed polymeric system in chapter four is improved and hence fosters the new targeted polymeric combined treatment scheme in chapter five, which argues that the PLGA-based NPs, acting as an "all-in-one" system, was used to obtain 3D MSOT images of the test mice. This work was the first to design a novel PLGA system co-loaded with AuNCs and EGCG acts as PAuE NPs. PAuE NPs archives to solve three important issues, specifically in addressing the complication in designing "all-in-one" system, difficulty in activated dual cancer cell death pathway and technical limitation in real-time monitoring NPs via 3D image. MSOT technology can also track the PAuE NPs in vivo to provide evidence for their pharmacokinetics upon administration. Also, the laser radiation induces a local temperature increase that contributes to the destruction of tumor tissues via mild PTT. This chapter intends to utilize the inhibition of HIF-1α pathway by EGCG and activate apoptosis via synergistic treatment effect. Finally, chapter six summarizes the thesis and provides a future direction of strategies integrating PTT or PTT‐based multimodal theranostics that could achieve synergistically enhanced therapeutic outcomes of both primary tumors and metastatic lesions, prevent cancer recurrence, and prolong the survival period via multispectral optoacoustic tomography.