Many target sites of synthetic supramolecular drug molecules are located inside cells. Since larger and highly charged molecules are typically not able to cross the cell membrane on their own, an efficient carrier is needed. Calcium phosphate nanoparticles were loaded with different artificial protein and DNA binders, i. e. a polyfunctional anionic polymer, a cationic calixarene dimer and amphiphilic molecular tweezers. The loading of calcium phosphate nanoparticles with these molecules was quantitatively determined by UV spectroscopy. As visualized by fluorescence microscopy and confocal laser scanning microscopy (CLSM), the functionalized calcium phosphate nanoparticles were easily taken up by HeLa cells together with their cargo. In contrast, the dissolved molecules alone were not able to penetrate the cell membrane.

This account presents a general method for the construction of polymeric surface binders for digestion enzymes. Two prominent parts, namely, the modification of the copolymer composition and the screening assay for the most powerful inhibitors are both amenable to parallelization. The concept hinges on the appropriate selection of amino-acid-selective comonomers, their free radical copolymerization, and subsequent screening of the resulting copolymer library for efficient enzyme inhibition. A microscale synthetic procedure for the copolymerization process was developed, which produces water-soluble affinity polymers that can be stored for years at room temperature. Initial parallel screening was conducted in standard enzyme assays to identify polymeric inhibitors, which were subsequently subjected to determination of IC values for their target enzyme. For all digestion enzymes, except elastase, a number of polymer inhibitors were found, some of which were selective toward one or two protein targets. Since the key monomers of the best inhibitors bind to amino acid residues in the direct vicinity of the active site, we conclude that efficient coverage of the immediate environment by the copolymers is critical. Strong interference with enzymatic activity is brought about by blocking the substrate access and product exit to and from the active site.

Rational design in combination with a screening process was used to develop affinity polymers for a specific binding site on the surface of immunoglobulin G (IgG) proteins. The concept starts with the identification of critical amino acid residues on the protein interface and their topological arrangement. Appropriate binding monomers were subsequently synthesized. Together with a sugar monomer (2-5 equiv) for water solubility and a dansyl monomer (0.5 equiv) as a fluorescent label, they were subjected in aqueous solution to linear radical copolymerization in various compositions (e.g., azobisisobutyronitrile (AIBN), homogeneous water/DMF mixtures). After ultrafiltration and lyophilization, colorless dry water-soluble powders were obtained. NMR spectroscopic and gel permeation chromatography (GPC) characterization indicated molecular weights between 30 and 500 kD and confirmed retention of monomer composition as well as the absence of monomers. In a competitive enzyme-linked immunosorbent assay (ELISA) screen of the polymer libraries (20-50 members), few copolymers qualified as strong and selective binders for the protein A binding site on the Fc fragment of the antibody. Their monomer composition precisely reflected the critical amino acids found at the interface. The simple combination of a charged and a nonpolar binding monomer sufficed for selective submicromolar IgG recognition by the synthetic polymer. Affinities were confirmed by fluorescence titrations; they increased with decreasing salt load but remained largely unaltered at lowered pH. Other proteins, including those of similar size and isoelectric point (pI), were bound 10-1000 times less tightly. This example indicates that interaction domains in other proteins may also be targeted by synthetic polymers if their comonomer composition reflects the nature and arrangement of amino acid residues on the protein surface.