title: Investigations on the effect of O(6)-benzylguanine on the formation of dG-dC interstrand cross-links induced by chloroethylnitrosoureas in human glioma cells using stable isotope dilution high-performance liquid chromatography electrospray ionization tandem mass spectrometry.
abstract: Chloroethylnitrosoureas (CENUs) are bifunctional alkylating agents widely used for the clinical treatment of cancer. They exert anticancer activity by inducing DNA interstrand cross-links (ICLs) within GC base pairs to form dG-dC cross-links. This lesion inhibits DNA double strand separation during replication and transcription and results in the apoptosis of cancer cells. However, O(6)-alkylguanine DNA alkyltransferase (AGT) repairs the DNA ICLs by removing the alkyl group at the O(6) position of either O(6)-(2-chloroethyl)deoxyguanosine (O(6)-ClEtdGuo) or N1,O(6)-ethanodeoxyguanosine (N1,O(6)-EtdGuo), which are intermediates in the formation of dG-dC cross-links. The action of AGT leads to drug resistance against CENUs. O(6)-Benzylguanine (O(6)-BG) was identified as an effective AGT inhibitor that enhances the antitumor effects of CENUs. In this study, the effect of O(6)-BG on the formation of dG-dC cross-links was investigated by treating human brain glioma SF767 cells with 1-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-3-(2-chloroethyl)-3-nitrosourea (ACNU). The levels of dG-dC cross-link were determined using stable isotope dilution high-performance liquid chromatography electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). The results indicated that ACNU induced higher levels of dG-dC cross-link in SF767 cells pretreated with O(6)-BG compared to cells without O(6)-BG pretreatment. The highest dG-dC cross-linking levels were generally observed at 12 h for all drug concentration groups, a result which was consistent with cytotoxicity assay. These results provided direct evidence for the enhancement of dG-dC cross-linking levels caused by the inhibition of AGT by O(6)-BG. These data indicate that dG-dC cross-links may be developed as a biomarker for evaluating the activity of novel O(6)-BG analogues as AGT inhibitors for combination therapy with CENUs.
authors.affiliation: Beijing Key Laboratory of Environmental & Viral Oncology, College of Life Science and Bioengineering, Beijing University of Technology , Beijing 100124, P. R. China.
authors.forename: Guohui
authors.initials: G
authors.lastname: Sun
authors.forename: Lijiao
authors.initials: L
authors.lastname: Zhao
authors.forename: Tengjiao
authors.initials: T
authors.lastname: Fan
authors.forename: Sisi
authors.initials: S
authors.lastname: Li
authors.forename: Rugang
authors.initials: R
authors.lastname: Zhong
mesh_terms: D000477:Alkylating Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D004247:DNA; D004249:DNA Damage; D003841:Deoxycytidine / Q000378:metabolism; D003849:Deoxyguanosine / Q000378:metabolism; D005038:Ethylnitrosourea / Q000031:analogs & derivatives / Q000494:pharmacology*; D005910:Glioma; D006147:Guanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry
chemical_list: D000477:Alkylating Agents; C064976:O(6)-benzylguanine; D003841:Deoxycytidine; D006147:Guanine; D004247:DNA; C427203:calf thymus DNA; D003849:Deoxyguanosine; D005038:Ethylnitrosourea