title: A comparison of noninternalizing (herkinorin) and internalizing (DAMGO) mu-opioid agonists on cellular markers related to opioid tolerance and dependence.
abstract: Previous studies established that Tyr-D-Ala-Gly-N-Me-Phe-Gly-ol (DAMGO) and (2S,4aR,6aR,7R,9S,10aS,10bR)-9-(Benzoyloxy)-2-(3-furanyl)dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-naphtho-[2,1-c]pyran-7-carboxylic acid methyl ester (herkinorin) are fully efficacious mu-agonists. Herkinorin (HERK), unlike DAMGO, does not recruit beta-arrestin and promote mu-receptor internalization, even in cells that over express beta-arrestin. We hypothesized that chronic HERK and DAMGO treatment will differentially affect cellular markers of tolerance and dependence. CHO cells expressing the cloned human mu-receptor were treated for 20 h with 10 microM DAMGO, HERK, morphine, or medium. Both DAMGO and HERK acted as full agonists in the [(35)S]GTP-gamma-S binding assay with E(MAX) values of 230% and EC(50) values of 12.8 and 92.5 nM, respectively. In the cAMP assay, DAMGO and HERK had similar E(MAX) values of approximately 80% and EC(50) values of 3.23 and 48.7 nM, respectively. Chronic exposure to both drugs produced moderate tolerance to both drugs ( approximately 2 to 5 fold) in the [(35)S]GTP-gamma-S binding assay. In the cAMP assay, chronic DAMGO produced tolerance to both drugs ( approximately 3 to 4 fold). Chronic HERK eliminated the ability of either drug to inhibit forskolin-stimulated cAMP accumulation. Chronic DAMGO increased, and chronic HERK decreased, forskolin-stimulated cAMP accumulation. Naloxone, after chronic HERK (but not DAMGO) induced a large increase in forskolin-stimulated cAMP accumulation. Viewed collectively with published data, the current data indicate that both internalizing and noninternalizing mu-agonists produce cellular signs of tolerance and dependence.
authors.affiliation: Clinical Psychopharmacology Section, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, DHHS, Baltimore, Maryland 21224, USA.
authors.forename: Heng
authors.initials: H
authors.lastname: Xu
authors.forename: John S
authors.initials: JS
authors.lastname: Partilla
authors.forename: Xiaoying
authors.initials: X
authors.lastname: Wang
authors.forename: John M
authors.initials: JM
authors.lastname: Rutherford
authors.forename: Kevin
authors.initials: K
authors.lastname: Tidgewell
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Prisinzano
authors.forename: Laura M
authors.initials: LM
authors.lastname: Bohn
authors.forename: Richard B
authors.initials: RB
authors.lastname: Rothman
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D016466:CHO Cells; D002462:Cell Membrane / Q000187:drug effects* / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000032:analysis / Q000378:metabolism; D004361:Drug Tolerance / Q000502:physiology*; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology*; D005663:Furans / Q000494:pharmacology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006801:Humans; D009292:Narcotic Antagonists / Q000494:pharmacology; D009293:Opioid-Related Disorders / Q000378:metabolism* / Q000503:physiopathology; D011753:Pyrones / Q000494:pharmacology*; D011869:Radioligand Assay; D017450:Receptors, Opioid, mu / Q000819:agonists* / Q000235:genetics / Q000378:metabolism
chemical_list: C502982:9-(benzoyloxy)-2-(3-furanyl)dodecahydro-6a,10b-dimethyl-4,10-dioxo-2H-naphtho(2,1-c)pyran-7-carboxylic acid methyl ester; D000701:Analgesics, Opioid; D005663:Furans; D009292:Narcotic Antagonists; D011753:Pyrones; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D005576:Colforsin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000242:Cyclic AMP