Improvements in single‐use bioreactor film material composition leads to robust and reliable Chinese hamster ovary cell performance

Identification of nonvolatile organic compounds (NVOCs) in biopharmaceuticals through non-target analysis and quantification using complexation-precipitation extraction

Single-use systems in biopharmaceutical manufacturing can potentially release chemical constituents (leachables) into drug products. Prior to conducting toxicological risk assessments, it is crucial to establish the qualitative and quantitative methods for these leachables. In this study, we conducted a comprehensive screening and structure elucidation of 23 leachables (nonvolatile organic compounds, NVOCs) in two antibody drugs using multiple (self-built and public) databases and mass spectral simulation. We identified 7 compounds that have not been previously reported in medical or medicinal extractables and leachables. The confidence levels for identified compounds were classified based on analytical standards, literature references, and fragment assignments. Most of the identified leachables were found to be plasticizers, antioxidants, slip agents or polymer degradants. Polysorbate (namely Tween) is commonly used as an excipient for protein stabilization in biopharmaceutical formulations, but its ionization in liquid chromatography-electrospray ionization mass spectrometry can interfere with compound quantification. To address this, we employed a complexation-precipitation extraction method to reduce polysorbate content and quantify the analytes. The developed quantitative method for target NVOCs demonstrated high sensitivity (limit of quantification: 20 or 50 μg/L), accuracy (recoveries: 77.2 to 109.5 %) and precision (RSD ≤ 8.2 %). Overall, this established method will facilitate the evaluation of NVOC safety in drug products.

Stable Chinese Hamster Ovary Suspension Cell Lines Harboring Recombinant Human Cytochrome P450 Oxidoreductase and Human Cytochrome P450 Monooxygenases as Platform for In Vitro Biotransformation Studies

In the liver, phase-1 biotransformation of drugs and other xenobiotics is largely facilitated by enzyme complexes consisting of cytochrome P450 oxidoreductase (CPR) and cytochrome P450 monooxygenases (CYPs). Generated from human liver-derived cell lines, recombinant in vitro cell systems with overexpression of defined phase-1 enzymes are widely used for pharmacological and toxicological drug assessment and laboratory-scale production of drug-specific reference metabolites. Most, if not all, of these cell lines, however, display some background activity of several CYPs, making it difficult to attribute effects to defined CYPs. The aim of this study was to generate cell lines with stable overexpression of human phase-1 enzymes based on Chinese hamster ovary (CHO) suspension cells. Cells were sequentially modified with cDNAs for human CPR in combination with CYP1A2, CYP2B6, or CYP3A4, using lentiviral gene transfer. In parallel, CYP-overexpressing cell lines without recombinant CPR were generated. Successful recombinant expression was demonstrated by mRNA and protein analyses. Using prototypical CYP-substrates, generated cell lines proved to display specific enzyme activities of each overexpressed CYP while we did not find any endogenous activity of those CYPs in parental CHO cells. Interestingly, cell lines revealed some evidence that the dependence of CYP activity on CPR could vary between CYPs. This needs to be confirmed in further studies. Recombinant expression of CPR was also shown to enhance CYP3A4-independent metabolisation of testosterone to androstenedione in CHO cells. We propose the novel serum-free CHO suspension cell lines with enhanced CPR and/or defined CYP activity as a promising "humanised" in vitro model to study the specific effects of those human CYPs. This could be relevant for toxicology and/or pharmacology studies in the pharmaceutical industry or medicine.

Risk analysis of leachables in cell and gene therapy using a CAR-T model process

With the rapidly emerging field of autologous therapies, Single-Use (SU) technologies are increasingly used in personalized medicine due to their manifold advantages. Although qualification of the starting material of autologous therapies such as the CAR-T process has been highlighted, little attention has been paid to the effect of leachables on cell-based therapies, even if recent studies indicate interactions of leachables with cells. To close this gap, this study presents a risk-analysis of SU-material on a CAR-T process and identifies hazards imposed by tubing materials and leachables thereof. In order to represent a CAR-T process in its entirety, two test systems, namely a lentivirus production process and primary T-cells, were used. While the effects on lentivirus production are comparable to those reported for antibody production processes in CHO cells, we found that PVC material and corresponding leachables, i.e. plasticizer, inhibit cell growth of primary T-cells to a great extent. Additionally, our results indicate that critical quality attributes are affected by the PVC material.

Untargeted proteomics reveals upregulation of stress response pathways during CHO-based monoclonal antibody manufacturing process leading to disulfide bond reduction

Monoclonal antibody (mAb) interchain disulfide bond reduction can cause a loss of function and negatively impact the therapeutic’s efficacy and safety. Disulfide bond reduction has been observed at various stages during the manufacturing process, including processing of the harvested material. The factors and mechanisms driving this phenomenon are not fully understood. In this study, we examined the host cell proteome as a potential factor affecting the susceptibility of a mAb to disulfide bond reduction in the harvested cell culture fluid (HCCF). We used untargeted liquid-chromatography-mass spectrometry-based proteomics experiments in conjunction with a semi-automated protein identification workflow to systematically compare Chinese hamster ovary (CHO) cell protein abundances between bioreactor conditions that result in reduction-susceptible and reduction-free HCCF. Although the growth profiles and antibody titers of these two bioreactor conditions were indistinguishable, we observed broad differences in host cell protein (HCP) expression. We found significant differences in the abundance of glycolytic enzymes, key protein reductases, and antioxidant defense enzymes. Multivariate analysis of the proteomics data determined that upregulation of stress-inducible endoplasmic reticulum (ER) and other chaperone proteins is a discriminatory characteristic of reduction-susceptible HCP profiles. Overall, these results suggest that stress response pathways activated during bioreactor culture increase the reduction-susceptibility of HCCF. Consequently, these pathways could be valuable targets for optimizing culture conditions to improve protein quality.

