Eleftherios Vairaktaris

Aim: In an effort to assess the role of plasminogen activator inhibitor-1 (PAI-1) in oral squamous cancer development and progression, two different carcinogen treatment protocols were conducted. Materials and Methods: Protocol I included mice from a PAI-1 transgenic (Tg) breed (n=56) and their wild-type (WT) counterparts (n=56), divided into one control group and two main experimental groups, treated with 7,12-dimethylbenz[a]anthracene (DMBA) for 8 and 16 weeks, respectively. Protocol II included the same number and types of animals and groups, which were similarly treated with 4-Nitroquinoline 1-oxide (4-NQO) in drinking water. Two drugs that affect plasma PAI-1 levels, enalapril and pravastatin, were administered to certain subgroups of animals in both protocols. Results: None of the animals developed macroscopically-visible oral cancer lesions. Eleven animals under Protocol I and 52 animals under Protocol II died. Skin lesions were noted only in DMBA-treated animals (n=9). Almost all animals administered with 4-NQO developed alopecia and lost weight, while two of them developed stomach tumours, and one female mouse developed a large ovarian cyst. Conclusion: Transgenic mice may respond differently when used in well-established carcinogen models and oral carcinogenesis is hard to achieve in these rodents.

EGFR kinase activity triggers numerous signaling pathways, such as the Ras/Raf/MAPK cascade, leading to the activation of various mitogen activated protein kinases, which are implicated in cell proliferation through induction of several genes, including c-fos. The possible effect of diabetes on the expression of the oncogenes EGFR, H-ras and c-fos was investigated in an experimental model of chemically induced oral oncogenesis in normal and diabetic (type I) Sprague-Dawley rats. Thirteen diabetic and twelve normal rats developed cancer after 4NQO treatment, while six diabetic and six normal animals were used as controls. The biopsies were classified pathologically (ranging from dysplasia to moderately differentiated oral squamous cell carcinoma) and were studied immunohistochemically. Several representative histological regions from each biopsy were analysed in regard to EGFR, H-ras and c-fos expression, and a comparison between normal and diabetic rats was effected. A trend of decreased EGFR expression in diabetic compared to normal rats was revealed throughout oncogenesis, which was significant in the stage of dysplasia (P<0.05). On the contrary, a trend of increased H-ras expression was observed in diabetic compared to normal rats during oncogenesis, which rose significantly in early invasion and well differentiated OSCC (P<0.001 and P<0.01 respectively). Finally, no statistical differences concerning c-fos expression were detected between diabetic and normal animals. In conclusion, it seems that diabetes reduces the expression of EGFR and initiates the Ras/Raf/MAPK signal transduction pathway by enhancing activation of other signalling molecules, such as the diabetes-associated Insulin Receptor Substrate-1, leading to increased cell proliferation without c-fos involvement.

H-ras and c-fos oncogenes interact in signalling pathways but their level and time course of expression during oral cancer development are unclear. The present study used an animal model for the simultaneous investigation of H-Ras and c-Fos expression in sequential stages of oral oncogenesis. Three experimental groups of Syrian golden hamsters (A, B and C; 10 animals each) and one control group (7 animals) were used. The buccal pouches of hamsters in groups A, B and C were treated with 0.5% of the carcinogen 9,10-dimethyl-1,2-benzanthracene and were excised at 10, 14 and 19 weeks, respectively. The biopsies, which included tissue stages ranging from normal oral mucosa to moderately differentiated carcinoma, were studied immunohistochemically. A reduction in both H-Ras and c-Fos expression was observed from group A to B and from hyperplasias to early tumour stages, while a simultaneous increase was noted from group B to C and from well-differentiated to moderately-differentiated carcinomas. The H-ras/c-fos expression ratio had a value of approximately (1.09 +/- 0.21) in five out of seven studied tissue stages. H-Ras and c-Fos exhibit a similar expression pattern throughout most stages of oral carcinogenesis, an observation supported by the known molecular pathway connecting H-ras signalling with subsequent c-fos gene transcription.

