Hybrid Enzyme-Loaded Silica Nanoparticles for Potential Therapeutic Applications

Enzymes are powerful biological catalysts that enable selective chemical reactions. Their ability to convert substrates to products at physiological pH and temperature have made them attractive as potential therapeutic agents. Since most enzymes are non-humanderived, their clinical use faces two main challenges: short functional half-life and immunogenicity. To address these limitations, there is a need for a versatile strategy that increases the functional half-life and safety profile of enzymes while preserving their efficacy. In this dissertation, I will report the design, syntheses, and applications of a Hybrid Enzyme-Loaded silica nanoParticle (HELP) platform used for therapeutic purposes. In this platform, enzymes are embedded inside nanoporous silica nanoparticles that prevent their interaction with large biomacromolecules but allow them to interact with small molecule substrates. This versatile encapsulation method has the potential to improve the stability of enzymes in circulation, eliminate immune responses, and prolong their functional half-life. First, I used catalase as a model enzyme because it has oxygen-generating properties that can be used for potential hypoxia relief and radiosensitization of tumors. Catalase was encapsulated in silica nanoparticles by modifying surface lysines to introduce a silica precursor, followed by silication in mild, aqueous phase conditions. These nanoparticles had high enzyme activity, optimal protection from proteases, and excellent stability over time. An in vivo pilot study demonstrated the ability of these particles to oxygenate tissues upon hydrogen peroxide infusion. Additionally, targeting moieties and radiotracers could be conjugated to the surface of these particles post-formulation. The HELP platform was also applied to asparaginase, a therapeutic enzyme used as first-line treatment to treat acute lymphoblastic leukemia (ALL), the most common childhood cancer. Unfortunately, it is bacterially derived and can elicit immune responses in pediatric patients. Asparaginase-loaded silica nanoparticles were formulated using a direct modification method and subsequent reverse emulsion conditions. These particles were monodisperse, had a mean diameter less than 50 nm, and demonstrated excellent protection from proteases and antibodies in vitro. Both immunogenicity and functional half-life of these particles are currently being investigated in vivo. Future studies will look at the therapeutic potential of these nanoparticles in an animal model of ALL.