肺癌患者血浆中APC基因启动子甲基化定量检测研究

背景与目的：APC基因编码的蛋白参与信号转导途径，大量研究证实APC启动子区的高甲基化在肿瘤的发生发展中起重要作用。本研究建立血浆APC基因实时荧光定量甲基化特异性基因扩增（methylation—specific PCR，MSP）检测方法，并对临床肺癌患者血浆进行检测，以确定该方法在肺癌诊断中的应用价值。方法：将APC基因启动子甲基化阳性肺癌细胞株NCI—H460细胞用有限稀释法获取单个集落形成的细胞，以经典的酚一氯仿法提取细胞DNA，并用MSP对APC基因甲基化进行验证，紫外分光光度计定量并以10倍稀释的浓度梯度依次投入到200μL健康人血浆中．得到模拟肺癌患者血浆，利用磁珠核酸提取方法从模拟肺癌及肺癌患者、肺部良性疾病患者和健康对照者血浆中提取DNA，对血浆DNA模板进行亚硫酸氢盐化学修饰；以模拟血浆样品作为标准品，采用外标准曲线法对各种血浆样品中APC甲基化进行定量分析。结果：所建立的实时荧光定量MSP检测方法的线性范围为1．5×10^2-1．5×10^5拷贝／mL。用该方法检测甲基化肿瘤细胞的DNA其最低检测限为1．5×10^2拷贝／mL。78例肺癌患者有40例组织中检测出APC基因甲基化阳性．其中的19例（47．5％）肺癌患者血浆中APC基因启动子甲基化阳性，APC甲基化浓度为1．67×10^2-6．78×10^3拷贝／mL，中位浓度为1．60×10^3拷贝／mL。38例组织阴性的肺癌患者、31例肺部良性疾病患者和23例健康者的血浆APC基因启动子甲基化均为阴性。结论：实时荧光定量MSP检测血浆APC基因甲基化在肺癌诊断方面具有潜在应用价值。

Methylation quantification of adenomatous polyposis coil(APC) gene promoter in plasma of lung cancer patients

Background and Objective： The protein encoded by adenomatous polyposis coil （APC） gene participates in the signaling transduction pathway. Substantial studies have revealed that hypermethylation of APC gene promoter is closely related to the pathogenesis and development of cancer. This study was to develop a real-time quantitative methylation specific PCR （real-time QMSP） method, and detect the methylation of APC gene promoter in plasma of lung cancer patients. Methods： Genomic DNA with methylated APC gene promoter was extracted from the lung cancer cell line NCI-H460 using phenol-chloroform and quantified by spectrophotometric measurements. DNA was added into 200 μL plasma samples of healthy volunteers to make 10-fold serial dilutions. Circulating DNA from simulated plasma samples, 78 lung cancer patients, 31 patients with benign lung diseases and 23 health controls was extracted using magnetic beads and modified by bisulfite. The concentration of cell-free methylated APC gene promoter in the plasma samples was quantified by the external reference method with the standard curve constructed using simulated plasma. Results： The linear range of the real-time QMSP assay was 1.5×10^2-1.5×10^5 copies/ mL and its lowest detectability was 1.5 ×10^2 copies per milliliter plasma. Of 78 lung cancer patients, positive methylation of the APC gene promoter was detected in tumor tissues of 40 cases. Among the 40 lung cancer patients, positive methylation of the APC gene promoter was found in the plasma of 19 patients （47.5%）. The concentrations of methylated APC promoter in the 19 lung cancer patients ranged from 1.67×10^2 to 6.78×10^3 copies/mL, with a median concentration of 1.67×10^3 copies/mL. No positive methylation of the APC gene promoter was detected in the plasma of 38 lung cancer patients without APC gene methylation in tissues, 31 benign lung diseases and 23 healthy controls. Conclusions： The newly developed real-time QMSP method allows the quantitative measurement of APC gene promoter met