Robust anti-obesity and metabolic effects of a dual GLP-1/glucagon receptor peptide agonist in rodents and non-human primates

AIMS

To characterize the pharmacology of MEDI0382, a peptide dual agonist of glucagon-like peptide-1 (GLP-1) and glucagon receptors.

MATERIALS AND METHODS

MEDI0382 was evaluated in vitro for its ability to stimulate cAMP accumulation in cell lines expressing transfected recombinant or endogenous GLP-1 or glucagon receptors, to potentiate glucose-stimulated insulin secretion (GSIS) in pancreatic β-cell lines and stimulate hepatic glucose output (HGO) by primary hepatocytes. The ability of MEDI0382 to reduce body weight and improve energy balance (i.e. food intake and energy expenditure), as well as control blood glucose, was evaluated in mouse models of obesity and healthy cynomolgus monkeys following single and repeated daily subcutaneous administration for up to 2 months.

RESULTS

MEDI0382 potently activated rodent, cynomolgus and human GLP-1 and glucagon receptors and exhibited a fivefold bias for activation of GLP-1 receptor versus the glucagon receptor. MEDI0382 produced superior weight loss and comparable glucose lowering to the GLP-1 peptide analogue liraglutide when administered daily at comparable doses in DIO mice. The additional fat mass reduction elicited by MEDI0382 probably results from a glucagon receptor-mediated increase in energy expenditure, whereas food intake suppression results from activation of the GLP-1 receptor. Notably, the significant weight loss elicited by MEDI0382 in DIO mice was recapitulated in cynomolgus monkeys.

CONCLUSIONS

Repeated administration of MEDI0382 elicits profound weight loss in DIO mice and non-human primates, produces robust glucose control and reduces hepatic fat content and fasting insulin and glucose levels. The balance of activities at the GLP-1 and glucagon receptors is considered to be optimal for achieving weight and glucose control in overweight or obese Type 2 diabetic patients.

Protein engineering and preclinical development of a GM-CSF receptor antibody for the treatment of rheumatoid arthritis

BACKGROUND AND PURPOSE

For antibody therapies against receptor targets, in vivo outcomes can be difficult to predict because of target-mediated clearance or antigen 'sink' effects. The purpose of this work was to engineer an antibody to the GM-CSF receptor α (GM-CSFRα) with pharmacological properties optimized for chronic, s.c. treatment of rheumatoid arthritis (RA) patients.

EXPERIMENTAL APPROACH

We used an in silico model of receptor occupancy to guide the target affinity and a combinatorial phage display approach for affinity maturation. Mechanism of action and internalization assays were performed on the optimized antibody in vitro before refining the modelling predictions of the eventual dosing in man. Finally, in vivo pharmacology studies in cynomolgus monkeys were carried out to inform the predictions and support future clinical development.

KEY RESULTS

Antibody potency was improved 8600-fold, and the target affinity was reached. The refined model predicted pharmacodynamic effects at doses as low as 1 mg kg(-1) and a study in cynomolgus monkeys confirmed in vivo efficacy at 1 mg kg(-1) dosing.

CONCLUSIONS AND IMPLICATIONS

This rational approach to antibody drug discovery enabled the isolation of a potent molecule compatible with chronic, s.c. self-administration by RA patients. We believe this general approach enables the development of optimal biopharmaceuticals.

A series of Fas receptor agonist antibodies that demonstrate an inverse correlation between affinity and potency

Receptor agonism remains poorly understood at the molecular and mechanistic level. In this study, we identified a fully human anti-Fas antibody that could efficiently trigger apoptosis and therefore function as a potent agonist. Protein engineering and crystallography were used to mechanistically understand the agonistic activity of the antibody. The crystal structure of the complex was determined at 1.9 Å resolution and provided insights into epitope recognition and comparisons with the natural ligand FasL (Fas ligand). When we affinity-matured the agonist antibody, we observed that, surprisingly, the higher-affinity antibodies demonstrated a significant reduction, rather than an increase, in agonist activity at the Fas receptor. We propose and experimentally demonstrate a model to explain this non-intuitive impact of affinity on agonist antibody signalling and explore the implications for the discovery of therapeutic agonists in general.

