At the present time, several hundred chemical agents, consisting of at least 30 distinct chemical groups, have been reported as cancer preventive agents in experimental animal models61, offering the possibility of application in cancer chemoprevention according to their efficacy. Furthermore, it is most noteworthy that over 30 clinical intervention trials are now underway at the NCI of the USA8 as the result of wide spread screening tests as well as the intensive studies on their activity, action mechanisms, and clinical safety. In other quarters as well, new types of cancer chemopreventive agents with high efficacy are much sought after, with the research on cancer chemoprevention at the clinical level having just been initiated recently. Certainly the search for cancer preventive agents from edible sources is also important. The potentiality of Thai edible plants as effective anti-tumour promoters seem to be high because cardamonin or ACA as pointed out in this study, exhibited higher inhibitory activity toward tumour promoter-induced EBV activation than the heretofore representative chemopreventive phytochemicals such as β-carotene or (-)-epigallocatechin gallate (Table 3). Needless to say, these EBV activation inhibitors from Thai plants must be further examined for their anti-tumour promoting activities in animal models. In addition to identification of further active constituents from strongly active Thai edible plants, investigation of the action and metabolism mechanisms, oral activity, and the assessment of clinical safety, are also required. Furthermore, combination tests of several types of anti-tumour promoters in a search for synergism might result in the design of highly effective cancer chemopreventive foods.
Acknowledgements - We would like to thank Professor Mark L. Wahlqvist for giving us an opportunity to write this review article