Self-organized pullulan/deoxycholic acid nanogels: Physicochemical characterization and anti-cancer drug-releasing behavior

Recent developments in natural biopolymer based drug delivery systems

Targeted delivery of drug molecules to diseased sites is a great challenge in pharmaceutical and biomedical sciences. Fabrication of drug delivery systems (DDS) to target and/or diagnose sick cells is an effective means to achieve good therapeutic results along with a minimal toxicological impact on healthy cells. Biopolymers are becoming an important class of materials owing to their biodegradability, good compatibility, non-toxicity, non-immunogenicity, and long blood circulation time and high drug loading ratio for both macros as well as micro-sized drug molecules. This review summarizes the recent trends in biopolymer-based DDS, forecasting their broad future clinical applications. Cellulose chitosan, starch, silk fibroins, collagen, albumin, gelatin, alginate, agar, proteins and peptides have shown potential applications in DDS. A range of synthetic techniques have been reported to design the DDS and are discussed in the current study which is being successfully employed in ocular, dental, transdermal and intranasal delivery systems. Different formulations of DDS are also overviewed in this review article along with synthesis techniques employed for designing the DDS. The possibility of these biopolymer applications points to a new route for creating unique DDS with enhanced therapeutic qualities for scaling up creative formulations up to the clinical level.

Traversing the diverse avenues of exopolysaccharides-based nanocarriers in the management of cancer

Exopolysaccharides are unique polymers generated by living organisms such as algae, fungi and bacteria to protect them from environmental factors. After a fermentative process, these polymers are extracted from the medium culture. Exopolysaccharides have been explored for their anti-viral, anti-bacterial, anti-tumor, and immunomodulatory effects. Specifically, they have acquired massive attention in novel drug delivery strategies owing to their indispensable properties like biocompatibility, biodegradability, and lack of irritation. Exopolysaccharides such as dextran, alginate, hyaluronic acid, pullulan, xanthan gum, gellan gum, levan, curdlan, cellulose, chitosan, mauran, and schizophyllan exhibited excellent drug carrier properties. Specific exopolysaccharides, such as levan, chitosan, and curdlan, have demonstrated significant antitumor activity. Moreover, chitosan, hyaluronic acid and pullulan can be employed as targeting ligands decorated on nanoplatforms for effective active tumor targeting. This review shields light on the classification, unique characteristics, antitumor activities and nanocarrier properties of exopolysaccharides. In addition, in vitro human cell line experiments and preclinical studies associated with exopolysaccharide-based nanocarriers have also been highlighted.

Pullulan in biomedical research and development - A review

Pullulan is an imperative microbial exo-polymer commercially produced by yeast like fungus Aureobasidium pullulans. Its structure contains maltosyl repeating units which comprises two α-(1 → 4) linked glucopyranose rings attached to one glucopyranose ring through α-(1 → 6) glycosidic bond. The co-existence of α-(1 → 6) and α-(1 → 4) glycosidic linkages endows distinctive physico-chemical properties to pullulan. It is highly biocompatible, non-toxic and non-carcinogenic in nature. It is extremely resistant to any mutagenicity or immunogenicity. The unique properties of pullulan make it a potent candidate for biomedical applications viz. drug delivery, gene delivery, tissue engineering, molecular chaperon, plasma expander, vaccination, etc. This review highlights the potential of pullulan in biomedical research and development.

Novel propyl karaya gum nanogels for bosentan: In vitro and in vivo drug delivery performance

The amphiphilic propyl Karaya gum (KG) with a degree of propyl group substitution of 3.24 was synthesized to design self-assembled nanogels as carriers for bosentan monohydrate, a poorly soluble antihypertensive drug. The drug was physically hosted into the hydrophobic core of the micellar nanogels by solvent evaporation method. TEM images revealed spherical shape and core-shell morphology of the nanogels. Depending upon polymer: drug weight ratio, the drug entrapment efficiency of >85% was attained. The carriers had hydrodynamic diameter in the range of 230-305 nm with narrow size distribution. The zeta potential of -23.0 to -24.9 mV and low critical association concentration (CAC) of 8.32 mg/l provided evidence that the colloidal nanogel system was physically stable. Thermodynamics of the propyl KG system in water favored spontaneous self-assembly of propyl KG. FTIR, thermal and x-ray analyses suggested that the drug was compatible in the hydrophobic confines of the nanogels. The micellar nanogels liberated their contents in simulated gastrointestinal condition in a pH-dependent manner over a period of 10 h. Peppas-Sahlin modeling of in vitro drug release data suggested that the polymer relaxation/swelling mechanism dominated the drug release process. Pre-clinical testing of the mucoadhesive nanogel formulations exhibited that the system could monitor the anti-hypertensive activity for a prolonged period. Overall, this propyl KG micellar nanogel system had a great potential and splendid outlook to serve as novel oral controlled release carriers for poorly soluble drugs with outstanding pharmacodynamics.

