Synthesis of lipo-glycopolymers for cell surface engineering

Engineering cell surfaces by introducing specific bioactive macromolecules is a powerful tool for exploring cell-to-cell communication and modulating cell function. Accordingly, it is of interest to devise simple and convenient methods for presenting bioactive macromolecules on cell membranes. Polysaccharides, as a representative class of macromolecules, can be anchored to lipid groups for membrane insertion. In this work a combination of reversible addition–fragmentation chain transfer polymerization (RAFT) and post-polymerization modification (PPM) was used for the first time to prepare glycans containing lipid groups. In the example system presented, a terpolymer (pSMF) of sodium 4-vinylbenzenesulfonate (SS), 2-methacrylamido glucopyranose (MAG) and fluorescein o-methacrylate (FluMA) was first synthesized by RAFT. Maleimide-functionalized 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (MAL-DPPE) was synthesized and attached to pSMF to give the lipid “anchored” polysaccharide, DPPE-pSMF. The polymer lipid-anchored poly(SS-co-MAG) (DPPE-pSM) without the FluMA fluorescent label was similarly prepared. Confocal fluorescence images of cell cross-sections demonstrated that DPPE-pSMF with lipid end-group functionality could be inserted into the membrane of HeLa cells. Also DPPE-pSM was shown to be able to promote the growth of L929 cells. The composition and molecular weight of the synthesized glycopolymers could be easily regulated by changing the feed ratio of the monomers and the time of RAFT copolymerization. This approach to the preparation of lipid anchored polysaccharides is in contrast to more conventional synthetic routes that are limited by the heterogeneity of the native materials used, and provides a convenient method for preparing a range of such glycopolymers from well-defined precursors. The resulting polymers may be used to control cell functions that, in general, are regulated by the cell-surface microenvironment.