Development of the molecular diagnostic tests for drug-resistant cancer cells based on gene expression profiling using microarray

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Drug resistance is a major obstacle in chemotherapy of leukemia patients. Since the treatment responsiveness is different among patients, the therapy should be tailored to specific subtypes of diseases such as defined by drug resistance. We attempted to develop the molecular diagnostic tests for drug-resistant cancer cells based on gene expression profiling using a microarray method. The aim of this study was to select a gene panel for a diagnostic array by analyzing function of candidate genes in the drug resistance. The ATM gene was chosen as a novel and candidate gene. ATM was found overexpressed in trimetrexate-resistant leukemia MOLT-3 cells (MOLT-3/TMQ200) as analyzed by gene expression profiling using a commercially available cDNA microarray (Human Cancer CHIP version 3.0, TaKaRa Biotechnology). It was confirmed by Northern blot analysis. When the plasmid with insertion of the siRNA for ATM was transfected to MOLT-3/TMQ200 cells, ATM expression was decreased as analyzed by RT-PCR. Expression levels of ATM as assessed by real-time PCR was increased in parallel with drug resistance degree in three sublines obtained from MOLT-3/TMQ cells. Resistance to irradiation as assessed by GO values in agarose clonogenic assay was increased in parallel with the ATM levels in three sublines. The novel gene which was demonstrated as functioning in the mechanisms of drug resistance would be a useful marker for molecular diagnostic tests for drug-resistant cancer cells based on gene expression profiling using a microarray method.