Research progress of self-assembled nanogel and hybrid hydrogel systems based on pullulan derivatives

Polymer nano-sized hydrogels (nanogels) as drug delivery carriers have been investigated over the last few decades. Pullulan, a nontoxic and nonimmunogenic hydrophilic polysaccharide derived from fermentation of black yeast like Aureobasidium pullulans with great biocompatibility and biodegradability, is one of the most attractive carriers for drug delivery systems. In this review, we describe the preparation, characterization, and 'switch-on/off' mechanism of typical pullulan self-assembled nanogels (self-nanogels), and then introduce the development of hybrid hydrogels that are numerous resources applied for regenerative medicine. A major section is used for biomedical applications of different nanogel systems based on modified pullulan, which exert smart stimuli-responses at ambient conditions such as charge, pH, temperature, light, and redox. Pullulan self-nanogels have found increasingly extensive application in protein delivery, tissue engineering, vaccine development, cancer therapy, and biological imaging. Functional groups are incorporated into self-nanogels and contribute to expressing desirable results such as targeting and modified release. Various molecules, especially insoluble or unstable drugs and encapsulated proteins, present improved solubility and bioavailability as well as reduced side effects when incorporated into self-nanogels. Finally, the advantages and disadvantages of pullulan self-nanogels will be analyzed accordingly, and the development of pullulan nanogel systems will be reviewed.

Current advances in self-assembled nanogel delivery systems for immunotherapy

Since nanogels (nanometer-sized gels) were developed two decades ago, they were utilized as carriers of innovative drug delivery systems. In particular, immunological drug delivery via self-assembled nanogels (self-nanogels) owing to their nanometer size and molecular chaperon-like ability to encapsulate large biomolecules is one of the most well studied and successful applications of nanogels. In the present review, we focus on self-nanogel applications as immunological drug delivery systems for cancer vaccines, cytokine delivery, nasal vaccines, and nucleic acid delivery, including several clinical trials. Cancer vaccines were the first practical application of self-nanogels as vehicles for drug delivery. After successful pre-clinical studies, phase I clinical trials were conducted, and it was found that vaccines consisting of self-nanogels could be administered repeatedly to humans without serious adverse effects, and self-nanogel vaccines induced antigen-specific cellular and humoral immunity. Cytokine delivery via self-nanogels led to the sustained release of IL-12, suppressed tumor growth, and increased Th1-type immune responses. Cationic self-nanogels were effective in penetrating the nasal mucosa and resulted in successful nasal vaccines in mice and nonhuman primates. Cationic self-nanogels were also used for the intracellular delivery of proteins and nucleic acids, and were successfully used to knockdown tumor growth factor expression using short interfering RNA with the immunological effect. These studies suggest that self-nanogels are currently one of the most unique and attractive immunological drug delivery systems and are edging closer to practical use.

Self-organized nanogel from pullulan/pheophorbide-A conjugate as a macromolecular photodynamic agent

The potential of pullulan(PL)/pheophorbide-A(phA) nanogel (PL/phA) was evaluated as a macromolecular photosensitizer (PS) for photodynamic therapy (PDT). Two samples with different degrees of substitution of phA (PL/phA1 and 2) were synthesized and analyzed by 1H NMR. The mean diameters of self-organized nanogels from PL/phA1 and 2 in aqueous solution were approximately 100 and 160 nm with mono-size distribution, respectively. The changes in nanogel photoactivity such as fluorescence intensity and singlet oxygen (1O2) production were observed in the solvents, dimethyl sulfoxide (DMSO) and phosphate buffered saline (PBS). Although, their photoactivity in DMSO, which cannot form self-organized nanogels, was similar to that of free phA, activities were suppressed in the aqueous solution due to self-quenching between phAs similar to a fluorescence resonance energy transfer (FRET) effect. Moreover, as the nanogels were co-incubated with HeLa cells, the self-quenching effect gradually disappeared as a function of time. Based upon confocal microscopy and cytotoxicity results, we infer that the nanogels were internalized in cancer cells by endocytosis and then degraded by various enzymes in the endosome and lysosome, leading to the restoration of photoactivity. Therefore, the self-organized PL/phA nanogels may be recommended for development of new PDT with minimal unfavorable phototoxic affects.