Biostable Double-Strand Circular Aptamers Conjugated Onto Dendrimers for Specific Capture and Inhibition of Circulating Leukemia Cells

BACKGROUND/OBJECTIVE: Circulating tumor cells (CTCs) are known as the root of cancer metastasis. Capture and inhibition of CTCs may prevent metastasis. Due to the rarity of CTCs in vivo, the current technology about CTCs capture is still challenging. The aim of our study was to conjugate the enhanced biostable double-strand (ds) circular aptamer (dApR) with dendrimers for capturing and restraining CTCs in vitro and in vivo. METHODS: CEM-targeting aptamer (Ap) was looped by ligation after phosphorylation to form circular ds aptamer dApR, which was then conjugated to dendrimers by biotin-streptavidin affinity reaction and named as G-dApR. The physicochemical properties of G-dApR were characterized by using PAGE gel electrophoresis, UV, DLS, AFM, fluorophotometer and laser confocal microscope. Biostability of G-dApR was also analyzed by gel electrophoresis. Confocal microscopy and flow cytometry were then performed to determine the binding specificity of G-dApR to CEM cells and the captured CTCs in mice and in human blood. Apoptosis of the captured cells was finally evaluated by using MTT assay, DAPI staining, AO/EB staining, cell cycle analysis and Annexin V-FITC/PI staining. RESULTS: Physicochemical characterization demonstrated the entity of dApR and G-dApR, and the nano-size of G-dApR (about 180 nm in aqueous phase). G-dApR exhibited the excellent biostability that confers their resistance to nuclease-mediated biodegradation in serum for at least 6 days. In our established CTCs model, we found that G-dApR could specifically and sensitively capture CTCs not non-target cells even in the presence of millions of interfering cells (10(8)), in mice and in human blood. Finally, the activity of captured CTCs was significantly down-regulated by G-dApR, resulting in apoptosis. CONCLUSION: We created the enhanced biostable dApR-coated dendrimers (G-dApR) that could specifically capture and restrain CTCs in vitro and in vivo for preventing CTC-mediated cancer metastasis.