Three opioid receptors, mu, delta and kappa are biologically and clinically important in mediating actions of endogenous and exogenous opioids. Opioid receptor genes have been identified and compounds which serve as specific agonists and antagonists for opioid receptor subtypes have been developed. All opioid analgesics currently in clinical use are mu-agonists that produce severe side effects such as respiratory depression and addiction. Attempts to develop strong analgestics devoid of these side effects have been so far unsuccessful. The recent reports of the first nonpeptide delta-agonist BW373U86 raise the possibility of developing a new class of delta-receptor-based drugs. Using this compound as well as other delta-specific ligands we discovered a yet unreported physiological response of delta-receptors in the CNS. In addition, delta-receptors of T and B lymphocytes were shown to be involved in the stimulation of immune responses, and these same receptors may be important in transplantation immunity as well as in the possible suppression of immunocompetent cells in drug addicts afflicted with AIDS. This project is aimed at better defining the biochemical and molecular basis of delta-opioid receptor system and actions. The delta-opioid receptor belongs to the superfamily of seven-transmembrane receptors and consists of at least three parts: a delta ligand binding protein, a guanine nucleotide regulatory protein (G-protein) that regulates the receptor affinity and serves as a signal transducer, and an effector protein that produces cellular biochemical responses such as inhibition of adenylate cyclase, stimulation of mitogen-activated protein kinase (MAP kinase), ion channel regulation or neurotransmitter release. The biological response to a delta-agonist is a complex function of receptor density, G-proteins class and density, effectors, as well as the ligand's affinity, concentration and intrinsic activity. Full length cDNAs of human delta-receptor and various G-alpha subunits have been cloned. The pertussis toxin-resistant mutants of G-alpha will be prepared and co-expressed with delta-receptor gene in CHO and HEK cells. The adenylyl cyclase inhibition and MAP kinase stimulation will be used to gauge the responses to a series of delta-ligands. Information generated from this proposal will aid in the elucidation of molecular mechanism(s) of delta-opioid receptor actions and provide a rationale for future clinical application, including AIDS, of delta-drugs.