We investigated the possible association of DNA polymorphisms −2548G/A and Q223R in the leptin (LEP) and leptin receptor (LEPR) genes, respectively, which both affect the amount of circulating cytokine-type hormone leptin, with risk for development of oral cancer. Polymerase chain reaction-based restriction analysis was performed in DNA samples of 150 patients with oral squamous cell carcinoma (OSCC) and 152 healthy control subjects of equivalent gender, age, and ethnicity (Greeks and Germans). Compared to controls, the homozygous high gene expression genotype A/A of the LEP −2548G/A polymorphism was significantly increased in the subgroups of patients with advanced cancer stages (P = 0.0001; OR 9.0, 95% CI 2.62–30.89), with a positive family history of cancer (P = 0.0346; OR 3.55, 95% CI 1.15–11.01), without tobacco abuse (P = 0.0051; OR 9.69, 95% CI 1.03–91.24), and without alcohol abuse (P = 0.0472; OR 2.16, 95% CI 0.87–5.37). The homozygous low-leptin-binding genotype G/G of the LEPR Q223R polymorphism was strongly associated with an increased risk for OSCC for all patients (P = 0.0028; OR 4.11, 95% CI 1.30–12.97) as well for most of the patient subgroups. The above findings are consistent with the growth-promoting role of leptin in cancer and its induction effect on angiogenesis and metastasis. This is the first study indicating the association of these LEP and LEPR gene polymorphisms with increased risk for OSCC.

In light of the recently found contribution of angiogenic and inflammation-related factors to malignancies, this study investigated the possible association of the angiotensinogen gene (AGT) with increased risk of oral cancer. The M235T polymorphism, which influences AGT gene expression, was evaluated by restriction fragment length polymorphism analysis in the DNA samples of 163 German and Greek patients with oral squamous cell carcinoma (OSCC) and 124 healthy controls of equivalent gender, ethnicity and age. No significant difference of the mutant (235T) allele, which results in higher AGT gene expression, was observed in the whole patient group in comparison with the normal controls. Similarly, compared to the controls no significant difference of either allele or carrier frequency was detected in almost every subgroup of patients. Only in the subgroup of patients with a positive family history of cancer was a significant increase of mutant T allele and carrier frequencies observed, compared to the controls (50% vs. 36.7% and 79.3% vs. 61.3%, respectively, p < 0.05 in both cases). In this particular subgroup of patients the odds ratio for OSCC of TT homozygotes was 3.57 (CI 95% 1.2-10.62), while for the MT heterozygotes it was 2.41 (CI 95% 1.06-5.49). This study did not reveal an association of the AGT M235T polymorphism with oral oncogenesis, but certainly suggested a possible association of this specific polymorphism with other types of cancer. The present findings support a previous suggestion that the pathway of oral oncogenesis is probably based on angiotensin-converting enzyme and bradykinin interaction and not on AGT and angiotensin peptides.

Stromal derived factor-1 (SDF-1), a protein related to angiogenesis and inflammation, has been correlated with the progression of a number of malignancies, but not with oral squamous cell carcinoma. In light of the known contribution to the development of oral cancer of other gene polymorphisms for proteins responsible for angiogenesis, inflammation and thrombosis, this study investigated whether the G801A polymorphism in the SDF-1 gene is associated with this malignancy. The G801A polymorphism was examined by restriction fragment length polymorphism analysis in DNA samples from 159 patients with oral squamous cell carcinoma and 101 matched healthy controls. The detected allele frequency of the "high production related" A allele in the control group was 25.3%. There was a slight decrease in allele frequency in patients (18.6%), but it was not statistically significant. The same pattern was observed in subgroups of patients in regard to smoking habits and family history of cancer or thrombosis. Interestingly, in comparison to controls, the A allele frequency was significantly lower in patients with advanced cancer stages III and IV (12.5%, p=0.005) and in patients with alcohol abuse (12.5%, p=0.02). The G801A polymorphism of the SDF-1 gene is associated with advanced stages of oral cancer, especially in alcohol abusers.