Efficient on-column conversion of IgG1 trisulfide linkages to native disulfides in tandem with Protein A affinity chromatography.

Protein trisulfide linkages are generated by the post-translational insertion of a sulfur atom into a disulfide bond. Molecular heterogeneity was detected in a recombinant IgG(1) monoclonal antibody (mAb) and attributed to the presence of a protein trisulfide moiety. The predominant site of trisulfide modification was the bond between the heavy and light chains. The trisulfide was eliminated during purification of the IgG(1) mAb via a cysteine wash step incorporated into Protein A affinity column chromatography. Analysis of the cysteine-treated mAb by electrophoresis and peptide mapping indicated that the trisulfide linkages were efficiently converted to intact disulfide bonds (13% trisulfide decreased consistently to 1% or less) without disulfide scrambling or an increase in free sulfhydryls. The on-column trisulfide conversion caused no change in protein folding detectable by hydrogen/deuterium exchange or differential scanning calorimetry. Consistent with this, binding of the mAb to its antigen in vitro was insensitive to the presence of the trisulfide modification and to its removal by the on-column cysteine treatment. Similar, high efficiency trisulfide conversion was achieved for a second IgG(1) mAb using the column wash strategy (at least 7% trisulfide decreased to 1% or less). Therefore, trisulfide/disulfide heterogeneity can be eliminated from IgG(1) molecules via a convenient and inexpensive procedure compatible with routine Protein A affinity capture.

Concentration of proteins and removal of solutes.

The dramatic advances in recombinant DNA and proteomics technology over the past decade have supported a tremendous growth in biologics applied to diagnostics, biomarkers, and commercial therapeutic markets. In particular, antibodies and fusion proteins have now become a main focus for a broad number of clinical indications, including neurology, oncology, and infectious diseases with projected increase in novel first-class molecules and biosimilar entities over the next several years. In line with these advances are the improved analytical, development, and small-scale preparative methods employed to elucidate biologic structure, function, and interaction. A number of established methods are used for solvent removal, including lyophilization, reverse extraction, solute precipitation, and dialysis (solvent exchange), ultrafiltration, and chromatographic techniques. Notably, advances in the miniaturization and throughput of protein analysis have been supported by the development of a plethora of microscale extraction procedures and devices that exploit a wide array of modes for small-scale sample preparation, including the concentration and desalting of protein samples prior to further analysis. Furthermore, advances in process handling and data monitoring at microscale have dramatically improved complex control and product recovery of small quantities of biologics using techniques such as lyophilization and precipitation. In contrast, the efficient concentration of feed streams during preparative chromatography has been enhanced by improvements to protein binding capacity achieved through advanced bead and ligand design. The objective of solvent removal may be to prepare or concentrate solutes for analysis, or to facilitate their production or modification. Here, we describe the most recent advances in these techniques, particularly focusing on improved capabilities for bench-scale preparative methods.

Purification of an Fc-fusion biologic: clearance of multiple product related impurities by hydrophobic interaction chromatography.

An hydrophobic interaction chromatography step was developed for the large-scale production of an Fc-fusion biologic. Two abundant product-related impurities were separated from the active monomer using a Butyl resin and a simple step-wash and step-elution strategy. Capacity and resolution of the HIC step was optimal when sodium sulfate was employed as the lyotropic salt and pore size of the Butyl resin was 750A. Factorial analysis identified critical parameters for the Butyl chromatography and an operating window capable of delivering high product quality and yield over a broad column loading range.

"One plate/three-reporter" assay format for the detection and validation of yeast two-hybrid interactions.

We describe a novel assay format for the Gal4-based yeast two-hybrid-system, in which the readout from three different reporter genes is measured sequentially in a single microplate. Activation of the URA3, MEL1, and lacZ reporters in response to a protein-protein interaction is monitored by measuring sequentially: (i) growth in medium lacking uracil, (ii) alpha-galactosidase activity, and (iii) beta-galactosidase. The data thus generated permit elimination of many false positive signals and provide a preliminary measurement of reporter activation-strength that may be confirmed by further analysis. The assay procedure is inexpensive and requires few liquid-handling steps. It is appropriate for automated high-throughput interaction mating assays, validation of putative interactor strains and hybrid-protein self-activator tests.

Cell-based assays for identification of novel double-strand break-inducing agents.

BACKGROUND: We are developing cell-based assays to identify anticancer agents that are selectively toxic to cells with defined mutations. As a test, we used a three-stage strategy to screen compounds from the National Cancer Institute's repository for agents that are selectively toxic to double-strand break repair-deficient yeast cells. METHODS: Compounds identified in the screen were further analyzed by use of yeast and vertebrate cell-based and in vitroassays to distinguish between topoisomerase I and II poisons. RESULTS: Of the more than 85 000 compounds screened, 126 were selectively toxic to yeast deficient in DNA double-strand break repair. Eighty-seven of these 126 compounds were structurally related to known topoisomerase poisons, and 39 were not. Twenty-eight of the 39 were characterized, and we present data for eight of the compounds. Among these eight compounds, we identified two novel topoisomerase II poisons (NSC 327929 and NSC 638432) that were equipotent to etoposide in biochemical tests and in cells, five (NSC 63599, NSC 65601, NSC 380271, NSC 651646, and NSC 668370) with topoisomerase I-dependent toxicity in yeast that induced DNA damage and toxicity in mammalian cells, and one (NSC 610898) that directly bound to DNA and induced strand breaks. CONCLUSIONS: Cell-based assays can be used to identify molecules that are selectively toxic to cells with a predetermined genetic background, including mutations in genes involved in the cell cycle and its checkpoints, for which there are currently no selectively toxic compounds.