Polymyxins are peptide antibiotics that are highly efficient against many multidrug resistant pathogens. However, the poor stability of polymyxins in the bloodstream requires the administration of high drug doses that, in turn, can lead to polymyxin toxicity. Consequently, different delivery systems have been considered for polymyxins to overcome these obstacles. In this work, we report the development of polymyxin delivery systems based on nanoparticles obtained from the self-assembly of amphiphilic random poly(l-glutamic acid-co-d-phenylalanine). These P(Glu-co-dPhe) nanoparticles were characterized in terms of their size, surface charge, stability, cytotoxicity, and uptake by macrophages. The encapsulation efficiency and drug loading into P(Glu-co-dPhe) nanoparticles were determined for both polymyxin B and E. The release kinetics of polymyxins B and E from nanoformulations was studied and compared in buffer solution and human blood plasma. The release mechanisms were analyzed using a number of mathematical models. The minimal inhibitory concentrations of the nanoformulations were established and compared with those determined for the free antibiotics.

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Polyethyleneimine, poly-L-lysine, chitosan and some others cationic polymers have been thoroughly studied as nucleic acid delivery systems in gene therapy. However, the drug release from these systems proceeds at a very low rate due to extremely high binding between a carrier and gene material. To reduce these interactions and to enhance drug release, we developed a set of amphiphilic polypeptides containing positively and negatively charged amino acids as well as a hydrophobic one. The copolymers obtained were characterized by size-exclusion chromatography, static light scattering, HPLC amino acid analysis and 1HNMR spectroscopy. All copolymers formed particles due to a self-assembly in aqueous media. Depending on polypeptide composition, the formation of particles with hydrodynamic diameters from 180 to 900 nm was observed. Stability of polymer particles, loading and release efficiency were carefully studied. Cellular uptake of the particles was efficient and their cytotoxicity was negligible. The application of polymer carriers, containing siRNA, to vascular endothelial growth factor (VEGF-A165) silencing of ARPE-19 cells was successful. The gene silencing was confirmed by suppression of both messenger RNA and protein expression.

In this work, a method to prepare hybrid amphiphilic block copolymers consisting of biocompatible synthetic glycopolymer with non-degradable backbone and biodegradable poly(amino acid) (PAA) was developed. The glycopolymer, poly(2-deoxy-2-methacrylamido-D-glucose) (PMAG), was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Two methods for modifying the terminal dithiobenzoate-group of PMAG was investigated to obtain the macroinitiator bearing a primary aliphatic amino group, which is required for ring-opening polymerization of N-carboxyanhydrides of hydrophobic α-amino acids. The synthesized amphiphilic block copolymers were carefully analyzed using a set of different physico-chemical methods to establish their composition and molecular weight. The developed amphiphilic copolymers tended to self-assemble in nanoparticles of different morphology that depended on the nature of the hydrophobic amino acid present in the copolymer. The hydrodynamic diameter, morphology, and cytotoxicity of polymer particles based on PMAG-b-PAA were evaluated using dynamic light scattering (DLS) and transmission electron microscopy (TEM), as well as CellTiter-Blue (CTB) assay, respectively. The redox-responsive properties of nanoparticles were evaluated in the presence of glutathione taken at different concentrations. Moreover, the encapsulation of paclitaxel into PMAG-b-PAA particles and their cytotoxicity on human lung carcinoma cells (A549) and human breast adenocarcinoma cells (MCF-7) were studied.

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