Selective Recognition of Co‐assembled Thrombin Aptamer and Docetaxel on Mesoporous Silica Nanoparticles against Tumor Cell Proliferation

Abstract

Generally, tumor development relies on the material, energy, signal transduction in the extracellular matrix and intracellular environment. An optimal systematic approach for cancer treatment can cut off the connection between the tumor cell and extracellular matrix and inhibit the intracellular activity. The combination of two or more therapeutic approaches can cooperatively promote tumor suppression and is a very effective strategy for synergistic or combined anticancer treatment. Recent attention has been devoted to the engineering of specialized vehicles that encapsulate traditional chemotherapeutic drugs for stimuli-responsive release, and the targeting of these vehicles to tumor cells with highly efficient ligands that selectively recognize tumor-associated or tumor-specific antigens. It has been found that nanoscale vehicles can offer prolonged circulation times and selective binding to cancer tissues through enhanced permeation and retention effects. Importantly, the size of these nanocarriers, in contrast to single molecules, allows them to provide a larger drug payload and to achieve higher targeting specificity. A wide variety of targeting molecules have been synthesized or separated for use in cancer therapy, including peptides, oligosaccharides or humanized antibodies. Interestingly, nucleic acid ligands, also called aptamers, have been developed as a novel class of targeting molecules for therapeutic and diagnostic applications. Aptamers are single-stranded DNA or RNA oligonucleotides that can fold by intramolecular interaction into specific three-dimensional conformations to recognize various kinds of targets with high affinity and specificity. As the first selected aptamer, 15-mer thrombin binding aptamer (TBA), which can fold into a compact intramolecular tetraplex with an antiparallel orientation of strands in the chair-like conformation, inhibits the enzymatic function of thrombin. The significant neoplastic biological effect of thrombin involves clotting-dependent mechanism and protease-activated receptor-1 (PAR-1) related signaling; this leads to several tumor functions, specifically proliferation and angiogenesis. To the best of our knowledge, although a considerable amount of research has been carried out to exploit TBA in the construction of biosensors, molecular machines, and anticoagulants, 32] little has been done to employ TBA to target thrombin for disturbing fibrin formation and suppressing tumor cell growth by restraining the unique proteolytic ability of thrombin and further breaking related signal transduction pathways. Here, we report a TBA-tethered lipid-coated mesoporous silica nanoparticle (TBA–lipid–MSN) hybrid as an extraand intracellular anticancer nanocarrier. A potent anticancer drug, docetaxel (Dtxl), was incorporated into this hybrid system. Selective recognition and drug release were demonstrated by using this co-assembled delivery platform (Scheme 1). Briefly, the modified thrombin binding aptamer, 5’-GGTTG GTGTG GTTGG AAAAA AAAAA AAAAA-C18-spacer-3 (TBAA15-C18) was reconstituted into hydrogenated soybean phosphatidylcholine (HSPC), mPEG2000–distearoylphosphatidylethanolamine (mPEG2000–DSPE) and docetaxel containing mixed lipid vesicles. The obtained vesicles were spread on the outer surface of MSNs, which were synthesized by a base-catalyzed sol-gel method. Introduction of MSN cores is helpful to improve the mechanical stability of aptamer–liposome conjugation. The final formulation obtained was 1 mg TBAA15– lipid–Dtxl–MSN with 3 nmol Dtxl and about 0.44 nmol TBAA15. After TBAA15–lipid–Dtxl–MSN were co-cultured with HeLa cells and thrombin, the co-assembled bioconjugates were expected to not only suppress cell growth in the extracellular matrix based on the specific antithrombin characteristics of the aptamer by disturbing PAR-1 receptor signaling, but also to achieve a much more effective cytotoxicity in the cytoplasm because of the contribution of Dtxl. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were performed to examine the self-assembly of the TBAA15–lipid–Dtxl–MSN bioconjugates. The monodispersed short, rod-shaped MSNs with a diameter of 100–200 nm and aspect ratio of about 2, are shown in Figure S1A in the Supporting Information. The [a] L. Gao, Dr. Y. Cui, Dr. J. Fei, Prof. Dr. J. Li Beijing National Laboratory for Molecular Sciences Key Laboratory of Colloid and Interface Science Center for Molecular Sciences, Institute of Chemistry Chinese Academy of Sciences, Zhong Guan Cun Beijing, 100190 (P.R. China) Fax: (+86)10-8261-4087 E-mail : jbli@iccas.ac.cn [b] Prof. Dr. Q. He Micro/Nano Technology Research Centre Harbin Institute of Technology, Harbin, 150080 (P.R. China) [c] Dr. Y. Yang National Center for Nanoscicence and Technology No. 11, Bei Yi Tiao, Zhong Guan Cun, Beijing, 100190 (P.R. China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201101658.