Developing targeted therapies for triple-negative breast cancer

描述（由申请人提供）：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可分为至少6种亚型，包括间充质样亚型和基底样亚型，其中大多数TNBC可归为间充质样亚型。TNBC约占所有乳腺癌病例的15-20%，最常见于年轻女性和非裔美国女性。TNBC患者一般预后较差，生存期较短。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。虽然转移性TNBC的妇女最初可以对传统的化疗药物有反应，但复发是不可避免的，肿瘤学家除了提供额外的非交叉反应性全身化疗方案外，几乎没有别的办法。因此，我们面临的挑战是为转移性三阴癌患者开发一种更有效的治疗方案。我们发现丝氨酸-苏氨酸磷酸酶PP2A是调节TNBC细胞耐药的限速因子（瓶颈）。我们发现PP2A抑制剂可以使敏感和耐药间充质样TNBC细胞对肿瘤坏死因子相关凋亡诱导配体（TRAIL）诱导的凋亡敏感。基于trail的药物目前正在临床试验中用于几种癌症的治疗。因此，这些考虑表明，间充质样TNBC可能受益于TRAIL治疗或联合PP2A抑制剂治疗。虽然间充质样TNBC细胞对TRAIL诱导的凋亡高度敏感，但基底样TNBC细胞对TRAIL有抗性。我们发现，PP2A抑制剂LB100是一种小分子，最近已被批准进入治疗几种癌症的I期临床试验，在体外增加常规化疗药物诱导的基底样TNBC细胞的抗癌活性，并在体内有效抑制基底样TNBC的肿瘤生长。这表明LB100单独或联合临床使用的化疗药物可能是治疗基底样TNBC的有效方法。此外，我们的初步数据显示，TRAIL处理导致TNBC细胞中PP2A的催化亚基PP2A/C的降解。在机制上，TRAIL处理导致PP2A/C被招募到诱导死亡的信号复合体（DISC），其中基于cullin -3的E3连接酶靶向PP2A/C进行泛素化和随后的降解。重要的是，在已经产生获得性TRAIL抗性的TNBC细胞中，PP2A/C蛋白对TRAIL诱导的降解具有抗性。在本提案中，我们将验证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引起间充质样TNBC细胞凋亡的假设，以及单独或联合常规化疗药物抑制PP2A生存信号有效抑制基底样TNBC生长的假设。我们建议通过以下三个具体目的来验证这些假设：1)评估TRAIL作为单一药物，与LB100或紫杉醇联合治疗间充质样TNBC细胞系和异种移植物的疗效；2)明确trail诱导的细胞凋亡中PP2A/C泛素化的分子机制；3)确定LB100单药或与紫杉醇联合治疗基底样TNBC细胞系和异种移植物的疗效。该申请将确定单独使用TRAIL靶向治疗与LB100（最近被FDA批准进入治疗几种癌症的I期临床试验）联合，或与临床使用的化疗药物联合治疗间充质样TNBC和LB100或与临床使用的化疗药物联合治疗基底样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.