Abstract: A cyclic tetrapeptide compound of the formula (I): wherein R1 is hydrogen; R2 is lower alkyl, aryl, optionally substituted ar(lower)alkyl, heterocyclic(lower)alkyl, cyclo(lower)alkyl(lower)alkyl, lower alkylcarbamoyl(lower)alkyl or arylcarbamoyl(lower)alkyl; R3 and R4 are each independently hydrogen, lower alkyl, optionally substituted ar(lower)alkyl, optionally substituted heterocyclic(lower)alkyl or cyclo(lower)alkyl(lower)alkyl, or R3 and R4 are linked together to form lower alkylene or condensed ring, or one of R3 and R4 is linked to the adjacent nitrogen atom to form a ring; R5 is lower alkylene or lower alkenylene, Y is [wherein RY1 is hydrogen, halogen or optionally protected hydroxy, RY2 is hydrogen, halogen, lower alkyl or phenyl, and RY3 is hydrogen or lower alkyl]; R8 is hydrogen or lower alkyl; and n is an integer of 1 or 2, or a salt thereof.