靶向干预干细胞亚群（HER2+/CD133+GSCs）增强胶质母细胞瘤放疗敏感性的机制研究

Glioblastoma multiform (GBM) is the most common and malignant primary brain tumor with currently only ∼12–18 month’s survival after diagnosis despite aggressive surgery and chemo-radiotherapy. Currently, radiotherapy is the major modality for the control of GBM; however, its effectiveness is often compromised by an adaptive resistance in tumor cells, which translates into a dire outcome for patients. Understanding the mechanisms causing the acquired radioresistance is critical for developing effective approaches to control GBM and significantly enhance the patient survival. . Accumulating evidence suggests that GBM stem cells (GSCs) are responsible for aggressive growth and therapy-resistance. Although cancer stem cells are identified in many solid tumors including GBM and have been extensively studied, currently no effective approaches are available to target the resistant GBM lesions. Identification of mechanistic insights causing GBM radioresistance will provide critical information and potential effective therapies to eliminate recurrent GBM and improve patient survival. . The rationale for this study is based on significant findings from our group indicating that a specific fraction of GBM cells with the stem-like features, i.e., HER2+/CD133+ and elevated pTyr705-STAT3 (part of the self-renewal/stemness network), are enriched in GBM population that survived from therapeutic doses of radiation. STAT3 is a well-defined oncogenic transcriptional factor and plays a key role in tumor aggressive growth. In addition, HER2 has been shown to activate STAT3 that can be translocated into nucleus to enhance target genes for DNA repair and cell proliferation. We found that HER2+/CD133+ GSCs are enhanced in the radioresistant GBM cells after therapeutic radiation. The hypotheses to be tested is that HER2+/CD133+ GSCs are enhanced during in vivo radiation due to activation of HER2-pY705-STAT3 pathway which results in the upregulation of DNA repair capacity and tumor cell survival, leading to the resistant, aggressive recurrent GBM. The overall purpose of this grant application is to reveal the mechanistic insights of HER2+/CD133+ GSCs, and to test if targeting HER2+/CD133+ GSCs can significantly enhance the radiosensitivity of GBM. We plan to characterize the radioresistant HER2+/CD133+ GSCs in irradiated GBM cells and clinical patients; to elucidate the DNA repair capacity and cell survival due to activation of HER2-pY705-STAT3 pathways in HER2+/CD133+ GSCs; and to evaluate the efficacy of radiosensitization by targeting pY705-STAT3 in GBM radiotherapy. The success of this project will shed new light on the dynamic repopulation of GBM stem cells under radiotherapy and invent efficacious modalities to control GBM.

多形性胶质母细胞瘤（GBM）是常见且恶性程度最高的神经系统肿瘤之一，预后极差。放疗是临床控制GBM的标准手段，然而GBM的适应性抵抗常致治疗失败。我们前期在放射抵抗GBM细胞和放疗后复发的标本中发现HER2+/CD133+GBM干细胞亚群（GSCs）富集，且这群细胞的磷酸化STAT3（pY705-STAT3）水平升高。HER2可以通过两种方式磷酸化修饰激活STAT3（pS727-STAT3和pY705-STAT3）。藉此，我们提出HER2+/CD133+GSCs可能是GBM中放疗抵抗的GSC亚群，其通过HER2激活形成pY705-STAT3入核，促进代谢重构、DNA修复和细胞增殖相关靶基因的表达，导致放射抵抗。本项目将聚焦HER2-pY705-STAT3影响GBM细胞放疗敏感性的机制，并通过细胞和多种动物模型验证靶向干预该通路对GBM的放疗增敏效果，为提高GBM放疗疗效的临床转化奠定基础。

近年来，肿瘤研究进展迅速，患者总体预后也有所改善，但胶质母细胞瘤（GBM）的临床疗效仍不容乐观，5年生存率不足10%。手术是GBM的首选治疗方式，然而因GBM浸润、弥漫性生长的特点，病灶难以完全切除，术后放疗对控制GBM复发和改善患者预后至关重要。然而，由于GBM细胞普遍存在适应性抵抗特性，绝大多数患者在治疗后很快复发。因此，阐明GBM的放疗抵抗机制对增加GBM的放疗敏感性、改善患者预后具有重要意义。本研究发现STAT3的表达水平与GBM患者预后显著负相关，且STAT3的患者对放疗不敏感。进一步研究发现pSTAT3 Y705促进GBM抵抗放疗，但抑制pSTAT3 Y705引起的ERK1/2活化使细胞抵抗放疗联合抑制pSTAT3 Y705治疗，唯有抑制pSTAT3 Y705并同时阻断ERK1/2活化方能联合放疗达到有效清除放射抵抗细胞、抑制放疗后肿瘤复发和生长的目的。此外，因放射抵抗的GBM细胞较敏感细胞pSTAT3 Y705丰度显著增加，抑制pSTAT3 Y705后放疗抵抗细胞内ERK1/2磷酸化水平显著增加而敏感细胞内ERK1/2丰度极低且无明显改变，抑制pSTAT3 Y705同时阻断ERK1/2信号活化对人星形胶质细胞无明显毒性。因此，本研究不仅为理解pSTAT3 Y705与ERK1/2这两个关键促癌分子的相互调控拓展理论基础，也为理解GBM抵抗放疗的复杂机制提供新的线索，放疗联合抑制pSTAT3 Y705和ERK1/2的新策略为GBM的临床治疗提供新的方向。