A CHO-Based Cell-Free Dual Fluorescence Reporter System for the Straightforward Assessment of Amber Suppression and scFv Functionality

A Cost-Effective Pichia pastoris Cell-Free System Driven by Glycolytic Intermediates Enables the Production of Complex Eukaryotic Proteins

Cell-free systems are particularly attractive for screening applications and the production of difficult-to-express proteins. However, the production of cell lysates is difficult to implement on a larger scale due to large time requirements, cultivation costs, and the supplementation of cell-free reactions with energy regeneration systems. Consequently, the methylotrophic yeast Pichia pastoris, which is widely used in recombinant protein production, was utilized in the present study to realize cell-free synthesis in a cost-effective manner. Sensitive disruption conditions were evaluated, and appropriate signal sequences for translocation into ER vesicles were identified. An alternative energy regeneration system based on fructose-1,6-bisphosphate was developed and a ~2-fold increase in protein production was observed. Using a statistical experiment design, the optimal composition of the cell-free reaction milieu was determined. Moreover, functional ion channels could be produced, and a G-protein-coupled receptor was site-specifically modified using the novel cell-free system. Finally, the established P. pastoris cell-free protein production system can economically produce complex proteins for biotechnological applications in a short time.

A disruptive clickable antibody design for the generation of antibody-drug conjugates

Background

Antibody-drug conjugates are cancer therapeutics that combine specificity and toxicity. A highly cytotoxic drug is covalently attached to an antibody that directs it to cancer cells. The conjugation of the drug-linker to the antibody is a key point in research and development as well as in industrial production. The consensus is to conjugate the drug to a surface-exposed part of the antibody to ensure maximum conjugation efficiency. However, the hydrophobic nature of the majority of drugs used in antibody-drug conjugates leads to an increased hydrophobicity of the generated antibody-drug conjugates, resulting in higher liver clearance and decreased stability.

Methods

In contrast, we describe a non-conventional approach in which the drug is conjugated in a buried part of the antibody. To achieve this, a ready-to-click antibody design was created in which an azido-based non-canonical amino acid is introduced within the Fab cavity during antibody synthesis using nonsense suppression technology. The Fab cavity was preferred over the Fc cavity to circumvent issues related to cleavage of the IgG1 lower hinge region in the tumor microenvironment.

Results

This antibody design significantly increased the hydrophilicity of the generated antibody-drug conjugates compared to the current best-in-class designs based on non-canonical amino acids, while conjugation efficiency and functionality were maintained. The robustness of this native shielding effect and the versatility of this approach were also investigated.

Conclusions

This pioneer design may become a starting point for the improvement of antibody-drug conjugates and an option to consider for protecting drugs and linkers from unspecific interactions.

Minimizing the Anticodon-Recognized Loop of Methanococcus jannaschii Tyrosyl-tRNA Synthetase to Improve the Efficiency of Incorporating Noncanonical Amino Acids

In the field of genetic code expansion (GCE), improvements in the efficiency of noncanonical amino acid (ncAA) incorporation have received continuous attention. By analyzing the reported gene sequences of giant virus species, we noticed some sequence differences at the tRNA binding interface. On the basis of the structural and activity differences between Methanococcus jannaschii Tyrosyl-tRNA Synthetase (MjTyrRS) and mimivirus Tyrosyl-tRNA Synthetase (MVTyrRS), we found that the size of the anticodon-recognized loop of MjTyrRS influences its suppression activity regarding triplet and specific quadruplet codons. Therefore, three MjTyrRS mutants with loop minimization were designed. The suppression of wild-type MjTyrRS loop-minimized mutants increased by 1.8–4.3-fold, and the MjTyrRS variants enhanced the activity of the incorporation of ncAAs by 15–150% through loop minimization. In addition, for specific quadruplet codons, the loop minimization of MjTyrRS also improves the suppression efficiency. These results suggest that loop minimization of MjTyrRS may provide a general strategy for the efficient synthesis of ncAAs-containing proteins.

Synthesis of an Anti-CD7 Recombinant Immunotoxin Based on PE24 in CHO and E. coli Cell-Free Systems

Recombinant immunotoxins (RITs) are an effective class of agents for targeted therapy in cancer treatment. In this article, we demonstrate the straight-forward production and testing of an anti-CD7 RIT based on PE24 in a prokaryotic and a eukaryotic cell-free system. The prokaryotic cell-free system was derived from Escherichia coli BL21 StarTM (DE3) cells transformed with a plasmid encoding the chaperones groEL/groES. The eukaryotic cell-free system was prepared from Chinese hamster ovary (CHO) cells that leave intact endoplasmic reticulum-derived microsomes in the cell-free reaction mix from which the RIT was extracted. The investigated RIT was built by fusing an anti-CD7 single-chain variable fragment (scFv) with the toxin domain PE24, a shortened variant of Pseudomonas Exotoxin A. The RIT was produced in both cell-free systems and tested for antigen binding against CD7 and cell killing on CD7-positive Jurkat, HSB-2, and ALL-SIL cells. CD7-positive cells were effectively killed by the anti-CD7 scFv-PE24 RIT with an IC50 value of 15 pM to 40 pM for CHO and 42 pM to 156 pM for E. coli cell-free-produced RIT. CD7-negative Raji cells were unaffected by the RIT. Toxin and antibody domain alone did not show cytotoxic effects on either CD7-positive or CD7-negative cells. To our knowledge, this report describes the production of an active RIT in E. coli and CHO cell-free systems for the first time. We provide the proof-of-concept that cell-free protein synthesis allows for on-demand testing of antibody−toxin conjugate activity in a time-efficient workflow without cell lysis or purification required.