Developing targeted therapies for triple-negative breast cancer

描述(申请人提供)：三阴性乳腺癌(TNBC)缺乏雌激素受体(ER)、孕激素受体(PR)和Her2的表达。TNBC至少可分为间充质样和基底样6种亚型，其中大部分为间充质样细胞。TNBC约占所有乳腺癌病例的15%-20%，最常见的是年轻女性和非裔美国女性。TNBC患者一般预后较差，近期存活率较低。这种侵袭性疾病对广泛使用的靶向治疗如曲妥珠单抗或内分泌治疗如他莫昔芬或芳香酶抑制剂没有反应。尽管患有转移性TNBC的女性最初对常规化疗药物有反应，但复发是不可避免的，肿瘤学家除了提供额外的无交叉反应的全身化疗方案外，几乎没有什么可提供的。因此，挑战是开发一种更有效的治疗转移性TNBC的治疗方案。我们发现丝氨酸-苏氨酸磷酸酶PP2A是调节TNBC细胞耐药性的限速因子(瓶颈)。我们发现，PP2A抑制剂可以使敏感和耐药的间充质样细胞对肿瘤坏死因子相关的凋亡诱导配体(TRAIL)诱导的细胞凋亡敏感。基于TRAIL的药物目前正在进行临床试验，用于治疗几种类型的癌症。因此，这些考虑提示间充质样的TNBC可能受益于TRAIL治疗或联合PP2A抑制剂治疗。尽管间充质样细胞对TRAIL诱导的细胞凋亡高度敏感，但基底样细胞对TRAIL具有抵抗力。我们发现，PP2A抑制剂LB100，一个最近被批准进入I期临床试验的小分子，用于治疗几种癌症，在体外增加了传统化疗药物诱导的基底样TNBC细胞的抗癌活性，并有效地抑制了体内基底样TNBC细胞的肿瘤生长。这提示LB100单独或与临床使用的化疗药物联合应用可能是治疗基底细胞样癌的有效方法。此外，我们的初步数据显示，TRAIL处理导致TRAIL处理导致TNBC细胞中PP2A催化亚单位PP2A/C的降解。从机制上讲，TRAIL处理导致PP2A/C被招募到死亡诱导信号复合体(DISC)，在那里基于Cullin-3的E3连接酶针对PP2A/C进行泛素化和随后的降解。重要的是，在已经产生TRAIL耐药的TNBC细胞中，PP2A/C蛋白对TRAIL诱导的降解具有抵抗力。在这项提议中，我们将检验以下假设：TRAIL单独或联合抑制PP2A介导的生存信号或临床使用的化疗药物足以导致间充质样TNBC细胞凋亡，以及单独抑制PP2A生存信号或与常规化疗药物联合有效地抑制基底样TNBC的生长。我们建议以以下三个具体目标来验证这些假说：1)评估TRAIL与LB100或紫杉醇作为单一药物在间充质样TNBC细胞株和异种移植瘤中的治疗效果；2)确定PP2A/C泛素化在TRAIL诱导的细胞凋亡中的分子机制；以及3)确定LB100作为单一药物或联合紫杉醇对基底样TNBC细胞株和异种移植瘤的治疗效果。这项申请将确定靶向治疗TRAIL单独与LB100(FDA新批准进入治疗几种类型癌症的I期临床试验)联合使用的疗效，或与临床美元化疗药物联合治疗间叶样TNBC和LB100单独或其与临床使用的化疗药物联合治疗基底细胞样TNBC的疗效。

DESCRIPTION (provided by applicant): Triple-negative breast cancer (TNBC) lacks the expression of estrogen receptor (ER), progesterone receptor (PR) and Her2. TNBC can be classified into at least six subtypes including mesenchymal-like and basal-like with the majority of TNBC categorized as mesenchymal-like. TNBC makes up approximately 15-20% of all breast cancer cases and most commonly affects younger women and African-American women. Patients with TNBC generally have a poor prognosis and short-term survival. This aggressive disease does not respond to widely used targeted therapies such as trastuzumab or endocrine therapies, such as tamoxifen or aromatase inhibitors. Although women with metastatic TNBC can initially respond to conventional chemotherapeutic agents, relapse is inevitable, and oncologists have little to offer other than additional non-cross reactive systemic chemotherapy regimens. Therefore, the challenge is to develop a more effective treatment regimen for women with metastatic TNBC. We find that serine-threonine phosphatase PP2A is a rate-limiting factor (bottleneck) that regulates drug-resistance in TNBC cells. We show that PP2A inhibitors can sensitize both sensitive and resistant mesenchymal-like TNBC cells to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. TRAIL-based drugs are currently being tested for the treatment of several cancer types in clinical trials. Therefore, these considerations suggest that mesenchymal-like TNBC may be likely to benefit from TRAIL therapy or in combination with PP2A inhibitor therapy. Although mesenchymal-like TNBC cells are highly sensitive to TRAIL-induced apoptosis, basal-like TNBC cells are resistant to TRAIL. We find that the PP2A inhibitor LB100, a small molecule that has recently been approved to enter phase I clinical trials for the treatment of several cancers, increases conventional chemotherapeutic agent-induced anticancer activity in basal-like TNBC cells in vitro and effectively inhibits tumor growth of basal-like TNBC in vivo. This consideration suggests that LB100 alone or in combination with clinically used chemotherapeutic agents could be an efficacious therapy for basal-like TNBC. In addition, our preliminary data show that TRAIL treatment causes the degradation of PP2A/C, a catalytic subunit of PP2A, in TNBC cells. Mechanistically, TRAIL treatment leads to the recruitment of PP2A/C to the death-inducing signaling complex (DISC) where a Cullin-3-based E3 ligase targets PP2A/C for ubiquitination and subsequent degradation. Importantly, in TNBC cells that have developed acquired TRAIL resistance, PP2A/C protein is resistant to TRAIL-induced degradation. In this proposal, we will test the hypotheses that TRAIL alone or in combination with inhibition of PP2A-mediated survival signals or clinically used chemotherapeutic agents sufficiently causes apoptosis in mesenchymal-like TNBC cells and that inhibition of PP2A survival signals alone or in combination with conventional chemotherapeutic agents effectively inhibits the growth of basal-like TNBC. We are proposing to test these hypotheses with the following three specific aims: 1) To evaluate the therapeutic efficacy of TRAIL as a single agent, in combination with LB100, or paclitaxel in mesenchymal-like TNBC cell lines and xenografts; 2) To define the molecular mechanism of PP2A/C ubiquitination in TRAIL-induced apoptosis; and 3) To determine the therapeutic efficacy of LB100 as a single agent or in combination with paclitaxel in basal-like TNBC cell lines and xenografts. This application will determine the efficacy of using TRAIL, a targeted therapy alone, in combination with LB100 (newly approved by the FDA to enter phase I clinical trials for the treatment of several types of cancer), or in combination with clinically usd chemotherapeutic agents to treat mesenchymal-like TNBC and LB100 alone or its combination with clinically used chemotherapeutic agents to treat basal-like TNBC.