Fusion-Dependent Formation of Lipid Nanoparticles Containing Macromolecular Payloads
This week we profile a recent publication in Nanoscale from Dr. Jayesh Kulkarni
(pictured, left) in the laboratory of Dr. Pieter Cullis (centre) at UBC.
Can you provide a brief overview of your lab’s current research focus?
The Cullis group (at UBC, Biochemistry and Molecular Biology) focuses on the development of lipid nanoparticle (LNP) formulations of nucleic acid. This work has led to a commercial product known as Onpattro (patisiran) which is an LNP formulation of siRNA, and currently is the only RNAi therapeutic approved by the FDA. Onpattro is the result of work undertaken in the Cullis group in collaboration with Alnylam Pharmaceuticals and Acuitas Therapeutics (previously Alcana). With entrapment efficiencies nearing 100% of the siRNA, a scalable formulation procedure, and a potent formulation requiring only 0.3 mg siRNA/kg body weight in humans, LNP-siRNA are at the forefront of gene therapy for hepatic targets. Our current efforts are focused on gaining a better understanding of the biophysics of these nanoparticles, and re-engineering them for mRNA and plasmid delivery.
What is the significance of the findings in this publication?
Previous work from our group (2011 – 2015) had suggested that the structure of these LNP contained inverted micelles (lipid head groups facing the siRNA, and tails facing outward) that protect the siRNA. This was the established paradigm and suggested that the mixing procedure used to manufacture LNP was responsible for the structure formed. More recent data suggested this is not the case, and it is in fact a self-assembly process that dictates particle formation, independent of the mixing procedure. Our latest publication provides further evidence to overturn the existing paradigm of LNP formation and provides insight into particle formation through a series of events involving the fusion of precursor particles as a result of neutralising the pH. We were also able to extend this hypothesis from siRNA systems to particles that contain mRNA, mini-circle DNAs, and plasmid DNA. Most importantly, this study moves in the direction of correcting the scientific record and establish a base for further improving LNP potency by understanding the methods of particle formation.
What are the next steps for this research?
Our publication suggests an overall mechanism of particle formation but does not provide an in-depth analysis of the lipid-lipid interactions which mediate stable entrapment of nucleic acids. From this dataset, we can start to further study these interactions and design more potent LNP formulations.
This work was funded by:
Dr. Pieter Cullis is funded by a CIHR Foundation Grant (FDN 148469) and a BCIC Ignite grant. We recently secured funding from an NCE competition to fund further nanomedicines research and establish the NanoMedicines Innovation Network (NMIN). We are working with UBC to bring this online as soon as possible.