Small interfering RNAs (siRNAs) are a new therapy that can be used to treat various diseases. This has led to an increasing demand for a selective, efficient and safe mode of delivery of siRNA in cells.
Now, in a collaboration between the universities of Amsterdam and Leiden in the Netherlands, researchers have developed a special molecular nanocage for siRNA delivery. In a paper in the journal Chem, they present nanocages that are easy to prepare and display tunable siRNA delivery characteristics.
The nano cages were developed within a research group for Homogeneous, Supramolecular and Bio-inspired catalysis from Joost Reek and Bas de Bruin at the Van ‘t Hoff Institute for Molecular Sciences of the University of Amsterdam, with further study in a group led by Alexander Kros at the Leiden Institute of Chemistry .
The researchers are motivated by the potential of siRNA in gene therapy, which requires an effective delivery system. They set out to develop nanocages with functional groups on the outside, making the cages capable of binding to siRNA strands. Since binding is based on reversible binding, siRNAs can in principle be released in the cellular environment. To explore the delivery characteristics of their nanocage, the researchers conducted laboratory studies using a variety of human cancer cells.
Nano cages are constructions of small molecular building blocks, called ditopic ligands, which are linked using metal atoms. A typical cage consists of 12 metal atoms and 24 ligands, hence the abbreviation M12L24. The researchers designed and synthesized five different ligands to form molecular cages with different siRNA binding affinities. They then prepared a series of siRNA-binding nanocage using platinum or palladium as the bridge metal. Palladium nanocage is less stable in the cellular environment, and decomposition is one mechanism of siRNA release.
After screening nanocage characteristics such as stability and siRNA-binding ability, delivery characteristics were tested in an assay based on siRNA-mediated green fluorescent protein (GFP) silencing. Cage is used to deliver siRNA to human GFP-expressing cells, so fluorescence measurement can ensure successful delivery of siRNA. Two types of human cell lines were used: HeLa and U2OS.
Cage composition determines siRNA delivery
The researchers said they were surprised that they could not only demonstrate satisfactory siRNA delivery, but also found differences depending on the metal used in the nanocage. Where the platinum-based Pt12L24 nanocage exhibited highly effective siRNA delivery to U2OS cells, it exhibited little efficiency for HeLa. In contrast, the palladium-based Pd12L24 nanocage, derived from the same ligand building blocks, delivered siRNA to HeLa but not to U2OS. Such differentiation could not be observed in experiments where a commercially applied delivery system (lipofectamine) was used. The M12L24 nanocage thus introduces the possibility of tuning the delivery characteristics of siRNA by tuning the composition of the nanocage.
In the paper, the researchers consider this unique cell selectivity feature of nanoparticles a promising addition to the field of targeted RNA gene material delivery, whose full potential has yet to be uncovered.
Although the current results were obtained in a highly controlled laboratory study, they hope that the regulated delivery of RNA from their nanocage will lead to the development of desired selective RNA nanomedicines in the future.
Several companies working in the siRNA space made progress last year. SiSaf’s main in-house program, SIS-101-ADO, is an ADO2-specific siRNA combined with the SiSaf Bio-Courier platform, which aims to suppress expression of the mutant CLCN7 gene and thereby salvage bone mass and quality to near-normal levels.
In addition, Eleven Therapeutics raised a total of $22 million in initial funding to develop a first-of-its-kind platform that designs ultra-long-lasting siRNAs by leveraging high-throughput combinatorial chemistry and artificial intelligence.
The Eleven platform aims to decipher the structure-activity linkage (SAR) of siRNAs.