An improved method for an efficient and easily accessible eukaryotic ribosome display technology

Ribosome display is a powerful in vitro technology for the selection and directed evolution of proteins. However, this technology has so far been perceived as being technically challenging owing to comparatively difficult protocols and the absence of tailored commercial reagents, particularly when using prokaryotic cell-free expression systems. Eukaryotic ribosome display is potentially a more accessible alternative because of the availability of suitable commercial reagents, yet despite published protocols, this method has been less widely used. For eukaryotic ribosome display, a novel mechanism of mRNA recovery compared with that of the well-proven prokaryotic method has been proposed. We have examined the eukaryotic ribosome display process with the aims of investigating the proposed mechanism of sequence recovery and of identifying aspects of the protocol that may have lead to poor performance and therefore so far limited its use. We demonstrate that the proposed novel method is in fact mechanistically comparable to the prokaryotic method and we provide a step-by-step protocol for eukaryotic ribosome display that is 20-fold more efficient than current published methods. Our findings should increase the ease of operating ribosome display technology, making it more accessible to the scientific community.

Structure-based chimeric enzymes as an alternative to directed enzyme evolution: phytase as a test case

Thermostability is a key feature for commercially attractive variants of the fungal enzyme phytase. In an initial set of experiments, we restored ionic interactions and hydrogen bonds on the surface of Aspergillus terreus phytase, which are present in the homologous but more thermostable enzyme from A. niger. Since these mutations turned out to be neutral, we replaced-in the same region and based on the crystal structure of A. niger phytase-entire secondary structure elements. The replacement of one alpha-helix on the surface of A. terreus phytase by the corresponding stretch of A. niger phytase resulted in an enzyme with improved thermostability and unaltered enzymatic activity. Surprisingly, the thermostability of this hybrid protein was very similar to that of A. niger phytase, although the fusion protein contained only a 31 amino acid stretch of the more stable parent enzyme. This report provides evidence that structure-based chimeric enzymes can be used to exploit the evolutionary information within a sequence alignment. We propose this method as an alternative to directed enzyme evolution if due to expression constraints the screening of large mutant populations is not feasible.

Tailoring in vitro evolution for protein affinity or stability

We describe a rapid and general technology working entirely in vitro to evolve either the affinity or the stability of ligand-binding proteins, depending on the chosen selection pressure. Tailored in vitro selection strategies based on ribosome display were combined with in vitro diversification by DNA shuffling to evolve either the off-rate or thermodynamic stability of single-chain Fv antibody fragments (scFvs). To demonstrate the potential of this method, we chose to optimize two proteins already possessing favorable properties. A scFv with an initial affinity of 1.1 nM (k(off) at 4 degrees C of 10(-4) s(-1)) was improved 30-fold by the use of off-rate selections over a period of several days. As a second example, a generic selection strategy for improved stability exploited the property of ribosome display that the conditions can be altered under which the folding of the displayed protein occurs. We used decreasing redox potentials in the selection step to select for molecules stable in the absence of disulfide bonds. They could be functionally expressed in the reducing cytoplasm, and, when allowed to form disulfides again, their stability had increased to 54 kJ/mol from an initial value of 24 kJ/mol. Sequencing revealed that the evolved mutant proteins had used different strategies of residue changes to adapt to the selection pressure. Therefore, by a combination of randomization and appropriate selection strategies, an in vitro evolution of protein properties in a predictable direction is possible.

Unbinding forces of single antibody-antigen complexes correlate with their thermal dissociation rates

Point mutants of three unrelated antifluorescein antibodies were constructed to obtain nine different single-chain Fv fragments, whose on-rates, off-rates, and equilibrium binding affinities were determined in solution. Additionally, activation energies for unbinding were estimated from the temperature dependence of the off-rate in solution. Loading rate-dependent unbinding forces were determined for single molecules by atomic force microscopy, which extrapolated at zero force to a value close to the off-rate measured in solution, without any indication for multiple transition states. The measured unbinding forces of all nine mutants correlated well with the off-rate in solution, but not with the temperature dependence of the reaction, indicating that the same transition state must be crossed in spontaneous and forced unbinding and that the unbinding path under load cannot be too different from the one at zero force. The distance of the transition state from the ground state along the unbinding pathway is directly proportional to the barrier height, regardless of the details of the binding site, which most likely reflects the elasticity of the protein in the unbinding process. Atomic force microscopy thus can be a valuable tool for the characterization of solution properties of protein-ligand systems at the single molecule level, predicting relative off-rates, potentially of great value for combinatorial chemistry and biology.

