p382M; pos. modified gene manifestation in drugresistant cells. Important node analysis showed that p38mitogenactivated protein kinase was a novel enzyme involved in MX2related resistance. p38 kinase activity in tolerant cells was PAT-048 increased in comparison to MX2sensitive parent cells. Blocking p38activity using inhibitors and p38knock down with small interfering RNA restored the sensitivity to MX2 in resistant cells with a decrease in p38 kinase activity as well as decreased manifestation of p38mRNA and phosphorylated p38protein. These findings may lead to a new strategy for treatment PAT-048 of drugresistant leukemia cells. Keywords: Drug resistance, important node search, leukemia, methylation array, morpholino anthracycline, p38 == Abbreviations == adriamycin False discovery rate Gene Ontology mitogenactivated protein kinase 3deamino3morpholino13deoxo10hydroxycarminomycin hydrochloride Topoisomerase == Introduction == Effective leukemia therapy is hampered by drug resistance, Itga3 which is a serious problem that results from various mechanisms. Pediatric leukemia individuals with cancer cells that show resistance to antileukemic providers in vitro have a more dismal prognosis than individuals with drugsensitive leukemia cells (Holleman et al. 2004). The pattern of gene expression in leukemia cells with attained resistance to standard therapy is most likely substantially diverse compared to leukemia cells prior to the initiation of treatment because drugresistant subpopulations grow selectively as treatment progresses. Nevertheless, how cells acquire drug resistance is usually unclear. Many signaling pathways and genes that may affect the response of leukemia cells to therapy have been determined. Because many factors are involved in the mechanism of acquisition of drug resistance, the one gene: one end result hypothesis cannot adequately describe acquired resistance in leukemia (Glasspool et al. 2006). Thus, multiple mechanisms and multiple genes rather than a single pathway or gene likely mediate attained resistance. Saugrenu methylation, including genomewide hypomethylation and regional hypermethylation of promoters PAT-048 to get genes such as tumor suppressors, is 1 mechanism of tumorigenesis (Eden et al. 2003). Methylation of eukaryotic DNA happens at CpGenriched promoters. Such epigenetic changes are critically involved in acquisition of drug resistance, which is mediated by changes in gene manifestation that occur following chemotherapy but that are not caused by genetic mutations. Wei et al. (2003) used drugresistant cell lines and differential methylation hybridization and showed many differences in CpG island methylation and epigenetic regulation after drug treatment. However , this group did not determine which genes were aberrantly methylated in resistant cells. In general, recent studies including ours possess investigated only a few CpG island markers in methylationrelated drug resistance (Asano et al. 2005). 3deamino3morpholino13deoxo10hydroxycarminomycin hydrochloride, also known as KRN 8602 (MX2), is actually a new morpholino anthracycline derivative that acts as a topoisomerase (Topo) IIinhibitor and is cytotoxic to tumor cells (Watanabe et al. 1988). MX2 is highly lipophilic and easily passes through the cell membrane in a Pglycoproteinindependent manner (Watanabe et al. 1988). The antitumor effects of MX2 are superior to those of adriamycin (ADR). MX2 is usually toxic to mouse and human tumor cell lines as well as multidrugresistant tumor cell lines that express large levels of Pglycoprotein (Watanabe et al. 1991). MX2 may thus be useful for eradicating multidrugresistant tumors. By constantly exposing cells grown in suspension to increasing amounts of MX2, we previously established the MX2resistant human myelogenous leukemia cell line K562/MX2, which is derived from the parent cell series K562/P (Asano et al. 2005). K562/MX2 cells show lower levels of Topo IImRNA and protein, and the Topo IIgene in these cells is usually aberrantly methylated at CpG islands. Thus, drug resistance in K562/MX2 cells may be due to saugrenu methylation (Asano et al. 2005). We therefore next investigated the relationship between global gene manifestation and methylation in drugresistant cells and identified genes that confer resistance. Highthroughput methylation analysis of multiple CpG sites can be performed with all the GoldenGate Methylation BeadArray (Illumina Inc. Tokyo, Japan) (Ang et al. 2010). Here, we evaluated the genomewide methylation status using the methyl array, in comparison gene manifestation.