Biological assays: their role in the development and quality control of recombinant biological medicinal products

Development and application of potency assays based on genetically modified cells for biological products

Potency assays are key to the development, registration, and quality control of biological products. Although previously preferred for clinical relevance, in vivo bioassays have greatly diminished with the advent of dependent cell lines as well as due to ethical concerns. However, for some products, the development of in vitro cell-based assay is challenging, or existing method has limitations such as tedious procedure or low sensitivity. The generation of genetically modified (GM) cell line with improved response to the analyte provides a scientific and promising solution. Potency assays based on GM cell lines are currently used for the quality control of biological products including cytokines, hormones, therapeutic antibodies, vaccines and gene therapy products. In this review, we have discussed the general principles of designing and developing GM cells-based potency assays, including identification of cellular signaling pathways and detectable biological effects, generation of responsive cell lines and constitution of test systems, based on the current research progress. In addition, the applications of some novel technologies and the common concerns regarding GM cells have also been discussed. The research presented in this review provides insights for the development and application of novel GM cells-based potency assays for biological products.

Rapid quantification of multi-cryoprotectant toxicity using an automated liquid handling method

Cryopreservation in a vitrified state has vast potential for long-term storage of tissues and organs that may be damaged by ice formation. However, the toxicity imparted by the high concentration of cryoprotectants (CPAs) required to vitrify these specimens remains a hurdle. To address this challenge, we previously developed a mathematical approach to design less toxic CPA equilibration methods based on the minimization of a toxicity cost function. This approach was used to design improved methods for equilibration of bovine pulmonary artery endothelial cells (BPAEC) with glycerol. To fully capitalize on the toxicity cost function approach, it is critical to describe the toxicity kinetics of additional CPAs, including multi-CPA mixtures that are commonly used for vitrification. In this work, we used automated liquid handling to characterize the toxicity kinetics of five of the most common CPAs (glycerol, dimethyl sulfoxide (DMSO), propylene glycol, ethylene glycol, and formamide), along with their binary and ternary mixtures for BPAEC. In doing so, we developed experimental methods that can be used to determine toxicity kinetics more quickly and accurately. Our results highlight some common CPA toxicity trends, including the relatively low toxicity of ethylene glycol and a general increase in toxicity as the CPA concentration increases. Our results also suggest potential new approaches to reduce toxicity, including a surprising toxicity neutralization effect of glycerol on formamide. In the future, this dataset will serve as the basis to expand our CPA toxicity model, enabling application of the toxicity cost function approach to vitrification solutions containing multiple CPAs.

Evaluation of Structural, Biological, and Functional Similarity of Biosimilar Granulocyte Colony Stimulating Factor to its Reference Product

PURPOSE

Granulocyte colony stimulating factor (GCSF; also known as filgrastim) is a growth factor used to induce production of granulocytes. As the first locally developed and approved biosimilar medicine of Turkey, Fraven® being a biosimilar of filgrastim has been ab initio manufactured from cell to finished product at two different production facilities. Comprehensive structural, biological and functional characterization studies were performed to compare Fraven® from two different production sites and its reference product Neupogen® sourced from Turkey.

METHODS

Primary and higher-order protein structures were analyzed by high performance liquid chromatography electrospray ionization-time of flight mass spectrometry, circular dichroism, and two-dimensional nuclear magnetic resonance spectroscopy. Isoelectric focusing, SDS-Page, size exclusion chromatography, and related proteins analyses were used to compare impurities. In order to assess functional similarity, surface plasmon resonance (SPR) was used. In vitro cell proliferation assay was also performed to show dose related drug response in NFS-60 cell line.

RESULTS

Primary, secondary and tertiary structures of biosimilar Fraven® manufactured at both sites were found to be highly similar to the reference Neupogen®. Product related substances and impurities were also highly similar to the reference. Comparability of GCSF receptor binding affinities of each product was shown using the K_D values of SPR analysis. In vitro cell proliferation similarity was also evaluated and proven by PLA.

CONCLUSION

Based on the similarity assessment, despite being manufactured at two different production sites, biosimilar Fraven® is highly similar to the reference product Turkey originated Neupogen®.

