INCREASED RESISTANCE TO N,N',N''-TRIETHYLENETHIOPHOSPHORAMIDE (THIOTEPA) IN CELLS EXPRESSING THE ESCHERICHIA-COLI FORMAMIDOPYRIMIDINE-DNA GLYCOSYLASE

Thiotepa (N,N',N ''-triethylenethiophosphoramide) is an alkylating age nt used in cancer chemotherapy. A reaction pathway by which thiotepa a lkylates purified DNA involves hydrolysis to aziridine, which forms N- 7-aminoethyl guanine and aminoethyl adenine. These lesions are repaire d in Escherichia coli by the formamidopyrimidine-DNA glycosylase (Fpg) protein. To determine whether such lesions are formed by thiotepa in mammalian cells, we have overexpressed the E. coli Fpg protein in Chin ese hamster ovary cells. The transfected cells were more resistant to the lethal and mutagenic effects of thiotepa than the parental cells. The number of replication-blocking lesions formed by thiotepa, measure d by quantitative PCR analysis, was lower in the transfected cells. Th ese results show that expression of the Fpg protein increases the cell resistance to thiotepa and suggest that this compound produces ring-o pened guanines, which are involved in its cytotoxic action.