Additionally, tests would further require an analysis of the labeling patterns of c- Fos following stereotypic and related responses to localize the brain regions involved in cortisol neuronal activation, as well as direct measurement of dopamine and its LP 20 hydrochloride receptors in response to IL-2 administration. Previous studies identified that gold nanoparticles show little cytotoxicity despite their efficient uptake into human cells by endocytosis, making them suitable candidates for nanomedicine. Besides their biocompatibility, the fact that they are easy to synthesize, characterize, and surface modify contributed to attract much attention in various biomedical applications. Au-NPs have been investigated as drug delivery vehicles and photothermal therapy and molecular imaging tools for potential biodiagnosis. Nanoparticle-based therapeutic strategies for cancer treatment are mainly based on the delivery of chemotherapeutic agents to induce apoptosis. The primary reasons for using nanoparticles as carriers for therapeutic delivery are to enable multimodal functionalities, such as imaging or specific targeting, to increase tissue permeability and site-specific drug accumulation, and to reduce side effects to healthy tissues. Currently, Au-NPs are used in different biomedical applications: not only can they be used as scaffolds for increasingly potent cancer drug delivery but they can also serve as transfection agents for selective gene therapy and as intrinsic antineoplastic agents. Dreaden et al. have shown that targeted Au-NPs are capable of altering the cell cycle, including cell division, signaling, and proliferation. Despite the widespread application of Au-NPs, a clear understanding of how biological systems respond to the nanoparticles is vital, and characterization of the unique size-dependent physicochemical properties of the Au-NPs is a critical component. For example, it was found that spherical Au-NPs with a diameter of 1.4 nm induce necrosis and mitochondrial damage in various cell lines via oxidative stress mechanisms, which may be associated with their well-known catalytic activity at that size. A recent study by Connor et al. reported that significant amounts of larger Au- NPs penetrate into cells, but that these Au-NPs are not inherently toxic to human cells. Chithrani et al. studied the relationship between Au-NPs and HeLa cells and suggested that Au-NPs entered the cells via receptor-mediated endocytosis at a threshold size of approximately 50 nm. Since there are no safety regulations yet, the effect of Au-NPs on cells still MEDICA 16 requires further study. Invasion and metastasis are important pathologic features of cancer cells. Invasive capacity is the single most important trait that distinguishes benign from malignant lesions. Indeed, invasive tumor cells can escape surgical resection and be responsible for tumor recurrence.