Microbial Biosynthesis of Polyglutamic Acid Biopolymer and Applications in the Biopharmaceutical, Biomedical and Food Industries

Bioderived polyelectrolyte nanogels for robust antigen loading and vaccine adjuvant effects

An easy but robust strategy for the synthesis of bioderived polyelectrolyte nanogels for protein antigen loading and vaccine adjuvant systems that can improve both humoral (Th2) and cellular immunity (Th1) is presented. The synthesized polyelectrolyte nanogels promote the uptake of antigens into antigen-presenting cells and strongly induce ovalbumin-specific INF-γ producing cells, cytotoxic T cell activity, and antibody production.

Integrin-assisted drug delivery of nano-scaled polymer therapeutics bearing paclitaxel

Angiogenesis plays a prominent role in cancer progression. Anti-angiogenic therapy therefore, either alone or in combination with conventional cytotoxic therapy, offers a promising therapeutic approach. Paclitaxel (PTX) is a widely-used potent cytotoxic drug that also exhibits anti-angiogenic effects at low doses. However, its use, at its full potential, is limited by severe side effects. Here we designed and synthesized a targeted conjugate of PTX, a polymer and an integrin-targeted moiety resulting in a polyglutamic acid (PGA)-PTX-E-[c(RGDfK)(2)] nano-scaled conjugate. Polymer conjugation converted PTX to a macromolecule, which passively targets the tumor tissue exploiting the enhanced permeability and retention effect, while extravasating via the leaky tumor neovasculature. The cyclic RGD peptidomimetic enhanced the effects previously seen for PGA-PTX alone, utilizing the additional active targeting to the α(v)β(3) integrin overexpressed on tumor endothelial and epithelial cells. This strategy is particularly valuable when tumors are well-vascularized, but they present poor vascular permeability. We show that PGA is enzymatically-degradable leading to PTX release under lysosomal acidic pH. PGA-PTX-E-[c(RGDfK)(2)] inhibited the growth of proliferating α(v)β(3)-expressing endothelial cells and several cancer cells. We also showed that PGA-PTX-E-[c(RGDfK)(2)] blocked endothelial cells migration towards vascular endothelial growth factor; blocked capillary-like tube formation; and inhibited endothelial cells attachment to fibrinogen. Orthotopic studies in mice demonstrated preferential tumor accumulation of the RGD-bearing conjugate, leading to enhanced anti-tumor efficacy and a marked decrease in toxicity as compared with free PTX-treated mice.

Chromosomal integration of a synthetic expression control sequence achieves poly-gamma-glutamate production in a Bacillus subtilis strain

Poly-gamma-glutamate (gamma-PGA) has applications in food, medical, cosmetic, animal feed, and wastewater industries. Bacillus subtilis DB430, which possesses the gamma-PGA synthesis ywsC-ywtAB genes in its chromosome, cannot produce gamma-PGA. An efficient synthetic expression control sequence (SECS) was introduced into the upstream region of the ywtABC genes, and this resulted in gamma-PGA-producing B. subtilis mutant strains. Mutant B. subtilis PGA6-2 stably produces high levels of gamma-PGA in medium A without supplementation of extra glutamic acid or ammonium chloride. The mutant B. subtilis PGA 6-2 is not only a gamma-PGA producer, but it is also a candidate for the genetic and metabolic engineering of gamma-PGA production.

Nanostructured bacterial materials for innovative medicines

The development of innovative medicines and personalized biomedical approaches require the identification and implementation of new biocompatible materials produced by methodologically simple and cheap fabrication methods. The biological fabrication of materials, mostly carried out by microorganisms, has historically provided organic compounds with wide-spectrum biomedical applications, including hyaluronic acid, poly(gamma-glutamic acid) and polyhydroxyalkanoates. Additionally, the implementation of new methodological platforms such as metabolic engineering and systems biology have facilitated the controlled production of natural nanoparticles produced by bacteria, including metallic deposits of Au, Ag, Cd, Zn or Fe, virus-like particles or other nanoscale protein-only entities. The unexpected potential of such self-organized and functional materials in nanomedical scenarios (especially in drug delivery, imaging and tissue engineering) prompts serious consideration of further exploitation of bacterial cell factories as convenient alternatives to chemical synthesis and as sources of novel bioproducts that could dramatically expand the existing catalog of biomedical materials.

Oral administration of poly-gamma-glutamate induces TLR4- and dendritic cell-dependent antitumor effect

Previously, we reported that the oral administration of high molecular mass poly-gamma-glutamate (gamma-PGA) induced antitumor immunity but the mechanism underlying this antitumor activity was not understood. In the present study, we found that application of high molecular mass gamma-PGA induced secretion of tumor necrosis factor (TNF)-alpha from the bone-marrow-derived macrophages of wild type (C57BL/6 and C3H/HeN) and Toll-like receptor 2 knockout (TLR2(-/-)) mice, but not those of myeloid differentiation factor 88 knockout (MyD88(-/-)) and TLR4-defective mice (C3H/HeJ). Production of interferon (IFN)-gamma-inducible protein 10 (IP-10) in response to treatment with gamma-PGA was almost abolished in C3H/HeJ mice. In contrast to LPS, gamma-PGA induced productions of TNF-alpha and IP-10 could not be blocked by polymyxin B. Furthermore, gamma-PGA-induced interleukin-12 production was also impaired in immature dendritic cells (iDCs) from MyD88(-/-) and C3H/HeJ mice. Downregulation of MyD88 and TLR4 expression using small interfering RNA (siRNA) significantly inhibited gamma-PGA-induced TNF-alpha secretion from the RAW264.7 cells. Gamma-PGA-mediated intracellular signaling was markedly inhibited in C3H/HeJ cells. The antitumor effect of gamma-PGA was completely abrogated in C3H/HeJ mice compared with control mice (C3H/HeN) but significant antitumor effect was generated by the intratumoral administration of C3H/HeN mice-derived iDCs followed by 2,000 kDa gamma-PGA in C3H/HeJ. These findings strongly suggest that the antitumor activity of gamma-PGA is mediated by TLR4.

Production of renewable polymers from crop plants

Plants produce a range of biopolymers for purposes such as maintenance of structural integrity, carbon storage, and defense against pathogens and desiccation. Several of these natural polymers are used by humans as food and materials, and increasingly as an energy carrier. In this review, we focus on plant biopolymers that are used as materials in bulk applications, such as plastics and elastomers, in the context of depleting resources and climate change, and consider technical and scientific bottlenecks in the production of novel or improved materials in transgenic or alternative crop plants. The biopolymers discussed are natural rubber and several polymers that are not naturally produced in plants, such as polyhydroxyalkanoates, fibrous proteins and poly-amino acids. In addition, monomers or precursors for the chemical synthesis of biopolymers, such as 4-hydroxybenzoate, itaconic acid, fructose and sorbitol, are discussed briefly.