The pathophysiological role of nuclear EGFR in TNBC

 描述(由申请人提供)：这项建议的目标是确定1)核表皮生长因子受体(NEGFR)是否通过其共转录功能导致三阴性乳腺癌(TNBC)对西妥昔单抗的耐药，2)如果靶向nEGFR，通过抑制其核转位，可以增加西妥昔单抗在TNBC的疗效，以及3)如果我们能够在功能上靶向nEGFR，则在TNBC患者中。三阴性乳腺癌(TNBC)是一种缺乏雌激素、孕激素和HER2受体的肿瘤，几乎没有治疗选择。因此，TNBC患者的预后仍然很差。最近的研究表明，大约50%的TNBC过表达癌基因EGFR，这预示着TNBC患者预后较差。不幸的是，测试抗EGFR单抗西妥昔单抗疗效的临床试验显示，对TNBC的预后几乎没有影响。这表明我们对EGFR如何推动TNBC以及如何在这种疾病中有效地靶向EGFR的了解存在差距。已经证实，EGFR在两个不同的信号区段中发挥作用：1)经典的膜结合信号和2)核信号。在细胞核内，EGFR具有两种功能：1)作为共转录因子，促进促癌基因的转录；2)作为酪氨酸激酶，负责磷酸化底物，促进DNA复制和修复。我们已经发表的数据显示，核EGFR(NEGFR)对西妥昔单抗治疗具有抵抗力，并且Src家族激酶(SFK)是EGFR核转位所必需的。在这一建议中，我们假设nEGFR通过其作为核共转录因子的作用而参与西妥昔单抗耐药，并在TNBC中作为功能分子靶点。为了验证这一假设，我们绘制了EGFR的C-末端结构域，以确定EGFR转录活性所必需的关键氨基酸。这导致了一种EGFR变异体，它缺乏转录活性，但保留了其信号转导能力，将用于阐明nEGFR在西妥昔单抗耐药中的转录功能(特异性目标1)。这项建议将进一步评估同时靶向经典和nEGFR信号通路的治疗益处，方法是通过SFK阻断(达沙替尼)消除核转位-随后在原位和患者来源的异种移植模型系统中使用西妥昔单抗靶向经典的EGFR信号通路(特定目标2)。最后，我们将在nEGFR阳性的TNBC患者中进行一项窗口试验，以确定我们是否可以靶向人类的nEGFR，并将EGFR的表达重新分配到质膜，在那里它可以被西妥昔单抗抑制(特定目标3)。总而言之，这些研究有可能通过靶向EGFR信号的两个部分，重新定义我们如何在TNBC和其他表达nEGFR的癌症(HNSCC、肺癌、膀胱癌)中靶向EGFR，从而将本来对西妥昔单抗耐药的肿瘤转变为现在对西妥昔单抗敏感的肿瘤。这一研究策略可以很容易地转化为临床治疗TNBC患者。

 DESCRIPTION (provided by applicant): The objectives of this proposal are to determine 1) if the nuclear epidermal growth factor receptor (nEGFR) drives resistance to cetuximab in triple-negative breast cancer (TNBC) via its co-transcriptional functions, 2) if targeting nEGFR, by inhibiting its nuclear translocation, can increase the efficacy of cetuximab in TNBC and 3) if we can functionally target nEGFR in TNBC patients. Triple-negative breast cancer (TNBC) is a tumor that lacks estrogen, progesterone and HER2 receptors, leaving minimal therapeutic options. As a result, the prognosis of patients with TNBC remains poor. Recent studies revealed that approximately 50% of TNBC overexpress the oncogene EGFR, which predicts poor patient outcome in TNBC. Unfortunately, clinical trials testing the efficacy of the anti-EGFR monoclonal antibody cetuximab revealed little impact on outcomes in TNBC. This suggests a gap in our knowledge of how EGFR drives TNBC and how to target EGFR effectively in this disease. It is well established that EGFR functions in two distinct signaling compartments: 1) Classical membrane bound signaling and 2) nuclear signaling. Within the nucleus, EGFR performs two functions: 1) as a co-transcription factor enhancing transcription of cancer-promoting genes, and 2) as a tyrosine kinase responsible for phosphorylating substrates that enhance DNA replication and repair. We have published data showing that nuclear EGFR (nEGFR) confers resistance to cetuximab therapy and that the Src Family Kinases (SFKs) are necessary for nuclear translocation of the EGFR. In this proposal we hypothesize that nEGFR contributes to cetuximab resistance via its role as a nuclear co-transcription factor and serves as a functional molecular target in TNBC. To test this hypothesis we have mapped the EGFR C-terminal domain to identify key amino acids necessary for transcriptional activity of the EGFR. This resulted in an EGFR variant that lacks transcriptional activity but retains its signaling capacity that will be used to elucidate nEGFR transcriptional function in cetuximab resistance (Specific Aim 1). This proposal will further assess the therapeutic benefit of targeting both the classical and nEGFR signaling pathways simultaneously by abrogating nuclear translocation via SFK blockade (dasatinib) - followed by subsequent targeting of the classical EGFR signaling pathway with cetuximab in both orthotopic and patient derived xenograft model systems (Specific Aim 2). Finally, we will perform a window trial in nEGFR positive TNBC patients, to determine if we can target nEGFR in humans and redistribute EGFR expression to the plasma membrane where it can be inhibited by cetuximab therapy (Specific Aim 3). Collectively, these studies have potential to re-define how we target EGFR in TNBC and other nEGFR expressing cancers (HNSCC, Lung, bladder), by targeting both compartments of EGFR signaling, and thus turning a tumor that is intrinsically resistant to cetuximab into a tumor that is now sensitive to cetuximab. This investigative strategy can be readily translated to the clinic for treatment of TNBC patients.