基于生物点击化学的肿瘤微环境响应性纳米载体的肿瘤靶向递药研究

Increasing attention has been paid on how to simultaneously improve the tumor targeting, penetration and retention efficiency of the drug delivery systems (DDS) to more effectively deliver drugs into the core of tumor with elevated anti-tumor effect. The permeability of DDS positively related with particle size of DDS, while the retention negatively related with it. Additionaly, click chemistry that based on 2-cyanobenzothialzole and D-cysteine could react in biological systems. Therefore, in this program, we designed a novel DDS: iRGD-DOX-DGL-ESAS. The iRGD-DOX-DGL-ESAS could effectively target to tumor and penetrate into the core of tumor because of the active targeting effect of iRGD and the small size of the DDS. Then under the triggering of legumain, which is overexpressed in tumor, the ESAS was digested and the groups for click chemistry were exposed. After click reaction, the iRGD-DOX-DGL-ESAS was condensed to large size that could retain in tumor and sustained release the DOX with long-term antitumor activity. This idea provided a novel strategy for tumor targeting therapy, which may further improve the drug delivery efficiency and antitumor outcome.

如何同时提高纳米递药系统的肿瘤靶向、渗透性和滞留性，以更好将药物递送至肿瘤内部，避免“化疗盲区”，是肿瘤治疗领域关注的热点。一方面纳米系统的渗透性与递药系统粒径呈负相关，而滞留性与粒径呈正相关；另一方面基于2-氰基苯并噻唑和半胱氨酸的点击化学反应能在生物体内可控进行。基于此，本项目构建了小粒径纳米系统iRGD-DOX-DGL-ESAS。该递药系统依靠肿瘤部位的EPR效应、iRGD的主动靶向性、iRGD介导的穿膜性和小粒径所具有的穿透性而高效靶向并渗透进入肿瘤深部。在肿瘤高表达的豆荚蛋白酶作用下，ESAS降解而暴露出点击化学反应基团并发生聚合，形成大粒径纳米聚集体，使递药系统滞留于肿瘤部位形成药物储库。阿霉素在肿瘤微环境下缓慢释放，以长效发挥抗肿瘤效果。该策略为肿瘤的靶向治疗提供了新的设计思路，有望进一步提高递药系统对肿瘤的递送和治疗效果，具有重要的研究价值和潜在的临床意义。

本项目针对纳米系统的肿瘤渗透性和滞留性对粒径要求相反的矛盾，设计一种具有酶响应性粒径聚集的纳米递药系统，以更好提高药物递送效果。通过本项目的深入研究，较为全面地证实了本项目设计思路的有效性和可行性。通过在小粒径递药载体表面修饰豆荚蛋白酶响应性的片段AK和CABT，使得递药系统在豆荚蛋白酶存在下，粒径从约40 nm增加到约300 nm，体外纳米粒样品透射电镜观察及细胞、组织超薄切片的结果同样证实了这一粒径变化，说明通过本设计，确实能够实现递药系统的响应性聚集。经过响应的设计，纳米载体在细胞内的摄取明显增加，且外排降低，同时肿瘤内的分布浓度是对照组的大约2倍，显著提高了小粒径递药系统的滞留性，从而有助于提高其抗肿瘤效果。同时体内肿瘤切片结果可以证实，该递药系统在肿瘤内具有较为均匀的分布，不仅在肿瘤血管周围，而且在远离肿瘤血管的区域仍然具有较高的分布，从而说明本设计确实有助于同时提高递药系统的渗透性和滞留性。为进一步提高其肿瘤靶向性，本项目组在前期基础上修饰了RRGD，使其可以特异性靶向至肿瘤部位，进而通过酶响应性聚集，实现良好的肿瘤内滞留。相比未修饰的对照组，修饰了RRGD后，体外肿瘤细胞摄取增加约1.5倍，体内肿瘤内分布增加约2倍，说明靶向分子修饰确实可以提高递药系统的肿瘤靶向递送效率。但由于靶向分子修饰于载体表面，而酶响应性聚集的片段也是修饰在载体表面，因此靶向分子的修饰可能影响到纳米载体的酶响应性。综上所述，本项目成功构建了一种肿瘤微环境酶响应性聚集策略，并对该策略进行了系统的评价，取得了良好的效果，证明了粒径响应性聚集可以有效提高药物递送效果和抗肿瘤效果。该项目的实施为药物递送领域，特别是肿瘤靶向药物递送纳米递药系统的设计，提供了良好的设计思路和有益的参考。