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无法治愈的疾病。耐药细胞群的持续存在，可能是MM干细胞引起疾病复发的原因。据报道，CD138-阴性（CD138-） 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，这使得很难特异性靶向这些细胞。我们的初步数据显示，与CD138+肿瘤细胞相比，RAR1是CD138- MM干细胞中上调最多的基因。RAR1有两个主要的同工异构体，RARa1和RARa2。Real-time PCR进一步证实，在CD138- MM干细胞中，RARa2而非RARa1表达增加。虽然RARa1在MM细胞中普遍表达，但约30%的新诊断患者的MM细胞中存在RARa2。表达RARa2的患者总生存期较短。RARa2+ MM细胞中RARa2-敲低诱导细胞生长停滞和凋亡。有趣的是，ATRA选择性地杀死过表达rara2的CD138- MM干细胞，同时保留CD138+肿瘤细胞。在RARa2缺失的MM肿瘤细胞中强制表达RARa2可以恢复对ATRA的敏感性。我们还发现Wnt信号在CD138- MM干细胞中被激活，ATRA下调Wnt信号。我们的假设是RARa2通过激活Wnt/2-catenin通路维持MM干细胞的“干性”和耐药；ATRA和其他类维生素a通过干扰Wnt信号发挥作用，从而导致“干性”特征的丧失。这项工作的目的是确定RAR12维持MM干细胞“干性”特征的机制，以及类维生素a如何杀死MM干细胞。在特定的Aim 1中，我们将阐明RARa2维持MM干细胞生长和存活的机制。在特定的Aim 2中，我们将阐明Wnt/2-catenin通路在atra诱导的MM干细胞生长和存活中的作用。最后，在特定的Aim 3中，我们将探索基于类维生素a药物和靶向Wnt通路的药物治疗SCID-hu和5TGM1小鼠MM模型中的MM干细胞和MM疾病的新方法。我们提出的研究可能会更好地了解RARa2在MM干细胞中的生物学功能，并可能为MM干细胞的新治疗方法提供有价值的信息，这可能会显著影响MM疾病的临床结果。由于癌症干细胞存在于不同的恶性肿瘤中，因此这项研究也可能对其他癌症的治疗产生重大影响。

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, RARa1 and RARa2. Real-time PCR further demonstrated that it was RARa2 but not RARa1 that increased in CD138- MM stem cells. While RARa1 was ubiquitously expressed in MM cells, RARa2 was present in MM cells from about 30% of newly diagnosed patients. Patients with RARa2 expression had shorter overall-survival. RARa2-knockdown in RARa2+ MM cells induced cell growth arrest and apoptosis. Interestingly, ATRA selectively killed RARa2-overexpressing CD138- MM stem cells while sparing CD138+ tumor cells. Forced expression of RARa2 in RARa2-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 RARa2 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 clarify the mechanisms by which RARa2 maintains MM stem cell growth and survival. In specific Aim 2, we will clarify the role of Wnt/2-catenin pathway in ATRA-induced MM stem cell growth and survival. 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 and 5TGM1 murine MM models. Our proposed study may provide better understanding of the biological functions of RARa2 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: Cancer stem cells are identified in an increasing list of malignancies, including multiple myeloma, and are thought to be responsible for treatment failure and regrowth 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.