Optimized aptamer functionalization for enhanced anticancer efficiency in vivo

Nucleic acid aptamers (Apt) are RNA or DNA fragments that can bind specifically to a target molecule or to a target substrate with great affinity, thus has attracted great attention for diagnosis and treatment of various malignant diseases. Two primary strategies reported for efficient incorporation of Apt into a nanocarrier include physical encapsulation via electrostatic interactions and chemical conjugation via covalent bonds. Generally, physical encapsulation offers an easier approach for Apt functionalization than covalent bonding that involves sophisticated chemical design as well as synthesis and purification procedures. However, the effect of Apt's incorporation strategies on the property and performance of Apt-functionalized nanocarriers, to our knowledge, remains unclear, which clearly hampers the biomedical applications and potential clinical translations of Apt-decorated delivery systems. To clarify this critical issue toward better performance of Apt for biomedical applications, an Apt moiety with a specific targeting property to liver cancer cells was introduced to a previously fabricated polymeric prodrug, chitosan-5-fluorouracil-1-acetic acid (CS-FU) via either an amide link or electrostatic interactions to afford two types of Apt-functionalized polymeric prodrugs, i.e., Apt/CS-FU and Apt-CS-FU with an equivalent amount of incorporated Apt, respectively. The in vivo and in vitro anti-tumor efficacy and targeting properties of these two Apt-functionalized polymeric prodrugs were investigated and further compared in detail. Interestingly, the two self-assembled micelles showed almost identical in vitro targeting and antitumor efficiency, but Apt-CS-FU mediated 1.5-fold greater tumor inhibition rate (TIR) than Apt/CS-FU in murine tumor models. The better performance of Apt-CS-FU than that of Apt/CS-FU was substantially attributed to the smaller size of Apt-CS-FU than that of Apt/CS-FU in the presence of serum for prolonged in vivo circulation. The first disclosed Apt incorporation strategy effects on the performance and property of Apt-decorated nanocarriers is believed to promote rational design and future clinical translations of Apt-functionalized nanoplatforms with greater therapeutic efficiency.