The present invention comprises unsubstituted and substituted piperazine-containing compounds having alkanoyl, alkylsulfonyl, alkylamido or alkoxycarbonyl substituents, and having the formula A, which inhibit prenyl-protein transferases. In particular, the invention relates to prenyl-protein transferase inhibitors which are efficacious in vivo as inhibitors of geranylgeranyl-protein transferase type I (GGTase-I) and that inhibit the cellular processing of both the H-Ras protein and the K4B-Ras protein. Such therapeutic compounds are useful in the treatment of cancer.