Development of molecular imaging tracers for anticancer drug resistant proteins

DNA修复蛋白O6-甲基鸟嘌呤-DNA甲基转移酶（MGMT， AGT）是肿瘤细胞对靶向鸟嘌呤O6位置的烷基化抗癌药物的抗性的决定因素。肿瘤中MGMT启动子甲基化被认为是胶质母细胞瘤对烷基化剂反应性的最常见预测因子。然而，MGMT启动子甲基化状态主要通过甲基化特异性PCR（MSP）进行研究，这是一种定性和主观的检测方法。此外，与MGMT甲基化状态相关的实际酶活性尚未被探索。在本研究中，我们的目标是创造一种新的非侵入性MGMT成像而不是MSP。首先，我们进行了亚硫酸盐焦磷酸测序，并使用一种新的定量分析方法确定了其与酶活性的相关性，以研究MGMT的功能活性。使用荧光标记的含有MGMT特异性DNA病变的寡核苷酸底物和毛细管电泳来检测和量化这些病变，评估MGMT酶活性。与现有的传统检测方法相比，该检测方法同样敏感，但耗时更短，更容易执行。采用亚硫酸氢盐法对41例胶质母细胞瘤的MGMT启动子甲基化进行了评估，并选择了5个不同值的样品与酶法进行比较。在比较研究中，亚硫酸氢盐焦磷酸测序获得的MGMT启动子甲基化值与测量的酶活性成反比。目前的结果表明，亚硫酸氢盐焦磷酸测序对MGMT甲基化的量化代表了它的酶活性，从而代表了它对烷基化剂的治疗反应。

The DNA repair protein O6-methylguanine-DNA methyltransferase(MGMT, AGT) is a determinant of the resistance of tumor cells to alkylating anticancer agents that target the O6 position of guanine. MGMT promoter methylation in tumors is regarded as the most common predictor of the responsiveness of glioblastoma to alkylating agents. However, MGMT promoter methylation status has been investigated mainly by methylation-specific PCR(MSP), which is a qualitative and subjective assay. In addition, the actual enzymatic activities associated with the methylation status of MGMT have not been explored. In the present study, we aimed to create a novel non-invasive MGMT imaging rather than MSP. First, we performed bisulfite pyrosequencing, and its correlation with enzymatic activity was determined using a novel quantitative assay for studying the functional activity of MGMT. MGMT enzymatic activity was assessed using fluorometrically labeled oligonucleotide substrates containing MGMT-specific DNA lesions and capillary electrophoresis to detect and quantify these lesions. In comparison with existing traditional assays, this assay was equally sensitive but less time consuming and easier to perform. MGMT promoter methylation was assessed in 41 glioblastomas by bisulfite pyrosequencing, and 5 samples with different values were chosen for comparison with enzymatic assays. In comparative studies, MGMT promoter methylation values obtained by bisulfite pyrosequencing were inversely proportional to the measured enzymatic activity. The present results indicate that the quantification of MGMT methylation by bisulfite pyrosequencing represents its enzymatic activity and thus, its therapeutic responsiveness to alkylating agents.