UC San Diego

With increasing discoveries in genetic and biological pathways with respect to disease treatment, the potential for gene therapy is growing exponentially. In parallel, gene modulating tools have also expanded; catalyzed by the discovery of the RNA interference and zinc finger proteins in the 1990s, the 21st century has seen a variety of mechanisms for editing genetic expression (e.g. double-stranded oligonucleotides, zinc finger nucleases (ZFNs), transcription activator-like effector nuclease (TALENS), clustered regularly interspaced short palindromic repeats (CRISPR/Cas), etc.). However, a primary roadblock in enabling these gene editing tools for clinical translation is the biological clearance and degradation mechanisms that prevent the tools from reaching the target cells. The fusogenic porous silicon nanoparticles (FNPs) present an effective solution to this delivery challenge.

Chapter one provides introductory overview of gene therapy, their limitations, as well as the current state-of-the-art technologies with the aim of delineating materials design criteria of RNAi therapeutics. Furthermore, a brief analysis and discussion on trends of publications and clinical translations of RNAi therapy formulations are provided.

Chapter two details the synthesis protocol of fusogenic porous silicon nanoparticles. As the FNPs comprise of multi-layer structure (ie. payload-loaded pSiNPs, calcium silicate sealing, lipid bilayer encapsulation, targeting peptide decoration), the protocol requires delicate and precise handling for formation of stable nanoparticles. Examples of successful versus unsuccessful syntheses are presented, and critical steps to positive outcome are highlighted. The potential for variations and alternative optimizations to the protocol are discussed.

Chapter three delves into the material properties that enable FNP function, and the biological pathways that FNPs depend on for its unique cellular uptake and processing. The intracellular fate and metabolism of individual components of the FNP system (e.g. oligonucleotide payload, pSiNP core, and lipid bilayer shell) are also presented. The fundamental information gained from studying the material interaction at a single-cell level is used to inform the following chapters that deal with application of FNPs in disease models.

Chapters 4-6 demonstrate the FNPs as a platform technology that can be developed into a wide range of therapeutic formulations. By simple exchange of targeting peptides and the siRNA payload, the FNPs demonstrate successful therapeutic outcomes in mouse models of cancer (Chapter 4) and bacterial infections (Chapters 5 and 6).