SBIR-STTR Award

One of the most powerful approaches to drug discovery today is the use of an X-ray crystal structure of the target protein. Termed structure based drug design (SBDD), this approach can accelerate the drug discovery process allowing drugs to reach the market place years sooner. At present, no G-Protein Coupled Receptor (GPCR) X-ray crystal structure has been accomplished. The first major obstacle in GPCR structure determination is the availability of milligram quantities of pure protein. We propose to eliminate this bottleneck through the development of a generally applicable expression and purification system for integral membrane proteins. Specifically, we will use the therapeutically relevant glucagon receptor (GGR) as a model to produce and purify milligrams of active receptor. Extensive protein engineering will be used to produce a protein amenable to crystallization. This will include genetically engineered fusions and truncations. Produced protein will be used to initiate crystallization trials. An X-ray crystal structure of GGR would have a major impact on the design of new pharmaceuticals for the treatment of diabetes and related diseases. PROPOSED COMMERCIAL APPLICATIONS: Drugs that target integral membrane proteins represent greater than 30% of the top selling pharmaceuticals with total annual sales exceeding $60 billion. The proposed research will have a significant impact on the discovery of ethical pharmaceuticals that target membrane proteins. At present, structure-based drug design approaches for G-protein coupled receptor targets are not feasible. This proposal provides an enabling solution to achieving structures of G-protein coupled receptors.

The major objective of this research program is to facilitate novel drug development for G-Protein Coupled Receptors (GPCRs) using high throughput screening (HTS) protein structure-based drug design (SBDD). GPCRs are integral membrane proteins found ubiquitously in human tissues, and are associated with many diseases. The primary focus of this SBDD effort will be based on engineered, soluble, N-terminal extracellular domain analogs of GPCRs. Many GPCRs use a large N-terminal domain as an essential ligand-binding component. Use of these analogs in drug discovery will eliminate the need for detergents and lipids that often complicate HTS and SBDD efforts for GPCRs.In Phase I we constructed a novel, soluble, N-terminal domain analog of the glucagon receptor (N-GGR). Characterization of N-GGR revealed that about80 percent of the binding free energy for glucagon resides within this domain. Importantly, N-GGR discriminates against the related peptide, GLP- 1, and competes with full-length GGR in functional assays. During the Phase II we will determine the X-ray crystal structure of N-GGR and use it as an HTS target for drug discovery. We will also validate N-GGR as a protein therapeutic. In Phase III we will optimize small molecule leads into potential drugs ready for in vivo pre-clinical and clinical testing. PROPOSED COMMERCIAL APPLICATION: Not Available