pH/Cathepsin B逐级响应纳米胶束用于DTX精准递送及其光疗化疗联用研究

Tumor microenvironment is the natural barrier for nanomedicine to enter the deep region of tumor, which directly leads to their low penetration and uptake in tumor, weakening their efficacy. This research intends to construct novel pH/cathepsin B hierarchical responsive micelles, and utilize their promoted osmotic and uptake effect of rapid micelle dissociation in mild acidic tumor site, modulation of tumor microenvironment by photodynamic (PDT) effect and lysosomal cathepsin B responsive drug release behavior, to achieve precise delivery of docetaxel (DTX) at the tumor as well as combined phototherapy and chemotherapy. The designed micelles are based on an ultra pH-sensitive diblock polymer PEG-PC7A, and DTX is linked to the polymer through GFLG polypeptide. Zinc tetraaminophthalocyanine modification can provide the polymer with amplification effect of flurescence signal and PDT efficacy in tumor. The micelles can rapidly dissociate in the tumor microenvironment, the particle size decreases significantly and expose the positive charge, enhancing the penetration and uptake of polymeric drugs into deep region of tumor. PDT can eliminate the barrier effect of tumor microenvironment by scavenging stromal cells, and further improve the drug diffusion inside the tumor mass. In addition, Cathepsin B in lysosome can effectively hydrolyze and release free DTX from polymer rapidly, maximizing the antitumor efficacy.

肿瘤微环境是纳米药物进入肿瘤深部的天然屏障，直接导致了其在肿瘤部位较低的渗透和摄取能力，严重影响了药效发挥。本研究拟构建新型pH/Cathepsin B逐级响应纳米胶束，利用其在肿瘤微酸环境快速解散促渗透摄取、光动力效应（PDT）调控肿瘤微环境以及溶酶体Cathepsin B响应药物释放，实现多西他赛（DTX）在肿瘤部位的精准递送和光疗化疗联用。该纳米胶束以pH超敏感二嵌段聚合物PEG-PC7A为骨架，DTX通过GFLG多肽连结到聚合物上，四氨基酞菁锌修饰可实现体内肿瘤荧光信号放大和PDT效应。设计的纳米胶束可在肿瘤微环境中快速解散，纳米药物粒径迅速减小并暴露出正电荷，促进纳米药物向肿瘤深部渗透和摄取。PDT可通过清除肿瘤微环境基质细胞降低肿瘤微环境屏障作用，进一步提高药物在肿瘤间隙中的扩散。此外，溶酶体中的Cathepsin B可有效水解释放出聚合物中的游离DTX，快速发挥抗肿瘤作用。

近年来，世界范围内癌症发病率和死亡率迅速增长。纳米药物递送系统可以提高化疗药物的血液循环时间，降低化疗药物带来的毒副作用，如何合理设计刺激响应型的纳米递送系统，实现在靶组织特异性响应的药物胞内释放成为关键科学问题。本课题设计并合成了pH/组织蛋白酶B程序响应型的聚合物药物偶联物用于递送多西他赛（Docetaxel，DTX）。该两亲性的聚合物在中性条件下可自组装形成纳米胶束HRNs （pH/cathepsin B hierarchical responsive nano-micelles），将化疗药多西他赛包载在疏水内核中。经静脉注射后，HRNs可在循环系统保持结构稳定，粒径维持在40 nm左右，并通过实体瘤组织的EPR效应在肿瘤区域蓄积，响应于肿瘤酸性微环境发生解散，此时粒径减小至5 nm左右，实现了肿瘤区域的深部渗透，增强了肿瘤细胞对制剂的摄取，同时暴露出组织蛋白酶B敏感的GFLG四肽，通过酶切作用释放出游离药物，从而发挥肿瘤杀伤作用。血浆药代动力学测量结果显示，HRNs所载总DTX的药时曲线下面积（Area under curve，AUC）是市售DTX注射液Taxotere的438倍。该体系将化疗药精准、高效地递送到肿瘤部位的同时，可以诱导肿瘤细胞免疫原性死亡，释放危险信号，提高树突细胞的抗原呈递能力，促进细胞毒性T淋巴细胞在肿瘤组织的浸润，激活机体免疫应答。与免疫检查点抑制剂（a-PD-1）联用，提高了小鼠黑色素瘤的治疗效果并有效抑制了肿瘤复发。该聚合物药物偶联物载药体系对多种小鼠肿瘤模型均具有良好的抑制效果，设计简单且功能可控，具有一定临床应用前景。