Background Breast cancer is the most common malignant tumor disease and the leading cause of female mortality. The evolution of nanomaterials science opens the opportunity to improve traditional cancer therapies, enhancing therapy efficiency and reducing side effects. Methods and major results Herein, protein cages conceived as enzymatic nanoreactors were designed and produced by using virus-like nanoparticles (VLPs) from Brome Mosaic Virus (BMV) and containing the catalytic activity of glucose oxidase enzyme (GOx). The GOx enzyme was encapsulated into the BMV capsid (VLP-GOx), and the resulting enzymatic nanoreactors were coated with human serum albumin (VLP-GOx@HSA) for breast tumor cell targeting. The effect of the synthesized GOx nanoreactors on breast tumor cell lines was studied in vitro. Both nanoreactor preparations VLP-GOx and VLP-GOx@HSA showed to be highly cytotoxic for breast tumor cell cultures. Cytotoxicity for human embryonic kidney cells was also found. The monitoring of nanoreactors treatement on triple negative breast cancer cells showed an evident production of oxygen by the catalase antioxidant enzyme induced by the high production of hydrogen peroxide from GOx activity. Conclusions and implications The nanoreactors containing GOx activity are fully suitable for cytotoxicity generation in tumor cells. The HSA functionalization of the VLP-GOx nanoreactors could result in a prevailing strategy to improve selective cancer targeting. The GOx containing enzymatic nanoreactors seems to be an interesting alternative to improve the current cancer therapy. In vivo studies are on going to reinforce the effectiveness of this treatment strategy.