Colorectal cancer (CRC) has become the fourth leading cause of cancer-related death in the worldwide. It is urgent to find more effective therapeutic strategies for it. Reactive oxygen species (ROS) play multiple roles in normal cellular physiology processes. Thus, a certain level of ROS is essential to keep normal cellular function. However, the accumulation of ROS shows dual roles for cells, which is mainly dependent on the concentration of ROS, the origin of the cancer cell and the activated signaling pathways during tumor progression. In general, moderate level of ROS leads to cell damage, DNA mutation and inflammation, which promotes the initiation and development of cancer. Excessive high level of ROS induces cancer cell death, showing an anti-cancer role. ROS are commonly higher in CRC cells than their normal counterpart cells. Therefore, it is possible that ROS induce cell death in cancer cells while not affecting the normal cells, demonstrating lower side effects. Besides, ROS also play a role in tumor microenvironment and drug resistance. These multiple roles of ROS make them a promising therapeutic target for cancer. To explore potential ROS-target therapies against CRC, it is worth to comprehensively understanding the role of ROS in CRC and therapy. In this review, we mainly discuss the strategies of ROS in CRC therapy, including direct CRC cell target and indirect tumor environment target. In addition, the influences of ROS in drug resistance will also been discussed.

Recent discoveries in cell biology and microbiology have spotlighted the increasing importance of cell-based therapy, which offers the potential of altering and treating the course of diseases that cannot be addressed sufficiently by existing pharmaceuticals. [1,2] The use of living cells, including transfusion of hematopoietic stem cells, chimeric antigen receptor T-cell therapy, and fecal microbiota transplantation, has been successful in treating a multitude of intractable diseases, such as, congenital defects, cancers, and inflammatory bowel disease. [3,4] Unfortunately, cells are often fragile to unfriendly environmental stressors, such as, temperature fluctuation and centrifugation encountered during preparation, as well as, host immune system and metabolic microenvironment suffered after transplantation, leading to unwanted cell death and a decline in therapeutic efficacy. [5,6] In addition, monomodal therapy always results in inadequately therapeutic response due largely to the complexity of cellular interactions and the multiplicity of cell targets. [7] Therefore, methods capable of simultaneously incorporating with a protection role and endowing with multiple therapeutic modalities are highly desirable to engineer satisfied cells for enhanced cell-based therapy. Surface decoration of living cells, which attaches functional motifs to cell surface, provides a unique tool for generating engineered cells, in a programmed manner, with exogenous characteristics that are neither inherent nor naturally achievable. [8] Particularly, a variety of elegant approaches have been developed to wrap cells chemically with synthetic cytoprotective coatings, forming a cell-in-shell structure. [9-14] For example, a number of mammalian cells have been encapsulated individually with polymers, silica, and calcium phosphate to enhance viability by protecting cells from external aggressors during manipulation, handling, and storage. [12-15] As a representative of fungi, yeast cells have been embedded within a complex of pyrogallol and Fe(III)-tannic acid to improve the tolerance against environmental attacks. [16] Recently, we have encased probiotics with biological membranes to protect bacteria from lethal factors in real-life settings. [17-20] For instance, a beneficial bacterium camouflaged with an erythrocyte membrane exhibits an immunogenic shielding effect, which reduces their clearance by macrophages. [17] However, conventional surface decoration involves tedious complicated fabrication and has limited Surface decoration of living cells by exogenous substances offers a unique tool for understanding and tuning cell behaviors, which plays a critical role in cell-based therapy. Here, a facile yet versatile approach for decorating individual living cells with multimodal coatings is reported. By simply co-depositing with dopamine under a cytocompatible condition, various functional small molecules and polymers can be encoded to form a multifunctional coating on a cell's surface. The accessibility and versatility of this method...