The Development and Evaluation of Next-Generation Metallic Nanomedicines for Oncology

Abstract

Nanoparticles (NPs) are ultrasmall objects with profound applications in research, industry, and medicine. Next-generation nanomedicines, such as gold, hafnium, iron, and copper nanoparticles, are particularly interesting due to their excellent physical, chemical, and quantum properties that can be exploited for cancer diagnosis and therapy. However, despite their demonstrated preclinical effectiveness, the potential of these inorganic nanomedicines, both in oncology and the broader medical field, is hampered by mechanistic uncertainty and a lack of detailed regulatory guidance. Together, these factors have resulted in many failed clinical trials and unexpected and sometimes severe side effects for approved formulations. The therapeutic efficacy and toxicity of nanomedicines are controlled by an extremely complex interplay of nanoparticle physicochemical properties and individual patient biology, where many confounding factors exist. This makes designing and evaluating nanomedicines a challenging task. To progress metal-based nanomedicines to the clinic and for them to be considered safe, even in the life-or-death circumstances of cancer, a deep understanding of nano-bio interactions is necessary across different stakeholders. This includes physicians, academia, industry, and government. By understanding and utilizing these in vivo behaviors, powerful nanomedicines and novel treatments can be applied to oncology.

This thesis begins with a summary of the fundamental concepts relating to nanotechnology and the origins, properties, and treatment of cancer. Chapter 2 expands this discussion for a comprehensive analysis of cancer nanomedicines and their structure-activity relationships (SARs) in the body, which are central to both treatment efficacy and safety. Fundamentally, SARs describe the interactions between NP properties and the biological systems that ultimately produce their effects. To assist in the communication of this information, identified SARs were integrated into a simple, adaptable, and guiding framework composed of a parameter space, a pathway model, and various evaluation metrics. By resolving the complexity of nanomedicine into three parts, representing the interactions of NPs with 1) whole organs, 2) individual cells, and 3) fundamental biochemical pathways, this framework provides a clear illustration of how to fine-tune nanomedicines via pathway analysis. This framework and SARs were then used to guide the design, application, and evaluation of next-generation nanomedicines containing gold and copper.

Gold nanoparticles (GNPs) have long been proposed as promising agents for cancer phototherapy and image-guided radiation therapy (IGRT) due to their strong absorption of near-infrared (NIR) light and X-rays. GNPs are also among the most studied NPs owing to their general biocompatibility and easy synthesis. Despite this, only one GNP has been approved for clinical use owing to long-term safety concerns. Among various SARs, those related to size are often the most critical parameters for both efficacy and safety. This stems from both the nanoparticles themselves and the size-restrictive nature of kidney, liver, and tumor filtration of blood. To optimize the use of GNPs for enhanced IGRT, drug delivery, and photothermal therapy (PTT), drug-loadable lipid NPs were utilized as a scaffold for GNP assembly, forming a versatile nanocomposite (Lipogold). Overall, this allows small NPs to function collectively as one larger nanoshell with plasmonic properties. Over time, this shell will degrade as the soft liposome core is stressed and deformed, resulting in renal-clearable NPs that can be cleared by the body following treatment. This thin shell of gold also optimizes the Auger process for RT and enables PTT, while the hollow core allows for encapsulation and delivery of drugs and molecular contrast agents. Thus, Lipogold nanocomposites demonstrate the advantages of both large and small NPs while adding multifunctionality. In this work (Chapter 3), medical radiation sources and cellular models were used to test their ability to sensitize cancer cells to megavoltage X-ray radiation therapy, provide contrast for computed tomographic (CT) imaging, deliver drugs, and engage in NIR-based PTT.

In addition to GNPs, plasmonic copper sulfide (Cu2-XS or just CuS) NPs are also emerging as increasingly popular nanomedicine candidates due to their photothermal properties, biodegradability, an ability to convert less-toxic H2O2 into more potent reactive oxygen species (ROS) for chemodynamic therapy (CDT). However, this approach in cancer therapy is fundamentally limited by several factors, principally the low concentration of H2O2 in the body. To overcome this issue, the properties of the tumor microenvironment (TME) were exploited for nanomedicine design, where CuS NPs were combined with the enzyme glucose oxidase (Gox) for a synergistic combination of starvation therapy, CDT, and PTT. Gox was used to convert glucose, which is upregulated in the TME, into H2O2 and acid, starving the cancerous cells and activating the Fenton-like reactivity of the CuS NPs. Deep-penetrating NIR could then be used for PTT and to enhance reaction kinetics specifically at the tumor site. The fundamental reaction mechanism was also investigated, highlighting the accelerative effect of chloride ions on the copper-Fenton reaction, which are present at high concentrations within skin and individual cells. In Chapter 4, the therapeutic efficacy and biocompatibility of the Gox@CuS nanocomposite were demonstrated using in vitro and in vivo melanoma models.

To further improve the safety profile of the Gox@CuS nanocomposite, the emerging technology of microneedle patches were explored as a transdermal drug delivery approach. Since conventional injections can lead to off-target uptake and toxicity, transdermal delivery may improve both efficacy and safety by maximizing local delivery and limiting blood exposure. This approach was extensively reviewed (Chapter 5) to determine the viability, design considerations, and fabrication methods of MNs containing light-responsive NPs such as Gox@CuS. Applications outside oncology were also reviewed to fully understand the advantages and limitations of this delivery system. Gox@CuS were then integrated into dissolvable polymeric microneedle (DPMN) patches and compared to hypodermic injection using another mouse melanoma model. In this study (Chapter 6), the microneedle patches were demonstrated to deliver a higher amount of Gox@CuS to the tumor site and reduce the risk of systemic toxicity. Further mechanistic insight into the catalytic behavior of CuS NPs was also collected, specifically identifying the effect of chloride ions on the generation of both hydroxyl radicals and singlet oxygen.

Overall, this thesis contributes to our overall understanding of cancer nanomedicine and demonstrates several novel next-generation treatment strategies using metal-containing NPs. The framework proposed in this work is an adaptable and potentially valuable resource for researchers and regulators to understand SARs. Additionally, the pathway modelling used by this framework can assist in the development and integration of machine learning models that will increasingly play a role in the regulatory and industrial development of nanomedicine formulations.