The 4-hydroxyestrone: Electron emission, formation of secondary metabolites and mechanisms of carcinogenesis

4-Hydroxyestrone (4-OHE1), a typical cancer-inducing metabolite, originating from 17β-estradiol (17β-E2), was chosen as a model for the studies. The aim was to get a deeper insight in the mechanisms of its ability to initiate cancer. It was found, that 4-OHE1 can eject electrons (eaq-), when excited in the singlet state by monochromatic UV-light (λ = 254 nm) in polar media (water:ethanol = 40:60 vol.%). The quantum yield Q(eaq-), determined for various 4-OHE1 concentrations, is found to be as high as that previously observed for 17β-E2. It decreases with increasing substrate concentration, but it is enhanced at higher temperature. The ability of 4-OHE1 to eject as well as to consume and to transfer electrons to other biological systems, classifies it as an electron mediator, similar to 17β-E2.The 4-OHE1 transients resulting of the electron emission process are leading to the formation of secondary metabolites. Surprisingly, it was established that the secondary metabolites possess likewise the ability to eject as well as to consume electrons. Hence, they behave similar like 17β-E2. However, the structure of the secondary formed metabolites, which determinates their biological properties and carcinogenity, depends on the nature of the available reaction partners involved in their formation. A probable reaction mechanism explaining the subject matter is discussed.