Bio-Derived Poly(${\gamma}$-Glutamic Acid) Nanogels as Controlled Anticancer Drug Delivery Carriers

We have developed a novel type of polymer nanogel loaded with anticancer drug based on bio-derived poly(${\gamma}$-glutamic acid) (${\gamma}$-PGA). ${\gamma}$-PGA is a highly anionic polymer that is synthesized naturally by microbial species, most prominently in various bacilli, and has been shown to have excellent biocompatibility. Thiolated ${\gamma}$-PGA was synthesized by covalent coupling between the carboxyl groups of ${\gamma}$-PGA and the primary amine group of cysteamine. Doxorubicin (Dox)-loaded ${\gamma}$-PGA nanogels were fabricated using the following steps: (1) an ionic nanocomplex was formed between thiolated ${\gamma}$-PGA as the negative charge component, and Dox as the positive charge component; (2) addition of poly(ethylene glycol) (PEG) induced hydrogen-bond interactions between thiol groups of thiolated ${\gamma}$-PGA and hydroxyl groups of PEG, resulting in the nanocomplex; and (3) disulfide crosslinked ${\gamma}$-PGA nanogels were fabricated by ultrasonication. The average size and surface charge of Dox-loaded disulfide cross-linked ${\gamma}$-PGA nanogels in aqueous solution were $136.3{\pm}37.6$ nm and $-32.5{\pm}5.3$ mV, respectively. The loading amount of Dox was approximately 38.7 ${\mu}g$ per mg of ${\gamma}$-PGA nanogel. The Dox-loaded disulfide cross-linked ${\gamma}$-PGA nanogels showed controlled drug release behavior in the presence of reducing agents, glutathione (GSH) (1-10 mM). Through fluorescence microscopy and FACS, the cellular uptake of ${\gamma}$-PGA nanogels into breast cancer cells (MCF-7) was analyzed. The cytotoxic effect was evaluated using the MTT assay and was determined to be dependent on both the concentration and treatment time of ${\gamma}$-PGA nanogels. The bio-derived ${\gamma}$-PGA nanogels are expected to be a well-designed delivery carrier for controlled drug delivery applications.