HIF-1α和STAT3介导LDLR上调在乏氧诱导的肺癌EGFR-TKIs继发耐药中的作用研究

Besides classical drug resistance mechanisms, hypoxia could also induce acquired resistance to EGFR-TKI in lung cancer. However, the underlying molecular mechanism remains unknown. Low density lipoprotein receptor (LDLR) is a critical factor in lipid metabolism regulation. Recently we found that high expression level of LDLR before treatment was associated with poor prognosis in lung cancer patients with EGFR mutations receiving EGFR-TKI. We also found that hypoxia could lead to increased expression of LDLR, which was closely related to the high expression level of Hypoxia-inducible Factor-1α (HIF-1α) and the activation of Signal Transducer and Activator of Transcription 3 (STAT3). In addition, LDLR, HIF-1α as well as STAT3 were all significantly up-regulated in tumor samples after acquired EGFR-TKI resistance. Furthermore, over-expression of LDLR could cause EGFR-TKI resistance in cell lines with sensitive EGFR mutations. We therefore hypothesized that hypoxia could induce up-regulation of LDLR via HIF-1α and STAT3，and then mediate the development of acquired resistance to EGFR-TKI. In this project, we will explore the regulation of LDLR by HIF-1α and STAT3 and the underlying mechanism. We will also investigate whether inhibition of LDLR could reverse EGFR-TKI resistance. This project might reveal the molecular mechanism of acquired EGFR-TKI resistance induced by hypoxia, and provide a new therapeutic strategy to overcome EGFR-TKI resistance.

除经典耐药机制外，乏氧也可诱导肺癌中EGFR-TKI继发耐药的产生，但具体机制不清。低密度脂蛋白受体（LDLR）是调控脂代谢的关键因子。近期我们发现在EGFR突变的肺癌患者中，使用EGFR-TKI前LDLR高表达与预后不良相关。进一步研究发现，在肺癌细胞系中，乏氧可诱导LDLR上调，且LDLR上调与HIF-1α表达升高及STAT3活化密切相关；EGFR-TKI耐药后的肺癌组织中，HIF-1α、STAT3和LDLR也均明显上调；此外，过表达LDLR可诱导具有EGFR敏感突变的细胞系产生耐药。因此我们假设乏氧通过HIF-1α和STAT3介导LDLR上调，进而诱导了EGFR-TKI继发耐药。本课题将分别研究HIF-1α和STAT3对LDLR的调节及分子机制，及抑制LDLR在逆转EGFR-TKI耐药中的作用。本研究将揭示乏氧诱导的EGFR-TKI继发耐药的分子机制，为克服耐药提供新的治疗策略。

此前的研究发现，在多种恶性肿瘤中均存在胆固醇代谢的异常。低密度脂蛋白受体（LDLR）及其配体低密度脂蛋白（LDL）是调控胆固醇代谢的关键因子。我们的前期研究发现，基线时LDLR高表达的EGFR突变阳性非小细胞肺癌患者接受靶向治疗疗效差。因此，我们开展了一系列研究，以探索EGFR通路与LDLR之间的调控关系，LDL对EGFR突变阳性非小细胞肺癌细胞系存活与增殖的影响，抗胆固醇治疗与EGFR酪氨酸激酶抑制剂（EGFR-TKI）之间是否存在协同作用，以及在更大人群中明确LDLR表达量的临床意义。首先，我们发现，EGFR通路的活化程度与LDLR的表达存在明确的调节关系，EGFR突变阳性的非小细胞肺癌细胞系较野生型的非小细胞肺癌细胞系，LDLR表达明显上调。此外，EGFR是通过Akt/SREBP-1途径调节LDLR的表达。第二，明确了LDLR的配体LDL对于EGFR突变非小细胞肺癌细胞系的生长和增殖有显著的影响，使用他汀类药物抑制胆固醇合成，可抑制EGFR突变非小细胞肺癌细胞的生长和增殖，联合使用他汀类药物和EGFR-TKI，具有协同抗肿瘤作用，并可能逆转EGFR-TKI耐药。最后，EGFR突变阳性非小细胞肺癌患者耐药后组织标本中LDLR的水平明显升高，且基线时LDLR的水平与预后明确相关，LDLR表达水平高的患者预后差。这些发现为进一步改善EGFR突变阳性患者的治疗策略提供了重要的理论基础。基于这些发现，我们团队拟开展前瞻性的临床研究，评估阿托伐他汀联合EGFR-TKI这种治疗策略的疗效及安全性，以期改善EGFR突变阳性非小细胞肺癌患者，尤其是基线时LDLR高表达患者的预后。