Ribosome display: an in vitro method for selection and evolution of antibodies from libraries

Combinatorial approaches in biology require appropriate screening methods for very large libraries. The library size, however, is almost always limited by the initial transformation steps following its assembly and ligation, as other all screening methods use cells or phages and viruses derived from them. Ribosome display is the first method for screening and selection of functional proteins performed completely in vitro and thus circumventing many drawbacks of in vivo systems. We review here the principle and applications of ribosome display for generating high-affinity antibodies from complex libraries. In ribosome display, the physical link between genotype and phenotype is accomplished by a mRNA-ribosome-protein complex that is used for selection. As this complex is stable for several days under appropriate conditions, very stringent selections can be performed. Ribosome display allows protein evolution through a built-in diversification of the initial library during selection cycles. Thus, the initial library size no longer limits the sequence space sampled. By this method, scFv fragments of antibodies with affinities in the low picomolar range have been obtained. As all steps of ribosome display are carried out entirely in vitro, reaction conditions of individual steps can be tailored to the requirements of the protein species investigated and the objectives of the selection or evolution experiment.

Comparison of Escherichia coli and rabbit reticulocyte ribosome display systems

Ribosome display is a technology for library selection and simultaneous molecular evolution in vitro. We present here a comparison between an optimized Escherichia coli system and different rabbit reticulocyte ribosome display systems, optimized in a number of parameters, as a coupled eukaryotic system had been suggested to result in high enrichment factors [He and Taussig (1997) Nucleic Acids Res. 25, 5132-5134]. With all systems, antibody scFv fragments, complexed to the ribosomes and the corresponding mRNA, were enriched by binding to their cognate antigen and enrichment was always dependent on the absence of a stop codon and the presence of cognate antigen. However, the efficiency of the E. coli ribosome display system was 100-fold higher than an optimized uncoupled rabbit reticulocyte ribosome display system, with separate in vitro transcription and translation, which was in turn several-fold more efficient than the reported coupled system. Neither the E. coli nor the rabbit reticulocyte ribosome display system was dependent on the orientation of the domains of an antibody scFv fragment or on the spacer sequence. In summary, we could not detect any intrinsic advantage of using a eukaryotic translation system for ribosome display.

Disordered C-terminal domain of tyrosyl-tRNA synthetase: secondary structure prediction

The C-terminal domain (residues 320-419) of tyrosyl-tRNA synthetase (TyrRS) from Bacillus stearothermophilus is disordered in the crystal structure and involved in the binding of the anticodon arm of tRNA(Tyr). The sequences of 11 TyrRSs of prokaryotic or mitochondrial origins were aligned and the alignment showed the existence of conserved residues in the sequences of the C-terminal domains. A consensus could be deduced from the application of five programs of secondary structure prediction to the 11 sequences of the query set. These results suggested that the sequences of the C-terminal domains determined a precise and conserved secondary structure. They predicted that the C-terminal domain would have a mixed fold (alpha/beta or alpha+beta), with the alpha-helices in the first half of the sequence and the beta-strands mainly in its second half. Several programs of fold recognition from sequence alone, by threading onto known structures, were applied but none of them identified a type of fold that would be common to the different sequences of the query set. Therefore, the fold of the C-terminal, anticodon binding domain might be novel.

Ribosome display efficiently selects and evolves high-affinity antibodies in vitro from immune libraries

Ribosome display was applied for affinity selection of antibody single-chain fragments (scFv) from a diverse library generated from mice immunized with a variant peptide of the transcription factor GCN4 dimerization domain. After three rounds of ribosome display, positive scFvs were isolated and characterized. Several different scFvs were selected, but those in the largest group were closely related to each other and differed in 0 to 5 amino acid residues with respect to their consensus sequence, the likely common progenitor. The best scFv had a dissociation constant of (4 +/- 1) x 10(-11) M, measured in solution. One amino acid residue in complementarity determining region L1 was found to be responsible for a 65-fold higher affinity than the likely progenitor. It appears that this high-affinity scFv was selected from the mutations occurring during ribosome display in vitro, and that this constitutes an affinity maturation inherent in this method. The in vitro-selected scFvs could be functionally expressed in the Escherichia coli periplasm with good yields or prepared by in vitro refolding. Thus, ribosome display can be a powerful methodology for in vitro library screening and simultaneous sequence evolution.

Recent advances in producing and selecting functional proteins by using cell-free translation

Prokaryotic and eukaryotic in vitro translation systems have recently become the focus of increasing interest for tackling fundamental problems in biochemistry. Cell-free systems can now be used to study the in vitro assembly of membrane proteins and viral particles, rapidly produce and analyze protein mutants, and enlarge the genetic code by incorporating unnatural amino acids. Using in vitro translation systems, display techniques of great potential have been developed for protein selection and evolution. Furthermore, progress has been made to efficiently produce proteins in batch or continuous cell-free translation systems and to elucidate the molecular causes of low yield and find possible solutions for this problem.