Dendrimer mediated small interfering RNA targeting strategy for cancer therapy

Abstract

Cancer is the leading cause of death worldwide. Lack of effective treatment makes the development of novel therapeutic methods in high demand. Small interfering RNA (siRNA)-based gene targeting brings new hopes for cancer treatment due to the specificity and effective in silencing specific target genes in cancer. Owing to the characteristics such as nano-sized volume, multivalency, water solubility, and biocompatibility, dendrimers are very suitable nanovectors for siRNA delivery. In this study, the anti-tumor effects of dendrimer-mediated siRNA delivery on different cancer genes were investigated in different cancer types.

Cancer stem cells (CSCs) are the driven force for tumor progression, metastasis, and recurrence initiation. In ovarian CSCs, p70S6K siRNA/G6 dendriplexes was formed and characterized for blocking stemness and metastasis in ovarian CSCs. The formed p70S6K siRNA dendriplexes could decrease p70S6K expression and stem marker genes expression in high efficacy, and inhibit the key steps in metastasis including cell proliferation, mesothelial adhesion, migration, invasion, and sphere formation. Using Cy5-labeled p70S6K siRNA/G6 intravenously injected into mice bearing subcutaneous SKOV-3 CSC tumors, it is found that the delivery occurred mainly within the tumor. The p70S6K siRNA dendriplexes also significantly inhibited ovarian tumor growth, peritoneal dissemination and ascites formation in vivo. Similar results were also observed with additional in vitro and in vivo experiments using the amphiphilic dendrimers (AmDM) in ovarian CSC model.

In nasopharyngeal carcinoma (NPC), we have identified BCL3 as a key regulator of tumorigenesis. BCL3 siRNA/AmDM dendriplexes specifically decreased BCL3 gene expression, inhibited cell proliferation via inducing apoptosis in EBV-positive C666-1 cells. In nude mice models, BCL3 siRNA dendriplexes by intravenously injection markedly inhibited tumor growth in C666-1 xenograft and patients’ derived xenografts without obvious toxicities even with long-time (29 days) administration. When combined with the chemotherapeutic agent cisplatin, BCL3 siRNA dendriplexes was superior to cisplatin alone, suggesting a chemosensitizing effect of BCL3 suppression. Among the many genes in the metastatic cascade, we focused on the P-cadherin (P-cad), which is involved in the tumor-mesothelium interaction, a key first step of the cascade. Using a recently established highly metastatic (HM) and non-metastatic (NM) ovarian cancer model, it is shown that there was a positive feedback loop between tumor and mesothelial cells upon P-cad-mediated adhesion. P-cad activated glycolysis in mesothelial cells and the lactate produced provides a substrate for tumor cell lipogenesis, forming a positive feedback loop to promote tumor cell growth. As a lactate transporter, it is hypothesized that MCT4 may play an important role in the crosstalk between lipogenesis in tumor cells and glycolysis in mesothelium. I showed that MCT4 was a target gene in this P-cad-regulated metabolic reprogramming upon the tumor-mesothelium interaction. For proof-of-concept efficacy studies, MCT4 siRNA-AmDM effectively suppressed lipogenesis gene expression in HM cells, and inhibited ovarian cancer metastasis in nude mice bearing intraperitoneally injected HM cells.

Collectively, the results provide a significant advance in our understanding of p70S6K, BCL3 and MCT4 in the regulation of tumorigenesis and progression and support the potential use of that dendrimer-mediated siRNA delivery as a therapeutic approach.