Abstract
ABSTRACTThe use of biological systems to synthesize complex therapeutic products has been a remarkable success. However, during product development, great attention must be devoted to defining acceptable levels of impurities that derive from that biological system, heading this list are host cell proteins (HCPs). Recent advances in proteomic analytics have shown how diverse this class of impurities is; as such knowledge and capability grows inevitable questions have arisen about how thorough current approaches to measuring HCPs are. The fundamental issue is how to adequately measure (and in turn monitor and control) such a large number of protein species (potentially thousands of components) to ensure safe and efficacious products. A rather elegant solution is to use an immunoassay (enzyme‐linked immunosorbent assay [ELISA]) based on polyclonal antibodies raised to the host cell (biological system) used to synthesize a particular therapeutic product. However, the measurement is entirely dependent on the antibody serum used, which dictates the sensitivity of the assay and the degree of coverage of the HCP spectrum. It provides one summed analog value for HCP amount; a positive if all HCP components can be considered equal, a negative in the more likely event one associates greater risk with certain components of the HCP proteome. In a thorough risk‐based approach, one would wish to be able to account for this. These issues have led to the investigation of orthogonal analytical methods; most prominently mass spectrometry. These techniques can potentially both identify and quantify HCPs. The ability to measure and monitor thousands of proteins proportionally increases the amount of data acquired. Significant benefits exist if the information can be used to determine critical HCPs and thereby create an improved basis for risk management. We describe a nascent approach to risk assessment of HCPs based upon such data, drawing attention to timeliness in relation to biosimilar initiatives. The development of such an approach requires databases based on cumulative knowledge of multiple risk factors that would require national and international regulators, standards authorities (e.g., NIST and NIBSC), industry and academia to all be involved in shaping what is the best approach to the adoption of the latest bioanalytical technology to this area, which is vital to delivering safe efficacious biological medicines of all types. Biotechnol. Bioeng. 2015;112: 1727–1737. © 2015 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.
Highlights
During manufacturing of therapeutic proteins destined for use in the clinic using cell-based systems, the product itself must be purified from any cell-based impurities to an acceptable level before administration in the clinic
We focus upon impurities that may be derived from mammalian expression systems (e.g., Chinese hamster ovary [CHO] cells), whereby is the product of interest secreted into the cell culture fluid that is collected for harvest, but host cell proteins (HCPs), nucleic acids, lipids, and other cellular material that may be released into the culture media along with product impurities (Guiochon and Beaver, 2011)
Evaluating all the HCP components individually traditionally created an unsustainable position; currently, we seek summative measures based on enzyme-linked immunosorbent assays (ELISAs) using antibodies raised against the spectrum of HCPs found in the host cell being used
Summary
During manufacturing of therapeutic proteins destined for use in the clinic using cell-based systems, the product itself must be purified from any cell-based impurities to an acceptable level before administration in the clinic. Some companies may believe it is sufficient to use commercial ELISA kits and set specifications at 100 ng/mg This approach does give a measure of a level of HCP but in reality, each process and product would benefit from its own specific HCP assay method using null cell lines (not producing product) to develop immunogen. The ICH guidance Q6B (1999) Specifications state that test procedures and acceptance criteria for biotechnological/biological products, guides the setting of acceptance criteria and specifications in which HCPs as process (cell substrate derived) impurities are considered This gives a very high level limit test driven approach, in the case of HCPs, this needs further levels of consideration, principally due to the rapid developments in protein analytical characterization methods. Utilization of polyclonal antibody-based ELISA and Western blot methodologies are invaluable in terms of mapping the potential diversity of HCP populations from initial cell substrate through to purified Drug Substance (Krawitz et al, 2005)
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