Design, Synthesis, and Evaluation of New Ligands for G Protein-Coupled Receptors and Kinases

Abstract

Peptidergic G Protein-Coupled Receptors (GPCRs) play a role in many of the most important biological functions, and the ability to modulate the activity of these critical proteins has tremendous potential to increase our understanding of biology and allow the development of new therapeutics. In some cases this knowledge will point towards the importance of interconnected proteins of the same or different classes, such as kinases, which interact in a complex and dynamic network in vivo. Understanding these systems will be crucial for addressing unmet therapeutic needs, and new chemical structures may be important at every step of the process.Our contribution to this pursuit includes the development of new ligands for the melanocortin receptors based on a bicyclic or tricyclic core structure. These were designed to be peptidomimetics, built from amino acids to leverage the accumulated knowledge of the group but with properties that complement those of peptides. Most of the molecules in this series bind to the melanocortin receptors, and many with significant selectivity. Some are selective for the MC5R, which may allow further study of this widely distributed but largely unexplored subtype. Others bind preferentially to the MC1R, a property which may be useful in the development of imaging agents targeting melanoma.Imaging using fluorescent probes can provide a tremendous amount of information in studies of receptor biology. With this in mind, we have developed new fluorescent ligands which bind to melanocortin receptors. These compounds use the previously discovered bicyclic template and incorporate the small organic fluorophores anthranilate and N-methylanthranilate.While these structures are in a sense bifunctional, as they exhibit both pharmacologic and fluorescent activity, other molecules may instead incorporate two different pharmacophores. We have synthesized designed multiple ligands (DMLs) of this type for the opioid and neurokinin receptors, as well as molecules which target both the opioid receptors and p38 MAP kinase. These structures merged known active ligands, such as fentanyl for the opioid activity, into one bifunctional molecule. In addition we have used our newly developed template to create a novel NK1R antagonist which may be part of the next generation of bifunctional ligands.