Methods and compositions for treating cancer and other diseases in which inhibition of telomerase activity can ameliorate disease symptoms or prevent or treat the disease relate to compounds characterized by the following structure: STR1 and their pharmaceutically acceptable salts. Y is selected from the group consisting of oxygen, sulfur, sulfonyl, sulfinyl, and --NR7 --. R1 is --TR8, where T is --C(X1)-- or --SO2 --, and R8 is selected from the group consisting of --OR9, --NHNHSO2 R9, --NHNHC(X2)OR9, --NR9 R10, --NHNHC(X2)NR9 R10, --NHCR9 R10 C(X2)NR11 R12, --NHC(X2)NR9 R10, and the piperazinyl moiety shown below: STR2 where n is 0 or 1, and Qn, for n=1, is --SO2 --, --C(X2)-- or --C(X2)NR10 --. R2 -R6 are selected independently from the group consisting of hydrogen, alkyl, aryl, hydroxyl, alkoxyl, aryloxyl, aralkoxyl, halogen, cyano, nitro, alkylcarbamido, arylcarbamido, dialkylcarbamido, diarylcarbamido, alkylarylcarbamido, alkylthiocarbamido, arylthiocarbamido, dialkylthiocarbamido, diarylthiocarbamido, alkylarylthiocarbamido, amino, alkylamino, arylamino, dialkylamino, diarylamino, arylalkylamino, aminocarbonyl, alkylaminocarbonyl, arylaminocarbonyl, dialkylaminocarbonyl, diarylaminocarbonyl, arylalkylaminocarbonyl, alkylcarbonyloxy, arylcarbonyloxy, carboxyl, alkoxycarbonyl, aryloxycarbonyl, sulfo, alkylsulfonylamido, arylsulfonylamido, alkylsulfonyl, arylsulfonyl, alkylsulfinyl, and arylsulfinyl. X1 and X2 are selected independently from the group consisting of oxygen, and sulfur. R7 -R12 are selected independently from the group consisting of hydrogen, alkyl, aryl, aralkyl, heterocycle, and heterocyclealkyl.