The GSH stability test was performed using a previously described method. For this purpose, a suitable HPLC method was applied that allowed sampling by injection every 20 min. To achieve the desired final inhibitor concentration of 10 μM, as well as a GSH concentration of 5 mM in a final volume of 1 mL, 1 μL of the inhibitor stock solution (10 mM), was added to 949 μL of phosphate buffer (pH 7.4) and 50 μL of the GSH stock solution (100 mM). The mixture was appropriately vortexed and subjected to HPLC. The autosampler was set to a temperature of 37 °C and 13 replicate measurements over 4 h were performed. The potential reaction of the inhibitor with GSH was monitored by comparing the decreasing area under the curve (AUC) of each compound. This was subsequently plotted graphically as percentage inhibitor concentration versus time.