CC49靶向分子探针用于结直肠癌PET显像的信号放大效应研究

Colorectal cancer shows high mortality due to its high recurrence, metastasis and difficulty in diagnosing on its early stage. PET imaging has the characteristics of high sensitivity and high resolution. However, for the early stage of colorectal cancer or small lesions, 18F-FDG PET often generates false positive results and lack of sensitivity.Therefore, it is urgent to develop new PET molecular probes with high specificity and sensitivity. Our preliminary results showed that the anti-CC49 has high affinity to CC49 receptors expressed in colorectal cancer cells. It’s also interesting to find that high tumor/non-tumor radioactivity ratios could be obtained with the using of pretargeting strategy. In this study, a novel amplification pretargeting approach will be applied, where a polymer with multiple copies of PNA is administered between injections of anti-CC49-cPNA and F-18 labeled cPNA, thus holds the potential to achieve a high tumor uptake and low background PET imaging of colorectal cancer. By virtue of this kind of method, accordingly, it will help to deliver an effective therapy to patients and improving survival rate.

结直肠癌具有早期诊断难、术后容易发生转移和复发的特点，致死率极高。PET显像尽管具有高灵敏度和高分辨率的特性，然而，对于早期结直肠癌或者微小病灶的显像，18F-FDG分子探针易产生假阳性及灵敏度欠缺的特点。因此，迫切需要研发出新的高特异性和灵敏度的PET分子探针。我们前期的研究结果表明anti-CC49对结直肠癌细胞具有很高的靶向性，而且通过采用预定位策略，可以提高显像的信噪比。因此本课题拟以anti-CC49-cPNA作为肿瘤靶向分子；借助末端连接PNA的树脂状聚合物来实现信号放大效应；通过F-18标记cPNA作为分子探针来实现高靶向、低非靶组织放射性辐射损伤的结直肠癌功能显像，期望能提高肿瘤的放射性浓聚及信噪比，有助于微小病灶的识别，具有早期诊断和及时术后监测的潜在应用价值。

结直肠癌是一种发病率和死亡率都很高的恶性肿瘤疾病，并且呈逐年上升的趋势，主要是由于其具有早期不易被诊断以及术后容易转移和复发的特点。单克隆抗体CC49对于结直肠癌具有较高的靶向性，但是由于其分子量较大，导致其在血液中循环时间较长，不利用从体内快速清除等缺点。本研究在预定位策略能够提高信噪比的基础上，选取树枝状聚合物PAMAM作为信号放大基团，利用其自身可以携带更多的18F标记化合物到达靶点的特点，从而达到对肿瘤的早期诊断和微小转移灶进行监测的目的。本研究首先通过“点击化学法”合成目标化合物18F-cPNA，放化纯度大于99％，体外实验结果表明该化合物具有较高的稳定性。而后利用化学法，实现PAMAM与PNA的结合，MALDI-TOF的结果表明，每个PAMAM聚合物分子上平均可以结合11.7个PNA分子。SE-HPLC结果表明，18F-cPNA与CC49-cPNA/G4-PNA具有较高的结合效率。最后，选取LS174T肿瘤细胞开展了信号放大实验的研究 ，结果表明，相比较传统的预靶向策略，聚合物的引入提高了肿瘤细胞的放射性浓集，表明该种方法具有对结直肠癌进行早期诊断和及时术后监测的潜在应用价值。