Breast cancer in women is a leading cause of cancer related deaths in the United States with metastatic disease being the chief cause of mortality. Metastatic breast cancer tumors are often found in their later stages making them difficult to remove or treat. Inhibition of tumor cell dispersion is therefore a key component to a reduction in mortality rates among women with breast cancer. Epithelial-Mesenchymal Transition (EMT) is the process by which cancer cells downregulate proteins associated with cell to cell adhesion (e.g. E-cadherin) resulting in cells that are able to mobilize. Breast cancer cells are known to commandeer the EMT process through overexpression of Twist1, thus allowing the cells to metastasize beyond the primary tumor. Twist1 therefore serves as an excellent therapeutic target whose disruption would result in fewer metastatic cancer cells and correspondingly reduce cancer mortality. Twist1 is also a desirable target because it is almost nonexistent in adult tissues and thus its silencing would have minimal side effects.

Our lab has elected to use an siRNA mediated gene silencing approach to decrease the expression levels of Twist1 in two highly invasive breast cancer cell lines (SUM 1315 and MCF7-Tw). Due to their fragile nature, siRNA molecules are often difficult to deliver at therapeutic levels. We have overcome these delivery limitations through the optimization and use of Poly (amidoamine) (PAMAM) dendrimers. We hypothesize that suppression of the activity of Twist1 via dendrimer-delivered Twist1 siRNA will inhibit metastatic behavior of aggressive breast cancer cells. Here we demonstrate successful delivery of Cy3-labled siRNA using two different dendrimers (Generation 5 and a modified Generation 3) with transfection efficiency results exceeding those of Lipofectamine 2000 and with far less toxicity to cells. We also show up to a 90% reduction (lasting at least 4 days) in Twist1 expression using Western Blot and qPCR analysis. Phenotypically we were able to appreciate a significant decrease in the invasive nature of the breast cancer cells using migration/invasion assays. Taken together these results demonstrate successful knockdown of Twist1 using siRNA dendrimer complexes resulting in an altered cellular phenotype. These data will serve as a foundation for optimization of future in vivo experiments with both orthotopic and metastatic breast cancer models.

Citation Format: James B. Finlay, Cai M. Roberts, Carlotta A. Glackin. Dendrimer delivery of RNA based Twist1 inhibitors to reduce breast cancer cell metastasis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2692. doi:10.1158/1538-7445.AM2013-2692