Cell line specific control of polyethylenimine-mediated transient transfection optimized with “Design of experiments” methodology

Efficient Transfection via an Unexpected Mechanism by Near Neutral Polypiperazines with Tailored Response to Endosomal pH

Cationic pH-responsive polymers promise to overcome critical challenges in cellular delivery. Ideally, the polymers become selectively charged along the endosomal pathway disturbing only the local membrane and avoiding unintended interactions or cytotoxic side effects at physiological conditions. Polypiperazines represent a novel, hydrophilic class of pH-responsive polymers whose response can be tuned within the relevant pH range (5-7.4). The authors discovered that the polypiperazines are effectively binding plasmid DNA (pDNA) and demonstrate high efficiency in transfection. By design of experiments (DoE), a wide parameter space (pDNA and polymer concentration) is screened to identify the range of effective concentrations for transfection. An isopropyl modified polypiperazine is highly efficient over a wide range of concentrations outperforming linear polyethylenimine (l-PEI, 25 kDa) in regions of low N*/P ratios. A quantitative polymerase chain reaction (qPCR) surprisingly revealed that the pDNA within the piperazine-based polyplexes can be amplified in contrast to polyplexes based on l-PEI. The pDNA must therefore be more accessible and bound differently than for other known transfection polymers. Considering the various opportunities to further optimize their structure, polypiperazines represent a promising platform for designing effective soluble polymeric vectors, which are charge-neutral at physiological conditions.

Polycation-Mediated Transfection: Mechanisms of Internalization and Intracellular Trafficking

Polyplex-mediated gene transfection is now in its' fourth decade of serious research, but the promise of polyplex-mediated gene therapy has yet to fully materialize. Only approximately one in a million applied plasmids actually expresses. A large part of this is due to an incomplete understanding of the mechanism of polyplex transfection. There is an assumption that internalization must follow a canonical mechanism of receptor mediated endocytosis. Herein, we present arguments that untargeted (and most targeted) polyplexes do not utilize these routes. By incorporating knowledge of syndecan-polyplex interactions, we can show that syndecans are the "target" for polyplexes. Further, it is known that free polycations (which disrupt cell-membranes by acid-catalyzed hydrolysis of phospholipid esters) are necessary for (untargeted) endocytosis. This can be incorporated into the model to produce a novel mechanism of endocytosis, which fits the observed phenomenology. After membrane translocation, polyplex containing vesicles reach the endosome after diffusing through the actin mesh below the cell membrane. From there, they are acidified and trafficked toward the lysosome. Some polyplexes are capable of escaping the endosome and unpacking, while others are not. Herein, it is argued that for some polycations, as acidification proceeds the polyplexes excluding free polycations, which disrupt the endosomal membrane by acid-catalyzed hydrolysis, allowing the polyplex to escape. The polyplex's internal charge ratio is now insufficient for stability and it releases plasmids which diffuse to the nucleus. A small proportion of these plasmids diffuse through the nuclear pore complex (NPC), with aggregation being the major cause of loss. Those plasmids that have diffused through the NPC will also aggregate, and this appears to be the reason such a small proportion of nuclear plasmids express mRNA. Thus, the structural features which promote unpacking in the endosome and allow for endosomal escape can be determined, and better polycations can be designed.

Design of transfections: Implementation of design of experiments for cell transfection fine tuning

Transfection is the process by which nucleic acids are introduced into eukaryotic cells. This is fundamental in basic research for studying gene function and modulation of gene expression as well as for many bioprocesses in the manufacturing of clinical‐grade recombinant biologics from cells. Transfection efficiency is a critical parameter to increase biologics' productivity; the right protocol has to be identified to ensure high transfection efficiency and therefore high product yield. Design of experiments (DoE) is a mathematical method that has become a key tool in bioprocess development. Based on the DoE method, we developed an operational flow that we called “Design of Transfections” (DoT) for specific transfection modeling and identification of the optimal transfection conditions. As a proof of principle, we applied the DoT workflow to optimize a cell transfection chemical protocol for neural progenitors, using polyethyleneimine (PEI). We simultaneously varied key influencing factors, namely concentration and type of PEI, DNA concentration, and cell density. The transfection efficiency was measured by fluorescence imaging followed by automatic counting of the green fluorescent transfected cells. Taking advantage of the DoT workflow, we developed a new simple, efficient, and economically advantageous PEI transfection protocol through which we were able to obtain a transfection efficiency of 34%.

