The mu-opioid receptor (MOR) is the primary target for opioid analgesics. While opioids are the most frequently used and effective analgesics for the treatment of moderate to severe clinical pain, their prolonged use leads to reduced efficacy and a number of adverse side effects, including post dosing-induced hyperalgesia and analgesic tolerance. MOR induces analgesia through several mechanisms including the inhibition of second messenger pathways and modulation of ion channel activity. Nevertheless, the opposite, opioid induced cellular excitation, has also been demonstrated and proposed to mediate reductions in efficacy, tolerance, and opioid-induced hyperalgesia following the exposure to opioids. While an array of mechanisms has been advanced that contribute to these use-dependence changes in MOR-mediated effects, we have recently identified a novel mechanism underlying the shift in MOR signaling: a MOR splice variant encoding a functional 6 transmembrane (6TM) receptor. This 6TM isoform was identified in a study designed to determine the genetic basis for variability in sensitivity to exogenous opiates. Importantly, morphine exposure to cells overexpressing the 6TM receptor isoform leads to excitatory cellular effects rather than the classic inhibitory effects that are produced by stimulating the canonical 7TM MOR isoform. The discovery of this new alternative 6TM isoform, which evokes responses that oppose the biological effects of the major 7TM isoform, provides a unique opportunity to identify pharmacological probes that will further our understanding of the mechanisms that mediate the pharmacodynamic effects of opioids and will enable the future development of new opioid compounds that show 7TM agonist and/or 6TM antagonist properties providing high analgesic efficacy with a diminished ability to produce post dosing-induced hyperalgesia, analgesic tolerance, and unwanted physiological side effects. To take maximal advantage of this opportunity, an interdisciplinary investigative team with unique, but complementary, areas of expertise has been assembled to develop, validate and characterize the in silico models of the major 7TM and alternative 6TM receptor isoforms can be used to identity putative isoform selective compounds. The long-term goal of this effort is to develop novel opioids that evoke high potency analgesia without deleterious short- or long-term consequences.

Public Health Relevance

While opioids are the most frequently used and effective analgesics for the treatment of moderate to severe clinical pain, their prolonged use leads to a number of treatment limiting side-effects in a large percentage of patients. An experienced multidisciplinary investigative team proposes a set of studies that have derived from new data on the molecular and signaling basis of opioid receptor pharmacology and associated side-effects. These studies will build in silico models of the human 5-opioid receptor isoforms whose activities differentially contribute to the clinical efficacy of opioids and allow identification of novel and potentially a new class of opioid compounds that will show high analgesic properties with a diminished ability to produce opioid-induced hyperalgesia, analgesic tolerance, and unwanted physiological side effects.

National Institute of Health (NIH)
National Institute on Drug Abuse (NIDA)
Small Business Technology Transfer (STTR) Grants - Phase I (R41)
Project #
Application #
Study Section
Special Emphasis Panel (ZRG1-IMST-K (11))
Program Officer
Rapaka, Rao
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Algynomics, Inc.
Chapel Hill
United States
Zip Code
Convertino, Marino; Samoshkin, Alexander; Gauthier, Josee et al. (2015) ?-Opioid receptor 6-transmembrane isoform: A potential therapeutic target for new effective opioids. Prog Neuropsychopharmacol Biol Psychiatry 62:61-7
Convertino, Marino; Samoshkin, Alexander; Viet, Chi T et al. (2015) Differential Regulation of 6- and 7-Transmembrane Helix Variants of ?-Opioid Receptor in Response to Morphine Stimulation. PLoS One 10:e0142826
Samoshkin, Alexander; Convertino, Marino; Viet, Chi T et al. (2015) Structural and functional interactions between six-transmembrane ?-opioid receptors and ?2-adrenoreceptors modulate opioid signaling. Sci Rep 5:18198
Dever, Seth M; Costin, Blair N; Xu, Ruqiang et al. (2014) Differential expression of the alternatively spliced OPRM1 isoform ?-opioid receptor-1K in HIV-infected individuals. AIDS 28:19-30
Diatchenko, Luda; Robinson, J Elliott; Maixner, William (2011) Elucidation of mu-Opioid Gene Structure: How Genetics Can Help Predict Responses to Opioids. Eur J Pain Suppl 5:433-438
Kota, Pradeep; Ding, Feng; Ramachandran, Srinivas et al. (2011) Gaia: automated quality assessment of protein structure models. Bioinformatics 27:2209-15
Serohijos, Adrian W R; Yin, Shuangye; Ding, Feng et al. (2011) Structural basis for ?-opioid receptor binding and activation. Structure 19:1683-90
Gris, Pavel; Cheng, Philip; Pierson, John et al. (2010) Molecular assays for characterization of alternatively spliced isoforms of the u opioid receptor (MOR). Methods Mol Biol 617:421-35
Gris, Pavel; Gauthier, Josee; Cheng, Philip et al. (2010) A novel alternatively spliced isoform of the mu-opioid receptor: functional antagonism. Mol Pain 6:33