Development of model and targeted therapy for BCR-ABL positive leukemia

最近的研究表明，白血病干细胞(LSCs)是传统药物或靶向药物治疗后白血病复发的原因，而mTOR信号的异常激活也参与了LSCs的复发。为了研究Ph阳性(Ph+)LSCs的耐药机制，寻找克服耐药的策略，将Ph+白血病患者细胞连续异种移植到免疫缺陷NOG小鼠体内。来自白血病NOG小鼠的脾细胞与S17基质细胞共培养(Minami等人，PNAS，2008)，并用伊马替尼和mTOR抑制剂伊波利莫斯治疗(RAD001)。当静止期的CD34+细胞对伊马替尼不敏感时，包括CD34+细胞在内的大量细胞死亡，包括CD34+细胞。在含有T315I突变的伊马替尼耐药Ph+白血病细胞系中，PI排除实验显示，伊波利莫诱导细胞死亡的IC50值较低。我们还在研究细胞死亡过程中的详细生物标志物，如磷酸化S6K和这些药物的体内效应。这些结果表明，伊维莫司可以克服Ph+LSCs或T315I突变细胞对伊马替尼的耐药性。

Recent studies suggest that leukemia stem cells (LSCs) are responsible for relapse of leukemia following conventional or targeted agents and that aberrant activation of mTOR signaling is involved in LSCs. To examine mechanisms of drug resistance in Ph-positive (Ph+) LSCs and seek strategies to overcome the resistance, Ph+ leukemia patient cells were serially xenotransplanted into immunodeficient NOG mice. Spleen cells derived from leukemic NOG mice were co-cultured with S17 stromal cells (Minami, et al., PNAS, 2008) and treated with imatinib and the mTOR inhibitor, everolimus (RAD001). While quiescent CD34+ cells were insensitive to imatinib in spite of BCR-ABL-dephosphorylation, substantial cell death including CD34+ population was induced by treatment with nM level of everolimus. In imatinib-resistant Ph+ leukemia cell lines harboring T315I-mutation, everolimus induced cell death with low IC50 values in PI-exclusion assays. We are also investigating detailed biomarkers during the cell death such as phospho-S6K and in vivo effects of theses drugs. These results imply that treatment with everolimus can overcome the resistance to imatinib in Ph+ LSCs or T315I-mutated cells.