Production of Recombinant Denileukin Diftitox: Assessment in the Lab-scale Bioreactor

Denileukin diftitox is a recombinant immunotoxin composed of truncated diphtheria toxin fused to human interleukin 2 (DT389-IL2). It is a candidate for protein therapy of lymphoma. This work aims to investigate DT389-IL2 production using a recombinant strain of Escherichia coli in the lab-scale bioreactor.

First, the effect of chemical composition in culture medium (the complex and defined) was investigated in DT389-IL2 expression in E.coli BL21 (DE3) containing pET-IDZ plasmid in shack flask and lab-bioreactor culture. To enrich the carbon source, we added glucose 6-8 g/L to the complex culture medium. The composition of the defined medium was enriched by adding amino acids (valine, 0.0502; phenylalanine, 0.0132; lysine, 0.0184; aspartic acid, 0.016; and serine, 0.0251 g/L). The growth cell was measured by the optical density method and the expression yield was investigated by SDS-PAGE.

The maximum growth rate was determined in a modified complex culture medium containing glucose (6 g/L).  The bacteria growth in the medium was achieved to the optical density of 5.5 in the shack flask culture, and under the same condition, the optical density of medium increased to 13 in the bioreactor. Adding amino acids to the defined medium significantly enhanced cell growth and expression of proteins. Also, the optical densities of 2.95 and 6.1 were achieved in the shack-flask and bioreactor culture, respectively. The specific growth rates of bacteria in the complex medium and the defined medium were determined as 0.89 and 0.47 h-1, respectively. 

Adding glucose (carbon source) to the complex medium and elemental enrichment by adding amino acids increased biomass production. The growth cell rate in the bioreactor through suitable control of the environmental conditions and proper mixing was higher compared with the shack-flask culture.