Synergistic methods and compositions for treating cancer

A method for the treatment of cancer which comprises administering to a mammalian specie in need thereof a synergistically, therapeutically effective amount of (1) at least one agent selected from the group consisting of anti-proliferative cytotoxic agents and cytostatic agents and (2) a compound of formula I

• 15
• or a pharmaceutically acceptable salt thereof wherein
• R1 is Cl, Br, CN, optionally substituted phenyl, or optionally substituted 2-,3- or 4-pyridyl;
• R2 is optionally substituted lower alkyl, or optionally substituted aralkyl;
• R3 and R5 are each independently optionally substituted lower alkyl, optionally substituted aryl, or optionally substituted heterocyclo;
• R4 is hydrogen or lower alkyl;
• Z1 is CO, SO2, CO2 or SO2N(R5)—;
• and
• n is 1 or 2;
• provided that the cytotoxic agent and/or cytostatic agent is administered simultaneously with or prior to the formula I compound.