The sensitization of cells treated with O-6-methylguanine to alkylation damage is affected by the number of O-6-methylguanine-DNA methyltransferase molecules escaped from inactivation

O-6-Methylguanine (MeG) can bind to the active site of O-6-methylguanine-DN A methyltransferase (MGMT) as a free base. The subsequent methyl transfer r eaction inactivates the repair protein. Hence, MeG is used to deplete the a ctive MGMT pools in Chinese hamster cell lines (CHO) transfected to express varying amounts of human MGMT. After treatment with the free base, a resid ual population of active protein molecules remains localized mostly in the cytoplasm. Depleted cells are then challenged with the alkylating drug mito zolomide. Genotoxicity of this agent varied among the cell lines, and the c ompound sensitivity seemed to be regulated by a steady state equilibrium of residual MGMT molecules between nucleus and cytoplasm. (C) 1998 Elsevier S cience B.V. All rights reserved.