Development of a high cell density transient CHO platform yielding mAb titers greater than 2 g/L in only 7 days

We developed a simple transient Chinese Hamster Ovary expression platform. Titers for a random panel of 20 clinical monoclonal antibodies (mAbs) ranged from 0.6 to 2.7 g/L after 7 days. Two factors were the key in obtaining these high titers. First, we utilized an extremely high starting cell density (20 million cells/ml), and then arrested further cell growth by employing mild hypothermic conditions (32°C). Second, we performed a 6-variable Design of Experiments to find optimal concentrations of plasmid DNA (coding DNA), boost DNA (DNA encoding the XBP1S transcription factor), transfection reagent (polyethylenimine [PEI]), and nutrient feed amounts. High coding DNA concentrations (12.5 mg/L) were found to be optimal. We therefore diluted expensive coding DNA with inexpensive inert filler DNA (herring sperm DNA). Reducing the coding DNA concentration by 70% from 12.5 to 3.75 mg/L did not meaningfully reduce mAb titers. Titers for the same panel of 20 clinical mAbs ranged from 0.7 to 2.2 g/L after reducing the coding DNA concentration to 3.75 mg/L. Finally, we found that titer and product quality attributes were similar for a clinical mAb (rituximab) expressed at very different scales (volumes ranging from 3 ml to 2 L).

High cell density transient transfection of CHO cells for TGF-β1 expression

High cell densities for transient transfection with polyethyleneimine (PEI) can be used for rapid and maximal production of recombinant proteins. High cell densities can be obtained by different cultivation systems, such as batch or perfusion systems. Herein, densities up to 18 million cells/mL were obtained by centrifugation for transfection evaluation. PEI transfection efficiency was easily determined by transfected enhanced green fluorescence protein (EGFP) reporter plasmid DNA (pDNA). A linear correlation between fluorescence intensity and transfection efficiency was improved. The transfection efficiency of PEI was highly dependent on the transfection conditions and directly related to the level of recombinant protein. Several factors were required to optimize the transient transfection process; these factors included the media type (which is compatible with low or high cell density transfection), the preculture CHO-K1 suspension cell density, and the pDNA to PEI level. Based on design of experiment (DoE) analyses, the optimal transfection conditions for 10 × 10⁶ cells/mL in the CHOMACS CD medium achieved 73% transfection efficiency and a cell viability of over 80%. These results were confirmed for the production of transforming growth factor-beta 1 (TGF-β1) in a shake flask. The purified TGF-β1 protein concentration from 60 mL supernatant was 27 µg/mL, and the protein was biologically active.

Optimization of a high-cell-density polyethylenimine transfection method for rapid protein production in CHO-EBNA1 cells

For pre-clinical evaluation of biotherapeutic candidates, protein production by transient gene expression (TGE) in Chinese Hamster Ovary (CHO) cells offers important advantages, including the capability of rapidly and cost-effectively generating recombinant proteins that are highly similar to those produced in stable CHO clones. We have established a novel CHO clone (CHO-3E7) expressing a form of the Epstein-Barr virus nuclear antigen-1 (EBNA-1) with improved TGE productivity relative to parental CHO cells. Taking advantage of a new transfection-compatible media formulation that permits prolonged, high-density culture, we optimized transfection parameters (cell density, plasmid vector and polyethylenimine concentrations) and post-transfection culture conditions to establish a new, high-performing process for rapid protein production. The growth media is chemically defined, and a single hydrolysate feed is added post-transfection, followed by periodic glucose supplementation. This method gave significantly higher yields than our standard low-cell density, F17-based CHO-3E7 TGE method, averaging several hundred mg/l for a panel of recombinant proteins and antibodies. Purified antibodies produced using the two methods had distinct glycosylation profiles but showed identical target binding kinetics by SPR. Key advantages of this new protein production platform include the cost-effectiveness of the transfection reagent, the commercial availability of the culture media and the ability to perform high-cell-density transfection without media change.

Comparative study of cytotoxicity and genotoxicity of commercial Jeffamines® and polyethylenimine in CHO-K1 cells

