Current studies are focused on formulation improvement to enhance hydrolysis and clearance time.

This review highlights the utilization of dendron-polymer conjugates as building blocks for the fabrication of nanosized drug delivery vehicles. The examples given provide an overview of the evolution of these delivery platforms, from simple micellar containers to smart stimuli- responsive drug delivery systems through their design at the macromolecular level. Variations in chemical composition and connectivity of the dendritic and polymeric segments provide a variety of self-assembled micellar nanostructures that embody desirable attributes of viable drug delivery systems.

Employment of polymeric nanomaterials in cancer therapeutics is actively pursued since they often enable drug administration with increased efficacy along with reduced toxic side effects. In this study, drug conjugated micellar constructs are fabricated using triblock dendron-linear polymer conjugates where a hydrophilic linear polyethylene glycol (PEG) chain is flanked by well-defined hydrophobic biodegradable polyester dendrons bearing an antiangiogenic drug, combretastatin-A4 (CA4). Variation in dendron generation is utilized to obtain a library of micellar constructs with varying sizes and drug loadings. In particular, a family of drug appended dendron-polymer conjugates based on polyester dendrons of generations ranging from G1 to G3 and 10 kDa linear PEG were obtained using [3 + 2] Huisgen type "click" chemistry. The final constructs benefit from PEG's hydrophilicity and antibiofouling character, as well as biodegradable nature of the hydrophobic polyester dendrons. The hydrophobic-hydrophilic-hydrophobic character of these constructs leads to the formation of flower-like micelles in aqueous media. In addition to generation-dependent subnanomolar range critical micelle concentrations, the resulting micelles possess hydrodynamic diameters suitable for passive tumor targeting through enhanced permeability and retention (EPR) effect; thereby they are suitable candidates as controlled drug delivery agents. For all constructs, in vitro cytotoxicities were investigated and inhibitory effect of Comb-G3-PEG on tube formation was shown on human umbilical vein endothelial cells (HUVECs).

Polymeric micellar systems are emerging as a very important class of nanopharmaceuticals due to their ability to improve pharmacokinetics and biodistribution of chemotherapy drugs, as well as to reduce related systemic toxicities. While these nanosized delivery systems inherently benefit from passive targeting through the enhanced permeation and retention effect leading to increased accumulation in the tumor, additional active targeting can be achieved through surface modification of micelles with targeting groups specific for overexpressed receptors of tumor cells. In this project, nontoxic, biodegradable, and modularly tunable micellar delivery systems were generated using two types of dendron-polymer conjugates. Either an AB type dendron-polymer construct with 2K PEG or an ABA type dendron-polymer-dendron conjugate with 6K PEG based middle block was used as primary construct; along with an AB type dendron-polymer containing a cRGDfK targeting group to actively target cancer cells overexpressing αβ/αβ integrins. A set of micelles encapsulating docetaxel, a widely employed chemotherapy drug, were prepared with varying feed ratios of primary construct and targeting group containing secondary construct. Critical micelle concentrations of all micellar systems were in the range of 10 M. DLS measurements indicated hydrodynamic size distributions varying between 170 to 200 nm. An increase in docetaxel release at acidic pH was observed for all micelles. Enhanced cellular internalization of Nile red doped micelles by MDA-MB-231 human breast cancer cells suggested that the most efficient uptake was observed with targeted micelles. In vitro cytotoxicity experiments on MDA-MB-231 breast cancer and A549 lung carcinoma cell lines showed improved toxicity for RGD containing micelles. For A549 cell line EC values of drug loaded micellar sets were in the range of 10 M whereas EC value of free docetaxel was around 10 M. For MDA-MB-231 cell line EC value of free docetaxel was 6 × 10 M similar to EC of nontargeted AB type docetaxel doped micellar constructs whereas the EC value of its targeted counterpart decreased to 5.5 × 10 M. Overall, in this comparative study, the targeting group containing micellar construct fabricated with a 2 kDa PEG based diblock dendron-polymer conjugate emerges as an attractive drug delivery vehicle due to the ease of synthesis, high stability of the micelles, and efficient targeting.

Biodegradable polymeric nanofibers have emerged as promising candidates for several biomedical applications such as tissue engineering and regenerative medicine. Many of these applications require modification of these nanofibers with small ligands or biomolecules such as peptides and other growth factors, which necessitates functionalization of these materials in mild and benign fashion. This study reports the design, synthesis, and functionalization of such nanofibers and evaluates their application as a cell culture scaffold. Polylactide based copolymers containing furan groups and triethylene glycol (TEG) units as side chains were synthesized using organocatalyzed ring opening polymerization. The furan moiety, an electron rich diene, provides "clickable" handles required for modification of nanofibers since they undergo facile cycloaddition reactions with maleimide-containing small molecules and ligands. The TEG units provide these fibers with hydrophilicity, enhanced biodegradability, and antibiofouling characteristics to minimize nonspecific adsorption. A series of copolymers with varying amounts of TEG units in their side chains were evaluated for fiber formation and antibiofouling characteristics to reveal that an incorporation of 7.5 mol % TEG-based monomer was optimal for nanofibers containing 20 mol % furan units. Facile functionalization of these nanofibers in a selective manner was demonstrated through attachment of a dienophile containing fluorophore, namely, fluorescein maleimide. To show efficient ligand-mediated bioconjugation, nanofibers were functionalized with a maleimide appended biotin, which enabled efficient attachment of the protein, Streptavidin. Importantly, the crucial role played by the TEG-based side chains was evident due to lack of any nonspecific attachment of protein to these nanofibers in the absence of biotin ligand. Furthermore, these nanofibers were conjugated with a cell adhesive cyclic peptide, cRGDfK-maleimide, at room temperature without the need of any additional catalyst. Importantly, comparison of the cell attachment onto nanofibers with and without the peptide demonstrated that fibers appended with the peptides promoted cells to spread nicely and protrude actin filaments for enhanced attachment to the support, whereas the cells on nonfunctionalized nanofibers showed a rounded up morphology with limited cellular spreading.