Synthesis of Chemically Diverse siRNA-Lipid Conjugates Enabled by Reversible Adsorption to Solid Support (RASS)

Small interfering RNAs (siRNAs) directly regulate gene expression and are, thus, attractive targets for clinical development to treat a variety of human diseases. While "naked" siRNAs are poor drug candidates, numerous chemical modifications of siRNAs have been developed to lower nuclease-sensitivity, increase cellular uptake, and enable cell-type-specific targeting. One class of modifications that has received attention is postsynthetic lipidation, as the pharmacokinetics of siRNA-lipid conjugates have been found to vary significantly based on the structure of the lipid moiety. While postsynthetic lipidation is a facile and effective means to render siRNAs more drug-like, most of these modifications occur in a single-step and in aqueous solution, engendering a limited chemical space. Herein, reversible adsorption of oligos onto a cationic solid support is demonstrated to facilitate postsynthetic, multistep modifications of single- and double-stranded siRNA in neat organic solvent to obtain siRNA-lipid conjugates with lipid moieties (e.g., long-chain alkyl thioethers, polyfluorinated biphenyl groups) that are challenging to incorporate using established postsynthetic lipidation procedures. RASS represents a rapid and convenient approach to generate siRNA-lipid conjugates encompassing a broad chemical space and ultimately a promising avenue to accelerate the discovery of potent siRNA therapeutics.