Jeffamines^® are a family of polymers containing primary amine groups attached to the extremities of polyether backbone which can be used as biomaterials. They have been used in combination with polyethylenimine (PEI) to improve biocompatibility in drug and gene delivery systems. Despite these facts, very few studies have been done on cytotoxicity and genotoxicity of pure Jeffamines^® or compared with PEI. The present study aimed to evaluate and compare the cytotoxic and genotoxic effects of Jeffamines^® and PEI in CHO-K1 cells. Specifically, polypropylene oxide 2000 (PPO 2000, Jeffamine^® D series), polyethylene oxide 1900 (PEO 1900, Jeffamine^® ED series), branched 25 kDa PEI, and linear 20 kDa PEI were evaluated at different concentrations. Cell viability and proliferation were assessed by 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) and 5-bromo-2'-deoxyuridine (BrdU) assays, respectively. Genotoxicity was evaluated using single cell gel electrophoresis assay and the cytokinesis-blocked micronucleus assay. PPO 2000 was the most cytotoxic Jeffamine^® , whereas PEO 1900 did not caused significant cell death at any tested concentration. Branched PEI was more cytotoxic than linear PEI (LPEI) and both were more cytotoxic than Jeffamines^® . Only PPO 2000 induced DNA damage when evaluated in comet assay probably due to its cytotoxicity. PPO 2000, PEO 1900, and PEI did not increase the frequency of micronuclei when tested at sub-cytotoxic concentrations. This work provides new insights about biocompatibility of Jeffamines^® and PEI and suggests the genotoxicological safety for further investigations of PEO 1900 in drug and gene delivery systems. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 742-750, 2018.

Optimized production of HIV-1 virus-like particles by transient transfection in CAP-T cells

HIV-1 virus-like particles (VLPs) have great potential as new-generation vaccines. The novel CAP-T cell line is used for the first time to produce Gag-GFP HIV-1 VLPs by means of polyethylenimine (PEI)-mediated transient transfection. CAP-T cells are adapted to grow to high cell densities in serum-free medium, and are able to express complex recombinant proteins with human post-translational modifications. Furthermore, this cell line is easily transfected with PEI, which offers the flexibility to rapidly generate and screen a number of candidates in preclinical studies. Transient transfection optimization of CAP-T cells has been performed systematically in this work. It is determined that for optimal production, cells need to be growing at mid-exponential phase, Protein Expression Medium (PEM) medium has to be added post-transfection, and cells can be transfected by independent addition of DNA and PEI with no prior complexation. A Box-Behnken experimental design is used to optimize cell density at time of transfection, DNA/cell and PEI/cell ratios. The optimal conditions determined are transfection at a density of 3.3E + 06 cells/mL with 0.5 pg of DNA/cell and 3 pg of PEI/cell. Using the optimized protocol, 6 × 10(10) VLP/mL are obtained, demonstrating that CAP-T is a highly efficient cell line for the production of HIV-1 VLPs and potentially other complex viral-based biotherapeutics.

Polyethyleneimine-based transient gene expression processes for suspension-adapted HEK-293E and CHO-DG44 cells

•

A brief overview of principles of TGE using mammalian cells.

•

Description of TGE processes for HEK293 and CHO cells.

•

Description of orbitally shaken bioreactors for suspension cell cultivation.

•

Description of polyethylenime-based transfection processes.

Transient gene expression (TGE) from mammalian cells is an increasingly important tool for the rapid production of recombinant proteins for research applications in biochemistry, structural biology, and biomedicine. Here we review methods for the transfection of human embryo kidney (HEK-293) and Chinese hamster ovary (CHO) cells in suspension culture using the cationic polymer polyethylenimine (PEI) for gene delivery.

Breaking limitations of complex culture media: functional non-viral miRNA delivery into pharmaceutical production cell lines

MicroRNAs (miRNAs) are promising targets for cell engineering through modulation of crucial cellular pathways. An effective introduction of miRNAs into the cell is a prerequisite to reliably study microRNA function. Previously, non-viral delivery of nucleic acids has been demonstrated to be cell type as well as culture medium dependent. Due to their importance for biopharmaceutical research and manufacturing, Chinese hamster ovary (CHO) and Cevec's Amniocyte Production (CAP) cells were used as host cell lines to investigate transfection reagents with respect to successful delivery of small non-coding RNAs (ncRNAs) and their ability to allow for biological activity of miRNAs and small interfering RNAs (siRNAs) within the cell. In the present study, we screened numerous transfection reagents for their suitability to successfully deliver miRNA mimics into CHO DG44 and CAP cells. Our investigation revealed that the determination of transfection efficiency for a given transfection reagent alone is not sufficient to draw conclusions about its ability to maintain the functionality of the miRNA. We could show that independent from high transfection rates observed for several reagents only one was suitable for efficient introduction of functional miRNA mimics into cells cultured in complex protein production media. We provide evidence for the functionality of transferred ncRNAs by demonstrating siRNA-mediated changes in protein levels and cellular phenotype as well as decreased twinfilin-1 (twf-1) transcript levels by its upstream miR-1 regulator. Furthermore, the process could be shown to be scalable which has important implications for biotechnological applications.