Ribozyme and free alkylated base: a dual approach for sensitizing Mex⁺ cells to the alkylating antineoplastic drug

Abstract

N-alkyl-nitrosoureas and alkyl-triazenes are alkylating antineoplastic drugs, the efficacy of which is strongly affected by the level of expression of the DNA-repair enzyme O⁶-methylguanine-DNA methyltransferase (MGMT). In tumors, MGMT activity reduces the chemotherapeutic potential of alkylating drugs; therefore, efforts have been made to down-regulate the protein. A partial sensitization of Mex⁺ cells to alkylating drugs has been obtained using either free alkylated bases or oligonucleotides targeted against MGMT mRNA. In the present work, O⁶-methylguanine and a chemically modified ribozyme, without a cationic liposome as a carrier, were coadministered to CHO47 cells, which express a high level of human MGMT protein. The reduction of MGMT mRNA and protein enhanced the genotoxicity of the alkylating drug mitozolomide. Furthermore, the sensitivity of CHO47 cells is the same as that of CHO5 cells, which lack MGMT protein. These data indicate that a strategy in which both mRNA and protein are degradation targets can be successfully applied to down-regulate the MGMT gene.