Biochemical studies on Oestradiol 17b in human mammary tumours and chemically induced rat mammary tumours
The involvement of oestrogens and related factors in the development and behaviour of mammary cancer is reviewed. The currently accepted view is that the selective retention of administered tritium labelled oestradiol 170 by certain mammary tumours is due to the possession of specific oestradiol binding components similar to those occurring in normal oestrogen target tissues such as uterus. The possession of such components may be related to the hormone responsiveness of the tumour. An established method for measuring binding of tritium labelled oestradiol to human mammary tumours by in vivo infusion (Braunsberg et al.. 1967) was set up with the aim of relating this property to the subsequent progress of the disease in infused patients after surgery, and their response to endocrine therapy. A method was sought which would reliably measure specific oestradiol binding in vitro. The first method used was a steady-state gel filtration method. The use of this method, and its relative merits, are discussed. Comparative results are presented on malignant mammary tumours whose binding ability had also been measured in vivo infusion. A more rapid and simple procedure became available with the publication of the method of Feherty et al. (1971). This was adopted in favour of the gel filtration method and the in vivo infusion method was also stopped. This assay was found to be suitable for measuring oestradiol binding by DMBA induced rat mammary tumours. The overall results in human and DMBA tumours and the relevance of these measurements to hormone responsiveness of tumours are discussed. Biochemical properties of the binding phenomenon in tumours were investigated. This was confirmed to be inhibitable by anti-oestrogens, apparently competitively, and by thiol blocking agents. Thiol containing compounds affected binding in varying ways:mercaptoethanol and dithiothreitoL were stimulatory, L-cysteine was inhibitory. The dithiothreitol effect was further investigated with respect to anti-oestrogen inhibition and the effect of increased oxygen tension on binding was also studied, these results being discussed in terras of their relationship to oestradiol binding, cell division and possible implications in vivo. Attempts to characterise the tumour binding components by polyacrylamide gel electrophoresis were generally unsuccessful. The thiol, dihydrolipoic acid, produced transformation of oestradiol to an as yet unidentified product, occurring as the free compound and in a water soluble form, apparently sulphate. The properties of this effect are discussed. The thesis concludes with a discussion of various proteinsteroid interactions that occur in the body tissues and fluids in general, and of specific steroid binding to target tissues in particular, in terms of molecular models for the mode of action of steroid hormones based on steroid-"receptor" interaction.