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Abstract 2135 Objective To establish an imatinib resistant Bcr-Abl positive acute lymphoblastic leukemia (ALL) cell line in vitro and to study imatibin resistance in Ph+ ALL. The reversal of the imatinib resistance by rapamycin, the second generation tyrosine kinase inhibitor and proteasome inhibitor was studied. Methods Ph(+) ALL SUP-B15 cell line was cultured in gradually increasing concentrations of imatinib to generate the imatinib resistant cell line at 6 μM imatinib. The cytotoxic effect of imatinib and other drugs was analyzed by MTT assay. RT-PCR, flow cytometry, Western blot analyses of proteins, DNA sequence analysis of ABL kinase domain were used to clarify the possible mechanisms of the imatinib resistance in the SUP-B15/RI cell line. Results We established the imatinib resistant Ph+ ALL cell line. The fusion bcr-abl gene was 6.1 times as high as that of the parental sensitive cell, and the mdr1 gene also increased 1.7 times in SUP-B15/RI cell line by the RT-PCR detection. However, the expression of hoct1 Abcl–2 and topoIIα gene were no difference between two cell lines by the RT-PCR detection. A K362S point mutation in the Abl kinase domain of SUP-B15/RI was found. The detection of cell signaling pathway of PI3K/AKT/mTOR, RAS/RAF, NF-κBA JNK and STAT showed the expression of PTEN and 4EBP-1 was down-regulated, AKT, mTOR and P70S6K was up-regulated and the expression of other cell signaling pathways in SUP-B15/RI was similar to its parental sensitive cell line. Dasatinib, nilotinib, and bortezomib could inhibit proliferation of SUP-B15/RI cells at nM concentration. SUP-B15/RI cell line also showed partial resistance to dasatinib and nilotinib, but not bortezomib. The combination of imatinib with rapamycin had synergistic effect to the resistance cell line. Conclusion In vitro, we establish imatinib resistant Ph + ALL cell line. Overexpression of bcr-abl and mdr1 gene, K362S point mutation in ABL kinase domain and up-regulation of the cell signaling pathways of PI3K/AKT/mTOR, RAS/RAF in SUP-B15/RI cell line were involved in the resistance mechanisms. The SUP-B15/RI cell line was also resistant to the second generation tyrosine kinaeses dasatinib and nilotinib,not bortezomib in vitro. However, the combination of imatinib with rapamycin can partially overcome the resistance. Blockade of the ubiquitin-proteasome could be a promising pathway to overcome resistance to imatinib. Disclosures: No relevant conflicts of interest to declare.