基于叶酸受体的MR分子影像学评价肿瘤疗效的可行性研究

Early evaluation of tumor response to therapy is crucial for subsequent therapeutic planning. Molecular imaging can be performed in a noninvasive manner and has great potential in oncology for monitoring tumor response to therapy. Folate receptor has been identified as a potential target in most cancers for diagnostic and therapeutic purposes, based on its overexpression in epithelial carcinoma. Our previous studies presented targeted gadolinium-loaded contrast media for tumor-specific magnetic resonance imaging. The objective of this study was to evaluate whether FR expression is altered by chemotherapy. FR-α and its mRNA expression was analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and semi-quantitative scoring of immunohistochemical staining on tissue microarrays (TMAs) in pulmonary adenocarcinoma (H460) before and after chemotherapy. A target-specific MRI contrast agent FA-PEG-PAMAM-DTPA-Gds was synthesized for targeting tumor cells expressing high affinity folate receptor. The value of the target-specific contrast agent in monitoring the response after therapy in xenograft tumors established in immunodeficient mice with human pulmonary adenocarcinoma was investigated. Potential application of this approach may include determination of the folate receptor status of tumors and monitoring of drug therapy.

及时、准确的疗效判断是进行临床治疗决策的重要依据，对肿瘤个体化治疗具有指导意义。相对于形态和功能成像，分子影像学能更及时、准确地评价疗效。叶酸受体在大多数恶性上皮肿瘤中过表达，是肿瘤分子影像学研究的常用靶点。本课题申请者在前期成功利用叶酸受体介导MRI靶向诊断肿瘤的基础上，拟对叶酸受体介导的分子影像学评价肿瘤疗效可行性进行探索性研究。拟采用逆转录-聚合酶链反应(RT-PCR)法和免疫组织化学(IHC)二步法半定量检测化学药物治疗对人肺腺癌(H460细胞) FR-α及其基因FOLR1转录水平的影响；并在此基础上，合成分子探针FA-PEG-PAMAM-DTPA-Gds，用于人肺腺癌裸鼠皮下瘤模型活体靶向叶酸受体的分子成像，通过分析治疗前后图像的变化，与细胞/组织病理学检查对照，评价靶向叶酸受体的分子影像学方法在肿瘤疗效评价中的应用价值，为实现叶酸受体介导肿瘤靶向诊断和个体化治疗奠定理论基础

及时、准确的疗效判断是进行临床治疗决策的重要依据，对肿瘤个体化治疗具有指导意义。相对于形态和功能成像，分子影像学能更及时、准确地评价疗效。（1）本项目运用免疫组织化学分析了140例非小细胞肺癌组织中的叶酸受体（FR-α）的表达情况，发现FRα阳性表达75例（53.6%, 75/140），鳞癌FRα阳性表达比率（71.2%, 37/52）高于腺癌（40.5%, 34/84）（χ2检验，p<0.05）。（2）比较了70例患者肿瘤组织中FR-α阳性及阴性表达患者的生存时间差异，发现37例FRα阳性表达的非小细胞肺癌患者中位生存期31月；阴性表达33例患者中位生存期33月，两组差异无统计学意义（log-rank test, χ2 = 0.14 , p=0.7042）。37例FRα阳性表达的患者中，FRα表达（+）11例，中位生存期23月，FRα表达（++）17例，中位生存期27月，FRα表达（+++）9例，中位生存期54月，差异有统计学意义（log-rank test, χ2 = 12.27 , p=0.0022）。结果表明，FRα是否表达不影响患者生存时间，但在FRα阳性表达的非小细胞肺癌患者中，表达的强弱程度与患者生存时间有相关性，表达强度越高，患者生存时间越长，提示FRα是潜在的患者预后指标。（3）观察了22例患者化疗前、后纵隔转移淋巴结及肺癌组织内叶酸受体表达及变化情况。经初步配对比较评价，化疗前、后纵隔转移淋巴结、肺癌组织内肿瘤组织FRα表达情况未见变化，化疗后坏死区域未见FRα阳性染色。（4）合成出叶酸受体靶向对比剂FA-PEG-PAMAM-DTPA-Gds，用于荷人肺腺癌叶酸受体阳性H460细胞裸鼠模型（n=12）MR活体成像实验，平扫和增强后1h、2h、4h瘤体信号-噪声比分别为8.6±0.4、20.4±1.5、16.9±1.0、13.7±2.5，强化峰值出现在增强后1h，各观察时间点肿瘤的信号-噪声比差异有统计学意义（经方差分析，F=123.9，P<0.001）。通过分析肿瘤模型MRI成像特点，发现靶向对比剂FA-PEG-PAMAM-DTPA-Gds能实现在肿瘤局部聚集的效果，后随着时间的推移逐步廓清，而此时裸鼠肝脏组织并未出现明显强化表现。