Background

Gene therapies and nucleic acid-based immunotherapies have garnered attention as next-generation treatments for intractable diseases due to their ability to directly control target genes or stimulate the immune system. However, traditional linear nucleic acid molecules face several physicochemical barriers upon administration. Due to their negatively charged phosphate backbone, they struggle to penetrate cell membranes independently and are vulnerable to rapid degradation when exposed to nucleases present in blood or tissues.

To overcome these limitations, transfection aids such as cationic lipids or polymer carriers have been used, but these complexes often cause side effects like toxicity or accumulation in unintended tissues. There was a desperate need for technology that could achieve high penetration efficiency without cell damage while stably delivering drugs to lymph nodes where immune cells are concentrated. This led researchers to focus on approaches that fundamentally improve biological stability and intracellular uptake efficiency by modifying the physical arrangement of the nucleic acid structure itself, rather than relying on external carriers.

Key Findings

Spherical Nucleic Acids (SNAs) are a new concept in nano-medicine, designed with oligonucleotides densely packed in a radial pattern around a central core or as core-free nanostructures. Compared to conventional linear nucleic acids, their structural characteristic of high-density alignment in a small area physically blocks enzymatic access, significantly enhancing nuclease resistance. They enter cells smoothly via the scavenger receptor-mediated endocytosis pathway without the need for separate cationic delivery agents.

This research focuses on the function of Liposomal Spherical Nucleic Acids (LSNA), which utilize a lipid bilayer core, as a cancer immunotherapy platform. The researchers identified that lipids are not merely drug carriers but key structural variables that determine lymph node distribution and immune cell uptake rates. They confirmed that the alkyl chain length of phospholipids, degree of unsaturation, membrane fluidity, and the binding strength of the hydrophobic anchor fixing the oligonucleotides dictate the in vivo fate of the complex. By establishing a stable lipid anchor structure, the delivery efficiency to antigen-presenting cells, such as dendritic cells in the lymph nodes, was maximized, followed by a powerful antigen presentation response and induction of anti-tumor T-cell immunity.

The flexibility of structural design leads to the expansion of therapeutic areas. The LSNA platform has demonstrated applicability not only to gene silencing using antisense oligonucleotides (ASO) or small interfering RNA (siRNA) but also to genome editing using CRISPR complexes and multimodal therapies that release drugs in response to the pH of the tumor microenvironment or specific enzymes. Tangible results have also been confirmed in actual clinical studies. NU-0129, based on a gold nanoparticle core, completed a Phase 0 clinical trial, demonstrating the effect of target gene suppression within tumors by crossing the blood-brain barrier (BBB) in patients with intractable recurrent glioblastoma. Cavrotolimod in the LSNA formulation, which is a Toll-like receptor 9 (TLR9) agonist, also demonstrated a significant anti-cancer immune response in combination clinical trials with immune checkpoint inhibitors in patients with solid tumors.

Significance and Outlook

SNA technology is evaluated as having solved the chronic challenges of cell membrane permeability and biological stability in nucleic acid drug development through a structural engineering approach. By precisely combining lipid chemistry and nanostructure control, it is possible to build customized immune modulation platforms that target the lymphatic system, the central hub of the immune system, and induce cross-presentation by dendritic cells.

Challenges remain to be solved before full integration into clinical practice. Engineering improvements are required to overcome multi-scale delivery barriers in vivo, such as the heterogeneous vasculature of tumor tissues and lymphatic drainage blockage. Establishing a large-scale production process (CMC) that can synthesize dozens or more oligonucleotides on the nanoparticle surface with uniform density and maintain consistent quality is also an essential task to accelerate commercialization.