Graphical Abstract

Spherical nucleic acids (SNAs) are a class of nanomaterials with a structure defined by a radial distribution of densely packed, short DNA or RNA sequences around a nanoparticle core. This structure allows SNAs to rapidly enter mammalian cells, protects the displayed oligonucleotides from nuclease degradation, and enables co-delivery of other drug cargoes. Here, we investigate the biodistribution of liposomal spherical nucleic acid (LSNA) conjugates, SNA architectures formed from liposome templates and DNA modified with hydrophobic end groups (tails). We compared linear DNA with two types of LSNAs that differ only by the affinity of the modified DNA sequence for the liposome template. We use single-stranded DNA (ssDNA) terminated with either a lowaffinity cholesterol tail (CHOL-LSNA) or a high-affinity diacylglycerol lipid tail (DPPE-LSNA). Both LSNA formulations, independent of DNA conjugation, reduce the inflammatory cytokine response to intravenously administered DNA. The difference in the affinity for the liposome template significantly affects DNA biodistribution. DNA from CHOL-LSNAs accumulates in greater amounts in the lungs than DNA from DPPE-LSNAs. In contrast, DNA from DPPE-LSNAs exhibits greater accumulation in the kidneys. Flow cytometry and fluorescence microscopy of tissue sections indicate that different cell populationsimmune and nonimmunesequester the DNA depending upon the chemical makeup of the LSNA. Taken together, these data suggest that the chemical structure of the LSNAs represents an opportunity to direct the biodistribution of nucleic acids to major tissues outside of the liver.

Two synthetic approaches that allow one to control PEG content within spherical nucleic acids (SNAs) have been developed. One approach begins with RNA-modified gold nanoparticles followed by a backfill of PEG 2K alkanethiols, and the other involves co-adsorption of the two entities on a gold nanoparticle template. These two methods have been used to explore the role of PEG density on the chemical and biological properties of RNA–SNAs. Such studies show that while increasing the extent of PEGylation within RNA–SNAs extends their blood circulation half-life in mice, it also results in decreased cellular uptake. Modified ELISA assays show that constructs, depending upon RNA and PEG content, have markedly different affinities for class A scavenger receptors, the entities responsible, in part, for cellular internalization of SNAs. In designing SNAs for therapeutic purposes, these competing factors must be considered and appropriately adjusted depending upon the desired use.

Liposomal spherical nucleic acids (LSNAs) are a class of nanomaterial used broadly for biomedical applications. Their intrinsic capacity to rapidly enter cells and engage cell surface and intracellular ligands stems from their unique three-dimensional architecture, which consists of densely packed and uniformly oriented oligonucleotides on the surface of a liposomal core. Such structures are promising for therapeutics because they can carry chemical cargo within the lipid core in addition to the nucleic acids that define them, in principle enabling delivery of multiple signals to a single cell. On the basis of these traits, we have designed novel dual-targeting LSNAs that deliver a nucleic acid specific for TLR9 inhibition and a small molecule (TAK-242) that inhibits TLR4. Toll-like receptors (TLRs) play a large role in pathogen recognition and disease initiation, and TLR subtypes are differentially located within the lipid membranes of the cell surface and within intracellular endosomes. Oftentimes, in acute or chronic inflammatory conditions, multiple TLRs are activated, leading to stimulation of distinct, and sometimes overlapping, downstream pathways. As such, these inflammatory conditions may respond to attenuation of more than one initiating receptor. We show that dual targeting LSNAs, comprised of unilamellar liposomal cores, the INH-18 oligonucleotide sequence, and TAK-242 robustly inhibit TLR-9 and TLR-4 respectively, in engineered TLR reporter cells and primary mouse peritoneal macrophages. Importantly, the LSNAs exhibit up to a 10- and a 1000-fold increase, respectively, in TLR inhibition compared to the linear sequence and TAK-242 alone. Moreover, the timing of delivery is shown to be a critical factor in effecting TLR-inhibition, with near-complete TLR-4 inhibition occurring when cells were pretreated with SNAs for 4 h prior to stimulation. The most pronounced effect observed from this approach is the benefit of delivering the small molecule within the SNA via the receptor-mediated internalization pathway common to SNAs.

The current standard of care for end stage liver disease is orthotopic liver transplantation (OLT). Through improvement in surgical techniques, immunosuppression, and general medical care, liver transplantation has become an effective treatment over the course of the last half-century. Unfortunately, due to the limited availability of donor organs, there is a finite limit to the number of patients who will benefit from this therapy. This review will discuss current research in experimental cellular therapies for acute, chronic, and metabolic liver failure that may be appropriate when liver transplantation is not an immediate option.