TARGETING OF O-6-METHYLGUANINE-DNA METHYLTRANSFERASE (MGMT) ACTIVITY BY ANTI-MESSENGER OLIGONUCLEOTIDE SENSITIZES CHO MEX(+) TRANSFECTED CELLS TO MITOZOLOMIDE/

The targeting of mRNA with antisense oligonucleotides is increasingly employed to inhibit the expression of gene function, Since the level o f the DNA repair protein O-6-methylguanine-DNA methyltransferase (MGMT ) is decisive in protection of cells against damage produced by alkyla ting agents, including cytostatic drugs, the targeted inhibition of th is repair activity might be of importance for therapeutic approaches, In order to investigate whether antisense targeted MGMT depletion is f easible to transiently modify the sensitivity of cells to anticancer d rugs, we studied the expression of MGMT and cellular sensitivity upon inhibitor and antisense treatment using CHO transfectants expressing h uman MGMT. It was shown by polymerase chain reaction that antisense ol igonucleotides specifically inhibited MGMT mRNA level, Nevertheless, M GMT protein was found not to be reduced significantly, as demonstrated by Western blotting, Correspondingly, no significant decrease in MGMT activity was observed, as measured 36 h after MGMT antisense oligonuc leotide administration. Given together with the MGMT depleting agent O -6-methylguanine, reduction in MGMT protein as well as activity was fo und. MGMT antisense oligonucleotide enhanced the sensitivity of cells to the tumor therapeutic drug mitozolomide, as measured by sister chro matid exchange formation, This sensitization was further enhanced by c ombined treatment with antisense oligonucleotide and O-6-methylguanine , indicating that MGMT antisense can be supportive in sensitization of cells to an alkylating drug.