الفهرس 
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Abstract
Oral squamous cell carcinoma (OSCC) represents 95% of all forms of head and neck cancers. The five-year survival rate of OSCC patients has been reported approximately 50%, which is not satisfactory despite constant improvement in the current treatment modalities.
Many tumor-targeted strategies have been used worldwide to limit the side effects of therapies such as chemotherapy and radiotherapy.
Nanotechnology application in medicine is providing significant opportunities for effective treatment of many disorders and great potential in health care system. The design and development of therapeutic and diagnostic agents in the nanoscale level ranging in diameters from 10 nm to 100 nm is known as nanomedicine, it has the ability to transport and deliver a variety of biomedical entities for the prevention, diagnosis and treatment of many diseases.
Gold nanoparticles (GNPs) have been proposed as agents having the ability to improve the localized delivery of heat in ablation cancer therapies. In particular, GNPs have been shown to be an ideal agent for enhancing laser-based ablation therapies mostly due to their adjustable optical properties and surface plasmon resonance (SPR) effect.
Photothermal therapy (PTT) is a minimally invasive cancer therapy technique that utilizes laser activated GNPs to convert photon energy into heat energy sufficient enough to induce tumor cells destruction through apoptosis or necrosis. It has attracted an increased interest since that type of therapy can be combined with customized functionalized nanoparticles (NPs).
Cell apoptosis occurs when the generated heating temperatures range from 41 to 47 degrees. Excessive cell necrosis occurs by heat shock when temperatures generated are higher than 50 degrees, producing a much faster protein denaturation cell death. Hyperthermia is a treatment modality that has the ability to minimize the toxicity of chemical and radioactive agents, destructing tumor cells, without harming the healthy ones.
Apoptosis may be triggered by two major pathways: the extrinsic pathway with the binding of death ligands to death receptors or cytotoxicity that initiates the intrinsic or the mitochondrial pathway.
C-Myc oncogene plays an essential role in the regulation of many physiological processes including cell cycle control, apoptosis, protein synthesis and cell adhesion. Several proto-oncogenes such as c-Myc are activated and tumor suppressor genes are inactivated, leading to the alteration of DNA repair system and apoptosis regulation. Accumulation of the DNA damages will eventually cause malignant cell transformation.
The current study was constructed to investigate the in vitro photothermal effect of GNSCs with and without laser exposure on oral squamous cell carcinoma cell lines.
MTT assay was used to evaluate the cytotoxic effect, while acridine orange/ethidium bromide fluorescence stain revealed the mode of cell death, where caspase-8 and cytochrome-c levels were evaluated with indirect ELISA technique and C- Myc oncogene expression was assessed by using PCR.
MTT assay showed that the percentage of cell viability of oral squamous cell carcinoma cell lines (SCC-27) was decreased by escalating the dose of GNSCs in presence of laser.
Treatment of SCC-27 cells, for 24 h, with either the IC50 concentration of GNSCs / Laser or its corresponding concentration of GNSCs without laser showed a significant decrease in the percentage of viable cells down to 50.5%, in presence of laser exposure, while in absence of laser exposure the cell viability was not affected as revealed by acridine orange/ethidium bromide fluorescence stain.
Indirect ELISA technique revealed that GNSCs treatment with or without laser exposure did not affect Cytochrome-C release in SCC-27 cell lysate.
Evaluation of caspase-8 apoptotic marker with ELISA technique revealed that caspase-8 levels in SCC-27 cell lysate in case of GNSCs treatment alone did not affect caspase-8 levels, but when GNSCs pre-treatment was followed by laser exposure, there was a remarkable increase in caspase-8 levels compared to control cells.
To evaluate the possible effect of GNSCs on the oncogenic signaling pathways, C-Myc oncogene was evaluated using PCR. A significant inhibition of the C-Myc gene expression was observed down to 73 % of the relative control expression by GNSCs accompanied with laser exposure, while a non-significant decrease in C-Myc gene expression was observed in cells treated with the same concentration of GNSCs alone.