Zwitterionic Amino Acid-Derived Polyacrylates as Smart Materials Exhibiting Cellular Specificity and Therapeutic Activity

The synthesis of new amino acid-containing, cell-specific, therapeutically active polymers is presented. Amino acids served as starting material for the preparation of tailored polymers with different amino acids in the side chain. The reversible addition-fragmentation chain-transfer (RAFT) polymerization of acrylate monomers yielded polymers of narrow size distribution (D <= 1.3). In particular, glutamate (Glu)-functionalized, zwitterionic polymers revealed a high degree of cytocompatibility and cellular specificity, i.e., showing association to different cancer cell lines, but not with nontumor fibroblasts. Energy-dependent uptake mechanisms were confirmed by means of temperature-dependent cellular uptake experiments as well as localization of the polymers in cellular lysosomes determined by confocal laser scanning microscopy (CLSM). The amino acid receptor antagonist O-benzyl-L-serine (BzlSer) was chosen as an active ingredient for the design of therapeutic copolymers. RAFT copolymerization of Glu acrylate and BzlSer acrylate resulted in tailored macromolecules with distinct monomer ratios. The targeted, cytotoxic activity of copolymers was demonstrated by means of multiday in vitro cell viability assays. To this end, polymers with 25 mol % BzlSer content showed cytotoxicity against cancer cells, while leaving fibroblasts unaffected over a period of 3 days. Our results emphasize the importance of biologically derived materials to be included in synthetic polymers and the potential of zwitterionic, amino acid-derived materials for cellular targeting. Furthermore, it highlights that the fine balance between cellular specificity and unspecific cytotoxicity can be tailored by monomer ratios within a copolymer.

Automated summary

This study presents a method for synthesizing new amino acid-containing, cell-specific, therapeutically active polymers. Starting materials were amino acids, which were used to prepare tailored polymers with different amino acids in the side chain. The reversible addition-fragmentation chain-transfer (RAFT) polymerization of acrylate monomers resulted in polymers with narrow size distribution. Glutamate-functionalized, zwitterionic polymers exhibited high cytocompatibility and cellular specificity, showing association with cancer cell lines but not with nontumor fibroblasts. Cellular uptake experiments and confocal laser scanning microscopy confirmed energy-dependent uptake mechanisms and localization of the polymers in cellular lysosomes. Copolymers with a specific monomer ratio of Glu acrylate and BzlSer acrylate demonstrated targeted cytotoxicity against cancer cells while leaving fibroblasts unaffected. These results highlight the importance of incorporating biologically derived materials in synthetic polymers and the potential of zwitterionic, amino acid-derived materials for cellular targeting.