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Polymer nanogels have gained considerable attention as a potential platform for drug delivery applications. Here we describe the design and synthesis of novel polypeptide-based nanogels with hydrophobic moieties in the cross-linked ionic cores. Diblock copolymer, poly(ethylene glycol)-b-poly(L-glutamic acid), hydrophobically modified with L-phenylalanine methyl ester moieties was used for controlled template synthesis of nanogels with small size (ca. 70 nm in diameter) and narrow particle size distribution. Steady-state and time-resolved fluorescence studies using coumarin C153 indicated the existence of hydrophobic domains in the ionic cores of the nanogels. Stable doxorubicin-loaded nanogels were prepared at high drug capacity (30 w/w%). We show that nanogels are enzymatically-degradable leading to accelerated drug release under simulated lysosomal acidic pH. Furthermore, we demonstrate that the nanogel-based formulation of doxorubicin is well tolerated and exhibit an improved antitumor activity compared to a free doxorubicin in an ovarian tumor xenograft mouse model. Our results signify the point to a potential of these biodegradable nanogels as attractive carriers for delivery of chemotherapeutics.

A series of novel polymeric nanogels with core-shell morphology was developed. Block ionomer complexes of comb-graft poly(ethylene oxide)-b-poly(polypropylene oxide)-b-poly(ethylene oxide)-g-poly(acrylic acid) copolymers (Pluronic-PAA) and divalent metal cations were utilized as micellar templates for the synthesis of nanogels with sizes ranging from 100 to 200 nm in diameter. The Pluronic-PAA nanogels were confirmed to possess ionic cross-linked PAA cores and flexible hydrophilic shells from the Pluronic copolymer chains. The ionic character of the core provided for pH-dependent swelling/collapse behavior of the nanogels. These prepared nanogels are expected to be of utility as carriers for charged therapeutic or diagnostic agents.

Self-assembling complexes from nucleic acids and synthetic polymers are evaluated for plasmid and oligonucleotide (oligo) delivery. Polycations having linear, branched, dendritic. block- or graft copolymer architectures are used in these studies. All these molecules bind to nucleic acids due to formation of cooperative systems of salt bonds between the cationic groups of the polycation and phosphate groups of the DNA. To improve solubility of the DNA/polycation complexes, cationic block and graft copolymers containing segments from polycations and non-ionic soluble polymers, for example, poly(ethylene oxide) (PEO) were developed. Binding of these copolymers with short DNA chains, such as oligos, results in formation of species containing hydrophobic sites from neutralized DNA polycation complex and hydrophilic sites from PEO. These species spontaneously associate into polyion complex micelles with a hydrophobic core from neutralized polyions and a hydrophilic shell from PEO. Such complexes are very small (10-40 nm) and stable in solution despite complete neutralization of charge. They reveal significant activity with oligos in vitro and in vivo. Binding of cationic copolymers to plasmid DNA forms larger (70-200 nm) complexes. which are practically inactive in cell transfection studies. It is likely that PEO prevents binding of these complexes with the cell membranes ("stealth effect"). However attaching specific ligands to the PEO-corona can produce complexes, which are both stable in solution and bind to target cells. The most efficient complexes were obtained when PEO in the cationic copolymer was replaced with membrane-active PEO-b-poly(propylene oxide)-b-PEO molecules (Pluronic 123). Such complexes exhibited elevated levels of transgene expression in liver following systemic administration in mice. To increase stability of the complexes, NanoGel carriers were developed that represent small hydrogel particles synthesized by cross-linking of PEI with double end activated PEO using an emulsification/solvent evaporation technique. Oligos are immobilized by mixing with NanoGel suspension, which results in the formation of small particles (80 nm). Oligos incorporated in NanoGel are able to reach targets within the cell and suppress gene expression in a sequence-specific fashion. Further. loaded NanoGel particles cross-polarized monolayers of intestinal cells (Caco-2) suggesting potential usefulness of these systems for oral administration of oligos. In conclusion the approaches using polycations for gene delivery for the design of gene transfer complexes that exhibit a very broad range of physicochemical and biological properties, which is essential for design of a new generation of more effective non-viral gene delivery systems.