Optimization of a Colorimetric Assay to Determine Lactate Dehydrogenase B Activity Using Design of Experiments

Lactate dehydrogenase B (LDH-B) is overexpressed in lung and breast cancer, and it has been considered as a potential target to treat these types of cancer. Herein, we propose a straightforward incomplete factorial (IF) design composed of 12 combinations of two reaction buffers, three pH values, three salt (NaCl) concentrations, and three incubation times, which we called IF-BPST (Buffer/pH/Salt/Time), for the optimization of a colorimetric LDH-B assay in a final volume of 100 µL using 96-well plates. The assay is based on the absorbance change at ~570 nm and the color change of the reaction mixture due to the release of NADH that reacts with nitroblue tetrazolium (NBT) and phenazine methosulfate (PMS), resulting in the formation of a blue-purple formazan. The results obtained using the IF-BPST were comparable with those obtained by response surface methodology. Our work revealed that the NBT/PMS assay with some modifications can be used to measure the activity of LDH-B and other dehydrogenases in a high-throughput screening format at the early stages of drug discovery. LDH-B containing lysates cannot be assayed directly, however, due to the sensitivity of the method toward detergents. Thus, we suggest precipitating the proteins in the lysates to remove the interfering detergents, and then to dissolve the protein pellet in a suitable buffer and carry out the assay.