CDK control of myeloma pathogenesis

描述(申请人提供)：多发性骨髓瘤(MM)是第二常见的血液系统肿瘤。当自我更新的MM细胞以未知的机制开始不受抑制的增殖时，MM最终变得难以治疗。我们的目标是通过明确MM中细胞周期失调和自我更新的机制来开发新的和更好的治疗策略。细胞周期重新进入和通过G1进行的进展一方面受细胞周期蛋白和细胞周期蛋白依赖性蛋白激酶(CDK)之间的平衡调节，另一方面受CDK抑制剂的调节。我们以前已经证明，在正常浆细胞分化过程中，CDK6被其生理抑制剂之一p18INK4c抑制是G1细胞周期停滞所必需的。我们进一步表明，在每个患者的原代骨髓(BM)骨髓瘤细胞中，三种D细胞周期蛋白中的一种(但不超过一种)在体内升高。CDK4/6与D细胞周期蛋白的协同上调和特异性配对使MM细胞易于增殖。此外，CDK4/6的调节失调与侵袭性的临床病程有关，这表明CDK4和CDK6是有希望的治疗靶点。我们现在已经发现了一种有效和特异的小分子CDK4/6抑制剂，即使在骨髓基质细胞存在的情况下，它也能在体外快速诱导原代骨髓瘤细胞G1期停滞，并防止播散性人骨髓瘤在异种移植瘤中的生长。PD 0332991抑制CDK4/6不能诱导细胞凋亡。然而，它显著增强了广泛用于MM治疗的蛋白酶体抑制剂Bortesomib(VELCADE，PS-341)对骨髓瘤细胞的杀伤作用。这些发现为发展MM基于细胞周期的联合治疗提供了强有力的理论基础。在此基础上，我们提出，骨髓增殖信号对骨髓瘤细胞自我更新过程中CDK4和CDK6的异常调节是MM发生、发展和耐药的关键事件。为了验证这一假说并推进更好的治疗干预措施，我们提出了以下具体目标：1.研究PD 0332991联合蛋白酶体抑制剂对MM细胞扩张和肿瘤生长的控制，并在体外和体内两个互补的系统中，研究一种有效的基于细胞周期的治疗方法；2.研究胞外结构域脱落在BM自愈性骨髓瘤发生中的作用，用PD 0332991调控其激活，确定其在浆细胞分化中的正常作用：3.阐明促进骨髓瘤细胞自我更新和耐药的BM信号和途径。

DESCRIPTION (provided by applicant): Multiple myeloma (MM) is the second most common hematopoietic cancer. MM ultimately becomes refractory to treatment when self-renewing MM cells begin unrestrained proliferation by unknown mechanisms. Our goal is to develop novel and superior therapeutic strategies for MM by defining the mechanism of cell cycle dysregulation and self-renewal in MM. Cell cycle re-entry and progression through G1 is modulated by the balance between cyclins and cyclin-dependent kinases (Cdks) on one hand, and Cdk inhibitors on the other. We have demonstrated previously that inhibition of Cdk6 by p18INK4c, one of its physiologic inhibitors, is required for G1 cell cycle arrest during normal plasma cell differentiation. We have further shown that one, but not more than one, of the three D cyclins is elevated in primary bone marrow (BM) myeloma cells of each patient in vivo. Coordinated elevation and specific pairing of Cdk4/6 with D cyclins predisposes MM cells to proliferation. Moreover, dysregulation of Cdk4/6 is associated with an aggressive clinical course, suggesting that Cdk4 and Cdk6 are promising therapeutic targets. We have now identified a potent and specific small molecule Cdk4/6 inhibitor, which rapidly induces G1 arrest in primary myeloma cells ex vivo even in the presence of BM stromal cells, and prevents the growth of disseminated human myeloma tumors in xenografts. Inhibition of Cdk4/6 by PD 0332991 does not induce apoptosis. However, it markedly enhances the killing of myeloma cells by Bortesomib (Velcade, PS-341), a proteasome inhibitor widely used in MM therapy. These findings provide a strong rationale for developing cell cycle- based combination therapy for MM. On this basis, we propose that dysregulation of Cdk4 and Cdk6 in self- renewing myeloma cells by BM proliferation signals is a critical event in the initiation, progression and drug resistance in MM. To test this hypothesis and to advance superior therapeutic interventions, we propose the following specific aims: 1. To investigate the control of MM cell expansion and tumor growth by PD 0332991 in combination with proteasome inhibitors and to develop an effective cell-cycle based therapy, in primary BM myeloma cells and representative MM cell lines ex vivo and in two complementary in vivo systems; 2. To characterize the role of ectodomain shedding in the generation of putative self-renewing myeloma, control their reactivation by PD 0332991 and define their normal counterparts in plasma cell differentiation; 3. To elucidate the BM signals and pathways that promote self-renewal of BM myeloma cells and drug resistance.