An experimental study of intraoral carcinogenesis in rats

Assessment of bromodeoxyuridine-labeled S-phase cells in experimentally induced precancerous lesions in the rat's tongue

Precancerous lesions and early invasive carcinomas were produced in the tongues of rats by oral administration of 0.001% 4-nitroquinoline 1-oxide in drinking water. The distribution and densities of S-phase cells were then studied in an attempt to clarify the mechanism of carcinogenesis from the viewpoint of cell cycle. Bromodeoxyuridine (BrdU)-labeled S-phase cells were demonstrated by an indirect peroxidase method, using anti-BrdU monoclonal antibody, and their percentage was determined as the labeling index (LI). The average BrdU LI was significantly higher in the precancerous lesions than in the normal epithelium. There was a wide range of LI found in cells showing such changes as hyperplasia, hyperparakeratosis, dysplasia and papilloma, but the differences among them were not significant. These findings also showed that there could be considerable differences in proliferative activity among lesions of the same grade, while the difference in histology did not mean a difference in proliferative activity. Additionally, many BrdU-labeled cells were seen in a few layers over the basement membranes of non-cancerous lesions immediately adjacent to early invasive carcinoma, suggesting that these layers had a higher possibility for advancing to early invasive carcinoma.

Estimation of proliferative activity of experimental tongue carcinoma in rats. Immunohistochemical and DNA cytofluorometric analysis

Precancerous lesions and carcinomas were produced in rat tongues by oral administration of 0.001% 4-nitroquinoline 1-oxide (4NQO) in drinking water, and the biological characteristics and tumor kinetics were studied. Bromodeoxyuridine labeling index (BrdU L.I.) was determined immunohistochemically, and the nuclear DNA content was measured by DNA cytofluorometry. The BrdU L.I. was lowest in normal epithelium (3.49 +/- 0.49%), higher in papillomas (8.24 +/- 1.76%) and highest in squamous cell carcinomas (13.36 +/- 4.40%). Normal lingual epithelial cells, papillomas and 18 of the 25 squamous cell carcinomas showed a diploid pattern, while 7 squamous cell carcinomas showed a diploid plus tetraploid pattern. The correlation between polyploidization and tumor progression was significant, but the correlation between BrdU L.I. and tumor progression was not significant. The results suggest that while polyploidization of tumors increases with tumor progression the growth rate of tumors does not necessarily do so.

Cell kinetic study on experimental tongue carcinoma in rats

Tongue carcinomas were produced in rats by oral administration of 0.001% 4-nitroquinoline 1-oxide (4NQO) in drinking water, and the biological characteristics and tumor kinetics were correlated. Bromodeoxyuridine (BrdU) was used to investigate cell kinetics of rat tongue tumors in vivo. BrdU-labeled S-phase cells were demonstrated by an indirect peroxidase method using anti-BrdU monoclonal antibody, and their percentage, the labeling index (L.I.), was determined. The average BrdU L.I. in normal tongue epithelium, well differentiated and moderately differentiated squamous cell carcinoma was 5.7 +/- 1.1, 8.8 +/- 3.7 and 14.9 +/- 5.4, respectively. The differences among the three groups are significant. These results indicate that the BrdU L.I. correlates well with the degree of differentiation of tongue epithelium. Furthermore, the distribution patterns of BrdU-labeled cells in the tissue sections of each group were different. If these cell kinetics studies using BrdU are applied to human tongue carcinomas, the data may provide information on the biological characteristics and help in establishing the diagnosis and in choosing treatment regimens.

Oral cancer

In the U.S. oral cancer accounts for 2.1% of all cancers and 1% of cancer deaths. Two to three times as many males as females are affected. Blacks have more intra-oral cancer than whites, and their incidence and mortality rates have increased in recent years. The etiologic process very likely involves several factors. The major etiologic agents are tobacco (all types) and alcoholic beverages. Herpes simplex virus, human papilloma virus, and Candida have been implicated. Host factors include poor state of dentition, nutritional aberrations, cirrhosis of liver, lichen planus, and immunologic impairmant. Cellular changes include amplification of some oncogenes, alterations in antigen expression, production of gamma-glutamyl transpeptidase, and disturbance of keratin and involucrin production. Experimentally, cancer is readily produced on the hamster cheek pouch and rat oral mucosa. Unlike oral cancer in humans, most experimental lesions are exophytic, and they rarely metastasize.

