## 5 Therapeutic Properties of Nanoparticles in Breast Cancer Treatment
### Temperature-Sensitive Nanoparticles  
Tumor tissues typically exhibit higher temperatures than normal tissues, allowing for controlled drug delivery at the tumor site through external heating. This characteristic has been harnessed in the development of intelligent drug delivery systems. Several preclinical studies have demonstrated that the efficacy of both radiotherapy and chemotherapy can be enhanced when combined with hyperthermic therapy [76]. [PERSON] et al. evaluated the photothermal efficacy of a palladium-ruthenium nanohybrid with a polypyridyl complex (PdRu-RCE@PCM NPs) against breast cancer cell lines [76]. The photothermal properties of PdRu facilitate the melting of the heat-sensitive PCM material under near-infrared light, leading to the release of PdRu and RCE in a laboratory setting. Additionally, PdRu not only damages tumor cells through photothermal therapy (PTT) but also catalyzes H2O2 to produce O2, thereby enhancing photodynamic therapy (PDT). The enzyme-like activity further elevates reactive oxygen species (ROS) levels within tumors [76]. Significantly, due to the effective accumulation of RCE, PdRu-RCE@PCM nanoparticles not only serve as photosensitizers but also function as superior fluorescent imaging agents [76]. Studies indicate that these nanoparticles, when combined with PTT and PDT, offer promising therapeutic outcomes in suppressing both primary and metastatic tumors while maintaining favorable biocompatibility in the body [76]. This provides valuable insights into the treatment of breast cancer, particularly the metastatic type. Pd is known for its robust catalytic activity, and Ru, with its ability to produce oxidation species at low potentials, enhances catalytic activity through both bifunctional and electronic mechanisms. The alloy of Pd and Ru is considered a crucial element often used as a cocatalyst [76]. Pd and Ru have demonstrated effectiveness as photothermal conversion agents, making them suitable for photothermal therapy in tumor treatments [76]. [PERSON] et al. have developed a gold-promoting satellite with a copper chalcogenide nanocrystal (Cu2-xS) [76]. Triple-negative breast cancer (TNBC) exhibits a high expression of programmed cell death-ligand 1 (PD-L1), which serves as an active targeting site. The authors leveraged this by attaching the extracellular domain of PD-1 to gold-promoting satellites on the Cu2-xSe surface. This resulted in the PD-1-modified GPS-CS@PD-1 nanocomposite, which demonstrated robust binding to PD-L1-expressing TNBC cells [76]. When this complex was introduced to TNBC tumor-bearing mice, photoacoustic and photothermal imaging revealed that the nanocomplex's accumulation in tumor areas peaked. This was evidenced by a prominent photoacoustic imaging (PAI) signal contrast and a peak temperature of 53.4 \({}^{\circ}\)C [76]. This elevated temperature induced hyperthermia, leading to the necrosis of cancer cells [77]. A targeted nanocarrier system enhances drug delivery to the epidermal growth factor receptor (EGFR)-expressing breast cancer (BC) cells, thereby amplifying the effects of photothermal therapy. [PERSON] et al. developed liposome-mediated magnetic nanoparticles conjugated with cetuximab and doxorubicin to specifically target EGFR [78]. These liposomes, sensitive to heat, encapsulate iron oxide nanoparticles within heat-sensitive liposomes that can be activated by near-infrared light for controlled drug release, showcasing effective photothermal therapy. This delivery mechanism presents a potential advancement in breast cancer treatment techniques [78]. [PERSON] et al. designed a thermo-responsive hydrogel by conjugating it with triptolide. This injectable hydrogel significantly enhances survival rates and minimizes side effects compared to unbound triptolide [79]. In another study, heat treatment at around 43 \({}^{\circ}\)C combined with lauric acid encapsulated in a biocompatible silica shell induced oxidative stress, variations in caspase levels, and morphometric changes [80].