Gold nanoparticles (GNPs) played an important role in cancer treatment due to their unique properties and the surface modifications that are the key in increasing the selectivity of chemotherapies. GNPs can be modified with antibodies, aptamers and peptides to increase the selectivity and targeting together. GNPs are used as drug vehicles to target cancer cells. For example, 5 nm GNPs were covalently attached to cetuximab and gemcitabine to target pancreatic cancer. Also, GNPs worked as, Radiosensitizer Stabilizers used for GNPs The mechanism of GNPs cellular uptake is endocytosis, depending on size and shape, or by direct penetration. The penetration can be controlled by changing the GNPs functionalising surface. Unfortunately, the GNPs tend to aggregate. This affects the cellular uptake and toxicity of GNPs. Stabilisers are crucial to decrease the aggregation. Also important in enhancing the selectivity of the GNPs. Different stabilising agents are available and have been reported by many studies. For example, citrate, Arabic gum and starch. Moreover, polyorganophosphazene has been working effectively in stabilising the GNPs and achieving the drug delivery. Furthermore, it was reported that the low molecular weight organic substances could improve the biocompatibility of the GNPs. Also, for the first time, lactose (carbohydrate) functionalised as a stabilising agent for GNP and a targeting agent in the case of breast cancer. When targeting nanoparticles enter the blood, their surface interacts with the blood and serum forming protein corona which deteriorates the targeting property of the targeting nanoparticles by preventing the nanoparticles from the interaction with the receptors present on the surface of the cells. Polyethene glycol (PEG) is Capable of inhibiting the absorption of protein. So, PEG became the most commonly used hydrophilic coating polymer. PEG allows the accumulation of the nanoparticles in the tumour by shielding them to prevent their uptake by the macrophages. Moreover, PEG increases the circulation time; prevent the aggregation of the NP. Toxicity of GNP GNPs possess cytotoxicity effect. The effect of the GNPs on the Cells is due to the interaction of the GNPs with the cell components. GNPs have different cytotoxicity mechanisms. They can cause apoptosis; organelles or DNA deterioration; mutagenesis; oxidative stress; and down-regulation of proteins. The available information about the cytotoxicity of GNPs is contradicted. For example, GNPs has been found non-toxic in case of leukaemia. In contrast, they showed a toxic effect on Cos-1. The cytotoxicity of the GNPs varies according to the size and shape of GNP the charge, the surface modification and the type of used cell. In order to assess the cytotoxicity of the GNPs, cytotoxicity assays are required.
