Rational design of peptide ligands for the kappa opioid receptor.

Interest in opioid receptors is focused on the development of strong analgesics devoid of abuse potential and adverse side effects. This task, however, cannot be accomplished without understanding the fundamental opioid receptors structure and function as well as the modes of interactions of ligands, and thus potential drugs, with these receptors. Research in our lab has generated data-verified ligand-receptor interaction models for closely related peptide series at the mu and delta types of opioid receptors. Together with mutagenesis and chimera studies, thus allowed the proposal of specific features of the ligands and their receptors that underlie the ligands' selectivity. Following the same approach, deciphering the details of ligand interactions with the third type of opioid receptor, the kappa opioid receptor (KOR), by analysis of a KOR homology model and examination of tetrapeptide and pentapeptide scaffolds for the development of KOR pharmacophore, is the broad scope of this dissertation project. Thus, starting with the homology model of KOR, structure-based ligands were designed based on JOM-13 (Tyr-c[D-Cys-Phe-D-Pen]OH, SS) and JOM-6 (Tyr-c[D-Cys-Phe-D-Pen]NH 2, SEtS) scaffolds. Specifically, cyclic tetrapeptides were synthesized with various changes in polarity, size, lipophilicity or electronic properties of residues in position 3 and 4 to investigate conformational preferences of diverse side chains within KOR binding pocket. Subsequently, cyclic pentapeptides were studied to develop a more flexible scaffold so that the energy difference between ground and bioactive state was smaller. This could potentially improve KOR binding affinity and selectivity. These studies resulted in the development of a tetrapeptide, MP133, with KOR affinity of 38.7 nM and a pentapeptide, MP148, with KOR affinity of 1.6 nM. In addition, we have developed a novel MOR ligand with 16 pM affinity and selectivity of more than 100 times higher for MOR over DOR or KOR. More importantly, we were able to understand the requirements and features of KOR selective ligands. Among them we discovered the importance of aromatic residue in positions 3 in trans conformation, the presence of D-Cys in place of D-Pen in position 4 (in tetrapeptides) or 5 (in pentapeptides), cyclization via disulfide, and a neutral C-terminus.Ph.D.Analytical chemistryHealth and Environmental SciencesPharmaceutical sciencesPharmacy sciencesPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125479/2/3192757.pd