Loss of epithelial cell surface carbohydrates during experimental oral carcinogenesis in the rat

4-nitroquinoline-1-oxide induced experimental oral carcinogenesis

Human oral cancer is the sixth largest group of malignancies worldwide and single largest group of malignancies in the Indian subcontinent. Seventy percent of premalignant cancers appear from premalignant lesions. Only 8-10% of these lesions finally turn into malignancy. The appearance of these premalignant lesions is one distinct feature of human oral cancer. At present there is dearth of biomarkers to identify which of these lesions will turn into malignancy. Regional lymph node metastasis and locoregional recurrence are the major factors responsible for the limited survival of patients with oral cancer. Paucity of early diagnostic and prognostic markers is one of the contributory factors for higher mortality rates. Cancer is a multistep process and because of constrain in availability of human tissues from multiple stages of oral carcinogenesis including normal tissues, animal models are being widely used, aiming for the development of diagnostic and prognostic markers. A number of chemical carcinogens like coal tar, 20 methyl cholanthrene (20MC), 9,10-dimethyl-1,2-benzanthracene (DMBA) and 4-nitroquinoline-1-oxide (4NQO) have been used in experimental oral carcinogenesis. However, 4NQO is the preferred carcinogen apart from DMBA in the development of experimental oral carcinogenesis. 4NQO is a water soluble carcinogen, which induces tumors predominantly in the oral cavity. It produces all the stages of oral carcinogenesis and several lines of evidences suggest that similar histological as well as molecular changes are observed in the human system. In the present review an attempt has been made to collate the information available on mechanisms of action of 4NQO, studies carried out for the development of biomarkers and chemopreventives agents using 4NQO animal models.

Prognosis of oral pre-malignant lesions: significance of clinical, histopathological, and molecular biological characteristics

The concept of a two-step process of cancer development in the oral mucosa, i.e., the initial presence of a precursor subsequently developing into cancer, is well-established. Oral leukoplakia is the best-known precursor lesion. The evidence that oral leukoplakias are pre-malignant is mainly derived from follow-up studies showing that between < 1 and 18% of oral pre-malignant lesions will develop into oral cancer; it has been shown that certain clinical sub-types of leukoplakia are at a higher risk for malignant transformation than others. The presence of epithelial dysplasia may be even more important in predicting malignant development than the clinical characteristics. Three major problems, however, are attached to the importance of epithelial dysplasia in predicting malignant development: (1) The diagnosis is essentially subjective, (2) it seems that not all lesions exhibiting dysplasia will eventually become malignant and some may even regress, and (3) carcinoma can develop from lesions in which epithelial dysplasia was not diagnosed in previous biopsies. There is, therefore, a substantial need to improve the histologic assessment of epithelial dysplasia or, since epithelial dysplasia does not seem to be invariably associated with or even a necessary prerequisite for malignant development, it may be necessary to develop other methods for predicting the malignant potential of pre-malignant lesions. As a consequence of these problems, numerous attempts have been made to relate biological characteristics to the malignant potential of leukoplakias. Molecular biological markers have been suggested to be of value in the diagnosis and prognostic evaluation of leukoplakias. Markers of epithelial differentiation and, more recently, genomic markers could potentially be good candidates for improving the prognostic evaluation of precursors of oral cancer. As yet, one or a panel of molecular markers has not been determined that allows for a prognostic prediction of oral pre-cancer which is any more reliable than dysplasia recording. However, these new markers could be considered complementary to conventional prognostic evaluation.

Lectin binding patterns in squamous epithelium in experimentally induced hamster buccal pouch carcinoma

The distribution pattern of certain monosaccharides in the epithelial cells of the hamster buccal pouch was studied during carcinoma development induced by 9,10-dimethyl-1,2-benzathrancene (DMBA). An avidin-biotin-peroxidase complex (ABC) immunohistochemical technique with high affinity biotinylated lectins was employed to identify monosaccharides. Lectins used in this experiment included Concanavalin A (Con A), for identifying mannose or glucose, Ricinus communis agglutinin I(RCA-I), for identifying galactose, and Ulex europaeus agglutinin I(UEA-I), for identifying fucose. The results show that in normal buccal pouch epithelial cells, fuctose or galactose were concentrated predominantly on the cellular membrane, while mannose and glucose were distributed in the cytoplasm. In the epithelial cells undergoing neoplastic transformation induced by DMBA, most cells showed decreased staining of the above-mentioned monosaccharides, while in other areas the cells were heavily stained. However, the most striking change which occurred was that galactose and fucose shifted from the cellular membrane to the intracytoplasmic area during the malignant transformation. Thus, the changes of anatomic location and intensity of staining of monosaccharides in the buccal pouch epithelium may be used as a criteria for early histochemical diagnosis of malignant transformation.

Differential lectin-bindings in normal and precancerous epithelium and squamous cell carcinoma of the oral mucosa

In order to establish a useful and objective marker of malignancy of oral mucosa, the binding sites for Ulex europaeus agglutinin I (UEA-I). Bandeiraea simplicifolia agglutinin I (BSA-I) and peanut agglutinin (PNA) were comparatively examined in the surgical materials from the normal, dysplastic and cancerous epithelium of the oral mucosa by a novel lectin-antilectin immunoperoxidase method. Based on the staining patterns of the normal keratinized epithelium, UEA-I was regarded as the marker for the prickle cells, BSA-I for the cells in the upper prickle to the horny layers, and PNA for those in the basal layer. As the degree of dysplasia advanced, all layers of epithelium came to react with UEA-I and PNA, whereas the BSA-I binding was negative. Positive reactions for UEA-I and PNA were seen in most carcinoma cells other than the keratinizing foci stained by BSA-I. The results indicate that a UEA-I-positive reaction in the basal cells, a PNA-positive in the prickle cells and loss of receptor for BSA-I occur in the course of malignant transformation of oral mucosa, and that these lectins may be regarded as useful markers of oral epithelial cytoplasmic differentiation.

The effect of 3T3 fibroblasts on the expression of anchorage independence and cornification of oral keratinocytes

This study examined the effect of 3T3 fibroblasts on the expression of anchorage independence and the degree of cornification in early cultures of three carcinoma-derived epithelial cell lines (R59, R63a, R63b) and in one cell line derived from non-malignant dysplastic epithelium where there was no evidence of invasion (R66a). The epithelial cell lines originated from the palatal (R63a, R66a) and the lingual (R59, R63b) mucosa of rats that had been painted with the carcinogen 4-nitroquinoline N-oxide. In the absence of 3T3 fibroblasts, progressive culture resulted in an increase in the colony forming efficiency (CFE) of R63a, R63b and R59 and a decrease in the percentage of cornified cells in all cell lines. 3T3 fibroblasts caused a decrease in the CFE and the degree of cornification in the 3T3-dependent cell line (R63a), particularly at the lower passages, but these parameters remained essentially unchanged by 3T3 fibroblasts in the 3T3-independent cell lines (R59, R63b). 3T3 fibroblasts did not influence the cornification of R66a and this cell line remained anchorage dependent throughout the study. The results suggest that in malignant cell lines characterised by being independent of 3T3 fibroblasts (R63b, R59) the CFE was inversely correlated to the degree of cornification. However, in the malignant cell line showing a greater dependence on support (R63a) the relationship between CFE and cornification was unclear because these parameters may have been modulated by the presence of 3T3 fibroblasts. The cell line from dysplastic non-invasive tissue (R66a) differed from its malignant counterparts in the fact that CFE and cornification were unaffected by 3T3 fibroblasts despite previous studies showing a dependence on mesenchymal support.