Nobuharu Yamamoto

Analysis of the ANA gene as a candidate for the chromosome 21q oral cancer susceptibility locus

Loss of heterozygosity (LOH) on the long arm of chromosome 21 (21q) is observed in several human malignancies. We identified novel tumour suppressor loci on this region in primary oral squamous cell carcinomas (OSCCs). To further determine the role of 21q deletions in oral cavity tumorigenesis, 63 OSCCs were examined for LOH at 21q using 7 microsatellite markers. LOH was observed in 32 of 63 cases (50.8%) that were informative for at least one of the loci analysed. Two distinct deleted regions were identified at chromosomal region 21q11.1. The possible involvement of ANA (abundant in neuroepithelium area), a candidate tumour suppressor gene (TSG) located on 21q11.2–21.1, was also evaluated for 20 OSCCs and 9 OSCC-derived cell lines. 60% of tumours (12/20) and 88.9% (8/9 cell lines) showed absent or reduced mRNA gene expression; only one OSCC case had a nucleotide substitution in the ANA gene. Interestingly, the frequency of the suppressed ANA mRNA expression was greater in stage IV tumours than in earlier stages. In addition, re-expression of the ANA gene mRNA was induced in 4 cell lines after treatment with 5-aza-2′-deoxycytidine, a DNA demethylating agent. These findings demonstrate that there may be at least 2 distinct TSGs on 21q11.1; loss of ANA gene expression could be involved in the progression of human OSCC; and aberrant methylation of the ANA gene promoter may participate in the transcriptional silencing of the gene in oral cancer cells.

The presence of candidate tumor suppressor gene loci at chromosome 3p for oral squamous cell carcinomas

We investigated the short arm of chromosome 3 (3p) for allelic imbalances, including loss of heterozygosity (LOH) and microsatellite instability (MSI) in 40 primary oral squamous cell carcinomas (SCCs) using 10 microsatellite markers and constructed a deletion map for this chromosome arm. We examined 40 primary tumor tissues, 40 corresponding normal tissues, and seven lymph node metastatic tissues. LOH at one or more loci was found in 24/40 (60%) of tumors. Deletion mapping of these tumors revealed at least three discrete, commonly deleted regions on the chromosome arm. Furthermore, we detected MSI in six of those tested cases (15%). We compared our results with the clinicopathologic features. A number of sites displaying LOH at 3p could be detected in early stage lesions, and the frequencies of LOH tended to be higher in later clinical stages. Thus, the frequent LOH was observed from early stage in pTNM classification. An unknown tumor suppressor gene in the genesis of oral squamous cell carcinoma may exist in 3p.

Susceptible genes and molecular pathways related to heavy ion irradiation in oral squamous cell carcinoma cells.

BACKGROUND AND PURPOSE Heavy ion beams are high linear energy transfer (LET) radiation characterized by a higher relative biologic effectiveness than low LET radiation. The aim of the current study was to determine the difference of gene expression between heavy ion beams and X-rays in oral squamous cell carcinoma (OSCC)-derived cells. MATERIALS AND METHODS The OSCC cells were irradiated with accelerated carbon or neon ion irradiation or X-rays using three different doses. We sought to identify genes the expression of which is affected by carbon and neon ion irradiation using Affymetrix GeneChip analysis. The identified genes were analyzed using the Ingenuity Pathway Analysis Tool to investigate the functional network and gene ontology. Changes in mRNA expression in the genes were assessed by real-time quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR). RESULTS The microarray analysis identified 84 genes that were modulated by carbon and neon ion irradiation at all doses in OSCC cells. Among the genes, three genes (TGFBR2, SMURF2, and BMP7) and two genes (CCND1 and E2F3), respectively, were found to be involved in the transforming growth factor beta-signaling pathway and cell cycle:G1/S checkpoint regulation pathway. The qRT-PCR data from the five genes after heavy ion irradiation were consistent with the microarray data (P < 0.01). CONCLUSION Our findings should serve as a basis for global characterization of radiation-regulated genes and pathways in heavy ion-irradiated OSCC.

Epidemiology of the Oral Cancer

Oral cancer is a malignant neoplasm that occurs in the oral cavity. Squamous cell carcinoma accounts for over 90 % of the oral cancers in Japan, and others include adenocarcinoma derived from minor salivary gland, sarcoma, malignant lymphoma, and metastatic cancer. A number of cohort studies and case–control studies have been conducted as epidemiological technique to elucidate oral cancers. The number of oral cancer patients in Japan was 2,100 in 1975 and 6,900 in 2005 and further is estimated to be 10,000 patients by 2015, which is 1.6 times higher than the current number. Age-adjusted male-to-female ratio is 3:2, which is higher in males than in females, and the incidence of oral cancers decreases with the aging of the population in developed countries with the exception of Japan, in which the ratio is increasing. Of oral cancers, tongue carcinoma is the most common and accounts for 40 % of oral cancers. The oral cavity, an entrance of the digestive system, is exposed to chemical stimuli such as smoking, drinking, and food as well as to mechanical stimuli including caries and ill-fitting prosthetic appliance and characterized by the existence of multiple circumstances in particular and risk factors associated with carcinogenesis. Examination of oral cancers can be easily conducted because these cancers can be confirmed directly by visual observation and palpation. The significance of oral cancer examination is early diagnosis and early treatment of not only oral cancers but also premalignant lesions, including leukoplakia and erythroplakia, and precancerous conditions, including lichen planus. It is reported that the detection rate of oral cancers and premalignant lesions is 0.99 % in oral cancer screening and that the prevalence of precancerous lesions is 2.5 % in Japanese. Some patients with oral cancer may synchronously or metachronously develop double cancers. In patients with head and neck cancer including oral cancer, 60–70 % of double cancers are found in the upper gastrointestinal tract or lung.

Mandibular Reconstruction with Free Vascularized Fibular Graft

An iliac block graft is the most commonly used biomaterial for reconstruction following resection of the mandible. Its use has some disadvantages, however, including limitations on the amount of bone that may be harvested, and the subsequent increase in burden on the iliac bone. Therefore, recently, free vascularized fibular grafts have been used as an alternative in some cases. Here, we report the advantages of, and issues related to reconstruction using free vascularized fibular grafts observed at Tokyo Dental College Chiba Hospital. Eight patients undergoing mandibular reconstruction using free vascularized fibular grafts between January 2003 and January 2017 were investigated. Of these, 6 were men, and 2 were women. Age ranged from 38 to 74 years (average, 54 years). Primary diseases comprised malignant tumor in 3 patients, benign tumor in 3, and radiation osteomyelitis of the mandible in 2. The defects were classified as follows according to the CAT system (Condylar Head, Mandibular Angle, Mental Tubercle): 3 cases of Body, 2 of AT, and 1 case each of TT, ATTA, and CATT. The resection range of the mandible was 5-16 cm (average, 10 cm). The single barrel technique was used in 7 cases, and the double barrel technique in 1. In terms of the flap survival ratio, complete engraftment was achieved in 6 out of the 8 cases. Two cases of radiation osteomyelitis of the mandible, with necrosis caused by vascular breakdown after wound infection, were observed, however. While the advantages of mandibular reconstruction by this method include comparatively safe conditions and functional recovery, there were also some problems. It was inappropriate for cases of radiation osteomyelitis of the mandible; those where anti-inflammatory therapy was ineffective; and those where greater resection of the soft tissue was required. Further study is needed to clarify the criteria for selecting this procedure.