## 5 Therapeutic Properties of Nanoparticles in Breast Cancer Treatment
### pH-Responsive NPs  
The acidic microenvironment induced by intense anaerobic glycolysis is a key characteristic of malignant tumors and a significant factor contributing to breast cancer (BC) incidence, metastasis, and therapy resistance [64]. In recent years, this acidic microenvironment has emerged as a novel target for both tumor detection and treatment. This recognition holds significant importance in the progress of pH-responsive nanomedicine and nanodiagnostic approaches [65]. A recent study focused on the intracellular delivery of Dox and pH-responsive drug release observed 76% of drug release under acidic conditions using bimetallic Prussian blue analogs with cobalt iron and polyethylene glycol methacrylate (PEGMA) as an intermediate, AS1411 aptamer (CuFePBA@PEGMA@AS1411), and CoFePBA@PEGMA@AS1411 [66]. The bimetallic Prussian blue analogs and cobalt-iron acted as a carrier of doxorubicin. The biocompatibility of these bimetallic materials was found to be pH-dependent, showcasing excellent survival at a responsive pH [66]. ZnO nanoparticles with pH-responsive properties were developed by [PERSON] et al. These nanoparticles were conjugated with phenylboronic acid (PBA), enhancing the absorption of drug molecules in tumor tissue through interaction with sialic acid. In acidic environments, ZnO undergoes degradation, leading to a higher release of curcumin in tumor cells compared to normal cells. This innovative approach presents a targeted treatment for breast cancer, with the goal of minimizing systemic toxicity. The study sheds light on how PBA functionalization precisely targets tumor cells. The anticancer efficacy of curcumin-loaded, pH-sensitive nanohybrids arises from the unique oxidative stress-triggering capabilities of both curcumin and Zn+2 ions [67]. [PERSON] et al. also developed pH-responsive nanohybrids, where they designed a dual pH-responsive nanoparticle system to specifically target BC by merging immunotherapy and chemotherapy treatments [68]. While the combination of these treatments shows promise as a potential breakthrough in cancer therapy, a significant challenge lies in simultaneously and accurately targeting both cancerous and immune cells. This inventive system employs poly(L-histidine) and hyaluronic acid, coencapsulating an immune regulator (R848) and chemotherapy drug (doxorubicin) using distinct encapsulation techniques. Exploiting the acidic pH levels within the tumor environment and specific intracellular structures, the nanoparticle system releases R848 externally while precisely guiding doxorubicin to breast cancer cells. This strategy opens up possibilities for a synergistic and enhanced therapeutic impact against breast cancer [68].  
A recent study introduced a formulation involving folic acid-conjugated polyacrylic acid-coated mesoporous silica nanoparticles for pH-sensitive targeted delivery of chrysin to breast cancer cells [69]. These nanoparticles loaded with chrysin were observed to induce apoptosis in MCF-7 cells by causing oxidative stress and mitochondrial dysfunction, leading to G1 arrest. In mouse tumor tests, the intravenous injection of chrysin-loaded nanoparticles enhanced the tumor-fighting effects of chrysin through specific accumulation at the tumor site [69]. This heightened chrysin cytotoxicity resulted in significant tumor reduction, restoration of typical tissue structure, and stable body weight. The research highlights chrysin's anticancer potential and its improved efficacy when delivered through