Sensitivity Multiple Myeloma Cells to mTOR Inhibitors

描述（由申请人提供）：本提案的长期目标是改善多发性骨髓瘤患者的医疗管理。我们之前的研究表明，用雷帕霉素或CCI-779靶向哺乳动物雷帕霉素（mTOR）在这种恶性肿瘤中具有很大的治疗潜力，AKT活性水平决定了对mTOR抑制剂的敏感性：当AKT活性升高时，骨髓瘤细胞对G1停止敏感，而AKT活性降低则诱导相对抗性。抑制mTOR通常会抑制帽依赖性翻译和关键细胞周期蛋白的表达。与这一观点相一致的事实是，mTOR抑制剂在敏感骨髓瘤细胞中诱导了cyclin-D和c-myc翻译的抑制，而在耐药细胞中翻译不受影响。这些发现提示了以下假设：具有高AKT活性的骨髓瘤细胞对mTOR抑制剂抑制D-cyclin和myc表达的能力非常敏感，从而解释了它们对G1停滞的敏感性。此外，我们假设AKT通过麻痹细胞周期蛋白/myc帽无关翻译的挽救通路来调节这种反应，并且这种依赖AKT的功能是由细胞周期蛋白/myc RNA和p38 MARK通路中的内核糖体进入位点（IRESes）的功能介导的。为了验证这些假设，我们的具体目标包括：

DESCRIPTION (provided by applicant): The long term objective of this proposal is to improve medical management of patients with multiple myeloma. Our prior studies demonstrated that targeting the mammalian target of rapamycin (mTOR) with rapamycin or CCI-779 has great therapeutic potential in this malignancy and that the level of AKT activity determines sensitivity to mTOR inhibitors: When AKT activity is heightened, myeloma cells are hypersensitive to G1 arrest, while lowered AKT activity induces relative resistance. Inhibition of mTOR often inhibits cap-dependent translation and expression of critical cell cycle proteins. Consistent with this notion is the fact that mTOR inhibitors induced inhibition of cyclin-D and c-myc translation in sensitive myeloma cells while translation was unaffected in resistant cells. These findings have prompted the following hypothesis: Myeloma cells with high AKT activity are hypersensitive to the ability of mTOR inhibitors to depress D-cyclin and myc expression, thus explaining their sensitivity to G1 arrest. Furthermore, we hypothesize that AKT regulates this response by paralyzing the salvage pathway of cyclin/myc cap-independent translation and that this AKT-dependent function is mediated by function of internal ribosome entry sites (IRESes) in cyclin/myc RNA and the p38 MARK pathway. To test these hypotheses, our specific aims include: I. To test if the AKT-dependent regulation of sensitivity to mTOR inhibitors is explained by differential effects on expression of D-type cyclins and/or c-myc. II. To test if AKT's regulation of cyclin/myc expression is mediated by effects on translational efficiency. III. To identify alterations in IRES-associated trans-acting factors (ITAFs) that may explain AKTregulation of cap-independent translation. These studies will performed in myeloma cell lines as well as primary patient marrow specimens