@article {Zhao947, author = {Guo-Min Zhao and Xuanxuan Qian and Peter W. Schiller and Hazel H. Szeto}, title = {Comparison of [Dmt1]DALDA and DAMGO in Binding and G Protein Activation at μ, δ, and κ Opioid Receptors}, volume = {307}, number = {3}, pages = {947--954}, year = {2003}, doi = {10.1124/jpet.103.054775}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {[Dmt1]DALDA (H-Dmt-d-Arg-Phe-Lys-NH2; Dmt = 2',6'-dimethyltyrosine) binds with high affinity and selectivity to the μ opioid receptor and is a surprisingly potent and long-acting analgesic, especially after intrathecal administration. In an attempt to better understand the unique pharmacological profile of [Dmt1]DALDA, we have prepared [3H][Dmt1]DALDA and compared its binding properties with that of [3H]DAMGO ([d-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin). Kinetic studies revealed rapid association of [3H][Dmt1]DALDA when incubated with mouse brain membranes (K+1 = 0.155 nM{\textendash}1 min{\textendash}1). Dissociation of [3H][Dmt1]DALDA was also rapid (K{\textendash}1 = 0.032 min{\textendash}1) and indicated binding to a single site. [3H][Dmt1]DALDA binds with very high affinity to human μ opioid receptor (hMOR) (Kd = 0.199 nM), and Kd and Bmax were reduced by sodium but not Gpp(NH)p [guanosine 5'-(β,γ-imido)triphosphate]. Similar Kd values were obtained in brain and spinal cord tissues and SH-SY5Y cells. The hMOR:hDOR (human δ opioid receptor) selectivity of [Dmt1]DALDA (\~{}10,000) is 8-fold higher than DAMGO. However, [Dmt1]DALDA is less selective than DAMGO against hKOR (human κ opioid receptor) (26-versus 180-fold). The Ki values for a number of opioid ligands were generally higher when determined by competitive displacement binding against [3H][Dmt1]DALDA compared with [3H]DAMGO, with the exception of Dmt1-substituted peptide analogs. All Dmt1 analogs showed much higher affinity for the μ receptor than corresponding Tyr1 analogs. [35S]GTPγS (guanosine 5'-O -(3-[35S]thio)triphosphate) binding showed that [Dmt1]DALDA and DAMGO are full agonists at hMOR and hDOR but are only partial agonists at hKOR. The very high affinity and selectivity of [3H][Dmt1]DALDA for the μ receptor, together with its very low nonspecific binding (10{\textendash}15\%) and metabolic stability, make [3H][Dmt1]DALDA an ideal radioligand for labeling μ receptors. The American Society for Pharmacology and Experimental Therapeutics}, issn = {0022-3565}, URL = {https://jpet.aspetjournals.org/content/307/3/947}, eprint = {https://jpet.aspetjournals.org/content/307/3/947.full.pdf}, journal = {Journal of Pharmacology and Experimental Therapeutics} }