Improvement of Biocatalytic Properties and Cytotoxic Activity of L-Asparaginase from Rhodospirillum rubrum by Conjugation with Chitosan-Based Cationic Polyelectrolytes

L-asparaginases (L-ASNases, EC 3.5.1.1) are a family of enzymes that are widely used for the treatment of lymphoblastic leukemias. L-ASNase from Rhodospirillum rubrum (RrA) has a low molecular weight, low glutaminase activity, and low immunogenicity, making it a promising enzyme for antitumor drug development. In our work, the complex formation and covalent conjugation of the enzyme with synthetic or natural polycationic polymers was studied. Among non-covalent polyelectrolyte complexes (PEC), polyethyleneimine (PEI) yielded the highest effect on RrA, increasing its activity by 30%. The RrA-PEI complex had increased stability to trypsinolysis, with an inactivation constant decrease up to 10-fold compared to that of the native enzyme. The covalent conjugation of RrA with chitosan-PEI, chitosan-polyethylene glycol (chitosan-PEG), and chitosan-glycol resulted in an increase in the specific activity of L-asparagine (up to 30%). RrA-chitosan-PEG demonstrated dramatically (by 60%) increased cytotoxic activity for human chronic myeloma leukemia K562 cells in comparison to the native enzyme. The antiproliferative activity of RrA and its conjugates was significantly higher (up to 50%) than for that of the commercially available EcA at the same concentration. The results of this study demonstrated that RrA conjugates with polycations can become a promising strategy for antitumor drug development.

Chemical and physical Chitosan modification for designing enzymatic industrial biocatalysts: How to choose the best strategy?

Chitosan is one of the most abundant natural polymer worldwide, and due to its inherent characteristics, its use in industrial processes has been extensively explored. Because it is biodegradable, biocompatible, non-toxic, hydrophilic, cheap, and has good physical-chemical stability, it is seen as an excellent alternative for the replacement of synthetic materials in the search for more sustainable production methodologies. Thus being, a possible biotechnological application of Chitosan is as a direct support for enzyme immobilization. However, its applicability is quite specific, and to overcome this issue, alternative pretreatments are required, such as chemical and physical modifications to its structure, enabling its use in a wider array of applications. This review aims to present the topic in detail, by exploring and discussing methods of employment of Chitosan in enzymatic immobilization processes with various enzymes, presenting its advantages and disadvantages, as well as listing possible chemical modifications and combinations with other compounds for formulating an ideal support for this purpose. First, we will present Chitosan emphasizing its characteristics that allow its use as enzyme support. Furthermore, we will discuss possible physicochemical modifications that can be made to Chitosan, mentioning the improvements obtained in each process. These discussions will enable a comprehensive comparison between, and an informed choice of, the best technologies concerning enzyme immobilization and the application conditions of the biocatalyst.

Mouse IP-10 Gene Delivered by Folate-modified Chitosan Nanoparticles and Dendritic/tumor Cells Fusion Vaccine Effectively Inhibit the Growth of Hepatocellular Carcinoma in Mice

Dendritic cells (DC) and tumor cell fusion vaccine (DC/tumor cell fusion vaccine) is considered an effective approach in cancer biotherapy. However, its therapeutic effects in early clinical trials have been suboptimal partially due to the immunosuppressive tumor environment. In this study, we used nanoparticles of folate (FA)-modified chitosan, a non-viral vector capable of targeting tumor cells with high expression of FA receptors. FA-chitosan nanoparticles were used as biological carriers for the expression plasmid of the mouse interferon-induced protein-10 (mIP-10) gene, a potent chemoattractant for cytotoxic T cells. The combination of FA-chitosan/mIP-10 and DC/tumor cell fusion vaccine against hepatocellular carcinoma (HCC) effectively inhibited the growth of implanted HCC tumors and prolonged the survival of mice. The combination therapy significantly reduced myeloid-derived suppressor cells (MDSC) in mouse spleen, local tumor, and bone marrow while increasing tumor-specific IFN-γ responses. Furthermore, the combination therapy significantly inhibited tumor cell proliferation while promoting their apoptosis. Taken together, our data illustrate that the mIP-10 enhances the anti-tumor effect of DC/tumor cell fusion vaccine by alleviating the immunosuppressive tumor environment.