Development and validation of a quantitative cell-based bioassay for comparing the pharmacokinetic profiles of two recombinant erythropoietic proteins in serum

An in vitro cell-based bioassay was developed and validated to assess the pharmacokinetic profiles of two novel therapeutic recombinant proteins (EP1 and EP2) with erythropoiesis stimulating properties in Sprague-Dawley rats. While immunoassays are the standard choice for evaluating the pharmacokinetic parameters of drugs, no immunoassay was available for EP2, necessitating the need for a quantitative bioassay capable of measuring both EP1 and EP2 separately so that appropriate comparisons could be made. The bioassay described here utilizes a sub clone of the murine 32D cell line transfected with the gene encoding for the human erythopoietin (HuEPO) receptor. Erythropoietin (EPO), EP1 and EP2 exert their proliferative effect on the cell line by signaling through the HuEPO receptor. The proliferation induced by the erythropoietic proteins was measured by [methyl-(3)H]thymidine incorporation into the cellular DNA. The assay was conducted in 96-well microtiter plates and had relatively high throughput. The Guidelines of the International Conference on Harmonization (ICH) were followed for the validation of the different assay parameters including robustness, linearity, accuracy, precision, limit of quantitation (LOQ) and specificity. The robustness of the bioassay is demonstrated by the lack of an effect of age of the 32D cell culture on the performance of the EP2 bioassay. The bioassay demonstrated good linearity, yielding a coefficient of determination of 0.99 or higher for both EP1 and EP2. The assay showed reproducible dose-response curves for EP1 in the range of 0.039-2.5 ng/mL and for EP2 in the range of 0.125-8 ng/mL. The accuracy estimates ranged between 98% and 108% for EP1 and between 90% and 110% for EP2 in the reproducible range mentioned above. Intermediate precision (within-plate R.S.D.) in the same range was within 26% and 17% for the EP1 and EP2 bioassays, respectively. The validated bioassays for EP1 and EP2 were utilized to quantitatively analyze serum samples from a pharmacokinetic study conducted to compare the profiles of the two compounds in Sprague-Dawley rats.

Progress in the use of biological assays during the development of biotechnology products

The complexity of the structure and function of many biotechnology derived products necessitates a wide range of analytical procedures to adequately characterize the product. In-depth characterization is required for the assessment of several criteria vital to the success of product development such as consistency, purity, stability, and potency. More recently, the concern over the immunogenicity of biologics has increased the need to develop assays to detect neutralizing anti-product antibodies. Although many physicochemical tests are available to characterize the structure of a protein and detect the presence of contaminants, they provide little, if any, information regarding biological potency or the neutralizing capacity of antibody responses in immunogenicity studies. There is a continual need to refine biological assays to increase their accuracy and reproducibility, in particular to replace in vivo bioassays with appropriate in vitro assays. There have also been several recent technological developments that could lead to more rapid and reproducible bioassays.

Development of a continuous IL-7-dependent murine pre-B cell line PB-1 suitable for the biological characterisation and assay of human IL-7

Human interleukin-7 (IL-7) is a cytokine that appears to be critical for early T- and B-cell development and although IL-7 is currently under investigation as a therapeutic agent in a variety of hematolymphopoietic disorders, there have been few instances of the detection or investigation of this cytokine using a biological assay. This has been due, in the main, to the lack of a widely available, stable, easy to maintain and use, IL-7 responsive cell line. We have developed a pre-B-cell line, PB-1, from murine bone marrow, that is dependent on IL-7 for growth and has been maintained continually for up to 1 year without loss of responsiveness. The cells survive freezing and reviving, having been stored for periods of up to 4 years. The IL-7 bioassay is reproducible and sensitive, able to reliably detect 50 pg/ml IL-7. The assay is completely unresponsive to any other stimulatory cytokines tested and is not affected by a wide variety of inhibitory cytokines, with the exception of high levels of interferon alpha. The assay can be made completely specific for human IL-7 by including specific neutralizing antibodies for IL-7 and has been shown to be suitable for the estimation of IL-7 in both plasma and serum samples.

WHO cytokine standardization: facilitating the development of cytokines in research, diagnosis and as therapeutic agents

The development and widespread application of recombinant DNA technology has dramatically increased the number of cytokines available for clinical evaluation. New and novel cytokines are being discovered, cloned and entered into clinical trials at such a rate that it is often the case that the biological activities of these proteins are poorly understood during their development as therapeutic agents. In addition, manufacturers of any one cytokine can produce the protein from different cellular sources resulting in materials that exhibit markedly different specific activities. When estimating the amount of biological activity of different preparations with different specific activities by bioassay, mass units cannot be used and biological activity is therefore expressed as 'biological potency units'. The biological unit requires definition by a standard that is assay-independent (especially when measuring a particular type of biological activity). In many cases, a variety of assay methods will be available and the material chosen for a standard should ideally be suitable for use with as many of them as possible. Once the unit is defined, this can be used in any laboratory, thus providing a means of ensuring uniformity throughout the world in the designation of potency of different biological preparations. The World Health Organisation (WHO) standardization programme involves the production of biologically stable, well characterised potency and immunoassay standards that are available world-wide using a single international unitage. Over the years, WHO international standards have been used to dramatically reduce the variation in estimates of cytokine preparations within and between laboratories for immunoassays and bioassays. WHO international standards are primary reference preparations against which secondary, or working standards (including regional standards, national standards, pharmacopoeial standards and in-house working standards) can be calibrated.