Aptamer Conjugated DNA Tetrahedron Drug Delivery System For Overcoming Drug Resisitance

Multidrug resistance (MDR), discovered in1976by Juliano and Ling, is the main reason that cancer eludes chemotherapy. MDR cancer cells are crossresistant to various chemotherapeutic agents, even chemically and functionally unrelated ones. To date, great efforts have been made to effectively suppress or circumvent MDR. The most common mechanism responsible for MDR is the expression or overexpression of efflux transporter. Many MDR inhibitors that inhibit MDR transporters have been identified. However, none of them has been proven to be clinically useful without side effects. In order to overcome the above mentioned challenge, novel approaches struggling with MDR need to be designed. Specially, nanotechnology has witnessed significant progress in the past few decades. Research in the field of cancer nanotechnology has made remarkable advances and hold great potential for overcoming MDR.Nanotechnology is a fast growing research field in recent years and has gained public and media interest worldwide. The promise of nanotechnology lies in the ability to engineer customizable nanostructure that can be loaded with one or more payloads such as targeting unit, imaging moiety, diagnostic and therapeutic agents. Multiply nanoparticle (NP)-based therapeutic systems have been developed to overcome MDR. They range from organic nanocarrier such as liposomes, polymer conjugates, micelles and dendrimers to inorganic nanocarrier such as carbon-based and metallic nanoparticles. Although various nanocarriers have been developed and reserve MDR to some extent, they have their respective limitations. The organic nanocarriers are usually heterogeneous in structure. As a result, it’s difficult to assemble them into higher-ordered structures. Also, cargo molecules are often loaded into nanocarriers nonspecifically and their efficacy may be weaken in physiological conditions. In addition, many inorganic nanocarriers contain toxic elements or residuals and they are usually difficult to be degraded, which raises safety concerns. Thus,"smart" theranostic nanovehicles are still required to realize sufficient clinical outcomes in MDR and cancer therapy. Structural DNA nanotechnology has been greatly developed with the combination of synthetic stable branched DNA and sticky-ended cohesion. Because of the high level of structural programmability, biostabilityand good biocompatibility, DNA nanostructures are among the most promising candidates to serve as nanoscale drug delivery vehicles. It was confirmed that DNA nanocages were capable of entering live mammalian cells. Chang et al. developed an aptamer conjugated DNA icosahedral drug delivery system that could efficiently kill cancer cells, which was one of the first DNA nanocarriers. Successively, several drug delivery systems were constructed for disease treatment. One extraordinary example is the adriamycin-loaded DNA Origami drug delivery system that developed by Ding’ group. The nanocarrier was employed as a carrier to effectively circumvent drug resistance. Although working effectively, the nanocarrier was too complicated because hundreds of DNA staple strains and a long scaffold strand were needed to construct the DNA origami. To solve this problem, a DNA tetrahedron was utilized for overcoming drug resistance. But the DNA tetrahedron-based nanocarrier is a passive targeting drug delivery system so it could equally enter normal cells and thus causes side effects. Therefore, a relatively easily constructed and active targeting drug delivery system is required for overcoming MDR.Herein, we report the construction of a drug delivery system based on aptamer conjugated DNA tetrahedron for overcoming MDR. We extended the nucleic acid strains of DNA tetrahedron with MUC1aptamer sequence to construct aptamer conjugated DNA tetrahedron. The MUC1aptamer conjugated nanocarrier can specifically target carcinoma cells via recognizing the MUC1protein overexpressed and aberrantly on cell surface. Adriamycin (ADM) was loaded into DNA tetrahedron through intercalating into DNA base pairs. The aptamer conjugated DNA tetrahedron drug delivery system can effectively reverse MDR with lower dosage. The results suggest that DNA nanostructures will be a promising platform for drug delivery and cancer therapy.The article was composed of three chapters. The research background and significance of the work were elaborated. Methods and results of the experiments were described. The potential application and development of the drug delivery system were also discussed.In chapter one, the definition of MDR was described, as well as the mechanisms for MDR. Multiply strategies for overcoming MDR were employed, especially nanoparticles based approaches. Recently, DNA nanotechnology is gaining increased attention and DNA nanostructure based drug delivery systems were summarized. DNA tetrahedron nanostructure was described in detail. Finally, the characteristics aptamers and its application were introduced.In chapter two, ADM was loaded into DNA tetrahedral nanostructure to construct DNA tetrahedron drug delivery system. The nanocarrier can transport ADM to drug resistant cancer cells effectively. ADM accumulation was increased and thus cancer cells were killed.Though DNA tetrahedron drug delivery system can kill drug resistant cancer cells, it was a negative targeting drug vehicle. It may harm normal cells as well and thus caused side effects. To solve this problem, a recognition moiety was assembled into the nanocarrier. MUC1aptamer was selected as targeting ligand, which can target MUC1protein on the surface of human breast cancer cells. An active targeting drug delivery system was constructed for overcoming drug resistance. As we know, it’s the first active targeting DNA nanostructure based drug carrier for MDR circumvention.