A Versatile Prodrug Strategy to In Situ Encapsulate Drugs in MOF Nanocarriers: A Case of Cytarabine-IR820 Prodrug Encapsulated ZIF-8 toward Chemo-Photothermal Therapy

Zeolitic imidazolate framework-8 (ZIF-8) is an attractive metal organic framework (MOF) in drug delivery. Strong interaction between drugs and ZIF-8 is essential for high drug loadings through in situ construction of MOFs. However, only limited drugs with unique functional groups (  COOH,  SO 3 H, et al.) can interact with ZIF-8 and be encapsulated satisfactorily so far. Drugs without these functional groups are difficult to be loaded due to the lack of strong interaction. Herein a versatile prodrug strategy is proposed to solve the problems encountered by MOFs. Cytarabine (Ara) is chosen as a model drug since it cannot be loaded in ZIF-8 satisfactorily by itself. New indocyanine green (IR820) is utilized to bond with Ara for the formation of prodrug (Ara-IR820) and endows the prodrug with fluorescence imaging-guided chemo-photothermal therapy, in which sulfonic groups strengthen the interaction between prodrug and ZIF-8. This prodrug loaded ZIF-8 is further functionalized with hyaluronic acid (HA) to result in active-targeting HA/Ara-IR820@ZIF-8 nanoparticles. The in vitro and in vivo results demonstrate its excellent visual cancer therapy with tumor-targeted and pH-responsive release behavior. This design offers a new concept to solve the drug loading problem of MOFs, exhibiting a flexible strategy to expand the biomedical applications of MOFs.