Development of small scale cell culture models for screening poloxamer 188 lot-to-lot variation

Synthesis of PEG-Polycycloether Block Copolymers: Poloxamer Mimics Containing a Rigid Helical Block

Poloxamers are amphiphilic block copolymers consisting of poly(ethylene glycol) (PEG) and poly(propylene glycol) segments. Their self-assembly and interfacial properties are tied to the relative hydrophilicity and hydrophobicity of each block and can therefore be adjusted by changing block lengths. Here, a series of PEG-polycycloether block copolymers is synthesized that have the same structure as a poloxamer, but they encompass a rigid polycyclic backbone as the hydrophobic block. A variety of polymer structures are synthesized, for example diblock or triblock architectures, with/without olefinic units, atactic or isotactic backbone, and different block lengths. Due to their amphiphilicity, self-assembly into spherical aggregates (diameters ranging from 64 to 132 nm) at low concentrations (critical aggregation concentration as low as 0.04 mg mL-1) is observed in water. Low surface tensions (as low as 26.7 mN m-1) are observed as well as the formation of stable high internal phase emulsions (HIPEs) irrespective of the oil/water ratio. This contrasts with the properties of the commonly used poloxamers P188 or P407 and illustrates the significance of the rigid polycycloether block. These new colloidal properties offer new prospects for applications in emulsion formulations for biomedicine, cosmetics, and the food industry.

Modulating and optimizing Pluronic F-68 concentrations and feeding for intensified perfusion Chinese hamster ovary cell cultures

Perfusion culture is often performed with micro-sparger to fulfill the high oxygen demand from the densified cells. Protective additive Pluronic F-68 (PF-68) is widely used to mitigate the adverse effect in cell viability from micro-sparging. In this study, different PF-68 retention ratio in alternating tangential filtration (ATF) columns was found to be crucial for cell performance of different perfusion culture modes. The PF-68 in the perfusion medium was found retained inside the bioreactor when exchanged through ATF hollow fibers with a small pore size (50 kD). The accumulated PF-68 could provide sufficient protection for cells under micro-sparging. On the other hand, with large-pore-size (0.2 μm) hollow fibers, PF-68 could pass through the ATF filtration membranes with little retention, and consequently led to compromised cell growth. To overcome the defect, a PF-68 feeding strategy was designed and successfully verified on promoting cell growth with different Chinese hamster ovary (CHO) cell lines. With PF-68 feeding, enhancements were observed in both viable cell densities (20%-30%) and productivity (~30%). A threshold PF-68 concentration of 5 g/L for high-density cell culture (up to 100 × 106  cells/mL) was also proposed and verified. The additional PF-68 feeding was not observed to affect product qualities. By designing the PF-68 concentration of perfusion medium to or higher than the threshold level, a similar cell growth enhancement was also achieved. This study systematically investigated the protecting role of PF-68 in intensified CHO cell cultures, shedding a light on the optimization of perfusion cultures through the control of protective additives.

Effective Cell Transfection in An Ultrasonically Levitated Droplet for Sustainable Technology

The levitation methodology, which enables us to operate a contactless reaction without a container, is likely to be a revolutionary technology in the fields of chemistry and biology to reduce the plastic waste in life science laboratories. Here, the authors show that plasmid DNA can be effectively transfected into animal cells in a floating droplet of culture medium levitated using ultrasonic standing waves. The data indicate that there is no significant damage to the plasmid and cells during the levitating transfection time, and the transgene expression efficiency and cellular uptake in the droplet are significantly higher than those in the conventional tube, with and without shaking. These results suggest the consolidation of the endocytic uptake pathway into macropinocytosis, indicating that ultrasonic levitation induced a change in cell characteristics. This study suggests that transfection methodology using ultrasonic levitation has the potential to advance the current experimental procedures in the field of cell engineering, in addition to presenting a revolutionary containerless reactor for sustainable technology.

Low-molecular-weight impurity in Poloxamer 188 responsible for atypical cell culture performance for mAb production

During a recent manufacturing campaign for a monoclonal antibody using a fed-batch process, poor cell culture performance was observed across two manufacturing sites with similar scales and equipment. Root cause analysis indicated that the poor cell culture performance was linked to the production basal media. Genealogy of the precursor raw materials used in the media revealed that a particular lot of Poloxamer 188 (P188) was the common link to the poor-performing media lots. P188 serves a critical role in protecting cells against shear in cell culture bioprocesses. However, the small-scale studies suggested that the poor cell culture performance was cytostatic in nature rather than being caused due to lack of shear protection. Several P188 lots were tested analytically using SEC-MS and RP-LC-MS methods and a unique low molecular weight species was identified in the suspect lot of poloxamer. The impurity was identified to be polypropylene oxide (PPO), a reaction intermediate in P188 synthesis. Spiking studies with PPO further confirmed its cytostatic nature. This case study highlights yet another scenario where lot-to-lot variability continues to impact bioprocesses and re-emphasizes the need for robust analytical and cell-culture raw material screening methods.

