Application of Genetic Engineering in Biotherapeutics Development

Comparison of Five Escherichia coli Strains to Achieve the Maximum Yield of a Recombinant Immunotoxin Consisting of an Antibody against VEGF Conjugated with MAP30 Toxin in a Benchtop Bioreactor

BACKGROUND

Cancer is among the leading causes of death worldwide, imposing high costs on the health systems of all societies. Extensive biological studies are required to discover appropriate therapies. Escherichia coli has long been regarded as one of the main biotechnological bio-factories to produce recombinant protein-based therapeutics. In the present study, five strains of E. coli were compared to achieve the maximum production of a previously designed recombinant immunotoxin-carrying MAP30 toxin against VEGF-overexpressed cancer cells in a benchtop bioreactor.

METHODS

The recombinant immunotoxin coding gene sequence was extracted from the NCBI database. The host used to produce the recombinant immunotoxin were five E. coli strains of BL21 (DE3), DH5α, SHuffle®T7, XL1-Blue, and Rosetta-gamiTM (DE3). CaCl2 method was used for bacterial transformation. Bacterial growth measurements were performed using optical density measurements at 600 nm. The immunotoxin production was measured using SDS-PAGE analysis. The best-producing strain was cultivated in a 10-L benchtop stirred tank bioreactor. Recent patents on this field were also studied.

RESULTS

The results demonstrated that the BL21 (DE3) strain had the highest expression of recombinant protein in comparison to other strains. Moreover, the cell growth of E. coli BL21 (DE3) and SHuffle®T7 strains before transformation in the LB medium, were significantly higher in comparison to other strains. Additionally, the transformation of Rosettagami was associated with decreased cell proliferation. The transformation of the XL1-Blue strain did not effect cell growth. Analysis of the growth kinetics demonstrated appropriate proliferation of the transformed BL21 (DE3) cells in the laboratory benchtop bioreactor.

CONCLUSIONS

Based on the results of this study, the BL21 (DE3) strain could be used as a suitable host for the production of the recombinant immunotoxin against VEGF in stirred tank bioreactor, which can be employed for the treatment of tumors. Yet, its precise mechanism must be explored in extensive studies.

Targeted integration in CHO cells using CRIS-PITCh/Bxb1 recombinase-mediated cassette exchange hybrid system

Recombinant Chinese hamster ovary (CHO) cell line development for complex biotherapeutic production is conventionally based on the random integration (RI) approach. Due to the lack of control over the integration site and copy number, RI-generated cell pools are always coupled with rigorous screening to find clones that satisfy requirements for production titers, quality, and stability. Targeted integration into a well-defined genomic site has been suggested as a possible strategy to mitigate the drawbacks associated with RI. In this work, we employed the CRISPR-mediated precise integration into target chromosome (CRIS-PITCh) system in combination with the Bxb1 recombinase-mediated cassette exchange (RMCE) system to generate an isogenic transgene-expressing cell line. We successfully utilized the CRIS-PITCh system to target a 2.6 kb Bxb1 landing pad with homology arms as short as 30 bp into the upstream region of the S100A gene cluster, achieving a targeting efficiency of 10.4%. The platform cell line (PCL) with a single copy of the landing pad was then employed for the Bxb1-mediated landing pad exchange with an EGFP encoding cassette to prove its functionality. Finally, to accomplish the main goal of our cell line development method, the PCL was applied for the expression of a secretory glycoprotein, human recombinant soluble angiotensin-converting enzyme 2 (hrsACE2). Taken together, on-target, single-copy, and stable expression of the transgene over long-term cultivation demonstrated our CRIS-PITCh/RMCE hybrid approach might possibly improve the cell line development process in terms of timeline, specificity, and stability. KEY POINTS: • CRIS-PITCh system is an efficient method for single copy targeted integration of the landing pad and generation of platform cell line • Upstream region of the S100A gene cluster of CHO-K1 is retargetable by recombinase-mediated cassette exchange (RMCE) approach and provides a stable expression of the transgene • CRIS-PITCh/Bxb1 RMCE hybrid system has the potential to overcome some limitations of the random integration approach and accelerate the cell line development timeline.