C03 • Boronic Acid Ester Chemistry for pHResponse Polymer Mediated Oligonucleotide Delivery
Oligonucleotide therapeutics represent a powerful strategy to treat diseases that are challenging or resistant to conventional medications, by intervening directly at the genetic level. Living organisms follow the central dogma, in which genetic information flows from DNA to messenger RNA (mRNA), and finally to proteins, facilitating biological processes. Consequently, nucleic acids at all domains of life represent potential therapeutic targets. Prominent examples include antisense oligonucleotides (ASOs), designed to suppress specific genes, and mRNA vaccines, exemplified by recent successes against COVID-19. Conversely, reflecting their vital roles within biological systems, organisms have evolved multiple robust defense systems against exogenous oligonucleotides, such as enzymatic degradation by nucleases, electrostatic barriers posed by negatively charged cellular membranes, and innate immune activation. Effective delivery, therefore, requires specialized nanocarriers capable of shielding nucleic acids from degradation and promoting efficient cellular uptake. Although cationic polymers and lipids are successfully employed in existing delivery systems, these methods frequently induce undesirable cytotoxicity and immune responses due to nonspecific interactions with negatively charged proteins and cellular membranes, limiting their otherwise broad therapeutic window.
To overcome these limitations, we set the long-term goal of this project for developing innovative nanocarriers utilizing the unique properties of the boronic acid ester chemistry. Boronic acids remarkably form reversible covalent ester bonds with diol compounds under mild conditions, exhibiting excellent pH responsiveness. This distinctive property enables targeted release of nucleic acid payloads specifically within the mildly acidic endosomal environment, following cellular internalization. Furthermore, boronic acid-based carriers are expected to exhibit minimal or no toxicity and immunogenicity, facilitating high payload capacities.
To realize this concept, we integrate expertise from polymer chemistry (Prof. Dr. Lutz Nuhn) and nucleic acid chemistry (Dr. Takumi Okuda). The Nuhn group will focus on synthesizing biodegradable polymer nanogel carriers containing boronic acid or diol groups, optimizing nanoparticle stability, oligonucleotide loading and responsiveness. Concurrently, the Okuda group will develop efficient methodologies for synthesizing oligonucleotides bearing multiple boronic acid or diol modifications. Once the synthetic methodologies are established, pH-driven oligonucleotide loading to the nanoparticles will be evaluated, optimizing nucleic acid loading density, stability, and targeted release. Additionally, as an advanced aim, enzymatic synthesis of modified oligonucleotides will be explored to extend this chemistry to longer nucleic acids of therapeutic impact, such as mRNA. Concurrent polymer optimization efforts will ensure the formation of poly(boronic acid ester) complex (PBAE) nanoparticles capable of efficiently encapsulating and delivering these larger nucleic acid payloads, ultimately achieving effective intracellular translation. This collaborative project is driven by the unique dynamic feature of the boron atom and sets a robust foundation for future therapeutic applications, potentially progressing toward validation in disease-specific animal models, representing a significant advancement in the field of nucleic acid delivery platforms.