Interaction of leachable model compounds and their impact on Chinese hamster ovary cell cultivation

The presence of leachables in biopharmaceutical processes using single-use technologies (SUT) is well known. For the detection and quantification of the latter, extractable studies of SUT are very common nowadays. Although a mixture of compounds is regularly found in extractable studies, research has only been carried out regarding the effect of individual compounds on cell culture and the cumulative effect of a mix of leachables has not been investigated yet. In this study, a set of leachable model compounds (LMCs) was chosen and the effect of the LMCs on a Chinese hamster ovary DG44 cell line producing an IgG antibody was investigated concerning cell growth, cell cycle distribution and productivity. It was shown that even if worst-case concentrations were used, the LMCs solely impact cell growth. Additionally, interaction studies revealed that the inhibiting effect of the mix is lower than the expected cumulative effect. A strong antagonism between the antioxidant butylated hydroxytoluene and the plasticizer Tris(2-ethylhexyl)trimellitate was found using an isobologram analysis.

Investigating the pre-lethal cytotoxic effects of bis(2,4-di-tert-butylphenyl)phosphate on Chinese hamster ovary cells using high content analysis

Bis(2,4-di-tert-butylphenyl)Phosphate (bDtBPP) leaches out of polyethylene films used by the biopharmaceutical industry in single-use systems (SUS) for the culturing of drug producing cell lines. Previous studies found bDtBPP (0.025 - 0.110 mg/L) negatively affects Chinese hamster ovary (CHO) cell growth and productivity. Less information is known about the potential early stages of subtle pre-lethal cytotoxic effects of bDtBPP. This study aimed to investigate the pre-lethal cytotoxic effects in CHO-K1 cells of bDtBPP (0.005 - 0.25 μg/ml) at process relevant concentrations following 2, 24 and 48 h exposure, using high content analysis to investigate multiple pre-lethal cytotoxicity markers. After 48 h exposure, bDtBPP (0.005 - 0.25 μg/ml; P ≤ 0.001) increased nuclear intensity. A dose- and time-dependent reduction in mitochondrial mass was seen after exposure to bDtBPP. Reactive oxygen species increased after 2 h exposure to 0.25 μg/ml bDtBPP, 24 and 48 h exposure to 0.05 - 0.25 μg/ml bDtBPP (P ≤ 0.01 and P ≤ 0.001). BDtBPP induced subtle pre-lethal cytotoxic effects on CHO-K1 cellular health. This study highlights the cellular health benefits of the biopharmaceutical industry switching to alternative SUS plastics which do not leach bDtBPP, which may enhance CHO-K1 cell productivity.

Zinc supplementation increases protein titer of recombinant CHO cells

In order to study the impact of zinc and copper on the titer levels of mAb and recombinant protein in CHO cells, the IgG-expressing (DP12) and EPO-expressing (SK15) cell lines were cultured in chemically defined media with increasing concentrations of either metal. Supplementation with 25 mg/l in CDM media resulted in a significant increase in EPO (1.7-fold) and IgG (2.6-fold) titers compared to control (no added zinc). Titers at this Zn concentration in CDM containing the insulin replacing agent aurintricarboxylic acid (ATA) (CDM + A) showed a 1.8-fold (EPO) and 1.2-fold (IgG) titers increase compared to control. ATA appeared to also reduce the specific productivity (Qp) enhancement induced by Zn-25, with up to 4.9-fold (DP12) and 1.9-fold (SK15) Qp increase in CDM compared to the 1.6-fold (DP12) and 1.5-fold (SK15) Qp increase observed in CDM + A. A 31% reduced Viable Cell Density (VCD) in DP12 was observed in both Zn-supplemented media (3 × 106 cells/ml vs 4.2 × 106 cells/ml, day 5), whereas SK15 Zn-25 cultures displayed a 24% lower peak only in CDM + A (2.2 × 106 cells/ml vs 3.2 × 106 cells/ml, day 5). Supplementation with copper at 13.7-20 mg/l resulted in less significant cell line/product-type dependent effects on titer, VCD and Viability. Analysis of the energetic phenotype of both cell lines in 25 mg/l Zn-supplemented CDM media revealed a twofold increase in the oxygen consumption rate (OCR) compared to non-supplemented cells. Together, these data suggest that high zinc supplementation may induce an increase in oxidative respiration metabolism that results in increased Qp and titers in suspension CHO cultures.