Prenylating enzymes are involved in modifying oncoproteins, such as RAS, so that growth of neoplastic cells becomes uncontrolled. Inactivation of such enzymes can prevent uncontrolled growth. α-Dicarbonyl compounds can be used to covalently modify and thereby inactivate prenylating enzymes such as protein farnesyltransferase and protein geranylgeranyltransferase. The compounds can be designed to enhance affinity and/or specificity for a particular protein substrate.