Mutational and inhibitory analysis of a catalytic antibody. Implication for drug discovery

Multitarget selection of catalytic antibodies with β-lactamase activity using phage display

β-lactamase enzymes responsible for bacterial resistance to antibiotics are among the most important health threats to the human population today. Understanding the increasingly vast structural motifs responsible for the catalytic mechanism of β-lactamases will help improve the future design of new generation antibiotics and mechanism-based inhibitors of these enzymes. Here we report the construction of a large murine single chain fragment variable (scFv) phage display library of size 2.7 × 10⁹ with extended diversity by combining different mouse models. We have used two molecularly different inhibitors of the R-TEM β-lactamase as targets for selection of catalytic antibodies with β-lactamase activity. This novel methodology has led to the isolation of five antibody fragments, which are all capable of hydrolyzing the β-lactam ring. Structural modeling of the selected scFv has revealed the presence of different motifs in each of the antibody fragments potentially responsible for their catalytic activity. Our results confirm (a) the validity of using our two target inhibitors for the in vitro selection of catalytic antibodies endowed with β-lactamase activity, and (b) the plasticity of the β-lactamase active site responsible for the wide resistance of these enzymes to clinically available inhibitors and antibiotics.

Exploitation of rolling circle amplification for the construction of large phage-display antibody libraries

Phage display antibody libraries have proven to have a significant role in the discovery of therapeutic antibodies and polypeptides with desired biological and physicochemical properties. Obtaining a large and diverse phage display antibody library, however, is always a challenging task. Various steps of this technique can still undergo optimization in order to obtain an efficient library. In the construction of a single chain fragment variable (scFv) phage display library, the cloning of the scFv fragments into a phagemid vector is of crucial importance. An efficient restriction enzyme digestion of the scFv DNA leads to its proper ligation with the phagemid followed by its successful cloning and expression. Here, we are reporting a different approach to enhance the efficiency of the restriction enzyme digestion step. We have exploited rolling circle amplification (RCA) to produce a long strand of DNA with tandem repeats of scFv sequences, which is found to be highly susceptible to restriction digestion. With this important modification, we are able to construct a large phage display antibody library of naive SJL/J mice. The size of the library is estimated as ~10(8) clones. The number of clones containing a scFv fragment is estimated at 90%. Hence, the present results could considerably aid the utilization of the phage-display technique in order to get an efficiently large antibody library.

Catalytic antibodies and their applications in biotechnology: state of the art

Catalytic antibodies are immunoglobulins endowed with enzymatic properties. Discovered in the second part of the 1980s, the enthusiasm they initially aroused was counterbalanced by the difficulty of their production and their low catalytic rates. Nevertheless, improvements in expression systems and engineering technologies, combined with various studies suggesting that catalytic antibodies play a role in the immune system, have opened the way to new applications for these proteins. Herein we review catalytic antibodies from a biotechnological point of view, focusing our study on the different production methods, expression systems and their potential clinical applications dedicated to these proteins.

Efficient refolding of a recombinant abzyme : structural and catalytic characterizations

Catalytic antibodies are currently being investigated in order to understand their role under physio-pathological situations. To this end, the knowledge of structure-function relationships is of great interest. Recombinant scFv fragments are smaller and easier to genetically manipulate than whole antibodies, making them well suited for this kind of study. Nevertheless they are often described as proteins being laborious to produce. This paper describes a highly efficient method to produce large quantities of refolded soluble catalytic scFv. For the first time, the functionality of a refolded catalytic scFv displaying a β-lactamase activity has been validated by three approaches: (1) use of circular dichroism to ensure that the refolded had secondary structure consistent with a native scFv fold, (2) development of enzyme-linked immunosorbant assay and surface plasmon resonance (SPR) approaches for testing that the binding characteristics of an inhibitory peptide have been retained, and (3) proof of the subtle catalytic properties conservation through the development of a new sensitive catalytic assay using a fluorogenic substrate.

Strategies for the selection of catalytic antibodies against organophosphorus nerve agents

Among the strategies aimed at biocompatible means for organophosphorus nerve agents neutralization, immunoglobulins have attracted attention in the 1990's and 2000's both for their ability to immobilize the toxicants, but also for their ability to be turned into enzymatically active antibodies known as catalytic antibodies or abzymes (antibodies--enzymes). We will present here a critical review of the successive strategies used for the selection of these nerve agent-hydrolyzing abzymes, based on hapten design, namely antibodies raised against a wide variety of transition state analogs, and eventually the strategies based on anti-idiotypic antibodies and reactibodies.

Antibody-enzyme fusion proteins for cancer therapy

Advances in biomolecular technology have allowed the development of genetically fused antibody-enzymes. Antibody-enzyme fusion proteins have been used to target tumors for cancer therapy in two ways. In one system, an antibody-enzyme is pretargeted to the tumor followed by administration of an inactive prodrug that is converted to its active form by the pretargeted enzyme. This system has been described as antibody-directed enzyme prodrug therapy. The other system uses antibody-enzyme fusion proteins as direct therapeutics, where the enzyme is toxic in its own right. The key feature in this approach is that the antibody is used to internalize the toxic enzyme into the tumor cell, which activates cell-death processes. This antibody-enzyme system has been largely applied to deliver ribonucleases. This article addresses these two antibody-enzyme targeting strategies for cancer therapy from concept to (pre)clinical trials.