Precise targeting and high therapeutic efficiency are the major requisites of personalized cancer treatment. However, some unique features of the tumor microenvironment (TME) such as hypoxia, low pH and elevated interstitial fluid pressure cause cancer cells resistant to most therapies. Bacteria are increasingly being considered for targeted tumor therapy owing to their intrinsic tumor tropism, high motility as well as the ability to rapidly colonize in the favorable TME. Compared to other nano-strategies using peptides, aptamers, and other biomolecules, tumor-targeting bacteria are largely unaffected by the tumor cells and microenvironment. On the contrary, the hypoxic TME is highly conducive to the growth of facultative anaerobes and obligate anaerobes. Live bacteria can be further integrated with anti-cancer drugs and nanomaterials to increase the latter's targeted delivery and accumulation in the tumors. Furthermore, anaerobic and facultatively anaerobic bacteria have also been combined with other anti-cancer therapies to enhance therapeutic effects. In this review, we have summarized the applications and advantages of using bacteria for targeted tumor therapy (Scheme 1) in order to aid in the design of novel intelligent drug delivery systems. The current challenges and future prospects of tumor-targeting bacterial nanocarriers have also been discussed.

精准靶向和高治疗效率是个性化癌症治疗的主要要求。然而，肿瘤微环境 (TME) 的一些独特特征，例如缺氧、低 pH 值和升高的间质液压力，会导致癌细胞对大多数疗法产生耐药性。细菌由于其固有的肿瘤趋向性、高运动性以及在有利的 TME 中快速定殖的能力，越来越多地被考虑用于靶向肿瘤治疗。与使用肽、适体和其他生物分子的其他纳米策略相比，靶向肿瘤的细菌在很大程度上不受肿瘤细胞和微环境的影响。相反，缺氧的TME非常有利于兼性厌氧菌的生长和专性厌氧菌。活细菌可以进一步与抗癌药物和纳米材料结合，以增加后者在肿瘤中的靶向递送和积累。此外，厌氧菌和兼性厌氧菌也已与其他抗癌疗法相结合以增强治疗效果。在这篇综述中，我们总结了使用细菌进行靶向肿瘤治疗（方案 1）的应用和优势，以帮助设计新型智能给药系统。还讨论了肿瘤靶向细菌纳米载体的当前挑战和未来前景。