Immunization procedures for E. coli proteins

An enzyme-linked immunosorbent assay for host cell protein contaminants in recombinant PEGylated staphylokinase mutant SY161

Staphylokinase, a bacterially-derived protein which functions as a plasminogen activator, has potential utility as a human therapeutic for thrombotic disorders. A recombinant version of this protein, SY161, contains 13 amino acid substitutions designed to decrease immunogenicity, and has been covalently modified by crosslinking a 5 kDa polyethyleneglycol (PEG) group to the N-terminal region to prolong the drug circulating half-life. The recombinant PEG-modified SY161 staphylokinase is currently in phase II clinical trials as a treatment for acute myocardial infarction. We have developed a sensitive product specific host cell protein (HCP) assay in the ELISA format to monitor in process host-derived contaminant clearance and final drug product purity. The assay is based upon use of goat polyclonal antibodies raised against E. coli host strain cell proteins from a null cell line, extracted by the same manufacturing process used to produce SY161. The identification and clearance of HCP contaminants was confirmed during drug product production using SDS-PAGE and Western blotting utilizing the same polyclonal HCP antibodies. The assay is specific for E. coli host cell strain proteins with a useful detection range from 1 to 100 ng/ml, and is not affected by product level. The level of residual HCPs in the clinical product produced by our manufacturing process was determined to be less than 1 ng/ml at a product concentration of 1 mg/ml.

High-yield purification of biosynthetic human growth hormone secreted in Escherichia coli periplasmic space

A six-step, high-yield purification procedure for the preparation of clinical grade recombinant human growth hormone (rhGH) secreted in bacterial periplasmic space is described. Particular emphasis is given to hormone recovery yields and maximum contaminant host cell elimination. The strategy adopted, in addition to using one precipitation and five chromatographic steps in a particularly efficient sequence, was also based on running E. coli proteins - immunoradiometric assay profiles right after each chromatographic elution. Thus, an overall rhGH recovery higher than 40%, with a final concentration of E. coli proteins below 10 ppm is described for the first time. The accuracy of hGH and total protein quantification, especially in the early steps of the process, and the maximum elimination of hGH-related forms were also studied in detail. For these purposes size-exclusion and reversed-phase HPLC were found to be extremely valuable analytical tools.

An immunoligand assay for quantitation of process specific Escherichia coli host cell contaminant proteins in a recombinant bovine somatotropin

We have developed a Threshold System immunoligand assay for the quantitation of residual, process-specific, Escherichia coli host cell contaminant proteins (HCP) in somavubove (a normal sequence recombinant bovine somatotropin). The assay has a dynamic range of 2 to 160 ng/mL, with a limit of quantitation of 2 ng/mL. Daily analytical precision (CV) for six replicates of the designated somavubove laboratory standard is 3.0%. Cumulative analytical precision for multiple assay runs of this standard (a total of 69 laboratory standard replicates) is 8.4%. A conservative alert limit of 100 ng/mL has been assigned in order to assure analytical precision for each assay sample under conditions of stoichiometric antibody excess. Although the assay was designed for use as a profile-release specification assay, it has also been used to validate removal of HCP by the proprietary somavubove purification process. This use is consistent with regulatory guidelines related to "well characterized" recombinant biopharmaceutical proteins.

Host cell contaminant protein assay development for recombinant biopharmaceuticals

The efficiency and consistency of a biopharmaceutical purification process determines drug quality, including which specific types and concentrations of residual host cell or process contaminants may remain. Commercial reagents and generic analytical methods are available for quantitating most of these contaminants. However, no generic assay is available for quantitation of the specific contaminant host cell proteins (HCPs) which are unique to a novel purification process. Because of this, proprietary reagents and assays must be developed for the quantitation of process-specific HCPs in each biopharmaceutical drug. The need to develop proprietary reagents which are both sensitive to, and specific for, potentially complex mixtures of unique contaminant proteins has defined what is acceptable methodology for development of quantitative HCP assays. Within the biopharmaceutical industry this need is most often satisfied by the development of multi-analyte HCP immunoassays based upon the null cell mock purification model. Confidence in the quantitative nature of a given HCP assay, and the validity of analytical measurement obtained by the assay, is dependent upon empirical demonstration of the unique stoichiometry of the HCP assay reagents. In conjunction with other analytical and validation methods, an HCP immunoassay may be thought of as a necessary quantitative tool for the optimization and validation of biopharmaceutical purification process efficiency and consistency, rather than as an end in itself.