The human DAO cell assay was performed using the following final assay conditions: 25,000 human DAO CHO-K1 stable cells/well, 50 mM D-Serine, 50 µM Amplex Red and 0.125 U/mL HRP. All cells and reagents were made up in 10 mM HEPES buffer (15630-056, ThermoFisher Scientific). The final assay volume was 25 µL/well. The human DAO CHO-K1 stable cells were trypsinised, resuspended in complete medium and centrifuged at 1200 rpm for 4 minutes at room temperature. The cell pellet was then washed in 10 mM HEPES buffer and centrifuged at 1200 rpm for 4 minutes at room temperature. The resulting cell pellet was resuspended in 10 mM HEPES buffer at 1.25x10 6 cells/mL. 25,000 human DAO CHO-K1 stable cells (20 µL in 10 mM HEPES buffer) were added to all the wells in the assay ready plate (containing 250 nL compound / DMSO vehicle per well). 5µl of a working solution containing 250 mM D-Serine, 250 µM Amplex Red and 0.625 U/mL HRP in assay buffer was added to all the wells except for the negative control wells. 5 µL of a working solution of 250 µM Amplex Red and 0.625 U/mL HRP in assay buffer was added to the negative control wells. The plate was incubated for 30 minutes in the dark at 25˚C before measuring fluorescence in each well using the Envision plate reader with excitation at 530 nm and emission at 595 nm. Dose response curves were generated using ActivityBase (IDBS). IC50 (Point of Inflection) values were determined by plotting % Inhibition vs Log10 compound concentration using a sigmoidal fit with a variable slope (four parameter fit).