NCT-501 hydrochloride is a highly potent and selective inhibitor of aldehyde dehydrogenase 1A1 (ALDH1A1), which is based on theophylline. It effectively inhibits hALDH1A1 with an IC50 value of 40 nM, exhibiting superior selectivity towards hALDH1A1 compared to other ALDH isozymes and dehydrogenases such as hALDH1B1, hALDH3A1, and hALDH2 (with IC50 values exceeding 57 μM).
CM39 is an ALDH inhibitor. Aldehyde dehydrogenase (ALDH) activity is commonly used as a marker to identify cancer stem-like cells. The three ALDH1A isoforms have all been individually implicated in cancer stem-like cells and in chemoresistance.