Design of Ionizable Lipids To Overcome the Limiting Step of Endosomal Escape: Application in the Intracellular Delivery of mRNA, DNA, and siRNA

The
intracellular delivery of nucleic acid molecules is a complex process
involving several distinct steps; among these the endosomal escape
appeared to be of particular importance for an efficient protein production
(or inhibition) into host cells. In the present study, a new series
of ionizable vectors, derived from naturally occurring aminoglycoside
tobramycin, was prepared using improved synthetic procedures that
allow structural variations on the linker and hydrophobic domain levels.
Complexes formed between the new ionizable lipids and mRNA, DNA, or
siRNA were characterized by cryo-TEM experiments and their transfection
potency was evaluated using different cell types. We demonstrated
that lead molecule 30, bearing a biodegradable diester
linker, formed small complexes with nucleic acids and provided very
high transfection efficiency with all nucleic acids and cell types
tested. The obtained results suggested that the improved and “universal”
delivery properties of 30 resulted from an optimized
endosomal escape, through the lipid-mixing mechanism.