ABSTRACT
Temozolomide(TMZ)is an anticancer agent used to treat glioblastoma,typically following radiation therapy and/or surgical resection.However,despite its effectiveness,at least 50％of patients do not respond to TMZ,which is associated with repair and/or tolerance of TMZ-induced DNA lesions.Studies have demonstrated that alkyladenine DNA glycosylase(AAG),an enzyme that triggers the base excision repair(BER)pathway by excising TMZ-induced N3-methyladenine(3meA)and N7-methylguanine le-sions,is overexpressed in glioblastoma tissues compared to normal tissues.Therefore,it is essential to develop a rapid and efficient screening method for AAG inhibitors to overcome TMZ resistance in glio-blastomas.Herein,we report a robust time-resolved photoluminescence platform for identifying AAG inhibitors with improved sensitivity compared to conventional steady-state spectroscopic methods.As a proof-of-concept,this assay was used to screen 1440 food and drug administration-approved drugs against AAG,resulting in the repurposing of sunitinib as a potential AAG inhibitor.Sunitinib restored glioblastoma(GBM)cancer cell sensitivity to TMZ,inhibited GBM cell proliferation and stem cell char-acteristics,and induced GBM cell cycle arrest.Overall,this strategy offers a new method for the rapid identification of small-molecule inhibitors of BER enzyme activities that can prevent false negatives due to a fluorescent background.
ABSTRACT
A liquid chromatography-tandem mass spectrometry ( LC-MSMS ) method has been developed for the simultaneous determination of N3-methyladenine ( N3-MeA ) and N3-ethyladenine ( N3-EtA ) in calf thymus DNA. The DNA samples has been purified and enriched by cation exchange cartridge ( Waters Oasis MCX) . d3-N3-MeA and d5-N3-EtA were used as isotope internal standard. The DNA samples were injected with autosampler. The injected volume was 3 μL and analysis time was 13 min. The sample separation was carried out on hydrophilic interaction chromatograph ( Waters XBridge HILIC ) with 10 mmol/L ammonium formate-acetonitrile (5:92, V/V, pH=4. 0) as mobile phase. The flow rate was set at 250 μL/min. Mass spectrometry was performed by electrospray ionization ( ESI ) with multi-reactions monitoring ( MRM ) . The optimized operation conditions of MS were as follows: nebulizer gas 369 Pa; curtain gas 185 Pa, turbo ionspray temperature 400 ℃, ionspray voltage 5500 V, dwell time 40 ms. The limits of detection were 0. 043 and 0. 007 μg/L for N3-MeA and N3-EtA, respectively. The recoveries were between 87. 8% and 103. 0%for N3-MeA and N3-EtA. This method was successfully applied to the determination of N3-MeA and N3-EtA in calf thymus DNA by cigarette smoke condensate ( CSC) exposure. This method is appropriate for routine analysis and accurate quantification of N3-MeA and N3-EtA by CSC exposure.