Poloxamer 188 as surfactant in biological formulations - An alternative for polysorbate 20/80?

Surfactants are used to stabilize biologics. Particularly, polysorbates (Tween® 20 and Tween® 80) dominate the group of surfactants in protein and especially antibody drug products. Since decades drug developers rely on the ethoxylated sorbitan fatty acid ester mixtures to stabilize sensitive molecules such as proteins. Reasons are (i) excellent stabilizing properties, and (ii) well recognized safety and tolerability profile of these polysorbates in humans, especially for parenteral applications. However, over the past decade concerns regarding the stability of these two polysorbates were raised. The search of alternatives with preferably less reservations concerning degradation and product quality reducing issues leads, among others, to poloxamer 188 (e.g. Kolliphor® P188), a nonionic triblock-copolymer surfactant. This review sums up our current knowledge related to the characterization and physico-chemical properties of poloxamer 188, its analytics and stability properties for biological formulations. Furthermore, the advantages and disadvantages as a suitable polysorbate-alternative for the stabilization of biologics are discussed.

Development of a small-scale rotary lobe-pump cell culture model for examining cell damage in large-scale N-1 seed perfusion process

Perfusion technology has been identified as a process improvement capable of eliminating some of the constraints in cell culture and allows for high cell densities and viabilities. However, when implementing this N-1 seed perfusion platform in large-scale manufacturing, unexpected cell damage was observed as early as Day 1. Given that the shear rate within recirculation hollow fibers was normalized and aligned correctly across bench, pilot, and manufacture scale, the primary mitigation was placed on the rotary lobe pump. Lowering the pump rate in manufacture scale successfully alleviated the cell damage. To understand the source of cell damage within the pump, a small-scale rotary lobe-pump robustness model was developed. Testing different pump flow rates and back pressures, it was concluded that high back pressure can cause cell damage. The back pressure within the system can cause back flow and high shear within small clearances inside the pump, which lead to the primary cell damage observed at a large scale. This shear level can be significantly higher than the shear in the hollow fiber. This pump robustness model can be utilized to aid the perfusion skid design, including pump operation efficiency and cell shear sensitivity. Methods to reduce the back pressure and cell shearing were determined to better predict manufacturing performance in the future.

A rapid cell-based assay for determining poloxamer quality in CHO suspension cell culture

Poloxamers are water-soluble polymers that are widely used in cell culture bioprocessing to protect cells against shearing forces. Use of poor-quality poloxamers may lead to a drastic reduction in cell growth, viabilities and productivities in cell culture-based manufacturing. In order to evaluate poloxamer quality and promote more consistent performance, a rapid cell membrane adhesion to hydrocarbon assay was developed based on the adhesive properties of cell membranes to selective hydrocarbons. The assay can identify a poor-performing poloxamer characterized by significant drop in viable cell density and percent viability. The assay was verified across multiple good and bad poloxamer lots, and the results were in agreement with established cell growth and high-performance liquid chromatography assays.

Development of a rapid and reliable analytical method for screening poloxamer 188 for use in cell culture process

Poloxamer P188 is a common nonionic surfactant additive used in cell culture media as a cellular protectant from the hydrodynamic forces and shear stress during bioprocessing. Presence of a hydrophobic high molecular weight impurity contaminant has been shown to compromise its protective properties and lead to batch failure. In this work we present, a reliable, sensitive, and rapid analytical method to detect and quantify the contaminant impurity in poloxamer 188. This method replaces a laborious and time-consuming functional test in the form of a shake flask assay. The method is based upon reversed-phase liquid chromatography with charged aerosol detection, simple mobile phase compositions, and a three-step gradient. The method was optimized to resolve the impurity from the main P188 fraction in less than 10 min. Analytical method qualification and functional test comparison demonstrate equivalent or better high throughput impurity screening performance. Attempts to identify the impurity and establish suitable method positive control standards are also discussed.

Impact of Pluronic® F68 on hollow fiber filter-based perfusion culture performance

High cell density is an important factor in achieving high bioreactor productivity. To meet the oxygen demand with density at >100 × 10⁶ cells/mL, a frit sparger is often used. In this study, the impact of Pluronic^® F68 on a perfusion process using a frit sparger was studied. The perfusion process was developed using an alternating tangential flow device with a 0.2 µm PES hollow fiber filter. Pluronic^® F68 at 2 g/L was sufficient in preventing cell damage at gas flow rate of ~0.20 vvm from a drilled hole sparger (0.5 mm) but inadequate at ~0.025 vvm from a frit sparger (20 µm). Increase of Pluronic^® F68 concentration to 5 g/L prevented cell death at up to ~0.10 vvm from the frit sparger and was able to maintain high cell density at high viability in the range of 60-80 × 10⁶ cells/mL. Such positive effect was demonstrated in both 3- and 200-L bioreactors. Supplementing additional Pluronic^® F68 was also effective in restoring cell growth/viability from low viability cultures. Increased Pluronic^® F68 concentration had no adverse impact on target antibody, HCP, and Pluronic^® F68 transmissions.