A Strategy for Reactivating p53 in Cancer Stem Cells Using a Novel HdmX Inhibitor

描述（由申请人提供）：近年来，由于我们对驱动癌症发展的信号通路的理解取得了重大进展，肿瘤学家可用的治疗方案数量急剧增加。一个关键的细胞周期检查点调节因子是p53肿瘤抑制因子，它在正常细胞中由HdmX和Hdm2控制。毫不奇怪，p53在大多数人类癌症中是失活的，要么是由于Hdm2或HdmX的突变，要么是过度表达。鉴于其最近在抑制癌症干细胞（CSC）转录谱中的作用，这是三阴性乳腺癌（TNBC）亚型的标志，我们提出了一种旨在重新激活p53的新策略，以造福TNBC患者。使用TNBC模型，我们的初步研究已经确定了CSC人群中高水平的HdmX蛋白。目前，dna损伤化疗是TNBC的一线治疗方法。然而，这种方法的副作用很明显，而且通常剂量有限，因为DNA损伤无法激活突变型p53或从HdmX中充分释放野生型p53。此外，与其他乳腺癌亚型相比，CSC的比例增加使得快速复发成为一个重要问题。目前在临床试验中用于p53再激活的最先进的分子包括Hdm2拮抗剂Nutlin-3和突变型p53再激活化合物PRIMA-1。然而，Nutlin-3特异性地破坏Hdm2-p53而不是HdmX-p53的相互作用。因此，最初对Nutlin-3的兴奋已经被观察到含有高水平HdmX的肿瘤对Nutlin-3治疗有抵抗力的结果所抑制。我们认为TNBC CSC不会对Nutlin-3或其他hdm2特异性分子产生反应。为了确定HdmX特异性抑制剂来帮助对抗TNBC，我们建立了一种检测p53在高水平HdmX表达下激活的方法，并进行了高通量筛选。我们在这里描述了HdmX选择性抑制剂CTX1的发现。本研究假设HdmX是TNBC中CSC的关键调控因子，联合抑制HdmX和Hdm2可有效杀伤TNBC CSC，阻止肿瘤生长。我们为目前的研究设计了两个目标。在AIM 1中，我们将确定ctx1介导的TNBC生长抑制的机制和疗效。我们将测试CTX1/Nutlin-3联合治疗对HdmX和Hdm2的抑制是否会导致野生型p53的持续激活，以及PRIMA-1重新激活的突变型p53。在AIM 2中，我们将使用体外生成的CSC异种移植模型和从原发性三阴性乳腺癌中分离的CSC，研究CTX1和Nutlin-3联合治疗对TNBC干细胞的抑制作用。综上所述，CTX1具有较高的抗癌活性，对HdmX具有较高的特异性，并且与Hdm2抑制剂Nutlin-3具有协同作用，因此CTX1是一个很好的化合物，值得进一步研究。此外，由于TNBC患者转移性疾病的风险增加，对当前化疗方案的反应较差，复发时间短，总生存率低，因此他们是理想的候选者，可以从p53-再激活联合治疗中获益最多，如本文所述。

DESCRIPTION (provided by applicant): The number of treatment options available to oncologists has dramatically increased in recent years due to major advances in our understanding of the signaling pathways that drive cancer development. A critical cell cycle checkpoint regulator is the p53 tumor suppressor, which is kept in check in normal cells by HdmX and Hdm2. Not surprisingly, p53 is inactivated in most human cancers, either by mutation or overexpression of Hdm2 or HdmX. Given its recently described role in suppressing a cancer stem cell (CSC) transcriptional profile, which is a hallmark of triple-negative breast cancer (TNBC) subtypes, we are proposing a new strategy aimed at reactivating p53 for the benefit of TNBC patients. Using a TNBC model, our preliminary studies have identified high levels of HdmX protein in the CSC population. Currently, DNA-damaging chemotherapy is the first-line therapy for TNBC. However, the side effects from this approach are significant and often dose limiting because DNA damage is unable to activate mutant p53 or sufficiently release wild-type p53 from HdmX. Moreover, an increased proportion of CSC compared to other breast cancer subtypes makes rapid recurrence a significant issue. The most advanced molecules currently in clinical trials for reactivating p53 include the Hdm2 antagonist Nutlin-3 and the mutant p53 reactivating compound PRIMA-1. However, Nutlin-3 specifically disrupts Hdm2-p53 but not HdmX-p53 interactions. Thus, the initial excitement over Nutlin-3 has been dampened by observations that tumors harboring high levels of HdmX are resistant to Nutlin-3 treatment. We propose TNBC CSC will not respond to Nutlin-3, or other Hdm2-specific molecules. Towards identifying HdmX- specific inhibitors to help combat TNBC, we established an assay to detect p53 activation in the presence of high-level HdmX expression and performed a high-throughput screen. We describe here the discovery of a selective inhibitor of HdmX named CTX1. The hypothesis of this proposal is that HdmX is a key regulator of CSC in TNBC, and that combined suppression of HdmX and Hdm2 will efficiently kill TNBC CSC and prevent tumor growth. We have devised two aims for the current study. In AIM 1, we will determine the mechanism and efficacy of CTX1-mediated growth suppression in TNBC. We will test whether suppression of both HdmX and Hdm2 by combined CTX1/Nutlin-3 therapy results in the sustained activation of wild-type p53, as well as mutant p53 reactivated by PRIMA-1. In AIM 2, we will examine the suppression of TNBC stem cells by combination therapy involving CTX1 and Nutlin-3 using xenograft models of CSC generated in vitro and CSC isolated from primary triple-negative breast cancers. In summary, CTX1 is an excellent compound for further studies as it exhibits high anti-cancer activity, high specificity for HdmX, and a synergy with the Hdm2 inhibitor Nutlin-3. Moreover, because TNBC patients have an increased risk of metastatic disease, respond poorly to current chemotherapeutic regimens, have a short time to recurrence, and poor overall survival, they are the ideal candidates who could benefit most from combined p53-reactivation therapy, as described here.