Structural and functional characterization of the trifunctional antibody catumaxomab.

The Triomab family of trifunctional, bispecific antibodies that maintain an IgG-like shape are novel tumor targeting agents. These chimeras consist of two half antibodies, each with one light and one heavy chain, that originate from parental mouse IgG2a and rat IgG2b isotypes. This combination allows cost-effective biopharmaceutical manufacturing at an industrial scale since this specific mouse/rat isotype combination favors matching of corresponding antibody halves during production by means of quadroma technology. Whereas every Triomab family member is composed of an anti-CD3 rat IgG2b half antibody for T cell recognition, the antigen binding site presented by the mouse IgG2a isotype is exchangeable. Several Triomab antibodies have been generated that bind to tumor-associated antigens, e.g., EpCAM (catumaxomab), HER2/neu (ertumaxomab), CD20 (FBTA05), gangliosides GD2/GD3 (Ektomun), on appropriate tumor target cells associated with carcinomas, lymphomas or melanomas. Catumaxomab (Removab) was launched in Europe for treatment of malignant ascites in April 2009. Here, we report the structural and functional characterization of this product. Mass spectrometry revealed an intact mass of 150511 Dalton (Da) and 23717 Da, 24716 Da, 51957 Da and 52019 Da of the reduced and alkylated rat light chain, mouse light chain, rat heavy chain, mouse heavy chain chains, respectively. The observed masses were in agreement with the expected masses based on the amino acid sequence obtained from cDNA sequencing. The glycosylation profile was similar to other human IgG consisting of biantennary oligosaccharides with different numbers of terminal galactose. CD spectroscopy showed mainly beta-sheets secondary structure that is typical for IgG antibodies. Binding measurement revealed the unique trifunctional features of catumaxomab. Other analytical tools were used to evaluate characteristics of catumaxomab preparations, including the presence of isoforms and aggregates.

Identification and characterization of oxidation and deamidation sites in monoclonal rat/mouse hybrid antibodies.

Oxidation of methionine residues and deamidation of asparagine residues are the major causes of chemical degradation of biological pharmaceuticals. The mechanism of these non-enzymatic chemical reactions has been studied in great detail. However, the identification and quantification of oxidation and deamidation sites in a given protein still remains a challenge. In this study, we identified and characterized several oxidation and deamidation sites in a rat/mouse hybrid antibody. We evaluated the effects of the sample preparation on oxidation and deamidation levels and optimized the peptide mapping method to minimize oxidation and deamidation artifacts. Out of a total number of 18 methionine residues, we identified six methionine residues most susceptible to oxidation. We determined the oxidation rate of the six methionine residues using 0.05% H(2)O(2) at different temperatures. Methionine residue 256 of the mouse heavy chain showed the fastest rate of oxidation under those conditions with a half life of approximately 200 min at 4 degrees C and 27 min at 37 degrees C. We identified five asparagine residues prone to deamidation under accelerated conditions of pH 8.6 at 37 degrees C. Kinetic characterization of the deamidation sites showed that asparagine residue 218 of the rat heavy chain exhibited the fastest rate of deamidation with a half live of 1.5 days at pH 8.6 and 37 degrees C. Analysis of antibody isoforms using free flow electrophoresis showed that deamidation is the major cause of the charged variants of this rat/mouse hybrid antibody.