Synergistic targeting of cholesterol metabolism and EGFR signaling in cancer

描述(申请人提供)：表皮生长因子受体(EGFR)及其家族成员的持续活性是癌症生长和耐药性的常见原因。在一系列生物信息学指导的siRNA文库筛选实验中，我们确定了一个影响抗性的蛋白质网络，其中包括SC4MOL(类固醇C4-甲基氧化酶)，这是一种很少研究的固醇生物合成途径的中间酶(AstSaturov，2010)。我们的工作是首次研究SC4MOL和NSDHL在癌症中的作用(Sukhanova，2013)，我们在癌症中建立EGFR信号和固醇代谢之间的相互作用旨在为提高靶向治疗的疗效提供新的机会。我们发现，沉默SC4MOL或NSDHL，或直接添加减数分裂激活类固醇(MAS)，这些酶的底物，显著增加癌细胞对EGFR抑制剂的敏感性(Sukhanova，2013)。我们还发现，在SC4MOL或NSDHL水平上阻止类固醇途径激活肝脏X受体(LXR)，从而诱导胆固醇外流蛋白(ABC转运体ABCA1和Abcg1)的表达，消耗细胞胆固醇，并减少低密度脂蛋白受体(LDLR)的表达。令人兴奋的是，我们发现SC4MOL或NSDHL的缺失与抗EGFR抗体西妥昔单抗具有深刻的协同作用，并在小鼠遗传模型中抑制了KRAS驱动的肿瘤的生长。我们的中心假设是，由于SC4MOL或NSDHL缺乏，MAS类固醇代谢物积累，并通过激活LXR，扰乱胆固醇的摄取和生物合成，抑制致癌的EGFR-KRAS信号，对细胞生长进行负面调节。我们将通过实现以下特定目标来解决这一假说：在目标1中，我们将确定SC4MOL和NSDHL的代谢底物调节胆固醇稳态的机制，并有助于癌细胞对抑制EGFR的药物的敏感性。在目标2中，我们将使用NSDHL缺乏症的遗传小鼠模型来确定SC4MOL、NSDHL及其底物如何调控正常细胞和EGFR依赖的癌细胞的生长。在目标3中，我们将测试相关的假设，即加速的胆固醇代谢定义了癌症对EGFR靶向治疗的侵袭性和耐受性，以及通过LXR联合靶向EGFR信号和胆固醇代谢将是协同的。该项目将阐明一种全新的调节EGFR功能的机制。最理想的是，这项工作将证明以SC4MOL、NSDHL或MAS甾醇下游的额外新靶点为靶点对包括头颈癌和胰腺癌在内的多种EGFR阳性人类癌症是有益的。

DESCRIPTION (provided by applicant): Persistent activity of epidermal growth factor receptor (EGFR) and its family members is a common cause for cancer growth and drug resistance. In a series of bioinformatics-guided siRNA library screening experiments we identified a network of resistance-influencing proteins that included SC4MOL (sterol C4-methyl oxidase-like), a little-studied intermediate enzyme in the sterol biosynthesis pathway (Astsaturov, 2010). Our work is the first to study SC4MOL and NSDHL in cancer (Sukhanova, 2013), and our establishment of reciprocal interactions between EGFR signaling and sterol metabolism in cancer are intended to provide new opportunities to improve the efficacy of targeted therapies. We have found that silencing of SC4MOL or NSDHL, or direct addition of meiosis activating sterols (MAS), a substrate for these enzymes, markedly sensitizes cancer cells to EGFR inhibitors (Sukhanova, 2013). We have also found that arrest of the sterol pathway at the level SC4MOL or NSDHL activates the liver X receptor (LXR), which induces the expression of cholesterol efflux proteins (the ABC transporters ABCA1 and ABCG1), depletes cellular cholesterol, and reduces expression of LDL lipoprotein receptors (LDLR). Excitingly, we found that loss of SC4MOL or NSDHL was profoundly synergistic with the anti-EGFR antibody cetuximab against human xenografts, and suppressed growth of KRAS-driven tumors in a mouse genetic model. Our central hypothesis is that MAS sterol metabolites accumulate as the result of SC4MOL or NSDHL deficiency and negatively regulate cell growth by activating LXR, disrupting cholesterol uptake and biosynthesis, and suppressing oncogenic EGFR-KRAS signaling. We will address this hypothesis by performing the following specific Aims: In Aim 1, we will determine the mechanism by which metabolic substrates of SC4MOL and NSDHL regulate cholesterol homeostasis and contribute to the sensitivity of cancer cells to agents inhibiting EGFR. In Aim 2, we will use a genetic mouse model of NSDHL deficiency to determine how SC4MOL, NSDHL, and their substrates regulate the growth of normal cells versus EGFR-dependent cancer cells. In Aim 3, we will test the linked hypotheses that accelerated cholesterol metabolism defines cancers' aggressiveness and refractoriness to EGFR-targeting therapies, and that combined targeting of EGFR signaling and cholesterol metabolism via LXR will be synergistic. This project will illuminate an entirely new mechanism for regulating EGFR function. Optimally, this work will justify the idea that targeting SC4MOL, NSDHL or additional new targets downstream of MAS sterols would be beneficial for a broad spectrum of EGFR-positive human carcinomas including head and neck and pancreatic cancers.