Cell kinetic alterations during epidermal carcinogenesis. EACR--Mühlbock Memorial Lecture, 1991

Colcemid alters S phase and other parameters in skin during chronic exposure to benzo(a)pyrene

The administration of Colcemid for collecting mitotic figures in a carcinogenesis study, using benzo(a)pyrene (BaP), diminished the experimental differences between exposed and control mice. A dose-related increase in noncollected mitotic index (n-mitotic index) was seen in keratinocytes in the dorsal epidermis of mice which received four weekly treatments of BaP at 16, 32 and 64 micrograms in 50 microliters of acetone. In contrast, the number of mitotic figures collected for 4 hr by Colcemid block (c-mitotic index) was depressed at 16 micrograms, unchanged at 32 micrograms, and elevated at 64 micrograms of BaP. Weekly treatments with 4,8 or 16 micrograms BaP for 3-8 months induced an elevation in both n-mitotic and c-mitotic indices. The differences in results produced by the two methods of determining mitotic index depended upon dose and duration of treatment with BaP. The administration of Colcemid to acetone-treated mice increased the labeling index (number of labeled cells) and reduced the rate of DNA synthesis (low grain count per keratinocyte nucleus). After chronic application of BaP, Colcemid abrogated the increase in labeling index, but produced no additional effect on the number of grains per labeled keratinocyte. The modifying effect of Colcemid was greatest when administered during the peak of the tissue response to BaP. A number of significant changes in morphology of the skin associated with chronic exposure to BaP were attenuated by the use of Colcemid.

Proliferation of epithelia of noninvolved mucosa in patients with head and neck cancer

BACKGROUND

Morphologically noninvolved mucosa in patients with head and neck cancer is altered by carcinogens. These alterations may include chromosome alterations, gene mutations, and other molecular abnormalities which may explain very high incidence of second tumors in this group of patients. The purpose of this study was to investigate the in vivo proliferative characteristics in epithelial tissues adjacent to the tumor in a series of patients with head and neck cancer.

METHODS

Twenty-one patients with head and neck tumors received IV infusions of iododeoxyuridine (IdUrd) and/or bromodeoxyuridine (BrdUrd). Surgical specimens containing normal-appearing epithelium adjacent to the tumor were selected and stained with the respective monoclonal antibody. The percentage of S-phase cells (labeling index, LI) was counted in the basal and suprabasal layers of the epithelium.

RESULTS

In 27 samples of oral epithelium obtained from 14 previously untreated patients, labeled (S-phase) cells were predominantly located in suprabasal layers with LI 31.6 +/- 3.1% (range 13.5-73.2%). In contrast, the LI of the basal layer was very low: 1.6 +/- 0.2% (range 0.5%-8.8%). There was no statistically significant difference between normal appearing and dysplastic samples (p > 0.05). In 10 samples obtained from 7 patients whose biopsies were studied 2 days to 2 month after concomitant radiation and chemotherapy, the LI of the oral mucosa basal layer was significantly higher (21.0 +/- 4.1%, range 6.3-39.2%). The LI of the suprabasal layer in treated patients was 14.3 +/- 2.4% (range 5.9-31.1%). The LI of nasal pseudostratified epithelium (4 samples) was 11.2%. The average LI of "basal" cells was 8.3% (range 5.9-11.9%) and that of "suprabasal" cells was 13.8% range (3.2-29.5%). The basal layer of the skin (5 samples) contained 9.3% labeled cells (range 3.3-16.3%); the LI of suprabasal layers of skin was 21.3% (range 7.8-33.2%).

CONCLUSION

Both the frequency and the spatial distribution of S-phase cells are disordered in noninvolved epithelia in patients with head and neck tumors. These observations suggest that disordered proliferation may be an early consequence of field cancerization, a consequence that occurs prior to appearance of morphologically apparent hyperplasia or dysplasia.

The storage of energy as a cause of malignant transformation: a 7-phase model of carcinogenesis

Although many theories for the development of cancer exist, a new hypothesis for carcinogenesis is suggested and a new 7-phase model of malignant transformation described. Both the hypothesis and the model are based on the principle of a critical point in local energy (entropy?) storage, at a certain level of structural organisation within the cells. This principle has been previously formulated by the author from the rules of non-equilibrium thermodynamics. The model introduces a new terminology and explores the concepts of both high work value of energy and bifurcation. The ability (A) of cells is suggested to be the most important cellular feature in respect to cell survival. This ability implies that the cells follow the requirement Kir > 1, even in dangerous situations and under harmful environmental influence. But, when the cells have lost their ability (A) and all levels of the cell defence machine have been exhausted, then the local energy storage may provoke a cascade of harmful events within the cells. The S-stage is the most unstable state of the cell cycle. If such harmful events take place during DNA synthesis within the 'premalignant' cell, in the phase 'promotion' at the 4th bifurcation, they lead ultimately to carcinogenesis (i.e. malignant transformation). The 7-phase model of carcinogenesis is consistent and offers many advantages in comparison to the previous hypotheses. This model could help the design of experiments, development of new drugs and optimization of medical treatment. The new hypothesis could contribute to a better understanding of the processes of carcinogenesis and the uncontrolled division, growth and lability of tumour cells.

Detection of thymine dimers in suprabasal and basal cells of chronically UV-B exposed hairless mice

An immunocytochemical method was developed to study induction and removal of DNA damage in specific cell populations in the epidermis of hairless mice during chronic ultraviolet (UV) exposure. Identification of mouse suprabasal cells was performed with an immunoperoxidase stain. This stain was shown not to affect the fluorescent nuclear stains, used to reveal DNA and DNA damage. In skin cells from hairless mice irradiated daily with 1500 J/m2 UV-B for 11 consecutive days, cyclobutane thymine dimers accumulated in epidermal cells and reached a maximum level after 3 d. Thereafter dimer levels dropped to a lower, more constant level. So epidermal cells in vivo, both suprabasal and basal cells, remove dimers effectively, in contrast to cultured rodent cells, which display hardly any repair in genomic DNA. Dimer content in suprabasal cells was higher than that in basal cells, but initially the patterns of induction and removal of dimers in both cell types were rather similar. At days 4-11, however, after the drop in dimer content, the amount of dimers in basal cells prior to UV exposure was almost as low as that in non-exposed cells. The results presented here suggest important roles for both UV-induced DNA repair and cell proliferation in protecting epidermal cells against the mutagenic and carcinogenic effects of UV.