基于乏氧和血管新生多模态分子成像技术的肺癌脑转移早期发现

Most cancer-related deaths are due to the development of metastatic disease rather than the growth of primary tumors. Early detection the brain metastatic proclivity of lung cancer at the cellular level is a major challenge because of heterogeneity of the primary tumor. One of the most important tests for molecular imaging is to determine whether it can image the brain micrometastases of lung cancer. Hypoxia is often found in large primary solid malignancies and is recognized as a negative determinant of clinical outcome, but is largely unknown in micrometastases. We have recently demonstrated that lung cancer peritoneal microscopic tumors were extremely hypoxic. The central HYPOTHESIS of the proposal is that severe hypoxia is a common feature of micrometastases involving a variety of anatomic sites, which plays a critical role on the early stage progression of metastases.To harness the strengths of different imaging methods, multimodality imaging has become an attractive strategy for in vivo studies. This project summarizes the current status of tumor angiogenesis imaging with optical techniques and hypoxia imaging with Micro-PET，using VEGFR2-luc report gene and 18F-FMISO probe.There are three specific aims:1.Characterize severe hypoxia is a common feature of lung cancer with brain metastases in nude mice using exogenous substance and endogenous hypoxia markers, we will relate this to angiogenesis. Knowledge obtained is expected for better understanding metastasis biology from hypoxia point-of-view. 2.Determine dynamic change in hypoxia in micrometastases using multimodility molecular imaging technique, and relate this to angiogenesis switch during early stage of brain metastases progression. The proposal research is expected to explore interaction among hypoxia and angiogenesis stromagenesis in metastases during their early stage of development. 3.Knowledge from the proposed research shall guide novel diagnosis strategies to prevent micrometastases from becoming clinically detectable and to guide the development of novel diagnosis strategies to metastases, decrease cancer mortality rates in cancer patients with metastases.

肺癌患者大多数死于脑转移，脑转移早期发现是指导临床治疗方式选择的关键，但缺少灵敏、准确的检查手段是目前面临的严峻挑战。利用分子成像技术能发现肿瘤基因、分子水平的异常，是国际肿瘤研究的前沿和热点。我们既往研究发现，肺转移癌早期70%～90%的肿瘤细胞乏氧，乏氧促进多种促血管生成因子高表达，提示同时靶向乏氧和促血管生成因子分子成像能更早、更敏感地发现转移癌，但乏氧和血管新生空间和时间的动态变化规律等关键问题仍需进一步深入探索。本研究拟建立转基因鼠肺癌脑转移模型，利用核素和光学多模态分子成像技术，活体、同时监测肿瘤乏氧（18F-FMISO分子探针成像）和血管新生（VEGFR2-luc报告基因或18F-FPPRGD2分子探针成像）的动态变化，对肿瘤乏氧和血管新生的空间分布、时间变化规律等进行定量分析，并与放射自显影和免疫荧光染色等结果对比验证，建立多角度、多模态分子成像早期发现肺癌脑转移的新方法。

肺癌脑转移发病率高，是原发性肺癌治疗失败的最重要原因。肺癌脑转移早期发现对指导治疗和判断预后意义重大，肺癌脑转移早期发现困难是临床面临的重要瓶颈问题。本项目针对肺癌脑转移早期发现难的问题，利用多模态、高灵敏分子成像技术，活体、实时监测肿瘤乏氧、增殖和血管新生的动态变化，通过对肿瘤乏氧和血管新生的空间分布、时间变化规律等进行定量分析。并结合分子生物学方法，包括应用放射自显影、RT-PCR、免疫荧光染色等技术，分析肿瘤血管形态学、结构改变与乏氧调控关系，进一步验证活体成像结果，为应用多模态分子成像技术早期发现肺癌脑转移提供理论依据及新方法。本研究主要发现：1.18F-FMISO对转移癌乏氧区域有高度特异性，而对坏死组织不敏感，肿瘤特异性高。2.18F-FMISO分子量小，可通过血脑屏障，在注射分子探针110分钟后脑转移癌组织吸收达到峰值。3.通过对比18F-FDG的肿瘤/组织比值，18F-FMISO探针较18F-FDG具有更好的药代动力学特征及靶向性。4.VEGFR2在肺癌原发灶和转移灶中新生血管内皮细胞表面高度表达，而在正常组织表达高度保守。5.增殖的肿瘤细胞18F-FLT高摄取，而乏氧的肿瘤细胞18F-FMISO和18F-FDG高摄取并且细胞增殖率低。6.转VEGFR2-luc基因光学分子成像方法成像迅速，能够评估肿瘤的新生血管VEGFR2表达水平的动态变化，其表达强度和表达率可作为评估肿瘤预后与转移能力的重要指标。7.受光学信号穿透能力限制，VEGFR2-luc基因光学分子成像在脑深部组织检查方面受限，而Micro-MRI在判断肿瘤组织边界和分级上有一定优势。本项目发现，乏氧和血管新生是转移癌早期重要分子特征，通过多模态分子成像技术，不仅可以提供更快捷、更精确、更高空间分辨率的解剖结构与功能信息，能在活体同时监测肿瘤乏氧、细胞增殖和血管新生等不同分子事件，对判断肿瘤转移潜能和研究转移癌发生发展机制具有重大意义。