Effect of excisional wounding on DMBA-induced hamster tongue carcinogenesis

The purpose of this study was to investigate histologically the effect of wounding on the hamster tongue after pretreatment with DMBA. The animals in which the tips of the tongues were pretreated with DMBA for 8 weeks, subsequently excised, and had no treatment or received applications of acetone, showed epithelial dysplasias. The animals which had the same pretreatment, excision, and received additional post-excision applications of DMBA for 9-13 days, developed squamous cell carcinomas. However, the animals which were pretreated with DMBA for 8 weeks but had no excision, did not show any pathologic changes, even though they received additional applications of DMBA for 9-13 days. The animals which received no pretreatment with DMBA for 8 weeks but had an excision, showed normal wound healing, even though they had a post-treatment with DMBA for 9-13 days. The results of the present study indicated that excisional wounding acted as a promotional stimulus in inducing the appearance of epithelial dysplasias or carcinomas of tongues initiated with the carcinogen DMBA.

Changes occurring in plasma membranes and intercellular junctions during the process of carcinogenesis and in squamous cell carcinoma

A 0.5% mineral-oil solution of 9.10-dimethyl-1.2-benzanthracene (DMBA) was applied to artificial cecal pouches in the lower lips of rats. Ultrastructural studies were made of plasma membranes and intercellular junctions during the process of malignant transformation in the oral mucosal epithelium and after squamous cell carcinoma had been induced by the carcinogen. After the administration of DMBA, the inner leaflet of the membranes where the microfilaments are attached showed high electron density and intramembranous particles on the P-face of basal cells decreased to about half that of controls. However, on the E-face the number of intramembranous particles increased by approximately 10% compared with controls. Though the normal size range for intramembranous particles was 9-12 nm, the administration of DMBA caused aggregations of from three to six particles on the P-face. In squamous cell carcinomas, only the outer leaflet of the membranes showed high electron density; the number of intramembranous particles was 30% higher on the P-face and approximately three times higher on the E-face compared with controls and the morphology of the intramembranous particles, which formed irregular aggregates of from five to 20 particles, was specific. In animals treated with DMBA, the number of gap junctions decreased by between 50% and 70%, although no structural changes occurred. In squamous cell carcinomas, the area of gap junctions was about 50% lower and the number of gap junctions about 40% lower than in controls. Changes in the number and area of desmosomes were similar to those of gap junctions both in the DMBA-treated animals and in squamous cell carcinomas.

Snuff-induced lesions of the oral mucosa - an experimental model in the rat

An experimental model in the white rat has been developed in order to study the influence of snuff on oral mucosa. A test canal in the lower lip, with one orifice buccally to the incisors and one on the lip side, was created by surgical means. The connection between the canal and the oral cavity was made to ensure the presence of saliva in the canal so that physiological conditions resembling those of the oral cavity were obtained. The canal was filled with snuff morning and night 5 days a week. The mean value for the maximal retention time of the snuff was 6 h. The animals tolerated the dose and time of exposure without signs of severe toxic symptoms. Histological examination of the canals after 9 months of exposure to snuff showed a mildly to moderately hyperplastic epithelium with hyperorthokeratosis. Locally deep proliferations of epithelium with acanthotic rete pegs could be seen. In the stratum basale hyperplasia with disturbed polarity and hyperchromatic nuclei and single mitosis were noted.

Animal models of intra-oral chemical carcinogenesis: a review

Early attempts to induce malignant oral tumours were largely unsuccessful, as the oral mucosa is considerably more resistant to the actions of chemical carcinogens than skin. The first consistent success came when strong carcinogens were applied to the hamster cheek pouch. This model remains the most popular for studies of intra-oral carcinogenesis and is discussed at length. The advantages and disadvantages are critically reviewed. The models of intra-oral carcinogenesis in extra-pouch sites in the hamster, mouse, rat and nonhuman primates are considered. The possible reasons for the relative resistance of oral mucosa to chemical carcinogens are discussed, particularly in relation to portals of entry and saliva. Finally, the relative merits of the more popular models of intra-oral carcinogenesis are briefly discussed.

Experimental intra-oral carcinoma

Fundamental studies of tumour host relationships in oral cancer cases would be assisted if a suitable animal model could be found. Current concepts in the use of animal models for the study of intra-oral carcinoma are reviewed and the development of a unique transplantable tumour system which had been induced and maintained only in syngeneic animals, is recorded.