FIELD: pharmacology.SUBSTANCE: invention relates to a pyridine derivative of formula (I) , a prodrug thereof, wherein A is a single bond or an oxygen atom； R1 represents a nitrogen atom or CH； one of X1-X5 is a nitrogen atom, and the remaining four are CR2； R2 each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a halogen atom, a trifluoromethyl group, a difluoromethyl group, a cyano group, an alkylcarbonyl group having 2 to 7 carbon atoms, an alkylsulfonyl group having 1 to 6 carbon atoms, a nitro group, an amino group, a dialkylamino group having 1 to 6 carbon atoms which optionally can form a ring, a formyl group, an alkoxy group having 1 to 6 carbon atoms (which may optionally have one or more substituents selected from a hydroxyl group, a phenyl group, a cyclohexyl group and a halogen atom), an alkylthio group having 1 to 6 carbon atoms, a phenyl a group (which may optionally have one or more substituents selected from an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms and a halogen atom) or a phenoxy group (which may optionally have one or more substituents selected from an alkyl group having 1-6 carbon atoms, an alkoxy group having 1-6 carbon atoms, and a halogen atom), provided that when two CR2 are located side by side, two R2 substituents can be optionally combined with cycle formation； R3 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms (which may optionally have one or more substituents selected from a hydroxyl group, an amino group, a dialkylamino group having 1 to 6 carbon atoms which can optionally form a ring, an imidazole ring, a pyrazole ring, a pyrrolidine ring, a piperidine ring, a morpholine ring and a piperazine ring (which may optionally have one or more substituents selected from an alkyl group having 1 to 6 carbon atoms and alkylsulfonyl group containing from 1 t
