ABSTRACT Nanoparticle-based technologies including theranostic nanomedicine are fast developing areas of biomedical research offering unprecedented potential for cancer treatment. This application is designed to bring this potential to translational level and investigate the application of our novel image-capable nanodrug for treatment of metastatic breast cancer in a large animal model. Breast cancer metastasis is the main cause of mortality among breast cancer patients, and for that reason the specific aims of this application respond to an unmet clinical need. This proposed strategy is based on our discovery that the survival of metastatic cells crucially depends on the high expression of microRNA-10b (miR-10b) and that miR-10b is responsible for metastatic cell viability. With this discovery it became possible to kill these cells at metastatic sites by inhibiting miR-10b. This is achieved using a nanodrug composed of anti-miR-10b antagomirs conjugated to dextran-coated magnetic nanoparticles (termed MN-anti-miR10b). These nanoparticles serve as delivery vehicles for the antagomirs. Also, the magnetic properties of these nanoparticles allow for monitoring of their delivery in vivo using magnetic resonance imaging (MRI), which is an added value for clinical implementation of this therapeutic approach. In pre-clinical studies in mice, we showed delivery of MN-anti-miR-10b to established metastases in the lymph nodes, lungs, bone and brain. Pilot studies in companion cats showed the delivery of the nanodrug to the metastatic lesions after intravenous injection. Therapeutic studies in the murine model of human MDA-MB-231 TNBC showed that delivery of MN-anti-miR10b to lymph nodes with established metastases resulted in arrest of metastatic growth by halting tumor cell proliferation and triggering apoptosis. When combined with a low-dose chemotherapy, MN-anti-miR10b caused complete elimination of lymph node metastases with no evidence of systemic toxicity after just four weekly treatments. Next, we showed the utility of the nanodrug in combination with low-dose chemotherapy for treatment of established lung metastases corresponding to Stage IV of human disease in immunocompetent murine model (4T1). We found that six weekly treatments were sufficient to cause complete regression of pre-existing lung metastases with no further dissemination to other organs in the remaining animals. With an outlook to clinical translation of our studies, in this application we propose to test our nanodrug strategy in large animals with spontaneous metastatic breast cancer (companion cats). Studies proposed here will serve as a necessary step towards first-in-human trials, because they will prove successful delivery of the nanodrug in large animals, which are anatomically and physiologically distinct from the murine models tested to date. Furthermore, these studies will provide us with additional information on PK/PD parameters in a large animal model. Finally, therapeu...