Carcinogenesis reversal

As we have seen, carcinogenesis is a prolonged multi-stage process which usually occurs over many years. Because of its complexity there are, in principle, many critical steps at which food-related substances or metabolic processes may interact with the sequence of events so as to accelerate, delay or even reverse it. Diet-related anti-carcinogenesis can usefully be classified into ... 

In contrast, promotion is reversible to some extent, and it is only effective following, not preceding, the initiating events. These discoveries suggest that only the initiation stage of carcinogenesis has an absolute requirement for the chemical carcinogen. 

Two specific suggestions concerning the role that the reversible physical binding of proximate and ultimate carcinogens derived from BP play in carcinogenesis have been made. The first is based on recognition that DNA-BPDE complex formation precedes re-... 

However, the mathematics describes an idealized situation, and the real situation in vivo may not be so straightforward. For example, with carbon monoxide, as already indicated, the toxicity involves a reversible interaction with a receptor, the protein molecule hemoglobin (see chap. 7 for further details of this example). This interaction will certainly be proportional to the concentration of carbon monoxide in the red blood cell. However, in vivo about 50% occupancy or 50% carboxyhemoglobin may be sufficient for the final toxic effect, which is cellular hypoxia and lethality. Duration of exposure is also a factor here because hypoxic cell death is not an instantaneous response. This time-exposure index is also very important in considerations of chemical carcinogenesis. 

Walker NJ, Miller BD, Kohn MC, et al. 1998. Differences in kinetics of induction and reversibility of TCDD-induced changes in cell proliferation and CYP1A1 expression in female Sprague-Dawley rat liver. Carcinogenesis 19 1427-1435. 

Recent advances in our understanding at the cellular and molecular levels of carcinogenesis have led to the development of a promising new strategy for cancer prevention, that is, chemoprevention. Chemoprevention is defined as the use of specific chemical substances - natural or synthetic, or their mixtures - to suppress, retard or reverse the process of carcinogenesis. It is one of the novel approaches of controlling cancer alternative to therapy, which has some limitations and drawbacks in the treatment of patients (Stoner and Mukhtar, 1995 Khafif et al., 1998 Kawamori et al., 1999 Bush et al., 2001 Jung et al., 2005). 

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