A novel compound of the formula: ##STR1## wherein a ring A stands for an optionally substituted 5-membered ring; B stands for an optionally substituted divalent cyclic or chain group; either one of Q.sup.1 and Q.sup.2 stands for N and the other stands for N or CH; X stands for an amino group, hydroxyl group or mercapto group; Y stands for H, halogen atom or a group bonded through C, N, 0 or S; Z stands for a straight-chain divalent group having 2 to 5 atoms constituted of optionally substituted carbon atoms or constituted of optionally substituted carbon atoms and one optionally substituted hetero-atom; COOR.sup.1 and COOR.sup.2 independently stand for an optionally esterified carboxyl group; n denotes an integer of 2 to 6; and R.sup.1 may be different in each of n repeating units, or their salts and it is useful as a therapeutic drug for tumor in mammals.