Design and Optimization of the Circulatory Cell-Driven Drug Delivery Platform

Neural Stem Cells as Carriers of Nucleoside-Conjugated Nanogels: A New Approach toward Cell-Mediated Delivery

Neural stem cells (NSCs) present attractive natural drug delivery systems (DDSs). Their migratory potential enables crossing of the blood-brain barrier and efficient and selective accumulation near malignant cells. Here, we present the potential of NSCs as DDSs for nucleoside analogue-conjugated nanogels (NGs). Two different approaches were investigated: the intracellular loading and extracellular cell surface decoration with NGs. For both designs, the tumor-specific migratory potentials of NSCs remained unchanged; however, the intracellular loading showed a shorter NG retention. The cell surface decoration protocol yielded a high loading capacity of 100% after 1 h and a prolonged drug retention. A redox-sensitive linker between NGs and the nucleoside analogue 5-ethynyl-2'-deoxycytidine (EdC) allowed a tumor environment-specific drug release and its efficient and preferential incorporation into the DNA of the tumor cells. Interestingly, the tumor-trafficking potentials of NSCs were significantly potentiated by irradiation of tumor cells. In conclusion, this study indicates the potentials of cell surface-decorated NSCs as DDSs for tumor-specific release, cellular uptake, and incorporation of EdC into DNA.

Cell-based drug delivery systems and their in vivo fate

Cell-based drug delivery systems (DDSs) have received attention recently because of their unique biological properties and self-powered functions, such as excellent biocompatibility, low immunogenicity, long circulation time, tissue-homingcharacteristics, and ability to cross biological barriers. A variety of cells, including erythrocytes, stem cells, and lymphocytes, have been explored as functional vectors for the loading and delivery of various therapeutic payloads (e.g., small-molecule and nucleic acid drugs) for subsequent disease treatment. These cell-based DDSs have their own unique in vivo fates, which are attributed to various factors, including their biological properties and functions, the loaded drugs and loading process, physiological and pathological circumstances, and the body's response to these carrier cells, which result in differences in drug delivery efficiency and therapeutic effect. In this review, we summarize the main cell-based DDSs and their biological properties and functions, applications in drug delivery and disease treatment, and in vivo fate and influencing factors. We envision that the unique biological properties, combined with continuing research, will enable development of cell-based DDSs as friendly drug vectors for the safe, effective, and even personalized treatment of diseases.