Optimization of trastuzumab production in the cytoplasm of the engineered Esherichia coli SHuffle strains

Herceptin or trastuzumab (anti-HER2) is a widely used therapeutic antibody to treat breast cancer with 2017 worldwide sales of US$ 7.5 billion. As the patent on Herceptin expired in Europe in July 2014 and in the US in June 2019, its biosimilars developments have been of great interest and some of them have already been approved in many countries. The production of monoclonal antibody is still relied heavily on mammalian cell culture. Nonetheless, for heterologous protein production, Escherichia coli (E. coli) is often considered first if possible as large scale bioprocessing in the bacterial system is simpler and cheaper than the mammalian system. Recently, E. coli strains called SHuffle strains were specifically engineered for expression of multi-disulfide bonded and difficult-to-express proteins. The aim of our study was to investigate the effects of temperature and induction level on full-length trastuzumab production in the cytoplasm of two different types of SHuffle strains at various growth phases in order to identify the suitable conditions. Trastuzumab was produced as `cyclonal' from pMAZ360-cIgG-Herceptin plasmid. Western blot was used to analyze the solubility and relative assembly of full-length trastuzumab produced under each investigated conditions. It was found that the most suitable condition from our study for trastuzumab production in the cytoplasm of the engineered E. coli was the expression at 30°C with 0.1 mM IPTG in SHuffle T7 express, which was developed based on a protease deficient B strain. In the future, these conditions may be used as guidelines for scaling up trastuzumab production in a fermenter for large-scale production.