肿瘤乏氧微环境靶向细菌递药微机器人的构建及其抗结肠癌作用研究

Most patients with colon cancer present with metastases at initial diagnosis, since no clearcut symptoms are recognized in their earliest stages. The conventional chemotherapy is effective for metastatic tumor; however, it suffered from severe systemic toxicity due to a lack of specificity for cancer cells. Encapsulation of chemotherapeutic drugs within nanocarriers greatly increases therapeutic efficacy and decreases side effects through the passive targeting of nanomedicine to tumors by the enhanced permeation and retention (EPR) effect, as well as the positive targeting by conjugating the surface of nanomedicine with specific antibodies or ligands. Nevertheless, the targeting efficacy is generally too low to reach tumor hypoxia area. Probiotic bacteria as anaerobe exhibit hypoxia-taxis. Moreover, they have been reported to be effective in the inhibition of colon cancer development mainly via modulation of gut microbiota which thereby enhances the host’s immune response. In the present proposal, bacteria microrobots composed of Bifidobacterium bifidum(B. bifidum) as a delivery vehicle loading with nanomedicine will be established to target tumor hypoxia zone. They integrate the merits of safe, stealth, targeting, diagnosis and therapy of cancer. More specifically, water-insoluble anti-cancer drug SN-38 will be conjugated with poly(γ-glutamic acid), which will be further complexed with polyethylene glycol (PEG) modified-chitosan to form the stealth nanomedicine with prolonged circulation time. The nanomedicine will be post-complexed with the surface of B. bifidum, and the bacteria will carry the cargos to target the tumor hypoxia and exert the therapeutic efficacy against colon cancer. Pharmacodynamics and in-vitro and in-vivo tumor targeting mechanisms of the bacteria microrobots will be investigated in order to explore an effective therapeutic approach for the clinical targeted treatment of colon cancer.

结肠癌因早期发病隐匿，大多患者首诊时已出现转移，常规化疗因缺乏对肿瘤组织的特异性，毒副作用大。基于化疗药物的纳米药物载体可通过被动或主动靶向作用靶向到肿瘤组织，但其靶向总体效率仍然较低，且难以到达肿瘤缺氧活性区。研究发现，益生菌具有良好的低氧环境生长趋向性，此外，它具有肠道微生态调节和机体免疫激发作用，可抑制肿瘤增殖。本项目拟构建一个以两歧双歧杆菌为运载体的具有肿瘤低氧微环境靶向的可负载纳米药物的细菌“微机器人”。该细菌“微机器人”集合了安全、隐形、靶向和诊疗一体化的优势，具体采用聚（γ-谷氨酸）修饰难溶性药物SN-38以增强其水溶性，并与聚乙二醇化壳聚糖复合形成长循环纳米药物，再装配至两歧双歧杆菌表面，利用其对肿瘤乏氧区域的趋向性运载药物以达到靶向治疗结肠癌的目的。通过对该细菌“微机器人”抗肿瘤活性和体内外肿瘤靶向机制的探讨，为临床上结肠癌新型药物靶向治疗探索一条新的高效途径。

治疗结直肠癌的大多数化疗药物因其水溶性低，结构稳定性差，缺乏对肿瘤组织的特异性，系统毒副作用强而受到临床限制，基于化疗药物的纳米药物虽然在一定程度上降低了系统毒性，但其也存在靶向效率低，难以到达肿瘤缺氧活性区的瓶颈，本课题利用益生菌良好的低氧环境生长趋向性和肠道微生态调节和免疫激发作用，开发了以两歧双歧杆菌为运载体的负载纳米药物的细菌“微机器人”，并取得了以下重要成果：（1）通过构建聚合物前药，极大地提高了药物的水溶性和稳定性，并将其与壳聚糖复合形成稳定的纳米药物，探索出了一条绿色、安全、温和的纳米粒制备工艺，为基于多糖的纳米药物的产业化应用提供了技术支持；（2）成功构建了安全、稳定性好、活性高的基于两歧双歧杆菌的药物递送复合系统，并将其用于肿瘤诊疗一体化研究，为临床提高结直肠癌的治疗效率提供了新策略；（3）拓展了靶向策略，开发了其他具有主动靶向的纳米药物递送系统，并取得了良好的肿瘤治疗效果，为结直肠癌的个性化治疗奠定了重要研究基础。