The introduction to this thesis reviews examples and characteristics of two-stage carcinogenesis, with particular reference to the promotion of mouse skin tumours by 12-O-tetradecanoylphorbol-13-acetate (TPA). The effects of TPA and other tumour promoters on mammalian cells in culture is also discussed together with current evidence for the existence of specific phorbol diester receptors on the membranes of target cells. Chapter 2 lists the materials and methods basic to the cell culture procedures used in succeeding chapters. The experimental work is presented in four parts. In Chapter 3, the effect of TPA on the frequency of both spontaneous and chemical-induced drug-resistant mutants of the Chinese hamster ovary cell line, CHO-K1, is described. The mutagen-specificity of the mutagenesis enhancing activity of TPA at the ouabain resistance (OuaR) locus in these cells is confirmed. Using this OuaR/CHO-K1 system the hypothesis that tumour promoting agents may act as in vitro mutagenesis enhancing agents via a free radical mechanism is investigated in Chapter 4. The influence of free radical scavenging compounds present in cell culture medium on the mutagenesis enhancing activity of TPA, benzoyl peroxide, formaldehyde and linear alkanes is examined. In Chapter 5 the effect of TPA on induced OuaR mutation in other Chinese hamster cells in culture is described. Chapter 6 comprises a preliminary investigation into the survival of CHO-K1 cells irradiated in suspension with monochromatic ultraviolet light (UV). With reference to its membrane activity the effect of TPA on cell survival following UV irradiation is also examined. A summary of findings is presented at the end of each experimental chapter. These are discussed in Chapter 7 in the light of recent hypotheses for in vitro mutagenesis enhancing activity.
|Date of Award||1985|