(141d) Block-Copolymer Stabilized Lipid Nanoparticles: A Novel Platform for Targeted Gene Delivery

Lipid nanoparticles (LNPs) have demonstrated their enormous potential as delivery vehicles, as evidenced by the approval of two COVID-19 mRNA vaccines. Gene delivery is the next frontier for LNPs. The current state-of-the-art LNPs include four main components: an ionizable lipid, a helper lipid, cholesterol, and a PEG-lipid. The PEG-lipid, while only at a small mole fraction, plays a vital role in LNP stability, transfection efficiency, and liver targeting. Indeed, the liver targeting of LNPs is due to the rapid shedding of PEG-lipid upon I.V. administration, followed by the subsequent adsorption of apolipoprotein E (ApoE), leading to low-density lipoprotein receptor (LDLR)-mediated uptake by hepatocytes. Although the PEG-lipid desorption is instrumental in exploiting the well-established delivery route to the liver, it severely hinders the ability of LNPs to target non-hepatic cells passively or actively. Therefore, to reduce liver targeting and to realize non-hepatic cell targeting, a novel LNP platform with a tightly anchored stabilizer is crucial.

We present LNPs prepared using block copolymer (BCP) stabilizers that do not shed, but rather stay anchored on the LNP surface. We systematically optimized several parameters (composition, concentration, payload) and identified the best BCP-stabilized LNP formulations with desired properties such as long-term stability, optimal sizes (~100 nm), high encapsulation efficiencies (>90%), and high transfection efficiencies in different immortal cell lines. While permanent PEG stabilizing layers on LNP surfaces might be expected to compromise either cellular internalization or endosomal escape. Surprisingly, these block copolymer PEG LNPs transfected more effectively than the corresponding PEG-lipid stabilized LNPs. Hence, this new construct enables the targeting of LNPs in a way that is not possible with PEG-lipids. Likewise, these BCPs can be conjugated with large ligands (antibodies) to target non-hepatic cells. The capability to conjugate targeting ligands and antibodies to block copolymer LNPs, without compromising transfection, potentially enables gene delivery formulations which cannot be delivered using conventional LNP constructs.