IC50: 80 nM (autophagin-1, FRET assay); 73 nM (autophagin-1, LRA assay)

ATG4B or autophagin-1 is a cysteine protease that cleaves ATG8 family proteins. ATG4B plays essential roles in the autophagosome formation and the autophagy pathway. FMK 9a shows strong inhibition of ATG4B, with IC ₅₀ values of 80 and 73 nM in the TR-FRET and cellular-based LRA assays, respectively. LC?MS/MS study indicates that FMK 9a forms an irreversible covalent bond with the more reactive thiol group of Cys74 located at the catalytic site of ATG4B and thus inactivates ATG4B proteolytic activity.

FMK 9a shows moderate solubility (LYSA: 41 μg/mL) and high human and mouse liver microsome clearances of 13.9 and 70 mL/kg per minute.