Bioassay Methods useful to select the natural product cancer chemopreventive agents

Abstract

Prevention of malignant disease such as cancer is obviously much more important than therapy, so primary prevention tactics should be invoked with the greatest possible effort. Because delaying a disease such as cancer is somehow equivalent to cure and it is now generally accepted that cancer can be managed through chemopreventive interventions. Since a considerable number of known cancer chemopreventive agents are naturally occuring, it is reasonable to assume that additional entities with desirable preventive activities exist in nature. In the field of cancer chemoprevention, definition of the best bioassay system remains subjective. Use of in vitro assays permits the identification of a suitable number of lead starting materials. Assays that are suitable for monitoring inhibition of carcinogenesis at the stages of initiation (antioxidant activity, antimutagenic activity, induction of quinone reductase activity in cell culture), promotion (inhibition of phorbol ester-induced ornithin decarboxylase activity in cell culture, inhibition of cyclooxygenase activity), and progression (induction of cell differentiation, anti-estrogenic activity) and inhibition of protein kinase C, are established. Unfortunately, animal models or in vitro test systems cannot be used to select a useful component due to logistical constraints, and it is virtually impossible for in vitro test system to fully epitomize the biological intricacies of a mammal. Thus, as an intermediate solution, a mouse gland organ culture model or rat tracheal epithelial cells are primarily employed for secondary evaluation. Prophylactic cancer chemoprevention in general population is fraught with logistical problems, but due to the magnitude of potential benefits, it is imperative to continue movement in this direction. Several assays are established for monitoring inhibition of carcinogenesis at different stages. The active plant extracts are selected in this procedure. Since the animal models or in vitro test systems cannot fully epitomize the biological system of a mammal, a mouse mammary gland organ culture or rat tracheal epitelial cell are employed for secondary evaluation.