Synergistic Targeting HER2 and EGFR with Bivalent Aptamer-siRNA Chimera Efficiently Inhibits HER2-Positive Tumor Growth.

HER2 overexpression is identified on 20-30% breast cancer and other cancers at different levels. Although HER2 targeted monoclonal antibody combined with chemical drugs has shown improved outcomes in HER2 expressing patients, drug resistance and toxicity have limited their efficacy. To overcome drug resistance, cotargeting  multiple HER receptors was proven to be effective. EGFR/HER2 dimerization can active PI3K/AKT pathway, and resistance to HER2-targeted drugs is associated with upregulation of EGFR. Here, we developed a novel HER2/EGFR targeted nucleic acid therapeutic to address current drug limits. The new therapeutic is constructed by fusing HER2 aptamer-EGFR siRNA sense strand with HER2 aptamer-EGFR siRNA antisense strand into one molecule: a bivalent HER2 aptamer-EGFR siRNA aptamer chimera (HEH). In breast cancer cell lines, HEH can be selectively taken up into HER2 expressing cells and successfully silence EGFR gene and down regulate HER2 expression. In breast cancer xenograft models, HEH is capable of triggering cell apoptosis, decreasing HER2 and EGFR expression, and suppressing tumor growth. The therapeutic efficacy of HEH is superior to HER2 aptamer only, which suggests that HEH has synergistic effect by targeting HER2 and EGFR. This study demonstrated that HEH has great potential as a new HER2 targeted drug to address toxicity and resistance of current drugs and may provide a cure for many HER2 positive cancers.