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

A New Approach for the Detection and Identification of Protein Impurities Using Combinatorial Solid Phase Ligand Libraries

We propose a novel method for detection of protein impurities present in plasma-derived and recombinant purified injectable biopharmaceuticals by enhancing the concentration of protein impurities, in essence "amplifying" their presence to detectable levels. The method is based on the capture of proteins using a combinatorial solid-phase hexapeptides ligand library previously described for the reduction of protein concentration difference in biological fluids. Three proteins have been investigated: Staphylococcus aureus Protein A, expressed in Escherichia coli and supplied as 99% pure, recombinant human albumin, expressed in Pichia pastoris and certified as 95% pure, and therapeutic albumin supplied as 96-98% pure injectable solution. In all cases, after treatment with the ligand libraries, a number of additional polypeptide chains, not visible in the control, could be detected and obtained in sufficient amounts for MS analysis. In the cases of the two recombinant proteins, it could be demonstrated that a number of these polypeptide chains were host cell proteins still present in the purified product. In addition, a substantial number of these spots were found to be cleavage products of the original recombinant DNA species. Such cleavage products were particularly abundant in the recombinant human albumin preparation. From pure injectable serum albumin, a number of human plasma protein impurities were also identified by LC-MS/MS analysis. Treatment with ligand libraries of purified proteins is thus seen as a very powerful method of capture and concentration of host proteins and cleaved products for further analysis to control better the quality of industrial biotechnology products.

A quantitative slot blot assay for host cell protein impurities in recombinant proteins expressed in E. coli

Residual host cell protein impurities in recombinant proteins intended for human use must be accurately quantified to help establish their safety. We describe a novel means of host cell protein quantitation, in which a slot blot system was employed together with scanning laser densitometry to allow picogram level sensitivity in detection of residual host cell proteins in unpurified fermentation products and final purified bulk samples. Two allelic forms of merozoite surface protein 1, a promising malaria vaccine candidate antigen currently undergoing evaluation in clinical trials, were expressed in E. coli as clinical grade proteins, refolded, and carried through several chromatographic purification steps. Several lots of these proteins were analyzed with this generic quantitative assay that uses rat polyclonal antibodies generated against soluble and insoluble E. coli proteins. The assay had a detection range of 6.1-1562 ng/mL, with a detection limit of 6.1 ng/mL, comparable to reported ELISA-based methods. This assay proved simple yet very sensitive and accurate, giving highly reproducible results. Thus it is suitable for evaluating host cell protein levels in clinical grade recombinant proteins expressed in E. coli.

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.

Development of a quantitative assay for residual host cell proteins in a recombinant subunit vaccine against human respiratory syncytial virus

We have developed and validated a process-specific immunoligand assay based on the Threshold system for the quantification of residual host cell proteins (HCPs) in a recombinant subunit vaccine candidate against the human respiratory syncytial virus (hRSV). The industrial process of this vaccine produced in Escherichia coli, involved five chromatography steps for the production of clinical-grade batches. The clearance of non-product-related protein throughout the purification process was documented by the evaluation of the HCP content in the chromatographic fractions at each step of the downstream processing. The assay had a detection limit of 0.5 ng/ml of HCP equivalent to 10 parts per million (ppm). The quantification limit was 1.3 ng/ml of HCP, giving a sensitivity range of the assay of 10 to 30 ppm. To our knowledge, this is the first sensitive HCP assay reported for a vaccine.

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.