Tz/Anti-CD146-mAb-TCO生物正交点击化学预定位体系用于肝癌诊疗研究

The poor prognosis of patients with hepatocellular carcinomas attributed to delaying diagnosis and lack of effective treatment. CD146 receptors were found over-expressed in varieties of tumor vascular endothelial including hepatocellular carcinomas, which can promote tumor growth, angiogenesis and metastasis. In our previous studies, I-125 labeled Anti-CD146-mAb was used for SPECT/CT imaging and RIT on mice bearing HepG2 tumors, it was found that this probe accumulated highly in tumor area, but blood and liver background was also high at early time points, which will reduce the imaging signal-to-noise ratios and produce high nonspecific radiation damage on bone marrow and other normal organs. According to our previous research and the properties of this antibody, we speculate that the pretargeting strategy can effectively resolve this conflict. Herein, this study will use the bioorthogonal click chemistry method to fabricate Anti-CD146-mAb coupling trans-cyclooctene (TCO) and F-18/Re-188 labeled 1,2,4,5-triazine (Tz) pretargeting system to improve the SNR of imaging and radioimmunotherapy, also reduce the normal tissue non-specific radiation injury. Therefore, this potential individual and integrated system will facilitate the accurate diagnosis of hepatocellular carcinomas, and screening suitable patients for RIT treatment.

肝癌的高死亡率通常与诊断较晚及缺乏有效的治疗方法有关。大量研究发现CD146在包括肝癌在内的多种肿瘤血管内皮细胞上高表达，可以促进新生血管形成、肿瘤生长及转移。我们前期使用I-125-Anti-CD146-mAb进行HepG2肝癌荷瘤小鼠SPECT/CT显像及放射免疫治疗，发现其在肿瘤具有高的浓集及生长抑制效应，但注射后早期血液及肝脏背景较高，因此，显像信噪比低，同时也会对骨髓以及其他正常器官产生高的非特异性辐射损伤。基于该抗体在肝癌组织具有高吸收和慢的药代动力学特性，通过肿瘤预定位策略将有效解决这一矛盾。本项目将采用生物正交点击化学方法，构建由反式-环辛烯（TCO）偶联的Anti-CD146-mAb和F-18/Re-188标记1,2,4,5-四嗪（Tz）组成的肿瘤预定位体系来提高肝癌PET显像及放射免疫治疗的靶向性，为实现肝癌“个体化、一体化”的诊疗模式进行临床前探索研究。

长半衰期放射性核素直接标记抗体进行放射显像存在药代动力学缓慢、组织渗透性差、靶/本比低和对正常组织器官毒副作用大等缺点。为了解决以上问题，我们采用预定位显像策略，它具有影像对比度好、对非靶组织器官辐射损伤小、能够使用短半衰期放射性核素进行显像等优点。目前，经典的预定位方法是基于1,2,4,5-四嗪（1,2,4,5-terazine，Tz）与反式-环辛烯（Trans-cyslooctene，TCO）的Diels-Alder环加成生物正交点击化学系统。本课题成功合成Atezolizumab-TCO/99mTc-HYNIC-PEG11-Tz分子探针，生物分布及显像提示肿瘤相对吸收值为2.036±0.299 %ID/g，明显高于对照组相对吸收值（0.218±0.054 %ID/g） （P＜0.05）；其他器官组织的相对吸收值低于0.5 %ID/g。提示预定位显像策略能评估肿瘤PD-L1表达水平，并显著降低非靶组织器官的辐射剂量。但99mTc-HYNIC-PEG11-Tz经肝胆-肠道途径代谢导致腹盆部本底高、影响该区域病灶观察。因此，我们对其结构进行改造合成了经泌尿系排泄的99mTc-HYNIC-Polypeptide-PEG11-Tz，并与Cetuximab-TCO进行点击反应。预定位（Cetuximab-TCO 48h/99mTc-HYNIC-Polypeptide-PEG11-Tz 6h）生物分布及显像示肿瘤/血液比值为1.40，分子探针完全通过泌尿系统排泄，腹部本底低，适用于结肠癌特异性显像。99mTc半衰期较长且为单光子核素，为进一步扩大预定位显像策略适用范围、提高图像质量，我们继续探索短半衰期正电子核素标记抗体，合成anti-CD11b-TCO/68Ga-NOTA-Polypeptide-PEG11-Tz。通过预定位（anti-CD11b-TCO/68Ga-NOTA-Polypeptide-PEG11-Tz）生物分布及小动物PET/CT显像确定预定位48小时，注射放射性配体1小时后显像效果最佳。与89Zr-DFO-anti-CD11b相比，预定位(anti-CD11b-TCO/68Ga-NOTA-Polypeptide-PEG11-Tz)显像策略在提高肿瘤与非靶组织吸收比，降低正常器官辐射累积方面更有优势，更适用于胃癌显像。

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