Characterization and prediction of positional 4-hydroxyproline and sulfotyrosine, two post-translational modifications that can occur at substantial levels in CHO cells-expressed biotherapeutics.

Biotherapeutics may contain a multitude of different post-translational modifications (PTMs) that need to be assessed and possibly monitored and controlled to ensure reproducible product quality. During early development of biotherapeutics, unexpected PTMs might be prevented by in silico identification and characterization together with further molecular engineering. Mass determinations of a human IgG1 (mAb1) and a bispecific IgG-ligand fusion protein (BsAbA) demonstrated the presence of unusual PTMs resulting in major +80 Da, and +16/+32 Da chain variants, respectively. For mAb1, analytical cation exchange chromatography demonstrated the presence of an acidic peak accounting for 20%. A + 79.957 Da modification was localized within the light chain complementarity-determining region-2 and identified as a sulfation based on accurate mass, isotopic distribution, and a complete neutral loss reaction upon collision-induced dissociation. Top-down ultrahigh resolution MALDI-ISD FT-ICR MS of modified and unmodified Fabs allowed the allocation of the sulfation to a specific Tyr residue. An aspartate in amino-terminal position-3 relative to the affected Tyr was found to play a key role in determining the sulfation. For BsAbA, a + 15.995 Da modification was observed and localized to three specific Pro residues explaining the +16 Da chain A, and +16 Da and +32 Da chain B variants. The BsAbA modifications were verified as 4-hydroxyproline and not 3-hydroxyproline in a tryptic peptide map via co-chromatography with synthetic peptides containing the two isomeric forms. Finally, our approach for an alert system based on in-house in silico predictors is presented. This system is designed to prevent these PTMs by molecular design and engineering during early biotherapeutic development.

Comparative label-free monitoring of immunotoxin efficacy in 2D and 3D mamma carcinoma in vitro models by impedance spectroscopy.

For selective killing of tumor cells, there are many novel and promising therapeutic approaches like immunotoxins. However, on the long way to clinical application, especially in vitro approved biologicals often fail due to loss of target sensitivity and efficacy in vivo. This is mostly explained with degradation or penetration disability in vivo. Although, these problems are well known, until today, there are no in vitro systems for reliable monitoring and quantification of therapeutic efficacy in 3D tumor models and the direct comparison to results from 2D models. In this context, we developed a combined label-free impedimetric monitoring system using our self-developed planar interdigital electrode arrays and our unique microcavity array technology. Therefore, we could demonstrate the time and concentration dependent monitoring and quantification of therapeutic efficacy in a 2D and 3D mamma carcinoma model. In detail, we synthesized a novel modular immunotoxin B3(dsFv)-PE38 (B3-PE38) in which the antibody fragment and the protein toxin are polyionic linked together. We compared the efficacy of the immunotoxin B3-PE38, the toxin E8C-PE38 (PE38) and the small molecule chemotherapeutic paclitaxel. The impedimetric screening revealed the highest cytotoxicity for the immunotoxin B3-PE38 in the 2D model. More strikingly, the immunotoxin efficacy was substantially higher in the 3D model when compared to PE38 and paclitaxel even though having a considerably lower penetration capability than paclitaxel. So our novel impedimetric monitoring system offers the comparative efficacy quantification of novel therapeutics in 2D and 3D in vitro tumor models.

Polyionic and cysteine-containing fusion peptides as versatile protein tags.

In response to advances in proteomics research and the use of proteins in medical and biotechnological applications, recombinant protein production and the design of specific protein characteristics and functions has become a widely used technology. In this context, protein fusion tags have been developed as indispensable tools for protein expression, purification, and the design of functionalized surfaces or artificially bifunctional proteins. Here we summarize how positively or negatively charged polyionic fusion peptides with or without an additional cysteine can be used as protein tags for protein expression and purification, for matrix-assisted refolding of aggregated protein, and for coupling of proteins either to technologically relevant matrices or to other proteins. In this context we used cysteine-containing polyionic fusion peptides for the design of immunotoxins. In general, polyionic fusion tags can be considered as a multifunctional module in protein technology.

Autoproteolysis and intramolecular dissociation of Yersinia YscU precedes secretion of its C-terminal polypeptide YscU(CC).

Type III secretion system mediated secretion and translocation of Yop-effector proteins across the eukaryotic target cell membrane by pathogenic Yersinia is highly organized and is dependent on a switching event from secretion of early structural substrates to late effector substrates (Yops). Substrate switching can be mimicked in vitro by modulating the calcium levels in the growth medium. YscU that is essential for regulation of this switch undergoes autoproteolysis at a conserved N↑PTH motif, resulting in a 10 kDa C-terminal polypeptide fragment denoted YscU(CC). Here we show that depletion of calcium induces intramolecular dissociation of YscU(CC) from YscU followed by secretion of the YscU(CC) polypeptide. Thus, YscU(CC) behaved in vivo as a Yop protein with respect to secretion properties. Further, destabilized yscU mutants displayed increased rates of dissociation of YscU(CC)in vitro resulting in enhanced Yop secretion in vivo at 30°C relative to the wild-type strain.These findings provide strong support to the relevance of YscU(CC) dissociation for Yop secretion. We propose that YscU(CC) orchestrates a block in the secretion channel that is eliminated by calcium depletion. Further, the striking homology between different members of the YscU/FlhB family suggests that this protein family possess regulatory functions also in other bacteria using comparable mechanisms.

Listeriolysin O as cytotoxic component of an immunotoxin.

Monoclonal antibodies (mAbs) have been developed over the past years as promising anticancer therapeutics. The conjugation of tumor specific mAbs with cytotoxic molecules has been shown to improve their efficacy dramatically. These bifunctional immunotoxins, consisting of covalently linked antibodies and protein toxins, possess considerable potential in cancer therapy. Many of them are under investigation in clinical trials. As a result of general interest in new toxic components, we describe here the suitability of the bacterial protein Listeriolysin O (LLO) as cytotoxic component of an immunotoxin. Unique characteristics of LLO, such as its acidic pH optimum and the possibility to regulate the cytolytic activity by cysteine-oxidation, make LLO an interesting toxophore. Oxidized LLO shows a substantially decreased cytolytic activity when compared with the reduced protein as analyzed by hemolysis. Both oxidized and reduced LLO exhibit a cell-type-unspecific toxicity in cell culture with a significantly higher toxicity of reduced LLO. For cell-type-specific targeting of LLO to tumor cells, LLO was coupled to the dsFv fragment of the monoclonal antibody B3, which recognizes the tumor-antigen Lewis Y. The coupling of LLO to dsFv-B3 was performed via cysteine-containing polyionic fusion peptides that act as a specific heterodimerization motif. The novel immunotoxin B3-LLO could be shown to specifically eliminate antigen positive MCF7 cells with an EC(50) value of 2.3 nM, whereas antigen negative cell lines were 80- to 250-fold less sensitive towards B3-LLO.