Acidic microenvironment triggered in situ assembly of activatable three-arm aptamer nanoclaw for contrast-enhanced imaging and tumor growth inhibition in vivo

Rationale: Static assembled multivalent DNA nanotheranostics system have encountered some bottleneck problems in cancer imaging and therapy, such as poor penetration and high immunogenicity.Herein, we proposed an acidic tumor microenvironment triggered assembly of activatable multivalent nanodevice, called "three-arm aptamer nanoclaw" (TA-aptNC), assembled from three pH-responsive aptamer-decorated DNA monomers (pH-aptDMs) to facilitate their functions of imaging and therapy. Methods:The activated TA-aptNC was constructed by acidic microenvironment triggered in situ assembly of three pH-aptDMs.Designer pH-aptDM was established based on the combination of a pH-responsive i-motif switch and an assembly module with a cell membrane anchoring aptamer ligand.Acidic microenvironment-triggered the assembly of the TA-aptNC was characterized by electrophoresis and atomic force microscopic (AFM).The binding affinity and stability of the TA-aptNC, comparing the monovalent pH-aptDM, were studied via the flow cytometry and nuclease resistance assays.Acidic microenvironment-activated contrast-enhanced tumor imaging and significantly antitumor efficiency were evaluated in vitro and in vivo.Results: At physiological pH environment, the pH-aptDMs with excellent tissue permeability exited as inactivated and monodispersed small monomer.When encountering acidic microenvironment at the tumor site, pH-responsive i-motif switch liberated from the pH-aptDMs, and the three unconstrained DNA modules (DM1, DM2 and DM3) subsequently assembled in situ into the TA-aptNC.Compared with monovalent pH-aptDMs, the spontaneously formed activatable TA-aptNC afforded 2-fold enhanced binding ability via the multivalent effect, which further facilitated the selective tumor cell uptake capability, thus enabling a contrast-enhanced tumor imaging and significantly antitumor efficiency in vivo without systemic toxicity.Conclusions: The proposed strategy offers valuable insight into excavating an endogenous stimuli-triggered assembly of multivalent nanodevice for accurate diagnosis and efficient tumor therapy.