Enzyme Assay: Method: The test compound or solvent was incubated at 25° C. for 15 min with enzyme solution (0.2 μg/mL) in Tris-HCl buffer of pH 7.5. 100 μM cGMP and 0.03 μM [3H] cGMP were then added to activate the reaction. The mixture was incubated for 20 min. The reaction was stopped at 100° C. By addition of snake venom nucleotidase, the product [3H] GMP was converted into [3H] Guanosine, which was separated with AG1-X2 resin. The amount of [3H] Guanosine was measured.
Inhibtion Assay: The PDE assay medium consisted of (final concentrations); 50 mM Tris-HCL, pH 7.5; 8.3 mM MgCl2; 1.7 mM EGTA; 0.5 mg/mL bovine serum albumin; and substrate (H-cAMP or H-cGMP). The BSA was lyophilized powder, essentially fatty acid free, >=96% pure from Sigma (A6003). 89 ul of assay medium and 1 ul of Compound 1 in 100% DMSO were added to a 96-well SPA plate and incubated for 1 minute at 30° C. The assay was initiated by addition of 10 ul of PDE10, and incubated for 21 minutes. Then 50 ul of SPA beads were added and the plate was sealed, shaken, and incubated at room temperature for 1 hour. The plate was then counted in a Wallac 1450 Microbeta Trilux plate scintillation counter. For the PDE10 IC50 experiment, the substrate was 125 nM H-cGMP. For the selectivity experiments, the substrates were 37 nM H-cAMP for PDEs 3, 4, 7, and 8; and 37 nM H-cGMP for PDEs 1, 2, 5, 9, 10, and 11. In all cases substrate concentrations were below the KM. The consumption of substrate was less than 6%, indicating that substrate concentrations did not change appreciably during the assay.