Current projects

1. Development of mixed efficacy opioid ligands
Several reports have suggested that simultaneous administration of mu opioid receptor (MOR) agonists with delta opioid receptor (DOR) antagonists results in analgesia with greatly reduced dependence and tolerance liabilities, features which limit opioid use clinically. Using our validated models for the active (agonist binding) and inactive (antagonist binding) states of MOR and DOR we are developing ligands that act as agonists at MOR and, simultaneously, as antagonists at DOR. Such compounds could have significant clinical value.

2. Design and synthesis of biologically active opioid peptides and peptidomimetics
A main interest in our opioid ligand studies is to be able to use our opioid receptor models to design ligands, sharing a common (or similar) structural scaffold, that are selective for the individual opioid receptors, MOR, DOR, KOR, and the related orphan receptor, ORL1. Many literature reports suggest potential clinical value for agents selective for each of these targets. However, peptides often have properties (too large; too polar; too enzymatically labile) that adversely affect their bioavailability and thus limit their potential as drugs. Consequently we have a strong interest in transferring the key elements of our peptide based structural templates to non-peptide structures (peptidomimetics) and, as in our peptide series, have as the ultimate goal the development of a single central scaffold (or closely related scaffolds) whose differential modification would result in selectivity for different receptors.

3. Investigations of MOR and DOR trafficking and crosstalk
To complement our development of MOR/DOR mixed efficacy ligands, we are also exploring the mechanism by which DOR antagonists, and the DOR receptor itself, affect the development of tolerance and dependence at MOR. To this end we have designed selective fluorescent ligands for MOR and DOR and plan to monitor the trafficking and crosstalk of MOR and DOR in live cell systems using confocal microscopy.

4. Structure-based design of novel thrombin inhibitors
Acute Coronary Syndrome (ACS) and other thrombotic disorders are the most common causes of death in developed countries. Thrombotic disorders most often develop as a result of reduced coronary artery blood supply due to ruptured atherosclerotic plaques, composed largely of aggregated platelets and fibrin clots. The serine protease thrombin plays a key role in both platelet aggregation and fibrin formation, and thus is an attractive target for the development of novel antithrombotic agents. We previously identified a promising lead peptide, FM-19 [D-Arg-Oic-Pro-D-Ala-(pMe)PheNH2], that inhibits thrombin’s actions. The recent x-ray structure of FM19 bound to thrombin facilitates the structure-based design (“rational design”) of new analogs of FM19.

5. Design of inhibitors of GPCR kinases (GRKs)
G protein-coupled receptor kinases (GRKs) catalyze the phosphorylation of serine and threonine residues in activated GPCRs, initiating processes that terminate GPCR signaling. Thus, inhibition of GRK-GPCR interactions represents a potential means of augmenting GPCR-mediated signaling. To pursue this novel approach, we are designing peptides based upon the GRK N-terminus as potential inhibitors of GRK phosphorylation of GPCRs. Since the alpha-helicity of the GRK N-terminus is known to be important for its interaction with receptor, our first approach is the design of peptides with enhanced helical content. This can be achieved by replacing native residues with residues of higher helical propensity or by covalent, helix-stabilizing modifications. Both approaches are being pursued.

6. Homology modeling of GPCRs, important drug targets
A combination of bioinformatics, molecular modeling and experimental techniques is used to obtain structural models of different G protein-coupled receptors, including opioid, melanocortin, PAR, adrenergic, glycoprotein and gonadotropin-releasing hormone receptors. These protein models are invaluable for guiding our design of opioid receptor-specific ligands with desired properties and, more generally, for examining ligand-protein interactions, mechanisms of signaling and transport, to analyze protein polymorphisms, to design site-directed mutagenesis studies, and to develop pharmaco-chaperones and other receptor-specific ligands.

7. Peptides and proteins in membranes
A comprehensive quantitative model of folding, insertion and association of a-helical peptides and proteins in membranes is under development. It combines thermodynamic theory of helix-coil transition in membranes, empirical energy functions derived from protein engineering data, and the new anisotropic solvent model of the lipid bilayer (PPM 2.0). As a part of this project, we have developed the OPM database which provides 3D structures of transmembrane, monotopic and peripheral proteins whose spatial positions are optimized with respect to the lipid bilayer.