Screening of reducing agents for the PEGylation of recombinant human IL-10.

PEGylation is a technology commonly used to enhance the bioavailability of therapeutic proteins in patients. Reductive alkylation of a protein amino terminal alpha amine in the presence of a polyethylene glycol (PEG) chain derivatized with propionaldehyde and a reducing agent, typically sodium cyanoborohydride, is one of the technologies available to achieve quantitative and site specific PEGylation. While cyanoborohydride has proven to be a robust and efficient reagent for this type of reaction, it generates aqueous cyanide as a reaction by-product (and its corollary, the very volatile hydrogen cyanide). We report here the screening of reducing agents such as dimethylamine borane, trimethylamine borane, triethylamine borane, tert-butylamine borane, morpholine borane, pyridine borane, 2-picoline borane, and 5-ethyl-2-methyl-pyridine borane as alternatives to cyanoborohydride for the PEGylation of recombinant human IL-10. The results of our study show that pyridine borane and 2-picoline borane promote rhIL-10 PEGylation at levels comparable to those observed with cyanoborohydride.

Liquid chromatography and mass spectrometry with post-column partial reduction for the analysis of native and scrambled disulfide bonds.

A method capable of detecting both native and scrambled disulfide bonds has been established. Nonreduced protein digests were separated using a reversed-phase C18 column, partially reduced by post-column addition of a reducing reagent, and then analyzed by mass spectrometry. Disulfide bond linkage was established by matching the retention times of cysteine-containing peptides and confirmed by the detection of the molecular weight of the disulfide-linked peptides. The application of this method was demonstrated by determination of the disulfide bond structures of an immunoglobulin G1 (IgG1) molecule and lysozyme and by the detection of four scrambled disulfide bonds in the IgG1 molecule.

Method to convert N-terminal glutamine to pyroglutamate for characterization of recombinant monoclonal antibodies.

Cyclization of N-terminal glutamine to pyroglutamate is a common modification of recombinant monoclonal antibodies that has often been identified by liquid chromatography mass spectrometry (LC-MS) analysis using separated fractions. An alternative approach of using glutaminyl-peptide cyclotransferase to convert the N-terminal glutamine to pyroglutamate was developed in the current study. Enzymatic conversion of the N-terminal glutamine to pyroglutamate not only provides an identification of the N-terminal amino acids without fraction collection but also can significantly simplify the chromatograms to assist fraction collections for the characterization of other antibody variants.

IL-10 elicits IFNγ-dependent tumor immune surveillance.

Tumor immune surveillance and cancer immunotherapies are thought to depend on the intratumoral infiltration of activated CD8(+) T cells. Intratumoral CD8(+) T cells are rare and lack activity. IL-10 is thought to contribute to the underlying immune suppressive microenvironment. Defying those expectations we demonstrate that IL-10 induces several essential mechanisms for effective antitumor immune surveillance: infiltration and activation of intratumoral tumor-specific cytotoxic CD8(+) T cells, expression of the Th1 cytokine interferon-γ (IFNγ) and granzymes in CD8(+) T cells, and intratumoral antigen presentation molecules. Consequently, tumor immune surveillance is weakened in mice deficient for IL-10 whereas transgenic overexpression of IL-10 protects mice from carcinogenesis. Treatment with pegylated IL-10 restores tumor-specific intratumoral CD8(+) T cell function and controls tumor growth.