Piperazinedione compounds of the formula: Each of and and independently, is a single bond or a double bond; A is H or CH(RaRb) when is a single bond, or C(RaRb) when is a double bond; Z is R3O—(Ar)—B, in which B is CH(Rc) when is a single bond, or C(Rc) when is a double bond; Ar is heteroaryl; and R3 is H, alkyl, aryl, heteroaryl, C(O)Rd, C(O)ORd, C(O)NRdRe, or SO2Rd; each of R1 and R2, independently, is H, C(O)Rd, C(O)ORd, C(O)NRdRe, or SO2Rd; and each of Ra, Rb, Rc, Rd, and Re, independently, is H, alkyl, aryl, heteroaryl, cyclyl, or heterocyclyl. Optionally, Ra and Rb taken together are cyclyl or heterocyclyl; and, also optionally, R1 and Ra or R1 and Rb taken together are cyclyl or heterocyclyl. Also disclosed is a method for treating tumor with the above described piperazinedione compounds.