Expression of cyclooxygenase-2, 12-lipoxygenase and inducible nitric oxide synthase genes in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma represent a major international health problem, accounting for the fifth most common type and cause of cancer-related death worldwide. Although certain risk factors for the development of head and neck squamous cell carcinoma including alcohol, tobacco, nutrition, occupation, viral infection and poor dentition are known, the exact molecular mechanisms responsible for mutational events leading to this disease have not been identified. These risk factors do not, however, adequately explain %5?10 of head and neck squamous cell carcinoma cases. Chronic inflammation has long been recognized as being associated with increased risk for human cancer at various sites and as an important component of tumorogenesis, although the mechanisms involved are not fully characterized.Eicosanoid metabolism leads to generation of bioactive lipids known to promote cancer. Metabolism of both cyclooxygenase (COX) and lipooxygenase (ALOX) pathway have been found to be elevated in tumor tissues, plasma and saliva obtained from patients with head neck cancer. In addition, altered expression of various enzymes and genes related to arachidonic acid metabolism are known to contribute to squamous cell carcinogenesis. Recently, attention has been drawn to the role of the COX enzyme and its involvement in tumorigenesis. A large volume of data exists showing that COX-2 is over-expressed in head and neck squamous cell carcinomas. Increased levels of COX-2 may contribute to carcinogenesis by modulating xneobiyotic metabolism, apoptosis, immun surveillance and angiogenesis. Substantial evidence supports a functional role for lipooxygenase-catalyzed arachidonic acid metabolism in cancer development. ALOX5 and platelet type ALOX12 are generally considered procarcinogenic. ALOX12 has been found in different cancer tissues including melanoma, prostate and epidermal cancers. 12-HETE is the only metabolite of the arachidonic acid-metabolizing enzyme ALOX12 suggested to act as regulator of tumor growth and motility. However, the role of 12-HETE in squamous cell carcinoma of head neck has not been adequately investigated.NO is synthesised from aminoacid L-arginine, by the enzyme nitric oxide synthase (NOS). There are at least three NOS isoenzymes; endothelial (eNOS), neuronal (nNOS) and inducible (iNOS). Since iNOS is independent of local calcium levels, it continues to produce NO for many hours or even days following induction. Several malignant neoplasms including breast, esophagus, intestine, prostate and as well as head and neck squamous cell carcinoma have been reported to express iNOS. The role of NOS in tumor biology is stil poorly understood, since NO appears to have both tumor promoting and inhibitory actions.In this study we have investigated whether COX-2, ALOX12 and iNOS were overexpressed in squamous cell carcinoma of head neck compared with normal adjacent mucosa. Cancer tissues and adjacent normal mucosa for the control group were obtained from 22 patients who underwent resection of their tumors. Pieces (5x5 mm) of squamous cell carcinoma were placed in sterile tubes and frozen immediately in liquid nitrogen. All tissue samples were stored at -80ºC until analysis. The real-time PCR was used to assess the expression of COX-2, ALOX12 and iNOS genes. The results showed that COX-2 and ALOX12 mRNA expressions are significantly increased in squamous cell carcinoma of head and neck compared with adjacent normal mucosa. Expression of iNOS was not significantly elevated in tumor tissues compared with normal mucosa. However iNOS expression was found to be significantly elevated compared with normal adjacent mucosa in patients with laryngeal cancer. These data suggest that COX-2 and ALOX12 may play role in carcinogenesis of head and neck cancer. iNOS as well as COX-2 and ALOX12 may play a role in laryngeal carcinogenesis.