DHODH and acute myeloid leukemia: Almost 20 years ago, Beuneu et al. reported that dihydro-orotate dehydrogenase (DHODH), a mitochondrial enzyme of de novo pyrimidine biosynthesis that catalyzes the ubiquinone-mediated conversion of dihydro-orotate (DHO) to orotate, could provide electrons to the ETC via ubiquinone in AML cells [105].