Synergistic targeting of cholesterol metabolism and EGFR signaling in cancer

描述（由申请人提供）：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（固醇c4 -甲基氧化酶样），这是一种在固醇生物合成途径中很少研究的中间酶（Astsaturov, 2010）。我们的工作是第一个研究癌症中的SC4MOL和NSDHL (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甾醇（MAS），这些酶的底物，显著使癌细胞对EGFR抑制剂敏感（Sukhanova, 2013）。我们还发现，在SC4MOL或NSDHL水平上抑制甾醇通路可激活肝脏X受体（LXR），从而诱导胆固醇外排蛋白（ABC转运蛋白ABCA1和ABCG1）的表达，消耗细胞胆固醇，并降低LDL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抗体西妥昔单抗对人类异种移植物具有深刻的协同作用，并在小鼠遗传模型中抑制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甾醇代谢物积累，并通过激活LXR、破坏胆固醇摄取和生物合成、抑制致癌EGFR-KRAS信号传导来负性调节细胞生长。我们将通过执行以下具体目标来解决这一假设：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Aim 2中，我们将使用NSDHL缺乏的遗传小鼠模型来确定SC4MOL、NSDHL及其底物如何调节正常细胞与egfr依赖性癌细胞的生长。在Aim 3中，我们将检验相关假设，即加速胆固醇代谢决定了癌症对EGFR靶向治疗的侵袭性和难治性，以及通过LXR联合靶向EGFR信号和胆固醇代谢将是协同的。该项目将揭示EGFR功能调控的全新机制。最理想的是，这项工作将证明靶向SC4MOL， NSDHL或MAS甾醇下游的其他新靶点将有益于广泛的egfr阳性人类癌症，包括头颈癌和胰腺癌。

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.