A needle-and-thread approach to bilayer transport: permeation of a molecular umbrella-oligonucleotide conjugate across a phospholipid membrane

A di-walled molecular umbrella, composed of two choloyl groups, one spermidine moiety, and a 5-thiol(2-nitrobenzoyl) "handle", was covalently attached to a 16-mer oligonucleotide (S-dT16) through a disulfide bond. Incubation of this conjugate (1) with vesicles made from 1-palmitoyl-2-oleyol-sn-glycero-3-phosphocholine and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (95/5, mol/mol) (200 nm diameter, extrusion) that contained entrapped glutathione (GSH) at 37 degrees C resulted in the liberation of the oligonucleotide and the umbrella-bound 5-mercapto(2-nitrobenzoyl) moiety (USH) via thiolate-disulfide interchange. The appearance of USH, together with the absence of leakage of entrapped GSH and a vesicular capture of the oligonucleotide that matches the extent of USH formation, provides compelling evidence for delivery of S-dT16 into the aqueous compartment of these vesicles. In a sense, the molecular umbrella functions like a "needle" in providing a pathway for the oligonucleotide (the "thread") to cross the membrane.