Studies on two major contaminating proteins of the cytoplasmic inclusion bodies inEscherichia coli

Identification and monitoring of host cell proteins by mass spectrometry combined with high performance immunochemistry testing

Biotherapeutics are often produced in non-human host cells like Escherichia coli, yeast, and various mammalian cell lines. A major focus of any therapeutic protein purification process is to reduce host cell proteins to an acceptable low level. In this study, various E. coli host cell proteins were identified at different purifications steps by HPLC fractionation, SDS-PAGE analysis, and tryptic peptide mapping combined with online liquid chromatography mass spectrometry (LC-MS). However, no host cell proteins could be verified by direct LC-MS analysis of final drug substance material. In contrast, the application of affinity enrichment chromatography prior to comprehensive LC-MS was adequate to identify several low abundant host cell proteins at the final drug substance level. Bacterial alkaline phosphatase (BAP) was identified as being the most abundant host cell protein at several purification steps. Thus, we firstly established two different assays for enzymatic and immunological BAP monitoring using the cobas® technology. By using this strategy we were able to demonstrate an almost complete removal of BAP enzymatic activity by the established therapeutic protein purification process. In summary, the impact of fermentation, purification, and formulation conditions on host cell protein removal and biological activity can be conducted by monitoring process-specific host cell proteins in a GMP-compatible and high-throughput (> 1000 samples/day) manner.

Host cell proteins in biologics development: Identification, quantitation and risk assessment

Host cell proteins (HCPs) are those produced or encoded by the organisms and unrelated to the intended recombinant product. Some are necessary for growth, survival, and normal cellular processing whereas others may be non-essential, simply carried along as baggage. Like the recombinant product, HCPs may also be modified by the host with a number of post-translational modifications. Regardless of the utility, or lack thereof, HCPs are undesirable in the final drug substance. Though commonly present in small quantities (parts per million expressed as nanograms per milligrams of the intended recombinant protein) much effort and cost is expended by industry to remove them. The purpose of this review is to summarize what is of relevance in regards to the biology, the impact of genomics and proteomics on HCP evaluation, the regulatory expectations, analytical approaches, and various methodologies to remove HCPs with bioprocessing. Historical data, bioinformatics approaches and industrial case study examples are provided. Finally, a proposal for a risk assessment tool is provided which brings these facets together and proposes a means for manufacturers to classify and organize a control strategy leading to meaningful product specifications.

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.

Characterization of inclusion bodies in recombinant Escherichia coli producing high levels of porcine somatotropin

The protein composition of inclusion bodies (IBs) formed in recombinant Escherichia coli producing high levels of porcine somatotropin (pST) was analyzed by one- and two-dimensional protein gel electrophoresis. Recombinant pST is exclusively recovered from the insoluble cell fraction. Results indicate that, in addition to the main species of pST, subspecies with different isoelectric points and degradative fragments are contained within IBs. The presence of outer membrane proteins in IB fractions results from coprecipitation of cell debris during IB preparation and not from specific in vivo or in vitro interaction of these proteins with IBs. Cells producing pST contain up to three IBs located in the cytoplasm. The implication of high level gene expression on the uniformity of the desired product is discussed.

Truncation of recombinant vimentin by ompT. Identification of a short motif in the head domain necessary for assembly of type III intermediate filament proteins

Recombinant vimentin expressed in E. coli JM 101 cells is cleaved after cell lysis between arginines 11 and 12. The truncated vimentin is assembly incompetent. Expression of the same cDNA construct in BL21 cells, which lack the protease ompT, provides intact and polymerization-competent vimentin. The ompT cleavage site is contained in a short sequence motif (YRRMF) shared by the head domains of type III and IV intermediate filament (IF) proteins. We propose that a related motif present in the N-terminal 32 residues of lambda CII accounts for the known IF formation of a fusion protein formed with a truncated GFAP.