Cholesterol-based lipophilic oligonucleotides incorporated into lipid membranes were studied using solid-state NMR, differential scanning calorimetry, and fluorescence methods. Lipophilic oligonucleotides can be used to build nanotechnological structures on membrane surfaces, taking advantage of the specific Watson-Crick base pairing. We used a cholesteryl-TEG anchor first described by Pfeiffer and Hook (J. Am. Chem. Soc. 2004, 126, 10224-10225). The cholesterol-based anchor molecules were found to incorporate well into lipid membranes without disturbing the bilayer structure and dynamics. In contrast to cholesterol, which is known to induce significant condensation of the membrane lipids, the cholesteryl-TEG anchor does not display this property. When the cholesteryl-TEG moiety was covalently bound to an oligonucleotide, the resulting lipophilic DNA molecules inserted spontaneously into lipid membranes without altering their structure. The duplex formed by two complementary cholesteryl-TEG oligonucleotides had increased thermodynamic stability compared to the same oligonucleotides without the anchor, both in solution and incorporated into lipid membranes. Since the cholesteryl-TEG anchor lacks the characteristic properties of cholesterol, oligonucleotides modified with this anchor are equally distributed between liquid-disordered and liquid-ordered domains in "raft" forming membranes. As an example of an application of these lipophilic oligonucleotides, cholesteryl-TEG-DNA was incorporated into supported lipid bilayers formed on polyelectrolyte-coated silica microparticles. The modified oligonucleotides were stably inserted into the lipid membrane and retained their recognition properties, therefore enabling further functionalization of the particles.

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The development of targeted and triggerable delivery systems is of high relevance for anticancer therapies. We report here on reduction-sensitive liposomes composed of a novel multifunctional lipidlike conjugate, containing a disulfide bond and a biotin moiety, and natural phospholipids. The incorporation of the disulfide conjugate into vesicles and the kinetics of their reduction were studied using dansyl-labeled conjugate 1 in using the dansyl fluorescence environmental sensitivity and the Förster resonance energy transfer from dansyl to rhodamine-labeled phospholipids. Cleavage of the disulfide bridge (e.g., by tris(2-carboxyethyl)phosphine (TCEP), dithiothreitol (DTT), l-cysteine, or glutathione (GSH)) removed the hydrophilic headgroup of the conjugate and thus changed the membrane organization leading to the release of entrapped molecules. Upon nonspecific uptake of vesicles by macrophages, calcein release from reduction-sensitive liposomes consisting of the disulfide conjugate and phospholipids was more efficient than from reduction-insensitive liposomes composed only of phospholipids. The binding of streptavidin to the conjugates did not interfere with either the subsequent reduction of the disulfide bond of the conjugate or the release of entrapped molecules. Breast cancer cell line BT-474, overexpressing the HER2 receptor, showed a high uptake of the reduction-sensitive doxorubicin-loaded liposomes functionalized with the biotin-tagged anti-HER2 antibody. The release of the entrapped cargo inside the cells was observed, implying the potential of using our system for active targeting and delivery.

Various new nucleosides bearing one or two lipophilic groups at the 2′‐position have been synthesized. The lipophilic substituents were attached to a 2′‐hydroxy, 2′‐amino, or 2′‐thio function. These lipophilic nucleosides anchor in large unilamellar POPC vesicles serving as phospholipid membrane models. The insertion of these molecules into the membranes was investigated by NMR techniques. For comparison, nucleosides with two or three lipophilic groups at the 2′‐, 3′‐, or 5′‐positions have also been studied.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Keywords: Nucleosides / Amphiphiles / Lipophilicity / Membrane anchoring / Synthesis Nucleosides were synthesized bearing one or two lipophilic groups at the 5Ј-position. The lipophilic substituents can be fixed at a 5Ј-amino group or at the 5Ј-phosphate moiety. Selected examples of these lipophilic nucleosides are shown by