Nitrogen-containing tetracyclic compounds represented by general formula (I) or pharmaceutically acceptable salts thereof, wherein Y1-Y2-Y3 represents N-C=N or C=C-NR3 (wherein R3 represents hydrogen, C¿1-5? alkyl or nitrogen-containing C2-10 alkyl); Y?4¿ represents S, SO, SO¿2?, CH2 or NR?4¿ (wherein R4 represents C¿1-5? alkanoyl or C1-5 alkyl); R?1 and R2¿ are the same or different and each represents hydrogen, C¿1-10? alkyl, C3-15 alkoxyalkyl or C3-15 alkylaminoalkyl, or R?1 and R2¿ form together with the adjacent nitrogen atom cyclic amino; X?1 and X2¿ are the same or different and each represents hydrogen, C¿1-5? alkyl, C1-5 alkoxy or halogeno; and n is 0, 1 or 2.