Sensitization of breast cancer to Herceptin by redox active nanoparticles

Herceptin-resistant tumor relapse remains a major clinical issue responsible for the poor prognosis of HER2⁺ breast cancer. Understanding the underlying mechanisms and finding a therapeutic solution are of paramount urgency to improve the patient management. Here we report that anticancer redox active cerium oxide nanoparticles (CONPs) can potently sensitize the cancer cells to the cytotoxicity of Herceptin. By comparing between Herceptin-sensitive and Herceptin-resistant human breast cancer cell lines under normoxic as well as hypoxic culture conditions, we found that in the presence of CONPs, Herceptin can kill the Herceptin-resistant cells equally effectively as it kills the Herceptin-sensitive cells under the hypoxic, but not normoxic, culture conditions by inhibiting the cell viability, survival and proliferation. Signaling analysis reveals that under the normoxic conditions, the levels of hypoxia induced factor 1α as well as vascular endothelial growth factor are higher in the Herceptin-resistant cells than that in the Herceptin-sensitive cells and are strongly induced once the culture is switched to the hypoxic conditions, which can be potently suppressed by CONPs. Treatment with CONPs plus Herceptin significantly slows down the primary tumor growth and lung metastasis of the Herceptin-resistant cells in a xenograft mouse model of orthotopic breast cancer through inhibiting the cell proliferation and survival as well as tumor angiogenesis. These results shed new lights on the mechanisms underlying the Herceptin resistance of the HER2⁺ breast cancer and provide insights into introducing CONPs-like agents to Herceptin-based therapy to improve treatment outcomes.