A Specific Aptamer-Cell Penetrating Peptides Complex Delivered SiRNA Efficiently And Suppressed Prostate Tumor Growth In Vivo

Objective: Specific and efficient delivery of siRNA into intended tumor cells remains as a challenge, even though RNAi has been exploited as a new strategy for prostate cancer therapy. Over recent years, while progress has been made in delivery agents to enhance specificity and efficacy, yet most of the delivery strategies focus on only one of these two aspects. It has become apparent that a combinatorial approach is highly desirable to enhance both of specificity and efficiency of siRNA delivery, especially for systemic administration in vivo. This work aims to address both specificity and efficiency of SURVIVIN-siRNA delivery by constructing a therapeutic complex using combinatorial strategies. Methods: The designed complex is composed of three parts: PSMA specific aptamer A10, a STREPTAVIDIN-TAT-DRBD fusion protein(STD) as a backbone, and a functional anti-cancer agent SURVIVIN siRNA(sur-siRNA). To link these three parts together, sur-siRNA binds with DRBD, and biotinylated A10 with STREPTAVIDIN(SA). A fusion protein STD was first expressed to serve as a backbone, consisting of streptavidin, a cell-penetrating peptide called Trans-Activator of Transcription(TAT) and a double-stranded RNA binding domain. A biotinylated Prostate Specific Membrane Antigen(PSMA) specific aptamer A10 and SURVIVIN-siRNA were then linked to STD protein to form the therapeutic complex. After the complex was constructed its function was verified in specificity, efficiency and tumor growth suppression effect by comparison with pure delivery strategy lipofectamine and aptamer-siRNA chimera. Results: As expected, STD recombinant protein is expressed using an efficient prokaryotic expression system pET-44 b plasmid and E. coli strain Rosetta-gami. The tight interaction between A10 or sur-siRNA and STD protein allows for a steady and easy construction of the therapeutic complex by a simple two-steps incubation. This complex could specifically targeted PSMA+ tumor cells. Compared to lipofectamine and A10-siRNA chimera, it demonstrated higher efficiency in delivering siRNA into target cells by 19.2% and 59.9%, and increased apoptosis by 16.8% and 26.1% respectively. Upon systemic administration, this complex also showed significant efficacy in suppressing tumor growth in athymic mice(p <0.001). Conclusions: We conclude that this therapeutic complex could specifically and efficiently deliver SURVIVIN-siRNA to target cells and suppressed tumor growth in vivo, which indicates its potential to be used as a new strategy in prostate cancer therapy.