title: Synthesis of a tritium-labeled indolidan analogue and its use as a radioligand for phosphodiesterase-inhibitor cardiotonic binding sites.
abstract: We have radiolabeled a structural analogue of indolidan, a potent phosphodiesterase-inhibitor cardiotonic, to permit biochemical studies regarding the interaction of this class of drugs with their pharmacological receptor. [3H]-LY186126 (1,3-dihydro-3,3-dimethyl-1-[3H3]methyl-5-(1,4,5,6-tetrahydro-4-me thyl-6- oxo-3-pyridazinyl)-2H-indol-2-one; [3H]-3) was selected as a synthetic target because of its potency as a cardiotonic and the ability to readily incorporate three tritia via the indolone N-CH3 substituent. Alkylation of a desmethyl precursor with tritium-labeled iodomethane resulted in [3H]-3 with a radiochemical purity of 98% and a specific activity of 79.2 Ci/mmol. This radioligand binds with high affinity to myocardial membrane vesicles. The binding was saturable, and Kd and Bmax values of 4.1 nM and 383 fmol/mg protein were obtained. A series of indolidan congeners displaced [3H]-3 bound to myocardial vesicles, and Ki values for inhibition of binding were highly correlated with canine inotropic ED50 values, suggesting the specific binding of [3H]-3 to cardiac vesicles is pharmacologically relevant.
authors.affiliation: Lilly Research Laboratories, Lilly Corporate Center, Indianapolis, Indiana 46285.
authors.forename: D W
authors.initials: DW
authors.lastname: Robertson
authors.forename: J H
authors.initials: JH
authors.lastname: Krushinski
authors.forename: B G
authors.initials: BG
authors.lastname: Utterback
authors.forename: R F
authors.initials: RF
authors.lastname: Kauffman
mesh_terms: D000818:Animals; D001665:Binding Sites; D055598:Chemical Phenomena; D002621:Chemistry; D004285:Dogs; D005260:Female; D007211:Indoles / Q000138:chemical synthesis* / Q000378:metabolism; D008024:Ligands; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D000078183:Oxindoles; D010726:Phosphodiesterase Inhibitors / Q000378:metabolism*; D011724:Pyridazines / Q000138:chemical synthesis* / Q000378:metabolism; D011869:Radioligand Assay; D013056:Spectrophotometry, Ultraviolet; D014316:Tritium
chemical_list: D007211:Indoles; D008024:Ligands; D000078183:Oxindoles; D010726:Phosphodiesterase Inhibitors; D011724:Pyridazines; C050325:indolidan; D014316:Tritium; C059371:LY 186126