Abstract: Provided is a method of treating a disease caused by a nidovirus that encodes Nsp15, such as a coronavirus, an arterivirus, or a torovirus, in a subject in need thereof comprising administering a therapeutically effective amount of an active agent selected from 3?-uridylic acid, 5?-uridylic acid, citrate, methacycline, meclocycline sulfosalicylate, mitoxantrone, epirubicin hydrochloride, daunorubicin hydrochloride, sorafenib, sunitinib malate, primaquine diphosphate, closantel, isopropyl ester of N4-hydroxycytidine, GpU dinucleotide or derivatives thereof, and tipiracil or N-substituted derivatives thereof. Further provided are a method of inhibiting an Nsp15 endoribonuclease of a nidovirus that encodes Nsp15 and compounds of formulas (I?) and (II?).