الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
Oral squamous cell carcinoma (OSCC) accounts for more than 90% of all OC cases. Despite advances in the detection and treatment, the unsatisfactory prognosis for OSCC has remained stable for decades. To date, cancer research is focused on improving cancer treatment methods using immunotherapy.
The Toll-like receptors (TLR) family has served that purpose. These are ten recognized mammalian members emerging as pattern recognition receptors (PRRs) which represent essential components of the host’s innate as well as adaptive immune responses. TLRs are mainly expressed by the immune cells, but their expression in different tumors has also been confirmed in various studies, including head and neck cancers. The TLR signaling can either dampen the antitumor functions of the immune cells or may enhance the tumor suppression by inducing an immune activation. Studies addressing the association of TLR7 to the tumorigenesis of OSCC are limited.
Imiquimod (IMQ), the main TLR7 agonist, is a low molecular weight immune response modifier that activates both human and murine TLR7. It elicits antiviral immune responses, but has also been investigated for its role in other states of pathology. It is the first FDA-approved TLR agonist to be used clinically for the topical treatment of various cutaneous disorders, such as external genital warts as well as basal cell carcinoma. However, investigating its antitumoral effects is still in progress.
The present work aimed to study the therapeutic effect of IMQ on a human OSCC cell line (SCC-4) in terms of cytotoxicity, cytokine release in addition to its effect on cancer cell apoptosis and proliferation. It additionally attempted to compare the IMQ-induced antitumor effects against a conventional chemotherapeutic drug (Cisplatin).
The immunohistochemical expression of TLR7 in 50 OSCC and 10 normal oral mucosa samples was first assessed using anti-TLR7 antibody. In
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addition, the verification of TLR7 expression in the OSCC cell line was attempted utilizing three different techniques: enzyme-linked immunocytochemistry using the light microscope, fluorescence immunohistochemistry using the confocal laser microscope, and a flow cytometric analysis using the anti-TLR7 antibody staining. The SCC-4 cells were then subjected to different doses of IMQ and Cisplatin for 24 hours, where the drug’s cytotoxic effects were assessed by means of the CCK-8 cell viability assay. Later on, flow cytometric analysis was performed using the Annexin V-FITC/PI staining to detect IMQ- and Cisplatin-induced apoptosis and necrosis of the treated cells, as well as the Ki-67 proliferative marker for the detection of tumor cell proliferation post IMQ and Cisplatin treatment. The last step was the assessment of cytokine (IL-8) release from the IMQ treated cells using ELISA.
The current work revealed that TLR7 was significantly overexpressed in the OSCC tissue specimens as compared to the normal tissue counterpart. Moreover, TLR7 was also expressed in the SCC-4 cell line as verified by all the utilized techniques. A dose-dependent cytotoxic effect of IMQ on the tumor cells was confirmed. As compared to the effect exerted by the conventional chemotherapy, both drugs resulted in a 50% reduction in the tumor cell viability. Furthermore, similar to Cisplatin, IMQ was shown to enhance the apoptotic as well as the necrotic cell death. The proliferation of the SCC-4 cells was not affected by IMQ at low concentrations as much as it was by Cisplatin. However, it was significantly affected by IMQ at a high drug concentration when compared to the untreated cells. The IL-8 release in the supernatants of IMQ- treated SCC-4 is suggestive of the functional TLR7 expression in SCC-4 cells.
Overall, the results of the current work imply that IMQ holds promise in the treatment of OSCC. It may represent a potential alternative therapy, owing to its direct cytotoxic and apoptotic effects on tumor cells. Further studies are warranted to confirm the IMQ potential in activating a TLR7-mediated antitumor immune response and to assess the drug safety in vivo.