ATB0,+转运体介导的氟尿苷结肠癌靶向治疗前药的研究

Cancer has become the first threat to the health of the people all over the world. Though the chemotherapy based on the target receptor and the signal channel saved many patients with cancer, it brought a lot of side effects to people. The particulate delivery system could increase the ability of anticancer drugs to target the tumor cell. But this strategy was not effective in some circumstance. The membrane transporters widely expressed in the tumor tissue have become promising targets for the drug delivery system. In the present study, some amino acid prodrugs of floxuridine targeted to amino acid transporter (ATB0, +, SLC6A14) highly expressed in the colon cancer were synthesized by attaching amino acid to the hydroxyl group. The prodrugs were evaluated by the affinity to ATB0, + and the activation rate. To help the rational design of successful prodrugs, the quantitative structure-affinity/hydrolysis rate relationships were constructed by analyzing the physiochemical and structural parameter of the prodrug. The pharmacokinetics, the tissue distribution and the pharmacodynamics of the candidate prodrug was studied in rat to delineate the hydrolysis mechanism, and the target efficiency. The preliminary result showed the present study was feasible.

癌症已经成为威胁人类健康的第一杀手，但是目前主要基于靶受体和信号通路的化学药物治疗，虽然挽救了很多患者的生命，但是也给患者带来了很多副作用。虽然有时可以通过微粒给药系统来提高药物的靶向性，但并不都能行得通。肿瘤细胞上高度表达的膜转运蛋白，利用它们为靶点来提高药物的肿瘤靶向是非常有前途的，而且适合我国目前新药创制的条件。本课题以高度表达在结肠癌细胞上的氨基酸转运蛋白(ATB0, +)为靶点，选择氟尿苷（Floxuridine）为模型药物，在氟尿苷的羟基位引入氨基酸，从与ATB0, +亲和性和前药激活速率两方面对氟尿苷氨基酸酯前药进行考察和筛选；结合药物理化和结构参数，建立定量结构-亲和性/降解速率关系，指导前药的合理设计。选择适宜的前药进行小鼠药动学、组织分布和药效学研究，考察体内的活化机制、分布行为，并筛选出最佳候选前药。前期工作结果表明本项目可行性良好。

合成了9个氟尿苷的氨基酸前药，包括3个L-缬氨酸的α-酯前药、3个L-门冬氨酸的β-酯前药和3个L-谷氨酸的γ-酯前药。并进行了结构确证。. 摄取抑制实验和直接摄取实验都表明，氟尿苷的氨基酸酯衍生物都是ATB0,+的底物，它们进入肿瘤细胞内部的过程可以利用米氏方程来拟合，Na+和Cl- 的激活动力学显示，在一个转运循环中， Na+、Cl-和底物的比例接近2：1：1，这和ATB0,+的转运动力学是一致的。以同源模建为基础的拟合显示，研究了5’-β-L-Asp-FUdR和ATB0,+之间的作用力最强，和前述细胞实验的结果一致。. 稳定性研究发现，前药能够提高母药对thymidine phosphorylase (TP)酶的代谢稳定性；β-和γ-酯前药在循环系统的稳定性高于α-酯前药。 . 体外抗肿瘤实验表明，9个前药在ATB0,+阳性肿瘤细胞（如ZR-75-1和PaCa-2 细胞）上的活性明显高于母药，但是前药之间的GI50之间没有显著差异；前药在ATB0,+阴性肿瘤细胞（MB232）上的活性和母药之间没有区别，提示ATB0,+在介导前药进入肿瘤细胞内部过程中发挥着重要作用。利用荷瘤鼠进行体内抗肿瘤发现5’-β-L-Asp-FUdR在荷ATB0,+阳性肿瘤鼠体内的活性高于在荷ATB0,+阴性肿瘤鼠，它在结肠癌上也有很好的靶向性。. 在荷ZR-75-1肿瘤（ATB0,+阳性）的裸鼠药动学和组织分布研究发现，与注射母药FUdR相比，注射5’-β-L-Asp-FUdR能显著肿瘤组织中FUdR的浓度，提高FUdR的肿瘤靶向指数（3.9 vs 0.55），同时降低血液循环中代谢产物5-FU的浓度。

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