Comparison of modification of a bacterial uricase withN-hydroxysuccinimide esters of succinate and carbonate of monomethoxyl poly(ethylene glycol)

Production of a novel N-terminal PEGylated crisantaspase

Crisantaspase is an asparaginase enzyme produced by Erwinia chrysanthemi and used to treat acute lymphoblastic leukemia (ALL) in case of hypersensitivity to Escherichia coli l-asparaginase (ASNase). The main disadvantages of crisantaspase are the short half-life (10 H) and immunogenicity. In this sense, its PEGylated form (PEG-crisantaspase) could not only reduce immunogenicity but also improve plasma half-life. In this work, we developed a process to obtain a site-specific N-terminal PEGylated crisantaspase (PEG-crisantaspase). Crisantaspase was recombinantly expressed in E. coli BL21(DE3) strain cultivated in a shaker and in a 2-L bioreactor. Volumetric productivity in bioreactor increased 37% compared to shaker conditions (460 and 335 U L^-1  H^-1 , respectively). Crisantaspase was extracted by osmotic shock and purified by cation exchange chromatography, presenting specific activity of 694 U mg^-1 , 21.7 purification fold, and yield of 69%. Purified crisantaspase was PEGylated with 10 kDa methoxy polyethylene glycol-N-hydroxysuccinimidyl (mPEG-NHS) at different pH values (6.5-9.0). The highest N-terminal pegylation yield (50%) was at pH 7.5 with the lowest poly-PEGylation ratio (7%). PEG-crisantaspase was purified by size exclusion chromatography and presented a K_M value three times higher than crisantaspase (150 and 48.5 µM, respectively). Nonetheless, PEG-crisantaspase was found to be more stable at high temperatures and over longer periods of time. In 2 weeks, crisantaspase lost 93% of its specific activity, whereas PEG-crisantaspase was stable for 20 days. Therefore, the novel PEG-crisantaspase enzyme represents a promising biobetter alternative for the treatment of ALL.

Extracorporeal delivery of a therapeutic enzyme

To remove circulating harmful small biochemical(s)/substrates causing/deteriorating certain chronic disease, therapeutic enzyme(s) delivered via vein injection/infusion suffer(s) from immunoresponse after repeated administration at proper intervals for a long time and short half-lives since delivery. Accordingly, a novel, generally-applicable extracorporeal delivery of a therapeutic enzyme is proposed, by refitting a conventional hemodialysis device bearing a dialyzer, two pumps and connecting tubes, to build a routine extracorporeal blood circuit but a minimal dialysate circuit closed to circulate the therapeutic enzyme in dialysate. A special quantitative index was derived to reflect pharmacological action and thus pharmacodynamics of the delivered enzyme. With hyperuricemic blood in vitro and hyperuricemic geese, a native uricase via extracorporeal delivery was active in the dialysate for periods much longer than that in vivo through vein injection, and exhibited the expected pharmacodynamics to remove uric acid in hyperuricemic blood in vitro and multiple forms of uric acid in hyperuricemic geese. Therefore, the extracorporeal delivery approach of therapeutic enzymes was effective to remove unwanted circulating small biochemical(s)/substrates, and was expected to avoid immunogenicity problems of therapeutic enzymes after repeated administration at proper intervals for a long time due to no contacts with macromolecules and cells in the body.

Polymerization of Ethylene Oxide, Propylene Oxide, and Other Alkylene Oxides: Synthesis, Novel Polymer Architectures, and Bioconjugation

The review summarizes current trends and developments in the polymerization of alkylene oxides in the last two decades since 1995, with a particular focus on the most important epoxide monomers ethylene oxide (EO), propylene oxide (PO), and butylene oxide (BO). Classical synthetic pathways, i.e., anionic polymerization, coordination polymerization, and cationic polymerization of epoxides (oxiranes), are briefly reviewed. The main focus of the review lies on more recent and in some cases metal-free methods for epoxide polymerization, i.e., the activated monomer strategy, the use of organocatalysts, such as N-heterocyclic carbenes (NHCs) and N-heterocyclic olefins (NHOs) as well as phosphazene bases. In addition, the commercially relevant double-metal cyanide (DMC) catalyst systems are discussed. Besides the synthetic progress, new types of multifunctional linear PEG (mf-PEG) and PPO structures accessible by copolymerization of EO or PO with functional epoxide comonomers are presented as well as complex branched, hyperbranched, and dendrimer like polyethers. Amphiphilic block copolymers based on PEO and PPO (Poloxamers and Pluronics) and advances in the area of PEGylation as the most important bioconjugation strategy are also summarized. With the ever growing toolbox for epoxide polymerization, a "polyether universe" may be envisaged that in its structural diversity parallels the immense variety of structural options available for polymers based on vinyl monomers with a purely carbon-based backbone.