RNA interference (RNAi), an exciting yet evolving gene-silencing technology, holds great promise for drug discovery and as a novel therapeutic approach. But troubling doubts have recently emerged as to how quickly that promise will deliver. Perhaps ominously, in November, Roche terminated its multimillion-dollar RNAi therapeutics programs.
One of the main bottlenecks vexing the field is functional delivery. Select Biosciences recent “RNAi Asia” conference discussed the latest developments and innovations, such as development of specialized nanoparticles for delivery, improvements in high-throughput screening, and new in vivo studies.
Delivery problems could be overcome with the use of specialized nanoparticles that entrap small interfering RNAs (siRNAs), suggested Andrew D. Miller, Ph.D., professor at King’s College London. He has an optimistic point of view about RNAi therapeutics.
“RNAi should be the closest thing to a magic bullet for the biopharmaceutical industry,” he said. “In principle, one can get high-quality knockdown with very few side effects or off-target effects. The problem is that RNAi effectors need to be delivered to the target site in a potent form using the smallest possible amount of material. At present, doses are too high. That problem can only be solved with better delivery technologies and improved methodologies.”
A possible solution envisioned by Dr. Miller is the use of cationic, lipid-based, self-assembly nanoparticles that entrap siRNAs into lipoplex nanoparticles, which themselves need to be further stabilized.
“Stabilized nanoparticles with improved circulation half-lives are realized using a polyethylene glycol (PEG) polymer layer to shield the nanoparticle surface. The best stabilized nanoparticles should then be those that are stable until triggered to release entrapped siRNAs by local changes in condition such as pH, or through an external trigger such as from a laser,” he said.
“Our approach is to use a Lego building block-like process to derive stabilized nanoparticle delivery systems in which purpose-designed components are allowed to self-assemble. We have designed RNAi delivery systems according to this paradigm and successfully formulated specialized nanoparticles for the delivery of siRNAs to in vivo targets such as liver and tumors. These are tailor-made delivery solutions.”
The nanoparticle systems are composed of nucleic acids condensed within functional concentric layers of lipid components, surrounded by a biocompatibility layer and equipped with an optional biological recognition/targeting layer, he explained.
There are still significant hurdles to be overcome. “We have achieved proof-of-concept for functional delivery in vivo, but not yet proof-of-therapy,” Dr. Miller said. “We still need time to make significant improvements to the delivery process. We believe that we may be facing a situation in general in which academics still need to solve basic delivery issues before biopharma finds RNAi as attractive as it did several years ago. Delivery will work eventually, but it is likely to take more time and effort than is commonly appreciated,” he concluded.