NUCLEOTIDE EXCISION-REPAIR OF MELPHALAN MONOADDUCTS

The nucleotide-excision repair (NER) system removes bulky DNA adducts and is thought to be involved in resistance to chemotherapeutic drugs, which act by damaging DNA. In this study, we have investigated the ab ility of the NER system to recognize and excise melphalan monoadducts from a 140-mer DNA substrate. We show that rodent and human cell-free extracts (CFEs) excise 26-29-nt-long oligomers from a synthetic 140-me r containing centrally located melphalan adducts. CFEs from cell lines with mutations in xeroderma pigmentosum group F or G genes did not ex cise these alkylated oligomers; however, mixing the two CFEs restored excision activity to the level found with wild-type CFEs. These result s demonstrate the ability of the NER system to excise melphalan monoad ducts, and are consistent,vith the hypothesis that NER may be involved in resistance to melphalan chemotherapy.