Polyethylene glycol chemical modification

Formulation strategies for stabilization of proteins commonly include additives such as other proteins (e.g., serum albumin), amino acids, and surfactants to minimize adsorption to surfaces. Modification of protein structure to enhance stability by genetic engineering may also be feasible, as well as chemical modification such as formation of a conjugate with polyethylene glycol. 

The improvement of its activity and stability has been approach by the use of GE tools (see Refs. [398] and [399], respectively). A process drawback is the fact that the oxidation of hydrophobic compounds in an organic solvent becomes limited by substrate partition between the active site of the enzyme and the bulk solvent [398], To provide the biocatalyst soluble with a hydrophobic active site access, keeping its solubility in organic solvents, a double chemical modification on horse heart cytochrome c has been performed [400,401], First, to increase the active-site hydrophobicity, a methyl esterification on the heme propionates was performed. Then, polyethylene glycol (PEG) was used for a surface modification of the protein, yielding a protein-polymer conjugates that are soluble in organic solvents. 

Gotoh, Y., Tsukada, M., and Minoura, N. (1993) Chemical modification of silk fibroin with cyanuric chloride-activated polyethylene glycol Analysis of reaction site by 1H-NMR spectroscopy and conformation of the conjugates. Bioconjugate Cbem. 4, 554-559. 

Chemical modification, particularly succinylation, or coupling to polyglycols, can also increase the plasma half-life of enzymes. Conjugation with polyethylene glycol [PEG H(OCH2CH2)nOH] has successfully been employed to stabilize and protect several therapeutic enzymes. Such modification, for example, increases the plasma half-life of superoxide dismutase from 5 h to over 30 h. PEG-coupled asparaginase was approved for general medical use by the FDA in 1994. 

Tsutsumi, Y., M. Onda, S. Nagata, B. Lee, R.J. Kreitman, and I. Pastan, Site-specific chemical modification with polyethylene glycol of recombinant immunotoxin anti-Tac(Fv)-PE38 (LMB-2) improves antitumor activity and reduces animal toxicity and immunogenicity. Proc Natl Acad Sci USA,... 

Katre, N.V., M.I Knauf, and W.J. Laird, Chemical modification of recombinant interleukin 2 by polyethylene glycol increases its potency in the murine Meth A sarcoma model. Rroc Natl Acad Sci USA, 1987. 84(6) 1487-91. 

Inada, Y., Matsushima, A., Hiroto, M., Nishimura, H., Kodera, Y. Chemical Modifications of Proteins with Polyethylen Glycols. Vol. 52, p. 129... 

Effect of Chemical Modification with Polyethylene Glycol on the Brightness Stability of Lignin Model Compounds and High-Yield Pulp... 

COLE ET AL. Chemical Modification with Polyethylene Glycol... 

Y. Kodera, R. Tanaka, A. Matsushima, and Y. Inada. Chemical modification of 1-asparaginase with a comb-shaped copolymer of polyethylene glycol and maleic anhydride. Btcckem. Biaphys. Res. Comnun. 1S4 144 (1992). 

Despite of hybridization with biological ligands, the general strategy for optimizing protein adsorption on biomaterial surfaces relies on chemical or physicochemical modulation of surface hydrophilicity [38,39]. The common approach is surface immobilization of hydrophilic polymers like polyethylene glycol [PEG] or polysaccharides. Four categories of surface-modification pathways have been developed ... 

The second approach involves chemical modification of the protein or peptide by attaching amphiphilic moieties composed of lipophilic alkyl groups and hydrophilic polyethylene glycol units to specific sites on the molecule.In addition to improving stability against enzymatic degradation, this modification is... 

Chemical modification such as adding polyethylene glycol polymers can improve the in vivo characteristics of peptides. An example is CT-025, which is a diconjugate of recombinant salmon calcitonin (sCT).62 The chemical modification of sCT results in an orally available diconjugate that retains hormonal activity while having increased amphiphilicity. Modification can occur at sites where an amine is available. On sCT, there are sites at Cys-1, Lys-11, and Lys 18, as shown in Figure 10.1. 

Although both primary H/T and D/T isotope effects were measured as a function of temperature, the focus of the interpretation was on primary D/T isotope effects, since the smaller commitment for D- than H-transfer leads to a more complete contribution of the chemical step to the measured parameters (see e.g. Section 10.21). The results obtained from this study [92], as well as the earlier work [91], indicate a striking trend in which the value of Ad /At moves from near unity to below unity as the surface of the protein is modified (either by glycosylation or addition of polyethylene glycol). A similar type of pattern has been seen in other enzyme systems, such as the thermophilic ADH [24] (Section 10.5.1.1) and soybean lipoxygenase (SLO) [43] (see Section 10.5.3.1 below) where modification of reaction conditions away from either optimal temperature (ht-ADH) or optimal protein packing (via... 

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