Raw materials as a source of contamination in large-scale cell culture.

Large-scale cell culture operations for biotechnology products use millions of litres of complex media and gases as well as huge quantities of organic and inorganic raw materials. These raw materials must always be assumed to contain contamination by adventitious agents such as Minute Virus of Mice (MVM). Genentech has had experience in dealing with two such contaminations. Although the source of these contaminations was not positively identified, there was strong evidence to suggest that the virus entered through a raw material used in cell culture. Analytical methods that can be used to detect the presence of viruses can be used as an early warning system and as part of a strategy to devise barriers against such contamination. Methods such as a polymerase chain reaction (PCR) assay and a cell culture-based infectivity assay have been found to be efficacious in providing early detection of MVM infection. In any contamination, timely interactions with regulatory authorities are vital in minimizing delays in product manufacture.

Specifications from a biotechnology industry perspective.

The emergence of new analytical technology and the production of pharmaceuticals for a global market in a cost-effective manner necessitate the establishment of worldwide specifications that are appropriate for the product and the manufacturing process. This requires a thorough knowledge of the protein and control of the systems that produce it as well as an understanding of the accuracy and precision of the assays used for testing. Harmonization of specifications among the worldwide regulatory authorities is critical for the future development of new pharmaceuticals. A continuing dialogue between industry and regulators to achieve this goal needs to be encouraged and supported.

Novel assays based on human growth hormone receptor as alternatives to the rat weight gain bioassay for recombinant human growth hormone.

Two methods, High-Performance Receptor Binding Chromatography (HPRBC) and Cell Proliferation (CP), have been developed as alternatives to the classical hypophysectomized rat weight gain bioassay for the determination of potency for recombinant human growth hormone (rhGH). In the HPRBC assay, rhGH is combined with an excess of the soluble extracellular domain of the recombinant human growth hormone receptor (referred to as 'receptor' in the discussion of the HPRBC assay). Nondenaturing size-exclusion chromatography is used to analyzed the resulting complex, which forms in a 2:1 receptor to rhGH ratio. The 2:1 complex is assayed at a concentration near the Kd (approximately 0.4 nM), providing high specificity for rhGH and detection of rhGH variants with reduced activity. In the CP assay, a mouse myeloid leukaemia cell line (FDC-P1) transfected with the full-length receptor is exposed to varying levels of rhGH for 16-20 h. The incorporation of 3H-thymidine into DNA is used as an index of cell proliferation. The results show that the HPRBC assay provides significantly improved precision with a relative standard deviation (RSD) of < or = 5% vs. an RSD of 23% for the rat bioassay. The CP assay has RSDs of 4-16%. Analysis of rhGH variants and mutants shows that the potencies measured by both the HPRBC and CP assays are in general agreement with the rat weight gain bioassay. Both of the HPRBC and CP assays are sufficiently rugged for operating in a Good Manufacturing Practices (GMP) routine batch release testing environment. In vitro alternatives such as the HPRBC and CP assays build a foundation for replacing the hypophysectomized rat weight gain bioassay by correlating receptor dimerization, binding specificity and signal transduction with the biological activity of rhGH.

Experience with viral contamination in cell culture.

Genentech has had direct experience with two contaminations of large-scale cell cultures by Minute Virus of Mice (MVM). No definitive source of either contamination has been identified, although the conclusions of the investigation were consistent with a raw material used in cell culture as the source. Effective analytical barriers were developed following the first contamination using polymerase chain reaction (PCR) and cell culture-based methodology for MVM, and these were employed on a routine basis. This approach was effectively used to detect and contain the second contamination, thus dramatically minimizing its impact. Close interactions with regulatory authorities were critical in the positive management of these situations.

Peptide mapping for detecting variants in protein products.

