Targeting MUC4 for chemosensitization of pancreatic cancer

描述（由申请人提供）：胰腺癌（PC）是美国癌症死亡的第四大原因，五年生存率仅为5%。目前的标准治疗晚期PC，吉西他滨，生存期只有几个星期，只有25%的患者对这种治疗有反应。吉西他滨耐药是胰腺癌治疗中的一个主要问题。我们最近发现MUC 4有助于PC细胞对吉西他滨诱导的细胞凋亡的抵抗。MUC 4粘蛋白是PC细胞异常表达的大分子糖蛋白。我们先前已经表明MUC 4下调诱导凋亡，抑制增殖，阻断侵袭和转移，并使PC细胞对吉西他滨敏感。这些结果表明，MUC 4可能是PC中非常相关的治疗靶点。然而，目前没有治疗策略来下调体内MUC 4表达。丙酸氟替卡松（FP）是一种有效的抗炎糖皮质激素，临床上用于治疗支气管哮喘，以前曾报道抑制培养的鼻息肉细胞MUC 4 mRNA的表达。然而，其在调节PC细胞中MUC 4表达和PC细胞行为中的作用从未被研究过。该提议的中心假设是，用糖皮质激素药理学下调MUC 4将增强PC细胞对化疗剂的敏感性，并且GC的组合将协同增强化疗的治疗功效。初步研究表明，FP通过糖皮质激素受体（GR）在转录水平下调MUC 4的表达。为了进一步研究FP影响MUC 4表达的机制，并评估其在PC中的潜在治疗相关性，我们提出了三个具体目标。在目标1中，我们将使用GR特异性shRNA、启动子-报告基因分析和染色质免疫沉淀来研究在PC细胞中观察到的FP下调MUC 4的机制。在目标2中，我们将检查FP治疗对体外PC细胞功能的影响，比较FP与地塞米松（目前用于与癌症化疗联合治疗的糖皮质激素）在影响PC细胞对吉西他滨的敏感性方面的作用，并检查FP治疗对裸鼠原位异种移植模型中PC肿瘤生长和体内化疗敏感性的影响。在目标3中，我们将在临床相关的自发性PC小鼠模型中检查FP治疗对PC肿瘤生长和体内化疗敏感性的影响。总之，拟议的研究将调查这种新型MUC 4抑制剂的治疗潜力，作为现有PC化疗方案的辅助治疗。

DESCRIPTION (provided by applicant): Pancreatic cancer (PC) is the fourth leading cause of cancer deaths in the U.S. and has a five-year survival rate of only 5%. The current standard of care for advanced PC, gemcitabine, prolongs survival by only a few weeks, and only 25% of patients respond to this treatment. Resistance to gemcitabine is a major problem in the treatment of pancreatic cancer. We have recently shown that MUC4 contributes to the resistance of PC cells to gemcitabine-induced apoptosis. MUC4 mucin is a large glycoprotein aberrantly expressed by PC cells. We have previously shown that MUC4 downregulation induces apoptosis, inhibits proliferation, blocks invasion and metastasis and sensitizes PC cells to gemcitabine. These results suggest that MUC4 could be an extremely relevant therapeutic target in PC. However, there are currently no therapeutic strategies to downregulate MUC4 expression in vivo. Fluticasone propionate (FP), a potent anti-inflammatory glucocorticoid used clinically in treating bronchial asthma, has previously been reported to repress the expression of MUC4 mRNA in cultured nasal polyp cells. However, its role in regulating MUC4 expression in PC cells and on PC cell behavior has never been examined. The central hypothesis of the proposal is that Pharmacological downregulation of MUC4 with glucocorticoids would enhance the sensitivity of PC cells to chemotherapeutic agents and a combination of GCs will synergistically enhance the therapeutic efficacy of chemotherapy. The preliminary studies have indicated that FP downregulates MUC4 expression at the transcript level via the glucocorticoid receptor (GR). To investigate further the mechanism by which FP affects MUC4 expression and to assess its potential therapeutic relevance in PC, we propose three specific aims. In aim 1 we will investigate the mechanisms underlying the observed downregulation of MUC4 by FP in PC cells using GR specific shRNAs, promoter-reporter assays and chromatin immunoprecipitation. In aim 2 we will examine the effect of FP treatment on PC cell function in vitro, compare FP with dexamethasone (a glucocorticoid currently used in co-treatment with cancer chemotherapy) in affecting the sensitivity of PC cells to gemcitabine, and examine the effect of FP treatment on PC tumor growth and chemosensitivity in vivo in an orthotopic xenograft model in nude mice. In aim 3, we will examine the effect of FP treatment on PC tumor growth and chemosensitivity in vivo in a clinically relevant spontaneous PC mouse model. Taken together, the proposed studies will investigate the therapeutic potential of this novel MUC4 repressing agent for possible application as an adjuvant to existing PC chemotherapy regimens.