Inhibition of VKOR activity by clinically used VKAs. (A) Chemical structures of the oral anticoagulants warfarin, phenprocoumon, acenocoumarol, and fluindione. The identical chemical structures of 4-hydroxycoumarin in warfarin, phenprocoumon, and acenocoumarol are shown in red. (B) VKA concentration titration against VKOR activity in DGKO FIXgla-PC/HEK293 reporter cells. Wild-type VKOR was transiently expressed in the reporter cells; the transfected cells were incubated with 5 µM KO with increasing concentrations of VKAs. (C) Inhibition efficiency of VKAs on VKOR activity. The IC₅₀ of each VKA was determined from panel B using GraphPad software. Data are presented as mean ± standard deviation (SD).