具脑和肿瘤双重靶向的脑肿瘤治疗药物的设计、合成及生物活性研究

Brain tumors remain a significant human health problem worldwide. Compared to radiation and surgical treatment, chemotherapy has shown a survival benefit to high-grade glioma patients. To be effective, a chemotherapy agent must be exposed to brain tumor cells at concentraitons tha can overcome intrinic resistance mechanisms. However, this is difficult for most drugs, owing to the blood-brain barrier (BBB), which is formed by a network of closely sealed endothelial cells in the brain’s capillaries. BBB only allows hydrophobic molecules with MW < 400 Da to pass through it, while blocks over 98% small molecule drugs and almost 100% large-molecule drugs such as recombinant proteins and monoclonal antibodies into the brain. Moreover it is difficult to maintain the therapeutic agents mainly accumulating in the tumor site but not to diffuse in the normal tissues due to the short duration time and non-specific binding in vivo, thus causing harmful side effects and even death of the patients..To meet the requirement of brain cancer therapy, there is a need for developing drug delivery systems with the double functions of passing through the BBB and targeting the tumor cells, thus reducing the adverse effects to the normal cells. Our research group has developed a widely known ligand, L-ascorbic acid (AA) familiar to us as vitamin C, as brain targeting carrier, because sodium-dependent vitamin C transporters (SVCT2) is highly expressed on the brain capillaries endothelial surfaces. With the targeting ligand of AA, the drug delivery systems can across the BBB through a receptor-mediated transport mechanism to reach the brain and further accumulate in tumor cells. The vitamin folic acid is another widely known ligand that displays extremely high affinity for the folate receptor on the tumor cells surface, and are internalized via receptor-mediated endocytosis. Because the FR is overexpressed on certain malignant cell types and is undetectable or present only at low levels in most normal tissues, targeting of the FR has been proposed as a potential mechanism for delivery of drugs to treat cancer. In this regard, combined brain-targeting of AA and tumor targeting or brain (brain tumors) targeting of folic acid, with broad-spectrum antitumor drugs doxorubicin as a model drug, we prepared to design and synthesize novel prodrugs of Folate-VitC-Dox 1. Thus, these folate-Vit C conjugates are expected to act synergistically, recognized by SVCT2 and induced by folate to efficiently transport through BBB. After entering the brain, the cojugations are accumulated in tumor cells via FR-mediated endocytosis and released drugs via a disulfide bond to reach the good therapeutic effect in the treatment of brain tumors.

脑肿瘤严重危害人类身体健康，然而由于血脑屏障（BBB）的存在，限制了药物进入脑中发挥治疗效果，BBB已成为中枢给药的瓶颈。本课题组在以维生素C作为载体的脑靶向前药研究的基础上，结合具有肿瘤靶向及脑(脑肿瘤时)靶向的叶酸，以广谱抗肿瘤药物阿霉素作为模型药物，设计并合成一类新型的叶酸-维生素C-阿霉素(Folate-VitC-Dox)的三元偶联物, 分子中的维生素C能够识别BBB上的SVCT2,血液中氧化形成的脱氢维生素C识别BBB上的GLUT1，从而可使得该偶联物高效地转运透过BBB。进入脑中后，分子中的叶酸部分识别肿瘤细胞高度表达的叶酸受体FR，将药物靶向进入到肿瘤细胞释放原药，必将对脑肿瘤起到很好的治疗作用。通过对Folate-VitC-Dox的靶向性、动力学和药效学研究及安全性评价，有望解决困扰医药学界治疗脑肿瘤的难题，为脑肿瘤的治疗创立新的思路和新方法，具有极高的学术和应用价值。

脑肿瘤严重危害人类身体健康，而血脑屏障（BBB）的存在，限制了药物进入脑中发挥治疗效果，BBB已成为中枢给药的瓶颈。本课题组在以维生素C作为载体的脑靶向前药研究的基础上，结合具有肿瘤靶向的叶酸，以广谱抗肿瘤药物阿霉素作为模型药物，设计并合成了一类新型的叶酸-维生素C-阿霉素(Folate-VitC-Dox, 1-3)的三元偶联物：分子中的维生素C能够识别BBB上的SVCT2，血液中氧化形成的脱氢维生素C识别BBB上的GLUT1，从而可使得该偶联物高效地转运透过BBB。进入脑中后，分子中的叶酸部分识别肿瘤细胞高度表达的叶酸受体FR，将药物靶向进入到肿瘤细胞释放原药。通过对比研究前药1、2、3和对照化合物前药C1、C2（二元偶合物）的体外稳定性实验，表明前药在循环过程中有一定的稳定，而在脑中可以释放原药。细胞毒性评价显示前药3（具有2个阿霉素、2个叶酸和1个维生素C）对肿瘤细胞的抑制作用最强，而对正常内皮细胞的生长所合成的前药1、2、3均无明显抑制作用。体外细胞摄取实验、体外BBB模型和靶向性评价的结果均说明通过对阿霉素进行修饰后得到的前药提高了靶向性，前药3的靶向性最强，而且其作用可以被竞争性底物所抑制。动力学研究表明前药相比于原药延长了血液中的半衰期，增加了其被转运入脑的机会，此结果也与体稳定性实验一致；另外前药1、2、3、C2、C1在脑内的AUC0-t分别是未被修饰的阿霉素的4.36、4.04、1.96、1.84和1.13倍，Cmax的结果也是前药3最高。对于荷瘤小鼠的治疗也表明前药3延长中位生存期的效果最佳、肿瘤抑制效果最强。此外，毒性实验结果也表明合成的阿霉素前药均表现出良好的生物相容性，提高了其安全性。以上研究成果将为解决治疗脑肿瘤的难题创立新的思路和新方法，具有极高的学术价值和应用价值。