Targeted delivery of doxorubicin to tumor cells using engineered circular bivalent aptamer

Abstract

Breast cancer is among the most frequent tumors in women and one of the main reasons of cancer death globally. Chemotherapy is among the leading cancer treatments, but because of its lack of selectivity, it can cause severe side effects. Therapeutic oligonucleotides and targeted drug delivery systems can largely overcome this problem. In this study, a targeted therapeutic complex containing doxorubicin (Dox), a chemotherapy drug, and AS1411 aptamer was designed using a circular bivalent system to treat breast cancer. The reason for naming the engineered circular bivalent aptamer system is the presence of AS1411 aptamers in circular shape on both sides of the system, and the engineered part includes a complementary sequence in the middle of the system. Finally, the therapeutic capability of the prepared targeted platform was assessed in vitro and in vivo. To prepare the system using two engineered AS1411 aptamers, both of them were incubated together at room temperature. Finally, a targeted therapeutic complex was formed by loading Dox between two complementary sequences. To analyze the properties and efficacy of the prepared complex, the loading rate of Dox in the complex, drug release at different pHs, and complex stability were verified. Also toxicity assay, flow cytometry analysis and fluorescence imaging were examined in nontarget cells (CHO cells, Chinese hamster ovary cells), and target cells (MCF-7 cells, human breast cancer cells, and 4T1 cells, mouse breast cancer cell). Also, the anti-tumor efficiency of the formulation was evaluated in mice bearing 4T1 tumor cells. The results showed that the targeted drug complex (Cb-Apt-Dox) has advantages such as high specificity for target cells, high stability in serum and simple preparation. According to results of the drug release test, the designed system is steady in the serum and blood environment. Cb-Apt-Dox could significantly increase cell uptake in MCF-7 and 4T1 cells (target, nucleolin positive) compared with CHO cells (nontarget, nucleolin negative). Based on the results of toxicity assay, Cb-Apt-Dox remarkably reduced cell viability in MCF-7 and 4T1 cells compared to CHO cells. Also, Cb-Apt-Dox significantly declined tumor growth in tumor-bearing mice compared to Dox and Cb-Apt. Our results verify that Cb-Apt-Dox can enhance antitumor effectiveness, minimize side effects of Dox and open up a new platform for breast cancer treatment.