The genetic stability of biotechnology production systems is of importance in evaluating the safety and efficacy of protein products. The analysis methods currently available for assessing the genetic stability of such systems are limited by the complexity of the eukaryotic genome and by their inability to predict the effects of post-transcriptional and post-translational events, such as glycosylation or host cell protein level changes, on the protein produced. Therefore, it is important to focus attention on the protein product itself in evaluating product consistency rather than on nucleotide sequence analysis for genetic stability of the production systems involved. Peptide mapping has arisen as the best method for the analysis of proteins as a surrogate measure of genetic stability. This method uses known chemical reactions or enzymes to cleave the protein at specific sites, resulting in discrete peptides whose structure and composition can be readily compared to that of the theoretical protein coded for by the DNA sequence of its gene. Peptide mapping, which is capable of detecting single amino acid changes in a molecule, can also be used for determining glycosylation sites. Peptide mapping requires sophisticated chromatographic techniques and equipment, and is limited to molecules of m.w. of c. 100,000. The method also requires careful validation to limit the potential for misinterpretation of artifactual peaks. Despite its limitations, no better method currently exists to evaluate product consistency and, thereby, the genetic stability of recombinant products.

Quality control issues in the analysis of lyophilized proteins.

The assessment of protein stability requires the use of many sophisticated analytical techniques. Lyophilization procedures, commonly used to improve the stability profile of protein products, may potentiate undesirable protein degradation. The potential effects of lyophilization on proteins may include denaturation, decreased potency, aggregation, oxidation, and deamidation. Methods such as high-performance size-exclusion chromatography (HPSEC), peptide mapping, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and high-performance ion-exchange chromatography (HPIEC) may be used to evaluate these effects as well as to predict the long-term stability of the product. Typical degradation mechanisms of protein products and examples of the methods used for their analysis are described. In addition, methods for monitoring residual moisture levels in lyophilized proteins are presented with emphasis on their relative advantages and disadvantages.

Safety aspects in the quality control of recombinant products from mammalian cell culture.

The recent approval of the recombinant DNA-derived biological, human tissue-type plasminogen activator (rt-PA), obtained from large scale mammalian cell culture, addressed a number of issues concerning the safety of recombinant products. The assurance of the safety of such highly complex proteins requires that the following topics be investigated: the characterisation of the recombinant production organism; control of large scale cell culture production conditions; design of the purification process and consistency of manufacture; the purity, safety, and stability testing of the final product; and clinical studies. Each of the topics described above is discussed with respect to those key quality control issues that ensure the safety of the product. The use of analytical techniques such as peptide mapping and multiantigen ELISA assays to guarantee both the genetic stability and the purity of the final product is also discussed.

The determination of recombinant human tissue-type plasminogen activator activity by turbidimetry using a microcentrifugal analyzer.

A method is described for determining the activity of recombinant human tissue-type plasminogen activator (rt-PA) by turbidimetry using a microcentrifugal analyzer (MCA). A mixture of thrombin and rt-PA is centrifuged into a mixture of fibrinogen and plasminogen to initiate clot formation and subsequent clot dissolution. The resultant profile of absorbance versus time is analyzed to determine the assay endpoint. Different rt-PA assay concentration ranges were studied in conjunction with profile endpoints for assay optimization. Spiked placebo recovery studies were used to evaluate assay accuracy and precision, which were determined to be 99.5 and 5% (relative standard deviation or RSD), respectively. Assay sensitivity was 0.5 ng/ml. Typical analysis time, including calculations, for a standard curve plus 14 samples was less than 30 min. The application of turbidimetry with the MCA for determining rt-PA activity provides rapid sample analysis and high throughput while maintaining accuracy and precision.

High-performance liquid chromatographic assay for sodium levothyroxine in tablet formulations: content uniformity applications.

Sodium levothyroxine was quantitated in 25-300 micrograms/tablet formulations. The procedure consisted of pulverization of a suitable sample, extraction into acetonitrile-water (40:60, v/v) containing 0.05% o-phosphoric acid, and injection onto a bonded-phase cyanopropyl column; the effluent was monitored by UV detection at 225 nm. Spiked placebo recovery studies demonstrated the linearity of the method over the range of 80-120% of the label claim. Stability studies indicated that no degradation products or excipients interfered with the quantitation of the intact drug. Data demonstrating the accuracy and precision of this assay are presented, and the method was applied to the measurement of single-tablet content uniformity.