Document Type


Degree Name



Dept. of Biomedical Engineering


Oregon Health & Science University


Despite the advent of novel targeted therapies and early diagnosis, breast cancer remains the second cause of cancer death in women in the US since 1950. More effective treatments are still needed to improve its prognosis. Her2-positive (HER2+) breast cancer represents 15-25% of invasive breast cancer. Although HER2-targeted therapy has significantly improved the prognosis of this breast cancer subtype, resistance is common. The Cancer Genome Atlas project has identified genomic aberrations in breast cancer which can be used to guide the development of a wide range of therapeutic agents. However, most attractive therapeutic targets, that may be used to overcome cancer resistance to current treatment modalities, are considered ‘undruggable’ by conventional small molecule inhibitors or monoclonal antibodies. RNA interference (RNAi) using small interfering RNAs (siRNAs) is a promising alternative to inhibiting these otherwise intractable therapeutic targets. This strategy has proven effective in vitro. However, because the delivery of siRNAs to tumors in patients is still challenging, this technology has yet to be fully capitalized.

In this dissertation project, a novel nanoparticle construct has been engineered for efficient delivery of siRNAs to tumors. The construct consists of a 47-nm mesoporous silica nanoparticle core coated with cross-linked polyethyleneimine– polyethyleneglycol copolymer, electrostatically loaded with the siRNA against human epidermal growth factor receptor type 2 (HER2) oncogene, and coupled to the anti-HER2 monoclonal antibody (trastuzumab). The construct has been engineered to increase siRNA half-life in the blood, enhance tumor-specific cellular uptake, and maximize siRNA knockdown efficacy. The optimized anti- HER2 nanoconstructs produced apoptotic death in HER2+ breast cancer cells grown in vitro but not in HER2-negative (HER2-) cancer or nonmalignant epithelial cells. One dose of the siHER2-nanoconstructs reduced HER2 protein levels by 60% in trastuzumab-resistant HCC1954 xenografts. Administration of multiple intravenous doses over 3 weeks significantly inhibited tumor growth (p < 0.004). The siHER2-nanoconstructs have an excellent safety profile in terms of blood compatibility and low cytokine induction when exposed to human peripheral blood mononuclear cells. In addition, mice that received multiple doses of siHER2-nanoconstructs did not show signs of liver or kidney toxicity, as determined by serum biochemistry markers and histology. The construct can be produced with high batch-to-batch reproducibility and the production methods are suitable for large-scale production.

In conclusion, the developed nanoconstructs have great potential for clinical translation. This platform development coupled with genome analysis and RNAi functional screening could provide a more effective treatment in HER2+ refractory breast cancer. Further, the nanoconstructs have capacity to load multiple cargos simultaneously, including chemotherapeutic drugs and a cocktail of siRNAs. This affords a targeted combination therapy that may provide better synergistic outcomes. Application to other types of cancers can be done with ease by utilizing appropriate siRNAs or other therapeutic cargos and targeting components.




School of Medicine



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