The invention discloses a method of treating cancer refractory to an anticancer agent comprising administering to a cancer patient a pharmaceutical composition comprising at least one compound of Formula 1 Where R1 is selected from the group consisting of —NH2, —NH—CH2—COOH, —NH—CH(CH3)—COOH, —NH—C(CH3)2—COOH, —NH—CH2—CH2—OH and —N—(CH2CH2OH)2 or a pharmaceutically acceptable salt of such a compound, and an anticancer agent.