Tandem Peptides Targeting HER2 for Delivery of CD44 siRNA into HER2+ Breast Cancer Cells in Vitro

More than 300,000 women will be diagnosed with breast cancer, and approximately 48,000 women will die this year due to the disease in the United States. HER2+ breast cancer accounts for 20-25% of invasive breast cancer, and it has a worse prognosis and higher early-stage mortality rate than other breast cancer subtypes. Common treatments for HER2+ breast cancer involve surgical removal of the breast or systemic therapy with chemotherapeutic drugs, both of which cause damage to healthy tissue. Due to the lack of a natural ligand for the HER2 receptor, there is a need for improved targeting strategies for the treatment of HER2+ breast cancer.Short interfering RNA, a type of RNA interference, is a promising tool for cancer treatment that works by silencing oncogenes on the mRNA level to reduce the expression of proteins contributing to cancer progression. siRNA requires a carrier to protect it from degradation and to mediate its delivery into a target cell. There are multiple types of carriers for siRNA delivery, including viral vectors and non-viral vectors such as polymeric nanoparticles, liposomes, and peptide-based nanoparticles. Peptides have advantages over other delivery mechanisms, such as control over functionalization, easier synthesis, and better biocompatibility. CD44, an oncogene correlated with HER2+ breast cancer, is directly involved in tumor growth and metastasis. CD44 is expressed in most healthy cells; therefore, silencing must be selective for HER2+ breast cancer.In this study, we investigated a novel strategy for treating HER2+ breast cancer utilizing peptide-mediated delivery of CD44-specific siRNA. We characterized two tandem peptides consisting of HER2 targeting peptides, P25 or P51, and the fusogenic peptide, DIV3W. By linking these two functional peptides, we aim to show that our tandem peptides can target the HER2 receptor and successfully deliver siCD44 to initiate the silencing of CD44 on the gene and protein level in HER2+ breast cancer cells. Characterization assays were performed to determine which tandem peptide possessed more optimal qualities as a carrier for siRNA. We observed that the tandem peptide, P25-DIV3W, protects siRNA from degradation, is cytocompatible, and promotes efficient internalization into HER2+ cell lines. P51-DIV3W showed poor siRNA protection and cytotoxic traits when delivered to HER2+ and HER2-normal cell lines. We then showed that P25-DIV3W loaded with siCD44 initiates the knockdown of CD44 and promotes cell death in HER2+ cell lines while not affecting the viability of normal breast epithelial cells in low concentrations.