Likewise, brequinar is a synthetic, small molecule, and quinoline-carboxylic acid derivative (Figure 7) that also inhibits dihydroorotate dehydrogenase. It eventually blocks the de novo biosynthesis of pyrimidine-based nucleotides [158,159]. Accordingly, brequinar possesses immunosuppressive effects. Furthermore, it also possesses antineoplastic properties that can be exploited to enhance the in vivo antitumor activity of other antineoplastic agents [160]. Alternatively, the drug has also antiparasitic effects [160,161]. More importantly, the drug exhibits a broad-spectrum antiviral activity against influenza viruses [162], HIV-1 [163], and foot-and-mouth disease virus [164]. In fact, a pre-print under review has documented the activity of dihydroorotate dehydrogenase inhibitors against RNA viruses, including SARS-CoV-2 [165]. Currently, the drug is being evaluated in a randomized, open-label trial to assess its safety and anti-coronavirus activity in hospitalized adults with COVID-19 (NCT04425252; n = 24).