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 --NR.sub.7 --. R.sub.1 is --TR.sub.8, where T is --C(X.sub.1)-- or --SO.sub.2 --, and R.sub.8 is selected from the group consisting of --OR.sub.9, --NHNHSO.sub.2 R.sub.9, --NHNHC(X.sub.2)OR.sub.9, --NR.sub.9 R.sub.10, --NHNHC(X.sub.2)NR.sub.9 R.sub.10, --NHCR.sub.9 R.sub.10 C(X.sub.2)NR.sub.11 R.sub.12, --NHC(X.sub.2)NR.sub.9 R.sub.10, and the piperazinyl moiety shown below: ##STR2## where n is 0 or 1, and Q.sub.n, for n=1, is --SO.sub.2 --, --C(X.sub.2)-- or --C(X.sub.2)NR.sub.10 --. R.sub.2 -R.sub.6 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. X.sub.1 and X.sub.2 are selected independently from the group consisting of oxygen, and sulfur. R.sub.7 -R.sub.12 are selected independently from the group consisting of hydrogen, alkyl, aryl, aralkyl, heterocycle, and heterocyclealkyl.