Retinoid Based Treatment Approaches to Target the Myeloma Stem Cell

描述（由申请人提供）：多发性骨髓瘤（MM）在很大程度上仍然是一种不治之症。持续存在的耐药细胞群，很可能是MM干细胞导致疾病复发的原因。据报告，CD 138阴性（CD 138-）MM细胞部分含有MM干细胞。然而，对MM干细胞的分子基础知之甚少，这使得难以特异性靶向这些细胞。我们的初步数据显示，与CD 138+肿瘤细胞相比，RAR 1是CD 138- MM干细胞中上调最多的基因。RAR 1有两种主要的亚型，RAR 11和RAR 12。Real-time PCR进一步证实了在CD 138- MM干细胞中增加的是RAR 12而不是RAR 11。虽然RAR 11在MM细胞中普遍表达，但RAR 12存在于约30%新诊断患者的MM细胞中。RAR 12表达的患者总体生存期较短。RAR 12 + MM细胞中的RAR 12敲低诱导细胞生长停滞和凋亡。有趣的是，ATRA选择性地杀死RAR 12过表达的CD 138- MM干细胞，而保留CD 138+肿瘤细胞。在RAR 12缺陷的MM肿瘤细胞中RAR 12的强制表达恢复了对ATRA的敏感性。我们还发现，Wnt信号在CD 138- MM干细胞中被激活，ATRA下调Wnt信号。我们的假设是，RAR 12通过激活Wnt/2-catenin途径维持MM干细胞的“干性”和耐药性; ATRA和其他维甲酸通过干扰Wnt信号传导发挥作用，导致“干性”特征的丧失。这项工作的目标是确定RAR 12维持MM干细胞的“干性”特征的机制以及类维生素A如何杀死MM干细胞。在具体目标1中，我们将评估原代MM干细胞中RARa 2的表达水平，并在动物模型中测试RARa 2在维持MM干性中的功能。在具体目标2中，我们将确定Wnt信号通路在ATRA/RARa 2诱导的MM干细胞凋亡中的功能作用。最后，在具体的目标3中，我们将开发基于类维生素A剂和靶向Wnt通路的药物的新方法，用于治疗SCID-hu小鼠中的MM干细胞和MM疾病。我们提出的研究可能会更好地了解MM干细胞中RAR 12的生物学功能，并可能为MM干细胞的新治疗方法提供有价值的信息，这可能会显着影响MM疾病的临床结果。由于癌症干细胞存在于变异的癌症恶性肿瘤中，因此拟议的研究也可能对其他癌症的治疗产生重大影响。 公共卫生相关性： 癌症干细胞在包括多发性骨髓瘤在内的越来越多的恶性肿瘤中被发现，并被认为是治疗失败和治疗后癌症再生长的原因。然而，癌症干细胞保持其“干性”特征的机制仍然知之甚少。我们已经在骨髓瘤干细胞中鉴定出一种蛋白质，它可能负责干细胞的生长和存活，也可能在骨髓瘤疾病的基于维甲酸的治疗中发挥关键作用。

DESCRIPTION (provided by applicant): Multiple myeloma (MM) remains largely an incurable disease. The persistence of a drug-resistant cell population, probably the MM stem cells may be the cause of disease relapse. CD138-negative (CD138-) MM cell fraction was reported to contain MM stem cells. However, little is known about the molecular base of MM stem cells, which makes it difficult to specifically target these cells. Our preliminary data show that RAR1 is the top one up-regulated gene in CD138- MM stem cells compared to CD138+ tumor cells. RAR1 has two major isoforms, RAR11 and RAR12. Real-time PCR further demonstrated that it was RAR12 but not RAR11 that increased in CD138- MM stem cells. While RAR11 was ubiquitously expressed in MM cells, RAR12 was present in MM cells from about 30% of newly diagnosed patients. Patients with RAR12 expression had shorter overall-survival. RAR12-knockdown in RAR12+ MM cells induced cell growth arrest and apoptosis. Interestingly, ATRA selectively killed RAR12-overexpressing CD138- MM stem cells while sparing CD138+ tumor cells. Forced expression of RAR12 in RAR12-deficient MM tumor cells restored sensitivity to ATRA. We also found that Wnt signaling is activated in CD138- MM stem cells and ATRA down-regulates Wnt signaling. Our hypothesis is that RAR12 maintains the "stemness" and drug-resistance of MM stem cells by activating the Wnt/2-catenin pathway; and ATRA and other retinoids work through interference with Wnt signaling, which leads to loss of "stemness" features. The goal of this work is to determine the mechanisms by which RAR12 maintains the "stemness" features of MM stem cells and how retinoids kill MM stem cells. In specific Aim 1, we will evaluate the expression levels of RARa2 in primary MM stem cells and to test RARa2 functions in maintenance of MM stemness in animal models. In specific Aim 2, we will determine functional roles of Wnt signaling pathway in the ATRA/RARa2-induced MM stem cell apoptosis. Finally, in specific Aim 3, we will exploit new approaches based on retinoid agents and drugs targeting Wnt pathway for the therapy of MM stem cells and MM disease in SCID-hu mice. Our proposed study may provide better understanding of the biological functions of RAR12 in MM stem cells and is likely to add valuable information on new therapeutic approaches for MM stem cells which may significantly impact the clinical outcome of MM diseases. Since cancer stem cells exist in variant cancer malignancies, the proposed study may also have a major impact on the treatment of other cancers. PUBLIC HEALTH RELEVANCE: Project Narrative Cancer stem cells are identified in an increasing list of malignancies, including multiple myeloma, and are thought to be responsible for treatment failure and re-growth of cancers after treatment. However, the mechanisms by which cancer stem cells maintain their "stemness" features are still poorly understood. We have identified a protein in myeloma stem cells that may be responsible for stem cell growth and survival and may also play a crucial role in retinoid-based therapy in myeloma disease.